Inverse dct in matlab

So I want to remove the higher frequency dct from an image and reconstruct it, so i followed an example by Matlab https://www.mathworks.com/help/images/ref/dct2.html. However, when i tried with my own image, it didn't turn out to be great. I'm using an image:

and i followed every step in the link with:

img = imread('giraffe.png');
img = rgb2gray(img);
J = dct2(img);
figure
imshow(log(abs(J)),[])
colormap(gca,jet(64))
colorbar

The colorbar

J(abs(J) < 10) = 0;
img_r = idct2(J);
imshow(img_r)

But my output image became:

Why did this happen?

Answer 1

[R.G.]

Hello! Just specify display range. Use imshow(img_r, [0 255]) instead.

I've checked it.

img = imread('giraffe.png');
img = rgb2gray(img);
J = dct2(img);
J(abs(J) < 100) = 0;
img_r = idct2(J);
imshow(img_r, [0 255])