Re: A ripping good profile ?
Re: A ripping good profile ?
- Subject: Re: A ripping good profile ?
- From: Graeme Gill <email@hidden>
- Date: Thu, 28 Oct 2004 12:37:28 +1000
- Organization: Color Technology Solutions
edmund ronald wrote:
Still I wonder - is it necessarily meaningless to profile a RIP in
RGB mode ? Or might this reflect a commercial choice on the part of
Caldera ?What is the point of a CMYK profile for a RIP if one uses it
for photo and fine art i.e. with RGB input files ? How does the RIP do
the RGB to CMYK separation ? In any case, my ex-friend diagnosed me as
a total failure and I never got to make that print :)
Think of what the printer is actually doing. If the device is natively CMYK
(which is true of almost all printers), then something has to convert from
other colorspaces to CMYK. The most direct way of doing this is to use a pair
of profiles (ie. input colorspace input profile -> PCS -> output profile device CMYK).
To profile the device you make the device print test patches in its native CMYK,
and measure their colors using an instrument (== PCS).
To support "RGB" profiling, a printer has to go to a lot of trouble, and
add a step that you then have much less control over. That step is some
sort of RGB to native CMYK conversion table. The color flow becomes:
input colorspace input profile -> PCS -> fake RGB output profile -> hidden RGB -> CMYK lookup table.
That hidden RGB->CMYK conversion often limits the gamut of the device, may make the
device look like it's badly behaved, and removes any control over black generation
(which sets important quality tradeoffs) and TAC.
Under the circumstances, it's no surprise that many manufacturers don't support
"RGB" profiling of printers. Either use the supplied profile setup, or if you want to
go one better and profile the device, learn enough to be comfortable doing it in CMYK.
Graeme Gill.
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