[cairo] A better image comparison tool

[Zack Rusin]

On Wednesday 24 September 2008 13:21:53 Behdad Esfahbod wrote:
> Adib Taraben wrote:
> > Hello Antoine,
> >
> > in the Inkscape team we had a GSOC project that set-up some rendering
> > tests. Currently there is only binary compare of the images (sounds
> > familiar ?)
> > There is also a tool for perceptual image difference
> > http://pdiff.sourceforge.net/
> >
> > I think/assume that this tool detects only "visible" differences using
> > hard stuff mathematics ;-) You might look at this tool too.
> >
> > 1.) perceptualdiff does not handle transparency in images.
>
> pdiff is what we currently use.  It causes more problem than it solves. 
> (and it's painfully slow).

Just so that you know Khronos uses pyramid diff for their conformance tests. 
I'm not sure if there's already a Free Software implementation of a pyramid 
diff algorithm but it's pretty simple.
The basic idea is that one computes gaussian pyramids of the images and 
compares those. They are pretty simple to create so it's not a complicated 
algorithm.

z