How to have Color panel report in gray levels instead of K

[markhayworth]

I'm working with an 8-bit gray scale image.  I'd like to work in normal 0-255 valued gray levels just like we do for color images.  However when the image mode is Grayscale, the color panel shows the brightness value of the pixel in K, which has values of 0-100 and is the opposite of gray levels, meaning a bigger number is a darker color rather than a brighter gray level.  How can I switch from reporting brightness in K units to the normal 0-255 gray level units?  And is there a way to make that the default so I don't have to switch unit every session?

[TheDigitalDog]

Best you can do is switch the Info to read in 0-256:

And you can select via 0-256 from here:

[markhayworth]

OK thanks @TheDigitalDog .  I guess that might be the only way - view it in RGB values - since no one else has offered up anything different.

By the way, my options panel looks a little different.  I'm using version 24.1.1 and then I call "Panel Options..." from the Info panel's pancake menu in the upper right, it looks like this:

I wish they would let you specify the gray level on the Color tab but I guess this will have to do.  Seems strange that they've added in some image processing capabilities and yet don't really have a convenient way to specify intensities in gray levels like nearly all other programs do, plus even Photoshop lets you do if you're using RGB.

[TheDigitalDog]

You can make a feature request:

https://community.adobe.com/t5/photoshop-ecosystem-ideas/how-do-i-write-a-feature-request/idi-p/1238...

[markhayworth]

Thanks again @TheDigitalDog I'll do that.

[Stephen_A_Marsh]

Grayscale mode was historically for print, thus the % scale. 

It is possible to losslessly move between Grayscale > RGB > Grayscale if you really need to use the 0-255 scale. Obviously the file size  and memory requirements will grow while working in RGB.

I just tested and this doesn't allow the grayscale to be represented as 0-255 in the color panel, it is still % based. Oh well!

[D Fosse]

Indeed. Adobe RGB <> Gray Gamma 2.2 will be internally consistent in terms of numbers. Both use a regular gamma 2.2 tone response curve.

Other consistent pairs are sRGB <> sGray, Display P3 <> sGray, and ProPhoto <> Gray Gamma 1.8.

Any other conversions will change the numbers. The dot gain profiles don't match any RGB profiles. Note that converted readouts will be based on your working spaces!

[Stephen_A_Marsh]

@D Fosse - great points!

There is another way, no profile transformations involved, values retained, lossless.

[markhayworth]

Not sure I understand what @Stephen_A_Marsh  and @D Fosse are saying.  I simply want to paint on the picture with a specified gray level, so that if I open the image in another program, like MATLAB or ImageJ, it will report the same gray level I painted with.  I don't really care what it looks like (I'm not using calibrated monitors for visual grading off monitors - I'm doing image analysis), so I don't think I care about any gamma.  I just want the digital value in the image file to be what I said it should be.

[D Fosse]

The point I'm trying to make is that there is no such thing as an absolute gray level. It depends on the grayscale profile of the document. The different grayscale profiles have different tone response curves.

Here I painted 58% K in two different grayscale profiles:

This isn't academic. If you create the document in, say, the default dot gain gray profile (15 or 20 % depending) - but you just display this in a standard image viewer, this is the difference you get. But obviously in the whole image.

If you're going to work in grayscale (which I don't recommend, for precisely this reason), the safest bet is to use Gray Gamma 2.2. throughout. That is not the default in Photoshop, so you need to change it in Color Settings, and/or convert existing documents.

Now, some image viewers do support grayscale profiles, but far from all.

[PECourtejoie]

Hi, @markhayworth FYI, the Digital Dog is not using the local menu, but simply clicking on the eyedropper to change its settings.