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Really NOT OT: Indexed color



Brett,

"Indexed RGB" or "indexed CMYK" differ from "regular RGB" and
"regular CMYK" (to coin phrases) in that for indexed color, there
are only 8-bits of color information for each pixel used as an "index"
into a table of either 24-bit RGB or 32-bit CMYK color definitions.

Where does the indexed color come from? The Distiller! In the process
of distillation, the Distiller analyzes every image. For any RGB or
CMYK image in which less than 256 distinct colors are actually referenced,
the Distiller automatically changes to indexed color. This most often
occurs with screen shots and bitmap logo images, for example. You would
least likely see any indexed color in photographic images. This optimization
is performed by the Distiller because simply stated, it can reduce the
size of a given image by up to 66% for RGB or 75% for CMYK if the image
qualifies (i.e., less than 256 distinct colors accessed in image).
As far as I know, PitStop does NOT change any image either to or from
indexed color.

In terms of how both PostScript and Acrobat/PDF handle indexed color,
there is NO difference between let's say 8-bit indexed RGB and 24-bit
RGB in terms of image quality, color, ability to separate, etc., again
assuming that the image in question has no more than 256 distinct colors.
If your print vendor is advising you that he cannot take indexed color 
in a PDF file or PostScript file either or both of the following is true:

(1) Your print vendor has a RIP or some software package that is highly
defective in that it is not obeying the PostScript and/or PDF language
specifications. He should update his RIP or prepress software packages.

(2) Your print vendor is highly uninformed as to what indexed color is
OR thinks that he is "protecting" you somehow. In the former case, you
may be dealing with the same type of ignorance that causes some printer
to refuse any documents that have been within 5 miles of a TrueType font.
In the latter case, the vendor may think that only 256 distinct colors is
an accident, that you effectively downsampled the number of colors in your
images.

In any case, you might need to have a heart-to-heart with your print vendor
and/or consider a change of print vendor to one who is more knowledgeable 
of the underlying technical issues.

        - Dov


At 4/25/2002 10:20 AM, litton@lexmark.com wrote:


>Howdy,
>
>Any help on this question would be greatly appreciated.
>
>Frame 6
>Acrobat 5
>Win 2k
>
>We've got docs that come from Frame, go to PDF, and are then "CMYKed" in
>Pitstop. Essentially Pitstop changes any and all colors (RGB, Pantone, Grey)
>into a CMYK version. This all works fine, but the CMYK ColorSpace is labeled as
>Indexed. I don't know why or exactly what this means, but our print vendor says
>they don't want it to be Indexed. I haven't found a way in Pitstop remove the
>Indexed label. Is there something I can do in Frame or with the AdobePS driver
>or Pitstop to get rid of the Indexed ColorSpace.
>
>Thanks,
>
>Brett Litton
>Lexmark International


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