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Main
Date: 19 Oct 2006 22:15:01
From: Antonio Zanardo
Subject: Bayer CCD vs. LRGB imaging
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What do you think about the color Bayer mask CCD versus the
monochromo+filters LRBG as far as results is concerned?
Antonio Zanardo
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Date: 20 Oct 2006 03:47:21
From: Chris L Peterson
Subject: Re: Bayer CCD vs. LRGB imaging
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On Thu, 19 2006 22:15:01 GMT, "Antonio Zanardo"
<antoniozanardoTOGLIMAIUSCOLE@ATlibero.it > wrote:
>What do you think about the color Bayer mask CCD versus the
>monochromo+filters LRBG as far as results is concerned?
The best images are RGB via separate filters. Next is LRGB. Worst is
one-shot color (Bayer RGGB, CMY, etc). The problems with the one-shot
are partly because of artifacts from the color components not lining up
perfectly, but mostly from the fact that the dye filters over the pixels
are a bit leaky, they don't have the correct bandpasses for astronomical
emission sources, and in many cases the passbands aren't even monotonic
(so there are ambiguous color combinations).
That's not to say that you can't get fair results with one-shot color
cameras, especially with targets that lean heavily towards continuous
emissions, but the results won't usually compare with what you can get
by combining individual RGB or LRGB frames.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Date: 20 Oct 2006 15:23:47
From: Trane Francks
Subject: Re: Bayer CCD vs. LRGB imaging
|
On 2006-10-20 12:47 +0900, Chris L Peterson wrote:
> The best images are RGB via separate filters. Next is LRGB. Worst is
Hi, Chris. Why would RGB be better than LRGB? Is it something to do with
binning on LRGB exposures?
I apologize if it's a stupid question. I haven't done any imaging yet
apart from some afocal lunar shots with a cheap hand-held.
Thanks,
trane
--
/////////////////////////////////////////////////////////
// Trane Francks trane@gol.com Tokyo, Japan
// Practice random kindness and senseless acts of beauty.
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Date: 20 Oct 2006 14:01:35
From: Chris L Peterson
Subject: Re: Bayer CCD vs. LRGB imaging
|
On Fri, 20 2006 15:23:47 +0900, Trane Francks <trane@gol.com > wrote:
>Hi, Chris. Why would RGB be better than LRGB? Is it something to do with
>binning on LRGB exposures?
RGB provides the purest chrominance information. With LRGB, your
luminance is normally out of balance with your chrominance (in many
cases, the L even has an IR component included). In other words, the
luminance signal is weighted by the spectral responsivity of the
detector, which is different than the spectral responsivity of the
convolved RGB components. Furthermore, the main reason that people use
LRGB is to reduce the total exposure time by collecting high resolution
luminance and low resolution color. So LRGB images contain less
information, even though this is usually not readily visible to the eye.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Date: 21 Oct 2006 00:10:50
From: Trane Francks
Subject: Re: Bayer CCD vs. LRGB imaging
|
On 2006-10-20 23:01 +0900, Chris L Peterson wrote:
Hi, Chris.
> On Fri, 20 2006 15:23:47 +0900, Trane Francks <trane@gol.com> wrote:
>
>>Hi, Chris. Why would RGB be better than LRGB? Is it something to do with
>>binning on LRGB exposures?
>
> RGB provides the purest chrominance information. With LRGB, your
> luminance is normally out of balance with your chrominance (in many
> cases, the L even has an IR component included). In other words, the
[ snip ]
Thanks for an easy-to-understand explanation. It is very much appreciated.
trane
--
/////////////////////////////////////////////////////////
// Trane Francks trane@gol.com Tokyo, Japan
// Practice random kindness and senseless acts of beauty.
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Date: 20 Oct 2006 07:26:30
From: RMOLLISE
Subject: Re: Bayer CCD vs. LRGB imaging
|
Chris L Peterson wrote:
> I disagree. I don't find getting data with a one-shot camera any easier
> at all- with a dedicated astrocamera, either way you push a button and
> let a data collection program run. The only complexity that using
> filters adds is the need to take additional darks and flats, but those
> normally come from a library, so the added work is needed only
> occasionally, not routinely. However, when you use a one-shot color
> camera (unless you simply don't care about reasonable color at all) you
> hugely increase the time it takes to process images. A separately
> filtered image might take 30 minutes to completely process; a one-shot
> image can take hours.
>
HI Chris:
You are allowed to disagree! Well...this one time, anyway. :-)
However, most of the rest of us--especially those who, like your Old
Uncle, could be best desribed as "imaging dabblers"--are gonna disagree
with _you_, since to do tricolor imaging:
You need three (or four) good exposures of the target, not just one.
Many of us have a hard time getting that one.
The exposure has to be right for each image.
Exposure time goes up for filtered shots, too, giving us more time to
screw up.
The resulting shots must be calibrated and have to be properly exposed
and registered and balanced. I've seen some "wizards" struggle with
this on occasion.
I've never seen that a one-shot image takes "hours." Quite the reverse.
OTOH, I don't aspire to appear in the back pages of S&T or challenge
Jack Newton. For my purproses, monochrome or one shot color does just
fine. I like black and white a lot, but when I have to have color, one
shot does fine for me.
'Course I'm in awe of what you and those other folks who actually know
what they are doing have accomplished. ;-)
Peace,
Rod Mollise
Author of:
Choosing and Using a Schmidt Cassegrain Telescope
and
The Urban Astronomer's Guide
<http://skywatch.brainiac.com/astroland >
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Date: 20 Oct 2006 14:58:49
From: Chris L Peterson
Subject: Re: Bayer CCD vs. LRGB imaging
|
On 20 2006 07:26:30 -0700, "RMOLLISE" <rmollise@hotmail.com > wrote:
>However, most of the rest of us--especially those who, like your Old
>Uncle, could be best desribed as "imaging dabblers"--are gonna disagree
>with _you_, since to do tricolor imaging:
>
>You need three (or four) good exposures of the target, not just one.
>Many of us have a hard time getting that one.
But you need the same total exposure time for the same S/N. Why is
taking three or four images more work than one? Either way, you push a
button and come back when it's done.
>The exposure has to be right for each image.
But it's always the same ratio, based on your filters. How hard is that?
>Exposure time goes up for filtered shots, too, giving us more time to
>screw up.
No, it doesn't. For a given S/N, you need a given amount of photons. If
you are shooting shorter one-shot exposures, it just means you are
settling for lower S/N. You can shoot the tri-color shorter too, and get
the same results.
>The resulting shots must be calibrated and have to be properly exposed
>and registered and balanced. I've seen some "wizards" struggle with
>this on occasion.
Exactly. This is by far the hardest part, and it is very much more
difficult with one-shot images. With good tri-color images, you can
normally calibrate on standard star colors and you're 90% of the way
there. Once you've worked out the calibration factors (once!), color
processing is almost automated. In fact, you can get quite acceptable
results with no user intervention at all. Not so with one-shot color.
Because of the leaky filters and poor bandwidths, you can't calibrate on
star colors and you need to apply manual color tweaks to selective parts
of the image (and selective colors) to get something reasonable unless
you have nothing but continuous sources in the image.
>I've never seen that a one-shot image takes "hours." Quite the reverse.
>OTOH, I don't aspire to appear in the back pages of S&T or challenge
>Jack Newton. For my purproses, monochrome or one shot color does just
>fine. I like black and white a lot, but when I have to have color, one
>shot does fine for me.
I prefer monochrome astroimages myself. But when discussing color, I
think you fall into a logical fallacy comparing tri-color and one-shot.
The reason you find one-shot simpler is because you are willing to cut a
lot of corners (shorter exposure time, simplified processing). You could
cut the same corners with tri-color and you'd still end up with better
results.
The only time I sometimes find one-shot simpler is when using a DSLR. In
a field setting, the ability to stick a camera on the back of a scope
without worrying about setting up a laptop and control software can be
very liberating. But I still end up with images that take far more
processing than would be required for tricolor. But the acquisition
component is somewhat simpler.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Date: 20 Oct 2006 05:56:42
From: RMOLLISE
Subject: Re: Bayer CCD vs. LRGB imaging
|
Antonio Zanardo wrote:
> What do you think about the color Bayer mask CCD versus the
> monochromo+filters LRBG as far as results is concerned?
>
> Antonio Zanardo
Hi:
There's no doubt that a filtered monochrome CCD (whether LRGB or some
other technique) produces superior results. HOWSOMEEVER...there's no
easier way to get color deep sky shots than with a one-shot color
camera (and there are some very capable models out now, like the SBIG
one-shot color St2000). For a lot of folks "easy and good enough"
trumps "difficult and more better." ;-)
Peace,
Rod Mollise
Author of:
Choosing and Using a Schmidt Cassegrain Telescope
and
The Urban Astronomer's Guide
<http://skywatch.brainiac.com/astroland >
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Date: 20 Oct 2006 14:08:29
From: Chris L Peterson
Subject: Re: Bayer CCD vs. LRGB imaging
|
On 20 2006 05:56:42 -0700, "RMOLLISE" <rmollise@hotmail.com > wrote:
>There's no doubt that a filtered monochrome CCD (whether LRGB or some
>other technique) produces superior results. HOWSOMEEVER...there's no
>easier way to get color deep sky shots than with a one-shot color
>camera (and there are some very capable models out now, like the SBIG
>one-shot color St2000). For a lot of folks "easy and good enough"
>trumps "difficult and more better." ;-)
I disagree. I don't find getting data with a one-shot camera any easier
at all- with a dedicated astrocamera, either way you push a button and
let a data collection program run. The only complexity that using
filters adds is the need to take additional darks and flats, but those
normally come from a library, so the added work is needed only
occasionally, not routinely. However, when you use a one-shot color
camera (unless you simply don't care about reasonable color at all) you
hugely increase the time it takes to process images. A separately
filtered image might take 30 minutes to completely process; a one-shot
image can take hours.
IMO, it is false economy to view one-shot color cameras as simpler or
easier to use.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Date: 20 Oct 2006 20:03:07
From: Antonio Zanardo
Subject: Re: Bayer CCD vs. LRGB imaging
|
"Antonio Zanardo" <antoniozanardoTOGLIMAIUSCOLE@ATlibero.it > ha scritto nel
messaggio news:FNSZg.9716$uv5.72668@twister1.libero.it...
> What do you think about the color Bayer mask CCD versus the
> monochromo+filters LRBG as far as results is concerned?
>
> Antonio Zanardo
Thank you all folks for clearing up a bit my ideas about color images taking
and processing.
Antonio Zanardo
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Date: 20 Oct 2006 11:48:44
From: atasselli@hotmail.com
Subject: Re: Bayer CCD vs. LRGB imaging
|
Chris L Peterson wrote:
> On Fri, 20 2006 15:23:47 +0900, Trane Francks <trane@gol.com> wrote:
>
> >Hi, Chris. Why would RGB be better than LRGB? Is it something to do with
> >binning on LRGB exposures?
>
> RGB provides the purest chrominance information. With LRGB, your
> luminance is normally out of balance with your chrominance (in many
> cases, the L even has an IR component included). In other words, the
> luminance signal is weighted by the spectral responsivity of the
> detector, which is different than the spectral responsivity of the
> convolved RGB components. Furthermore, the main reason that people use
> LRGB is to reduce the total exposure time by collecting high resolution
> luminance and low resolution color. So LRGB images contain less
> information, even though this is usually not readily visible to the eye.
>
For the same amount of time LRGB contains more information not less.
Andrea T.
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Date: 20 Oct 2006 19:12:58
From: Chris L Peterson
Subject: Re: Bayer CCD vs. LRGB imaging
|
On 20 2006 11:48:44 -0700, "atasselli@hotmail.com"
<atasselli@hotmail.com > wrote:
>For the same amount of time LRGB contains more information not less.
That's an over-generalization. The information content is a complex
function of S/N and actual intent. There is less spatial information in
the chrominance (assuming it's binned) in an LRGB than an RGB, unless
you are working at the noise limit to begin with (unlikely).
There is a reason that science images are rarely (if ever) made using
LRGB. The technique is primarily useful for aesthetic imaging, because
the eye is very insensitive to low resolution chrominance.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Date: 21 Oct 2006 16:59:17
From: Anthony Ayiomamitis
Subject: Re: Bayer CCD vs. LRGB imaging
|
Chris L Peterson wrote:
> On 20 2006 11:48:44 -0700, "atasselli@hotmail.com"
> <atasselli@hotmail.com> wrote:
>
>
>>For the same amount of time LRGB contains more information not less.
>
>
> That's an over-generalization. The information content is a complex
> function of S/N and actual intent. There is less spatial information in
> the chrominance (assuming it's binned) in an LRGB than an RGB, unless
> you are working at the noise limit to begin with (unlikely).
>
> There is a reason that science images are rarely (if ever) made using
> LRGB. The technique is primarily useful for aesthetic imaging, because
> the eye is very insensitive to low resolution chrominance.
How do things change when LRGB is shot strictly with 1x1 binning?
Also, I remember reading somewhere that for each hour of Lum (unbinned),
we need approximately 2.5 hours of chrominance (for each of RGB and
unbinned) ... any thoughts?
Anthony.
>
> _________________________________________________
>
> Chris L Peterson
> Cloudbait Observatory
> http://www.cloudbait.com
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Date: 21 Oct 2006 14:38:21
From: Chris L Peterson
Subject: Re: Bayer CCD vs. LRGB imaging
|
On Sat, 21 2006 16:59:17 +0300, Anthony Ayiomamitis
<anthony@perseus.no2spam.gr > wrote:
>How do things change when LRGB is shot strictly with 1x1 binning?
That's a good question, and I'm not sure off-hand just how to analyze
the problem. When you image using LRGB, you are collecting redundant
data- there is overlapping content between the L frame and each of the
color frames. That should improve your noise statistics, but it is
unclear whether it does so any better than applying that L time to the
individual RGB frames would.
I don't really see the point in shooting unbinned LRGB (well, shooting
it is fine, but you need to bin at some point in your processing).
Binning doesn't of itself reduce exposure times- the total S/N is the
same whether you bin or not, and is determined by exposure time. What
binning does is let you trade resolution for reduced noise. The more
pixels groups you sum, the lower the noise in those superpixels (and the
lower the resolution). LRGB takes advantage of the fact that the
eye/brain is insensitive to both chrominance spatial resolution and
chrominance noise. By providing a high resolution, low noise luminance
component, we get away with RGB frames that would be considered
significantly underexposed if they were used alone.
>Also, I remember reading somewhere that for each hour of Lum (unbinned),
>we need approximately 2.5 hours of chrominance (for each of RGB and
>unbinned) ... any thoughts?
Not really. Is this just some empirically determined rule?
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Date: 21 Oct 2006 19:23:28
From: Anthony Ayiomamitis
Subject: Re: Bayer CCD vs. LRGB imaging
|
Chris L Peterson wrote:
> On Sat, 21 2006 16:59:17 +0300, Anthony Ayiomamitis
> <anthony@perseus.no2spam.gr> wrote:
>
>>Also, I remember reading somewhere that for each hour of Lum (unbinned),
>>we need approximately 2.5 hours of chrominance (for each of RGB and
>>unbinned) ... any thoughts?
>
>
> Not really. Is this just some empirically determined rule?
Unfortunately I do not remember the rational cited. After reading that
comment, I paid more attention to other people's exposures and indeed I
started noting this particular ratio. In other words, I would see 50
minutes Lum (1x1 binning) and 20 minutes (2x2 binning) for each of R, G
and B. The total RGB exposure is effectively the same as that for the
Lum but the binning is dramatically different.
Anthony.
>
> _________________________________________________
>
> Chris L Peterson
> Cloudbait Observatory
> http://www.cloudbait.com
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Date: 20 Oct 2006 11:46:39
From: atasselli@hotmail.com
Subject: Re: Bayer CCD vs. LRGB imaging
|
Michael McCulloch wrote:
> Along the same topic, but slightly different...
>
> How do you feel about the oversaturation applied to the color in many
> astro shots? I think it is taken to the extreme at times and can give
> the uninformed unrealistic expectations for observing.
>
> My personal opinion is that the new mural at the Griffith Observatory
> is a little "over the top" if the color saturation shown in the APOD
> pic of the same accurately reflects the public display:
>
> http://antwrp.gsfc.nasa.gov/apod/ap061011.html
Awful processing. Are they really going to display THAT on a wall?
Andrea T.
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Date: 20 Oct 2006 14:33:16
From: Michael McCulloch
Subject: Re: Bayer CCD vs. LRGB imaging
|
Along the same topic, but slightly different...
How do you feel about the oversaturation applied to the color in many
astro shots? I think it is taken to the extreme at times and can give
the uninformed unrealistic expectations for observing.
My personal opinion is that the new mural at the Griffith Observatory
is a little "over the top" if the color saturation shown in the APOD
pic of the same accurately reflects the public display:
http://antwrp.gsfc.nasa.gov/apod/ap061011.html
---
Michael McCulloch
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Date: 20 Oct 2006 18:44:51
From: Chris L Peterson
Subject: Re: Bayer CCD vs. LRGB imaging
|
On Fri, 20 2006 14:33:16 -0400, Michael McCulloch
<michaelm@nospam.invalid.net > wrote:
>Along the same topic, but slightly different...
>
>How do you feel about the oversaturation applied to the color in many
>astro shots? I think it is taken to the extreme at times and can give
>the uninformed unrealistic expectations for observing.
Personally, I couldn't care less about "unrealistic expectations for
observing", since visual astronomy and imaging are completely different
things.
How color is presented depends on intent: oversaturation may be useful
if you are emphasizing chemical makeup, in the same way that
oversharpening may be useful for emphasizing physical structure. For
images with aesthetic intent, I definitely prefer less saturation
(actually, I usually prefer B&W, which is about as unsaturated as you
can get <g >).
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Date: 21 Oct 2006 19:35:05
From: Michael McCulloch
Subject: Re: Bayer CCD vs. LRGB imaging
|
On Fri, 20 2006 18:44:51 GMT, Chris L Peterson
<clp@alumni.caltech.edu > wrote:
>Personally, I couldn't care less about "unrealistic expectations for
>observing", since visual astronomy and imaging are completely different
>things.
I guess you haven't been at a star party event where the newbies
complain all night about how the objects "don't look like the
pictures" even through our club's 20" scope. ;-)
---
Michael McCulloch
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Date: 22 Oct 2006 02:46:42
From: Chris L Peterson
Subject: Re: Bayer CCD vs. LRGB imaging
|
On Sat, 21 2006 19:35:05 -0400, Michael McCulloch
<michaelm@nospam.invalid.net > wrote:
>I guess you haven't been at a star party event where the newbies
>complain all night about how the objects "don't look like the
>pictures" even through our club's 20" scope. ;-)
Oh, I have. I try to convince them to buy cameras <g >.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Date: 21 Oct 2006 13:28:59
From: atasselli@hotmail.com
Subject: Re: Bayer CCD vs. LRGB imaging
|
Anthony Ayiomamitis wrote:
> Chris L Peterson wrote:
> > On Sat, 21 2006 16:59:17 +0300, Anthony Ayiomamitis
> > <anthony@perseus.no2spam.gr> wrote:
> >
> >>Also, I remember reading somewhere that for each hour of Lum (unbinned),
> >>we need approximately 2.5 hours of chrominance (for each of RGB and
> >>unbinned) ... any thoughts?
> >
> >
> > Not really. Is this just some empirically determined rule?
>
> Unfortunately I do not remember the rational cited. After reading that
> comment, I paid more attention to other people's exposures and indeed I
> started noting this particular ratio. In other words, I would see 50
> minutes Lum (1x1 binning) and 20 minutes (2x2 binning) for each of R, G
> and B. The total RGB exposure is effectively the same as that for the
> Lum but the binning is dramatically different.
>
I don't think there is no hard and fast rule, albeit empirical. I may
shot 2x more luminance than RGB although, obviously, the more the
better.
Andrea T.
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| | |
Date: 22 Oct 2006 02:38:58
From: Anthony Ayiomamitis
Subject: Re: Bayer CCD vs. LRGB imaging
|
atasselli@hotmail.com wrote:
> Anthony Ayiomamitis wrote:
>
>>Chris L Peterson wrote:
>>
>>>On Sat, 21 2006 16:59:17 +0300, Anthony Ayiomamitis
>>><anthony@perseus.no2spam.gr> wrote:
>>>
>>>
>>>>Also, I remember reading somewhere that for each hour of Lum (unbinned),
>>>>we need approximately 2.5 hours of chrominance (for each of RGB and
>>>>unbinned) ... any thoughts?
>>>
>>>
>>>Not really. Is this just some empirically determined rule?
>>
>>Unfortunately I do not remember the rational cited. After reading that
>>comment, I paid more attention to other people's exposures and indeed I
>>started noting this particular ratio. In other words, I would see 50
>>minutes Lum (1x1 binning) and 20 minutes (2x2 binning) for each of R, G
>>and B. The total RGB exposure is effectively the same as that for the
>>Lum but the binning is dramatically different.
>>
>
>
> I don't think there is no hard and fast rule, albeit empirical. I may
> shot 2x more luminance than RGB although, obviously, the more the
> better.
I have seen shots where, for example, there was 300 minutes Lum and 30
minutes each for RGB. I suspect for faint galaxies, there would be a
much greater bias towards Lum (ex. 3x and 4x) whereas planetaries would
be mostly RGB.
Anthony.
>
> Andrea T.
>
|
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Date: 24 Oct 2006 11:37:09
From: nytecam
Subject: Re: Bayer CCD vs. LRGB imaging
|
Antonio Zanardo Wrote:
> What do you think about the color Bayer mask CCD versus the
> monochromo+filters LRBG as far as results is concerned? Antonio
> Zanardo
There's a common perception that resultant colour images, splendid as
they are even from RGB, are 'true' colours - they are not. In reality
the colour saturation in imaging maybe greatly exaggerated and a minor
bias will produce strange results. The 'natural' colours are quite
muted but this is rarely shown in finished images. It worth
remembering the human eye doesn’t to cope well with emission line
objects - which is why that fluorescent tube near you looks white but
is in reality a blend of many discrete colours to give an illusion of
white.
Much of today’s ‘expectation’ of colour goes back to the colour
photography decades ago where, in emission objects, red hydrogen-alpha
emission sat on the peak sensitivity of the red layer of tripack [or
RGB] whilst green OIII and H-beta line sat in the dip between blue and
green and were weakly recorded – result glorious red nebulae!
My interest is astro-spectroscopy so I’m not limited to a blend of
three primary colours. I’m even able to appreciate near IR that CCDs
record so well that are normally ‘killed’ in full colour imaging
because they degrade results! In conclusion, if colours are
exaggerated then it doesn’t matter much which colour system is used to
record them.
Nytecam 51N 0.1W
www.astroman.fsnet.co.uk
--
nytecam
|
| | |
Date: 24 Oct 2006 15:44:20
From: Paul Schlyter
Subject: Re: Bayer CCD vs. LRGB imaging
|
In article <nytecam.2g6gxn@spacebanter.com >,
nytecam <nytecam.2g6gxn@spacebanter.com > wrote:
>
>Antonio Zanardo Wrote:
>> What do you think about the color Bayer mask CCD versus the
>> monochromo+filters LRBG as far as results is concerned? Antonio
>> Zanardo
>
>There's a common perception that resultant colour images, splendid as
>they are even from RGB, are 'true' colours - they are not. In reality
>the colour saturation in imaging maybe greatly exaggerated and a minor
>bias will produce strange results. The 'natural' colours are quite
>muted but this is rarely shown in finished images. It worth
>remembering the human eye doesn’t to cope well with emission line
>objects - which is why that fluorescent tube near you looks white but
>is in reality a blend of many discrete colours to give an illusion of
>white.
...which means the color is white. You're making the common mistake of
considering colors to be equal to wavelength. As a matter of fact, the
colors we see also depend on other things than just the wavelength mix
of light entering our eyes. And you also consider the actual colors we
see as an "illusion", while they are in fact the colors themselves.
Light with fairly narrow emission lines is more likely to emphasize
the individual differences between the eyes of different people, making
them see different colors more often than if the light is continuous.
No, we cannot accurately transfer our color perception from one
person to another - all we can do is label the colors. However, we
can put two colored objects in e.g. fluorescent light, and ask
different people if they think the two colors are the same or if
they differ -- and sometimes people will disagree about this.
>Much of today’s ‘expectation’ of colour goes back to the colour
>photography decades ago where, in emission objects, red hydrogen-alpha
>emission sat on the peak sensitivity of the red layer of tripack [or
>RGB] whilst green OIII and H-beta line sat in the dip between blue and
>green and were weakly recorded – result glorious red nebulae!
The "natural color" of almost all nebulae is grey, since they are too
week for the cones in our retina to see them. Only our rods see them,
but our rods just see neutral colors (= shades of gray). And color
film see a bit outside the visual wavelength range, both on the blue
and the red side of the spectrum. And to talk about "natural color"
of light outside the visual wavelength range is an oxymoron!
>My interest is astro-spectroscopy so I’m not limited to a blend of
>three primary colours. I’m even able to appreciate near IR that CCDs
>record so well that are normally ‘killed’ in full colour imaging
>because they degrade results! In conclusion, if colours are
>exaggerated then it doesn’t matter much which colour system is used to
>record them.
>
>Nytecam 51N 0.1W
>www.astroman.fsnet.co.uk
>
>
>
>
>--
>nytecam
--
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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: 24 Oct 2006 14:14:43
From: David Knisely
Subject: Re: Bayer CCD vs. LRGB imaging
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nytecam posted:
> It worth
> remembering the human eye doesn’t to cope well with emission line
> objects - which is why that fluorescent tube near you looks white but
> is in reality a blend of many discrete colours to give an illusion of
> white.
Actually, the eye does fairly well with a number of emission lines, as
anyone can see using a simple spectroscope and a gas discharge tube.
Indeed, the Oxygen [III] lines at 4959 and 5007 Angstroms are readily
visible and are dominant in producing the bluish-green color of many of
the brighter planetary nebulae. It is only for lines near the edges of
the visual spectrum that the eye does not respond well to, such as
H-alpha where the eye's sensitivity in the red part of the spectrum is
fairly low. Clear skies to you.
--
David W. Knisely KA0CZC@navix.net
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/
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