Thanks for the pointers. I found the problem. In refactoring to use multiple cores, I had moved adding the comment section to after generating the image. Most programs seem to ignore this but some are a little more sensitive. With the comment section back before the image chunks, QImage and the new Photoshop can read all of my files.

It opens OK in CS6 but not in the latest version. The "unexpected EOF" may be a clue as to why QImage fails. Resaving files from CS6 is a workaround....

Here is an example image file

I am evaluating QImage, which seems a very capable app. However it cannot read most of my image files. It fails with a "Report zero pixels as height or width" message (see attached). I have also attached XPlorer2 (WinExplorer replacement) view showing it's reading of dimensions etc and view of actual files. The files can be read with no faults by Xplorer2, ImageEye, Photoshop, Paint etc. I cannot find any logs which may indicate the actual reason for failure. Certainly the zero pixels error message is spurious.

My app is FractalCanvas an app written in java which generates PNG files in 24 bit RGB format (using PNGJ library).