How can I turn a grayscale image into a 8x8 block and then show the DCT coefficients in each block as an image?

So basically, I have to divide up an entire image into 8x8 blocks, and perform the 2D DCT for each block, outputting the results into a new image such that the new image shows DCT coefficients for each corresponding image block.

So far this is what I have;

 % code
 I = imread('lenagray.jpg');
I = im2double(I);
T = dctmtx(8);
dct = @(block_struct) T * block_struct.data * T';
B = blockproc(I,[8 8],dct);
figure;
imagesc(B)

just need help with making a image of the DCT coefficients

Answer 1

[Image Analyst]

An adaptation of the example in the help for dctmtx() is:

grayImage = imread('lena.jpg');
grayImage = im2double(grayImage);
D = dctmtx(size(grayImage,1));
dct = D*grayImage*D';
imshow(dct)

[Osman]

that code doesn't put the DCT coefficients of each 8x8 block into a picture though

[Walter Roberson]

The above code is not correct, as .jpg images are always 3D and you cannot use matrix multiplication with a 3D array. You need an rgb2gray() step

[Image Analyst]

Even the attached JPG image?

theImage = imread('lena.jpg');
size(theImage)

ans =
   512   512

[Osman]

this is the question im trying to figure out ;

Write a script to divide up an entire image (assume grayscale) into 8x8 blocks, and perform the 2D DCT for each block, outputting the results into a new image (such that the new image shows DCT coefficients for each corresponding image block). [HINT]: you can use the blockproc() function in matlab to simplify this process

Answer 2

[TUMMALA ANIL CHOWDARY]

imshow(T);

This will give you DCT Coefficients