Thanks for your input! :)
I have something like that in mind but I don't think that a complicated algorithm is needed here; we're basically working with two alpha bitmaps of (roughly) the same size. I would simply compare the bitmaps on a pixel-by-pixel basis, weigh the results by the max. possible difference and get the average of all differences. That way it would also be simple to add a threshold - may it be absolute or relative. In the end, the result can also be applied to a logarithmic scale - something that I would play around with to find the optimal solution for the needs of FreeType.
On 19/03/2018 19:00:48, Nikolaus Waxweiler <address@hidden> wrote:
I'm not familiar with graphics testing, but maybe algorithms exist that look for a magnitude of a difference between two images (maybe something like this exists in video encoding land?). Then you could ignore changes less than 1% or something.