Deblurring an Image using inverse filtering
I am trying to deblur an image using inverse filtering that was blurred using a 25x25 gaussian blur function with sigma = 15. I am extracting the blurred image from a .mat file, displaying it which works correctly. Next I define my gaussian filter and then compute frequency reponse of the filter. To deblur the image, I divide blurred image by frequency response of the filter and take ifft. The blurred image displays correctly in figure 1, but figure 2 which should display deblurred image displays all purple. I am trying to keep my code as simple and minimal as possible. What I am doing wrong here? I will appreciate any hints or inputs images = load('project_images.mat'); % Load the mat file containing images m_blur = images.mandrill_blurred; % Extract the first image imagesc(m_blur); % display the blurred image h = fspecial('gaussian',[25 25],15); % 25x25 Gaussian blur function with sigma = 15 hf = fft2(h,size(m_blur,1),size(m_blur,2)); m_deblur = real(ifft2(m_blur)./hf); %inverse filter figure(2) imagesc(m_deblur) % Display deblurred image
Prashant Kumar answered .
2025-11-20
A bit of data exploration shows that you have quite an outlier in your image:
figure(3),clf(3) histogram(m_deblur) set(gca,'YScale','log') axis([-10 140 0.1 max(ylim)])
Once you replace that with a 0, the automatic scaling should work as expected again. In the code below I went a bit further and set the caxis value manually to something that felt about right.
figure(2) imagesc(m_deblur) % Display deblurred image caxis([-0.15 0.15])
So in conlusion: this image is not ready yet.
The reason for this is that you didn't put the blurred image in the Fourier domain yet, so the division doesn't make a lot of sense.
images = load('mandrill_blurred.mat'); % Load the mat file containing images
m_blur = images.mandrill_blurred; % Extract the first image
imagesc(m_blur); % display the blurred image
h = fspecial('gaussian',[25 25],15); % 25x25 Gaussian blur function with sigma = 15
hf = fft2(h,size(m_blur,1),size(m_blur,2));
m_deblur = real(ifft2(fft2(m_blur)./hf)); %inverse filter
% ^^^^^ ^ ^
% you forgot this
figure(2)
imagesc(m_deblur) % Display deblurred image