Luminous Landscape Forum
Raw & Post Processing, Printing => Colour Management => Topic started by: Bob Rockefeller on July 31, 2015, 02:32:56 pm
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I've seen discussed here in a few threads the concept of the gamut volume of a profile as a way to understand the likely gamut volume of the paper it is used for.
I have a couple of papers I'd like to compare on something other than a purely subjective basis. How can I determine the gamut volume of several profiles I have?
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I have a couple of papers I'd like to compare on something other than a purely subjective basis. How can I determine the gamut volume of several profiles I have?
ColorThink Pro has a 'gamut volume' metric it reports. That said, I'm not certain if what it reports is what you desire ;)
I asked the fine folks at CHROMIX what this value provides, here's what I heard back:
The ColorThink Grapher calculates the gamut volume in terms of cubic Lab values. A Lab value of one is one delta E (dE76 considering the way the Grapher is currently made). So each of these cubic Lab values represent the smallest discernible color difference, and each cubic Lab value represents a unique human-discernable color. So in that sense, the larger gamut will necessarily represent more distinct, humanly-perceptable colors than a smaller gamut. (Now that statement comes with our usual caveat that this volume number is a rough estimate, not a precise one - and it works well for and is intended for making comparisons between profiles, not for defining absolute volume numbers.)
ON the OTHER hand…..
There is a philosophical issue at stake here: Just what constitutes a color? Depending on how the numbers are encoded, you can have several million combinations of different numbers representing different colors in theory, but some will point out that these different number combinations do not constitute individual “colors” since they are not distinct enough to be *different* to the human vision system.
- gamut volumes in ColorThink are calculated using color values and refer to the number of unique color values
- unique color values in ColorThink refer to the number of distinct colors (as per human vision) that exist in a color gamut or a color image or color list or whatever.
- In color gamuts we just use cubic Lab values, the idea being that one delta-E76 value away from a color *should* result in a perceptually different color
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Once you've compared the gamut volumes in CTP you will of course have comparative statistics, but what those statistics mean in terms of the comparative reproduction of real-word photographs is another matter - depends very much on the gamut of the image being printed.
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All that sounds as if it provides at least a common reference from which to make some comparisons.
I have ColorThink 2.3, which doesn't seem able to calculate a gamut volume. ColorThink Pro is a pretty expensive upgrade.
Are there other tools to make the calculation? Or perhaps reference web sites that have the volumes for a number of papers?
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PatchTool can:
(http://digitaldog.net/files/PatchTool.jpg)
http://www.babelcolor.com/#PatchTool
Here lies the rub. ColorThink Pro reports Adobe RGB as having a gamut volume of 1,207,520.
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(http://s1.postimg.org/dfxg5pvu7/image.jpg)
or
(http://s11.postimg.org/knssq36j7/image.jpg)
or apple one
(http://s15.postimg.org/n76xg1gpn/image.jpg)
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Using average dE error of a profile as the basis for gamut computation instead of 1 dE and discarding everything with dE larger than 6 gives a better perspective, and fo a good printer with a good profile may result in volume numbers 2 orders of magnitude lower.
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Here's an interesting site I saw reference to somewhere or other:
http://www.iccview.de
It's in German, but is easy enough to figure out most of.
It provides comparative 3D gamut diagrams, with calculated gamut volumes, from uploaded ICC profiles.. That volume is reported in "cubic color units." MOAB's profile for their Juniper Baryta Rag is calculated at 8,125,647 cubic color units, for example.
Does anyone have an experience with that site? Is it a worthwhile tool?
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Does anyone have an experience with that site? Is it a worthwhile tool?
Hi Bob,
Since there are somewhat different methods of computing gamut volumes used by different applications, as long as you compare profiles on that website against eachother, you'll be fine.
Cheers,
Bart
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Since there are somewhat different methods of computing gamut volumes used by different applications, as long as you compare profiles on that website against eachother, you'll be fine.
Which method is correct (does that matter)?
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Which method is correct (does that matter)?
Hi Andrew,
Correct is a big word, as they are all approximations based on some assumptions (e.g. which delta E method is used, or how is rounding done, and at which precision is the calculation done, to name a few). And no, it usually doesn't matter much. But comparing the volume (even of the same profile) from one application against that from another application, may/will show some differences in total volume. Hence my suggestion to stay within the same (whatever) application for comparisons.
Cheers,
Bart
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Correct is a big word, as they are all approximations based on some assumptions (e.g. which delta E method is used, or how is rounding done, and at which precision is the calculation done, to name a few). And no, it usually doesn't matter much. But comparing the volume (even of the same profile) from one application against that from another application, may/will show some differences in total volume. Hence my suggestion to stay within the same (whatever) application for comparisons.
I'd totally agree to stick with apples to apples comparisons, but it would be useful to know which is closer to the goal and how the dE formula applies. We have differing dE formulas and there are reasons we'd use one over the other (dE 2000 is said to be 'more accurate' (better) with smaller dE values being calculated).
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Well, you've shown a discrepancy of about 20% between PatchTool and ColorThink Pro, the latter with the calculation methodology stated. Some people may question a procedure starting with the dE (1976) formula vs the later ones. So it makes one wonder whether there is a "correct" method (based on what criteria? what purpose?) and whether the comparison of values within any one approach is perhaps more relevant and useful. Not sure - as it's hard to relate gamut volume to tangible reality in prints of real-world photographs, except when differences are truly large. I've considered it more prospective using these measurements - within one tool (CTP in my case) as indicatively useful comparative markers to predict how my image editing approach may differ between substantially different papers and what kind of limitations I should expect to encounter.
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I'd totally agree to stick with apples to apples comparisons, but it would be useful to know which is closer to the goal and how the dE formula applies. We have differing dE formulas and there are reasons we'd use one over the other (dE 2000 is said to be 'more accurate' (better) with smaller dE values being calculated).
What goal?
If dE 2000 is "more accurate", would you consider CTP to be less useful relative to "a goal", or does it remain just as valid as any other approach if being used for comparative purposes?
I.O.W. how does one relate different "goals" to different "methodologies" in gamut volume calculations?
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What goal?
If dE 2000 is "more accurate", would you consider CTP to be less useful relative to "a goal", or does it remain just as valid as any other approach if being used for comparative purposes?
I.O.W. how does one relate different "goals" to different "methodologies" in gamut volume calculations?
All excellent questions Mark. I can't answer them. Gamut Volume isn't something I've paid much attention to, not sure it's even useful ???
For example, I have seen cases where the reported Gamut Volume for sRGB is a larger number than some output devices. But when I plot the two in 3D, I see where colors clip from sRGB should I use that working space. I think that's more useful. Or let's say more telling. Adding the ambiguity of how gamut volume might be calculated makes that metric even more confusing as to it's goal. At least on the Colorwiki for ColorThink, there's not much I can find about how this metric is useful: http://www.colorwiki.com/wiki/Evaluate_Device_Gamut_Volume
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My personal take is it's not so much the final 'volume' # but where and how the volume is distributed ala 2 & 3D space rendering.
Case in point: Hahn PR308 may have a greater volume than some other paper but 308 has deficiencies in the dark greens so
even if the volume is 'better' or 'greater', it may not be the optimal choice.
Feels like a lot of measurbating to me.
YMMV, no colors were harmed in the production of this posting. :D
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My personal take is it's not so much the final 'volume' # but where and how the volume is distributed ala 2 & 3D space rendering.
Exactly! It's like looking at some spec for the weight of a car alone, when you're wondering about it's gas mileage which we know vary. I don't see the number being very useful but I'd love to know why that might be an incorrect opinion (I'd love to learn more).
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All excellent questions Mark. I can't answer them. Gamut Volume isn't something I've paid much attention to, not sure it's even useful ???
For example, I have seen cases where the reported Gamut Volume for sRGB is a larger number than some output devices. But when I plot the two in 3D, I see where colors clip from sRGB should I use that working space. I think that's more useful. Or let's say more telling. Adding the ambiguity of how gamut volume might be calculated makes that metric even more confusing as to it's goal. At least on the Colorwiki for ColorThink, there's not much I can find about how this metric is useful: http://www.colorwiki.com/wiki/Evaluate_Device_Gamut_Volume
OK, we're largely in the same quandary. That said, I see this as being possibly useful at two levels, and this applies at least to CTP, which is the application I've been using. (1) Comparing gamut volumes between papers or printers does tell us something about the relative gamut limitations of our printing environment; this <could be> indicative of differing image editing challenges. (2) A bit geekier, one can use CTP to graph the gamut of a photographic image (reduced size so the program can cope) and compare it to the gamut of the printer/paper combination. This would provide an indication of whether the latter is likely to be constraining the appearance of the former. In both of these cases CTP is used for relative rather than absolute measurements, the purpose is conveyed by the nature of the comparison being made and the comparison is indicative rather than firmly predictive.
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Case in point: Hahn PR308 may have a greater volume than some other paper but 308 has deficiencies in the dark greens so
even if the volume is 'better' or 'greater', it may not be the optimal choice.
Yes I agree - the shape can be as important as the volume. Again, however, where the rubber should hit the road, is how to relate these numbers to observed real-world outcomes. That is where the CTP image graphing tool may be handy, but it would seem ones needs to do this often enough to make it useful for predictive purposes. Perhaps it's easier and faster just to run a few comparison prints with test images and we know all we need to know without the "measurebating". :-) ?
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My personal take is it's not so much the final 'volume' # but where and how the volume is distributed ala 2 & 3D space rendering.
Case in point: Hahn PR308 may have a greater volume than some other paper but 308 has deficiencies in the dark greens so
even if the volume is 'better' or 'greater', it may not be the optimal choice.
Indeed, and that's why it's more important to compare the specific shape of the hul, and in particular for colors that are in the images we want to output (!)
The Argyll Colormanagement System allows to do that with these command line utilities that also produce a VRML file that can be viewed an appropriate browser plugin:
iccgamut (http://argyllcms.com/doc/iccgamut.html) Create a gamut file or VRML file of the color gamut of an ICC profile.
tiffgamut (http://argyllcms.com/doc/tiffgamut.html) Create a gamut file or VRML file of the color gamut of a TIFF or JPEG image.
viewgam (http://argyllcms.com/doc/viewgam.html) Convert one or more gamuts into a VRML 3D visualization file. Compute an intersection.
Cheers,
Bart
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We have differing dE formulas and there are reasons we'd use one over the other (dE 2000 is said to be 'more accurate' (better) with smaller dE values being calculated).
I don't understand why the calculation of dE should matter when calculating the volume of the color space solid in LAB space. Don't all the applications report numbers in cubic LAB units (not cubic dE)? This volume might mean different things with different dE values, but the actual volume of the space shouldn't be ambiguous beyond rounding errors, should it? Certainly not to by 20% and especially for simple matrix-based profiles.
Here's a method I played around with a couple years ago when I had a similar question to the OP.
http://www.photo-mark.com/notes/calculating-color-space-volumes/
I think the theory is sound, but I'm a hobbyist programmer so there's no guarantee my implementation is without flaw. My results match Bruce Lindbloom's reported volumes quite closely, which gave me some confidence.
My personal take is it's not so much the final 'volume' # but where and how the volume is distributed ala 2 & 3D space rendering.
This exact observation along with an alternative solution was proposed in a paper last October by Kiran Deshpande, Phil Green, and Michael R Pointer. They came up with a "Gamut Comparison Index" which takes volume and the percentage of each gamut contained within the other and boils it down to a single metric. They hope this is a more useful value to help understand how well and efficiently a target gamut and an encoding gamut match.
Sadly, the paper is behind a paywall, but you can read the abstract here, which is enough to understand the essence of what they are proposing:
http://onlinelibrary.wiley.com/doi/10.1002/col.21930/abstract
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I don't understand why the calculation of dE should matter when calculating the volume of the color space solid in LAB space. Don't all the applications report numbers in cubic LAB units (not cubic dE)?
I have no idea Mark. I was responding to Bart who stated:
Correct is a big word, as they are all approximations based on some assumptions (e.g. which delta E method is used, or how is rounding done, and at which precision is the calculation done, to name a few).
All I know two applications report differing gamut volumes from the same profile.
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I don't understand why the calculation of dE should matter when calculating the volume of the color space solid in LAB space. Don't all the applications report numbers in cubic LAB units (not cubic dE)? This volume might mean different things with different dE values, but the actual volume of the space shouldn't be ambiguous beyond rounding errors, should it? Certainly not to by 20% and especially for simple matrix-based profiles.
Cubic LAB units would not be useful, since that would not take into account just notable differences between colors. A difference of one LAB unit may not be visually perceptible. See this Wikipedia article (https://en.wikipedia.org/wiki/Color_difference) and take a look at the MacAdam ellipses which enclose colors that are not visually different and therefore are not discrete colors. Bruce Lindbloom uses ΔE3 in his color space tabulation.
Bill
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Cubic LAB units would not be useful, since that would not take into account just notable differences between colors. A difference of one LAB unit may not be visually perceptible. See this Wikipedia article (https://en.wikipedia.org/wiki/Color_difference) and take a look at the MacAdam ellipses which enclose colors that are not visually different and therefore are not discrete colors. Bruce Lindbloom uses ΔE3 in his color space tabulation.
Bill
Hi Bill,
I understand that a distance of a single unit in LAB space is not necessarily a just-noticeable difference, but I don't think anyone reporting gamut volumes is saying they are a precise count of discernible, discreet colors. Rather they are saying it's simply the volume of the solid that we see graphed in LAB space. They often (like Bruce Lindbloom) report the unit as ΔE3, but I've always assumed (maybe incorrectly) that they were reporting this because most people are okay with the small inaccuracy of conflating ΔE and LAB values. That's what appears to be going on the in the quote Andrew provided from CHROMIX.
If we wanted to report volumes in a way that was a more precise calculation of discernible colors we would need to report volumes of a 3D object in a space other than CIELAB. But I've never seen anyone suggest they are doing this (or that it would be worth the effort). Lindbloom gives a couple details of his method here (http://www.brucelindbloom.com/index.html?WorkingSpaceInfo.html). Using the technique he suggests — tessellating the hull of the gamut surface — will result in cubic LAB units because the surface he is tessellating is calculated in LAB space.
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The Argyll Color management System allows to do that with these command line utilities that also produce a VRML file that can be viewed an appropriate browser plugin:
iccgamut (http://www.argyllcms.com/doc/iccgamut.html) Create a gamut file or VRML file of the color gamut of an ICC profile.
tiffgamut (http://www.argyllcms.com/doc/tiffgamut.html) Create a gamut file or VRML file of the color gamut of a TIFF or JPEG image.
viewgam (http://www.argyllcms.com/doc/viewgam.html) Convert one or more gamuts into a VRML 3D visualization file. Compute an intersection.
I've used these a lot. And the latest versions no longer require a plugin to display 3D files (on most modern browsers) because they use x3dom (http://www.x3dom.org/) (Javascript and HTML5) instead of VRML.
They report gamut size in "cubic colorspace units." This is handy if you are, for example, examining variants of the same profile. I'm learning ArgyllCMS and was experimenting with preconditioning (http://www.argyllcms.com/doc/targen.html#c). Here is the 2D version of a profile done without preconditioning overlaid with one done with preconditioning.
(http://pics.fishcreekstudio.com/photos/i-DvL3mRC/0/M/i-DvL3mRC-M.jpg)
This is a static 2D version and I had to do a screen shot and upload the screenshot to SmugMug. Bleh. Much better to look at the real 3D version (http://www.frogymandias.org/profiles//gamuts-xd3_html/xd3/ArgyllCMS_HP-7640_Argyll_7640_BJs-Glossy-Photo-Paper_NoPC_392-patches_ArgyllCMS_HP-7640_Argyll_7640_BJs-Glossy-Photo-Paper_PC_392-patches_wrl.x3d.html) (no plugin required--just click to see the 3D version.)
I made this for my own use and the labels are cryptic. The one that has "NoPC" is the one without preconditioning. The one that has "PC" has had preconditioning. Scroll down past the 3D graph to see data from the profiles (including cubic colorspace units.)
Here is one that compares sRGB and Adobe RGB (1996)
(http://pics.fishcreekstudio.com/photos/i-H5CrBSq/0/M/i-H5CrBSq-M.jpg)
Here is the real 3D version (http://www.frogymandias.org/profiles//gamuts-xd3_html/xd3/sRGB_AdobeRGB_wrl.x3d.html).
FWIW, here are more 3D plots of profiles that I am currently looking at (http://www.frogymandias.org/profiles//gamuts-xd3_html/hp-7640.html). Again, the labels might be cryptic. Most of them are from me making various profiles for my HP 7640 using either Argyll or ColorMunki Display. The other profiles are mostly stock profiles I collected from various places.
I really, really like iccgamut and viewgam (and the rest of ArgyllCMS.) 3D plots make comparing profiles be a lot easier.
Wayne
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I've used these a lot. And the latest versions no longer require a plugin to display 3D files (on most modern browsers) because they use x3dom (http://www.x3dom.org/) (Javascript and HTML5) instead of VRML.
They report gamut size in "cubic colorspace units." This is handy if you are, for example, examining variants of the same profile. I'm learning ArgyllCMS and was experimenting with preconditioning (http://www.argyllcms.com/doc/targen.html#c). Here is the 2D version of a profile done without preconditioning overlaid with one done with preconditioning.
I really, really like iccgamut and viewgam (and the rest of ArgyllCMS.) 3D plots make comparing profiles be a lot easier.
Wayne
Is it easy to do? I have no problems with the command line.
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Is it easy to do? I have no problems with the command line.
The page I linked (http://www.frogymandias.org/profiles//gamuts-xd3_html/hp-7640.html) that has a bunch of 3D plots to was generated with a Perl script that I wrote that reads config files that describe the profiles and then runs the appropriate Argyll programs to generate the xd3dom files. I haven't published this script anywhere because I wrote it for my own use.
But I did write a page that documents how to use iccgamut and viewgam (http://www.frogymandias.org/gamuts/make-3d-plots.html) to combine multiple 3D plots in the same graph. This uses simple Windows .bat files. It shouldn't be too difficult to adapt it to Linux or Mac, but I haven't tested this because I only use Argyll on Windows.
Wayne
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But I did write a page that documents how to use iccgamut and viewgam (http://www.frogymandias.org/gamuts/make-3d-plots.html) to combine multiple 3D plots in the same graph. This uses simple Windows .bat files. It shouldn't be too difficult to adapt it to Linux or Mac, but I haven't tested this because I only use Argyll on Windows.
Wayne,
Thanks for that writing that page - coincidentally I found it earlier this weekend when I was trying to find a way to generate 3D gamut plots of the custom profiles I have been creating for a new printer. Since I already had Argyll installed, it was simple using your instructions. I am on a Mac, so I couldn't use the .BAT file directly, but it was easy enough to copy and past the commands into a terminal window.
-Scott
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I don't understand why the calculation of dE should matter when calculating the volume of the color space solid in LAB space.
It comes down to the algorithm used. One way for instance, would be to march through the L*a*b* space at unit intervals, and decide whether each point is in or out of gamut by doing a B2A then A2B table round trip, using a delta E threshold to decide.
An alternative is to generate a bounding volume around the values in the A2B table. This is complicated by the lack of any concrete ink limit information in an ICC profile for CMYK profiles (at best it can be guessed from the contents of the B2A table) and the fact that gamut volumes are often convex.
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It comes down to the algorithm used.
So what algorithm do you use to calculate "cubic colorspace units"?
Wayne
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So what algorithm do you use to calculate "cubic colorspace units"?
First step is creating a gamut surface. The gamut surface is computed using a variation of
Jan Morovic's Segment Maximum approach. Points are generated from the contents of the
A2B table, with either explicit or guessed ink limits. The segments are filtered with an adaptive
depth structure, so that approximately the same detail is kept on the gamut surface. Multiple
direction vectors at each point are retained. The resultant points are used to create the overal
convex hull, but in an adaptive, non-linearly scaled radial space, that allows for a level of
convexity in the PCS result.
Since the resulting surface is a closed set of polygons, a standard volume computation
can be used, in this case the formula from "Area of planar polygons and volume of polyhedra"
by Ronald N. Goldman, from Graphics Gems II, pp 170.
The major sources of inaccuracy are: 1) The surface not following the gamuts actual convexity
2) The surface showing convexity where it doesn't exist, 3) Not following surface detail due to
insufficient sampling density (this can be selected with a parameter), 4) Inaccurate ink limit
boundary due to the use of an ink limit that is not a simple sum of inks.
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The graphs presented here seem to suggest orthogonality between LAB channels. I don't understand what criterion was used to establish that fact?
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The graphs presented here seem to suggest orthogonality between LAB channels. I don't understand what criterion was used to establish that fact?
Convenience of presentation ;)
If gamut volume is calculated by counting, and not by computing the volume of the resulting figure in 3 orthogonal axes, should not affect the results.
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The page I linked (http://www.frogymandias.org/profiles//gamuts-xd3_html/hp-7640.html) that has a bunch of 3D plots to was generated with a Perl script that I wrote that reads config files that describe the profiles and then runs the appropriate Argyll programs to generate the xd3dom files. I haven't published this script anywhere because I wrote it for my own use.
But I did write a page that documents how to use iccgamut and viewgam (http://www.frogymandias.org/gamuts/make-3d-plots.html) to combine multiple 3D plots in the same graph. This uses simple Windows .bat files. It shouldn't be too difficult to adapt it to Linux or Mac, but I haven't tested this because I only use Argyll on Windows.
Wayne
Thanks.
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Convenience of presentation ;)
If gamut volume is calculated by counting, and not by computing the volume of the resulting figure in 3 orthogonal axes, should not affect the results.
Thanks for the reply. Will the procedure to calculate gamut vol as pointed out by GwGill be affected by the non-orthogonality of the axes? Perhaps, the relative comparison between different color gamuts may not be affected as one which is supposed to have higher volume would still have a higher number. But, the absolute number may be affected? Right?
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All that sounds as if it provides at least a common reference from which to make some comparisons.
I have ColorThink 2.3, which doesn't seem able to calculate a gamut volume. ColorThink Pro is a pretty expensive upgrade.
A bit late to the party but I also have V 2.3. You could show two different profiles in the 3D L*a*b* view, in two different colors and switch them back and forth or show them less opaque in different colors. I assume you're not looking for absolutely perfect registration?
rgds,
Ted