TIFF Tag Indexed
|346 (hex 0x015A)
|0 (not indexed)
Aims to broaden the support for indexed images to include support for any color space.
Indexed images are images where the pixels do not represent color values, but rather an index (usually 8-bit) into a separate color table, the ColorMap.
ColorMap is required for an Indexed image.
The specification supplement defines these values:
0 = not indexed
1 = indexed
The specification supplement not being very clear, presumably it means that palette images can be coded either:
- With PhotometricInterpretation = PaletteColor. A ColorMap must be included, and the ColorMap values are RGB. If the Indexed field is included, it must equal 0, but it is probably best to not
include it in this case.
- With PhotometricInterpretation = some other color space. A ColorMap must be included, and the ColorMap values are to be interpreted as indicated by the PhotometricInterpretation. The Indexed field must be included, and it must equal 1.
In both cases, SamplesPerPixel must be 1.
This explains the specification supplement warning not to use both the Indexed flag and PhotometricInterpretation = PaletteColor for the same image.