zlib filtering PNGs etc

[zx80user]

I am writing some code to improve the compression of PNGs and I am having some difficulties with PNGs that have been edited with the GIMP (as JPEGs) and then transformed into PNGs on the fly by Perl Magick.

Essentially, if I turn on Z_FILTERED in the compression code the PNGs will not display, though a casual look over them in a hex editor reveals no problem.

If Z_DEFAULT is used then there is no problem... sorry to be vague about this but I really don't know why this happens and wonder if anyone could give me some clues to what might be up?

[glennrp]

Please provide a sample image. You could email it to glennrp@imagemagick.org or post a URL.

[zx80user]

Generating PNG with Z_DEFAULT_STRATEGY

http://hatemytory.com/tory-cgi/displays ... pl?index=4

Generating PNG with Z_FILTERED

http://hatemytory.com/tory-cgi/testtory.pl?index=4

[zx80user]

I may have broken the links now because I've been fiddling with the code, inserting break points etc...