Photoshop: Divide blending mode and 0/0 special case.

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  • Updated 7 years ago
If I have an image and I duplicate it onto a second layer and set the layer blend mode to Divide, the resulting composite image is all white (any number divided by itself is one).
The only exception to this is if both images have the same pixel set to zero brightness. Then the result is a black pixel (the calculation is done per channel, so it could also be any primary or secondary color.)

Is there any reason not to change the channel math so 0/0=1 ?

Also, inverting the top layer and setting it to Color Dodge is the same as setting it to Divide, and has the same math issues.
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David Jensen

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Posted 7 years ago

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Chris Cox

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Yes, continuity, plus backward compatibility.
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David Jensen

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Well, that's almost always a good reason to not change something :-) (unless continuity has some mathematical meaning I don't know)
I should have known to add that as an exception to my question.

It's easy enough to work around.... now if only the patch tool were way faster...
I patch an object out of the top of two identical layers, than use the Divide blend mode to isolate the object.
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Chris Cox

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Yes, continuity has a mathematical meaning. Yeah, patch tool and CAF over a large area are not the fastest operations. Patch and healing converge decently over small areas, but not large.