Colormap function

The Colormap function 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

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 inputs for this function are the following:

• Input Raster
• Colormap

There are several default colormaps that can be chosen from the drop-down arrow, these include one for elevation data, two used to display an NDVI image, one to display a grayscale ramp, and another to assign a random color map. You can also input a *.clr file or an *.act file from Adobe Photoshop. The .clr file 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

A color map can be created for data with up to 63356 values (unsigned 16-bit). Negative values are not supported.

You can create a .clr file from the Raster Properties dialog box; see Creating a custom CLR file.

The .act file 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.