"Repairing" an out-of- focus picture
in [DSP]
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From: Nitram on 28 May 2010 23:52 Hi, My question might be simplistic as neither optics nor image processing is my field. Firstly, I was wondering if it is possible to compensate for a picture taken by an out-of-focus digital camera by doing a 2D deconvolution on it (MMSE filtering or something like that), in order to recover the in-focus picture Secondly, can the optical transfer function between a properly focused picture and an out of focus picture be parameterized in such a way that a user could recover the image by gradually varying that parameter until the image is in focus? If this is indeed possible, what is that transfer function? (any references to existing literature would be welcome). Thank you for your help.
From: Jerry Avins on 29 May 2010 00:02 On 5/28/2010 11:52 PM, Nitram wrote: > Hi, > > My question might be simplistic as neither optics nor image processing is > my field. > > Firstly, I was wondering if it is possible to compensate for a picture > taken by an out-of-focus digital camera by doing a 2D deconvolution on it > (MMSE filtering or something like that), in order to recover the in-focus > picture Yes, but not perfectly. Do you remember how the Hubble telescope started out? > Secondly, can the optical transfer function between a properly focused > picture and an out of focus picture be parameterized in such a way that a > user could recover the image by gradually varying that parameter until the > image is in focus? If this is indeed possible, what is that transfer > function? (any references to existing literature would be welcome). I think you need to start with the blurred image of a point somewhere in the frame. It is certainly easiest to get the point-spread function that way. > Thank you for your help. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
From: Steve Pope on 29 May 2010 00:02 Nitram <morris.vian(a)n_o_s_p_a_m.gmail.com> wrote: >Firstly, I was wondering if it is possible to compensate for a picture >taken by an out-of-focus digital camera by doing a 2D deconvolution on it >(MMSE filtering or something like that), in order to recover the in-focus >picture Sure, that's what they did with the Hubble before they had a chance to physically correct the out-of-focus objects. It only works on a bright clean picture though, as you are amplifying noise. That's about all I know. Steve
From: glen herrmannsfeldt on 29 May 2010 00:10 Jerry Avins <jya(a)ieee.org> wrote: > On 5/28/2010 11:52 PM, Nitram wrote: >> My question might be simplistic as neither optics nor image processing is >> my field. >> Firstly, I was wondering if it is possible to compensate for a picture >> taken by an out-of-focus digital camera by doing a 2D deconvolution on it >> (MMSE filtering or something like that), in order to recover the in-focus >> picture > Yes, but not perfectly. Do you remember how the Hubble > telescope started out? Specifically, the transfer function of Hubble was known extrememly accurately. They knew exactly what (wrong) curve had been applied to the mirror. >> Secondly, can the optical transfer function between a properly focused >> picture and an out of focus picture be parameterized in such a way that a >> user could recover the image by gradually varying that parameter until the >> image is in focus? If this is indeed possible, what is that transfer >> function? (any references to existing literature would be welcome). Get the book "Deconvolution of Images and Spectra" which has a good explanation of non-linear deconvolution. As the intensity can't go below zero, the non-linear techniques are probably best. Also, you need a really good signal to noise ratio. The early hubble pictures were of bright objects for that reason. > I think you need to start with the blurred image of a point somewhere in > the frame. It is certainly easiest to get the point-spread function that > way. -- glen
From: dbd on 29 May 2010 19:54
On May 29, 1:51 pm, spop...(a)speedymail.org (Steve Pope) wrote: > .... > > Yes. In the simplest case I believe the blur of defocusing is > like a 2-D sinc function. > > Steve > Sinc functions go negative in the first sidelobe. None of my blurred pictures have negative values. Dale B. Dalrymple |