Re: Postershop and Ink Limits
Re: Postershop and Ink Limits
- Subject: Re: Postershop and Ink Limits
- From: Graeme Gill <email@hidden>
- Date: Tue, 09 Jul 2002 12:49:12 +1000
Roger Breton wrote:
>
> Graeme Gill wrote:
>
> It depends on the profiling package. A poor package may not cope
>
> with the hue shift. As long as the hue shift is not more
>
> abrupt than the resolution of the profile, then a good
>
> package should cope with the hue shift without a problem.
>
>
Interesting. You mean as long as it is within the # of grid points in the
>
Lab to CMYK transform?
Yes, but that is only the final step. The "native" device profile
is from CMYK -> PCS (usually Lab), and it needs to have sufficient
resolution to capture the nature of the device response.
A CMS that relies heavily on a particular mathematical model
for a device (ie. Neugebauer) will get into trouble if the
effective colorants are really composite.
The inversion needs to be precise enough, and then the resulting
PCS -> CMYK grid resolution needs to be of sufficient resolution.
>
Would you say the same thing applies for gray balance? Like, I noticed that
>
the more greenish steps of equal % of CMY appear (10Á0%m10%y,
>
20Â0%m20%y, ... 100Á00%m100%y) the worst the profile calculated gray
>
axis will be. So much so that I have the impression, like Thomas Holm said
>
once in a recent post about the EPSON 2000, that no amount of profiling will
>
be able to correct this and that, in these conditions, the profile's gray
>
axis will never be neutral.
Everything could be a limitation. The resolution and placement of
the test chart test points is often the first thing to limit the
accuracy of a profile, rather than the resolution of the multi-dimensional
grids (in my experience).
>
To make matters worse, on the EPSON 10000, on many media I have tested, to
>
get rid of that greenish CMY scale, one has to either restrict the cyan and
>
yellow together, therefore reducing the total gamut size -- which isn't
>
good, or increase the magenta ink, which is impossible if one already starts
>
with the maximum of magenta in the system (100%). It is a catch 22
>
situation. And I don't think a prelinearisation stage like that used in
>
ColorBlind can solve the problem either.
I'm not sure how you are trying to manipulate the color. A general
purpose color correction system will create a color conversion
that achieves a proper (emulated) gray balance without limiting
the gamut in any way. If you are just manipulating curves, then
what you can achieve is very restricted.
>
And I have found that because the gray axis is wrong, so are many of the
>
profile's colors. Like the reds or the yellows will often be off by many
>
degrees. And tht goes for all profiling apps I have used, including
>
ProfileMaker 4. I wish that profile manufacturers would state in their
>
documentation what are the boundaries within which their profiling algorithm
>
will work and we'll adapt instead of promising us the moon and let us waste
>
paper and ink.
It is often difficult to characterize the range of device behaviour
over which a particular approach will work. Often the only way is
try it and see what happens. Many subtleties about dealing with
printing device behaviour are still being figured out.
Graeme Gill.
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