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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]>
Wed, 25 Feb 1998 12:22:10 -0500
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Hi Clara,

>>If PS thinks in LAB colors then when you convert to them from the raw scan
in RGB there is no loss of info, right???  Can you keep going back and
forth without losing info?  What about CMYK to LAB?<<

LAB colorspace includes all of the colors found in RGB. So a conversion
from RGB to LAB should not have to alter any pixel values. In theory, this
allows for one to move between them without losing/changing any pixel color
info. Same with CYMK to LAB and back. But since the RBG colorspace include
many colors not found in CYMK, translating RGB>CYMK will permanently alter
many pixels. RGB contains almost twice as many colors as CYMK. Once the
conversion take one of those brilliant (but unprintable) RGB colors and
deadens it to a printable CYMK variant, there is no way for the program to
remember from which variant the color was derived from. Hence when
converting back to RGB, the image will retain those deadened colors. I
believe that RGB include all of the colors found in CYMK, so CYMK>RGB
should not alter any pixel values.

>>Is there a down-side to just automatically doing it that way, is
that what you all actually do??<<

Well the down side is that the "automatic" conversion is controlled by the
separation setup settings which you may or may not need to tweak. The
variables found within may seriously effect the output. Or it may have no
bearing at all. It's important to understand the needs of the printer. Or
at the very least, find out from them if the Photoshop default will work in
this instance. Many times it will do just fine.