Bart,
Roger Clark has also demonstrated use of RL in lieu of or in addition to traditional unsharp masking. However, he did not explain how he derived the point spread function parameters (PSP) used for that restoration. Just guessing?
Hi Bill,
Yes, it is basically guessing (although with visual feedback from a small image area that guess can be pretty good!), unless one has a good method of determining the characteristics of the optical system. I use Imatest to calculate the PSF of my optical system (lens/aperture/AA-filter/microlens/sensel aperture), and I am able to derive a pretty good PSF that way. The guessing part also works fine though .
I understand that deconvolution can also be used for defocusing error and and diffraction correction. Some photographers report good results using deconvolution (FocusMagic) to offset the effect of a blur filter in capture sharpening. Unfortunately, it is difficult to derive the PSP function to be used in the deconvolution. Do you have any pointers in this area?
The interesting thing is that an application like FocusMagic can already do an impressive job based on a single (radius) parameter. It is capable of tackling defocus/diffraction/AA-filtration, even motion blur, which all have distinctly different PSF shapes, so I assume its PSF assumption may be a bit more elaborate (or an average of different shapes) than a simple defocus model of a PSF, or the algorithm is somewhat adaptive. Anyway, it proves that with limited input one can already achieve impressive improvement results.
As an example, a C1 conversion of an EOS-1Ds3 image at f/8 without sharpening, and the FocusMagic version with a small PS layer blending tweak:
[attachment=19347:OPF_Debl...rop01_1_.png] [attachment=19348:OPF_Debl..._125__1_.jpg]
IMHO those who seek for a solution by removing an AA-filter will add more problems than the benefits of an AA-filtering + proper sharpening can deliver ...
Cheers,
Bart
P.S. I've kept the unsharpened image in the losslessly compressed PNG file format to allow comparisons with other sharpening utilities.