Digital Light & Color

When adding or moving an image compare transformation, for which the output image is set to the input image, downstream branch recomputations should not be triggered.

Not all of the compare options pass the input image through unchanged, even if you are comparing it to itself.

You are right, what I wrote is not what I meant.
I should have written:

When adding or moving an image compare transformation, whenever the output image is set to the input image, the downstream branch should not be recomputed.

This is an example of a much larger set of optimizations that could theoretically be performed by checking if the output image is always identical to the input image. For example, a brightness curve that does not change the input image. While I do in most cases detect these cases and simply copy the input to the output, I have so far chosen not to implement these optimizations as the code that handles propagation of changes is already quite complicated and every time I make changes to it the program becomes unstable for a few weeks or months as special cases emerge that I did not test for.