Re: Review of Large-Format Inkjet Contract Proofers
Re: Review of Large-Format Inkjet Contract Proofers
- Subject: Re: Review of Large-Format Inkjet Contract Proofers
- From: Graeme Gill <email@hidden>
- Date: Tue, 13 May 2003 13:52:46 +1000
Terry Wyse wrote:
>
You're both right. The CMYK min L* is what matters but the K density has a
>
lot to do with this. And, in general, I've NOT found the min L* value of
>
most Ultrachrome printers to be low enough for accurate commercial offset
>
proofing, especially if an analog/film-based proofed is used as a reference.
>
>
Analog proofs will generally show a min L* of less than 10 (6-8 typically)
>
while the BEST I've seen with UC inks is around 12-13 but is more typically
>
higher than 15. Now if it's a press profile you're using as a reference, the
>
situation isn't quite so bad as the min L* can easily be about +5 compared
>
to the analog proof reference.
It gets kind of fuzzy when talking about analog proofs, since they happily
cope with 400% TAC, unlike a real press.
For instance, for Analog Cromalin:
400% : 1.000000 1.000000 1.000000 1.000000 [CMYK] -> Lut -> 7.513468 3.460499 -10.653447 [Lab]
equivalent to a visual density of 2.05
250% : 0.500000 0.500000 0.500000 1.000000 [CMYK] -> Lut -> 9.750513 3.033327 -6.538441 [Lab]
equivalent to a visual density of 1.94
but any real artwork intended for a press should have less than 400% coverage.
As a data point, an Epson 10000CF using media to match the Cromalin (240% TAC):
0.000000 0.000000 0.000000 1.000000 [CMYK] -> Lut -> 9.024757 -0.041632 -4.121772 [Lab]
equivalent to a visual density of 2.01
0.470000 0.470000 0.470000 1.000000 [CMYK] -> Lut -> 6.151903 1.183823 2.625911 [Lab]
or a reverse lookup for the Cromalin 400% target:
7.513468 3.460499 -10.653447 [Lab] -> Lut -> 0.827638 0.660270 0.022157 0.914075 [CMYK]
Lim 2.42414 (clip) [Actual 8.261478 1.959833 -9.373296, deltaE 2.109574]
reverse lookup for 250% target:
9.750513 3.033327 -6.538441 [Lab] -> Lut -> 0.549725 0.484136 0.017455 0.923798 [CMYK] Lim 1.975115
So this particular device/ink/paper setup seems to have the capability of
matching real artwork for analog proof target with zero error,
and even an unrealistic 400% black is matched within 2 delta E.
Looking at the 10600 with UC inks, Epson Proofing Paper Semi Mat (a different media
to that used above):
0.000000 0.000000 0.000000 1.000000 [CMYK] -> Lut -> 17.653983 1.228634 0.641474 [Lab]
0.430000 0.430000 0.430000 1.000000 [CMYK] -> Lut -> 11.571207 2.309131 2.746697 [Lab]
so not as good as the pigment ink combo. Doing a reverse lookup of 400% Cromalin target
7.513468 3.460499 -10.653447 [Lab] -> Lut -> 0.796394 0.608814 0.000294 0.869988 [CMYK]
Lim 2.275490 (clip) [Actual 9.981514 1.594421 -9.787754, deltaE 3.212930]
so this is out of gamut by 3.2 delta E, while for the 250% Cromalin:
9.750513 3.033327 -6.538441 [Lab] -> Lut -> 0.712714 0.667544 0.000023 0.902857 [CMYK] Lim 2.283138
which is within gamut.
Compared to the pigment ink this combination isn't quite as good, but it seems good enough
for real artwork proofing, and the worst case error for unrealistic artwork is 3 delta E.
Graeme Gill.
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