问题描述:

An image is given to us that has been corrupted by:

- Gaussian blur
- Gaussian noise
- Motion blur

in that order. The parameters of all the above (filter size, variance, SNR, etc) are known to us.

How can we restore the image?

I have tried to compute the aggregate degradation function by convolving the above and then used the Weiner filter to restore, but the attempts have failed so far, since the blur still remains.

Could anyone please shed some light?

For Gaussian and motion blur, it is a matter of deducing the convolution kernel. Once it is known, deconvolution can be done in Fourier space. The Fourier transform of the image, divided by the Fourier transform of the kernel, gives the Fourier transform of a (hopefully) improved image.

Gaussians transform into other Gaussians, so there is no problem with divide by zero. But Gaussians do fall of rather fast, as exp(-x^2), so you'd be dividing by small numbers to obtain large whacky high frequency amplitudes. So, some sort constant bias or other way of keeping the FT of the kernal from getting small must be applied. That's where the Wiener filter comes in. The bias is usually chosen in relation to random noise levels, or quantization.

For motion blur, a typical case is when the clean image is convolved with a short line segment. Unfortunately, sharply cut-off line segments have plenty of zeros. Again, Wiener filter to the rescue.

Additive Guassian noise cannot be removed, but can be averaged out. The simplest quickest way is to blur the image with Gaussian, box, or other filter. Biggest problem with that - you end up with a blurred image! Median filters are somewhat better at preserving edges and details if not too small. There are many noise reduction techniques out there.

Sometimes noise reduction is easy for certain types of images. For Cassini imaging work, most image features were either high-contrast hard edges (planet edges, craters), or softly varying (cloud details in atmospheres) so I used an edge detector, fattened (dilated) its output, blurred it, and used that as a mask to protect parts of the image from a small-radius blur filter. Applying different filters.

There's Signal Processing Stack Exchange site (in beta for now) which may have questions and answers about restoring corrupted images. http://dsp.stackexchange.com/questions

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