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Author Topic: converting from prophoto to sRGB: tip  (Read 33393 times)
Schewe
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« Reply #20 on: November 21, 2007, 12:12:20 AM »
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Only when I assign a profile to the image (ex: a costco ICC profile, or as a default, sRGB) for finalizing do I see a change in the histogram, which usually shows clipping.
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Uh, are you actually using "assign"? If so, this is wrong...are you referring to using soft proof or Convert to Profile?
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Hermie
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« Reply #21 on: November 21, 2007, 12:56:19 AM »
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... or using a profile with perceptual rendering. This rendering does not exist for matrix profiles such as sRGB, but a forum member informed me of another profile for this purpose, but I can't remember the name. It used lookup tables.

Bill
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PhotoGamutRGB
[a href=\"http://www.photogamut.org/E_Index.html]http://www.photogamut.org/E_Index.html[/url]
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Mark D Segal
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« Reply #22 on: November 21, 2007, 07:16:07 AM »
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To screw with your heads...

:~)

Actually, the Convert to Profile SHOULD dim out non-available rendering intents, but that logic hasn't been added to the app...yet.
[a href=\"index.php?act=findpost&pid=154591\"][{POST_SNAPBACK}][/a]

Thanks Jeff. I assume the word "yet" means it's one of those minor issues they know about and will get around to fixing in some future release.
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Mark D Segal (formerly MarkDS)
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bjanes
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« Reply #23 on: November 21, 2007, 07:36:56 AM »
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PhotoGamutRGB
http://www.photogamut.org/E_Index.html
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Yes, this is the profile. Thanks.
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bjanes
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« Reply #24 on: November 21, 2007, 07:48:53 AM »
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Jeff,

Very interesting. What would happen if you used the new profile with a non-V4 ProPhoto profile? I guess one could download the new profile and give it a try.

Bill
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I have no idea...I haven't had time to test the v4 profiles...(been kinda busy)

:~)
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Apparently, the answer is in ICC White Paper 26, but I have not been able to locate this paper on the ICC web site. Can anyone help?

"Advice for caution

Ideally the ICC v4 profile should not be combined with ICC v2 profiles. If that is unavoidable, see the intermediate-level ICC White Paper 26 'Using the sRGB_v4_ICC_preference.icc profile' for additional information and recommendations."
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Mark D Segal
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« Reply #25 on: November 21, 2007, 07:54:24 AM »
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Actually, I do not notice a change in the appearance of an image when I switch between pro photo and sRGB, despite the histogram changes.  I think this observation strikes at the heart of the problem- when I soft proof, I don't see a histogram change, and so I don't yet know what the limits of the output space are.  Only when I assign a profile to the image (ex: a costco ICC profile, or as a default, sRGB) for finalizing do I see a change in the histogram, which usually shows clipping.  I "Preview" the image in sRGB in camera RAW because an sRGB image seems to yield decent results from most offsite RGB commercial printers that don't provide ICC profiles (Walgreens, etc).  If I could preview with an ICC profile, I'd use that instead if I wanted to print the image from that printer.

John
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Softproofing does not change the histogram. It changes the appearance of the image on the display to mimic what the print will look like. It is like a filter which says "if you configure me this way, this is what I'll do to the appearance of your image", without actually doing it. Therefore because the image itself has not been altered, the histogram remains the same. However, if you were to actually convert to another colour space, you are altering the image and the change should show on the histogram.

Now, the rest of your post concerns what one could call "best practice". Normally, best practice is to work your images conserving the most data possible so that some time in the future you will have everything that was originally available to repurpose the image. If you render the raw file into an 8 bit sRGB working space and build a whole slew of adjustments on that basis because it is suitable for a Costco printer today, should the time come that you want to do something else with that image which can take advantage of more bit depth and a wider colour palette, you would need to go back to the raw file and start processing all over again by rendering the raw file in - say - 16 bit ProPhoto and redoing all the subsequent work. It is easier - usually - to start with the maximum information, then scale it down to the specific purpose at the moment using adjustment layers, as these can be repurposed in the future. The image you take to Costco would be a flattened file resaved with another name so you don't lose anything from your "Gold Master". If, however, you have a very high degree of confidence that you will never need anything more than an sRGB working space from this file, you could begin the process in sRGB and save yourself some steps. But I would recommend retaining the image in 16-bit mode till the very last point when you need to make a conversion that does not support 16 bit depth, because you have much less risk of damaging the image by eidting in 16 bit.
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Mark D Segal (formerly MarkDS)
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« Reply #26 on: November 21, 2007, 08:12:49 AM »
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Jeff, if that's the case, why does PS give us the option to select the three others?
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Well two (you can use an Absolute Colorimetric intent). Absolute and Relative share the same table and for all practical purposes are identical except for how white is handled. And Abs would look pretty awful in nearly all such cases.

On one hand, it would be useful for Adobe to dim Perceptual and Saturation in these cases but since picking them doesn't do anything but force RelCol, I guess they did this to make it 'easier'? And when more V4 profiles come about, they would have to rewire everything anyway. If someone toggles such matrix conversions between say Saturation and Perceptual and really feels one is better than the other visually, they deserve the RelCol rendering <g>.
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Andrew Rodney
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« Reply #27 on: November 21, 2007, 08:17:59 AM »
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What springs to mind here is the fact that no monitor can fully display the gamut of ProPhoto.

Nor any image. Its important to realize that ProPhoto RGB (like all the other RGB working spaces) are synthetically manufactured using simple math. In the case of ProPhoto RGB, there ARE colors defined that fall outside human vision. I only point this out as now that we are seeing displays that get close to, match and exceed Adobe RGB (1998), people are now asking about the same capability for ProPhoto RGB. Ain't going to happen. We need really large synthetic color spaces for certain tasks but that doesn't mean all the colors defined are useful or in this case even visible.
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Andrew Rodney
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« Reply #28 on: November 21, 2007, 08:48:50 AM »
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Uh, are you actually using "assign"? If so, this is wrong...are you referring to using soft proof or Convert to Profile?
[a href=\"index.php?act=findpost&pid=154607\"][{POST_SNAPBACK}][/a]

My mistake, Jeff.  I should have said "convert."  I haven't experimented with "assign profile yet," as I'm not sure how to use it.  

Mark, I agree with you.  The "costco" files are ones that I use for that printer only- I save all my masters separately.

John
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bjanes
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« Reply #29 on: November 21, 2007, 09:10:23 AM »
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Actually, I do not notice a change in the appearance of an image when I switch between pro photo and sRGB, despite the histogram changes.  I think this observation strikes at the heart of the problem- when I soft proof, I don't see a histogram change, and so I don't yet know what the limits of the output space are.  Only when I assign a profile to the image (ex: a costco ICC profile, or as a default, sRGB) for finalizing do I see a change in the histogram, which usually shows clipping.  I "Preview" the image in sRGB in camera RAW because an sRGB image seems to yield decent results from most offsite RGB commercial printers that don't provide ICC profiles (Walgreens, etc).  If I could preview with an ICC profile, I'd use that instead if I wanted to print the image from that printer.

John
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John,

If you want to see the histogram in the printer color space, I think you would have to convert to that color space (convert, not assign). When you are soft proofing, the data are in the original color space and the histogram will be for that space, not the destination space. To view out of gamut colors, you can use the gamut warning in Photoshop soft proofing, but that does not tell you how far the image is out of gamut.

If you want to use the Costco profiles from Drycreek.com, you have to convert to the profile with the desired rendering intent. If you assign the profile, you have not changed the numbers in the file, but only how they are interpreted by Photoshop.

If you want to compare the gamut of the file to that of the printer, you need appropriate software such as ColorThink (expensive) or Norman Koren's GamutVision (more reasonable). Then you can see which colors are out of gamut and how far they are out of gamut.

sRGB works reasonably well for the Costco printers (which may be Nortisu or Fuji Frontier, depending on the store), because the gamut of these printers is not significantly larger than the sRBG gamut. If you look at the interactive gamut display on Drycreek.com and compare sRGB with the Noritsu 3101 and Crystal Archive paper, you will see that the printer can handle some yellows and cyans that are out of the sRGB gamut. If you use aRGB, a few yellows in the Costco gamut still can't be represented.

The newer inkjet printers have a considerably larger gamut, and it is best to use ProPhotoRGB when outputting to them. Modern digital cameras can capture colors well outside of the aRGB and sRGB gamut, and such out of gamut colors can be contained in rather innocuous appearing images, as Jeff shows with a ColorThink plot on p. 12 of the ACR book.

Bill
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papa v2.0
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« Reply #30 on: November 25, 2007, 11:01:55 AM »
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Its important to realize that ProPhoto RGB (like all the other RGB working spaces) are synthetically manufactured using simple math.
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mmm can you explain how sRGB is a synthetic colour space as opposed to a real colour space.

Are the sRGB  primaries not based on actual phosphors as specified in CCIR 709??
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digitaldog
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« Reply #31 on: November 25, 2007, 11:09:31 AM »
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mmm can you explain how sRGB is a synthetic colour space as opposed to a real colour space.

Are the sRGB  primaries not based on actual phosphors as specified in CCIR 709??

sRGB is a synthetic color space but based on the behavior of (at the time) a CRT display with P22 phosphors and the spec was even based on the ambient conditions under which this theoretical display resided in. But its synthetic in that its based on simple math specifications (gamma, white point and chromaticity values).


From the father of sRGB (posted a very long time ago on the ColorSync list):
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1. sRGB is not base on "standard" "typical" or any other type of PC monitor,
but is directly derived from the HDTV standard ITU-R BT.709/2
2. sRGB does represent not only average PC monitors, but is within the
factory tolerances of  almost all CRTs on the market today, including Barco
professional CRTs. This is due to the shared family set of P22 phosphors
which almost all CRTs use today. While this "family" of P22 phosphors has
some differences between manufacturers, these differences fall within each
manufacturer's factory tolerances. Saying that sRGB chromaticities are
"quite small" is simply saying that CRT phosphors in general are quite
small.
3. While the 2.2 gamma was directly derived from HTDV, it has been
independently verified by Sony, Barco and others to represent the native
physical state of CRTs today. It is also very close to the native human
perceptual lightness scale when viewing CRTs. This combination makes this
gamma the optimal for CRTs to physically operate at. This also goes a long
way in explaining the compatibility with Windows and PCs in general since
these systems have not imposed any arbitary or proprietary system
adjustments.
4. The white point again is derived directly from the television industry
and is the standard is televisions and also in many aspects of photography.
Achieving a bright enough D50 white point to comfortably adapt to continues
to be a technical challenge for CRT vendors.

Michael Stokes
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Andrew Rodney
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« Reply #32 on: November 25, 2007, 12:57:16 PM »
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sRGB is a synthetic color space but based on the behavior of (at the time) a CRT display with P22 phosphors and the spec was even based on the ambient conditions under which this theoretical display resided in. But its synthetic in that its based on simple math specifications (gamma, white point and chromaticity values).
From the father of sRGB (posted a very long time ago on the ColorSync list):
[a href=\"index.php?act=findpost&pid=155806\"][{POST_SNAPBACK}][/a]


Are the primaries of sRGB not within the CIE x,y chromaticity diagram and their coordinates are that of current CRT phosphors, within the specified tollerences, (and the same as LCD filters) hence making it a 'real' colour space as opposed to ProPhoto (ROMM RGB - Reference Output Medium Metric RGB) which has two of its primaries CIE x,y coordinates out side the spectral locus, thus making it a hypothetical or 'synthetic' colour space.
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« Reply #33 on: November 25, 2007, 01:50:13 PM »
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Are the primaries of sRGB not within the CIE x,y chromaticity diagram and their coordinates are that of current CRT phosphors, within the specified tollerences, (and the same as LCD filters) hence making it a 'real' colour space as opposed to ProPhoto (ROMM RGB - Reference Output Medium Metric RGB) which has two of its primaries CIE x,y coordinates out side the spectral locus, thus making it a hypothetical or 'synthetic' colour space.
[a href=\"index.php?act=findpost&pid=155836\"][{POST_SNAPBACK}][/a]

Its a matter of semantics. Is it real because a CRT display can hit it? Sure. Of course, if you calibrate said CRT, will it exactly match the sRGB spec's, down to the exact location of the primaries? Probably not. Is it synthetic because its manufacturer is based on a theoretical device (one based on a real world device but not one we know for a fact exactly defines this space)? I'd say yes to that.

When you output hundreds of patches and measure them to build a printer profile, I'd say that is absolutely a 'real world' profile.
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« Reply #34 on: November 25, 2007, 02:09:58 PM »
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Solution- Open files in camera RAW (RAW files, jpegs, whatever) and set the editing preference (in the bottom center of the screen) to 8 bit sRGB.  Correct the exposure and all other global adjustments in camera RAW that you wish.  When done, change the preference to 16 bit prophoto- watch the histogram become more compressed as this happens.  Now, open the image in photoshop from camera RAW (which will be 16 bit prophoto), and apply whatever local adjustments you want- masks, hue/saturation, whatever.  When done, convert back to 8 bit sRGB (if output is for the web or an offsite printer without ICC profile), or assign the printer's profile if available.  Watch the histogram jump back to what you saw in camera RAW under the initial 8 bit sRGB settings.  This will help prevent blown highlights (and crushed shadows) in your prints.

Any critique or comments appreciated.

Kinda stupid and pointless IMO. There is no point at all in using ProPhoto as an editing space when you're dumbing down all the colors to fit into sRGB before the image leaves the RAW converter. If you're going to keep all colors within sRGB, then just use sRGB as your editing space and be done with it. But that's a really stupid approach given that most printers can print at least some colors outside sRGB, and as printer and display technology is improving the proportion of usable gamut outside sRGB is getting larger all the time.

A much better approach is to stay in ProPhoto, edit the image until it looks the way you want it to, and then save that as the master copy. When necessary, perform selective desaturation or whatever other edits you need to do to fit the image into a particular device's output gamut, convert the image to the device's profile, and then save that as a copy of the image. That way as print technology improves, you can go back to the master copy of the image and make a less-compromised version of the image for a new printer without having to go all the way back to the original RAW.
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papa v2.0
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« Reply #35 on: November 25, 2007, 02:38:46 PM »
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A much better approach is to stay in ProPhoto, edit the image until it looks the way you want it to, and then save that as the master copy.
[a href=\"index.php?act=findpost&pid=155866\"][{POST_SNAPBACK}][/a]


MMM you guys are missing something here.

You cant edit in Prophoto until you 'it looks the way you want' because you are viewing in sRGB space  (or the monitor space which is near to sRGB). so really the visual editing of ProPhoto is not a good idea.


The next colourspace outside of sRGB that manufacturers can now achieve is AdobeRGB as with the Eizo ColorEdge CG221.
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« Reply #36 on: November 25, 2007, 02:51:35 PM »
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MMM you guys are missing something here.

You cant edit in Prophoto until you 'it looks the way you want' because you are viewing in sRGB space  (or the monitor space which is near to sRGB). so really the visual editing of ProPhoto is not a good idea.
The next colourspace outside of sRGB that manufacturers can now achieve is AdobeRGB as with the Eizo ColorEdge CG221.
[a href=\"index.php?act=findpost&pid=155874\"][{POST_SNAPBACK}][/a]

Well yes and no. Yes, you can see an awful lot of the image which is falling into sRGB on an sRGB display. The colors that fall outside, the very saturated colors no but its not like the image you see on an sRGB display next to an Adobe RGB display look hugely different, they don't (I have such a setup). Does a spectral gradient look more saturated in ProPhoto RGB on the Adobe RGB display then the sRGB? Yes. Does the relationship of the image look so different I don't have any idea which is correct? Nope. I have to soft proof the image anyway to an output device which is vastly different in terms of gamut and as importantly, dynamic range. Then I have to view the reflective print and try to mentally compare it to an emissive display. Had to do this with chrome film and prints, chrome film and ink on paper from a CMYK press. Is this a prefect WYSIWYG? No, but its pretty close.

So, do you squash the colors in a working space to fit your display so you can see everything? Sure, if your only output is that display. But most of us have to output our files to all kinds of differing devices. Devices that far exceed sRGB. Then the question becomes, do you keep the colors you can output, outside the sRGB display? For most, the answer is yes.

We're dealing with, and always will deal with different reference media. Unless your life is really simple, you're just using a display as an output device, you have to live with these differences. One approach then is to throw away colors you can't see but can output. The other is output the colors you can't see but can output.
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« Reply #37 on: November 25, 2007, 03:33:53 PM »
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Another thing that you don't mention is where does the image gamut lie.

If most of your imaging fall inside the sRGB space then use sRGB if not use Adobe RGB if not use
Prophoto - which covers the gamut of Real world surface colours.

But as for workflows.

If you want to VISUALLY edit colours, we are at the moment restricted to editing in monitor space sRGB or AdobeRGB.

These space will include some output spaces but not all. For those image gamuts outside the display gamuts there is NO VISUAL editing and we must 'go by the numbers'.

Eg image captured in sRGB, viewed in Photoshop on a AdobeRGB compliant monitor and converted to ISO Coated v2 CMYK.

The  file can be viewed and visually edited in both inputspace and outputspace (if needed).

If the image gamut is outside that of AdobeRGB and  ROMM encoding is used and the destination outputspace is  for eg ISO Coated v2 CMYK, then any editing  is done by numbers and the results evaluated after printing. This is fine if you are an experienced repro operator but not for the average (and even a lot of pros) photographers to work.

Most are making a VISUAL assessment of the file prior to saving  or output.

The new sRGBv4.0 along with the other ICC v4.0 input and output profiles will make for a better sRGB workflow for most workflows.
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« Reply #38 on: November 25, 2007, 03:48:13 PM »
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If you want to VISUALLY edit colours, we are at the moment restricted to editing in monitor space sRGB or AdobeRGB.

Again, yes and no. If you're editing based on a soft proof of an output device, you're going to be all over the map here with what does and doesn't fall within the gamut of your display, sRGB or otherwise.

Quote
These space will include some output spaces but not all. For those image gamuts outside the display gamuts there is NO VISUAL editing and we must 'go by the numbers'.

What numbers? You're editing for an Epson 3800 on luster paper, a SWOP press, a Lambda, or any other output device you want to mention. The ICC profiles you use to soft proof provide the output numbers but do you know what to aim for? What's middle gray for a Pictrography 4500 supposed to be? Or a Canon ipf 5000 running fine art paper?

Quote
The  file can be viewed and visually edited in both inputspace and outputspace (if needed).

But again, even with something like SWOP, there are colors that fall outside an sRGB display so we're back to square one here (and square one isn't really a big deal).


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The new sRGBv4.0 along with the other ICC v4.0 input and output profiles will make for a better sRGB workflow for most workflows.
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How so?
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« Reply #39 on: November 25, 2007, 06:21:47 PM »
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You keep saying yes and no to some of my remarks without providing a a proper answer.

I dont think you are really understanding the point I am trying to make which was initially in reference to the comment

"that ProPhoto RGB (like all the other RGB working spaces) are synthetically manufactured using simple math'

You also state
'In the case of ProPhoto RGB, there ARE colors defined that fall outside human vision.'

mmm  I think most people would challenge you on that one!

Colours outside the HVS?Huh

I think what you mean is that ProPhoto is a colour encoding space which includes coordinates NOT COLOURS outside the HVS.

Same can be said of CIEXYZ and CIELAB.
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