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

[Tman]

Hi Michael, best we would talk about it in German, only the other members here would pull one's hair out (or so ).

I dont know the FFT method so far, but it seems to be fundamental when programming high quality picture editing software. After a quick search in the web I found very interesting examples - but a.t.m. definitively too difficult to me.

Did you wrote a program for the FFT caculation that now works automatically when processing the MER pics?
My only hope is that you could programming a plug-in to PhotoShop with it
When you get satisfactory results then, I would be the first customer!

[MichaelT]

Hi Michael, best we would talk about it in German, only the other members here would pull one's hair out (or so ).

Probably / Vielleicht

I think that my program works quite well now, though, you have to treat every image individually - not fully automatic, yet. Well, you only have to tune one parameter.

Here are some examples:
Sol 107, before and after anti-vignetting:


Sol 581 partial panorama (Autostitch):


Looks quite promising.

Did you wrote a program for the FFT caculation that now works automatically when processing the MER pics?
My only hope is that you could programming a plug-in to PhotoShop with it 
When you get satisfactory results then, I would be the first customer!

Unfortunately, I use a data language called IDL, which is a commercial product and fairly expensive That's what we use at our institute. I wish I'd be able to write a Photoshop plug-in, but I am not If anybody else here would like to transfer this into another language, I could provide commented code.

Michael

ps: Ich schicke Dir gleich noch eine persönliche Nachricht auf Deinen Account.

[Nirgal]

Probably / Vielleicht 

Looks quite promising.
Unfortunately, I use a data language called IDL, which is a commercial product and fairly expensive That's what we use at our institute. I wish I'd be able to write a Photoshop plug-in, but I am not If anybody else here would like to transfer this into another language, I could provide commented code.

Michael

ps: Ich schicke Dir gleich noch eine persönliche Nachricht auf Deinen Account.

Hi Micheal,

your approach sounds interesting: surely more involved than the ad-hoc method
I implemented in my "unstrip" program (I've just started to research vignetting problems and was very surprised that such a comparatively simple method
(even without FFT) could remove the "stripes" in multi-frame mosaics.





not perfect, but could be used for "cleaning" up existing panoramas without re-stitching ...

However, I'm interested in implementing your FFT-based method in the C language
(provided that it fits within my existing image processing libraries (FFT, etc)
so I could possibly provide a windows stand-alone program that anyone could use
as a simple command line utility...