Vignetting, discussion about methods of resolution Options

[Tman]

Hi Nirgal and all, I would like to discuss about vignetting and methods of resolution for it. I'm mainly interested in mathematical methods that could automatically calculate and adjust the right grey value for each pixel in a single picture.

My current method works with more or less transparent layers over the original picture that so roughly are able to balance the grey values. A perfect layer have to be the exact inverted brightness difference of each picture with this shadow effects. This method is very effective if you get the correct inverted values. These shots of the Mars sky come nearly at such a perfect mask, but not always. And of course the center of the pictures lose much of theirs original brightness/luminance sadly.

I have in mind a mathematical method that can adjust each grey value in a pic in order to obtain a completely balanced brightness over the entire picture. But I'm not in the position to reach that. I only know one have to start with the calculation of the grey values in the center of the picture. In the center are quasi the reference values of the whole picture, if I'm correct.
Is there a possibility (mathematical method) to get (roughly) the same brightness and luminance like in the center over the whole picture from the MERs?

Greetings, Peter

[MichaelT]

I have now modified the anti-vignetting-program (using IDL) such that it can deal with any kind of jpeg-image. Also, it does not use FFT any longer but simply takes a 2D-cosine-shaped mask. That mask is fitted to the chosen image and the amount of vignetting automatically determined (that can be done RGB-channel specific). It also allows to save images as 16-bit-tiff so that none of the original information is lost in the out-put image. You can also do manual adjustments if the amount of vignetting is over- or underestimated by the program (depends on the structure of the image). All that has to be done with each single image and cannot be aplied to a ready panorama.

Below are two examples (SOL 582).

Without anit-vignetting:


After anti-vignetting:


After anti-vignetting the sky shows a very even color distribution, without these nasty green edges. These are obviously due to different amounts of vignetting in the RGB-channels.

I also tested that program with scanned slides and digital camera images and it works very well. So it does not only work with martian craters but also with terrestrial ones The image below shows Wolfe Creek meteorite crater in Western Australia. Its got a diameter of 850 m and is about 30-40 meters deep. Like martian craters it is filled with sand and dust (80 meters).

Panorama from three frames.


The only draw-back is that I cannot provide a stand-alone version of that program Though, a pre-compiled version of the program can be run with RSI's "Virtual Machine". It's free, but requires registering and is a 115 MB download
Is there anybody here who's got a license to turn this IDL-program into a stand-alone one?

Michael

[Bob Shaw]

MichaelT:

Do you think your anti-vignetting app could be tweaked to sort out the tone variations seen across the Surveyor frames?

Bob Shaw

[MichaelT]

MichaelT:

Do you think your anti-vignetting app could be tweaked to sort out the tone variations seen across the Surveyor frames?

Bob Shaw

Bob, have you got one for me to try it out? At the moment I don't quite know what those images look like. These tone variation would have to be roughly rotation-symmetric to eliminate them. I could also change it that way that it uses some polynomial fitting functions. Then it might work with non-rotation-symmetric variations, too.

Michael