Loading a Default Color Table
IDL uses color tables to associate pixel values in indexed images with specific RGB color values. IDL's predefined color tables are listed in the table below. To open a dialog with the list of predefined colors, type XLOADCT at the IDL command prompt.
You can also define custom color tables with the COLORTABLE function.
|
Index Value |
Name |
Sample |
|---|---|---|
|
0 |
B-W LINEAR |
|
|
1 |
BLUE/WHITE |
|
|
2 |
GRN-RED-BLU-WHT |
|
|
3 |
RED TEMPERATURE |
|
|
4 |
BLUE/GREEN/RED/YELLOW |
|
|
5 |
STD GAMMA-II |
|
|
6 |
PRISM |
|
|
7 |
RED-PURPLE |
|
|
8 |
GREEN/WHITE LINEAR |
|
|
9 |
GRN/WHT EXPONENTIAL |
|
|
10 |
GREEN-PINK |
|
|
11 |
BLUE-RED |
|
|
12 |
16 LEVEL |
|
|
13 |
RAINBOW |
|
|
14 |
STEPS |
|
|
15 |
STERN SPECIAL |
|
|
16 |
Haze |
|
|
17 |
Blue - Pastel - Red |
|
|
18 |
Pastels |
|
|
19 |
Hue Sat Lightness 1 |
|
|
20 |
Hue Sat Lightness 2 |
|
|
21 |
Hue Sat Value 1 |
|
|
22 |
Hue Sat Value 2 |
|
|
23 |
Purple-Red + Stripes |
|
|
24 |
Beach |
|
|
25 |
Mac Style |
|
|
26 |
Eos A |
|
|
27 |
Eos B |
|
|
28 |
Hardcandy |
|
|
29 |
Nature |
|
|
30 |
Ocean |
|
|
31 |
Peppermint |
|
|
32 |
Plasma |
|
|
33 |
Blue-Red |
|
|
34 |
Rainbow |
|
|
35 |
Blue Waves |
|
|
36 |
Volcano |
|
|
37 |
Waves |
|
|
38 |
Rainbow18 |
|
|
39 |
Rainbow + white |
|
|
40 |
Rainbow + black |
|
|
ColorBrewer Schemes |
||
|
41 |
CB-Accent |
|
|
42 |
CB-Dark2 |
|
|
43 |
CB-Paired |
|
|
44 |
CB-Pastel1 |
|
|
45 |
CB-Pastel2 |
|
|
46 |
CB-Set1 |
|
|
47 |
CB-Set2 |
|
|
48 |
CB-Set3 |
|
|
49 |
CB-Blues |
|
|
50 |
CB-BuGn |
|
|
51 |
CB-BuPu |
|
|
52 |
CB-GnBu |
|
|
53 |
CB-Greens |
|
|
54 |
CB-Greys |
|
|
55 |
CB-Oranges |
|
|
56 |
CB-OrRd |
|
|
57 |
CB-PuBu |
|
|
58 |
CB-PuBuGn |
|
|
59 |
CB-PuRd |
|
|
60 |
CB-Purples |
|
|
61 |
CB-RdPu |
|
|
62 |
CB-Reds |
|
|
63 |
CB-YlGn |
|
|
64 |
CB-YlGnBu |
|
|
65 |
CB-YlOrBr |
|
|
66 |
CB-BrBG |
|
|
67 |
CB-PiYG |
|
|
68 |
CB-PRGn |
|
|
69 |
CB-PuOr |
|
|
70 |
CB-RdBu |
|
|
71 |
CB-RdGy |
|
|
72 |
CB-RdYlBu |
|
|
73 |
CB-RdYlGn |
|
|
74 |
CB-Spectral |
|
Tip: If you are running IDL on a TrueColor display, set DEVICE, DECOMPOSED = 0 before using your first color table-related routine in an IDL session or program.
Load a default color table as follows:
- IDL functions: For functions that include the RGB_TABLE property, enter the index number. If you do not define a color table, these graphics display in gray scale.
- iImage: In the IDL iImage dialog, click Edit Palette on the Image panel.
- Object Graphics: Use the LoadCT method of an IDLgrPalette object to define the color table (see IDLgrPalette::LoadCT for details). Associate the palette object with another object using the Palette property (for example, see the PALETTE property of the IDLgrImage object).
- Direct Graphics: Use the LOADCT Procedure or another color table-related routine to set the color table.
See Color Table Manipulation 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 Procedure: Allows you to preview and select among predefined color tables.
- XPALETTE Procedure: Allows you to preview and adjust predefined color tables.
- MODIFYCT Procedure: Shows how to add modified color tables to IDL’s list of predefined 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).
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).
Color tables are associated with indexed images. RGB images already contain their own color information. To derive a color table for an RGB image, convert it to an indexed image with the COLOR_QUAN routine. Also, set the COLOR_QUAN CUBE keyword to 6 to ensure the resulting indexed image is an intensity representation of the original RGB image. See COLOR_QUAN for more information.
The following topics include examples:
- IDLgrPalette provides an example that creates, defines and applies a palette object to an image.
- TVLCT Procedure 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.