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7. (Optional step)
If you are not satisfied with your choice of gray
ramp (e.g. not neutral enough) you can fine-
tune it. To do this press the Advanced button in
the Calibrate Raster Image Processing window.
Press the Print Gray Scale button.
A printout like the following will appear:
Check the 255 levels ramp under the final image viewing conditions and decide whether it
is good enough or it has some color cast (greenish, bluish, reddish).
If the ramp is OK proceed with step 8; otherwise, find out new values for Red, Green and
Blue and go back to step 6. If after several attempts you are still not satisfied, proceed as
follows.
Construct a Look-Up Table (LUT) file: whilst the standard Gray Balance adjusts the shape of
the RGB curves with simple gamma curves, with the Advanced Gray Balance option and
the LUT file you can adjust the RGB curves to any desired shape.
Before proceeding with the LUT creation please note that this procedure is prone to errors
and you will probably have to make many attempts before getting the desired result, so
only proceed if you are really not satisfied with the steps taken so far.
If you decide to proceed, create the LUT file according to the following guidelines:
a.
The LUT file should be a CSV-file (comma separated
values file).
The "//" sign indicates that the line is a comment and
shall be ignored.
Each
line
in
"Index,RedValue,GreenValue,BlueValue", where all
values range from 0 to 255.
Index is the gray tone value: in the sample file, for
example, the gray tone value 64 should be created
using Red=Green=Blue=118. Note that the file does
not need to contain 256 entries: the entries are taken
as fix points for a transfer function, meaning that
values in between them will be calculated by the LUT
Color Reproduction for the HP Large Format Color Copiers family: cc800ps, 815mfp, 5500mfp and 4200 scanner
the
file
has
the
A sample LUT file:
// Gray balance LUT file
0,0,0,0
format
64,118,118,118
128,174,174,190
176,195,195,221
208,227,227,233
255,255,255,255
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