Hi
It depends on your noise type. If it is white noise, averaging is good, but if it is like salt and pepper, using min or max or median filter are good. Matlab has a good demo, see it.
hi,
denoising is like subtracting a image with noise and ur original image without noise.
u can use various filters and check which one produces good SNR finally.
also u can apply wavelet transform for image denoising.