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TIFF Tag Decode

IFDImage
Code433 (hex 0x01B1)
NameDecode
TypeSRATIONAL
Count2 * SamplesPerPixel (= 6, for ITULAB)
DefaultSee Description

Description

Used in the TIFF-F and TIFF-FX standards, holds information about the ITULAB (PhotometricInterpretation = 10) encoding.

In general, the values are taken in pairs and specify the minimum and maximum output value for each color component. For the base color fax mode, Decode has a count of 6 values and maps the unsigned ITULAB-encoded sample values (Lsample, asample, bsample) to signed L*a*b* values, as follows:

L* = Decode[0] + Lsample x (Decode[1] - Decode[0]) / (2^n -1)
a* = Decode[2] + asample x (Decode[3] - Decode[2]) / (2^n -1)
b* = Decode[4] + bsample x (Decode[5] - Decode[4]) / (2^n -1)

where n is the BitsPerSample, either 8 or 12.

Another way of looking at this, is saying:

Decode[0], Decode[2] and Decode[4] are the minimum values for L*, a* and b*
Decode[1], Decode[3] and Decode[5] are the maximum values for L*, a* and b*

When PhotometricInterpretation=10 and BitsPerSample=8, the default value for Decode is (0, 100, -21760/255, 21590/255, -19200/255, 31800/255).

When PhotometricInterpretation=10 and BitsPerSample=12, the default value for Decode is (0, 100, -348160/4095, 347990/4095, -307200/4095, 511800/4095).

Related tags

PhotometricInterpretation

See also

RFC 2301 - File Format for Internet Fax