Use the DCT to interpolate the images

Use the DCT to interpolate the images by factors 1.75 and 0.6 to the nearest integer. This means if the original image is 1000x1000 a factor of 1.75 interpolation will result in the output image 1750x1750. Also note that in MATLAB you have to use the function 'dct2' for all 2D image processing applications.

Can anyone please guide me?

Answer 1

[Harsh]

Hi Nabiha,

From my understanding of the question, you want to interpolate the original image by a fixed constant factor. You can specify the output image row size and column size in the “dct2” function input arguments itself. Below is an example code which shows how to compute new row size and column size based on their original respective values and the factor.

% Get the size of the original image 
[rows, cols] = size(img); 
 
% Interpolation factor 
factor=1.75; 
 
% Calculate new size 
new_rows = round(rows * factor); 
new_cols = round(cols * factor); 
 
% Apply DCT 
dct_img = dct2(img,new_rows,new_cols); 

Please refer to the following documentation to understand more about “dct2” function - https://www.mathworks.com/help/images/ref/dct2.html

[Walter Roberson]

%example
img = im2double(imread('cameraman.tif'));
imshow(img)

% Get the size of the original image 
[rows, cols] = size(img); 
 
% Interpolation factor 
factor1=1.75;
factor2=0.6; 
 
% Calculate new size 
new_rows = round(rows * factor1); 
new_cols = round(cols * factor2); 
 
% Apply DCT 
dct_img = dct2(img,new_rows,new_cols); 

imshow(dct_img)

restored_img = idct2(dct_img);
imshow(restored_img)