[XeTeX] Grey fonts with XeTeX

Zdenek Wagner zdenek.wagner at gmail.com
Mon Jun 27 12:56:41 CEST 2016


Hi Philip,

there is one more important thing. For printing the file should conform to
PDF/X which means PDF 1.4. It is important for colour printing, for
printing in black higher minor versions of PDF are often acceptable but
transparency is not allowed. If you specify colour in the \font primitive
as non-transparent black, it might be optimized by the engine to grayscale.
If the colour specification contains four bytes, it is RGBA, i.e. it
defines transparency which is not allowed. Lookig at your samples it seeme
to me that the \font command has higher priority than \color. It seems to
me that the preflight is right but there are cases when Adobe Acrobat
Professional is not able to fix the PDF properly, in some (but not all)
cases ghostscript is more successfull (by ps2pdf14). It is better to solve
the problem in the TeX source.

If you forget transparency and no one notices it, then it is transparent on
the screen, it will be transparent on your office printer but the
transparent areas will be printed as black on the offset device. That's why
I double-check all included bitmap images.


Zdeněk Wagner
http://ttsm.icpf.cas.cz/team/wagner.shtml
http://icebearsoft.euweb.cz

2016-06-27 12:06 GMT+02:00 Philip Taylor <P.Taylor at rhul.ac.uk>:

>
>
> David Carlisle wrote:
>
> see the color package documentation
>
> \color[cmyk]{0.1,0.2,0.3,0.4} hello
>
>
> Zdenek Wagner wrote:
>
> if you want to use the colour feature of the OpenType fonts, only RGB
> is supported. The color package allows you to use both CMYK and
> grayscale (both are allowed in the printing industry). You can, of
> course, set the colour by promitives. You have to use both k and K for
> CMYK and both g and G for grayscale (r and R are for RGB). We have a
> nice article on simple graphics in CSTUG Bulletin, but only in Czech,
> see http://bulletin.cstug.cz/doi.php/10.5300/2013-1/13
> Zdeněk Wagnerhttp://ttsm.icpf.cas.cz/team/wagner.shtmlhttp://icebearsoft.euweb.cz
>
> My thanks to you both.  I am beginning to realise just how complex the
> world of colour is when it comes to typesetting/printing (a fact of which I
> have remained in blissful ignorance until now).  I am also starting to
> think that the pre-flight check for "List non B/W objects" in Adobe Acrobat
> 7.1 are not as reliable as one might hope -- the behaviour does not seem to
> be deterministic, nor does it appear to tally with reality :  all six pages
> of the PDF generated by code below are reported as "Object uses black only
> is not true".   But I am even more confused to discover that in XeTeX, the
> first four blocks all yield visibly black-on-white text, yet only two
> instances yields true black while two of the others yield RGB black and the
> fifth yields RGB white -- this must indicate that I do not understand the
> function of the "transparency" byte in XeTeX's font syntax.  And the sixth
> and final block yields RGB black despite the call to \color [cmyk] ...
>
> \nopagenumbers
>
> \input eplain
>
> \beginpackages
>
> \usepackage {color}
>
> \endpackages
>
> \font \thisfont = "Arial Unicode MS"
>
> \thisfont
>
> I appear in black-on-white and am true black (0.0)
>
> \vfill \eject
>
> \font \thisfont = "Arial Unicode MS:color=000000"
>
> \thisfont
>
> I appear in black-on-white and am RGB black (0/0/0)
>
> \vfill \eject
>
> \font \thisfont = "Arial Unicode MS:color=FFFFFF"
>
> \thisfont
>
> I appear in black-on-white and am true black (0.0)
>
> \vfill \eject
>
> \font \thisfont = "Arial Unicode MS:color=0000007F"
>
> \thisfont
>
> I appear in black-on-white and am RGB black (0/0/0)
>
> \vfill \eject
>
> \font \thisfont = "Arial Unicode MS:color=FFFFFF7F"
>
> \thisfont
>
> I appear in white-on-white and am RGB white (1/1/1)
>
> \vfill \eject
>
> \font \thisfont = "Arial Unicode MS:color=000000"
>
> \thisfont \color [cmyk] {0.1, 0.2, 0.3, 0.4}
>
> I appear in black-on-white and am RGB black (0/0/0) despite the call to
> \string \color \space [cmyk] ...
>
> \vfill \eject
>
>
> \end
>
> --
>
> Philip Taylor
>
>
>
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