5.4 PaPCo color scheme

One of the requirements that arose through the use of PaPCo was the ability to have several active color bars, to display color spectra with different color bars together on the same plot. This is not possible with the standard IDL color scheme, which has one color table of 255 colors; changing it changes the colors globally for ALL panels.

This restriction does NOT apply when you write a PostScript file, as it is a sequential file. Each time you change to a new color table this gets loaded into the PostScript file, and you can have as many color table changes as you like.

PaPCo now subdivides the IDL color table to provide up to four simultaneous color tables at the cost of lowering the number of colors available to each table - now near 50 - but this has not significantly affected the quality of the display. The scheme used is shown in Table 5.1 to 5.3.

Table 5.1: Color index assignments for drawing (foreground) and background colors.

Index	0	1
Use	background	foreground

Table 5.2: Color subtable index assignment.

Index	$2 \rightarrow 2+nc$	$2+nc \rightarrow 2+2 \times nc$	$2+2 \times nc \rightarrow 2+3 \times nc$	$2+3 \times nc \rightarrow 2+4 \times nc$
Use	subtable 1	subtable 2	subtable 3	subtable 4

Table 5.3: Fixed prime color index assignment.

Index	$2+4 \times nc \rightarrow 2+4 \times n + 16$
Use	Fixed primary colors for line plots

PaPCo internal color table scheme: If nc_total are the total number of colors available to IDL, then the number available for the subtables is nc_avail=nc_total-16-2, and nc is the number of colors per subtable: nc=nc_avail/4.

The last entry in the color table is at an index equal to !D.N_colors, the IDL system variable which contains the total number of available colors. This number is usually less than 255, since your X-window system needs some colors. PaPCo checks the number of available colors at startup: If there are too few it will exit with an error message. You then need to close other applications you have running that are ``color hungry'' such as NetScape, another session of IDL, etc.

The color scheme and the utility routines which allow the user to choose the color subtable and to define his own color table into one of the subtable slots is explained in more detail in the papco_color.pro file in the papco_XX\PAPCO directory. papco_color.pro supplies a complete set of routines to manipulate this color scheme - you can replace any of the pre-loaded color tables with your own, interrogate which subtables have been used, etc.

PaPCo by default selects the subtable 1 (GSFC rainbow). If your panel editor included the color table choice widgets (see Section 5.2) then the index of the chosen color table can be passed to your routine through the keyword SUBTABLE (see Section B.2.3).

The first color subtable (GSFC rainbow) is the papco default color table. You need to choose a different color table or load a different color table of your own in your own plot routine. Remember that your color plot routine must be able to handle the PaPCo color scheme. The color plot routine supplied with PaPCo, plot_clr.pro (in papco_XX\papco_lib\color_plot) does this.