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Re: Comparing NSImages

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Re: Comparing NSImages

Subject: Re: Comparing NSImages
From: Greg Guerin <email@hidden>
Date: Thu, 23 Jul 2009 14:39:29 -0700

Benjamin Rister wrote:

Question 2: Assuming TIFFRepresentation isn't unique, what's the best practice to verify programmatically, say in a unit test, that the output matches an expected output?

Subtract the test's output image from the reference image, pixel by pixel, and look for any non-zero differences. This assumes compatible representations and no differences introduced by any other image-handling steps (e.g. device-RGB is device-dependent, so can't be assumed to be unvarying).

Even so, you might encounter small non-zero differences that originate from outside your code-under-test. If these are larger than +/-1 they could be significant; +/-1 I'd probably accept as within the margin-of-error for rounding.

  -- GG

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