How to create a diff/patch with binary data

Hi!

Creating diffs for changes in ASCII files works very well using "svn diff".
Also applying this diffs using "patch" works like a dream :)

But now I want to create a "mixed" diff containing changes to ASCII files and
to png image files. But "svn diff" says

--
Cannot display: file marked as a binary type.
svn:mime-type = application/octet-stream
--
on the png files. That is of course correct and expected. 
But how can I create a diff (or something similar) containing this binary 
changes? And how could this be applied? Does Subversion support this 
currently? If not, are they any plans?
Thanks.
cu,
  Emmy