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Author Topic: Photoshop's Gamut Warning  (Read 26174 times)
shewhorn
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« on: December 27, 2007, 02:14:35 AM »
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I highly suspect one of the following things:

1) I don't understand what the gamut warning feature is supposed to be telling me and I'm attempting to use it incorrectly (operator error)
2) I'm clueless (entirely possible... the more I learn, the more I realize how clueless I really am)
3) The Gamut Warning feature has a bug.

Now before I start I'm working under the assumption that:
1) A good RA-4 printer (Durst, Chromira) properly profiled can reproduce the sRGB color space and a little bit beyond.
2) A properly profiled inkjet can easily reproduce the sRGB gamut and beyond. This is supported by my own experience of looking at the same test prints produced on a Chromira, a Durst Lamda, and an Epson 2200 (I trust the labs I got the test prints back from did a decent job with their profiles (Pechmans for the Durst and Fotoworks for the Chromira... their output is much better than a lab like WHCC which doesn't in my opinion produce very good profiles).

I wanted to create a very basic test file. I created a 2400x3000 pixel file in the sRGB color space at 8 bits (I actually started out with ProPhoto but after seeing the results I was getting I dumbed it down to sRGB). I then created 14 divisions, each with a gradient in it (the divisions were running vertically on the page). I created two sets of gradients for each color those being X to black (where X is the color) and X to white. The values I used are as follows (numbers are in the format of Red, Green, Blue)

255,0,0
0,255,0
0,0,255
255,0,255
255,255,0
0,255,255

So with two sets of that (one going to black, the other going to white) I had 12 gradient strips. I also created a white to black gradient and finally one strip that was grey (128, 128, 128).

Now here's where I got thrown for a complete and total loop. I selected Canon's Premium Matte Highest for their IPF6100 as my profile and then turned on Gamut Warning. If I'm to believe what the Gamut Warning is telling me, with a file in an sRGB color space being printed to Canon Premium Matte paper with an IPF6100, the printer can not reproduce reds above 79,0,0, greens above 0, 199 0 (there was also a gap in the middle of the green) and blues above 0,0,52. The only color it seemed to do good with was yellow which pretty much went to 255, 255, 0.

Also, if I'm to believe the Gamut Warning feature in Photoshop, for the same paper the Epson 2200 has a wider Gamut than the IPF5000 (compared canned profiles for Ilford Smooth Pearl). Now, the Epson 2200 was a great little inkjet for its day but the Lucia inks are by far superior to the first generation UltraChrome inks. I know that wider gamut does not necessarily translate to a better print but, I did not expect to see that.

So, the results I'm seeing don't reconcile with the results I'm expecting to see which is what brings me here. Set me straight folks! I've attached a screen shot of what it looks like with Gamut Warning turned on so you can get an idea of what I'm seeing.



Cheers, Joe
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Farmer
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« Reply #1 on: December 27, 2007, 07:06:08 AM »
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Which rendering intent did you use and did you set paper white/black point compensation etc?  Did you create a 16 or 8 bit image?  What dimensions (in order to tell how many steps it's taking from 0-255)?
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Geoff Wittig
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« Reply #2 on: December 27, 2007, 08:36:06 AM »
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I can pass along a couple of things I have learned.
First, gamut warning is an all or nothing kind of thing; a color that is just barely outside the gamut of your ink/printer/paper combination will be grey'd out just as much as a science fiction color far outside the gamut. So an image can be almost entirely grey'd out in Photoshop's gamut warning display, yet still print very well if most of those colors are just barely outside the gamut.

Second, matte papers with any pigment printer yield a much more restricted gamut than you'll get from any semi-gloss or luster type paper. Just use one of the utilities that provide comparative 3-d gamut plots and check out the difference between the gamut of (say) your printer's standard glossy paper and any matte you want to try. The gamut restriction imposed by matte papers can be quite dramatic.

Thirdly, there are significant gamut differences between various printers. For example, the Epsons have a wider gamut in dark reds/oranges, while the HP Z3100 has a wider gamut in lighter greens/blues. So an artificial "gamut test" like you're performing will uncover gamut limits from any printer. Exactly where will depend on the printer.
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digitaldog
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« Reply #3 on: December 27, 2007, 08:38:30 AM »
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The gamut warning overlay is legacy stuff that was kind of useful before Photoshop 5.0 and true soft proofing, its pretty useless today.
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Andrew Rodney
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shewhorn
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« Reply #4 on: December 27, 2007, 08:40:42 AM »
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Which rendering intent did you use and did you set paper white/black point compensation etc?  Did you create a 16 or 8 bit image?  What dimensions (in order to tell how many steps it's taking from 0-255)?
[a href=\"index.php?act=findpost&pid=163355\"][{POST_SNAPBACK}][/a]

They're using canned profiles... either way, as far as I know regardless of what those settings are they wouldn't explain the differences I'm seeing here (the gamut warning is supposed to display out of gamut colors for the selected soft profile compared to the source file so regardless of whether or not you're using a relative or perceptual rendering intent, it doesn't matter, if the source is out of gamut, it's out of gamut and none of those settings will make a difference.. they merely describe whether or not the rendering method used is going to truncate out of gamut data, or remap everything to be in gamut, etc.).

Cheers, Joe
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Bruce Watson
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« Reply #5 on: December 27, 2007, 08:54:03 AM »
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The gamut warning overlay is legacy stuff that was kind of useful before Photoshop 5.0 and true soft proofing, its pretty useless today.
[a href=\"index.php?act=findpost&pid=163363\"][{POST_SNAPBACK}][/a]
Would you please expound on that a little? Why is it useless, and what should we use instead?
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digitaldog
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« Reply #6 on: December 27, 2007, 08:57:01 AM »
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Would you please expound on that a little? Why is it useless, and what should we use instead?
[{POST_SNAPBACK}][/a]

Load the profile for the print process in Customize Proof Setup. Instead of an ugly overlay, you see the colors map into the output color space (of course, using your display gamut). Far more useful.

[a href=\"http://www.ppmag.com/reviews/200410_rodneycm.pdf]http://www.ppmag.com/reviews/200410_rodneycm.pdf[/url]

http://www.ppmag.com/reviews/200411_rodneycm.pdf
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Andrew Rodney
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KeithR
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« Reply #7 on: December 27, 2007, 09:07:00 AM »
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Would you please expound on that a little? Why is it useless, and what should we use instead?
[a href=\"index.php?act=findpost&pid=163366\"][{POST_SNAPBACK}][/a]

In the Camera to print tutorial it was mentioned that it was there before soft proofing became known, and is no longer valid,per se, when soft proofing. Using it will indicate out of gamut color, but not by how much. Michael indicated that he used it to see which specific areas he needed to work on as far as out of gamut color was concerned. Jeff just rolled his eyes..
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shewhorn
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« Reply #8 on: December 27, 2007, 09:13:46 AM »
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Have to run out to meet a client... be back in a bit to respond to the rest of the posts. Thanks for now though. Be back later.

Cheers, Joe
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bjanes
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« Reply #9 on: December 27, 2007, 10:07:11 AM »
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The gamut warning overlay is legacy stuff that was kind of useful before Photoshop 5.0 and true soft proofing, its pretty useless today.
[a href=\"index.php?act=findpost&pid=163363\"][{POST_SNAPBACK}][/a]

I think there is still a place for the gamut warning, since soft proofing is limited by the gamut of our monitors. Most monitors approximate the gamut of sRGB and a few the gamut of aRGB, but ProPhotoRGB is the recommended working space and many of our better inkjet printers easily exceed the gamut of aRGB. What we need to know is not only is a color out of gamut, but by what amount. Currently one must use gamut mapping software such as ColorThink or GamutVision for this task.

For example, here is a picture of a saturated red flower in ProPhotoRGB with a lot of out of gamut colors in aRGB, sRGB, and the printer space. The printer out of gamut amount (in terms of ΔC CMC, which takes color but not luminance into account) is shown by Gamutvision:



And by Photoshop's out of gamut display (yes, one should use 16bpc with ProPhoto, but this is for demonstration only):



If one prints this image with relative colorimetric rendering, much of the flower is a red blob with no texture. Softproofing is limited by the monitor, which can not display the full gamut of the printer. One can use perceptual rendering (which most admit is brain dead) or edit the image to bring the red saturation down a bit so that some texture appears in the flower.

Bill
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digitaldog
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« Reply #10 on: December 27, 2007, 10:22:43 AM »
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I think there is still a place for the gamut warning, since soft proofing is limited by the gamut of our monitors.
[a href=\"index.php?act=findpost&pid=163378\"][{POST_SNAPBACK}][/a]

If you can't see it on your monitor, what can you see it on? The print. Print it out. Use the soft proof to help you pick a rendering intent and decide if you wish to edit (a copy) of the image further  based on the soft proof and original image in your working space (which I would submit is out of display gamut too).

If you find the overlay useful, great. Just keep in mind when it was invented and for what based on the current technology then consider what we have today. For most users, the feature could go away (and probably should but Adobe hates to ever remove anything despite nearly everyone agreeing its too complicated).
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Andrew Rodney
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Bruce Watson
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« Reply #11 on: December 27, 2007, 01:26:06 PM »
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Load the profile for the print process in Customize Proof Setup. Instead of an ugly overlay, you see the colors map into the output color space (of course, using your display gamut). Far more useful.[a href=\"index.php?act=findpost&pid=163369\"][{POST_SNAPBACK}][/a]
I do this already. What it doesn't tell me is where I'm going out of gamut.

This brings up another point. Might be obvious to everyone but me, but here goes anyway. It seems to me that one would want to print with everything in gamut. That is, set up soft proofing, find out what is out of gamut, decide the best way to bring it in gamut, then make the appropriate adjustment(s) as required. Then print.

But from the sounds of this conversation, it sounds like many people print with some colors out of gamut. What would be the advantage of printing out of gamut colors? Since they can't print as sent to the printer they have to be clipped by whatever method (rendering intent) the printer/profile are programmed to use.

Instead of printing out of gamut images and letting the rendering intent and profile decide how to clip the image and rearrange your colors, doesn't it make since to pull everything in gamut first before printing? Sorry to be dull, but what am I missing here?
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digitaldog
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« Reply #12 on: December 27, 2007, 01:55:31 PM »
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The profiles in large part do the heavy lifting here with gamut mapping. If its out, its out. Now what do you do? Do you clip all colors to the boundary of the new color space or alter all colors in a relationship which is very specific to how the manufacturer of the profile builds this mapping. You can see significant differences in three custom profiles to the same device, built from three different packages when you examine the Perceptual matching even in the soft proof.

We're dealing with, in this case, an ultimate output. A print. It has a specific gamut, one that exceeds what we can see on our displays in some areas. At some point, you've got to take the colors you have and map them to the colors of your output device. That's the only time you'll see them.

We're also dealing with two vastly different output mediums (reflective and emissive).
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Andrew Rodney
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shewhorn
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« Reply #13 on: December 27, 2007, 01:58:04 PM »
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I've posted this question to another forum as well and one of my friends asked an obvious question with regards to what the prints look like. My interest initially wasn't really in how the gamut warning applies to prints (I've usually relied upon soft proofing and a hard proof when I'm unsure), rather it was merely academic but, the question prompted me to print out these silly color bars to see what would happen. The results were extremely educational to say the least and I think the response I posted is worth posting here as well so here goes....

My curiosity is merely academic at this point. Gamut warning is not a feature I really use all too often (I just soft proof, if I'm loosing detail due to an oversaturated color I can usually spot the offending egregious loss of detail) but I do occasionally use it for another point of information.

Anyhow when you said "printed image" I figured... what the heck, I'll print out these stupid bars and see what happens. I created a new file, 16 bits, ProPhoto color space, same configuration as above. The first file was uncorrected... just printed it straight out. With the 2nd file I selected the proper profile for soft proofing (in this case I used a relative colorimetric rendering intent), enabled the gamut warning, and then used a hue saturation layer and eyedrop selecting each bar and kicking down the saturation to bring them into gamut.

I printed to Canon Photo Paper Plus (it's a glossy paper, gamut is not as good as something like Hahnemuhle Photo Rag Pearl but... I don't have any more of that paper and it's a bit expensive to be doing this kind of testing on (at least until I have a clear goal in mind)... I hate glossy papers thus any excuse I can find to... ahhh you get the idea) using Canon's 16 bit driver (which is really 12 bits) set to unidirectional printing at the highest quality (16 pass).

The results were extremely interesting to say the least. I'm still trying to process what I'm seeing, I think it will take me a while to mull it over and make sense of it. A few quick observations... Blue gradient fading to black starting at 0,0,255. It may as well have been a big black bar and I'm not exaggerating all that much. The equivalent on screen seems to be about 0,0,22. It is THAT dark. The blue fading to white was also interesting. It starts out at the top (which should be 0,0,255) at what appears to be the equivalent on my screen to 0,0,22, fades to a bright blue (at which the point on screen measures at about 62, 62, 255). So, bright blues would appear to be limited with this paper (I'd be curious to see a 3D plot of that in ColorThink... which I need to buy). On the "corrected" print, the blues looked MUCH better, not bright but they definitely appeared to have more of a tonal range. I'm still not quite sure what to make of this, there's a few things that don't sit well with me but I need to sleep on it to figure out just how to precisely convey the "what" part.

Aside from the blues I can't say that one was clearly better than the other. I'm leaning towards saying that the colors on the corrected print were more accurate but that accuracy came at a rather high cost. Yellows and reds even though the gamut warning indicating things were out of range looked much better on the uncorrected version as they were far more vibrant. I wouldn't want to desaturate any print to the extent with which I had to do so in order to bring those colors "in line". The blues CLEARLY benefited in the corrected file, no doubt about that. Greens... I'd say the corrected version was slightly more accurate (the uncorrected had a slight shift towards yellow towards the top end of things). There's a bunch of other observations as well but I could ramble on quite a bit. Bottom line is, neither print was optimal.

Another thought on the blues... desaturating the blues on screen was as far as my perception is concerned, equivalent to ADDING saturation to the final print. Very counter intuitive (this is one of the things I'm grappling with... the engineering brain wants to know what's going on with the numbers to cause such an effect).

Now... using a perceptual rendering intent things were far more accurate however, the relative colorimetric print with the corrected blues definitely won in the blue department. In the real world however I've found that the perceptual rendering intent screws around with my colors a bit too much because of what it's doing.

I'm just scratching the surface here with everything this little test has taught me (I also learned some interesting things about the ProPhoto color space). Fortunately most things in nature aren't as vibrant as the ProPhoto color space or even Adobe RGB... well at least wedding subject matter, fall foliage might be a different story. UNfortnautely there is one color that appears in nature quite a bit... deep blues right after sunset. Of course... I love that time of day and tend to like to take it to a surreal level and love to saturate the CRAP out of it which makes for an interesting challenge.

Anyhow... I still have a lot more to chew on.

Cheers, Joe
« Last Edit: December 27, 2007, 02:01:50 PM by shewhorn » Logged
timhurst
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« Reply #14 on: December 27, 2007, 02:08:11 PM »
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I have certainly found the gamut warning useful and use it to make localised saturation adjustments (not global adjustments). Open fires and lit candles in interior shots are what springs to mind. If I don't bring the reds/oranges down they will print green and it's just a wasted print.
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shewhorn
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« Reply #15 on: December 27, 2007, 02:17:03 PM »
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From the tests I did today I'm starting to form an opinion which is a mix of what I'm reading here and that is, the gamut warning feature isn't entirely useless but on the same token, it's an extremely imprecise tool for making judgments about correcting such flaws and it is more likely than not to lead you astray.

Wish I could remember the details, I caught the tail end of one of John Paul Caponigro's lecture at Photoshop World in Boston and he didn't seem to be a huge fan of the gamut warning tool either. He had another (more accurate) technique for soft proofing out of gamut colors but I can't for the life of me remember what it was. I'll have to dig up the notebook to see if it's in there.

Cheers, Joe
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digitaldog
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« Reply #16 on: December 27, 2007, 02:25:21 PM »
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Wish I could remember the details, I caught the tail end of one of John Paul Caponigro's lecture at Photoshop World in Boston and he didn't seem to be a huge fan of the gamut warning tool either. He had another (more accurate) technique for soft proofing out of gamut colors but I can't for the life of me remember what it was. I'll have to dig up the notebook to see if it's in there.

Cheers, Joe
[a href=\"index.php?act=findpost&pid=163428\"][{POST_SNAPBACK}][/a]

Hint, I bet it required the use of a gradient.
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Andrew Rodney
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Roy
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« Reply #17 on: December 27, 2007, 02:42:49 PM »
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Hint, I bet it required the use of a gradient.
[a href=\"index.php?act=findpost&pid=163429\"][{POST_SNAPBACK}][/a]

Andrew, you coy fellow, share with rest of us! ;-)
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Roy
shewhorn
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« Reply #18 on: December 27, 2007, 03:08:11 PM »
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Hint, I bet it required the use of a gradient.
[a href=\"index.php?act=findpost&pid=163429\"][{POST_SNAPBACK}][/a]

Ahh... interesting (do share) BUT... I'm pretty sure he wasn't using and gradients. I seem to remember using the Hue/Sat filter, perhaps as a layer in a certain blend mode. By enabling soft proofing and observing what would happen when you tweaked the saturation slider you could more readily identify colors that were going to be a real problem in print.

I'll have to dig.

Cheers, Joe
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Schewe
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« Reply #19 on: December 27, 2007, 03:37:09 PM »
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Ahh... interesting (do share) BUT... I'm pretty sure he wasn't using and gradients.
[{POST_SNAPBACK}][/a]

...and I'm POSITIVE he WAS using gradients...it's called "Bracket Proofing" where he uses a gradient on an adjustment layer where the adjustment goes from WAY too strong to  too weak. You choose the location in the gradient that gives you the optimal results and then fill the gradient with the level of tone to achieve that level of adjustment. He has a PDF available for free at [a href=\"http://www.johnpaulcaponigro.com/lib/downloads/index.php#]Downloads[/url] look for the Bracket Proofing in the "Technique" section.
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