Color masters for publications

GDDM V3R2 Base Application Programming Guide

Color masters for publications

GDDM V3R2 Base Application Programming Guide
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You can use the family-4 (page) printers to create color-separation masters for printing text and graphics in full color in publications. There is normally one monochrome master for each of three subtractive primary colors (yellow, magenta, and cyan), and a fourth for black. Each master records where ink of the color that it represents has to be deposited, as illustrated by Figure 111. The images on the masters have to be transferred photographically to the printing plates.

Figure 111. How a picture is changed into a number of color masters

In GDDM programs, you specify color attributes by numbers: 1 means blue, 2 means red, and so on. The numbers are listed in full in "Setting the current color, using GSCOL" in topic 2.3.1. For example, 4 in a GSCOL call means green, so if you draw a line after executing this statement:


     CALL GSCOL(4);

it appears in the publication as green. For this to happen, the line should be present on the yellow and cyan masters, but not on the magenta or black ones.

The method of defining how much of each color is on each of the plates is as follows. For each of GDDM's colors, a particular density is required on each plate. The amount is specified by means of a shading pattern and a color-master table entry. The pattern defines the density of the color. The table defines, for each master, which pattern is used to print each color.

The patterns belong to a pattern set created using the Image Symbol Editor. The patterns must be 32 pixels square, this being the notional cell size that GDDM uses for family-4 devices. Each pattern represents the density at which one of the four printing process colors should be printed so that it depicts a particular GDDM numbered color correctly. For instance, to print the correct shade of GDDM color 4, green, you may require a pattern for the yellow master in which 33% of the pixels are present, and another for the cyan master in which 50% of the pixels are present.

The GDDM-supplied symbol set, ADMDHIPK (see Figure 112), gives an indication of what such a pattern set might be like.

Figure 112. ADMDHIPK, the GDDM sample symbol set for color masters

To tell GDDM which patterns it must use on each master for each GDDM color, you code and assemble a macro, ADMMCOLT. The macro creates a color-master table. The macro must be assembled into a load module with the name ADMDJCOL. ADMMCOLT is described in the GDDM Base Application Programming Reference book. Here is an example of a color master table:


     ADMDJCOL CSECT
              ADMMCOLT START,SETS=1
     ADM00001 ADMMCOLT PATTERN=ADMDHIPK,COLORS=10,MASTERS=4,SETID=ADM00001
     *
     *                  YEL  MAG  CYN  BLK
     *
     DEFAULT  ADMMCOLT ( 41,  41,  41,  42)
     BLUE     ADMMCOLT ( 41,  43,  44,  41)
     RED      ADMMCOLT ( 43,  44,  41,  41)
     PINK     ADMMCOLT ( 41,  42,  41,  41)
     GREEN    ADMMCOLT ( 43,  41,  44,  41)
     TURQSE   ADMMCOLT ( 41,  41,  42,  41)
     YELLOW   ADMMCOLT ( 42,  41,  41,  41)
     NEUTRAL  ADMMCOLT ( 41,  41,  41,  42)
     BACKGRD  ADMMCOLT ( 41,  41,  41,  41)
     ALLBLK   ADMMCOLT ( 42,  42,  42,  42)
              ADMMCOLT END
              END

In the first line of this macro, the number of sets being defined is specified. In the second, the pattern set from which the patterns are to be selected is specified as the GDDM-supplied one, ADMDHIPK. The number of GDDM colors is specified as 10. The number of masters is specified as four. The name of the color-master table is specified as ADM00001. Names have the form ADMnnnnn, where n is numeric.

The remaining lines specify the hexadecimal numbers of the patterns to be used. Each line represents a GDDM color and each column a master. The first line gives the four patterns for GDDM color 0, the second for color 1, and so on. For user-created patterns the numbers must be in the range 65 through 239 (X'41' through X'EF') in the same way as for user-defined patterns in the GSPAT call, which is described in "Setting the current shading pattern, using GSPAT" in topic 2.3.6.

The example specifies that, for instance, color 4 (green) is to generate pattern X'43' for the first master, X'41' (that is, nothing) for the second, X'44' for the third, and X'41' (nothing again) for the fourth. Patterns X'43' and X'44' in ADMDHIPK have a pixel density of 50%. The pixels are arranged so that they do not overprint. The first master is used to make the yellow printing plate, the second for the magenta, the third for the cyan, and the fourth for the black.

The required patterns vary from one printing establishment to another, because of variations in inks, papers, printing technology, and so on. To get the required shade of green, for instance, you might need a 60% pattern for yellow, a 40% for cyan, and a 10% for black. Patterns can be determined only by trial and error. However, for many applications, such as printing business charts, it is not necessary to obtain precise shades, and the amount of experimentation required may be small.

GDDM supplies a number of sample color-master tables, based on the pattern set ADMDHIPK. GDDM also supplies some sample color-toning tables, based on another GDDM-supplied pattern-set ADMDHIPL. These are designed to show each input color as a different shade of gray. The definition and use of the color-toning tables are the same as for the color master tables, except that only one color master output file is created. The tables are contained in a GDDM-supplied module called ADMDJCOL.

When the program that creates the masters is executed, you must ensure that the file containing ADMDHIPK, or whatever pattern set you have specified, is available. Under CMS, for instance, you must ensure that a disk containing the pattern set has been accessed.

Subtopics:

20.15.1 DSOPEN statement for color masters

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