Digital BW, The Print

elauq wrote:
> I printed a yellow patch and then ran the paper through a second time
> and overprinted with a cyan patch.  The reverse was also done, first
> cyan then yellow.  A third paper had one patch with 100% yellow and
> 100% cyan printed in one pass.  All three looked different.  
> 
> It seems to get the correct blend of two colors, or grays for that
> matter, each dot must be printed adjacent to another but not on top of
> one another.

Dye inkjet inks and pigment inkjet inks are somewhere between
transparent and opaque. Like all other inks in fact. Even
thick solid silkscreen inklayers have some transparency,
possible exception the metal inks and ironoxyde based (opaque)
black.

In CMYK color printing, subtractive mixing is the base for
color rendering. The highlights where no color overlap happens
is in fact the problematic part of CMYK mixing. One of the
reasons why CcMmYK inksets are working better and even
increasing the gamut, the larger cm dots with more overlap
increase subtractive mixing compared to smaller CM dots with
lots of white paper in between.

Even with the more transparent dye inks you will see
differences between color mixing samples when Y and C are used
in reversed orders. Partly because the ink penetration in the
coating differs between the two samples, partly because the
primaries are not selective in their spectral filtering.

So subtractive mixing (overlapping dots) isn't the problem but
the less than ideal hue and transparency characteristics of
CMYK inks are the problem. Anyway it is still better than
additive mixing with RGB inks on paper, dots next to one
another, the light you can get through the RGB dots and back
isn't sufficient, the dot registration has to be perfect too.
That kind of mixing is good for CTRs and LCDs.


Met vriendelijke groeten,Ernst


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