[tex-live] ICC profiles for PDF/A compliance

[Zdenek Wagner]

út 11. 9. 2018 v 3:36 odesílatel Norbert Preining <preining at logic.at>
napsal:

> Hi Peter,
> ...
>
> > Moreover, as I understand it, RGB profiles are not really meant for
> > professional use (most professional printers will prefer CMYK
>
> It was like this for long time (I often did print posters for
> conferences, books etc) and CMYK separation was necessary for most
> printers. But in recent years I have seen a move - at least in the
> normal print business, not the high class super value stuff though I
> guess - to be completely fine with RGB.
>

Yes, CMYK is prefered because colours on print are mixed subtractively and
thus CMY is required. Black is added for technical reasons (I do not want
to go into details). RGB implies additive mixing used on monitors.
Luminants on the monitors as well as pigments for printing do not work
according simple equations, their spectra are complex. In addition, the
resulting colour of the printed output depend not only on the colours of
the pigment but also on the colour of the paper which is never exactly
white. Thus the selection of the CMYK profile depends on the type of the
process colours as well as on the paper. The RGB profiles differ mostly on
the gamut, i.e. the range of colours that can be represented. AdobeRGB and
Wide Gamut RGB are wider than sRGB. Each RGB is wider than CMYK profiles,
so the conversion process must know what to do with colours that are out of
the gamut of the target CMYK and how to optionally modify other colours in
order not to lose details in the out-of-gamut colours. This means that in
addition to a proper ICC selection it is necessary to set also "intent". If
you have plots with a few colours or a text with a few HTML colours, then
these colours are usually highly saturated RGB. they are always out of the
CMYK gamut and since there is no risk of losing details, the intent should
be set to saturation and any profiles can be used. Even the simplest
equations can be applied because nothing better can be done. This is not
the case of colour photographs where the correct intent is perception. I
have Q60 target (less precise than IT8) and my scanners are calibrated. I
use the software that came with the scanner to calibrate my colour inkjet
printer and using a colour table available as a file and printed on the
calibrated printer I visually set the monitor. Thus I use the RGB profiles
for my scanners. I choose the CMYK profile by making tests on the printer
which wil be used and using the same paper, if the exact colours are
important. It is of course expensive but if high quality is needed you have
to pay. Generic ICC profiles are not good enough for high quality printing.

Good printers have their equipment and papers for high quality colour
printing calibrated and they distribute their ICC profiles for free but
they are good for their equipment and their papers.

>
> All the best
>
> Norbert
>

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




>
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> PREINING Norbert                               http://www.preining.info
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