[webkit-dev] How to deal with 1-pixel differences in reftests ?

Carlos Alberto Lopez Perez clopez at igalia.com
Wed Nov 18 04:36:34 PST 2015


Some reference tests give a 1-pixel or very few pixel differences [1].

I'm not sure if this really indicates a problem in the WebKit code, or
it indicates that we are just too strict not allowing even a very small
percentage in pixel differences for this kind of tests.

Should we tolerate a few pixel differences for reftests ?

I have done some tests, and the test in [1] passes for any value of
tolerance >= 0.00001% (with the GTK port).

I'm inclined to allow a very small value, for example a 0.001% (that
would be 100 times stricter than the tolerance value we use for the
other tests)



For example, this is happening in the GTK port:
The diff image normalized (so you can see where is the diff):

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