Color map for palette color images. 0x0140 ∙ 320
IG_ISIS_TAG_COLORMAP describes a Red-Green-Blue color map (often called a look-up table) for palette color images, and is used by PIXFPACK and the individual file format filters (*.PXIs) to pass color palette information along with the image.
IG_ISIS_TAG_TYPE_SHORT (array)
PIXFPACK.
IG_ISIS_TAG_COLORMAP contains the palette values for a palette image. It has 3 x 2BitsPerSample values. A four-bit palette requires 48 values; an eight-bit palette requires 756 values. All red values come first, followed by all green values, then by all blue values. A value of zero (0) is the absence of that color; a value of 65535 is the maximum amount (saturation) of that color.
In a palette color image, a pixel's value is used to index into an RGB look-up table. For example, a palette color pixel having a value of 0 would be displayed according to the color specified in the 0th entry in IG_ISIS_TAG_COLORMAP.
The IG_ISIS_TAG_COLORMAP tag is set automatically by ISIS file reading and file writing drivers when they are handling a palette image, and so in most cases, the application developer need not be concerned with this tag.