Re: beginner: function definition confusion

[Geordie McBain]

Jeff:
I don't know much about digital image processing, but I think I can get 
this going.  First, the function name passed to nlfilter should be 
quoted; i.e. nlfilter (img, [3,3], "avg").  Also, in octave-forge 
there's a function mean2 you can use which does the same thing as avg.m; 
as it avoids for-loops it might be quicker.  Third, you might want to 
restructure T1 a bit to return blur instead of writing it to the 
standard output.  I put this together as

   function blur = T2 (pngf)
     img = imread("black-white.png");
     blur = nlfilter(img,[3,3],"mean2");
   endfunction

which I call like

   octave> b = T2 ("black-white.png");
   octave> imshow (b);

Hope this helps.

Geordie McBain
www.aeromech.usyd.edu.au/~mcbain


Jeff Abrahamson wrote:

> I'm confused trying to use nlfilter.  (The ultimate goal is to do
> convolutions on images.)  I'm not sure if I'm misunderstanding
> nlfilter or if I'm even maybe just defining the function avg
> incorrectly.  Here's what I wrote
>
>    function T1 ( )
>      img = imread("black-white.png");
>      blur = nlfilter(img,[3,3],avg)
>    endfunction
>
>
>    function ret = avg ( blk )
>      ret = 0;
>      for i = 1:3
>         for j = 1:3
>           ret += blk(i,j);
>         endfor
>      endfor
>      ret /= 9;
>    endfunction
>
>    T1()
>
>
> The error is this:
>  octave:1> T1()
>  error: `blk' undefined near line 22 column 14
>  error: evaluating assignment expression near line 22, column 11
>  error: evaluating for command near line 21, column 5
>  error: evaluating for command near line 20, column 3
>  [...]
>
> Anyone see what I'm doing wrong?
>
>
> Note, by contrast, that avg works in the form I thought I needed it
> to:
>
>  octave:1> m=rand(3)
>  m =
>
>    0.30486  0.74804  0.28817
>    0.54096  0.62247  0.70384
>    0.67811  0.58588  0.38752
>
>  octave:2> avg(m)
>  ans = 0.53998
>  octave:3> 
>
> Thanks in advance.
>
>  



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