how to find mean for the values in an image

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Sharen H
Sharen H 2013-7-20
回答： Sujit Singh 2017-3-15
i have to divide my image into n number of small 2X2 matrix and find the mean value and replace that 2x2 matrix with the mean value . example
x=
[2 3 4 5
2 3 4 5
1 2 3 4
1 2 3 4]
i have to find the mean of
[2 3
2 3]
similarly for others and replace that concerned matrix with that mean value
the output should get is
[2 2 4 4
2 2 4 4
1 1 3 3
1 1 3 3]

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回答（3 个）

Wayne King
Wayne King 2013-7-20
编辑：Wayne King 2013-7-20
Do you have the Image Processing Toolbox? You can use blockproc(), but I'm not sure how you are getting your expected output above. You say you need the mean of 2x2 chunks submatrices like [2 3; 2 3]. Do you mean that you want the column means of those, which are 2 and 3, or you want the mean of all 4 elements which is 2.5? How are you taking the mean and ending up with a matrix the same size as the original?
I'll show you how to use blockproc() to return the column means for each 2x2 submatrix in x. That means for each 2x2 submatrix, you'll get back a 1x2 with the two column means. Accordingly, a 4x4 matrix reduces to a 2x4.
fun = @(block_struct) mean(block_struct.data);
Y = blockproc(x,[2 2],fun);
If you want the overall mean of each 2x2 submatrix, giving you a 2x2 matrix at the end:
fun = @(block_struct) mean(block_struct.data(:));
Y = blockproc(x,[2 2],fun);
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Wayne King
Wayne King 2013-7-20
I think you do not have the blockproc() function from the Image Processing Toolbox, blockproc() was only added to the Image Processing Toolbox in R2009b, which is 7.9

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Andrei Bobrov
Andrei Bobrov 2013-7-20
编辑：Andrei Bobrov 2013-7-23
for youe case without blockproc (without Image Processing Toolbox):
kron(cellfun(@mean2,mat2cell(x,2*[1 1],2*[1 1])),[1 1; 1 1])
or use Peter J. Acklam' idea. Thanks to the cyclist for this link.
m = [2 2]; % size your small block
s = size(x);
n = s./m;
a = permute(reshape(x,m(1),n(1),n(2),[]),[1 3 2 4]);
out = kron(reshape(mean(reshape(a,[],prod(m))),n(1),[]),ones(n))
use function blkproc
sizeblock = [2 2];
Y = blkproc(x,sizeblock,@mean2);
out = kron(Y,ones(size(x)./sizeblock));
  2 个评论
Sharen H
Sharen H 2013-7-23
can u please help me to generalize as [n,n] matrix
Sharen H
Sharen H 2013-7-23
when i try for a [3,3] small block i am not able to process...

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Sujit Singh
Sujit Singh 2017-3-15
We can assume given image size is 4X4 and you want to divide and calculate the mean of 2X2 block size and then get the mean processed image, so for this we can use blkproc in your case: 1.Img=imread('Img.tiff')% Read the image 2.meanFilterFunction = @(x)mean2(x(:))*ones(size(x),class(x)); % this is mean function 3. BS=[2 2] % block size 2X2 4.Mean_image = blkproc(Img, BS, meanFilterFunction); 5. imshow(Mean_image, []);
I hope this will help you , now you can change the size of image and size of block also .

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