Simulating the highlight recovery tool from Photoshop

Question

I'm interested in processing a bitmap in Java using the same (or similar) technique as the Highlight recovery tool in Photoshop. (That would be the Image->Adjustments->Shadow/Highlight tool in CS4.)

I googled around, and found very little outside of discussion about existing tools that do the job.

Any ideas?

Answer 1

Just guessing because I don't have Photoshop - only going by the descriptions I find on the web.

The Radius control is probably used in a Gaussian Blur to get the average value around a pixel, to determine its level of highlight or shadow. Shadows will be closer to 0 while highlights will be closer to 255. The exact definition of "close" will be determined by the Tonal Width control. For example, at 100% maybe the shadows go from 0-63 and the highlights go from 192-255.

The Amount corresponds to the amount of brightness change desired - again I don't know the scale, or what equates to 100%. Changing the brightness of the shadows requires multiplying by a constant value - for example to brighten it by 100% would require multiplying by 2. You want to scale this by the shadow value determined above. The highlights work similarly, except working down from 255 instead of up from 0.