public void AdjustContrast(float contrast)
{
float s = contrast + 1.0f;
float o = 128 * (1.0f - s);
float[] mtx =
{
s, 0, 0, 0, o,
0, s, 0, 0, o,
0, 0, s, 0, o,
0, 0, 0, s, 0
};
ConcatMatrix(this, mtx);
}