Hello list, cc. Robert L Krawitz
If a output-device behaves not linear, the number of patches for
profiling has to grow.
In the case of inkjet printers, the linearity depends very much on the
limit for every CMYK-channel.
For every combination og paper an Ink, there is a point were more Ink
results not to more saturated color, but to huge shift in the Hue.
The normal way to detect this, is to print steps from 0 to 100% of every
pure color, measure it and plot the results in an a-b diagram in the
Lab-colorspace. The point, were the hue began significantly to change,
is the point to set the inklimit for every channel.
After setting this limit, a 1-D LUT for every channel should calculated
which results to equal steps of the pure colors and a good
CMY-greybalance. For doing this step, softwares are using differnt
models. Some are based on density, and some are based an Lab-values...
In the last step, it is necessary to detect the max. inklimit / TAC
(Total amounf of color) for a given combination of paper and Ink. This
is mainly done by a visual inspection of a testchart where big patches
with different TAC an fine details are printed. If the fine details are
detroyed be "bleeding" og the big patches with a given TAC, this is
point to set the max. Inklimit.
After this three steps, the testchart for profiling is printed.
In most cases a Testchart with e.g. 1485 patches like the ECI2002 gives
good results.
So good profiles for inkjets are first depending on optimized
driver-settings for every combinationn of paper and ink. Second is the
number of patches and the profiling software.
As the gutenprint team announced to work on integration of
colormanagement in their CMYK-drivers incl. inklimiting and
linearization, this is in my eyes the most important open source project
for printer profiling for having a good basis for using argyllcms.
In the long way, it would be very useful, if we get a closer integration
of gutenprint and argyll, that the user has e.g. predefined testcharts
for measuring, visualizing und setting individual inklimits etc.
One last point to Epson Ultrachrome-printers:
For this printers, it is very hard to get a visual nice greybalance. I´m
getting significant better results by using a strong GCR starting at 0,
so that neutral tones are mainly rendered with black and light black.
Such black generation can only be used, if the printer has additional
grey ink, otherwise the strong black produces a "peppering" in
skin-tones (big black dots...)
greetings from europe :-) Jan-peter
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homann colormanagement ------ fon/fax +49 30 611 075 18 Jan-Peter Homann ------------- mobile +49 171 54 70 358 Kastanienallee 71 ------- http://www.colormanagement.de 10435 Berlin --------- mailto:homann@xxxxxxxxxxxxxxxxxx
