#417 Wrong quality score for PNGs

[Khavish]

GM
gm identify -format "%Q" green.png

Output : 75

Imagemagick

identify -format "%Q" green.png

Output: 92

You can find a list of high quality pngs here
https://drive.google.com/drive/u/0/folders/0B0w_eoSgaBLXY1JlYUVOMzM5VFk

[Glenn Randers-Pehrson]

The "quality" report for ImageMagick and GraphicsMagick are both meaningless for PNG files, so it does not matter that they are different.

[Bob Friesenhahn]

PNG is lossless so it has no notion of quality. The value reported is a default quality value such as used while writing JPEG files.