TIFF 6.0 Specification
Final—June 3, 1992
The TIFF CIELAB Fields
PhotometricInterpretation
Tag
= 262 (106.H)
Type = SHORT
N
=1
8 = 1976 CIE
L*a*b*
Usage of other Fields.
BitsPerSample: 8
SamplesPerPixel - ExtraSamples: 3 for
L*a*b*,
1 implies
L*
only, for mono-
chrome data.
Compression: same as other multi-bit formats. JPEG compression applies.
PlanarConfiguration: both chunky and planar data could be supported.
WhitePoint: does not apply
PrimaryChromaticities: does not apply.
TransferFunction: does not apply
Alpha Channel information will follow the lead of other data types.
The reference white for this data type is the
perfect reflecting diffuser
(100%
diffuse reflectance at all visible wavelengths). The
L*
range is from 0 (perfect
absorbing black) to 100 (perfect reflecting diffuse white). The
a*
and
b*
ranges
will be represented as signed 8 bit values having the range -127 to +127.
Converting between RGB and CIELAB, a Caveat
The above CIELAB formulae are derived from CIE
XYZ.
Converting from
CIELAB to
RGB
requires an additional set of formulae for converting between
RGB
and
XYZ.
For standard NTSC primaries these are:
0.60700.17400.2000
0.29900.58700.1140
0.00000.06601.1110
*
R
G
B
=
X
Y
Z
Generally, D65 illumination is used and a perfect reflecting diffuser is used for the
reference white.
Since CIELAB is not a directly displayable format, some conversion to RGB will
be required. While look-up table accelerated CIELAB to RGB conversion is
certainly possible and fast, TIFF writers may choose to include a low resolution
RGB subfile as an integral part of TIFF CIELAB.
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