sepia constant
A matrix that turns the image into sepia-tone.
Implementation
static const List<double> sepia = <double>[
0.393,
0.769,
0.189,
0,
0,
0.349,
0.686,
0.168,
0,
0,
0.272,
0.534,
0.131,
0,
0,
0,
0,
0,
1,
0,
];