how can i make such an image by apllying DC processing?

input image is a 256X256 gray image, and I used dct2 to make a DCT image. then professor said I should set DC 32 X 32 =0 and IDCT back to get the output image,

and i dont know how to set 32X32 to 0....

please tell me the way to set 32x32 part of the dct input image to 0.

Answer 1

[Image Analyst]

Regarding your new, edited question, just figure out the rows and columns to set to zero. If you use fft2(), the origin is at the 4 corners. You'd have to erase each corner one at a time. Or else use fftshift() to move the origin to the middle, then erase, and then use ifftshift() to shift the origin back to the corners before caling ifft2. Here's a start

[rows, columns] = size(grayImage);
ft = fft2(grayImage);
ft = fftshift(ft);
row1 = rows/2 - 15;
row2 = row2 + 31;
col1 = ....
col2 = ....
ft(row1:row2, col1:col2) = 0;
ft = ifftshift(ft);
grayImage = real(ifft2(ft));
imshow(grayImage, [])

[DOHYUN JANG]

thank you very much!

Answer 2

[Image Analyst]

Yes, but not if you erase the central 32x32 chunk of it, representing the low spatial frequencies. It will have the effect of a high pass filter since you're setting all the low frequencies to zero. You will see enhanced edges, or even mostly all edges, in the output.