Writing invalid values to the PNG PixelsPerUnitX/Y tags does return an error message, where other numeric tags will return a message of Not a integer/floating point number for
Example
C:\>exiftool -P -overwrite_original -PNG:PixelsPerUnitX=junk -PNG:PixelsPerUnitY=junk Y:\!temp\Test4.png
0 image files updated
1 image files unchanged
I thought I should bring this up, though it's probably not high priority.
Great, thanks. An easy fix that will appear in 13.09. I also added an automated test for a missing check like this and found another table in the Jpeg2000 code with this issue.
- Phil