[R] R plots pdf() does not allow spotcolors?

[Barry Rowlingson]

2011/4/13 Matthieu Stigler <matthieu.stigler at gmail.com>:
> Jim
>
> Thanks for your feedback! The problem is that the people "those responsible
> for layout" are us... We are doing the book in Latex, and till now did not
> need any other software.
>
> But I am scared we will need use kind of Indesign & co softwares to be able
> to use our R plots, since R can't export into spotcolor...

 I've just had a look into how PostScript handles spot colours, having
been hacking PS files for many years its not something I'd played with
before.

 This page gave me a PS file that used spot colours:

http://pslib.sourceforge.net/examples.php

and it seems that you can set a colour using a colour space array:

    [ /Separation (PANTONE Violet C)
  /DeviceCMYK { dup 0.750000 mul exch dup 0.940000 mul exch dup
0.000000 mul exch 0.000000 mul }
    ] setcolorspace 1.00 setcolor

Now, my screen previewer has no idea what colour PANTONE Violet C is,
so there's an alternative CMYK colour space version. In fact PANTONE
Violet C is just a label. The idea is that when processed for colour
separations the software will use the separation colours.

Now, to get this into R is tricky. Either you have to rewrite the PS
driver or hack the PS output file. I produced a simple R plot with one
purple (col="#FF00FF") blob and saved to a PS file. The bit of the PS
that set the colour was this:

 /bg { 1 0 1 rgb } def
 1 0 1 rgb

 - the two settings here are for the outline and fill of the blob,
which was created using pch=19.

 To specify this as a spot colour (with a CMYK alternative for
preview), I changed that to this:

/pvc {
    [ /Separation (PANTONE Violet C)
  /DeviceCMYK { dup 0.750000 mul exch dup 0.940000 mul exch dup
0.000000 mul exch 0.000000 mul }
    ] setcolorspace
} def

/bg {
pvc 1.00 setcolor
} def
pvc 1.00 setcolor

Now if you only have one or two spot colours and only a few places
where they occur then it might be possible for you to do this kind of
edit/replacement - either manually or automatically. And beware I'm
not even sure this is right or that your publisher would be happy
anyway.

 Anyway, thats enough PS hacking for one day.

Barry