Blockproc error when including BorderSize argument
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Stewart Tan
on 8 Aug 2019
Answered: Walter Roberson
on 8 Aug 2019
I'm working on the exercise by Matlab on dct https://www.mathworks.com/help/images/discrete-cosine-transform.html
and i ran the following code:
I = imread('cameraman.tif');
I = im2double(I);
imshow(I)
T = dctmtx(8);
dct = @(block_struct) T * block_struct.data * T';
B = blockproc(I,[8 8],dct,'BorderSize',[4 4],'Trim',false) %modification made here
The code was from the link above, but i included the 'BorderSize' criteria to allow for overlapping of the blocks. Upon running the code, i get the error saying:
Error using blockprocFunDispatcher
BLOCKPROC encountered an error while evaluating the user-supplied function handle,FUN.
Error in blockprocInMemory
[u1_output fun_nargout] = blockprocFunDispatcher(fun,block_struct,...
Error in blockproc
result_image = blockprocInMemory(source,fun,options);
What could be the issue causing the error message above? If i remove 'BorderSize',[4 4], 'Trim',false it works as normal like in the link but am i using it wrongly?
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Accepted Answer
Walter Roberson
on 8 Aug 2019
I = imread('cameraman.tif');
I = im2double(I);
T = dctmtx(8);
dct = @(block_struct) T * block_struct.data * T';
B = blockproc(I,[4 4],dct,'BorderSize',[2 2],'Trim',false, 'padpartial', true); %modification made here
size(I)
size(B)
Note that B comes out larger than I because you have trim set to false.
Notice the pad partial being needed: without it then when you reach the edge of the image, you run off the edge. blockproc() keeps moving the window until the last of the [4 4] windows is at the right (or bottom) edge, leaving the specified border padding "hanging over" the end of the image.
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