Colour spaces

[Panopeeper]

From the FAQ's on Munsell Color Science Laboratory:

A gamut is defined as the range of colors that a given imaging device can display

This is his definition, not the definition.

While it is certainly possible that two colors that are visually distinct might be mapped into the same color signals by a camera, that does not mean that the camera could not detect those colors. It just couldn't discriminate them

According to this explanation, the gamut of sRGB is the same as that of ProPhoto: one can input the ProPhoto in the sRGB encoding. Although some colors can not be reproduced any more, that does not matter, right?

Look further for definitions, and you will find, the the reproduction of the colors is important.

Example:

Color gamut is the subset of colors, which can be accurately represented...

Depending on the cameras (sensors), certain colors can not be accurately represented (one can not distingush between the colors; in other words, when you see a certain color from the sensor, you can not tell, what color it was originally). This is the reason, that the gamuts of cameras are different.

[Schewe]

Uh huh...and I've used Rawnalyze to look at a raw file before Zalman told me how to output a raw file from DNG Verify...it doesn't alter the fact that something, somewhere has to be able to determine that a specific pixel in a specific coordinate represents R, G, & B. And it's that interpretation of the Bayer array that then represents the grayscale as color data instead of demosiacing. But the original capture is grayscale...

So, Bill, you like the true linear image better? I actually have created both a linear gamma working space in Photoshop as well as a ProPhoto RGB with a linear gamma so I could work with linear gradients in grayscale and color. But the original posted files WERE originally in linear until I transformed into sRGB for the original posting.

[Panopeeper]

without any demosaicing. If so, he is not an imaging moron, even though he doesn't use gamut in the sense that it is used in digital cameras

Actually, Rawnalyze works with the camera's color space in the sense, that not only no de-mosaicing takes place, but the mapping from camera colors to CIE XYZ is not carried out either. (Of course, this is not correct, because the raw channels do not represent single colors almost the entire spectrum).

Btw, the wording in the DNG specification (written by Adobe) is:

Mapping [span style=\'font-size:14pt;line-height:100%\']Camera Color Space [/span]to CIE XYZ Space

[PeterLange]

In a nutshell, a color mixing function, also called a color matching function, is a mathematical defined representation of a measured color based on three monochromatic RGB primaries that would duplicate the observed color of a measured wavelength. Until its mapped into a defined RGB space, it can’t have a color gamut.

So I sincerely hope that camera manufacturers a.) and Adobe Camera Raw b.) are sharing the same definition for CIE XYZ:

a.) to shape the spectral response of the sensor in a way to represent a linear combination of CIE XYZ matching functions.

b.) to facilitate a somewhat correct interpretation of the camera’s gamut by assignment of a matrix space representing an appropriate subset of same CIE XYZ master.

Peter

--

[bjanes]

So, Bill, you like the true linear image better? I actually have created both a linear gamma working space in Photoshop as well as a ProPhoto RGB with a linear gamma so I could work with linear gradients in grayscale and color. But the original posted files WERE originally in linear until I transformed into sRGB for the original posting.
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Jeff, you already know most of what I am saying below, but others may be interested in the information.

The linear files do not display well without color management, because a gamma of 2.2 is assumed, at least with Windows. I don't know that much about Macs, but I understand they no longer use a gamma of 1.8. If you assign your custom ProPhotoRGB with a gamma of one to the linear file when you open it in Photoshop it will display with normal tonality, but the colors will be off unless your original has ProPhoto primaries. If you take a file with a bit depth of 12 and dump into a 16 bit linear space, it will still look very dark.

An alternative way of viewing a linear file in a gamma 2.2 or gamma 1.8 space is to apply a curve in Photoshop that undoes the gamma encoding. Shown below is a gamma 2.2 curve

[attachment=4018:attachment]

Here is the flower image at gamma = 1 on the left (in sRGB), with the gamma 2.2 curve applied in the middle, and with a contrast boost via an S-curve on the right. Simply applying a gamma of 2.2 results in a very flat image.

[attachment=4019:attachment]

Most HDR encodings use linear gamma without any tone curve (scene referred) and they display normally in Photoshop. If you want to reproduce a scene exactly, there must be a one to one relationship between the source (the scene) and the reproduction. When you view a gamma encoded file or print it, a reverse gamma function is applied but any compression is not undone, or else the image would clip due to limited dynamic range of the print or screen.

[digitaldog]

Uh huh...and I've used Rawnalyze to look at a raw file before Zalman told me how to output a raw file from DNG Verify...it doesn't alter the fact that something, somewhere has to be able to determine that a specific pixel in a specific coordinate represents R, G, & B. And it's that interpretation of the Bayer array that then represents the grayscale as color data instead of demosiacing. But the original capture is grayscale...
[a href=\"index.php?act=findpost&pid=155692\"][{POST_SNAPBACK}][/a]

Exactly! And this has been discussed by the color scientist at Munsell (quote above) when he writes that the camera has no gamut. You can't define the gamut or a color space until you place specific coordinates of RG and B. Bruce said this as well.

This is getting to be a big cluster-fu*% of semantics but I'd far prefer to take the side of the color scientists and Bruce, among just a few who state I believe correctly and for the last time, the Raw data is essentially Grayscale and the capture device has no gamut.

And yet another quote from Phil Green:

Bruce is right, there's no gamut boundary associated with a capture
device. If you took a colour at the saturation limit of visual
perception, it would probably be outside any reproduction media gamut
(display, print whatever) but would still be a stimulus to which a
capture device would respond. You do have dyanamic range and
sensitivity limitations that would mean that a whole bunch of colours
would tend to generate the same response - but it would be a response
nonetheless. You could think of the sensitivity limit of a capture device as being its
'effective' gamut, but it makes more sense to me to keep the gamut
boundary concept for physical media and choosing a working space that
corresponds to the gamut of the input media.

--
Phil Green
Colour Imaging Group
School of Printing and Publishing

And again:

On 4/5/99 10:48 AM, "Richard F. Lyon" wrote:
The discussion of profiling Leaf and other cameras is very interesting,
but doesn't go far enough in clarifying the connections with underlying
color science and photographic science (these are very different things!).

Bruce's and Andrew's comments below are right on, but as I say don't go
far enough. A camera (or a scanner) doesn't "HAVE" an RGB gamut unless
it has computation built in to convert its measurements to an RGB space.
If a camera measures a scene through filters that are 'color matching
functions' (see Hunt, especially the section on Television signal
processing) as it should, then ALL colors can be correctly measured and
represented. But then the numbers are usually matrixed to somebody's
standard RGB space, based on a set of primaries. In this process, some
of the pixels can get negative values of R, G, or B, meaning that those
colors are not inside the triangle bounded by the primaries. It is at
this point that the gamut becomes limited, because nobody's output file
formats allow negative values (not even in 16-bit files, stupidly!), so
they clip them one way or another.

So usually what comes out of a camera or scanner is in an ordinary RGB
space that the engineers picked or defaulted to, and of course you can
profile to figure out what the primaries seem to be, what the gamut
limitations are, etc.

[bjanes]

And here is a demonstration of a color image from raw without any demosaicing. One takes the raw file and splits out the red, blue, green1 and green2 portions of the CFA with the Iris SPLIT_CFA command. This gives four files: red, blue, green1 and green2. The files are in the FIT format, which Photoshop can not read, so they have to be converted to TIFF, which I did with the freeware program ImageJ. The result is three gray scale files. They can then be loaded into Photoshop and merged into an RGB file. I used only one of the green separations. This proves that color can be generated without demosaicing.

[attachment=4021:attachment]

The result is gamma 1

[attachment=4022:attachment]

One can then use the gamma 2.2 curve and a contrast boost to get the final result. The background is ugly, but I used what was available to demonstrate the point.

[attachment=4024:attachment]

[digitaldog]

The result is three gray scale files. They can then be loaded into Photoshop and merged into an RGB file.

An RGB file in WHAT color space? How did you decide how to map the scale of the RGB primaries from the Raw data? This is the meat and potatoes here. You've got a pile of numbers. What's the scale and how did YOU or your Raw splitting software decide how to define these primaries? That would give us a color space definition. Read what the color scientists and experts I've quoted have said about this assignment. How do YOU define the gamut by defining the scale of the primaries of what isn't a color file?

And I suspect this goes back to the DNG spec you keep mentioning. Where does it tell us the scale of the primaries so we can define a color space and gamut? As I posted by another author, someone, somewhere makes it up more or less.

At the time of demosicing, the primaries are defined, you have a color image. Richard F. Lyon explains it the best:the numbers are usually matrixed to somebody's standard RGB space, based on a set of primaries. The color scientists at Munsell said it too:In the color world, encoding is based on some explicit or implied display.

[digitaldog]

And here is a demonstration of a color image from raw without any demosaicing.
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No, here is a color image from Raw WITH demosaicing!

[a href=\"http://en.wikipedia.org/wiki/Demosaicing]http://en.wikipedia.org/wiki/Demosaicing[/url]

A demosaicing algorithm is a digital image process used to interpolate a complete image from the partial raw data received from the color-filtered image sensor (via a color filter array or CFA) internal to many digital cameras in form of a matrix of colored pixels. Also known as CFA interpolation or color reconstruction, another common spelling is demosaicking.

[bjanes]

An RGB file in WHAT color space? How did you decide how to map the scale of the RGB primaries from the Raw data? This is the meat and potatoes here. You've got a pile of numbers. What's the scale and how did YOU or your Raw splitting software decide how to define these primaries? That would give us a color space definition. Read what the color scientists and experts I've quoted have said about this assignment. How do YOU define the gamut by defining the scale of the primaries of what isn't a color file?

And I suspect this goes back to the DNG spec you keep mentioning. Where does it tell us the scale of the primaries so we can define a color space and gamut? As I posted by another author, someone, somewhere makes it up more or less.

At the time of demosicing, the primaries are defined, you have a color image. Richard F. Lyon explains it the best:the numbers are usually matrixed to somebody's standard RGB space, based on a set of primaries. The color scientists at Munsell said it too:In the color world, encoding is based on some explicit or implied display.
[a href=\"index.php?act=findpost&pid=155781\"][{POST_SNAPBACK}][/a]

This is only a proof of concept demonstration with unmanaged colors. Your comments are irrelevant to the demonstration, but the colors could be scaled by performing a 3 by 3 matrix conversion from the camera space to CIE XYZ and then another transformation to one's preferred working space.

[digitaldog]

This is only a proof of concept demonstration with unmanaged colors. Your comments are irrelevant to the demonstration, but the colors could be scaled by performing a 3 by 3 matrix conversion from the camera space to CIE XYZ and then another transformation to one's preferred working space.
[a href=\"index.php?act=findpost&pid=155784\"][{POST_SNAPBACK}][/a]

NO, my points are very relevant to the original post you made far too many posts ago:

QUOTE(digitaldog @ Nov 22 2007, 08:23 AM)
Raw has no color space. You encode a rendering into a color space and hopefully, you can control as much noise reduction in the Raw rendering state as possible prior to encoding.

-----you said----

That statement is debatable. Look at the Adobe DNG Specifiation on page 47 where mapping from the camera color space to the CIE XYZ space is discussed. The conversion is done with a three by three matrix, just like a conversion from sRGB to ProPhotoRGB is done. If you look at the source code of DCRaw you can review the actual matrix coefficients and conversion code.

Apparently the folks at Adobe think that the camera has a color space.

You say the statement is debatable. We have a debate, one in which you haven't, as yet proven to me (and perhaps anyone else) that a Raw file has a color space. I say its essentially Grayscale, it has no color space. I stick to that opinion. You've quoted page 47 where it states "from camera color space" assuming that this is defined, I've mentioned several well qualified experts who say, its whatever you want to assign the scale of the primaries at encoding which I'll add is happening AT the state of demosaicing. You attempted to demonstrate this above, and so I again ask, what's the color space you made up? And how does this make it 'correct' and further prove that prior to this part of the process, the camera had a gamut?

[bjanes]

Exactly! And this has been discussed by the color scientist at Munsell (quote above) when he writes that the camera has no gamut. You can't define the gamut or a color space until you place specific coordinates of RG and B. Bruce said this as well.

This is getting to be a big cluster-fu*% of semantics but I'd far prefer to take the side of the color scientists and Bruce, among just a few who state I believe correctly and for the last time, the Raw data is essentially Grayscale and the capture device has no gamut.

And yet another quote from Phil Green:
And again:
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Digidog, you are confusing the issue. I did not state that a digital camera has a gamut. A raw file is gray scale according to your nomenclature, and Bruce stated p. 119 of Real World PSCS2, "In Photoshop, files saved in the RGB mode typically uses a set of three 8 bit grayscale files..." [bold added for emphasis]. The grayscale files can form a color image because the three primary colors of the image are represented by the grayscale files. The raw file is also gray scale, but a color image can be formed from the red, blue and green elements of the Bayer array. In the latter case, all three primaries are encoded into one file rather than three separate files. If you can't see the analogy, I don't think you are very bright.

[digitaldog]

Digidog, you are confusing the issue. I did not state that a digital camera has a gamut.

Fine

A raw file is gray scale according to your nomenclature, and Bruce stated p. 119 of Real World PSCS2, "In Photoshop, files saved in the RGB mode typically uses a set of three 8 bit grayscale files..." [bold added for emphasis].

Where do you see him referring to Raw files in this context?

The grayscale files can form a color image because the three primary colors of the image are represented by the grayscale files. The raw file is also gray scale, but a color image can be formed from the red, blue and green elements of the Bayer array. In the latter case, all three primaries are encoded into one file rather than three separate files. If you can't see the analogy, I don't think you are very bright.
[a href=\"index.php?act=findpost&pid=155789\"][{POST_SNAPBACK}][/a]

The difference, and Jeff clearly stated this, is that the Raw is a single channel Grayscale file. In fact, this all goes back to me saying, "Raw is Grayscale data" which I continue to state and stand by.

That a single channel Grayscale file is different from a three channel Grayscale file shouldn't even have to be discussed here. Its a big Duh!

The fact that a Raw Grayscale file was produced with color filters, or that you can somehow split this data into now, three Grayscale files to represent a color image (something we know is the case, we've discussed demosicing), doesn't change the facts as I and Jeff and others have presented them. Yes, a Raw, Grayscale file HAS the potential to be a color image. Another big Duh moment. That doesn't make the single channel Grayscale Raw file a color file, cause it's not. ITS GRAYSCALE, something I said almost in passing, and something you said was debatable thus bringing on this entire sh*&-storm.

Lets cut to the chase. If a Raw file isn't Grayscale, are you saying its a color file?

[bjanes]

NO, my points are very relevant to the original post you made far too many posts ago:
You say the statement is debatable. We have a debate, one in which you haven't, as yet proven to me (and perhaps anyone else) that a Raw file has a color space. I say its essentially Grayscale, it has no color space. I stick to that opinion. You've quoted page 47 where it states "from camera color space" assuming that this is defined, I've mentioned several well qualified experts who say, its whatever you want to assign the scale of the primaries at encoding which I'll add is happening AT the state of demosaicing. You attempted to demonstrate this above, and so I again ask, what's the color space you made up? And how does this make it 'correct' and further prove that prior to this part of the process, the camera had a gamut?
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For the last time, what do you think of chapter 6 of the DNG specification?

You might also want to look at this thread on the [a href=\"http://www.adobeforums.com/webx?14@@.3bc2e802/2]Abobe Forums[/url]. Mr. Knoll put the camera color space in quotes, but he seems to be recognizing that it exists as per the DNG spec.

[digitaldog]

Mr. Knoll put the camera color space in quotes, but he seems to be recognizing that it exists as per the DNG spec.
[a href=\"index.php?act=findpost&pid=155791\"][{POST_SNAPBACK}][/a]

Yes he puts it in quotes for exactly the reasons I've explained (well others have explained far better) in the numerous quotes above. Thomas puts them in quotes because he's saying as far as I'm concerned, that he agrees with the concepts expressed by both Phil and Richard which I don't think you've read. That basically, the color space is whatever anyone wants to say it is based on how they want to encode the data. Otherwise, both the DNG spec AND Thomas's quote would be far from vague, which clearly they are.

[bjanes]

Fine
Where do you see him referring to Raw files in this context?
The difference, and Jeff clearly stated this, is that the Raw is a single channel Grayscale file. In fact, this all goes back to me saying, "Raw is Grayscale data" which I continue to state and stand by.

That a single channel Grayscale file is different from a three channel Grayscale file shouldn't even have to be discussed here. Its a big Duh!

The fact that a Raw Grayscale file was produced with color filters, or that you can somehow split this data into now, three Grayscale files to represent a color image (something we know is the case, we've discussed demosicing), doesn't change the facts as I and Jeff and others have presented them. Yes, a Raw, Grayscale file HAS the potential to be a color image. Another big Duh moment. That doesn't make the single channel Grayscale Raw file a color file, cause it's not. ITS GRAYSCALE, something I said almost in passing, and something you said was debatable thus bringing on this entire sh*&-storm.

Lets cut to the chase. If a Raw file isn't Grayscale, are you saying its a color file?
[a href=\"index.php?act=findpost&pid=155790\"][{POST_SNAPBACK}][/a]

I agree that a raw file is gray scale. How many times do I have to state that? (So are the channels of an RGB file. Bruce has confirmed this, but you don't seem to get it.) However, if you understand the Bayer grid, you can extract the color information from a gray scale raw file. It is a special type of gray scale file.

Of course an RGB file in ProPhotoRGB contains no color. It merely has the data necessary to construct color when viewed with the proper software. The raw file contains no color, but it also has the information necessary to produce color

[digitaldog]

I guess my assumption that you are not too bright is confirmed. I agree that a raw file is gray scale. How many times do I have to state that?

Just once, after you said this:

That statement is debatable. Look at the Adobe DNG Specifiation on page 47 where mapping from the camera color space to the CIE XYZ space is discussed. The conversion is done with a three by three matrix, just like a conversion from sRGB to ProPhotoRGB is done. If you look at the source code of DCRaw you can review the actual matrix coefficients and conversion code.
Apparently the folks at Adobe think that the camera has a color space.
[a href=\"index.php?act=findpost&pid=155113\"][{POST_SNAPBACK}][/a]

In closing, here's the bottom line. We have a Raw file that I say is Grayscale. You read the DNG spec and say, based on what is said in the document, a Raw file is a color file because at some point, the Raw data is encoded into a color space. So, is a Raw file a color file or a Grayscale file? Not what it may become based on some processing, the damn file sitting on your flash card?

This seems (it is) all so simple.

I'll ignore your ill manners and comment at the top of this thread since I can feel your frustration at having to admit that you were barking up the wrong tree from the get go.

[bjanes]

Yes he puts it in quotes for exactly the reasons I've explained (well others have explained far better) in the numerous quotes above. Thomas puts them in quotes because he's saying as far as I'm concerned, that he agrees with the concepts expressed by both Phil and Richard which I don't think you've read. That basically, the color space is whatever anyone wants to say it is based on how they want to encode the data. Otherwise, both the DNG spec AND Thomas's quote would be far from vague, which clearly they are.
[a href=\"index.php?act=findpost&pid=155794\"][{POST_SNAPBACK}][/a]

You have addressed only one part of my post. Again, what do you think of Chapter 6 of the DNG specification? Make what you will of Mr. Knoll's quotes. You can't read his mind.  Since you do not respond to reason, this is my last reply to you on this issue.

[digitaldog]

Of course an RGB file in ProPhotoRGB contains no color. It merely has the data necessary to construct color when viewed with the proper software. The raw file contains no color, but it also has the information necessary to produce color
[a href=\"index.php?act=findpost&pid=155795\"][{POST_SNAPBACK}][/a]

And to go even deeper, its neither, its just a big pile of numbers.

[digitaldog]

Again, what do you think of Chapter 6 of the DNG specification?
[a href=\"index.php?act=findpost&pid=155798\"][{POST_SNAPBACK}][/a]

I told you what I thought of chapter 6 of the DNG spec. As explained by Phil and Richard.