Req: Revised Optimize HDR function

[photoken]

The recent discussion about recovering shadow data from a scanned slide caused me to examine various methods of doing that, and the best programs for doing that are in the field of astrophotography. Because astrophotography images have a huge dynamic range, programs have been written to "stretch" the original image data in order to bring out faint details in the dark regions while not overexposing the light regions. This is exactly what we want to do with our everyday photographs.

The best (and free) program I found is the FITS Liberator:
http://www.spacetelescope.org/projects/fits_liberator/

This is a before-and-after sample from its User Manual:

FITS sample 01.png

The FITS Liberator offers several non-linear functions to do this. Quoting from their User Manual (which is referring to the above sample image):

Astronomical images contain many more greyscale levels than can be viewed on a computer
monitor or printed. In the image to the left a “normal” or linear representation of the image is shown. To
the right the effect of a non-linear Stretch, a Logarithmic Stretch, is shown. By using a non-linear Stretch
it is possible to enhance some greyscale levels in the image more than others and so to make faint
details visible without saturating the brighter parts of the image.

I won't go into detail about the controls that the program offers, but for our everyday photographs, the key controls are:

• The Histogram, with its associated black point and white point controls.
• The Scaling control, which sets the "background" value.
• The Stretch control, which has the several formulas that can be used.

FITS Liberator interface.jpg

I think that if the current PL Optimize HDR feature was re-written to accommodate those 3 controls (and their options) we would have a very valuable feature.