Step 4- Apply Disrete Cosine Transform to the image

DCT_tf_img = dct_full_image(IMG,macrobock_size,Q);

Now lets look in to the function

function transformed = dct_full_image(img,macroblock_size,Q)

%k1 = macroblock row index

%k2 = macroblock column index

%macroblock_size = number of side pixels in a macroblock

for i = 1:size(img,1)

for j = 1:size(img,2)

transformed(i,j)={ floor(dct2(cell2mat(img(i,j)))./Q ) };

end

end

end

Here I have used the inbuilt DCT transform. But before applying we have to convert cell arrays to matrices. Then we divide it by quantization matrix. These are predefined. Then we round off so that lots of zero components in the high frequency side of the matrix which is right bottom corner.