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Author Topic: Colour spaces  (Read 49375 times)
bjanes
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« Reply #80 on: November 25, 2007, 11:30:35 AM »
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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.
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Andrew,

I am sorry that my frustration affected my manners. Please accept my apology. Also, thank you for taking the high road and not replying in kind. I have edited my offending post. Just as in the Adobe forum postings on the same topic, agreement was not reached, and we will have to agree to disagree.

Bill
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Schewe
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« Reply #81 on: November 25, 2007, 02:13:11 PM »
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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 Abobe Forums. Mr. Knoll put the camera color space in quotes, but he seems to be recognizing that it exists as per the DNG spec.
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As it relates to DNG what I think is throwing you is that DNG ASSIGNS a color space based upon Thomas' testing of the spectral response of the sensor at D65 and Standard Illuminate A. Then based upon the white point in the metadata an arbitrary white point is assigned. Assigned mind you...and this is only on a DNG whose sensor has been decoded by Thomas and whose spectral properties have been measured.

Until Thomas MEASURES the the response and ASSIGNS a color space, there is no color space. Note that a DNG is a PROCESSED file, no longer a native raw file...

We are also hung up on the term "demosaicing"...well, the reason I pointed out the Wikipedia article is that my understanding of the term demosaicing is based upon that: "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."

So, splitting a single channel grayscale file into 3 grayscale files and combining them into a single RGB file is a "demosaicing algorithm" even if the process of assigning the red, green and blue pixels is manually done. Something, somewhere is saying, "ok, these pixels represent the red pixels, etc."

Taking the original raw, grayscale file and looking at it in any viewer app that does NOT designate which pixel are which colors and interpret those grayscale pixels as colors, will show the raw image as a single channel, grayscale file. Right? So, something, somewhere needs to do something to interpret the color of the Bayer Array, and I call that process a "Demosaicing" consistent with the definition on Wikipedia.

If you or Pannopeeper have a problem with that definition, I suggest you sign up on Wikipedia and do some updating of the article in question.
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Panopeeper
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« Reply #82 on: November 25, 2007, 02:30:58 PM »
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Note that a DNG is a PROCESSED file, no longer a native raw file...

LOL, that does it for me.
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« Reply #83 on: November 25, 2007, 03:29:38 PM »
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LOL, that does it for me.
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Do you dispute that DNG Converter processes the proprietary raw file into a DNG file? It's also what Camera Raw does when it opens a proprietary raw file...
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bjanes
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« Reply #84 on: November 25, 2007, 04:41:06 PM »
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As it relates to DNG what I think is throwing you is that DNG ASSIGNS a color space based upon Thomas' testing of the spectral response of the sensor at D65 and Standard Illuminate A. Then based upon the white point in the metadata an arbitrary white point is assigned. Assigned mind you...and this is only on a DNG whose sensor has been decoded by Thomas and whose spectral properties have been measured.

Until Thomas MEASURES the the response and ASSIGNS a color space, there is no color space.
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Well, I thought that assigning a profile does not change the numbers in the file, but only determines how they are interpreted or what they represent. When Mr. Knoll measures the response of the camera at D65 he is determining the coefficients needed to perform a 3 by 3 matrix conversion from the "camera color space" to CIE XYZ or perhaps the PhotoProRGB chromaticity with a linear TRC. He is not creating a new space but merely describing the inherent properties of the sensor, i.e. the "native color space" of the camera  . It is my thesis that those coefficients are implicit to the camera space. I don't know the details, but Mr. Knoll has stated that CIE XYZ has no white point. Perhaps you can help us in understanding the significance of this difference.

Furthermore, I don't think a white point is assigned at the time the DNG is created, but it can be interpolated from the D65 and Illuminate A profiles that are present in the DNG when needed. The AS SHOT white point is encoded in the raw file and can be used in this process.

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Note that a DNG is a PROCESSED file, no longer a native raw file...
[a href=\"index.php?act=findpost&pid=155869\"][{POST_SNAPBACK}][/a]

Form the Adobe [a href=\"http://www.adobe.com/products/dng/pdfs/DNG_primer_manufacturers.pdf]DNG Primer for Manufacturers[/url] it is apparent that part of the DNG consists of metadata that the converter fills in describing the characteristics of the camera that are necessary for raw conversion.

The camera's actual image data are then "stored in a linear non-white balanced color space, usually the native color space of the camera". The data can be in mosaic form or demosaiced, but the mosaiced form is preferred, since it represents the original data captured by the camera.

In the preferred case, the actual image data are the same as in the raw file. If the file is demosaiced, then it is heavily processed and it would not be possible to apply a better demosaicing algorithm that might be developed in the future. Note that Adobe again mentions the native color space of the camera, which is not in accordance with your strict definition of a color space. As I initially stated, whether a raw file has a color space is debatable. Depending on one's definition, one can make either argument. However, I am not contending that this "native color space" can be used in Photoshop as one would use a printer profile. You discuss the pros and cons of camera profiling in your book, and make a good case that its absence in ACR is not a handicap.

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We are also hung up on the term "demosaicing"...well, the reason I pointed out the Wikipedia article is that my understanding of the term demosaicing is based upon that: "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."

So, splitting a single channel grayscale file into 3 grayscale files and combining them into a single RGB file is a "demosaicing algorithm" even if the process of assigning the red, green and blue pixels is manually done. Something, somewhere is saying, "ok, these pixels represent the red pixels, etc."

Taking the original raw, grayscale file and looking at it in any viewer app that does NOT designate which pixel are which colors and interpret those grayscale pixels as colors, will show the raw image as a single channel, grayscale file. Right? So, something, somewhere needs to do something to interpret the color of the Bayer Array, and I call that process a "Demosaicing" consistent with the definition on Wikipedia.
[a href=\"index.php?act=findpost&pid=155869\"][{POST_SNAPBACK}][/a]

Strictly speaking the SPLIT_CFA command is demosaicing in the sense that it separates the red, blue and green components of the raw file into separate components. But it does no interpolation and does not fulfill the definition of demosaicing on Wikipedia. It does not attempt to determine the two primary colors that are absent in each Bayer array pixel. I can't speak for Panopeeper, but I have no quarrel with that definition.
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« Reply #85 on: November 25, 2007, 04:58:16 PM »
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Strictly speaking the SPLIT_CFA command is demosaicing in the sense that it separates the red, blue and green components of the raw file into separate components. But it does no interpolation and does not fulfill the definition of demosaicing on Wikipedia. It does not attempt to determine the two primary colors that are absent in each Bayer array pixel. I can't speak for Panopeeper, but I have no quarrel with that definition.
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Uh huh...but putting the 3 split channels into a single 3 channel file (which is what you were talking about) DOES constitute a "CFA interpolation or color reconstruction"...the fact it does no resampling doesn't mean it ain't a "demosaicing algorithm", it just means it's not doing any upsampling. You take a single channel file, split it into 3 channels then combine them into an RGB file. I call that "demosaicing".
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Schewe
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« Reply #86 on: November 25, 2007, 05:11:10 PM »
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Well, I thought that assigning a profile does not change the numbers in the file, but only determines how they are interpreted or what they represent. When Mr. Knoll measures the response of the camera at D65 he is determining the coefficients needed to perform a 3 by 3 matrix conversion from the "camera color space" to CIE XYZ or perhaps the PhotoProRGB chromaticity with a linear TRC. He is not creating a new space but merely describing the inherent properties of the sensor, i.e. the "native color space" of the camera  . It is my thesis that those coefficients are implicit to the camera space. I don't know the details, but Mr. Knoll has stated that CIE XYZ has no white point. Perhaps you can help us in understanding the significance of this difference.
[a href=\"index.php?act=findpost&pid=155912\"][{POST_SNAPBACK}][/a]

Well, considering that camera sensors suffer from metameric failure at different spectral illuminates, (the whole reason Thomas tests the sensor at D65 AND Illuminate A), the spectral response of the camera's sensor is a sliding scale and thus would not have a single "color space" but potentially many "color spaces" depending on the illuminate.
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bjanes
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« Reply #87 on: November 25, 2007, 05:22:34 PM »
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Uh huh...but putting the 3 split channels into a single 3 channel file (which is what you were talking about) DOES constitute a "CFA interpolation or color reconstruction"...the fact it does no resampling doesn't mean it ain't a "demosaicing algorithm", it just means it's not doing any upsampling. You take a single channel file, split it into 3 channels then combine them into an RGB file. I call that "demosaicing".
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You may call it demosaicing, but I don't think that the Wikipedia definition is met as there is no interpolation. Since, I have already conceded that by a strict definition, what I performed could be considered demosaicing, I don't know why you even brought up the subject other than to have the last word. Interpolation is making up values that did not exist. As you know, the Bayer array can capture only one color per pixel, and the other two colors are interpolated by best guess from surrounding pixels. My process did not invent any new data to "fill in the blanks" as Wikipedia states it, but merely looks at the same data in a different way.

Anyway, I don't see how this affects the argument that the raw file has no color space. If it has no space before the demosaicing, then it has no space after the demosaicing. What has changed that would make it a color space after demosaicing? The file may acquire characteristics to fulfill your definition of a color space later in the process.
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« Reply #88 on: November 25, 2007, 05:28:47 PM »
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Anyway, I don't see how this affects the argument that the raw file has no color space. If it has no space before the demosaicing, then it has no space after the demosaicing. What has changed that would make it a color space after demosaicing? The file may acquire characteristics to fulfill your definition of a color space later in the process.
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It has no color space before because its not a color image, it has a color space after because someone has encoded the demoasiced data into a color space. That's exactly what encoding does.

[a href=\"http://www.color.org/ICC_white_paper_20_Digital_photography_color_management_basics.pdf]http://www.color.org/ICC_white_paper_20_Di...ment_basics.pdf[/url]
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Andrew Rodney
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bjanes
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« Reply #89 on: November 25, 2007, 05:33:51 PM »
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Well, considering that camera sensors suffer from metameric failure at different spectral illuminates, (the whole reason Thomas tests the sensor at D65 AND Illuminate A), the spectral response of the camera's sensor is a sliding scale and thus would not have a single "color space" but potentially many "color spaces" depending on the illuminate.
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You are obsessing on white point, which is part of the ICC profile, but CIE XYZ lacks a white point and is widely considered to be a color space. Look at [a href=\"http://en.wikipedia.org/wiki/CIE_1931_color_space]Wikipedia[/url]. Is it a color space by your definition?
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Schewe
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« Reply #90 on: November 25, 2007, 05:46:20 PM »
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You are obsessing on white point, which is part of the ICC profile, but CIE XYZ lacks a white point and is widely considered to be a color space. Look at Wikipedia. Is it a color space by your definition?
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Yep...cause it has known and defined set of tristimulus values...a raw capture doesn't. The  tristimulus values at D65 will be different than at Illuminate A (or presumed to be which is why Thomas tests cameras at both).
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bjanes
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« Reply #91 on: November 25, 2007, 05:47:36 PM »
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It has no color space before because its not a color image, it has a color space after because someone has encoded the demoasiced data into a color space. That's exactly what encoding does.

http://www.color.org/ICC_white_paper_20_Di...ment_basics.pdf
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Your link does not work, so I can't comment. The demosaicing does not encode a color space, but merely separates out the color information from the Bayer array and fills in the missing information. As Jeff explains on pp 4-5 of his Camera Raw book, colorimetric interpretation, white balance, and tone mapping are separate steps and I think the encoding to which you refer takes place during these steps. As I stated, the demosaicing per se has no effect on whether the image has a color space or not. After the demosaicing, it is a color image by your definition, but apparently still lacks a  color space.
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bjanes
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« Reply #92 on: November 25, 2007, 05:57:33 PM »
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Yep...cause it has known and defined set of tristimulus values...a raw capture doesn't. The  tristimulus values at D65 will be different than at Illuminate A (or presumed to be which is why Thomas tests cameras at both).
[a href=\"index.php?act=findpost&pid=155930\"][{POST_SNAPBACK}][/a]

Now we are expanding on the definition of a color space, and dropping the requirement of a white point. Hard to hit a moving target. BTW, illuminate is a verb. I think you mean illuminant.
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Schewe
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« Reply #93 on: November 25, 2007, 06:11:20 PM »
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Now we are expanding on the definition of a color space, and dropping the requirement of a white point.
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Yep, it _IS_ hard to hit a moving target...and a sensor's response at D65 and Illuminant A means that a camera sensor DOESN'T have a fixed "color space".

Absolute color space: A color space in which colors are unambiguous, that is, where the interpretations of colors in the space are colorimetrically defined without reference to external factors.

Since the spectral response of a sensor depends on the illuminant (because of metameric failure) then a camera doesn't have an "Absolute color space". (there is another definition but I don't think it applies). Ref: [a href=\"http://en.wikipedia.org/wiki/Absolute_color_space]Absolute color space[/url]
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digitaldog
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« Reply #94 on: November 25, 2007, 07:00:37 PM »
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Your link does not work, so I can't comment.

The links on the ICC web page are kind of hosed, but the article discusses the role of color space encoding. I'll email them to fix this link.

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The demosaicing does not encode a color space, but merely separates out the color information from the Bayer array and fills in the missing information.

After which, the color has to be encoded into a color space. IF you'd only read the posts made by Phil, and could get to the ICC link, you'd see this is a somewhat arbitrary process that someone has to define.


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As Jeff explains on pp 4-5 of his Camera Raw book, colorimetric interpretation, white balance, and tone mapping are separate steps and I think the encoding to which you refer takes place during these steps.

They have to happen, at what step in the process, once we have a true color image that can have a color space may be questionable but at some point, the numbers have to have an associated scale placed on them. IT is at this point that these values have a color space. Prior to this, its Grayscale data (which you finally admit), it can't have a color space association.

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As I stated, the demosaicing per se has no effect on whether the image has a color space or not. After the demosaicing, it is a color image by your definition, but apparently still lacks a  color space.

No, at such a point, a color space is assigned if you want to use the term. Again, this is very clearly stated in the post I provided by Richard and Phil:

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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.

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But then the numbers are usually matrixed to somebody's
standard RGB space, based on a set of primaries.

It again, is pretty simple. I don't know why you don't wish to accept this.
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Andrew Rodney
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bjanes
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« Reply #95 on: November 25, 2007, 07:31:17 PM »
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very clearly stated in the post I provided by Richard and Phil:
It again, is pretty simple. I don't know why you don't wish to accept this.
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The posts by Rich and Phil were concerning the lack of a gamut for digital cameras. I'm not certain what I should have learned from their posts that affects the current discussion.

It was Panopepper who was confused on the issue of camera gamut. I was well aware of that issue, having made the same mistake some time previously in a different thread. It is easy to slip up, and even an expert like Peter Lange mentioned the gamut of a digital camera.
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« Reply #96 on: November 25, 2007, 07:38:29 PM »
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The posts by Rich and Phil were concerning the lack of a gamut for digital cameras. I'm not certain what I should have learned from their posts that affects the current discussion.

I think its time to give up here.

You can't define a color gamut without a color space. They clearly indicate encoding of the data after a color file is produced using what you are calling demosaicing.

The original set of debates started because YOU questioned that a Raw file was Grayscale. Then you accepted it was Grayscale (because it is). A Grayscale file doesn't have a color space right? You can't define the boundaries of the primaries which is all a color space is. OK, we've got a color image now, we used demosaicing. So what's the color space? You keep going back to an article that doesn't define this to point out you feel Raw is a color image but we all know now, as you admit its not. Once we DO have a color file, what's the color space? Phil AND Rich have explained this.

Why do we keep going around in circles here?

The acceptance of yours that a digital camera has no color gamut AND that a Raw file has no color (nor color space) indicates to me we're at least making some progress. Again, read what Phil and Richard have written.
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Andrew Rodney
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bjanes
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« Reply #97 on: November 25, 2007, 07:40:34 PM »
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Yep, it _IS_ hard to hit a moving target...and a sensor's response at D65 and Illuminant A means that a camera sensor DOESN'T have a fixed "color space".

Absolute color space: A color space in which colors are unambiguous, that is, where the interpretations of colors in the space are colorimetrically defined without reference to external factors.

Since the spectral response of a sensor depends on the illuminant (because of metameric failure) then a camera doesn't have an "Absolute color space". (there is another definition but I don't think it applies). Ref: Absolute color space
[a href=\"index.php?act=findpost&pid=155933\"][{POST_SNAPBACK}][/a]

Well, metameric failure occurs not only with printers, but also printers. The Epson 2000 was noted for prominent metameric failure. Yet people still made profiles for the printer.
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bjanes
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« Reply #98 on: November 25, 2007, 08:32:55 PM »
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I think its time to give up here.
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Yes, I think so. You keep reiterating the same things and my responses also have become repetitious. Your ability to see another point of view is limited if it does not fit into your preconceived ideas, which are usually but not invariably correct.

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You can't define a color gamut without a color space. They clearly indicate encoding of the data after a color file is produced using what you are calling demosaicing.
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First of all, we are not trying to define the color gamut of a camera, because it has none, as you have already pointed out. However, if you extended the analysis into the deep infra-red and ultra-violet a gamut would emerge.
 
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The original set of debates started because YOU questioned that a Raw file was Grayscale. Then you accepted it was Grayscale (because it is).
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Your memory is rather selective and defective here. I did not deny that a raw file was gray scale, but I also pointed out that an RGB file is also gray scale as per Bruce Fraser's writings. Please refer back to post #11 in this thread. I have not changed my opinion. The raw file is gray scale because it records only luminance, not color.

The channels of an RGB file are gray scale for the same reason. The difference, which you don't seem able to grasp, is that both of them contain color information. Once we know what the channels of the RGB file represent, we can generate color. By the same token, once we know what the gray scale pixels in the Bayer array represent, we can also generate color. Demosiacing is not necessary to generate the color. It was Jeff who went off on that tangent.

A monochrome file can have a color space if it contains color information that, when properly decoded, defines colors.

Furthermore, I merely stated at the outset that raw files lack a color space is debatable, which this thread certainly has proved. To paraphrase Bill Clinton, who said, "it depends on what the meaning of IS is", it depends on what the definition of a color space is. I have yet to see your definition of what constitutes a color space; lacking this, we can go nowhere.
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« Reply #99 on: November 25, 2007, 09:05:45 PM »
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Schewe has it spot on!
1. Noise comes from high ISO (sensor) long before the color space gets applied. A wider gamut simply stretchs it, but doesn't add to nor subtract from it. To cure noise, shoot at ISO 100 or maybe 200. At 400 or beyond, you are going to have to deal with the noise.

2. Sensors and RAW are LINEAR gamma, which is NOT how humans perceive things. That is why the linear data needs to be converted into a color space. Schewe pointed that out, but the significance is enormous.

3. If you choose a wide gamut, such as ProPhoto and edit in 16-bit, then there is "room" for gradations of color. If you don't EDIT a photo, color space doesn't mean much -- colors are what they are.

4. Lastly, RAW is 12 bit. If you edit in 8-bit, then you are throwing out some info (like rounding pennies to nearest dollar). If you are fussy about colors and detail (I am), then edit in 16-bit and print in high resolution. It makes a difference in skin color and details like hair. And if fine hair detail matters, then use a tripod so you aren't editing a 16-bit blur.
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