Using the Colormap process

The Colormap process is a type of raster data renderer. It transforms the pixel values to display the raster data as either a grayscale or a red, green, blue (RGB) image, based on a color map. You can use a color map to represent analyzed data, such as a classified image, or when displaying a topographic map (or index color scanned image).

Classified image

Topographic map

The input raster dataset for the Colormap process is a one-band, unsigned 8-bit dataset, with a grayscale color space. The output is a three-band, unsigned 8-bit dataset, with an RGB color space.

Color maps contain a set of values that are associated with colors and are used to display a single-band raster consistently with the same colors. Each pixel value is associated with a color, defined as a set of RGB values.

The color map source can be an *.act file from Adobe Photoshop or a .clr file. The .clr format is an ASCII file containing information for 256 RGB colors. The entries in the ASCII color map file are listed as "pixel_value red green blue". Below is an example of the contents of a .clr file:

1 255 0 0

2 100 0 100

3 50 200 10

4 45 60 100

The .act format from Adobe Photoshop is a non-ASCII file containing information for 256 RGB colors. The first color in the table has a zero index, and the color is ordered as red, green, and blue. Each color is represented by three bytes.