targetFor method
The ratio to aim for on a face of luminance faceY.
Implementation
double targetFor(double faceY) {
if (darkFaceBoost && faceY < darkFaceY && darkFaceRatio > minRatio) {
// White on a face with Y < 0.05 is ≥ 10.5:1, so this is reachable.
return darkFaceRatio;
}
return minRatio;
}