I get some warnings with fvwm-crystal:
libpng warning: Ignoring incorrect gAMA value .55 when sRGB is also present
Finally, I opened 2 png files with gimp, and exported them to png, but with other options. And now the warnings for those files are gone.
I am not sure of the old options. I think this was the default gimp options for exporting png files. For the new files, only save resolution and save creation date was selected,
Is it something I must report to fvwm (well, it’s done with this thread) or to libpng upstream?
Edit: I found more pics with imagemagick:
# for i in $(ls); do convert $i $i; done
convert: Ignoring incorrect gAMA value .55 when sRGB is also present `assistant.png' @ warning/png.c/MagickPNGWarningHandler/1777.
Edit 2: It was necessary to run the convert command several times on some files. I think this must have to do with how libpng is dealing with the files. As a side effect, Fvwm feel faster