Advanced Sharpen and dual threshold

[tomczak]

This is a little off topic, but still on the same theme: restricting sharpening of the smooth areas (e.g. noise/grain), but also restricting sharpening of the roughest edges (those that will produce visible halos) while sharpening the 'middle roughness' details.

Setting the threshold in AS's Sharpen Tab, can accomplish the first task - the second (i.e. reducing rough edges halos) can at present be simulated, albeit coarsely, by using an edge mask, as described above.

Bilateral Sharpen can actually accomplish both in one go, but in a less controllable fashion and without flexible soft thresholds as AS could.

(see the link below for how to speed up the Bilateral Sharpen Preview while adjusting the Radius and the Threshold).

http://www.dl-c.com/board/viewtopic.php?f=5&t=444

Here is my recipe for the Bilateral Sharpen use:

1) Set the Sharpen Factor and the Sharpen Threshold sliders to zero. From now on imagine that the smoothing you see in preview will be reversed when actually sharpening the image (i.e. what you see smoothed in preview will be sharpened later, what is not smoothed will be preserved and e.g. won't produce halos).

2) Adjust Blur Threshold slider so that the roughest edges that are likely to produce halos are not smoothed (smoothing at this stage means sharpening later) - this is your upper, rough edges halo threshold.

3) Move Sharpen Factor Slider to some value greater than 1 (anything above 1 will sharpen the previously smoothed areas). Adjust Blur Radius - this has similar meaning to the USM Radius.

4) Adjust Sharpen Threshold slider so that the fine texture (e.g. noise/grain) is not sharpened in the preview - this is is your lower, smooth areas/noise anti-sharpening threshold (similar to the AS Threshold sliders below the roughness histogram). this seems to be a 'Hard Threshold' - use delicately for realistic results.