[_CDCSL_93-16_]<1>Cedar>release>ColorRegistry>ColorRegistry2Doc.tioga~

ColorRegistry2Doc.tioga

Giordano Beretta, November 18, 1988 1:03:14 pm PST

gbb July 11, 1989 11:26:19 am PDT

Whole shmeer color correction

CEDAR 7.0 — FOR INTERNAL XEROX USE ONLY

Whole shmeer color correction

Giordano Beretta

Abstract: This document explains how to achieve the the fast color correction based on the Beatty-Cowan-Stone and Lamming-Rhodes algorithm.

Created by: Giordano Beretta

Maintained by: Giordano Beretta <Beretta:PARC:Xerox>

Keywords: Bitmapper, Color, Color Correction, Color Encoding Standard, Imager, Interpress, Printing

XEROX Xerox Corporation
Palo Alto Research Center
3333 Coyote Hill Road
Palo Alto, California 94304

For Internal Xerox Use Only

Beatty-Cowan-Stone color correction

In ImagerColorES color correction is done differently than in the old ImagerColor. While in the latter it is implemented in each device driver, in the former there is a table for each printer. This table is registered with ImagerColorES. This mechanism makes code easier to maintain (simply load a new table in the print server) and 1040 times faster (without cashing).

Procedure:

1. Generate the calibration charts with a Xerox/Research color model operator (to defeat the preexisting Beatty-Cowan-Stone color correction and use the Lamming-Rhodes color correction). If you would use the Xerox/process color model operator, you would not get any color correction.

2. Print the charts either using the Lamming-Rhodes color correction alone (-a switch in SendIpMaster), or using the Lamming-Rhodes gray balancing (-b switch in SendIpMaster). Ask Maureen Stone what the current philosophy is. If you do not user either switch, you will not get a black printer in the color correction code (this error has been done systematically in the past).

3. Measure the printed charts and generate the Beatty-Cowan-Stone correction files.

4. Bringover [CedarChest7.0]<Top>ColorRegistry.df
Bringover [CedarChest7.0]<Top>CalibratedColor.df
pushV ///7.0/ColorCorrection/
Copy [CedarServices]<C2700>*.trc
Pop
Install CES CalibratedColor ImagerPrintColor ImagerPrintContext

5. Edit StoneCalibrationImpl.Mesa if you want to change the parametrization (you probably do not want to change it).

6. Execute the RGBcorr command. You have to use the same switches as you used in step 2. If you do not do this, the color correction will be bogus. The difference in the parametrization of this command with respect to SendIpMaster is that in the -h switch you specify a printer type rather than a printer name.
Example: to create a color correction module for a Versatec C2700, type
RGBcorr -b -h C2700
if you obtained the data from a chart printed with
SendIPMaster -b -h TimsToy Chart.Interpress

7. After about an hour (for a resolution of 16 per color axis), you will be prompted a MakeDo command, which you should execute. You should be running the Summoner compute server to distribute the compilation on all available machines.

8. Smodel [CedarChest7.0]<Top>ColorRegistry.df

9. Trickle charge ColorRegistry to the appropriate XNS file server.

10. Reinstall the print service on the print server.

Bitmapper colors

The Bitmapper Interpress masters use the Xerox/YESLinear color model operator. The YES values were obtained by printing the CMY values of their colors on their printer (important because the resulting color depends on the halftone dot, etc.) and then measuring the XYZ values. These we converted to RGB, assuming the paper illuminated with D50 was the reference white, and then to YES. (The procedure is described in CES Sections 3.1.2 and 6.3.3.)

Their printer software contains a simple lookup table that converts the specific YES values they use - and there are only about a hundered of them - back to the original CMY values.

Therefore, Bitmapper colors print correctly only if the same lookup table is used. Currently in Cedar this is done using the registration mechanism for color correction. There are two modules in [CedarChest7.0]<ColorRegistry>:

BitmapperVersionE: If this module is executed on a machine driving a CMY or CMYK device, the machine behaves exactly like a Bitmapper printer release 2.0 version E for those colors that are specified using the Xerox/YESLinear color model operator, except that for a CMYK device black it printed as single-color black.

BitmapperOnlyVersionE: If this module is executed on a machine driving a CMY or CMYK device, in the case of colors in the Bitmapper palette, the machine behaves like a Bitmapper printer release 2.0 version E (except that for a CMYK device black it printed as single-color black). All other colors are printed as usual.