Photo to Poster (was Preserving the black channel)
Photo to Poster (was Preserving the black channel)
- Subject: Photo to Poster (was Preserving the black channel)
- From: "Peter Merck" <email@hidden>
- Date: Sun, 14 Apr 2002 18:42:35 -0400
>
> Color servers like iQueue and Helios as well as many RIPs have a
>
> switch that disables matching for R0 G0 B0 and K 100%. However, if
>
> you define pure black as L 100 a0 b0 then by the nature of the game
>
> you are saying that your blacks must be matched to composite CMYK
>
> black.
>
>
0,0,0,100 (cmyk) would not be L 100, a0, b0 from what I understand of
>
that color model.
>
>
Perhaps 100,1001,100,100 would but 0,0,0,100 would certainly be lighter.
Try making the device profile total ink at 360 if 400 over saturates the
paper. Postershop, when linearized properly will not let this happen with
400% ink coverage.
>
>
I'm starting to think that what we need is not possible through a color
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managed inkjet worklow.
>
>
As others have stated we should turn off the profiling and try to
>
linearize the output device.
Postershop has an elaborate linearization/ink limit procedure and as far as
I can tell only produces a CMYK machine/paper/ink profile. So, as brought
up by Terry, Henrick, and Niall any greyscale will be converted to 4c. But
with the profile/linearization set up in Postershop I have had good success
printing a 4c grey image, but first I had to convert it to 4c before sending
it to postershop ( I only have one customer who likes b&w as part of the
whole 4c file and so haven't experimented to much a whole greyscale file).
I also haven't tried the pure hue selection boxes in the input profile side
of Postershop for K. Have tried Y because my pure yellows have too much
cyan added to it trying to match Lab numbers for yellow, but vector only.
At least that's my theory.
>
>
This is the technique we've used for decades in graphic arts.
>
>
Unfortunately, the hues of the colorants make this not work since they
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don't match our "standard" process colors.
Using 'no profile selected' (input side)in Postershop will default to use
only ink limit/liearization information and so your print will look good for
saturation but not for color. Althought the HP has good matching color
compared to 'standard'. Whereas my Arizona would be useless if it wasn't
profiled to compensate for very off SWOP inks, but Gretag (Oce') is coming
out with a new formulation soon.
Now for a couple of quick questions. Most of my files come from outside
soures, Photoshop 4c without an embedded profile. I use PS5.5 and don't
convert on opening. If I convert the file to my device profile (unknown
cmyk to device cmyk) is it using the profile listed in my setup as the
starting point (input)? IOW, regardless of what profile I have in my set
up, will the conversion result in the same priniting file (make sense?) It
is important to know because Postershop needs an input profile (see above)
and I don't have one from the customer, then I have to pick one of the many
supplied or made profiles trying to guess what the customer file is supposed
to look like.
In this case, embedding a 4c profile is a good thing and using a color
copier print as a proof is a very bad thing.
Thanks to all
Pete Merck
P.S. my 4c greyscale balance for midtone K is about 45C,49M, 58Y on the
Arizona.
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