rec709_to_linear
lin_y = (COEFF(0.2627, 255) * rec709_to_linear(r) +
COEFF(0.6780, 255) * rec709_to_linear(g) +
COEFF(0.0593, 255) * rec709_to_linear(b)) >> 16;
lin_r = rec709_to_linear(*r);
lin_b = rec709_to_linear(*b);
lin_y = rec709_to_linear((y * 255) / (full ? 255 : 219));