BESTColor and Black Generation
BESTColor and Black Generation
- Subject: BESTColor and Black Generation
- From: Ulf Großmann <email@hidden>
- Date: Thu, 15 Feb 2001 14:51:55 +0100
How does BESTColor handle black generation?
In Best's internal color management the black generation is handled by the
paper profile. For that reason you can control the black generation only in
your profiling software.
Why do you need a base linearization?
The base linearization is the first step in the profiling workflow. During
base linearization you set the gray balance and the dot gain in
consideration of the inkjet printer and paper you use. The base
linearization works directly with the printer and is independent from Best's
color management.
The base linearization is based on color densities. You can control the gray
balance by changing your 100 percent densities. (You can control each
channel for itself.) If you want a reddish gray, just use a higher density
for magenta and yellow (and so on). We can give no rules for the settings,
because ink / paper combinations perform too different.
Example:
A good setting for Epson SP5000 (measured with status E):
Paper: BESTSemiMatt 6180
Ink: Epson DYE Ink with CMYKcm
Resolution: 720 dpi
Dot size: fine
Densities: C: 1,65 M: 1,66 Y: 1,63 B: 1,69
Lab-Values: C: 52,56 -33,4 -56,26 M: 50,75 80,67 4,56 Y: 86,52 5,75
99,23 B: 15,32 3,55 1,04
BUT
a good setting for ROLAND FJ52 (measured with Status E)
Paper: BESTSemiMatt 8180 (for Pigment Ink)
Ink: ROLAND Pigment CMYKOG
Resolution: 720 dpi
Dot size: fine
Densities: C: 1,56 M: 1,46 Y: 1,34 B: 1,64
Lab-Values: C: 57,54 -41,33 -54,82 M: 49,12 79,39 -18,48 Y: 91,82
-7,13 100,08 B: 16,96 -,013 -1,72
If you have the chance to get the Lab values then evaluate them
supplementary to the density-values. But which value from Lab is
interesting? This depends on the color.
C: a-Value M: b-Value Y: b-Value
If you have too much ink on the paper the color will exceed its maximum
saturation, and you will get non-steady Lab values (e. g. -45, -46, -43,
-41, -38 for the cyan a value) which is a drawback for profiling. For
profiling, a steady order of the numbers is desirable (e. g. -38, -41, -43,
-45, -46). You can set each color channel separately during creation of your
base linearization. (Per-color ink limit.)
How does total ink reduction work?
First: total ink reduction doesn't change the color separation, it only
limits the ink.
What should you know?
If you set an per-color ink reduction during a base linearization, you can't
reach 400 percent.
Example: Ink reduction per color was set to: C 60, M 75, Y 80, B 60. This
adds to 275 percent total ink. Each total ink limit value higher than 275
percent will take no effect in this case. Now you set 180 percent Total ink
inside BESTColor. Every color which puts less then 180 percent total ink
onto the paper is not changed. Only colors which put more then 180 percent
on the paper will be reduced to 180 percent. This way, you obtain the
maximum gamut from this printer / paper combination.
What is the difference between base linearization and printer linearization?
Base linearization: describes the "working point" from Paper and Printer and
Linearization of the Gray balance. Necessary for profiling.
Printer linearization (should be called "printer calibration"):
recalibration of the printer regarding its working point. This is a
supplement to the base linearization and is only for recalibration of a
printer that was base linearized before.
How does BC handle 6 or 8 inks?
CMYKcm:
The information about using light and norm ink for cyan and magenta is
inside the base linearization. The user can't change this setting. BC uses
all 6 inks for printing, but these 6 inks are basically handled like 4
colors CMYK.
CMYKccmm: like CMYKcm
CMYKOG: BC has an internal separation table for CY to G and MY to O
CMYKcmOG: CMYKcm and CMYKOG together
The color management is always based on CMYK or RGB, because it is very
simple to use by our customers and 95 percent of the jobs arrive as CMYK or
RGB.
ProfileKeeper:
The ProfileKeeper writes all information (ink limit, resolution, printer
type etc.) into the profile which BC needs for using the profile. You can
use the profile without this additional information, but than you must do
every setting manually in BC.
Back to black generation: I hope you understand now how BC handles profiles
and black generation. If you have done your own base linearization and set
the total ink limit to a correct value, you should use a 100/400 setting for
black and total ink limitation in your profiling software. This way, the
profiling software can calculate the profile with the maximum gamut the
printer is capable using the specific paper.
If you have any further questions, just ask and I will try to answer them.
BEST regards
Ulf Gro_mann