clean noise from an image

Question

I need to know how to clean noise from an image with Matlab.

lets look at this example:

Answer 1

Since this question is tagged MATLAB, I translated @belisarius's solution as such (which I think is superior to the currently accepted answer):

%# read image
I = imread('http://i.stack.imgur.com/nGNGf.png');

%# complement it, and convert to HSV colorspace
hsv = rgb2hsv(imcomplement(I));
I1 = hsv(:,:,3);                %# work with V channel

%# Binarize/threshold image
I2 = im2bw(I1, 0.92);

%# Perform morphological thinning to get the skeleton
I3 = bwmorph(I2, 'thin',Inf);

%# prune the skeleton (remove small branches at the endpoints)
I4 = bwmorph(I3, 'spur', 7);

%# Remove small components
I5 = bwareaopen(I4, 30);

%# dilate image
I6 = imdilate(I5, strel('square',2*3+1));

%# show step-by-step results
figure('Position',[200 150 700 700])
subplot(711), imshow(I)
subplot(712), imshow(I1)
subplot(713), imshow(I2)
subplot(714), imshow(I3)
subplot(715), imshow(I4)
subplot(716), imshow(I5)
subplot(717), imshow(I6)

Finally you can apply some form of OCR to recognize the numbers. Unfortunately, MATLAB has no built-in function equivalent to TextRecognize[] in Mathematica... In the meanwhile, look in the File Exchange, I'm sure you will find dozens of submissions filling the gap :)