converting 3D matrix to 2D image

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kush 2012-3-25

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how to convert 3D matrix C(4x4x64) into 2D W1(32x32) plz help i have divided an image into 4x4 blocks & saved them into matrix C1(a,b,c) now i want to reconvert it into image

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Answer 1

Image Analyst 2012-3-25

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We have no idea how you want these blocks to be arranged. Please read your message from our point of view and try to figure out what you meant. I don't know what a "block" is - is it a cell? A slice out of a 3D image like C? Is C the original matrix, or the one you have after dividing your image into blocks? You could have 8 4x4 blocks in each direction to get 32 pixels along a dimension, or 64 blocks to make up a 32x32 2D image. Am I supposed to know how all those 64 blocks are to be arranged? In what order?

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kush 2012-3-26

sir,i have divided original image I (32x32) into an array of blocks/cells each of 4x4 size by

[a b] = size(HL31);

c=4;d=4; % reshape it into 4*4 matrices

l=1;

for i=1:c:a-3

for j=1:d:b-3

C1(:,:,l)=HL31((i:i+3),(j:j+3));

C1(:,:,l)=dct2(C1(:,:,l));

l=l+1;

end

then i have performed idct on each block

for i=1:size(C1,3)

C5(:,:,i)=idct2(C1(:,:,i));

end

now i want to convert C5 back to a 32x32 image

can u plz help

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Answer 2

Andrei Bobrov 2012-3-26

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在 MATLAB Online 中打开

f = @(block_struct)dct2(block_struct.data);
f2 = @(block_struct)idct2(block_struct.data);
C1 = blockproc(HL31,[4 4],f);
C5 = blockproc(C1,[4 4],f2);

OR

ij = {4*ones(size(HL31,1)/4,1),4*ones(size(HL31,2)/4,1)}
C1 = cell2mat(cellfun(@(x)dct2(x),mat2cell(HL31,ij{:}),'un',0))
C5 = cell2mat(cellfun(@(x)idct2(x),mat2cell(C1,ij{:}),'un',0))

OR in your case

s3 = size(C5);
s2 = s3(1:2)*s3(3)/2;
ji = arrayfun(@(x)1:s3(x):s2(x)-s3(x)+1,1:2,'un',0);
[j1,i1] = ndgrid(ji{:});
ii = 0:s3(1)-1;
jj = 0:s3(2)-1;
out = zeros(s2);
for k = 1:numel(j1)
    out(i1(k) + ii,j1(k) + jj) = C5(:,:,k);
end

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kush 2012-3-26

thank u

Oleg Komarov 2012-3-26

Please accept his answer if you think it solved your problem.

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Answer 3

Sandip 2013-8-8

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I guess I have a similar problem. I have an image (tiff). I want histogram of this image/grey scale. However, when I read in the image, I find that my image (tiff) is in 3 D matrix form. How can I convert the image to 2D matrix! imhist command works only for images with 2D matrix form.

Regards,

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Jan 2013-8-8

Please post a new question in a new thread. If you highjack an existing thread, it is not clear, which answer belongs to which question, and you cannot selected an accepted answer.

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