Re: mapping extreme colours perceptually
Re: mapping extreme colours perceptually
- Subject: Re: mapping extreme colours perceptually
- From: Henrik Holmegaard <email@hidden>
- Date: Tue, 21 Aug 2001 10:31:09 +0200
neilB <email@hidden> wrote:
There appear to be occasional issues in Perceptually mapping colour
[I've seen >it strong blue and green] which is pretty much on the
edge of a large - ish >space like A-RGB to, say an Epson 7000
printer space. One sees blocked, detail >less areas of printed
colour which look almost relatively mapped - could this >be an issue
of the data a profile is <expecting>?
The perceptual mapping is different, and so is the internal Lab gamut
in profiling application. If the source color is outside this gamut,
it gets mapped using a type of relative colorimetry. You might get
into this situation with synthetic colors (defined with color pickers
that reference the whole of Lab or a really large RGB working space),
and as you note with large gamut printers. For instance, the HP5K
reaches out to *b 105 for yellow. So in any case there are two
parameters, the size of the internal Lab gamut and the quality of the
Perceptual smarts. BTW I'm kind of surprised that the Eye-One smarts
work out so well with so few patches.
Dan Margulis has suggested [I think, didn't read this part myself -
yet] that a >conversion to ColorMatch RGB [or at least sticking to
ColorMatch as a source] >can assist in rescuing the situation - but
it would seem that this would clip >the strongest colours and
therefore cause it's own problems.
Of course, you're switching to a small source space. And you can't
have in CMYK what you didn't have in RGB to begin with. So the effect
is that having thrown the baby out with the bathwater you go on to
use less of your inkjet gamut than you could with a better RGB
working space like Adobe RGB and/or better print profiling software.
ColorMatchRGB is for low gamut production printing. For big gamut
inkjet art prints and for better sheetfed production printing,
eciRGB10 and Adobe RGB 1998 are preferable.