[Octave-patch-tracker] [patch #8059] [new function for image package] ranktf.m

[Ming Liu]

Follow-up Comment #4, patch #8059 (project octave):

Actually rank transform is a good way of implementing "stereo matching" in
computer vison. Because it ideally reduces the noise that is harmful to
perform the stereo matching. In fact Matlab does not have a similar function.
Here is a website for such kind of info:
http://siddhantahuja.wordpress.com/tag/rank-transform/
The author uses three for loops to achieve this.
Rank transform uses a sliding window algorithm, aims to find the rank of every
pixel in its neighbors(4,9,16,25... neighbors,the square of 2,3,4,5...). This
is why I used two for loops. Considering it is very slow, I am trying to
vectorize it. 
So take the window size 3 and an image with the size of 10*10 for example. I
think:
1. Firstly I need to convert the image to a vector. 
2. Then start at the item 1:3 and item 11:13 and item 21:23 as the first step.
Try to find the rank of item 2 in all these items
3. ...
Is it a clear and a correct way to go? Or anyone has a better solution?

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