Replace Color – Cannot Specify Exact Values

SP
Posted By
Sid_Phillips
May 9, 2007
Views
405
Replies
1
Status
Closed
In Photoshop CS2 I am trying to use Replace Color to specify an exact RGB color value. But if you look at the Info Window you can see that the Result color isn’t even close.

The original color is (RGB) 40/41/49. The target value, that I specify in Replace Color by clicking on the Result box, is 100/41/49. Looking at the Info Window, it shows the resulting color as 74/62/62. And sure enough, when you OK the replacement the Info Window shows the new color as 74/62/62.

Why isn’t this working correctly? Is it a bug? Or is there some underlying logic to being able to specify an exact value without actually getting the result?
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George_Austin
May 14, 2007
Sid,

Like all other PS commands, the Replace Color algorithm is nowhere to be found except, in this case, it defies all deductions and reasonable guesses. So far, all I can say is that the hue of the replacement color is exhibited by the resultant. Saturation and Brightness act inconsistently. I can’t formulate their behavior in a way that remains valid no matter how the the original and replacement colors are varied.

In your case the resultant hue is 0 degrees, whereas the replacement hue is 352 degrees. That discrepancy may bother you but consider that (1)0 degrees is the same as 360 degrees,(2)the difference between 352 and 360 is within the tolerance to be expected in that the brightness and saturation parameters are introduced on a 0-100 scale, not 0-255, and the hue scale is 0-360, not 0-255, and (3)Digitized values make step changes rather than continuously as with analog variables. Put this all together and accept that 352 is as good as 360 in this game. If you can put aside EXACT correspondence, I think you can depend on the resultant hue always matching the replacement hue. That’s a start. What goes on with saturation and brightness is still obscure.

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