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Author Topic: Prophoto RBG  (Read 12796 times)
tho_mas
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« Reply #20 on: August 22, 2008, 03:53:55 AM »
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So the profile has no idea about the illuminant under which the scene is captured, it assumes one. [a href=\"index.php?act=findpost&pid=216578\"][{POST_SNAPBACK}][/a]
hmh... of course you can set one. You can make profiles for every ligthing situation.
The profiles have an illuminant. Specific profiles are more accurate than generic profiles. But even the generic profiles work very well.
Check any camera profiling software and you will get an idea of it ;-)

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You'll excuse me if I am skeptical that this process is defining device behavior.
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Sure. It's not my problem...
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Peter_DL
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« Reply #21 on: August 23, 2008, 05:37:11 AM »
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... his statement sums up nicely some of the common objections to ProPhotoRGB: why waste space on colors that you can't see or print. The answer is to gain access to colors that you can see or print. [a href=\"index.php?act=findpost&pid=216453\"][{POST_SNAPBACK}][/a]
Hi Bill,

Yes – this is easy to agree from 3D gamut comparisons.

Considering that it was a “beginner's question”
I’d just like to add an annotation about possible pitfalls.

With a large gamut working space such as ProPhoto RGB (or a linear gamma version thereof, such as used as an intermediate space inside ACR) there’s some risk to increase the amount of out-of-gamut colors with reference to any final target space (such as Adobe RGB, sRGB, or any media/paper profile for print) simply in the course of image editing.
In such large gamut environment, even a tone curve can blow light saturated colors out-of the reach e.g. of tiny sRGB gamut, and of course all adjustments which effect saturation are prone to add another bunch of oog colors. Hence, it can easily be that a good part of the final conversion problem, or let’s call it challenge which then has to be solved in whatever ‘controlled’ way, is in fact self-made.

Actually I was thinking about another ACR feature request in this regard. IF the user wants Adobe RGB or sRGB for output (for whatever reason which shall not be questioned here) it would be nice to have a checkbox which could be called: “use linear gamma version of the selected output space for internal working space”. Arguable though - however, I think that in many cases it might be better (in terms of less clipping) to convert scene-referred data straight from the camera profile into the limits of smaller 1.0 Adobe RGB or 1.0 sRGB gamut, rather than doing so after application of all the given creative controls in 1.0 ProPhoto RGB.

Best regards, Peter

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bjanes
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« Reply #22 on: August 23, 2008, 07:11:37 AM »
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By whom? Sorry, it was a lot of work ;-)
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Sorry, Andrew. I was referring to another article which was supporting and explaining my point, but your article is much more pertinent to the topic and your 2D and 3D gamut plots are great. I would encourage anyone intersted in the topic to read your excellent white paper on the subject.

Andrew Rodney:
[a href=\"http://www.adobe.com/digitalimag/pdfs/phscs2ip_colspace.pdf]http://www.adobe.com/digitalimag/pdfs/phscs2ip_colspace.pdf[/url]

Schewe & Fraser:
http://www.adobe.com/digitalimag/pdfs/phsc..._colormgraw.pdf

Bill
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bjanes
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« Reply #23 on: August 23, 2008, 09:06:34 AM »
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Simple matrix profiles of RGB working spaces when plotted 3 dimensionally illustrate that they reach their maximum saturation at high luminance levels. The opposite is seen with print (output) color spaces. Printers produce color by adding ink or some colorant, working space profiles are based on building more saturation by adding more light due to the differences in subtractive and additive color models. To counter this, you need a really big RGB working space like ProPhoto RGB again due to the simple size and to fit the round peg in the bigger square hole. Their shapes are simple and predictable. Then there is the issue of very dark colors of intense saturation which do occur in nature and we can capture with many devices. Many of these colors fall outside Adobe RGB (1998) and when you encode into such a space, you clip the colors to the degree that smooth gradations become solid blobs in print, again due to the dissimilar shapes and differences in how the two spaces relate to luminance.
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It is correct that simple matrix spaces such as sRGB have restricted saturation at low luminance, but maximal saturation is reached at about L = 50, which is midgray and not really high luminance, depending on your definition of high luminance. For example, refer to the [a href=\"http://www.fho-emden.de/~hoffmann/cielab03022003.pdf]gamut plots[/url] (Warning: large document) provided by Gernot Hoffmann.

On page 20 the gamut of sRGB at L = 10 is shown. Page 20 demonstrates the gamut at L = 50, and page 25 shows the gamut at L = 99, which hardly extends beyond white. A stacked 3D view of the sRGB gamut is shown on page 44.

Even ProPhoto has limited gamut at L = 10 (page 35) and L = 90 (page 43).

Bill
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digitaldog
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« Reply #24 on: August 23, 2008, 10:51:01 AM »
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It is correct that simple matrix spaces such as sRGB have restricted saturation at low luminance, but maximal saturation is reached at about L = 50, which is midgray and not really high luminance, depending on your definition of high luminance.

My concern isn't the definition of maximal saturation but saturation in general. And in terms of saturation of dark colors near L*star zero.

Here's a blow up (zoomed in) area of sRGB versus ProPhoto RGB (wire frame) plotted over a printer gamut (Epson 3800) and an image (the colored squares). Hopefully this shows up well on the web.

What you see here with the bigger encoding gamut is more "headroom" and you should be able to see that the dark, saturated colors in the image (squares) in relationship to the printer are not going to be output as a blob of dark tones (as severely) when mapped into the printer gamut at these low L*star values.
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Andrew Rodney
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Mark F
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« Reply #25 on: August 24, 2008, 08:40:06 PM »
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I'm the guy who started this thread and would like to thank everyone who answered, although to be truthful the discussion went beyond my current ability to understand. But I think I do now understand where ProPhoto RGB fits in. A couple of hours at Barnes & Noble works wonders. By the way, I looked at the new Lightroom 2 book by Martin Evening and at least for a beginner like me, it is great.
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bjanes
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« Reply #26 on: August 25, 2008, 08:15:37 AM »
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My concern isn't the definition of maximal saturation but saturation in general. And in terms of saturation of dark colors near L*star zero.

Here's a blow up (zoomed in) area of sRGB versus ProPhoto RGB (wire frame) plotted over a printer gamut (Epson 3800) and an image (the colored squares). Hopefully this shows up well on the web.

What you see here with the bigger encoding gamut is more "headroom" and you should be able to see that the dark, saturated colors in the image (squares) in relationship to the printer are not going to be output as a blob of dark tones (as severely) when mapped into the printer gamut at these low L*star values.
[a href=\"index.php?act=findpost&pid=216828\"][{POST_SNAPBACK}][/a]

I presume that this is a ColorThinkPro plot, but I can't see any significant difference between the two and may not know what to look for.

Here are Gamutvision plots demonstrating the ProPhotoRGB and sRGB gamuts (wireframe) vs the gamut of my current printer (Epson 2200) with PremiumLuster paper using the Epson supplied profiles. The newer Epsons probably have a larger gamut and would demonstrate larger differences. However, with this printer one sees clipping in the blues and greens at low luminance and clipping of the oranges and greens at higher luminances. The falloff in maximal saturation in both the higher and lower luminances is well demonstrated.


[attachment=8066:attachment]
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digitaldog
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« Reply #27 on: August 25, 2008, 08:19:01 AM »
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I presume that this is a ColorThinkPro plot, but I can't see any significant difference between the two and may not know what to look for.

Yes

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The newer Epsons probably have a larger gamut and would demonstrate larger differences.

Significantly more!
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Andrew Rodney
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bjanes
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« Reply #28 on: August 25, 2008, 09:11:02 AM »
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I presume that this is a ColorThinkPro plot, but I can't see any significant difference between the two and may not know what to look for.
[a href=\"index.php?act=findpost&pid=217101\"][{POST_SNAPBACK}][/a]
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Yes
[a href=\"index.php?act=findpost&pid=217102\"][{POST_SNAPBACK}][/a]

If the answer to both of my questions is "yes", what should I be looking for?
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digitaldog
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« Reply #29 on: August 25, 2008, 09:21:51 AM »
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If the answer to both of my questions is "yes", what should I be looking for?
[a href=\"index.php?act=findpost&pid=217109\"][{POST_SNAPBACK}][/a]


You've got to at least zoom in way, way closer to the lower L*Star of the maps than what I see. If you look at mine, you're seeing maybe the wireframe, map from say L*0 to 20 if that.

Yes, the K3 ink set is wider than what you're using. As far as I recall, K3 was the ink set that exceeded Adobe RGB (1998) gamut pretty significantly in certain colors.
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Andrew Rodney
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