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Frank Ippolito <[log in to unmask]>
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SciArt-L Discussion List-for Natural Science Illustration- <[log in to unmask]>
Tue, 24 Feb 1998 15:53:49 -0500
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>i'm hoping to tap into your collective wisdom before i set out on unknown
>waters... <

And dark waters they are, Wendy <g>.

For the digital artist, the conversion from RGB to CYMK is one of the more
important and little understood parts of the digital chain. Many
professionals choose to leave the conversion to production houses who have
much greater expertise in these matters. However, this takes away a level
of control that we artists are often resistant in acquiescing. As the
digital age plows forward, we artists are being asked more and more to wear
hats that go beyond our understanding and capabilities. Usually these
responsibilities are implicit without offering any compensation for the
additional headaches.

Still there are a few questions which might help you when considering these
possibilities. The translation to CYMK will allieveate the issue of working
with too many colors in RGB. However, unless you have established a
calabration against your eventual output, it in no way guarantees that what
you then see on the screen will be accurately reproduced. All it does is
guarantee that what you are seeing COULD be reproduced (under specific
circumstances) in print. As a backup, be sure to save your original RGB
file as such, since the door to CYMK swings one way. Once the brilliant
colors of RGB are converted, there's no way to figure out which colors they
were converted from. Another nice trick is to not use the actual
conversion, but to simply *preview* the conversion using the menu item
view/CYMK preview and continue to tweak.

NOTE: Keep in mind that when asked to do each conversion, Photoshop will
refer to the separation setup settings which determines the exact CYMK
value for a given RGB color. Adjustments made here may not show up on a
non-postscript printer (ie. ink jets, etc), which generally generate their
own black values. Setting such values as Ink Limits is dependant on the
output device, so a dialog with the printers involved would be more than
simply a good work practice here. Ditto the choice of using Undercolor
Addition, which compensates for loss in shadow detail. BTW the current
issue (#30) of the excellent mag Design Graphics from Australia has a very
good article on retaining rich blacks in the CYMK printing process. It
documents some neat tricks that goes beyond the separation setup options.

>i heard a tip at macworld expo that you can sharpen images quite nicely by
>converting them to Lab and applying an unsharp mask filter to the L channel.
>if i do this, then convert to CMYK, am i going to get wild and weird color
>shifts that i won't like? in effect, i'll be going from RGB to Lab to CMYK.

Yes. This is a great way of sharpening an image without "popping" out the
color. Since you will be moving through LAB on your way to CYMK, this is a
nice side effect. By sharpening the luminosity channel there, you don't
affect the colors at all. For those who don't understand, LAB color is
actually the real way Photoshop thinks: 3 channels, 1 of luminosity and 2
of color. In essence LAB contains all of the RGB & CYMK colorspaces. So it
is a important place to begin the conversion.

BTW many pros don't really like the way Photoshop handles the conversion.
They often cite other software as having better options etc. One of these
is Linocolor VisuaLab.

Good luck in your dark water paddling. Let us know how the journey goes.