The Color Matrix primitive maps each RGB and Alpha
value to a new value. The transformation is described by a
5 × 5 matrix with the bottom row fixed, thus a general
transformation is described by a 5 × 4 matrix. The fifth
column adds a value that is independent of RGB or Alpha,
allowing for nonlinear color correction.
Four types of transformations are defined, of which three are special
classes of the first.
-
Matrix: The full 5 × 4 matrix is defined. This is the most general
case.
-
Saturate: The saturation is reduced by specifying one
number, s. The range
of s is 0.0 (completely desaturated) to 1.0
(unchanged). Only the RGB values are changed. The exact formula
is:
-
R' = (0.213 + 0.787s)R + 0.715 × (1 − s)G + 0.072 × (1 − s)B;
-
G' = 0.213 × (1 − s)R + (0.715 + 0.285s)G + 0.072 × (1 − s)B;
-
B' = 0.213 × (1 − s)R + 0.715 × (1 − s)G + (0.072 + 0.928s)B.
-
Hue Rotate: The hue is shifted by specifying one number.
Like the Saturate case, only RGB values are changed. The exact formula
is quite complicated. It is not just a red to yellow to green and so on rotation.
-
Luminance to Alpha: The luminance is converted to Alpha via a fixed formula:
Alpha = 0.2125 × R + 0.7154 × G + 0.0721 × B
(from ITU-R Recommendation BT709, the HDTV color standard).
A “negative” can be made by setting the RGB
diagonal matrix elements
(a00, a11, a22) to −1.00
and the top three elements of the fifth column
(a04, a14, a24) to 1.00.
Partially implemented, No user interface.
The Component Transfer primitive changes the RGB and
Alpha of an object by applying independent functions to each of
the RGB and Alpha input values. The following modes for
defining the functions are available: Identity, Table, Discrete, Linear,
and Gamma.
