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Main
Date: 07 Aug 2006 19:58:37
From: Stephen Paul
Subject: Primary colors
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Since the primary colors are Red, Blue, and Yellow, shouldn't we use
those for imaging instead of Red, Blue, and Green?
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Date: 08 Aug 2006 00:16:48
From: Chris L Peterson
Subject: Re: Primary colors
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On Mon, 07 Aug 2006 19:58:37 -0400, Stephen Paul
<smarshallpaul@gmail.com > wrote:
>Since the primary colors are Red, Blue, and Yellow, shouldn't we use
>those for imaging instead of Red, Blue, and Green?
The choice of primary colors depends entirely on the color space being
used. The standard additive primaries are red, green, and blue because
these are well matched to the gamut of the human eye. The most common
subtractive primaries are cyan, magenta, any yellow because these map
directly to red, green, and blue.
I assume that the primary colors you are talking about are the ones
traditionally used by artists. Artists use pigments, which means their
primaries are subtractive. You wouldn't normally want to use them for
imaging. Some imaging systems do use CMY, but they generally produce
inferior results to RGB.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Date: 08 Aug 2006 09:23:39
From: Odysseus
Subject: Re: Primary colors
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In article <3jlfd21rv6j28b8ula6g88te0e9u5lj2bv@4ax.com >,
Chris L Peterson <clp@alumni.caltech.edu > wrote:
<snip >
>
> I assume that the primary colors you are talking about are the ones
> traditionally used by artists. Artists use pigments, which means their
> primaries are subtractive. You wouldn't normally want to use them for
> imaging. Some imaging systems do use CMY, but they generally produce
> inferior results to RGB.
Any imaging system that works by putting pigments or dyes on paper must
use subtractive colour. Most printing presses use CMYK (where K stands
for blacK) process inks, and inkjet printers sometimes use six colours
(CcMmYK, the small c and m indicating light cyan and light magenta
respectively) or seven (CcMmYKk), but no such device can print in RGB
directly.
Since RGB has a larger colour gamut than CMYK, many printers using more
than four colours can produce a better reproduction when sent an RGB
file than they do with one in CMYK, but at some point in the "workflow"
any additive colour models *must* be converted to subtractive in order
to print the image.
--
Odysseus
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Date: 08 Aug 2006 18:27:42
From: Stephen Paul
Subject: Re: Primary colors
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Chris L Peterson wrote:
> On Mon, 07 Aug 2006 19:58:37 -0400, Stephen Paul
> <smarshallpaul@gmail.com> wrote:
>
>> Since the primary colors are Red, Blue, and Yellow, shouldn't we use
>> those for imaging instead of Red, Blue, and Green?
>
> The choice of primary colors depends entirely on the color space being
> used. The standard additive primaries are red, green, and blue because
> these are well matched to the gamut of the human eye. The most common
> subtractive primaries are cyan, magenta, any yellow because these map
> directly to red, green, and blue.
>
> I assume that the primary colors you are talking about are the ones
> traditionally used by artists.
Right.
How easy it seems to get a human to believe something made inaccurate
through simplification and language, and how difficult it then becomes
to get them to accept the underlying reality. First, I suppose they have
to accept that the language they've learned isn't technically correct.
Then they have to care enough to want to know how things really work, as
revealed through the scientific process.
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Date: 08 Aug 2006 22:46:30
From: Chris L Peterson
Subject: Re: Primary colors
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On Tue, 08 Aug 2006 18:27:42 -0400, Stephen Paul
<smarshallpaul@gmail.com > wrote:
>How easy it seems to get a human to believe something made inaccurate
>through simplification and language, and how difficult it then becomes
>to get them to accept the underlying reality. First, I suppose they have
>to accept that the language they've learned isn't technically correct.
I'm not sure what you mean. There is nothing inaccurate or
over-simplified about the choice of a RBY color space. The only real
inaccuracy I think is teaching (usually by omission) that there isn't
just one set of primary colors.
>Then they have to care enough to want to know how things really work, as
>revealed through the scientific process.
I think I was in 6th grade when we first touched on color spaces. I
remember being fascinated by the different primaries than I had learned
about a few years earlier, and by mixing experiments using colored
slides and projectors. That was long before small computers, and only a
few years after color TVs started becoming common. I never lost interest
in that. But those that never cared in the first place... well, that's
unfortunate, but they aren't the ones asking your original question,
either.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Date: 09 Aug 2006 22:33:05
From: Stephen Paul
Subject: Re: Primary colors
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Chris L Peterson wrote:
> On Tue, 08 Aug 2006 18:27:42 -0400, Stephen Paul
> <smarshallpaul@gmail.com> wrote:
>
>> to accept that the language they've learned isn't technically correct.
>
> I'm not sure what you mean. There is nothing inaccurate or
> over-simplified about the choice of a RBY color space.
You speak as if it were offered as a choice. They are simply "taught"
these to be the primary colors, without mention of a "space" (an idea
that I myself don't consider too useful regarding primary colors).
And, they believe their teachers the infallible gods of knowledge.
Beginning with the idea of the energy spectrum, and then discussing the
reflection and absorption of light seems a stretch for K through 2. I
guess.
If asked the question prior to this discussion of color spaces, I would
have answered that the primary colors are all those that have a visible
frequency (wavelength) in the contiguous energy spectrum.
All non-primary colors are then created by combining reflections of
different visible wavelengths using point sources with a separation
closer than that which can be resolved by the human eye.
There is then just one color space. The primaries are seen by use of a
prism, and a beam of "white" light.
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Date: 10 Aug 2006 04:08:49
From: Chris L Peterson
Subject: Re: Primary colors
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On Wed, 09 Aug 2006 22:33:05 -0400, Stephen Paul
<smarshallpaul@gmail.com > wrote:
>You speak as if it were offered as a choice. They are simply "taught"
>these to be the primary colors, without mention of a "space" (an idea
>that I myself don't consider too useful regarding primary colors).
>
>And, they believe their teachers the infallible gods of knowledge.
Yes, well. There are all sorts of ideas about how early education should
work.
>If asked the question prior to this discussion of color spaces, I would
>have answered that the primary colors are all those that have a visible
>frequency (wavelength) in the contiguous energy spectrum.
>
>All non-primary colors are then created by combining reflections of
>different visible wavelengths using point sources with a separation
>closer than that which can be resolved by the human eye.
>
>There is then just one color space. The primaries are seen by use of a
>prism, and a beam of "white" light.
But now we have had this discussion about color spaces, so you know that
primary colors aren't that <g >.
In any case, be careful about mixing the idea of color and wavelength.
One is a matter of perception, the other of physics.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Date: 09 Aug 2006 17:13:38
From: Paul Schlyter
Subject: Re: Primary colors
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In article <ri4id2ll6p52j2ie6cehvi3auaff2anjrq@4ax.com >,
Chris L Peterson <clp@alumni.caltech.edu > wrote:
> On Tue, 08 Aug 2006 18:27:42 -0400, Stephen Paul
> <smarshallpaul@gmail.com> wrote:
>
>> How easy it seems to get a human to believe something made inaccurate
>> through simplification and language, and how difficult it then becomes
>> to get them to accept the underlying reality. First, I suppose they have
>> to accept that the language they've learned isn't technically correct.
>
> I'm not sure what you mean. There is nothing inaccurate or
> over-simplified about the choice of a RBY color space. The only real
> inaccuracy I think is teaching (usually by omission) that there isn't
> just one set of primary colors.
"Primary colors" isn't merely just any set of colors chosen by a whim.
Sure, you can create color spaces based on red-blue-yellow, red-green-yellow,
purple-blue-brown, or whatever .... but neither of them are the optimum
colors for a color space which is as wide as possible.
IMO, "primary colors" should be based on the physiology of the human eye
in such a way as to mimicing, as closely as possible, the color sensitivity
of the three kinds of cones in the human fovea. Of course this means that
different people have different primary colors in their vision, although
the variation usually is small. But in some cases, particularly among
color-blind people, the difference is large.
And there are even a few people who are tetrachromats, i.e. they have
four different kinds of cones in their fovea. This is extremely rare,
but these people see all the colors we can see, plus a lot of other
colors we cannot even imagine! From their point of view, almost all
of us are color-blind.
--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/
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Date: 09 Aug 2006 20:19:22
From: Chris L Peterson
Subject: Re: Primary colors
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On Wed, 09 Aug 2006 17:13:38 GMT, pausch@saaf.se (Paul Schlyter) wrote:
>IMO, "primary colors" should be based on the physiology of the human eye
>in such a way as to mimicing, as closely as possible, the color sensitivity
>of the three kinds of cones in the human fovea.
In many contexts, they are. But the definition of primary colors goes
beyond that. They are simply the set of colors that can't be obtained by
mixing other colors in any given color space- not necessarily the one
described by human color vision.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Date: 10 Aug 2006 10:43:00
From: Paul Schlyter
Subject: Re: Primary colors
|
In article <hlgkd2ldoa5221souk8htis5ajurtcra5d@4ax.com >,
Chris L Peterson <clp@alumni.caltech.edu > wrote:
> On Wed, 09 Aug 2006 17:13:38 GMT, pausch@saaf.se (Paul Schlyter) wrote:
>
>> IMO, "primary colors" should be based on the physiology of the human eye
>> in such a way as to mimicing, as closely as possible, the color sensitivity
>> of the three kinds of cones in the human fovea.
>
> In many contexts, they are. But the definition of primary colors goes
> beyond that. They are simply the set of colors that can't be obtained by
> mixing other colors in any given color space- not necessarily the one
> described by human color vision.
OK ..... so in a grayscale, white and black are the primary colors.
--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/
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Date: 10 Aug 2006 14:26:33
From: Chris L Peterson
Subject: Re: Primary colors
|
On Thu, 10 Aug 2006 10:43:00 GMT, pausch@saaf.se (Paul Schlyter) wrote:
>OK ..... so in a grayscale, white and black are the primary colors.
Not exactly, because black and white aren't colors in the usual sense
(where are white and black on the visible spectrum?). A grayscale is
defined by a single value, for instance 0=black, 0.25=dark gray,
1.0=white. Grayscale is just intensity information.
A two primary color space is called dichromatic. Two primaries are the
minimum required to define a color space. Most mammals except primates
have dichromatic color vision; an evolved dog that painted could work
with just two primaries and cover most of the color gamut of his
species.
Primate vision is trichromatic, so we use three primary colors to
describe color spaces with gamuts approximating our own. The most common
spaces are based on RBY, RGB, and CMY. None of these completely match
our own gamut- not surprising since the color receptors in our eyes are
actually blue-violet, green-yellow, and orange-yellow.
Birds are tetrachromatic; if you are researching their vision you need
to work with a more complex color space.
To bring things back to astronomy, one of the most complex color theory
problems involves converting between spaces. Some of our space probes
have high order color spaces- images may consist of intensity data in 10
or more wavelength bands, some of which may be narrowband (not
overlapping adjacent bands). It is a challenge to take such data and map
it to a trichromatic space like RGB. Perhaps you recall how long it was
before Mars Rover images finally started being released showing
approximately "true" colors, and even now many are never converted.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Date: 10 Aug 2006 11:31:55
From: Jim Hewitt
Subject: Re: Primary colors
|
"Chris L Peterson" <clp@alumni.caltech.edu > wrote in message
news:0vemd2dkc8d3o0eae1ttus3lcp4s0r2771@4ax.com...
> On Thu, 10 Aug 2006 10:43:00 GMT, pausch@saaf.se (Paul Schlyter) wrote:
>
> To bring things back to astronomy, one of the most complex color theory
> problems involves converting between spaces. Some of our space probes
> have high order color spaces- images may consist of intensity data in 10
> or more wavelength bands, some of which may be narrowband (not
> overlapping adjacent bands). It is a challenge to take such data and map
> it to a trichromatic space like RGB. Perhaps you recall how long it was
> before Mars Rover images finally started being released showing
> approximately "true" colors, and even now many are never converted.
Yes, astronomy and color are challenging to mix!
One must remember that color is a combination of three things: illuminant,
and object, and an observer. Sometimes just two: something that glows, and
observer. The problem with space probes is that they are not designed to
capture true color. Rather they are designed for other spectroscopic
analysis or often weight/stability, or data bandwidth limitations.
The real issue is that most imagers capture only sparsely sampled spectra,
or abbreviated spectra. If we had a detailed spectrum, we could
reconstitute the measured color quite easily by using the color matching
functions of the human visual system and obtaining the XYZ tristimulus
values. These can be converted into any other trichromatic color space - of
which there have been dozens defined/created.
But think of the Nyquist sampling theorem: if the rate of sampling is not
high enough [in whatever space you are working] then the true waveform can't
be captured due to aliasing. Thus the Mars Pancam images are multi-spectral
images, but only 6 channel, narrow band. One must make assumptions about
the general shape of the spectrum to convert to XYZ so they are only
approximate true color.
If you assume that the approximation is close enough, you will note that we
have only captured the measured color - we still have to consider the color
_appearance_ to the human observer. There are color appearance models that
attempt to take into account the numerous color appearance effects as
observed in the human visual system to predict how the colors would appear
to a human. This requires one to carefully choose parameters for the model
to match the viewing conditions.
This last part of predicting the color appearance is the most difficult part
of the process of creating color astronomical images. It is further
compounded by the gamut mapping that must occur when converting to/from the
theoretical color spaces to device color spaces of the imaging device
[camera] and the rendering device [printer/display]. When you combine the
limitations of the imager, with the limitations of the renderer, factoring
in the color appearance effects, then you can see that it is indeed an
incredibly complex problem.
---------------------------------
Jim Hewitt, Color Scientist
Color and Imaging Team
Advanced Technology Section
Hewlett-Packard Company
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Date: 10 Aug 2006 19:43:35
From: Paul Schlyter
Subject: Re: Primary colors
|
In article <0vemd2dkc8d3o0eae1ttus3lcp4s0r2771@4ax.com >,
Chris L Peterson <clp@alumni.caltech.edu > wrote:
> On Thu, 10 Aug 2006 10:43:00 GMT, pausch@saaf.se (Paul Schlyter) wrote:
>
>> OK ..... so in a grayscale, white and black are the primary colors.
>
> Not exactly, because black and white aren't colors in the usual sense
White and black are colors "in the usual sense" very much! Go into
a paint shop and ask for white paint and black paint -- you should
have no problem getting these!
> (where are white and black on the visible spectrum?).
Where is purple on the visible spectrum? Or brown?
Only a small minority of all the colors we see are pure spectral
colors, which meaningfully can be assigned a specific wavelength on
the visible spectrum. Most natural colors contain light all over the
visible spectrum, but in different proportions. So when you're
talking about colors as they appear in nature, you should ask for its
spectral curve rather than where "on the visible spectrum" they are
(almost all of them are all over the visible spectrum!).
I think you'll agree with me that white and black also have spectral
curves.
> A grayscale is defined by a single value, for instance 0=black,
> 0.25=dark gray, 1.0=white. Grayscale is just intensity information.
Which means one cannot pick any colors to define a color space. Right?
> A two primary color space is called dichromatic. Two primaries are the
> minimum required to define a color space. Most mammals except primates
> have dichromatic color vision; an evolved dog that painted could work
> with just two primaries and cover most of the color gamut of his
> species.
>
> Primate vision is trichromatic, so we use three primary colors to
> describe color spaces with gamuts approximating our own. The most common
> spaces are based on RBY, RGB, and CMY. None of these completely match
> our own gamut- not surprising since the color receptors in our eyes are
> actually blue-violet, green-yellow, and orange-yellow.
>
> Birds are tetrachromatic; if you are researching their vision you need
> to work with a more complex color space.
And some species of tropical fish are pentachromatic - what colors these
fishes see we cannot even imagine.
> To bring things back to astronomy, one of the most complex color theory
> problems involves converting between spaces. Some of our space probes
> have high order color spaces- images may consist of intensity data in 10
> or more wavelength bands, some of which may be narrowband (not
> overlapping adjacent bands). It is a challenge to take such data and map
> it to a trichromatic space like RGB. Perhaps you recall how long it was
> before Mars Rover images finally started being released showing
> approximately "true" colors, and even now many are never converted.
I suppose several of these 10 wavelength bands are outside the
visible spectrum - they are then useless for creating "true color"
images. But if they were all within the visible spectrum, it would
be easier to create a good "true color" image: the more wavelength
bands you have available, the better.
I think the Pioneer 10 and 11 (or was it Voyager 1 and 2?) returned
images in red and blue - from these "true color" images were created,
and the missing "green" image was synthesized from the red and blue
images - of course, this required making an educated guess of the
green intensity from the red and blue intensities.
> _________________________________________________
>
> Chris L Peterson
> Cloudbait Observatory
> http://www.cloudbait.com
--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/
|
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Date: 10 Aug 2006 20:42:19
From: Chris L Peterson
Subject: Re: Primary colors
|
On Thu, 10 Aug 2006 19:43:35 GMT, pausch@saaf.se (Paul Schlyter) wrote:
>White and black are colors "in the usual sense" very much! Go into
>a paint shop and ask for white paint and black paint -- you should
>have no problem getting these!
Just goes to show that "usual" has more and less usual meanings! <g >
In color theory, black and white do not have any color information (hue,
chrominance, or other related values). White and black are considered
opposite extremes of a one-dimensional continuum, usually obtained by
mixing equal amounts of each primary.
>Where is purple on the visible spectrum? Or brown?
Understanding that these terms are only loosely defined (and that the
definition is tied to perception, not physics), purple can be found
around 425nm (although there are many other ways to stimulate the
perception of purple). Brown is just a desaturated, dark orange, say
around 600nm. The point being that these named colors each have a hue
component that can be found somewhere in the visible spectrum. Black and
white do not- any wavelength (or mixture of wavelengths) with zero
intensity gives black; white can only be produced by mixing at least
three widely separated wavelengths in the correct proportion.
>Only a small minority of all the colors we see are pure spectral
>colors, which meaningfully can be assigned a specific wavelength on
>the visible spectrum. Most natural colors contain light all over the
>visible spectrum, but in different proportions. So when you're
>talking about colors as they appear in nature, you should ask for its
>spectral curve rather than where "on the visible spectrum" they are
>(almost all of them are all over the visible spectrum!).
>
>I think you'll agree with me that white and black also have spectral
>curves.
Generally, yes, when you are talking about actual objects. But that
doesn't necessarily make them "colors" in all senses.
>> A grayscale is defined by a single value, for instance 0=black,
>> 0.25=dark gray, 1.0=white. Grayscale is just intensity information.
>
>Which means one cannot pick any colors to define a color space. Right?
I don't understand the question.
>And some species of tropical fish are pentachromatic - what colors these
>fishes see we cannot even imagine.
I'm not so sure that's true. I could say that I can't imagine what
colors _you_ see. For all I know what you call "red" I call "cold". But
for simplicity, lets just say that all species with color vision
perceive the same thing: an apparent continuum from red to violet. What
distinguishes them is their gamut- how finely they can resolve color
differences. A perfect visual system would have an infinite gamut over
some range- this is essentially what a spectrograph is. You can do an
experiment with people, where you compare how finely they can
distinguish shifts in pure spectral wavelengths, or how well they can
distinguish various mixtures. There is a wide variation. I found in the
lab that I am able to see colors many others can't- that is, there are
combinations of two and three wavelengths that I can distinguish but
other people see as the same color. What I may see is two slightly
different shades of yellow; what most people see is just one shade of
yellow. That's easy enough to imagine, isn't it? It isn't as if I'm
seeing some new color that is beyond everyone else's comprehension. I
think the situation is the same with tetrachromatic or pentachromatic
animals. It isn't that they see colors we can't imagine, it's simply
that they have a much finer color resolution. They will perceive a range
of spectral mixes as different colors, where we would just see one.
>I suppose several of these 10 wavelength bands are outside the
>visible spectrum - they are then useless for creating "true color"
>images. But if they were all within the visible spectrum, it would
>be easier to create a good "true color" image: the more wavelength
>bands you have available, the better.
Yes, more data is good. But it is harder to generate true color from
many discrete narrow bands than it is from three overlapping broad
bands. By harder I mean that it is a complex mathematical problem, not
that you don't necessarily end up with a more accurate image in the end.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
|
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Date: 11 Aug 2006 09:12:47
From: Paul Schlyter
Subject: Re: Primary colors
|
In article <4h4nd2heh0alajsmt0g6hj71o0399tbbu5@4ax.com >,
Chris L Peterson <clp@alumni.caltech.edu > wrote:
> On Thu, 10 Aug 2006 19:43:35 GMT, pausch@saaf.se (Paul Schlyter) wrote:
>
>> White and black are colors "in the usual sense" very much! Go into
>> a paint shop and ask for white paint and black paint -- you should
>> have no problem getting these!
>
> Just goes to show that "usual" has more and less usual meanings! <g>
...and if you want to buy white paint, you'll have to decide what kind
of white you want .... yes, the different kinds of white paint can have
slightly different hue....
> In color theory, black and white do not have any color information (hue,
> chrominance, or other related values).
Black, gray and white have an indeterminate hue of course, but their
saturation is well defined: they have zero saturation. In colorimetry,
they're referred to as "neutral color" rather than "no color".
> White and black are considered opposite extremes of a one-dimensional
> continuum, usually obtained by mixing equal amounts of each primary.
If white and black are used as primaries, they define a 1-dimensional
color space containing only the grayscale, i.e. all neutral colors.
>> Where is purple on the visible spectrum? Or brown?
>
> Understanding that these terms are only loosely defined (and that the
> definition is tied to perception, not physics), purple can be found
> around 425nm (although there are many other ways to stimulate the
> perception of purple).
You're confusing purple with violet.
Look up a CIE chromaticity diagram, e.g. on Wikipedia. The visible
colors are there bounded by a curved line representing the spectral
colors. At the bottom a straight line runs between the extreme spectral
red and the extreme spectral violet. That line is the "purple line".
> Brown is just a desaturated, dark orange, say around 600nm.
And what's the bandwidth of the peak around 600 nm ? Since brown is
desaturated, it (probably) contains wavelengths all over the visible
spectrum.
> The point being that these named colors each have a hue component
> that can be found somewhere in the visible spectrum. Black and
> white do not- any wavelength (or mixture of wavelengths) with zero
> intensity gives black; white can only be produced by mixing at least
> three widely separated wavelengths in the correct proportion.
Suppose we have a purple color, composed of equal amounts of spectral
deep violet around 425 nm and spectral deep red around 650 or 700 nm.
Now, try to (meaningfully) assign a single wavelength to THAT
color.... if you take the average of these two wavelengths you'll
get ca 540 nm, i.e. in the green area of the spectrum. But to label
purple "green" would be very wrong.
Not all hues can be assigned a single wavelength in the visible
spectrum.
>> Only a small minority of all the colors we see are pure spectral
>> colors, which meaningfully can be assigned a specific wavelength on
>> the visible spectrum. Most natural colors contain light all over the
>> visible spectrum, but in different proportions. So when you're
>> talking about colors as they appear in nature, you should ask for its
>> spectral curve rather than where "on the visible spectrum" they are
>> (almost all of them are all over the visible spectrum!).
>>
>> I think you'll agree with me that white and black also have spectral
>> curves.
>
> Generally, yes, when you are talking about actual objects. But that
> doesn't necessarily make them "colors" in all senses.
The terminology is indeed confusing here ..... the neutral colors
are sometimes said to have "no color", as in e.g. a black-and-white
photograph or TV set. But white is also sometimes said to be "all
colors". And if you go into a paint shop to buy paint, white, and
black, is just "one color".
>>> A grayscale is defined by a single value, for instance 0=black,
>>> 0.25=dark gray, 1.0=white. Grayscale is just intensity information.
>>
>> Which means one cannot pick any colors to define a color space. Right?
>
> I don't understand the question.
You said earlier that one could pick any colors as the primary colors
to define a color space - of course some of these color spaces are more
confined than others. A color space based on white and black as primary
colors would contain just the neutral colors, i.e. the grayscale.
>> And some species of tropical fish are pentachromatic - what colors these
>> fishes see we cannot even imagine.
>
> I'm not so sure that's true. I could say that I can't imagine what
> colors _you_ see. For all I know what you call "red" I call "cold". But
> for simplicity, lets just say that all species with color vision
> perceive the same thing: an apparent continuum from red to violet. What
> distinguishes them is their gamut- how finely they can resolve color
> differences. A perfect visual system would have an infinite gamut over
> some range- this is essentially what a spectrograph is. You can do an
> experiment with people, where you compare how finely they can
> distinguish shifts in pure spectral wavelengths, or how well they can
> distinguish various mixtures. There is a wide variation. I found in the
> lab that I am able to see colors many others can't- that is, there are
> combinations of two and three wavelengths that I can distinguish but
> other people see as the same color. What I may see is two slightly
> different shades of yellow; what most people see is just one shade of
> yellow. That's easy enough to imagine, isn't it? It isn't as if I'm
> seeing some new color that is beyond everyone else's comprehension. I
> think the situation is the same with tetrachromatic or pentachromatic
> animals. It isn't that they see colors we can't imagine, it's simply
> that they have a much finer color resolution. They will perceive a range
> of spectral mixes as different colors, where we would just see one.
You're reducing all kinds of color vision to just one dimension: the
spectral wavelength. Consider spectral green at 550 nm wavelength.
Then consider a less saturated green, with dominant wavelength at 550 nm.
Next consider an even less saturated green, again with dominant
wavelength 550 nm. Finally consider white with a very weak green tint,
again with a dominant wavelength of 550 nm. These colors all have the
same "wavelength", yet they're quite different as colors.
You're thinking of tetrachromats and pentachromats as not seeing any
"new" colors we don't see, but merely seeing "finer detail" in the
colors. Let's go in the other direction, and consider dichromatic
and monochromatic vision - do they see all the colors we see, but
with just less detail? Consider for instance red-green blind people:
they cannot distinguish red from green (perhaps they perceive both of
them as yellow, seeing only a blue-yellow color space?). Or consider
those rare people who are completely color blind: they see the world
in a grayscale (or perhaps a red-scale, or yellow-scale, or ...
nevertheless they see a monochrome world). I think you'll agree
with me that trichromats see colors which dichromats and monochromats
just cannot perceive. It's just not a matter of "more detail", it's
a matter of new dimensions in the color space.
For a trichromat, color can be described with three numbers: brightness,
hue, and saturation.
For a monochromat, brightness is enough to describe a color - that's all
he can see.
For a dichromat, brightness and saturation would be enough to
descibe the colors he can see. He can see two hues though, but this
can be handled by allowing the saturation to also have negative values
(e.g. letting yellow have positive and blue negative saturation).
A tetrachromat ought to need four numbers to fully describe the colors
he can see: brightness, hue, saturation - PLUS SOMETHING ELSE.
Maybe the concept of "hue" needs to be made two-dimensional for a
tetrachromat.
And a pentachromat ought to need five numbers to fully describe the
colors he can see.
> >I suppose several of these 10 wavelength bands are outside the
> >visible spectrum - they are then useless for creating "true color"
> >images. But if they were all within the visible spectrum, it would
> >be easier to create a good "true color" image: the more wavelength
> >bands you have available, the better.
>
> Yes, more data is good. But it is harder to generate true color from
> many discrete narrow bands than it is from three overlapping broad
> bands. By harder I mean that it is a complex mathematical problem, not
> that you don't necessarily end up with a more accurate image in the end.
True - if you have many discrete narrow bands, they must be grouped,
and a weighted average must be computed to convert these many signals
into three signals representing the broad bands. Figuring out the
correct weight factors would be the hardest problem - the weight
factors are also dependent on the spectrum of the imaged object. And
if there are gaps between these many discrete narrow bands, there's
always the risk of a bright narrow emission line falling into one of
these gaps - such a line would not be included in the "true color"
image, which therefore would get a less true color.
--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/
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Date: 11 Aug 2006 14:27:31
From: Chris L Peterson
Subject: Re: Primary colors
|
On Fri, 11 Aug 2006 09:12:47 GMT, pausch@saaf.se (Paul Schlyter) wrote:
>You said earlier that one could pick any colors as the primary colors
>to define a color space - of course some of these color spaces are more
>confined than others. A color space based on white and black as primary
>colors would contain just the neutral colors, i.e. the grayscale.
I'd argue that a true color space requires the primaries to have hues. I
wouldn't consider black and white to be primaries, nor grayscale to be a
color space. Of course, it is all a matter of definition. I've studied
color theory, but never seen this fine point discussed.
>You're reducing all kinds of color vision to just one dimension: the
>spectral wavelength. Consider spectral green at 550 nm wavelength.
>Then consider a less saturated green, with dominant wavelength at 550 nm.
>Next consider an even less saturated green, again with dominant
>wavelength 550 nm. Finally consider white with a very weak green tint,
>again with a dominant wavelength of 550 nm. These colors all have the
>same "wavelength", yet they're quite different as colors.
They are different colors, and I'm not making this reduction. The
testing apparatus I mentioned does allow reducing the saturation, and it
does mix multiple wavelengths. It allows for direct, A/B comparison of
quite complex spectral patterns.
>You're thinking of tetrachromats and pentachromats as not seeing any
>"new" colors we don't see, but merely seeing "finer detail" in the
>colors...
All good points, but not really addressing what I was speaking of, which
is _perception_. Having more primaries defining your color space does
not require the ability to see new colors that those with a smaller
gamut can't grasp. The mechanism used by the brain to quantify color can
use the same percepts, but finer resolution.
Who knows? To answer this you would need to be able to look into a mind
and study details of perception in a way currently beyond our ability.
You can easily do experiments to determine the gamut of the visual
system, but you can't determine what the inner eye is seeing. I don't
know that monochromats don't [internally] see a range of colors that I
would call red through violet.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Date: 10 Aug 2006 23:37:30
From: Ioannis
Subject: Re: Primary colors
|
"Paul Schlyter" <pausch@saaf.se > wrote in message
news:ebg1c8$1jtk$1@merope.saaf.se...
[snip]
> Where is purple on the visible spectrum? Or brown?
[snip]
I think "purple" deserves a bit more attention mainly because people
usually confuse the terminology.
I take it that by "purple" you probably mean what's commonly referred
to as "magenta". And indeed, magenta is produced by varying combined
doses of red and blue.
"Violet" usually denotes the corresponding pure spectral hue.
An interesting paradigm of how these two can misbehave is the
following:
Pure "violet" hues are usually approximated as "magenta" hues on RGB
screens, such as CRT displays. But on color LCD displays violet hues
are rendered accurately enough.
Reason being that RGB displays do not have "violet" dots, so they are
forced to approximate the hue using red and blue dots. But on color
LCD displays, such as on the displays of laptops, the screen is
illuminated by a mini triphosphor fluorescent tube, which is basically
a low pressure mercury vapor lamp. As mercury lamps always emit two
lines at 404nm and 407nm (which are pure violet), the violet hue is
rendered accurately there.
Here's an example. This is a fluorescent blacklight. On laptop LCD
screens, the "violet" is rendered accurately. On RGB screens, it will
be rendered as magenta.
http://misc.virtualcomposer2000.com/Blacklight.jpg
> Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
--
Ioannis
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Date: 09 Aug 2006 23:08:33
From: Ioannis
Subject: Re: Primary colors
|
"Paul Schlyter" <pausch@saaf.se > wrote in message
news:ebd4mt$i85$1@merope.saaf.se...
[snip]
> And there are even a few people who are tetrachromats,
i.e. they have
> four different kinds of cones in their fovea. This is
extremely rare,
> but these people see all the colors we can see, plus a lot
of other
> colors we cannot even imagine! From their point of view,
almost all
> of us are color-blind.
And then there's a third kind of people, those who can see
into UV. Most people's ability to discern light in the UV is
limited to around 390-410nm. But exceptions do exist, as
with yours truly, who can see the 365nm UV mercury line in
his spectroscope :-P
> --
> Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm,
SWEDEN
--
Ioannis
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Date: 10 Aug 2006 10:43:00
From: Paul Schlyter
Subject: Re: Primary colors
|
In article <1155154120.182485@athnrd02 >, Ioannis <morpheus@olympus.mons> wrote:
> "Paul Schlyter" <pausch@saaf.se> wrote in message
> news:ebd4mt$i85$1@merope.saaf.se...
> [snip]
>
>> And there are even a few people who are tetrachromats,
>> i.e. they have four different kinds of cones in their fovea.
>> This is extremely rare, but these people see all the colors
>> we can see, plus a lot of other colors we cannot even imagine!
>> From their point of view, almost all of us are color-blind.
>
> And then there's a third kind of people, those who can see
> into UV. Most people's ability to discern light in the UV is
> limited to around 390-410nm. But exceptions do exist, as
> with yours truly, who can see the 365nm UV mercury line in
> his spectroscope :-P
While ability to see into the UV enables you to see other wavelengths,
it won't enable you to see other colors. People who can see more into
the UV than most of the rest are often people who've had their eye
lens removed in a cataract operation. From their reports, the color
of UV is indistinguishable from the color of very deep blue.
--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/
|
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Date: 10 Aug 2006 14:25:47
From: Ioannis
Subject: Re: Primary colors
|
"Paul Schlyter" <pausch@saaf.se > wrote in message
news:ebf21g$17so$1@merope.saaf.se...
[snip]
> While ability to see into the UV enables you to see other
wavelengths,
> it won't enable you to see other colors.
I never claimed so.
> People who can see more into
> the UV than most of the rest are often people who've had their eye
> lens removed in a cataract operation.
Often, yes. But not in my case. My eyes function perfectly without any
cataract operations.
> From their reports, the color
> of UV is indistinguishable from the color of very deep blue.
Very deep UV resembles more of a grey hue, rather than deep blue.
> --
> Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
--
Ioannis
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Date: 10 Aug 2006 19:43:33
From: Paul Schlyter
Subject: Re: Primary colors
|
In article <1155209154.388900@athnrd02 >, Ioannis <morpheus@olympus.mons> wrote:
> "Paul Schlyter" <pausch@saaf.se> wrote in message
> news:ebf21g$17so$1@merope.saaf.se...
> [snip]
>
>> While ability to see into the UV enables you to see other
>> wavelengths, it won't enable you to see other colors.
>
> I never claimed so.
>
>> People who can see more into
>> the UV than most of the rest are often people who've had their eye
>> lens removed in a cataract operation.
>
> Often, yes. But not in my case. My eyes function perfectly without any
> cataract operations.
>
>> From their reports, the color
>> of UV is indistinguishable from the color of very deep blue.
>
> Very deep UV resembles more of a grey hue, rather than deep blue.
>
> Ioannis
Interesting .... apparently, different people see different hues in
UV light. To most people, UV appears pitch black....
Most digital cameras "see" into the IR. This feature can be used to
e.g. test a remote control of a TV, VCR or DVD player (if it operates
through IR; as usually is the case nowadays): direct the control to
the camera, press some button on the remote control and see the LED
blink, if viewed through the camera. If viewed directly with the
eyes, one sees no blinks from the LED.
And if the blinking IR LED is viewed throught the camera, its hue
is not red. It's instead whitish, perhaps with a tint of green.
Of course this hue depends on the camera. One camera I tested
didn't "see" this IR at all - which of course means it sees the
world more like the human eye.
--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/
|
| |
Date: 07 Aug 2006 17:07:41
From: Jan Owen
Subject: Re: Primary colors
|
"Stephen Paul" <smarshallpaul@gmail.com > wrote in message
news:cKednQ_xRZ46TkrZnZ2dnUVZ_t-dnZ2d@comcast.com...
> Since the primary colors are Red, Blue, and Yellow, shouldn't we use those
> for imaging instead of Red, Blue, and Green?
My primary color is peus... Or is that pews? Or pues? Or ACK (I don't
CARE about my shoes)!!!
But then, we KNEW this...
--
Jan Owen
To reach me directly, remove the Z, if one appears in my e-mail address...
Latitude: 33.6
Longitude: -112.3
http://community.webshots.com/user/janowen21
|
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Date: 07 Aug 2006 17:20:26
From: Howard Lester
Subject: Re: Primary colors
|
"Jan Owen" wrote
> "Stephen Paul" wrote
>> Since the primary colors are Red, Blue, and Yellow, shouldn't we use
>> those for imaging instead of Red, Blue, and Green?
>
> My primary color is peus... Or is that pews? Or pues? Or ACK (I don't
> CARE about my shoes)!!!
>
> But then, we KNEW this...
Beulah the Buzzer says "BZZZZZZZZZZZZT!!" Sorry, the correct answer is
"puce."
|
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Date: 07 Aug 2006 17:27:57
From: Jan Owen
Subject: Re: Primary colors
|
"Howard Lester" <heylester@dakotacom.net > wrote in message
news:12dfm75j9otan0f@corp.supernews.com...
>
> "Jan Owen" wrote
>
>> "Stephen Paul" wrote
>
>>> Since the primary colors are Red, Blue, and Yellow, shouldn't we use
>>> those for imaging instead of Red, Blue, and Green?
>>
>> My primary color is peus... Or is that pews? Or pues? Or ACK (I don't
>> CARE about my shoes)!!!
>>
>> But then, we KNEW this...
>
> Beulah the Buzzer says "BZZZZZZZZZZZZT!!" Sorry, the correct answer is
> "puce."
Depends on whether you care about your SHOES!!! {;^)
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Date: 07 Aug 2006 18:53:27
From: Howard Lester
Subject: Re: Primary colors
|
"Jan Owen" wrote
>>> My primary color is peus... Or is that pews? Or pues? Or ACK (I don't
>>> CARE about my shoes)!!!
>>>
>>> But then, we KNEW this...
>>
>> Beulah the Buzzer says "BZZZZZZZZZZZZT!!" Sorry, the correct answer is
>> "puce."
>
> Depends on whether you care about your SHOES!!! {;^)
You have purple-brown shoes?? Or is it that you're afraid if you drink too
much wodka you'll puce all over them?
"You can do anything, but lay offa my buh-lue suede shoes!"
- Parl Gerkins
|
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Date: 08 Aug 2006 14:28:08
From: nytecam
Subject: Re: Primary colors
|
Stephen Paul Wrote:
> Since the primary colors are Red, Blue, and Yellow, shouldn't we use
> those for imaging instead of Red, Blue, and Green?
Where did you get that idea????
--
nytecam
|
| | |
Date: 08 Aug 2006 09:52:36
From: Brian Tung
Subject: Re: Primary colors
|
Stephen Paul Wrote:
> Since the primary colors are Red, Blue, and Yellow, shouldn't we use
> those for imaging instead of Red, Blue, and Green?
nytecam wrote:
> Where did you get that idea????
In the U.S., it is common to teach schoolchildren red, blue, and yellow
as the primary colors, when learning to paint.
--
Brian Tung <brian@isi.edu >
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.html
|
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Date: 08 Aug 2006 13:39:51
From: Bob May
Subject: Re: Primary colors
|
OH, great! Not only are the kids not being taught much, but they're being
taught wrong!
--
Why do penguins walk so far to get to their nesting grounds?
|
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Date: 08 Aug 2006 14:50:36
From: Brian Tung
Subject: Re: Primary colors
|
Bob May wrote:
> OH, great! Not only are the kids not being taught much, but they're being
> taught wrong!
It's not wrong for paints. If you mix red, blue, and yellow in pairs,
you get purple, green, and orange, giving kids a perfectly useful set of
colors to work from. If you were to use red, blue, and green, how on
earth would you get yellow?
It's a popular pastime to decry education today, but I think, based on
comparing what my kids get and what I got (and I turned out all right*),
that things are OK from the teacher's end.
--
Brian Tung <brian@isi.edu >
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.html
*I can even spell "all right" correctly. :)
|
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Date: 09 Aug 2006 14:54:40
From: Bob May
Subject: Re: Primary colors
|
By the way, go take a look at some of the things that Edward Land did with
colors back in the '50s. Might supprise you a bit.
--
Why do penguins walk so far to get to their nesting grounds?
|
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Date: 09 Aug 2006 14:53:46
From: Bob May
Subject: Re: Primary colors
|
Yep, your right as far as it goes. HOWEVER, the colors don't fill the
colorspace as well as the correct colors do. Cyan is a greenish blue color
so a blue can indeed be substituted for it but you lose a bit of color
range, Magenta is a purpulish red so you will end up losing a bit of the
range again. Yellow is the third color and the only one stated in the
question.
Each of these subtractive colors is the opposite polarity and phase in any
of the color spaces that I've seen. All of the primary additive and
subtractive colors are shown in the color bars that are on a TV test pattern
of that name.
--
Why do penguins walk so far to get to their nesting grounds?
|
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Date: 09 Aug 2006 17:13:37
From: Paul Schlyter
Subject: Re: Primary colors
|
In article <ebb0vc$ab6$1@praesepe.isi.edu >, Brian Tung <brian@isi.edu> wrote:
> Bob May wrote:
>> OH, great! Not only are the kids not being taught much, but they're being
>> taught wrong!
>
> It's not wrong for paints. If you mix red, blue, and yellow in pairs,
> you get purple, green, and orange, giving kids a perfectly useful set of
> colors to work from.
It works to some degree, yes -- perhaps enough for the needs of most kids.
But if you used cyan, magenta and yellow instead as your primaries, you
would be able to create a wider range of colors: cyan and magenta gives
blue, cyan and yellow gives green, and yellow and magenta gives red.
> If you were to use red, blue, and green, how on earth would you get yellow?
By mixing red and green - by additive mixing, that is! It won't work
for paints, but shine a red light and a green light, with balanced
identities, on the same white screen, and you'll get yellow. Or watch
closely, preferably with a magnifying glass, a yellow area on your TV
screen or computer screen -- you won't find any yellow dots there, only
red and green dots.
That's how you create yellow from red, green and blue.
There's a frequent confusion between additive primary colors and
subtractive primary colors - they're a different set of colors really,
but closely related: each subtractive primary color is the complementary
color of an additive primary color.
The additive primary colors are red, green, blue. No question about that,
color TV relies on that basic fact. If there would be a different set of
primary colors, able to produce a wider range of colors, that set would
have been used instead.
In additive color mixing, you start with black and then you add the
primaries, in the proportion you want, until you get the desired final
color. If you add them all with full intensity, you'll end up with white.
Each additive primary color has a corresponding subtractive primary color:
Additive red corresponds to subtractive cyan (removes red)
Additive green correspinds to subtractive magenta (removes green)
Additive yellow corresponds to subtractive blue (removes yellow)
In subtractive color mixing, you start with white, and then put on
the dyes (which are assumed to be transparent) until you get the
desired color. If you add all dyes in full concentration, you'll end
up with black.
The subtractive primary colors cyan, magenta, yellow are also well
established, color slides, color prints and magazine/newspaper prints
all depend on them.
Claiming that "red, blue, yellow" are the primary colors is a confusion
of additive and subtractive primary colors.
Mixing non-transparent paints is of course a whole other matter: it's
the paint which ends up on top which determines the color. A color
mixture must then be obtained by small dots of different paints ending
up on top.
> It's a popular pastime to decry education today, but I think, based on
> comparing what my kids get and what I got (and I turned out all right*),
> that things are OK from the teacher's end.
....I think we need more than just "the teacher is satisfied" to judge
whether an education really is good or not.
--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/
|
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Date: 09 Aug 2006 10:19:38
From: Brian Tung
Subject: Re: Primary colors
|
Paul Schlyter wrote:
> It works to some degree, yes -- perhaps enough for the needs of most kids.
> But if you used cyan, magenta and yellow instead as your primaries, you
> would be able to create a wider range of colors: cyan and magenta gives
> blue, cyan and yellow gives green, and yellow and magenta gives red.
It's possible that if that had been the choice to start out with (and
they had simpler names, which they likely would have), it might have
worked out better, by *some* metric. But not enough better to switch.
So I stand by my assertion that it's not wrong to use RBY for kids
learning to paint. I didn't imply that it was wrong to use anything
else.
> > If you were to use red, blue, and green, how on earth would you get yellow?
>
> By mixing red and green - by additive mixing, that is! It won't work
> for paints, but shine a red light and a green light, with balanced
Did you flip on the context-free switch in your newsreader again, Paul?
We're *talking* about paints, and other parts of the thread have already
gone into additive color mixing.
> Claiming that "red, blue, yellow" are the primary colors is a confusion
> of additive and subtractive primary colors.
I never said they were the primary colors. For kids learning to paint,
I think it is a good first introduction. The rest can be learned later
without any penalty.
> > It's a popular pastime to decry education today, but I think, based on
> > comparing what my kids get and what I got (and I turned out all right*),
> > that things are OK from the teacher's end.
>
> ....I think we need more than just "the teacher is satisfied" to judge
> whether an education really is good or not.
Where on earth did you get "the teacher is satisfied" from what I wrote?
Of course I base my perception on actually watching what is being
taught, and how. I can't imagine how you misread that.
--
Brian Tung <brian@isi.edu >
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.html
|
| | | | | | | |
Date: 10 Aug 2006 10:43:00
From: Paul Schlyter
Subject: Re: Primary colors
|
In article <ebd5fa$l3q$1@praesepe.isi.edu >, Brian Tung <brian@isi.edu> wrote:
> Paul Schlyter wrote:
>> It works to some degree, yes -- perhaps enough for the needs of most kids.
>> But if you used cyan, magenta and yellow instead as your primaries, you
>> would be able to create a wider range of colors: cyan and magenta gives
>> blue, cyan and yellow gives green, and yellow and magenta gives red.
>
> It's possible that if that had been the choice to start out with (and
> they had simpler names, which they likely would have), it might have
> worked out better, by *some* metric. But not enough better to switch.
> So I stand by my assertion that it's not wrong to use RBY for kids
> learning to paint. I didn't imply that it was wrong to use anything
> else.
Do you still think it's OK to present RBY as THE set of fundamental colors,
implicitly implying it's the only set? I believe that's they way it's
usually presented to kids -- as THE fundamental colors, not as one
possible choice among a large number of other choices.
>>> If you were to use red, blue, and green, how on earth would you get yellow?
>>
>> By mixing red and green - by additive mixing, that is! It won't work
>> for paints, but shine a red light and a green light, with balanced
>
> Did you flip on the context-free switch in your newsreader again, Paul?
> We're *talking* about paints, and other parts of the thread have already
> gone into additive color mixing.
You asked how to get yellow from RGB, and I told you how..... I also
hinted that it's not possible through subtractive mixing. Btw
dithering with paints produce an effect eqiuivalent to additive color
mixing - that ought to be the only possible way to mix
non-transparent colors.
>> Claiming that "red, blue, yellow" are the primary colors is a confusion
>> of additive and subtractive primary colors.
>
> I never said they were the primary colors.
So you used another word, "fundamental" colors perhaps?
> For kids learning to paint, I think it is a good first introduction.
> The rest can be learned later without any penalty.
A lot of people don't learn "the rest", and still believe RBY are the
primary (or fundamental, or whatever) colors when they've become adults.
>>> It's a popular pastime to decry education today, but I think, based on
>>> comparing what my kids get and what I got (and I turned out all right*),
>>> that things are OK from the teacher's end.
>>
>> ....I think we need more than just "the teacher is satisfied" to judge
>> whether an education really is good or not.
>
> Where on earth did you get "the teacher is satisfied" from what I wrote?
You wrote "things are OK from the teacher's end", didn't you?
> Of course I base my perception on actually watching what is being
> taught, and how. I can't imagine how you misread that.
--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/
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Date: 10 Aug 2006 07:26:18
From: Brian Tung
Subject: Re: Primary colors
|
Paul Schlyter wrote:
> Do you still think it's OK to present RBY as THE set of fundamental colors,
> implicitly implying it's the only set? I believe that's they way it's
> usually presented to kids -- as THE fundamental colors, not as one
> possible choice among a large number of other choices.
I think it is not correct, strictly speaking, but it is a harmless first
introduction, *provided* that the correct treatment is given later on.
Unfortunately, it isn't always, and I agree with Chris: It is that
omission that is the failing, not the earlier simplification.
> You asked how to get yellow from RGB, and I told you how...
With *paints*. If I talk about paints from the beginning of the post, I
shouldn't need to say the word "paints" in each sentence to restrict the
scope to them. Evidently, with you, I do.
> So you used another word, "fundamental" colors perhaps?
No. I said that in the U.S., kids are *taught* that those are the
primary colors. I *never* said that they *are* the primary colors. I
was explaining how some folks have arrived at the conclusion that they
are the primary colors.
> > Where on earth did you get "the teacher is satisfied" from what I wrote?
>
> You wrote "things are OK from the teacher's end", didn't you?
In context, that meant that the teacher is doing a fine job, not that
the teacher is satisfied. The latter may also be true, of course, but
that is not what I was talking about. I talked about comparing what I
got and what my son got, right? I did not mention talking to the
teacher and hearing about her satisfaction with her job.
There are evidently some subtle English language issues here. I think
you are missing a few contextual cues that native English speakers are
catching.
--
Brian Tung <brian@isi.edu >
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.html
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Date: 10 Aug 2006 19:43:35
From: Paul Schlyter
Subject: Re: Primary colors
|
In article <ebffma$tjf$1@praesepe.isi.edu >, Brian Tung <brian@isi.edu> wrote:
> Paul Schlyter wrote:
>> Do you still think it's OK to present RBY as THE set of fundamental colors,
>> implicitly implying it's the only set? I believe that's they way it's
>> usually presented to kids -- as THE fundamental colors, not as one
>> possible choice among a large number of other choices.
>
> I think it is not correct, strictly speaking, but it is a harmless first
> introduction, *provided* that the correct treatment is given later on.
> Unfortunately, it isn't always, and I agree with Chris: It is that
> omission that is the failing, not the earlier simplification.
>
>> You asked how to get yellow from RGB, and I told you how...
>
> With *paints*. If I talk about paints from the beginning of the post, I
> shouldn't need to say the word "paints" in each sentence to restrict the
> scope to them. Evidently, with you, I do.
As pointed out by Chris L Petersen, color mixing with opaque paints can
be done through dithering, which pretty much resembles additive color
mixing. And then one can obtain yellow from red and green.
>> So you used another word, "fundamental" colors perhaps?
>
> No. I said that in the U.S., kids are *taught* that those are the
> primary colors. I *never* said that they *are* the primary colors. I
> was explaining how some folks have arrived at the conclusion that they
> are the primary colors.
>
>>> Where on earth did you get "the teacher is satisfied" from what I wrote?
>>
>> You wrote "things are OK from the teacher's end", didn't you?
>
> In context, that meant that the teacher is doing a fine job, not that
> the teacher is satisfied. The latter may also be true, of course, but
> that is not what I was talking about. I talked about comparing what I
> got and what my son got, right? I did not mention talking to the
> teacher and hearing about her satisfaction with her job.
>
> There are evidently some subtle English language issues here. I think
> you are missing a few contextual cues that native English speakers are
> catching.
Probably this is so. And I guess that's a very common situation with the
English language: most English-speaking people do not have English as
their native language.
> Brian Tung <brian@isi.edu>
> The Astronomy Corner at http://astro.isi.edu/
> Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
> The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
> My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.html
--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/
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Date: 10 Aug 2006 15:04:37
From: Brian Tung
Subject: Re: Primary colors
|
Paul Schlyter wrote:
> As pointed out by Chris L Petersen, color mixing with opaque paints can
> be done through dithering, which pretty much resembles additive color
> mixing. And then one can obtain yellow from red and green.
Fair enough. However, I don't think that one can teach pointillism to
all six-year-olds. Some with good fine-motor control, perhaps, but not
most.
--
Brian Tung <brian@isi.edu >
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.html
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Date: 10 Aug 2006 08:32:32
From: Odysseus
Subject: Re: Primary colors
|
In article <ebd4lq$i36$1@merope.saaf.se >,
pausch@saaf.se (Paul Schlyter) wrote:
> In article <ebb0vc$ab6$1@praesepe.isi.edu>, Brian Tung <brian@isi.edu> wrote:
>
<snip >
>
> > If you were to use red, blue, and green, how on earth would you get yellow?
>
> By mixing red and green - by additive mixing, that is! It won't work
> for paints, but shine a red light and a green light, with balanced
> identities, on the same white screen, and you'll get yellow. Or watch
> closely, preferably with a magnifying glass, a yellow area on your TV
> screen or computer screen -- you won't find any yellow dots there, only
> red and green dots.
Another way to 'mix' colours additively is with a spinner of some kind:
rapidly alternating colours has more or less the same perceptual effect
as adding them. A sanding disk for a hand drill, with red and green
sectors mounted on it, will look yellow when rotating at a sufficient
speed.
--
Odysseus
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Date: 10 Aug 2006 10:43:01
From: Paul Schlyter
Subject: Re: Primary colors
|
In article <odysseus1479-at-43D2B2.02323210082006@news.telus.net >,
Odysseus <odysseus1479-at@yahoo-dot.com > wrote:
>In article <ebd4lq$i36$1@merope.saaf.se>,
> pausch@saaf.se (Paul Schlyter) wrote:
>
>> In article <ebb0vc$ab6$1@praesepe.isi.edu>, Brian Tung <brian@isi.edu> wrote:
>>
><snip>
>>
>>> If you were to use red, blue, and green, how on earth would you get yellow?
>>
>> By mixing red and green - by additive mixing, that is! It won't work
>> for paints, but shine a red light and a green light, with balanced
>> identities, on the same white screen, and you'll get yellow. Or watch
>> closely, preferably with a magnifying glass, a yellow area on your TV
>> screen or computer screen -- you won't find any yellow dots there, only
>> red and green dots.
>
> Another way to 'mix' colours additively is with a spinner of some kind:
> rapidly alternating colours has more or less the same perceptual effect
> as adding them. A sanding disk for a hand drill, with red and green
> sectors mounted on it, will look yellow when rotating at a sufficient
> speed.
>
> --
> Odysseus
It's actually a bit more complex than that, when you mix colors in the
time domain....
A spinning disk with only white and black sectors on it can be perceived
as red, green, blue, or any other color, depending on the order and sizes
of the white and black sectors. The non-neutral colors created in that
way will have low saturation though. Do a web search for "subjective
colors" to find out more.
--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/
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Date: 08 Aug 2006 20:57:03
From: Chris L Peterson
Subject: Re: Primary colors
|
On Tue, 8 Aug 2006 13:39:51 -0700, "Bob May" <bobmay@nethere.com > wrote:
>OH, great! Not only are the kids not being taught much, but they're being
>taught wrong!
It's not wrong. Any particular color space has its own primary colors
(and not necessarily three). The choice of red, blue, and yellow for
simple painting is a pretty good one. The fact that the resulting gamut
is less than that of the human eye isn't really important for elementary
school art classes. Colors in that environment are produced by mixing
pigments.
More serious artists have traditionally considered pink, blue, and
yellow to be primaries. This gives a little wider gamut. Printers
generally use cyan, magenta, and yellow since that gives a reasonably
wide gamut. But those colors are not mixed, but placed in dots close to
each other. CMY would not be a good choice for primary paint colors.
What primary colors would you like to see presented to kids just
learning to work with paint? After all, that's the grade school exposure
to color, not physiology.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Date: 09 Aug 2006 08:51:59
From: nytecam
Subject: Re: Primary colors
|
Brian Tung Wrote:
> Stephen Paul Wrote: -
> Since the primary colors are Red, Blue, and Yellow, shouldn't we use
> those for imaging instead of Red, Blue, and Green?-
>
> nytecam wrote:-
> Where did you get that idea????-
>
> In the U.S., it is common to teach schoolchildren red, blue, and
> yellow
> as the primary colors, when learning to paint.
>
> Brian Tung brian@isi.edu
>
> Thanks Brian for the info. I thought perhaps I'd been a little curt
> with my response and subsequently thought that reference was being made
> to subtractive CMY [M = reddish C = green/blue Y = yellow] as used in
> some camcorder chip like Sony's and also my SX MX5c camera but clearly
> was too obtuse from your explanation. Simple explanations are probably
> right!
>
> Nytecam 51N 0.1W
--
nytecam
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Date: 08 Aug 2006 12:43:32
From: Paul Schlyter
Subject: Re: Primary colors
|
In article <cKednQ_xRZ46TkrZnZ2dnUVZ_t-dnZ2d@comcast.com >,
Stephen Paul <smarshallpaul@gmail.com > wrote:
> Since the primary colors are Red, Blue, and Yellow, shouldn't we use
> those for imaging instead of Red, Blue, and Green?
No we shouldn't, since the (additive) primary colors are Red, Green
and Blue. Take a close look, with a magnifying glass, on some yellow
area of your TV or computer screen, and you might be quite surprised!
--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/
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Date: 08 Aug 2006 15:17:08
From: decaf
Subject: Re: Primary colors
|
Chris L Peterson wrote:
>CMY would not be a good choice for primary paint colors.
As a professional artist for about 3 decades, I can do far more with
CMY paints than I can red, blue and yellow. If I was restricted to
three colors in addition to B&W, CMY would be the best three to paint
realistically representationally the natural world.
Dan C.
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Date: 08 Aug 2006 22:50:24
From: Chris L Peterson
Subject: Re: Primary colors
|
On 8 Aug 2006 15:17:08 -0700, "decaf" <dchaffee@blitz-it.net > wrote:
>As a professional artist for about 3 decades, I can do far more with
>CMY paints than I can red, blue and yellow. If I was restricted to
>three colors in addition to B&W, CMY would be the best three to paint
>realistically representationally the natural world.
I don't think you can make such a broad statement. At the very least,
your choice of primary colors depends on the medium and style. How
pigments mix depends on whether they are opaque or transparent. I don't
see how CMY would be a good choice for opaque colors (oils and acrylics)
unless you happen to be a pointillist.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Date: 09 Aug 2006 09:08:36
From: dan chaffee
Subject: Re: Primary colors
|
On Tue, 08 Aug 2006 22:50:24 GMT, Chris L Peterson
<clp@alumni.caltech.edu > wrote:
>On 8 Aug 2006 15:17:08 -0700, "decaf" <dchaffee@blitz-it.net> wrote:
>
>>As a professional artist for about 3 decades, I can do far more with
>>CMY paints than I can red, blue and yellow. If I was restricted to
>>three colors in addition to B&W, CMY would be the best three to paint
>>realistically representationally the natural world.
>
>I don't think you can make such a broad statement. At the very least,
>your choice of primary colors depends on the medium and style. How
>pigments mix depends on whether they are opaque or transparent. I don't
>see how CMY would be a good choice for opaque colors (oils and acrylics)
>unless you happen to be a pointillist.
No, I'm not a pointalist. I'm a representational painter who paints
opaquely almost exlusively with oil paint. Why don't you think I know
what I can or cannot do with my palette? I can make the vast majority
of the colors I want for assorted landscapes with CMY. Fortunately I'm
not restricted to three colors --for where I need something outside
that possible range, but the vast majority of the paint in most of my
paintings could be achieved with CMY with B&W. Buying colors that
are between the primaries are often more for convienience and economy.
There are certain colors, ie. "rose madder" that are not possible by
mixing any primary, but most such colors fall outside of the range of
what I'm interested in.
Dan
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Date: 09 Aug 2006 08:02:24
From: starburst
Subject: Re: Primary colors
|
Dan wrote:
> There are certain colors, ie. "rose madder" that are not possible by
> mixing any primary
Clearly rose madder can be mixed. For while Titian was mixing rose
madder, his model reclined on a ladder. Her position to Titian suggested
coalition, so he leapt up the ladder and had her.
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Date: 09 Aug 2006 09:57:30
From: Brian Tung
Subject: Re: Primary colors
|
starburst wrote:
> Clearly rose madder can be mixed. For while Titian was mixing rose
> madder, his model reclined on a ladder. Her position to Titian suggested
> coalition, so he leapt up the ladder and had her.
You like Asimov too? :)
--
Brian Tung <brian@isi.edu >
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.html
|
| |
Date: 09 Aug 2006 20:22:22
From: Matthew Ota
Subject: Re: Primary colors
|
What is taught in elementary school is wrong, it just allows the
children to mix paints and come up with other secondary colors.
If you took a color theory class in college, as I did , you leran the
subtractive and additive color models, which deal with reflected versus
projected light.
RGB is the rule for projected light, as the chemical receptors in our
cone cells are highly receptive to those colors.
CMY (K) rules in the print industry.
Cyan
Magenta
Yellow
Black (K)
Your color inkjet printer uses these colors to print on paper.
But your phosphors on your monitor are RGB.
Two completely different color models.
BTW, to convert RGB colors to paint colors, got to
www.easyrgb.com
Also, it is an interesting poit that the human eye is most strongly
receptive to green light. We simpy eveolved that way. Note that most
plant life is green colored.
Also we see green laser beams easily.
Matthew Ota
Brian Tung wrote:
> Stephen Paul Wrote:
> > Since the primary colors are Red, Blue, and Yellow, shouldn't we use
> > those for imaging instead of Red, Blue, and Green?
>
> nytecam wrote:
> > Where did you get that idea????
>
> In the U.S., it is common to teach schoolchildren red, blue, and yellow
> as the primary colors, when learning to paint.
>
> --
> Brian Tung <brian@isi.edu>
> The Astronomy Corner at http://astro.isi.edu/
> Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
> The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
> My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.html
|
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Date: 10 Aug 2006 04:14:43
From: Chris L Peterson
Subject: Re: Primary colors
|
On 9 Aug 2006 20:22:22 -0700, "Matthew Ota" <otakenji@bigvalley.net >
wrote:
>What is taught in elementary school is wrong, it just allows the
>children to mix paints and come up with other secondary colors.
It isn't wrong. You could argue that its wrong to teach them that these
are THE primary colors, as opposed to the primaries for a particular
gamut, but I think most people would argue those concepts are a little
beyond most first graders. That sort of thing is done all the time, like
teaching that you can't subtract a big number from a smaller one, and
then teaching that you can a few years later.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Date: 10 Aug 2006 10:43:01
From: Paul Schlyter
Subject: Re: Primary colors
|
In article <1155180142.188090.13460@75g2000cwc.googlegroups.com >,
Matthew Ota <otakenji@bigvalley.net > wrote:
> What is taught in elementary school is wrong, it just allows the
> children to mix paints and come up with other secondary colors.
>
> If you took a color theory class in college, as I did , you leran the
> subtractive and additive color models, which deal with reflected versus
> projected light.
>
> RGB is the rule for projected light, as the chemical receptors in our
> cone cells are highly receptive to those colors.
>
> CMY (K) rules in the print industry.
>
> Cyan
> Magenta
> Yellow
> Black (K)
>
> Your color inkjet printer uses these colors to print on paper.
>
> But your phosphors on your monitor are RGB.
>
> Two completely different color models.
These two models are not "completely different". They are quite related;
the CMY colors are the complementary colors of the RGB colors.
> BTW, to convert RGB colors to paint colors, got to
>
> www.easyrgb.com
>
> Also, it is an interesting poit that the human eye is most strongly
> receptive to green light. We simpy eveolved that way. Note that most
> plant life is green colored.
>
> Also we see green laser beams easily.
>
> Matthew Ota
>
>
> Brian Tung wrote:
>> Stephen Paul Wrote:
>>> Since the primary colors are Red, Blue, and Yellow, shouldn't we use
>>> those for imaging instead of Red, Blue, and Green?
>>
>> nytecam wrote:
>>> Where did you get that idea????
>>
>> In the U.S., it is common to teach schoolchildren red, blue, and yellow
>> as the primary colors, when learning to paint.
--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/
|
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Date: 09 Aug 2006 12:37:53
From: decaf
Subject: Re: Primary colors
|
Brian Tung wrote:
worked out better, by *some* metric. But not enough better to switch.
> So I stand by my assertion that it's not wrong to use RBY for kids
> learning to paint. I didn't imply that it was wrong to use anything
> else.
Yes, I'd go go along with this as well. Reason being, it is a simpler
matter to
learn to mix these three to approximate the majority of colors found in
nature, with the important exception being deep violet and intense
purples. Children and GWB tend to
think of colors as either one or the other and not much in between.
They also tend to think of black or white, but not much in the way of
greys. CMY is a better choice foradvanced students because it affors a
greater range, yet a more sophisticated
understanding and sensitivity to finding the right balances.
Dan
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Date: 09 Aug 2006 12:23:25
From: decaf
Subject: Re: Primary colors
|
starburst wrote:
> Dan wrote:
>
> > There are certain colors, ie. "rose madder" that are not possible by
> > mixing any primary
>
> Clearly rose madder can be mixed. For while Titian was mixing rose
> madder, his model reclined on a ladder. Her position to Titian suggested
> coalition, so he leapt up the ladder and had her.
How long have you been waiting to use that one? ;-)
D.
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Date: 10 Aug 2006 05:34:58
From:
Subject: Re: Primary colors
|
Chris L Peterson wrote:
> I don't think you can make such a broad statement. At the very least,
> your choice of primary colors depends on the medium and style. How
> pigments mix depends on whether they are opaque or transparent. I don't
> see how CMY would be a good choice for opaque colors (oils and acrylics)
> unless you happen to be a pointillist.
>
If you use the pointilist technique of placing small dots of pigment
adjacent to one another, not overlapping, you can actually use the
additive primaries, RGB. The light reflected from a pattern of small
(unresolved) red and green spots does mix to give the sensation of
yellow, whereas if you either mix the pigments or superimpose red and
green dots of pigment, you get the subtractive result, ie, a kind of
purplish brown, depending upon exactly what red and green pigments your
are using. Similarly, unresolved patterns of adjacent green and blue
dots give the impression of cyan and red and blue dots give the
impression of magenta, but only if they are not overlapped.
Clif
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| | |
Date: 10 Aug 2006 14:32:20
From: Chris L Peterson
Subject: Re: Primary colors
|
On 10 Aug 2006 05:34:58 -0700, WA2GUF@optonline.net wrote:
>If you use the pointilist technique of placing small dots of pigment
>adjacent to one another, not overlapping, you can actually use the
>additive primaries, RGB...
You can. I mentioned pointillism because that is essentially how process
printing works. Colors are not formed by mixing the CMY pigments, but by
placing dots of the ink close together. Straight mixing produces much
muddier colors. When you look at a printed page you see the individual
dots of CMY (and usually black).
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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| |
Date: 10 Aug 2006 18:52:37
From: Paul Winalski
Subject: Re: Primary colors
|
Color vision is quite complicated. The cone cells in the retina
contain pigments that, when a light photon hits them, can
reversibly change their electrochemical configuration. This results
in nerve impulses along the optic nerve to the brain, which processes
the nerve signals into the image colors that we comprehend. There
are three main types of retinal pigments in cone cells, and each
has a different pattern of light absorption and activation (e.g.,
one pigment may respond more to red wavelengths than the other two).
It is the different response of the different pigments that lets us
distinguish one color from another.
One consequence of this mechanism is that if you take a particular
wavelength of light, say, for example, one of the two yellow
colors emitted by sodium vapor, any combination of other wavelengths
that happens to excite the eye pigments in the same way will be
seen as that color. This is how you can mix red and green light and
get a combination of wavelengths that is seen as yellow, even though
there isn't a single photon whose wavelength falls in the yellow part
of the spectrum. This is also how the optical illusions work where
you spin a black and white pattern real fast and end up seeing
colors.
Dr. Land at Polariod did extensive studies on color perception, and
he found that just about any trio of colors will work to some degree,
but some combinations are more effective than others.
So the bottom line is that there's no such thing as "THE primary
colors". There are several primary color systems. Red/blue/yellow is
one that happens to work well for the sorts of pigments used in
elementary school art. Red/green/blue works well for television
phosphors. Cyan/magenta/yellow is yet a third system. They all work
in the same general physiological fashion--by sending a combination
of wavelengths to the eye that tickle the cone pigments in the same
way as a color (or set of colors) whose wavelengths aren't present.
-Paul W.
On Mon, 07 Aug 2006 19:58:37 -0400, Stephen Paul
<smarshallpaul@gmail.com > wrote:
>Since the primary colors are Red, Blue, and Yellow, shouldn't we use
>those for imaging instead of Red, Blue, and Green?
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