how wa can discard 75% of small coefficients after get the DCT conversion of each image block?

Hi, i want to do this step on one image but i don't know how i can discard 75% of smal coefficients after get the DCT, please help me .

Can i do this without using for and if?

step:

Divide the input image into smaller blocks with dimensions nXn.

Get the DCT conversion of each image block.

Discard 75% of small coefficients.

Recreate and view the image

my code:

im=imread('s1.jpg');
im = rgb2gray(im);
figure;
imshow(im)
title('Original image');
img_dct=dct2(im);
figure;
imagesc(img_dct);
colormap(gray);
im_dct=idct2(img_dct);
title('DCT Compress Image');
figure;
imagesc(im_dct);
colormap(gray);

Answer 1

[Jonas]

use the

Y = prctile(block,75,'all')

command to get the 75% percentile, you can then set all values smaller than this threshold to 0 by

block(block<=Y)=0;

[mohammad nemat]

I get this error

Error using :

For colon operator with char operands, first and last operands must be char.

Error in prctile (line 48)

perm = [dim:max(nDimsX,dim) 1:dim-1];

simple code for test : my picture size 1024*1024

clc

close all

im=imread('j2.jpg');

im = rgb2gray(im);

Y = prctile(im,75,'all');

block(block<=Y)=0;

[Jonas]

the problem seems to be your image, using a matlab demo image works for me, does it for you?

im=imread('cameraman.tif');
imDct=dct2(im);
Y=prctile(abs(imDct),75,'all');
imDct(abs(imDct)<=Y)=0;
imshow(rescale(idct2(imDct)))

[Jonas]

you used the block variable before you assigned it! i thought you are doing block wise dct

edit: you wrote in your question that you have to do blockwise dct, have a look into the block processor

https://de.mathworks.com/help/images/ref/blockproc.html