TIFF Tag ColorMap
| IFD | Image |
|---|---|
| Code | 320 (hex 0x0140) |
| Name | ColorMap |
| LibTiff name | TIFFTAG_COLORMAP |
| Type | SHORT |
| Count | 3 * (2**BitsPerSample) |
| Default | None |
Description
A color map for palette color images.
This field defines a Red-Green-Blue color map (often called a lookup table) for palette-color images. In a palette-color image, a pixel value is used to index into an RGB lookup table. For example, a palette-color pixel having a value of 0 would be displayed according to the 0th Red, Green, Blue triplet.
In a TIFF ColorMap, all the Red values come first, followed by the Green values, then the Blue values. The number of values for each color is 2**BitsPerSample. Therefore, the ColorMap field for an 8-bit palette-color image would have 3 * 256 values. The width of each value is 16 bits, as implied by the type of SHORT. 0 represents the minimum intensity, and 65535 represents the maximum intensity. Black is represented by 0,0,0, and white by 65535, 65535, 65535.
ColorMap must be included in all palette-color images.
In Specification Supplement 1, support was added for ColorMaps containing other then RGB values. This scheme includes the Indexed tag, with value 1, and a PhotometricInterpretation different from PaletteColor then next denotes the colorspace of the ColorMap entries.