Re: CMYK is BAD
Re: CMYK is BAD
- Subject: Re: CMYK is BAD
- From: Graeme Gill <email@hidden>
- Date: Wed, 30 Oct 2002 10:58:11 +1100
DuWayne wrote:
>
4 color CMYK a bad way to handle multichannel devices becuase you think your
>
getting controlling.
>
Putting Roland Ornage/Green aside. It assumes that Light Cyan & Light
>
Magenta are the same ink.
>
When you dilute the ink by 50plus % do you really think that they will have
>
the same soectral response, big maybe.
>
Who says that the manufacture are just diluting, I believe some are using a
>
different dye or pigment.
>
This causes big problem when trying to do CMYK UCR/GCR calculations.
You are making some assumptions about how color profiling
systems work. For many profiling systems it doesn't
matter if the light inks are a different hue to the dark inks,
as their operation doesn't depend on them being so.
As long as the fake CMYK space is well behaved (ie. doesn't
have sudden changes in the output color for small changes in
the input CMYK values), then a sample based profiling system
will compensate for any variation in the hue of the primaries
as the density increases. If the light inks are crossed over
to the dark inks reasonable smoothly, then this all works well.
A profiling system that is model based on the other hand, could
be expected to have problems with a light/dark composite primary
that changes its basic hue as the density increases, since this
is probably not allowed for in the model.
>
> In fact, you CAN'T do any of that control stuff!
>
This is why the most rips/printer drivers don't print correctly --- they
>
lack controls on something that needs to be controlled or the controlls are
>
so comples that the average user has no chance.
Maybe. There comes a point though, where more controls don't
help, because even though in theory you can get the right result by
"just setting the controls to the right value", there are
too many of them, and their effect is too cryptic for
any mere mortal to figure out what the "right value" is.
Two of the aspects that are hard to "see", are how the light/extra
ink separation parameters affect the linearity of the
fake CMYK space, and the size of the available device gamut.
If small changes in the fake CMYK space values result in large jumps
in the output color, then even a high resolution sampling
based profiling system will struggle to compensate for
these jumps. [Witness the problems people have apparently
had in creating good profiles for the Epson printers
when running through their RGB drivers.]
It is also not obvious how the separation settings affect
the available gamut. I've seen several examples of CMYK devices
being run through RGB drivers where the commonly used separation
algorithms result in a gamut that is artificially limited by the
separation, and not by the underlying printer capabilities.
So both of these issues crop up badly in the simple case
of turning RGB into some sort of CMYK, never mind
turning CMYK into CMYKlclmOG !
[As the inkjets get higher resolution, and the number of
different dot sizes they support increases, I expect that
the use of light inks will become a historical curiosity
that will ultimately be abandoned.]
Graeme Gill.
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| | >CMYK is BAD (From: "DuWayne" <email@hidden>) |