Re: A "slanted edge" analysis program

Bart van der Wolf wrote: 

"Lorenzo J. Lucchini" <ljlbox@xxxxxxxxxx> wrote in message
news:CGa0f.9459$133.3815@xxxxxxxxxxxxxxxxxxxxxxxx
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This is what it can look like on your (odd looking) "testedge.tif":
<http://www.xs4all.nl/~bvdwolf/main/foto/Imatest/testedge.zip>
The Luminance channel was HP-filtered in "Image Analyzer" with a "user defined filter" of 7x7 support.

Why is my edge odd-looking? Does it still look like it's not linear gamma?
The behavior of my driver is puzzling me more and more, expecially wrt the differences between 8- and 16-bit scans.

The mean S/N ratio has decreased from 241.9:1 to 136.3:1, while the 10-90% edge rise went from 4.11 to 2.64 pixels. Unfortunately the scan suffers from some CA like aberration (especially the Red channel is of lower resolution), which may become more visible as well.

Note that I had disabled all color correction, and the three channels look much more consistent when my driver's standard color correction coefficients are used.


By the way - I'm experimenting a bit with the Fourier method for reconstructing the PSF that's explained in the book's chapter you pointed me to (I mean the part about tomography).

I don't think I have much hope with that, though, as there is interpolation needed, and it appears that interpolation in the frequency domain is a tough thing.

OTOH, I think I've understood the way you're trying to reconstruct the PSF; I'm not sure I like it, since as far as I can understand you're basically assuming the PSF *will be gaussian* and thus try to fit a ("3D") gaussian on it. Now, perhaps the inexactness due to assuming a gaussian isn't really important (at least with the scanners we're using), but it still worries me a little.

Also, the book says that gaussian PSFs have gaussian LSFs with the same parameters -- i.e. that a completely simmetrical gaussian PSF is the same as any corresponding LSF.

Our PSFs are generally not symmetrical, but they *are* near-gaussian, so what would you think about just considering the two LSFs we have as sections of the PSF?

I think in the end I'll also try implementing your method, even though there is no "automatic solver" in C, so it'll be a little tougher. But perhaps some numerical library can be of help.


by LjL
ljlbox@xxxxxxxxxx
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