im2col error in size

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Andrea
Andrea 2012-7-16
Hi this is my code:
R=rand(162,72);
r=im2col(R,[2 2],'sliding');
R1=col2im(r,[2 2],size®,'sliding');
the size of R is [162 72];
when I use line 1 it is OK. It gives me a a matrix r with size of r=[4 11431]
but at line 2 to obtain R, when I want to convert them to the original matrix via col2im, it give me this error:
"To RESHAPE the number of elements must not change."
Can anybody help me please and tell me what is the problem?

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Image Analyst
Image Analyst 2012-7-16
What are you really trying to do? im2col() and col2im() are confusing functions that are probably going to be deprecated soon. How did you ever stumble upon those? Can't you do what you want to do with reshape() or blockproc() or something?
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Image Analyst
Image Analyst 2012-7-16
编辑：Image Analyst 2012-7-16
I'm glad you explained that because now I can recommend nlfilter() as the proper way to do what you want to do. My advice is to not use reshape() but to use nlfilter(), or alternatively blockproc() if you don't have the Image Processing Toolbox.
Andrea
Andrea 2012-7-17
Thanks so muchhhhh. I will do.

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更多回答（1 个）

Sean de Wolski
Sean de Wolski 2012-7-16
Because you are using a 'sliding' block with im2col the number of elements in r is much bigger than the number in R. Compare:
numel(R)
numel(r)
What you have works with 'distinct' blocks as you would expect:
R=rand(162,72);
r=im2col(R,[2 2],'distinct');
R1=col2im(r,[2 2],size(R),'distinct');
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Image Analyst
Image Analyst 2012-7-17
That won't happen if you don't do that im2col/col2im stuff and use nlfilter instead.
Andrea
Andrea 2012-7-17
编辑：Andrea 2012-7-17
I know it from your previous answer. Thanks. Both nlfilter and blockproc are amazing. I haven't seen them before! I used them and they perfectly works. Now, I just to realize the difference between these two functions. I should go to the depth a little more. Thank you so much.

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