CMYK blacks to RGB blacks
CMYK blacks to RGB blacks
- Subject: CMYK blacks to RGB blacks
- From: "Jorge ." <email@hidden>
- Date: Sun, 02 Dec 2012 21:27:51 +0100
Hi,
I regularly need to mass convert images in CMYK to sRGB for onscreen
viewing. The color conversion should aim for visual appeal, not color
accuracy, meaning 100% black ink (be it mixed with others or not)
should always map to 0 RGB.
Most CMYK profiles used in desktop publishing these days do not always
produce those conversions (images I deal with mostly come with FOGRA39
and US Web Coated SWOP v2 embedded). Rich blacks that Photoshop would
create with those profiles (i.e. made of a mix of all 4 CMYK inks) do
convert, with perceptual rendering intent, to 0 RGB, but solid blacks
(i.e. made only of 100% K ink) convert to dark gray RGB. Some rich
blacks I have come against with, that were created manually by
someone, containing 100%K + a mix of the other inks, return dark grays
too.
I have noticed that discarding the original profile and assigning
either Adobe Photoshop 4 or 5 Default CMYK, both rich and solid blacks
do convert, again if perceptual intent is used, to 0 RGB blacks.
Of course the problem is that by changing the profile altogether it is
not only the luminance of dark areas which becomes altered, but also
the hue and saturation of all colors.
So the question is, what is it that makes the profile Photoshop 5
Default CMYK not distinguish between what color solid or rich blacks
produce whereas FOGRA39 or US Web Coated SWOP v2 does, and is there
then a specific modification I can make to the image's original
profile so that I get proper sRGB blacks while altering colors as
little as possible?
I do not know if it is of any importance to this issue the fact that
ColorSync Utility reports that Photoshop 5/4 Default CMYK have a bkpt
label, whereas FOGRA39 or US Web Coated SWOP v2 do not.
PS: A related question with the same thread name was sent to
quartz-dev, but while that one was ultimately about how to build a
command-line rasterizer tool that modifies an input PDF on the fly
(hence quartz-dev), this one is more about understanding what makes
these profiles produce different colors for CMYK blacks, hence
(colorsync-users). I hope no one thinks I am spamming or double
posting, then.
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