Post any defects you find in the released or beta versions of the ImageMagick software here. Include the ImageMagick version, OS, and any command-line required to reproduce the problem. Got a patch for a bug? Post it here.
My jpeg sampling-factor used to be set by -quality. Now it is being carried over from in.jpg (through a -strip, through a png file, and through a -quality setting).
The JPEG sampling factors and colorspace properties are preserved in PNG text chunks. It is a side effect of
preserving them when converting a jpeg to another jpeg. We should probably exclude the jpeg properties when
writing a PNG.
This is fixed in the SVN repository revision 12739, and the fix will appear in IM-6.8.6-7