Coyote Graphics Routines

Date: Fri Mar 27 12:14:20 2015

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cgLoadCT [, table] [, /ADDCMD] [, /BREWER] [, BOTTOM=integer] [, CLIP=integer] [, RGB_TABLE=btye] [, FILENAME=string] [, GET_NAMES=string] [, NCOLORS=integer] [, /REVERSE] [, /ROW] [, /SILENT] [, /WINDOW] [, WINID=integer]

This is a drop-in replacement for the IDL-supplied program LOADCT. The same keywords used with LOADCT apply. In addition, a REVERSE keyword is supplied to reverse the color table vectors, and a CLIP keyword is supplied to be able to clip the normal LOADCT color table. This is extremely useful if you wish to use a reduced number of colors. All color table loading is handled silently. And Brewer color tables can be loaded.


table in optional type=integer default=0

Optional color table number to load. Integer from 0 to the number of tables in the color table file, minus 1.


ADDCMD in optional type=boolean default=0

Set this keyword to add the command to the resizeable graphics window cgWindow.

BREWER in optional type=boolean default=0

Set this keyword if you wish to use the Brewer Colors, as implemented in the Coyote Library file, fsc_brewer.tbl. This program will look first in the $IDL_DIR/resource/colors directory for the color table file, and failing to find it there will look in the same directory that the source code of this program is located, then in the IDL path. Finally, if it still can't find the file, it will ask you to locate it. If you can't find it, the program will simply return without loading a color table.

BOTTOM in optional type=integer default=0

The lowest color table index. The colors in the color table start loading here.

CLIP in optional type=integer

A one- or two-element integer array that indicates how to clip the original color table vectors. This is useful if you are restricting the number of colors, and do not which to have black or white (the usual color table end members) in the loaded color table. CLIP[0] is the lower bound. (A scalar value of CLIP is treated as CLIP[0].) CLIP[1] is the upper bound. For example, to load a blue-temperature color bar with only blue colors, you might type this:

IDL> cgLoadCT, 1, CLIP=[110,240] IDL> CINDEX Or, alternatively, if you wanted to include white at the upper end of the color table:
IDL> cgLoadCT, 1, CLIP=110 IDL> CINDEX

RGB_TABLE out optional type=btye

If this keyword is set to a named variable, the color table is returned as an [NCOLORS,3] array and no colors are loaded in the display.

FILENAME in optional type=string

The name of a color table file to open. By default colors1.tbl in the IDL resource directory.

GET_NAMES out optional type=string

If set to a named variable, the names of the color tables are returned and no colors are loaded in the display. Note that RGB_TABLE cannot be used concurrently with GET_NAMES. Use two separate calls if you want both.

NCOLORS in optional type=integer default=256

The number of colors to be loaded into the color table.

REVERSE in optional type=boolean default=0

If this keyword is set, the color table vectors are reversed.

ROW in optional type=boolean default=0

Set this keyword to indicate you are getting the RGB_TABLE vectors for use in the IDL's object graphics routines. Whereas TVLCT expects color tables to be 256x3 (column vectors), the object graphics routines expect them to be 3x256 (row vectors). Setting this keyword will transpose the vectors before they are returned.

SILENT in optional type=boolean default=1

This keyword is provided ONLY for compatibility with LOADCT. All color table manipulations are handled silently.

WINDOW in optional type=boolean default=0

Set this keyword to add the command to an cgWindow application.

WINID in optional type=integer

The window index number of an cgWindow to receive the color vectors. If this parameter is absent, the color table vectors are sent to the current cgWindow.


Suppose you wanted to create a color table that displayed negative values with red-temperature values and positive values with blue-temperature values, and you would like the red-temperature values to be reversed in the color table (so dark colors adjoin in the color table and indicate values near zero). You could do this:

cgLoadCT, 0 cgLoadCT, 3, /REVERSE, CLIP=[32,240], BOTTOM=1, NCOLORS=10 cgLoadCT, 1, CLIP=[64, 245], BOTTOM=11, NCOLORS=10 cgColorbar, NCOLORS=20, BOTTOM=1, DIV=10, RANGE=[-10,10]
Here is an example that shows the difference between LOADCT and cgLoadCT:
ERASE, COLOR=cgCOLOR('Charcoal) LoadCT, 5, NCOLORS=8 cgColorbar, NCOLORS=8, DIVISIONS=8, POSITION=[0.1, 0.65, 0.9, 0.75], XMINOR=0, XTICKLEN=1 cgLoadCT, 5, NCOLORS=8, CLIP=[16, 240] cgColorbar, NCOLORS=8, DIVISIONS=8, POSITION=[0.1, 0.35, 0.9, 0.45], XMINOR=0, XTICKLEN=1

Author information



David W. Fanning 1645 Sheely Drive Fort Collins, CO 80526 USA Phone: 970-221-0438 E-mail: Coyote's Guide to IDL Programming:


Copyright (c) 2007-2015, Fanning Software Consulting, Inc.


Change History:

Written by David W. Fanning, 30 October 2007. Added ability to read Brewer Color Table file, if available, with BREWER keyword. 14 May 2008. DWF. Small change in the way the program looks for the Brewer file. 8 July 2008. DWF. Changed the way the program looks for the Brewer color table file. Now use the Coyote Library routine cgFindPathTo to look for the file. 29 June 2010. DWF. Renamed Colorbar procedure to cgColorbar to avoid conflict with IDL 8 Colorbar function. 26 September 2010. DWF. Added ROW keyword to transpose color table vectors for new graphics functions in IDL 8. 23 Nov 2010. DWF. Added WINDOW and WINID keywords. 26 January 2011. DWF. Added ADDCMD keyword. 29 Jan 2011. DWF. Program delevopment ended and code transferred to cgLoadCT as of 4 Feb 2011. DWF. Added missing ADDCMD keyword. 28 April 2011. DWF. Fixed a problem that occurred when the BOTTOM keyword was used in conjuntion with the WINDOW keyword, resulting in incorrect colors in cgWindow programs. 28 April 2011. DWF. Added CubeHelix color table from code written by James R. A. Davenport. 5 Nov 2012. DWF. Made sure NCOLORS default takes BOTTOM value into account. 18 June 2013. DWF. Changed the way the brewer color table is searched for. Speed-up over 300x. 27 Jan 2014. DWF. Added two additional color tables to the "Brewer" color table file, fsc_brewer.tbl: "sunset" and "cgrainbow". These color tables are especially formulated to assist people with color blindness. See `this reference <>`. 16 Jan 2015. DWF.

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