TIFF 6.0 Specification
Final—June 3, 1992
The chromaticities of the primaries of the image. This is the chromaticity for each
of the primaries when it has its ReferenceWhite value and the other primaries
have their ReferenceBlack values. These values are described using the 1931 CIE
xy chromaticity diagram and only the chromaticities are specified. These values
can correspond to the chromaticities of the phosphors of a monitor, the filter set
and light source combination of a scanner or the imaging model of a rendering
package. The ordering is red[x], red[y], green[x], green[y], blue[x], and blue[y].
For example the CCIR Recommendation 709 primaries are:
640/1000,330/1000,
300/1000, 600/1000,
150/1000, 60/1000
No default.
TransferFunction
Tag
=301 (12D.H)
Type = SHORT
N
= {1 or 3} * (1 << BitsPerSample)
Describes a transfer function for the image in tabular style. Pixel components can
be gamma-compensated, companded, non-uniformly quantized, or coded in some
other way. The TransferFunction maps the pixel components from a non-linear
BitsPerSample (e.g. 8-bit) form into a 16-bit linear form without a perceptible loss
of accuracy.
If N = 1 << BitsPerSample, the transfer function is the same for each channel and
all channels share a single table. Of course, this assumes that each channel has the
same BitsPerSample value.
If N = 3 * (1 << BitsPerSample), there are three tables, and the ordering is the
same as it is for pixel components of the PhotometricInterpretation field. These
tables are separate and not interleaved. For example, with RGB images all red
entries come first, followed by all green entries, followed by all blue entries.
The length of each component table is 1 << BitsPerSample. The width of each
entry is 16 bits as implied by the type SHORT. Normally the value 0 represents
the minimum intensity and 65535 represents the maximum intensity and the val-
ues [0, 0, 0] represent black and [65535,65535, 65535] represent white. If the
TransferRange tag is present then it is used to determine the minimum and maxi-
mum values, and a scaling normalization.
The TransferFunction can be applied to images with a PhotometricInterpretation
value of RGB, Palette, YCbCr, WhiteIsZero, and BlackIsZero. The
TransferFunction is not used with other PhotometricInterpretation types.
For RGB PhotometricInterpretation, ReferenceBlackWhite expands the coding
range, TransferRange expands the range of the TransferFunction, and the
TransferFunction tables decompand the RGB value. The WhitePoint and
PrimaryChromaticities further describe the RGB colorimetry.
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