Re: Behaviour of Hough Transform

[Hartmut]

(reposting after subscription to the mailing list)

> Hello,
> 
> hough is listed as a missing function on the wiki.
>
> However hough_line appears to already implement MATLAB's hough.
>
> If hough is not hough_line and not hough_circle, what would be the desired
> behaviour of hough?
>
> Best Wishes,
>
> Chris

Hey Chris,

you are right, the hough function is currently still misssing in the image
package of Octave. Here is what it does in Matlab: [1]. Basically it does
the Hough transformation to detect lines in images.

There exist already two relevant functions in the image package: hough_line
and hough_circle. Especially hough_line is close to what Matlab does in
hough. But to make a Matlab compatible hough function there are still some
parts missing:
* The return value of hough_line is currently only [Hough, Roh]. The Matlab
function returns [Hough,
   Theta, Roh].
* The possible input parameters are also different. Hough_lines accepts an
Angles parameter, this seems 
   to be similar to what Matlab accepts as the values of its Theta
parameter-value pair. The Matlab
   parameter-values pair of RhoResolution seems to be missing in the Octave
version.

I have not used the Octave function hough_lines a lot, so there might well
be more incompatibilities to its Matlab pendant.

If you are interested in improving (or creating) the Octave hough function
you are very welcome. I see two ways to do this:
* write a new Matlab compatible m-file wrapper hough.m around the already
existing hough_lines.cc
  (This will only work out if houg_lines.cc is reasonable compatible in its
calclation output already).
* change the current hough_lines.cc code, to make the above work. You can
have a look at it here: [2]

Cheers

    Hartmut


[1] http://de.mathworks.com/help/images/ref/hough.html
[2] http://hg.code.sf.net/p/octave/image/file/6cd0d6b5cc1e/src/hough_line.cc



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