How does Mean Filter work?

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Sukhdev Singh 2016-5-26

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/285865-how-does-mean-filter-work

评论： Walter Roberson 2018-7-3

I created a small code to see how does Mean Filter work.

How does it get values?? What is the equation?

A = [ 1 2 3; 4 5 6; 7 8 9]
h = ones(3,3)
imfilter(A,h)
    12    21    16
    27    45    33
    24    39    28

I get this as output, I don't understand how exactly 12,21,16,27 is calculated using imfilter command with 3 by 3 filter.

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Beena Bethel 2018-7-3

Its taking the sum of the neighboring pixels in the example shown here and not the average. I did not understand how whether it takes sum or average of its neighboring pixels....

Walter Roberson 2018-7-3

在 MATLAB Online 中打开

This is taking the sum, according to the weighting stored in h. Except for the edge cases you can use

imfilter(A, h/numel(h))

to get the average.

Getting the edge cases right is a little tougher:

imfilter(A, h) ./ imfilter(ones(size(A)), h)

The denominator is effectively counting the number of pixels that are in the neighborhood -- the number of pixels whose value contributed to the sum.

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Answer 1

Walter Roberson 2016-5-26

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https://ww2.mathworks.cn/matlabcentral/answers/285865-how-does-mean-filter-work#answer_223455

在 MATLAB Online 中打开

>> conv2(A,fliplr(flipud(h)))
ans =
     1     3     6     5     3
     5    12    21    16     9
    12    27    45    33    18
    11    24    39    28    15
     7    15    24    17     9
>> conv2(A,fliplr(flipud(h)), 'same')
ans =
      12    21    16
      27    45    33
      24    39    28
>> imfilter(A,h)
ans =
      12    21    16
      27    45    33
      24    39    28