Photoshop: Possible rounding problem with opacity

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  • Updated 2 years ago
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I was sitting somehow studying how opacity works, decided to count the color on calculator and check myself in Photoshop to understand, correctly whether I understood and correctly whether i counted. The example was as follows:
First layer R=46 G=164 B=154
Second layer R=215 G=190 B=49  Opacity=66%

And it turned out that I, according to all the rules of rounding, counted:
R=158 G=181 B=85
But Photoshop say: "No! it:
R=157 G=181 B=85"

P.S. 157,54 by any rounding rules rounded to 158

Maybe I'm wrong, but I definitely counted everything correctly and rounded it up

Of course this is not a global problem, but it's still a problem

Sorry for my English, I'm just starting to learn it and use the translator
Photo of Ilya


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Posted 2 years ago

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Photo of Kukurykus


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I'm not sure is the bug I just found now, but do this test to see how much values are unstable:

Open Color Picker and put into 3 RGB fields some different values (you can use one of your above sets).

Now with up / down arrow keys change custom value of one of HSB or LAB or else CMYK of one degree. Don't close Color Picker box but use opposite arrow to step back.

You will see that RGB values you entered at beginning are not the same like after change you did that you undone then.

RGB is changed although values of other color mode are again the same.

That I think RGB with opacity you did is recalculated from other source mode that by default is LAB or HSB. It's why result of RGB is so unreliable.