EXORCIST - a VirtualDub filter
1. What is this filter for?

This filter was developed to remove ghost copy of the signal. This kind of noise is usually caused by interferences or (in case of aerial) signal is reflected by some neighbour big object like building in the front of your house. On the image on the right you can see example of this kind of noise. Instead on one big '4' sign, there are two extra copies on the right of original '4'.

Note for people familiar with TMPG encoder: this filter is similar to "Ghost remove" feature of TMPG encoder.
1b. Download

You can download latest Exorcist release.

2. Exorcist in action

This is frame from example video signal taken from aerial and the same frame processed by Exorcist:


Settings used for processing are two instances of Exorcist:
  1. 12 pixels right, 6% darken
  2. 49 pixels right, 4% darken
3. Parameters

Exorcist configuration dialog box

Filter have only two parameters:

SHIFTThis parameter determines how far from original signal is ghosted copy. Shifting is horizontal and wrapped over borders:
| 1 2 3 4 5 | shifted 2 pixels right becomes | 4 5 1 2 3 |
INTENSITYThis parameter determines how much ghosted copy is visible.

Performing shifted 2 pixels right with -10% intensity on | 1 2 3 4 5 | outputs:

  |   1   2   3   4   5 |
- | 0.4 0.5 0.1 0.2 0.3 |
--------------------------
  | 0.6 1.5 2.9 3.8 4.7 |
Best method to get meaning of the parameters is to load some video, run filter configuration, click "Preview" button then play with sliders.

4. ToDo

This is list of features that are planned to be included in next releases of Exorcist.
  1. MMX optimizations
5. Author

This filter was written by Krzysztof (eng. Christopher) Wojdon and is available under Gnu Public License (GPL) license as it is based on some GPL code by Avery Lee.

You can reach author at voidon@poczta.fm or vander@tempus.ii.uni.wroc.pl. It is possible that my university email account will be closed (I have just finished my education) in few weeks, so you can find me on asiab@hist.uni.wroc.pl.