Inkjet Printer Colors
How many colors can an inkjet printer can produce?
"I use a HP680C in the office, and it have two
cartridges, one for black and one for color
(yellow/cian/magenta?). If the printer fire one drop
of each ink at a given point, we can have only 6
different colors (ignoring white and black). If it
can fire two or more drops at a given point, maybe
we can have more colors, but I suspect that the
printer use this to control quality of the
presentation, not the number of colors. Anybody
knows for sure? With dithering it can make more
colors, with reduced resolution."
Like most print processes you only have a limited
selection of inks to use. Full colour can be derived
from three primary colors, just like a monitor. For
monitors, these are Red, Green, and Blue because
monitors emit light resulting in an additive color
process. Inks, on the other hand, absorb light so
printing is a subtractive process. The resulting
inks should then be cyan (blue+green or -red),
magenta (red+blue or -green), and yellow (red+green
or -blue).
Therefore, the colors used in common inkjet printers
are not really capable of producing true full
spectrum photorealistic quality results since they
are red (not magenta), blue (not cyan), and yellow.
These are optimized for nice saturated primary
colors when used independently. Also see the
section: Why are red, blue, and yellow inkjet
primaries?.
In addition, the combination of the three primary
colors should be capable of being combined to
produce black but due to misregistration and the
pigments used, this black would be somewhat muddy
and brown. Therefore, a separate black ink cartridge
is normally used for black printing.
(From: Tony Hardman (AHED_CIJ@f54x19.demon.co.uk).)
With printing there are more problems than solutions
and I do not know which method HP use in their
printing.
If you can vary the drop size, you can change the
drop spread on the paper. This can be done by firing
bigger slugs of ink, or multiples of the drop at the
same position. As you can figure the ink will either
spread and make a bigger drop, or stay the same size
and become denser. Depending on the resolution you
want these could both improve colour density. This
depends on two key components.. The ink, and the
paper.
The problems with laying down multiple drops on
paper is that if you do a large block the paper will
curl up and the overall image becomes worse. This is
why you can pay 1 a sheet for 'quality' paper.
Another problem with this is speed. Firing two drops
in the exact same place is difficult... Unless the
head is stationary but that is not good either. You
may notice that most DOD printers in high resolution
mode do a number of passes over the same place. This
does allow dithering and other techniques for
resolution / colour enhancement. They usually only
print while going in one direction for improved
mechanical control.
In the 1600 printer there is a heater to assist with
the drying times and reduce the curling problem.
Inks are a problem too. They can dry at different
times because of the different dyes used, or they
may not mix how you expect if you place two colours
on top of each other. Its only ink ... but to get
the best balance of surface tension, drying time,
viscosity, colour, stability.... and more is not as
straight forward as it might seam. I have noticed
that the water based inks are improving, and there
are some that do not run if they get wet (after
drying on the paper).
I think the spec in your manual may suggest what
method they use.. The printer resolution (best) is
600dpi (I guess), and I recon the best full colour
resolution is lower. Also the print head is only
300dpi so you must do two passes to get 600dpi black
(single black ink cartridge). This suggests a
partial step of 1/600 inch between the passes. What
happens when you print black using the colour head?
How many passes, how much slower? The resolutions
quoted may also be 600 * 300, or what ever. If they
make blocks of colour from a potential 600dpi
machine, the resultant image is probably only 75dpi
(possibly less). This still might be called 600dpi,
because the drop placement uses this resolution, but
it is not 600dpi at full colour. The resolution of
quality picturers / poster is several thousand dpi,
but not a variable image (not ink jet).
In the Lyra publications they did publish the real
print head specifications for the machines they
review. They also include some of the methods of
colour printing.
After all this I have noticed that I have not
answered the question of how do HP et al get their
colour resolutions. All I have mentioned is a few of
the parameters that the designers have to deal with
Printer and Photocopier Troubleshooting and Repair
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