Re: A "slanted edge" analysis program


"Lorenzo J. Lucchini" <ljlbox@xxxxxxxxxx> wrote in message news:5KYZe.49331$nT3.33343@xxxxxxxxxxxxxxxxxxxxxxxx
Well, my Imatest trial is up, and I'm not going to buy it (though it is a very nice program that I'd recommend!), but I'd still like to play with ESF, PSF, MTF and all that.

Yes, once you really grasp what you are actually looking at, it will help with improving the results. e.g. by allowing to optimize capture sharpening.

Specifically, I'm still very interested in findout out what the "best sharpening" for my scanner is by analysing the edge spread function.

Exactly. There are several possibilities to use the ESF to check for that (e.g. edge halo), and the PSF can be used as input in several deconvolution programs. The MTF allows to compare systems in an unambiguous way (assuming test conditions are under control).

There is another interesting "slanted edge tester" at http://www.i3a.org/downloads_iso_tools.html (if I'm not mistaken, Imatest is actually based on its code),

Not really based on it, but it helped as an inspiration and discussion tool with, amongst others, the programmers of the original ISO demo sourcecode. Imatest uses the basic idea of the slanted edge target, as it is described in the relevant ISO standards 16067-1&2 for scanners, and 12233 for digital still cameras.


but it doesn't give nearly as much information as Imatest does... even though perhaps the MTF alone could be turned into the correct deconvolution for my scanner in the hands of "some of the people here"! ;-)

The MTF is more suited for judging the effect of such a sharpening on the various spatial frequencies, and the associated risk of aliasing artifacts when down-sampling afterwards. The PSF is needed for deconvolution (or for the creation of a high-pass convolution kernel).

But. In the last few days I've been busy writing my own "slanted edge" program. It now sort of works, meaning that it doesn't (often) crash, and that it gives results that are similar to what Imatest or SFRWin give.
Similar, not really identical... that's why I would be glad if Bart, 

Reporting for duty ;-)

Kennedy, or anybody who's into this kind of things could help me a little. 

I'll add some program related comments in a separate message.

Bart 

.

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