[OS X TeX] White vs. Transparent?

V. Yu. Shavrukov vshavruk at science.uva.nl
Sun Apr 2 13:17:17 EDT 2006

On Apr 2, 2006, at 17:56, Peter Dyballa wrote:
> Am 02.04.2006 um 16:06 schrieb V. Yu. Shavrukov:
>> Anyway, it looks like what I would need is the "Assign a profile"  
>> filtering step.  I am inclined to believe that assigning Generic  
>> RGB profile would accomplish what William Adams suggested.   
>> However, that profile is designated by ColorSync Utility as a  
>> "display profile" which makes me wonder if "most" printing devices  
>> would consider it worthy of attention.
> You need the default "display profile" to see on screen a close  
> approximation of the "colours in the graphics file." I think a  
> similiar "default profile" is already built into a colour printer.  
> If you create your own "printer profile," you could adjust exactly  
> to the paper and (re-fill) ink actually used. Therefore, to be  
> exact and not just generic, you'd need to calibrate your screen, too.

I guess by "default "display profile"" you mean a profile, typically  
provided by display manufacturer, that describes the behaviour of  
that display model but not individual unit variation for which I'd  
need to either calibrate or at least profile my screen.  I agree with  
that, but the trouble is that this by itself is not sufficient for  
producing reliable device-independent colour in pdf files with pdftex.

The way I see it, there are no such things as "colours in the  
graphics file" (as long as we are talking untagged rgb or cmyk data,  
as has been the case in this discussion).  The problem is that the  
colour data produced by \color-like commands from various pdftex  
packages apparently goes into the pdf untagged.  Now I, the author,  
am seeing the result through a pdf viewer that, if some sources are  
to be believed, treats untagged rgb data "as though" it carried a  
specific profile (Generic RGB - that's an actual icc profile).  This  
convention is unique to Mac OS X (or perhaps even its current  
incarnation).  Now of course I am going to evaluate and adjust  
colours according to what I see on my screen.  I wish to enforce a  
similar interpretation of colour on every viewer's screen and  
printer.  Failing to put a profile of my choice into the pdf using  
pdftex, the answer appears to be to embed the GRGB profile into the  
file in post-processing as that file's default profile - this would  
give 3rd parties the best chance to see eye to eye with me.

Printers need two profiles to print correct colours - the printer's  
own profile which as you point out should be known to the printer (or  
printer driver) but also the source profile that tells the printer  
(driver) what the numbers in the file mean.  It is the source profile  
that worries me with pdftex.

best wishes,
Volodya Shavrukov

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