I want to filter the noised images.

Take a photo, add random noises to this image. I have to remove this noises by means of filtering.

hint :: conv2, gauss, fft2, ifft2, fftshift, mat2gray, imshow etc for display and basic operations.

hint :: I may also use median, mean, max, min, sort, etc.

============================================================================ I don't know how I do this.

Here is my current step....

I = imread('.jpg');

and make gray image, Igray.

Noise N. N = rand(size(Igray)); FI = fft2(Igray+N);

How do I use filters?

Answer 1

[Image Analyst]

You just run the filter function on your (badly-named) I image. For example, run medfilt2(), conv2(), wiener2(), etc. Here's a demo I've posted before to remove salt and pepper noise via a modified median filter:

clc;  % Clear command window.
clear;  % Delete all variables.
close all;  % Close all figure windows except those created by imtool.
imtool close all;  % Close all figure windows created by imtool.
workspace;  % Make sure the workspace panel is showing.
fontSize = 15;

% Read in a standard MATLAB demo image.
folder = fullfile(matlabroot, '\toolbox\images\imdemos');
baseFileName = 'coins.png';
% Get the full filename, with path prepended.
fullFileName = fullfile(folder, baseFileName);
if ~exist(fullFileName, 'file')
  % Didn't find it there.  Check the search path for it.
  fullFileName = baseFileName; % No path this time.
  if ~exist(fullFileName, 'file')
    % Still didn't find it.  Alert user.
    errorMessage = sprintf('Error: %s does not exist.', fullFileName);
    uiwait(warndlg(errorMessage));
    return;
  end
end
grayImage = imread(fullFileName);
% Get the dimensions of the image.  numberOfColorBands should be = 1.
[rows columns numberOfColorBands] = size(grayImage);
% Display the original image.
subplot(2, 2, 1);
imshow(grayImage);
title('Original Gray Scale Image', 'FontSize', fontSize);
% Enlarge figure to full screen.
set(gcf, 'Position', get(0,'Screensize')); 

% Generate a noisy image with salt and pepper noise.
noisyImage = imnoise(grayImage,'salt & pepper', 0.05);
subplot(2, 2, 2);
imshow(noisyImage);
title('Image with Salt and Pepper Noise', 'FontSize', fontSize);

% Median Filter the image:
medianFilteredImage = medfilt2(noisyImage, [3 3]);

% Find the noise.  It will have a gray level of either 0 or 255.
noiseImage = (noisyImage == 0 | noisyImage == 255);
% Get rid of the noise by replacing with median.
noiseFreeImage = noisyImage; % Initialize
noiseFreeImage(noiseImage) = medianFilteredImage(noiseImage); % Replace.
% Display the image.
subplot(2, 2, 3);
imshow(noiseFreeImage);
title('Restored Image', 'FontSize', fontSize);