Vignette removal

(Gustavo Adolfo) #1

Hi, I’m doing some experimets in scanning old slides and negatives by using my own small and very, very limited camera (Canon PowerShot A3100 with an almost dead sensor). While a friend of mine doesn’t lend me his better camera, I’ll try to push as far as I can the limits of mine.
My method is to open a blank document in Libre Office, hold the slide around 15, 20 cm away from the screen, and shoot with the camera’s builtin macro.
The main issue, for now, is vignetting.
What I did in Darktable was:

  1. applying a lens model as close to mine as I figured out (PowerShot A640);
  2. increase the distance to subject until I got the maximum vignette removal effect;
  3. On the vignette tool, tweak the settings to get some kind of “negative” vignette effect (lighter borders instead of darken)

While shooting, I also shoot the computer screen only, to get a pure camera vignette. A kind of flat frame. I thought that I could use this frame to be subtracted from the main frame, but I couldn’t get good results. This was in Gimp.

Am I going the right way, given all limitations I have?

Just tone mapping:

After “removing” vignette, as described above, plus geometric distortion:

The “flat” frame:

(Mica) #2

This isn’t a helpful comment… but I like it with the vignette. :smile:

(Gustavo Adolfo) #3

:smiley:… I also thought about that… I’m not discarding the idea.

Maybe a vignette fits well in this specific image, but there are others where it doesn’t.

(Shreedhar Inamdar) #4

Here is what one gets with RawTherapee’s vignette filter applied at -.2.9 (with rectangular shape)