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TIFF Tag ColorMap

IFDImage
Code320 (hex 0x0140)
NameColorMap
LibTiff nameTIFFTAG_COLORMAP
TypeSHORT
Count3 * (2**BitsPerSample)
DefaultNone

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.

Related tags

PhotometricInterpretation
Indexed