# average filter in Matlab

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Franzi on 8 Jun 2020
Commented: Rik on 19 Jun 2020
This question was flagged by Image Analyst
Hello!

#### 1 Comment

Rik on 19 Jun 2020
Question recovered from Google cache (as posted by Franzi):
Hello! I have an error for my implementation of the average filter on a variable window, can someone help me? That's my code:
function newpic = MeanFilt (pic, M)
[rows, cols] = size(pic);
[a,b]=size(M);
for i = ceil(a/2):rows-floor(a/2)
for j = ceil(b/2):cols-floor(b/2)
for ii = i-ceil(a/2):i+ceil(a/2)
for jj = j-ceil(b/2):j+ceil(b/2)
for k=1:a
for l=1:b
sum = sum + pic(ii,jj)*M(k,l);
endfor
endfor
endfor
endfor
newpic(i,j) = ceil(sum/(a*b));
endfor
endfor
endfunction

Bjorn Gustavsson on 8 Jun 2020
Why not use imfilter (if you have the image-processing toolbox) or conv2 - both should do this task in one line.
To your problem. You haven't told us what problem you run into, always do that when asking. The problem I manage to spot is that you don't initialize the variable sum before trying to access its value. Further, you don't re-set it to zero before starting to work on the next pixel. Then you increment the variable newpic, this is time-consuming, pre-allocate that variable first - you know it should have the same size as pic. Then I've never seen endfor in matlab.
HTH

#### 1 Comment

Bjorn Gustavsson on 8 Jun 2020
When you get to know about a matlab-function (I'll use conv2 as an example here) you've never heard of before do this at the command-line:
help conv2
Then you get to read the matlab help-documentation for the function, and can browse further to the "online documentation". These are typically very good since they are written by Mathworks by people working with help and documentation of the functions with the explicity purpose of being instructive.

Image Analyst on 8 Jun 2020
See my manual convolution program attached. It does this.
Also, don't use sum for the name of your varaible since sum is the name of a very important built-in function that you don't want to blow away.