What Have I Forgotten About Greys?

[TestTools]

Back in my youth, I remember something about 50% grey not being 50% grey and a trove of mystical perceptual knowledge things. Is this one of those?

You will notice on this "all for education, not a copyright infringement, I promise" 2020 color space version of the MacBeth chart that I am fumbling around with (attached). I put 18% grey behind all the swatches. How did I do that? By racking up the R in the 16-bit RGB picker and typing 65,535*.18, then copy pasting the result into G and B as well. But, when I pull down to Greyness, that turns out to be 25%.

In this iteration, the swatch marked 18% is "Grayness" 18% so you can see the difference between the two colors.

The numbers are different for 40% (a 5% difference) and 20% (a smaller difference, 2 or 3% but I didn't write the numbers down to say for certain.)

Background: The concept is to use this slide in a cinema projector that can correctly portray the 2020 gamut, and I am expecting that I can do the primaries and secondaries and greys by numbers. The little boxes in the arbitrary top two rows are the original Hex numbers (unfairly since they were made for D50 and a much smaller gamut and reflective, no emmisive), while most all of the larger sections are just my putzing around trying to use combinations of 25% increments to somewhat imitate what I understand to have been the original intention.

But it is this grey issue that I am wondering about – shouldn't I expect that Greyness 18% be equal to 18% of the 3 color values?

Thanks! 

MacBethStyle-16RGB-2020-ColorChart.afdesign

[NotMyFault]

1 hour ago, TestTools said:

 

But it is this grey issue that I am wondering about – shouldn't I expect that Greyness 18% be equal to 18% of the 3 color values?

Only in SRGB profile. Not when using other color profiles.

 

Below a screenshot of a grey gradient from 0 to 100% interpreted in a bunch of colour profiles. all files RGB/16.

Rec.2020 differs the most in darker tones.

[NotMyFault]

The main difference is the gamma curve. Use the scope panel to inspect.

If you use sRGB as reference: scope (Intensity waveform) shows linear response. (and Display P3)

If you import (place) others:

Adobe RGB: 

All remaining:

[TestTools]

Wow! Thank you. This is going to take me a bit of study to wrap my head around.

Many thanks for thinking it through and the details of explaining with graphics.  I guess I have to make in-situ tests to find out what gets through the entire system most accurately.

 

[TestTools]

@NotMyFault Thanks again. 

I think the issue you are describing may not apply to what I am describing. (…though I could be wrong.) I can see how different spaces may interpret with different ramps when placing something – But I am not 'placing' anything. 

I am creating 2 squares, then filling in the color.

I don't understand why 65535 x .18=11796 in each of RGB doesn't equal the pulldown of 18% Greyness. I would presume them to be the same.

But now I have tried even the most elementary example, using 256 color picker and even 8-bit Grey or 8-bit RGB in 709 space, and many in between my original 2020 16-bit space.

50% greyness and 256/2 (…or 256*.5) don't equal the same color. This happens on an iPad as well. And, I can't get help on "Grayness" in the manual.

 

2SquaresGrayness.afdesign

[NotMyFault]

We may cross-talking a bit. The most important part: we have at least 2 color pickers, and they work differently in case the display or document is not plain sRGB. One is bound to sample inside the document window, the other (in color panel) can sample outside the window, anywhere at the display. 

The difference is: one samples the color values inside the document, the other the result after applying the color profile and converting to the display profile. This may explain your observations.

 

 

[lacerto]

Obsolete.