Loading a Default Color Table

Although you can define your own color tables, IDL provides 41 pre-defined color lookup tables (LUTs). Each color table contained within this routine is specified through an index value ranging from 0 to 40, shown in the following table.

Tip
If you are running IDL on a TrueColor display, set DEVICE, DECOMPOSED = 0 before your first color table related routine is used within an IDL session or program. See Foreground Color for more information.

Table 5-5: Pre-defined Color Tables
Number	Name	Number	Name
0	Black & White Linear	21	Hue Sat Value 1
1	Blue/White Linear	22	Hue Sat Value 2
2	Green-Red-Blue-White	23	Purple-Red + Stripes
3	Red Temperature	24	Beach
4	Blue-Green-Red-Yellow	25	Mac Style
5	Standard Gamma-II	26	Eos A
6	Prism	27	Eos B
7	Red-Purple	28	Hardcandy
8	Green/White Linear	29	Nature
9	Green/White Exponential	30	Ocean
10	Green-Pink	31	Peppermint
11	Blue-Red	32	Plasma
12	16 Level	33	Blue-Red 2
13	Rainbow	34	Rainbow 2
14	Steps	35	Blue Waves
15	Stern Special	36	Volcano
16	Haze	37	Waves
17	Blue-Pastel-Red	38	Rainbow18
18	Pastels	39	Rainbow + white
19	Hue Sat Lightness 1	40	Rainbow + black
20	Hue Sat Lightness 2

You can load a default color table in an iImage display, an Object Graphics Display or a Direct Graphics display as follows:

iImage — select the Edit Palette button on the image panel. See Using the Image Panel (iTool User's Guide) for details.

Object Graphics — use the LoactCT method of an IDLgrPalette object to define the color table (see "IDLgrPalette::LoadCT" (IDL Reference Guide) for details). Associate the palette object with another object using the Palette property (for example, see the PALETTE property of the IDLgrImage object). Also see Color in Object Graphics (Object Programming) for information on using color with indexed and RGB color models in Object Graphics.

Direct Graphics — use the LOADCT routine or another color table related routine to set the color table. Also see Using Color in Direct Graphics.

Note
See "Color Table Manipulation" (IDL Quick Reference) for a list of related routines.

Modifying and Converting Color Tables

IDL contains two graphical user interface (GUI) utilities for modifying a color table, XLOADCT and XPALETTE (. The MODIFYCT routine lets you create or modify and store a new color table. See the following topics for examples:

XLOADCT — allows you to preview and select among pre-defined color tables

XPALETTE — allows you to preview and adjust pre-defined color tables

MODIFYCT — shows how to add modified color tables to IDL's list of pre-defined color tables.

These examples are based on the default RGB (red, green, and blue) color system. IDL also contains routines that allow you to use other color systems including hue, saturation, and value (HSV) and hue, lightness, and saturation (HLS). These routines and color systems are explained in Converting to Other Color Systems.

Highlighting Features with a Color Table

For indexed images, custom color tables can be derived to highlight specific features. Color tables are usually designed to vary within certain ranges to show dramatic changes within an image. Some color tables are designed to highlight features with drastic color change in adjacent ranges (for example setting 0 through 20 to black and setting 21 through 40 to white).

Note
Color tables are associated with indexed images. RGB images already contain their own color information. If you want to derive a color table for an RGB image, you should convert it to an indexed image with the COLOR_QUAN routine. You should also set COLOR_QUAN's CUBE keyword to 6 to insure the resulting indexed image is an intensity representation of the original RGB image. See COLOR_QUAN for more information

See the following topics for examples:

IDLgrPalette provides an example that creates, defines and applies a palette object to an image

TVLCT creates, defines and applies a color table in a Direct Graphics display

H_EQ_CT applies histogram equalization to a color table to reveal previously indistinguishable feature