You can use interpolated bisection instead of a straight one (I've tried using polynomial interpolation in imgmin and it saves a step or two). I also wonder wh

You can use interpolated bisection instead of a straight one (I've tried using polynomial interpolation in imgmin and it saves a step or two). I also wonder whether it would be possible to narrow down the range with only a sample of the image (i.e. pick "representative" subregion(s), bisect on that, then try that quality on the whole image).