Discover MakerZone

MATLAB and Simulink resources for Arduino, LEGO, and Raspberry Pi

Learn more

Discover what MATLAB® can do for your career.

Opportunities for recent engineering grads.

Apply Today

To resolve issues starting MATLAB on Mac OS X 10.10 (Yosemite) visit: http://www.mathworks.com/matlabcentral/answers/159016

I would like to apply DCT to each element in a matrix

Asked by Andrew on 17 Feb 2013

I have a code where i take every 8*8 block of a 512*512 image and find its average, and subtract it away, storing the result into a new matrix(64*64).

n = 1;
for i = 1:bs:row;
    m = 1;
    for j = 1:bs:col;
        ave = mean(mean(I(i:i+bs-1, j:j+bs-1)));
        A(i:i+bs-1, j:j+bs-1) = I(i:i+bs-1, j:j+bs-1) - ave;
        DC(n,m) = ave;
        m = m + 1;
    end
    n = n + 1;
end

But i would like to apply DCT transform to each of the 8*8 blocks, without applying it to the entire image at once, and then store my results in a new matrix of the same size as the original image matrix. I am not sure how to continue from here. Can someone please guide me through this?

0 Comments

Andrew

Products

No products are associated with this question.

1 Answer

Answer by Matt J on 18 Feb 2013
Accepted answer

I'll assume you have a dct function of some kind and also MAT2TILES from the File Exchange

   Icell = mat2tiles(I,[8,8]);
   ave=Icell;
   for i=1:numel(Icell)
    ave{i}=mean(Icell{i}(:));
    Icell{i}=dct(Icell{i}-ave{i});
   end
 DC=cell2mat(ave);
 result=cell2mat(Icell);

11 Comments

Matt J on 18 Feb 2013

As the error message says, in imread(filename), the 'filename' variable must be a string. Did you check that it is? If so, how?

Andrew on 18 Feb 2013

I am not sure how to do that.

Walter Roberson on 18 Feb 2013

Read the function you are using! It starts

%% LOSSY COMPRESSION-DECOMPRESSION USNIG DISCRETE COSINE TRANSFORM TECHNIQUE.
function[]=mydct(filename,n,m)
% "filename" is the string of characters including Image name and its
% extension.
% "n" denotes the number of bits per pixel.
% "m" denotes the number of most significant bits (MSB) of DCT Coefficients. 

This documents that you must pass exactly 3 parameters to mydct(), the first of which must be a file name, and the other two must be scalars. But instead your code is passing in an array of data values as the first parameter, and you are not passing in the second or third parameter at all.

Matt J

Contact us