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Question

gamut warning/selection discrepancy

Forum|Forum|8 years ago
January 2, 2018
4 replies
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I have my gamut warning color set to gray (this is not essential to the problem; I mention it only to make it easier to describe my gamut warning color).

Two issues:

(1) When I use View>Gamut Warning, all the out of gamut pixels are grayed out, as they should be. However, when I use Select>Color Range>Out of Gamut, the selected pixels are not exactly all and only the grayed out pixels.

In other words, View>Gamut Warning and Select>Color Range>Out of Gamut do not agree. They might agree on some pixels but not others.

(2) When I use View>Gamut Warning, usually I turn the grayed out pixels to in gamut by desaturating them or painting over them. However, sometimes this causes nearby pixels that were NOT grayed out to become grayed out as if they are now out of gamut. So what I don't understand is how desaturating an IN gamut pixel could cause it to go out of gamut, or how painting over an IN gamut pixel with an IN gamut color could cause the pixel to go out of gamut.

This topic has been closed for replies.

Conrad_C

Community Expert

I'm replying to this old thread because of what I seem to have discovered after getting confused about the gamut warnings in Photoshop. (This came up because I'm updating a book.)

I was finding, as marks60810224 did in the original post, that View > Gamut Warning and Select > Color Range / Out of Gamut returned different selections. So I tried changing profiles in various places, and came to the following conclusion:

View > Gamut Warning is based on, as discussed, the profile selected in the Device to Simulate menu in the Customize Proof Condition dialog box. Change the profile, the gamut warning changes. But the gamut warning in Select > Color Range / Out of Gamut was not changing. After experimenting, it seems like Color Range / Out of Gamut corresponds to the profile selected for CMYK Working Space in the Color Settings dialog box. Which seems weird. But if true, it means we cannot use Select > Color Range / Out of Gamut to accurately select for RGB printing workflows. (I never used Color Range to edit for my Epson printer anyway, but some might have tried.)

Anyone want to try and verify that, in case I missed something? What I did was do a Color Range / Out of Gamut, then save that selection as the mask for a Solid Color layer so that I could see multiple Color Range / Out of Gamut in the Layers panel, repeat for different profile selections in Customize Proof Condition and then Color Settings, then turn the different solid color layers on and off to compare their areas.

D Fosse

Community Expert

The problem with desaturation is that it affects all channels, at all tonalities. If the clipping is at the low end of the blue channel, there is no reason to touch the high end of the green and red channels. Then you should specifically target the low end of the blue channel and nothing else. This can be done with, say, "Blend If" and a Selectice Color or Channel Mixer layer, just to sketch out an alternative approach.

Very often you can remove clipping with no perceptible loss of overall saturation.

M

marks60810224Author

Known Participant

Yes, I can see that desaturating could be a crude method. I'll have to research more about how to use the methods you mentioned.

D Fosse

Community Expert

From what I can see, Gamut Warning just has a higher threshold than the other indicators - IOW smaller areas are indicated.

Personally I have always found these overlays of zero value, simply because they don't tell you how much out of gamut. A visual soft proof (ctrl Y) gives you much more realistic feedback. This is where a wide gamut monitor is useful. It should cover all CMYK profiles and most RGB inkjet profiles completely, so that you actually see the clipping. It's very hard to make reliable judgements when you can't see what's going on.

A wholesale desaturation of all out-of-gamut areas, regardless of how much, is a very heavy-handed way to do it. You should also consult the histogram, and view individual channels, for a more targeted approach. Some even argue that you should just leave it to the profile - just pick the rendering intent that works best visually. I wouldn't go that far, but often small areas can be allowed to clip without any ill effects.

M

marks60810224Author

Known Participant

Thanks Barbara and D for your help.

But I don't understand, which is my fault because I'm not used to thinking in the framework you mention.

I'll state my workflow (in detail for sake of exactness) and how I understand it, then maybe we can figure out more from there:

I shoot RAW Adobe RGB. I open the RAW in Photoshop as Adobe RGB (1998), 16 bit, 300 ppi.

I have two intended outputs: (1) prints (on a certain paper) and (2) web.

I have an NEC wide gamut monitor and SpectraView.

PRINTS

I created a SpectraView profile so that (as best I could devise) what I see in Photoshop matches the prints. I have the monitor set to that SpectraView profile.

In Photoshop, View>Proof Setup>Custom with: 'Device to Simulate' set to the paper/printer profile I downloaded from the paper manufacturer. 'Rendering Intent' set to Perceptual. Checked for 'Black Point Compensation'.

Then I work on the image. I do quite a bit, but usually the most important part is overall increasing brightness and overall desaturating (in other words, if I printed the image with no adjustment, the print would look too dark and saturated). And one of the things I do when working on the image is to check for out of gamut by View>Gamut Warning. My understanding is that this should mark all pixels that are out of gamut relative to the View>Proof Setup>Custom settings I've made (in other words, all the pixels that are out of gamut for the printer and paper I'll be printing with).

I usually don't worry about a few scattered out of gamut pixels (I don't think the human eye would see them in the print), but for larger areas, I use various techniques to bring them into gamut. Usually, I gradually test more and more desaturation until right around the point the pixels pop from gray back to color. Also, for the pixels that have popped back to color, I can see what that color is, so I can tell whether the desaturation has resulted in too great of harm to the image.

However, also I would like to take advantage of Select>Color Range>Out Of Gamut, so that when I use the desaturation brush, it doesn't cover any in gamut pixels. This is why I've asked why Select>Color Range>Out Of Gamut doesn't match View>Gamut Warning. And usually, the selection is greater than just the gray alert pixels. So Select>Color Range>Out Of Gamut is saying there is more in the photo that is out of gamut than View>Gamut Warning says. This seems to be the opposite of "If the out of gamut colors are borderline out of gamut, they may not appear to be selected." Also, I don't understand pixels being only partially selected (isn't a pixel either in a selection or not?), as indeed I've never understood feathering values that include fractions of pixels.

Then I save to TIF.

In the Photoshop Print Settings box I have: 'Color Handling' set to Photoshop Manages Color. 'Printer Profile' set to the paper profile I downloaded from the paper manufacturer. Normal Printing. 'Rendering Intent' set to Perceptual. Checked for 'Black Point Compensation'. And Print Settings>Main has 'Color Intensity' set to Manual, and 'Color Correction' set to None.

This results in prints that pretty much match what I see in Photoshop (though I'd like to improve the match even more).

WEB

With SpectraView, I switch the monitor to the SpectraView preset profile called 'SRGB Emulation'.

In Photoshop, I turn off View>Proof Colors (or, it looks exactly the same with View>Proof Setup set to Internet Standard RGB (sRGB)).

I open the TIF I made for print, set Convert To Profile>Profile to sRGB IEC61966-2.1. Then usually the image doesn't need much work other than overall decreasing brightness and overall more saturation (i.e. reversing what I did for the print version. And then checking for out of gamut, mutatis mutandis, as with the print. Then Save As to JPEG.

barbara_a7746676

Community Expert

Thanks. Would you please tell me more about what you mean by "check the C and M percentages and usually adjust the percentages manually"? How do you do that?

Sorry for the delay in answering. I'm working on a project with a tight deadline.

Open the Info panel and select the Color Sampler tool. Many people like to set the Color Sampler to 3 x 3 pixels instead of 1 x 1 pixel. Click in an area of blue pixels. The Info panel will display the color value. Regardless of the image color mode, you can change the display to any mode. If an exclamation mark appears next to C, M, Y, or K, those colors are out of gamut.

Using any number of techniques, you can then adjust the color values until they are within gamut. The Info panel will update the ink percentages accordingly. The numbers on the left are the original color values and the ones on the right, after the slash, are the newly adjusted values.

I know from experience that I don't want the M to be higher than the C percentage, and preferably lower than the C percentage. Otherwise, you end up with a purplish blue. If your vendor is using Pantone inks, you can use the Pantone CMYK books to get a good idea of what the ink percentages will look like when printed. I'm referring to the Pantone books that are printed on paper. Looking at the colors on the web is, of course, not as accurate. If your vendor is in the USA, they are probably using Pantone. Other ink manufacturers, like TruMatch and Toyo, have similar books.

barbara_a7746676

Community Expert

Photoshop displays a selection around pixels that are 50% or more selected. If the out of gamut colors are borderline out of gamut, they may not appear to be selected. It is also possible that some averaging is going on.

Aside from the technical issues, it seems that mainly you want to get all the colors in gamut. You can do that by choosing Image > Mode > CMYK. As long as you're working in CMYK all colors will be in gamut. If you prefer to work in RGB, you can choose Image > Mode > RGB to switch back again.

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