private byte GetL8(Color c)
{
byte red = c.R;
byte green = c.G;
byte blue = c.B;
// Luma (Y’) = 0.299 R’ + 0.587 G’ + 0.114 B’ from wikipedia
return (byte)(((0x4CB2 * red + 0x9691 * green + 0x1D3E * blue) >> 16) & 0xFF);
}