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Brushing in Photoshop channel uses the colors chosen in the color mode picker, not channel selection

New Here ,
Apr 18, 2024 Apr 18, 2024

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I have an RGB image backed with a Spot color channel. With ONLY the spot channel viewed and selected, when I choose my colors (essentially 10% gray and 30% gray though chosen using RGB values) and paint using the brush tool, all is great.

 

Once I simultaneously view the the color channels, the color selector immediately changes to whatever was picked when the color channels were selected. Even if the RGB/Lab values match and I have the Spot channel selected, the brush paints darker (32% when viewing color VS 30% when not viewed.)

 

Is there a way to be able to view the color image and paint the colors selected when only the Spot channel is viewed? Is there a better way to select essentially gray values for the Spot channel? This may be a glitch in PS. I'm on Mac using the latest version of CS.

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Adobe
Community Expert ,
Apr 21, 2024 Apr 21, 2024

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When using B in HSB in the Coor picker the values seem to be laid down as intended (or rather 100-x). 

Could you please post screenshots taken at View > 100% with the pertinent Panels (Toolbar, Layers, Channels, Info, Options Bar, …) visible to illustrate? 

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Community Expert ,
Apr 21, 2024 Apr 21, 2024

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It has to do with your working gray.

 

A single channel is represented in your working gray.  Since this is essentially an untagged grayscale image, it takes on your working gray's tone response curve.

 

In full RGB display, the embedded RGB color profile takes over, and it has a different tone response curve. It you set a matching working gray it should be more consistent.

 

sRGB = sGray

Adobe RGB = Gray Gamma 2.2

ProPhoto RGB = Gray Gamma 1.8

Display P3 = sGray

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New Here ,
Apr 22, 2024 Apr 22, 2024

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Thank you for your response. It did work! I'm still confused as why they designed it to work this way. I would think it would apply the same values to gray within the document regardless of viewing other channels or not. Anyway, solved! Thank you.

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Community Expert ,
Apr 22, 2024 Apr 22, 2024

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The basic problem is that they still use the outdated Dot Gain profiles as default working gray. The default today should be Gray Gamma 2.2 as the least common denominator. ACR does that.

 

The dot gain profiles don't match anything else and just cause a lot of problems. Dot gain means ink spread in paper, and a long time ago they were used as generic profiles for grayscale offset print. Today you use the K component in a standard CMYK profile.

 

Why the single channel representation is using the working gray is pretty straightforward. It's not an RGB image, so the document RGB profile simply cannot be used. It has to use a grayscale profile. So you set the one that has the same tone curve as your RGB profile, and they will match.

 

 

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Community Expert ,
Apr 22, 2024 Apr 22, 2024

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Does Gray Gamma 2.2 have any advantages over sGray?

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Community Expert ,
Apr 22, 2024 Apr 22, 2024

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It depends. The main overriding concern is that it should work (produce the appropriate values) when color management stops, which it very quickly does with grayscale. So then it needs to match the target output.

 

Gray Gamma 2.2 and 1.8 are perfectly regular and ideal gamma curves, like Adobe RGB and ProPhoto.

 

The sRGB/sGray curve is very irregular, and it has this toe near black that squashes the very lowest values. It was made to mimic a CRT monitor, which once made sense - but modern LCDs don't have this exact curve, so it's just convention now without the real-life benefits of actually matching a display.

 

The single channel representation in Photoshop is just one example of non-color managed grayscale. InDesign and Illustrator are others - grayscale content in these applications just go straight to the K channel in whatever CMYK profile is used. There's no attempt at conversion.

 

Windows "Photos" actually does grayscale color management, but most other applications don't. I don't think web browsers do. So, for screen viewing, you need to use a gray profile that matches the display. That's probably somewhere between sGray and Gamma 2.2, so you can probably use either. But if you need it to be consistent with a document RGB profile, pick the corresponding one according to the table:

 

sRGB = sGray

Display P3 = sGray

Adobe RGB = Gray Gamma 2.2

ProPhoto RGB = Gray Gamma 1.8

 

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