spritecss.png.FormatError: FormatError: PNG file has invalid signature.

Please change the error message to display the invalid file.

More often than not (as reported in other issues), the following error message is issued:

spritecss.png.FormatError: FormatError: PNG file has invalid signature.

It is not helpful as it is unrelated to the actual error. It seems to indicate a parsing error on an unsupported image format, sometimes. But other issues seem to indicate that it can happen when a parse error occurs on a background: stanza. I've tried numerous combinations of my CSS input file and always got the same error message. I used strace to try to guess where it failed but did not get more information. I tried --verbose which reported to use a number of files but did not report which would be invalid.

I eventually removed the jpg file and it solved the problem.

I hope the short storry of my frustrating experience will inspire someone to produce a patch that displays a clear error message such as "XXX.jpg : unsupported file format" ;-)

[marcoqu]

This would really help.
I also don't understand what's wrong with my .pngs.