Name:         PGCTAB

Purpose:      install the color table to be used by PGIMAG

Category:     GRAPHICS

File:         pgplot.src

Author:       T.J. Pearson

Use:          see description below.

Description:

            SUBROUTINE PGCTAB(L, R, G, B, NC, CONTRA, BRIGHT)
            INTEGER NC
            REAL    L(NC), R(NC), G(NC), B(NC), CONTRA, BRIGHT
      
       Use the given color table to change the color representations of
       all color indexes marked for use by PGIMAG. To change which
       color indexes are thus marked, call PGSCIR before calling PGCTAB
       or PGIMAG. On devices that can change the color representations
       of previously plotted graphics, PGCTAB will also change the colors
       of existing graphics that were plotted with the marked color
       indexes. This feature can then be combined with PGBAND to
       interactively manipulate the displayed colors of data previously
       plotted with PGIMAG.
      
       Limitations:
        1. Some devices do not propagate color representation changes
           to previously drawn graphics.
        2. Some devices ignore requests to change color representations.
        3. The appearance of specific color representations on grey-scale
           devices is device-dependent.
      
       Notes:
        To reverse the sense of a color table, change the chosen contrast
        and brightness to -CONTRA and 1-BRIGHT.
      
        In the following, the term 'color table' refers to the input
        L,R,G,B arrays, whereas 'color ramp' refers to the resulting
        ramp of colors that would be seen with PGWEDG.
      
       Arguments:
        L      (input)  : An array of NC normalized ramp-intensity levels
                          corresponding to the RGB primary color intensities
                          in R(),G(),B(). Colors on the ramp are linearly
                          interpolated from neighbouring levels.
                          Levels must be sorted in increasing order.
                           0.0 places a color at the beginning of the ramp.
                           1.0 places a color at the end of the ramp.
                          Colors outside these limits are legal, but will
                          not be visible if CONTRA=1.0 and BRIGHT=0.5.
        R      (input)  : An array of NC normalized red intensities.
        G      (input)  : An array of NC normalized green intensities.
        B      (input)  : An array of NC normalized blue intensities.
        NC     (input)  : The number of color table entries.
        CONTRA (input)  : The contrast of the color ramp (normally 1.0).
                          Negative values reverse the direction of the ramp.
        BRIGHT (input)  : The brightness of the color ramp. This is normally
                          0.5, but can sensibly hold any value between 0.0
                          and 1.0. Values at or beyond the latter two
                          extremes, saturate the color ramp with the colors
                          of the respective end of the color table.

Updates:      Oct 16, 1998: JPT automatically extracted from source.