gm convert: CMYK to sRGB distorts colors
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#331 gm convert: CMYK to sRGB distorts colors
http://ipic.su/img/img7/fs/cmyk.1453220405.jpg
GraphicsMagick 1.3.23 2015-11-07 Q16
gm convert -colorspace srgb cmyk.jpg gm.jpg
http://ipic.su/img/img7/fs/gm.1453220399.jpg
ImageMagick 6.9.3-0 Q16 x86 2016-01-02 works as expected:
convert -colorspace srgb cmyk.jpg im.jpg
http://ipic.su/img/img7/fs/im.1453220397.jpg
"-colorspace rgb" don't distort colors, but "srgb" also must works because GM don't show error "Unrecognized image colorspace"
BTW, by default GM produces a worse picture: quality 75 with chroma subsampling vs q94 w/o subsampling.
In GraphicsMagick "srgb" actually refers to Kodak PhotoCD sRGB which is for internal use only. The GraphicsMagick utilities documentation does not list "srgb" as a supported -colorspace argument. Use plain "rgb" instead.
Since multiple people have encountered this by accident, I intend to make "srgb" an alias for "rgb" (so use of "srgb" does not cause harm) and rename the C enumeration so it is more clear what it refers to. Maybe later true "srgb" support will be added (whatever that might mean).
The term "sRGB" technically refers to images which appear correct when displayed on a typical well-adjusted CRT from the early '90s. Some formats offer a "sRGB" flag which may be set in lieu of adding an ICC CMS profile to achieve a smaller size. In practice, it is likely that few images produced today are really sRGB since they are adjusted for uncalibrated LCD displays or come from a digital camera with a sensor with different properties.