Convert images with pngquant to disable libpng warning: iCCP: known incorrect sRGB profile

I am using the latest libpng 1.6.2 in my SH4 receiver. When I restarting enigma2 I have libpng warning: ICCP: known Incorrect sRGB profile.
Looking at the changes in the code I see that in libpng 1.6.2 has added the warnin. The error is also in earlier versions, but there's no warnin in the console.
I am using:
pngquant - ext. png - force 256 *. png * / *. png
so that all images have the correct sRGB profile.