TIFF 6.0 Specification
Final—June 3, 1992
The difference between the prediction value and the input is calculated modulo
2**16. Therefore, the prediction can also be treated as a modulo 2**16 value. In
the decoder the difference is decoded and added, modulo 2**16, to the prediction.
Huffman Coding of the Prediction Error
The Huffman coding procedures defined for coding the DC coefficients are used
to code the modulo 2**16 differences. The table for DC coding is extended to 17
entries that allows for coding of the modulo 2**16 differences.
Point Transformation Prior to Lossless Coding
For the lossless processes only, the input image data may optionally be scaled
(quantized) prior to coding by specifying a nonzero value in the point transforma-
tion parameter. Point transformation is defined to be division by a power of 2.
If the point transformation field is nonzero for a component, a point transforma-
tion of the input is performed prior to the lossless coding. The input is divided by
2**Pt, where Pt is the value of the point transform signaling field. The output of
the decoder is rescaled to the input range by multiplying by 2**Pt. Note that the
scaling of input and output can be performed by arithmetic shifts.
Overview of the JPEG Extension to TIFF
In extending the TIFF definition to include JPEG compressed data, it is necessary
to note the following:
• JPEG is effective only on continuous-tone color spaces:
Grayscale
RGB
CMYK
YC
b
C
r
(Photometric Interpretation = 1)
(Photometric Interpretation = 2)
(Photometric Interpretation = 5)
(Photometric Interpretation = 6)
(See the CMYK Images section.)
(See the YCbCr images section.)
• Color conversion to YC
b
C
r
is often used as part of the compression process
because the chrominance components can be subsampled and compressed to a
greater degree without significant visual loss of quality. Fields are defined to
describe how this conversion has taken place and the degree of subsampling
employed (see the YCbCr Images section).
• New fields have been defined to specify the JPEG parameters used for com-
pression and to allow quantization tables and Huffman code tables to be incor-
porated into the TIFF file.
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