# [pdftex] color-separation with PDFTex

Jeffrey McArthur jeffmcarthur at comcast.net
Tue Aug 30 05:19:03 CEST 2005

On Tue, 30 Aug 2005 01:34:00 +0000, you wrote:

In the past, I used a method to do color separation. This is not for the
timid, and trying to do it with LaTeX (as opposed to Plain TeX) may be an
impossibility.

What I did was create multiple sets of fonts. You take your average .TFM
file and use tftopl to create the PL file. Then with a few manual changes
you can convert the PL into a VPL. Now the fun begins. For one project I
worked on I ended up creating four sets of VPL files. One for each color
plate. For example in the black set of VPL files all the characters in black
print. In the cyan set of VPL files only the characters in cyan print, the
rest are replaced with move commands in the VPL file. You then use vptovf to
create the VF files.

Once you have all that set up, then all you have to do is switch which set
of VF files your DVIPS uses to create the output. Actually, the same method
with work if you are using PDFTeX. You just have to switch the virtual font
path to point to the black fonts or cyan fonts, etc.

The only thing this does not do is separate any graphics you have loaded.

I have used this method in the past. The biggest problem is that it is sort
of at odds with the many of the concepts of the way LaTeX wants to select
fonts. You need to have absolute control over what TFM files TeX loads.

It is possible to expand this method to include the color separated
graphics. If you can create separate color graphics, then you could use a
customized font to include them using the VPL commands. There are some
interesting limitations on your sizes (this is because fonts have a limited
number of character widths). Then instead of setting a graphic, you just
typeset a character. The VPL/VF file actually issues the special command to
place the graphic.

The key to this approach is TeX does not really care about the shape of a
character. TeX just uses the informtion in the TFM file. TeX does not even
look at the VPL or VF file. That is for the DVI tools (PDFTeX is sort of an
exception because it bypasses the generation of the DVI if you generate a
PDF). From one DVI file you can generate all four plates by playing tricks
with the VPL/VF files.

I did this many years ago because I had to. I had no other tools I could use
to get the job done.

>On Sunday 28 August 2005 6:16 pm, Andreas Demant wrote:
>> Hi,
>> is it possible to generate color-seperated PDF's?
>>
>> I want a black PDF and a color-PDF without black, so i could print the
>> black version on a normal laser-printer and only the colors with a
>> colorlaser.
>
>Sorry, Andreas, this is more a sympathetic than a helpful reply ....
>
>We have the same need and not just for DTP. Our printers use classic offset
>machines, but have to send off PDFs for colour separation for quadrichrome
>(CMYK) separation .... which is time consuming.
>
>For two colour printing we often do a 'cheat' separation in-house. (Two
>colour is usually black and a spot colour.)
> - Text can be flipped in and out using (in Latex) \textcolour{COLOUR}{the
>wanted/unwanted text}
>(Also there are the Tex 'phantom' commands, but I never got that far ...)
> - For images we resorted to making an 'empty' image file of the same size.
>(I did consider Latex 'draft' mode which nicely removes the images, but
>leaves a box and the image name -there must be some way of 'printing' those
>in white, but I took the easy if tedious way out ....).
>
>Then you have two PDF files, one for each colour. (The Latex 'crop' package
>will give you nice alignment marks.)
>(Actually we wanted three files. The two seperated colours, each in black on
>white for making the films, and one with both colours to print out
>drafts/proofs for pre-submission approval, on a small colour laser. The whole
>business is ripe for 'automation', but thus far it's only once every several
>months ...)
>
>
>
>
>One could extend this to full colour separation, but it would be tedious.
>Also previous discussion on this list has commented on the problems of
>conversion of RGB images to CMYK .....
>
>Hope someone else can be of more help ....
>
>Michael
>
>BTW Trying to 'register' your two colour runs may well be problematic.
>We even have problem getting B&W laser printers to _roughly_ put text on a
>consistent place when doing two-sided printing.
>A friend with a large printing business wanted to do small print run
>perfectly aligned two-sided laser printing. Tells me he hasn't got a quote
>under 500,000 yet ...
>
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Jeffrey M\kern-.05em\raise.5ex\hbox{\b c}\kern-.05emArthur
a.k.a. Jeffrey McArthur          ATLIS Publishing Services