COLOR is used to load a new color look-up table from a file, or to create a new color map. Color maps (look-up tables) are used to translating pixel data values into displayed colors. The new look-up table will be loaded into the display without needing to reloading the image.
To load a black and white map, type
To invert the order of the colors, type
Color maps are assumed to be in the color directory. (Type PRINT
DIRECTORIES to display the directories). Many color maps are available
with the default VISTA distribution. Get a directory listing of the color
directory to see the names of the distribution color maps. You can specify
color files that are in specific directories with the usual manner. For
example:
A color map is a list of length 256, each entry of which holds three numbers for the mapping to Red, Green, and Blue, respectively. These entries, or 'levels', run from 0-255 for each color. The 256 entries in the table give the proportions of each of these colors to use to display each of the 256 intervals of intensity (8-bits). COLOR defines these numbers, either by loading them from a pre-determined list, or by creating a new list.
If you wish to create a new list, type the command 'COLOR' with no arguments. The program will ask you to define the proportions of red, green, and blue intensity to use for each of the entries in the color map. The entries are numbered from 0 to 255. The proportions of each color are linear functions of entry number. You define a starting entry number and value, and an ending entry number and value. You may chain several linear segments together to produce various effects in the color map. You must define all 256 entries in the map. Typing in color maps by hand is tricky and tedious, and not advised for most users.
The last thing the COLOR program will ask you is to specify the color of the label and tick marks.
As an example of defining a color map, consider the black and white map. For each level of intensity, the proportions of red, green, and blue are equal. We want increasing brightness to correspond to higher intensity, so each color should have zero intensity at the bottom of the map, and full intensity (255) at the top of the map. The sequence of responses for defining this color map would be:
COLOR(begins the sequence)
Red: starting level 0 enter initial value: 0
Go to level 255
with intensity 255
Green: starting level 0 enter initial value: 0
Go to level 255
with intensity 255
Blue: starting level 0 enter initial value: 0
Go to level 255
with intensity 255
Define label intensities: Red: 200
Green: 230
Blue: 50
Save color file: Y or N
In this example, all three colors have zero intensity at the bottom level of the color file, and full intensity at the top level. The label color is green with slightly less red, with a tinge of blue.