Re: Sharpening

Discussion in 'Digital Photography' started by Martin Brown, Mar 23, 2013.

  1. Martin Brown

    Martin Brown Guest

    On 22/03/2013 22:38, Alfred Molon wrote:

    > Is there anything better than unsharp mask to sharpen an image? More
    > specifically, to compensate for a not so sharp lens or a (small)
    > autofocus error.
    >

    If you can characterise the exact point spread function *and* it in
    invariant across the field of view then astronomical deconvolution codes
    will do a better job but at a cost of some artefacts.

    That was how they sorted out the early Hubble images when it was
    hopelessly myopic but very precisely made to an incorrect shape.

    --
    Regards,
    Martin Brown
    Martin Brown, Mar 23, 2013
    #1
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  2. Martin Brown

    Martin Brown Guest

    On 23/03/2013 08:54, Alfred Molon wrote:
    > In article <WZd3t.925$>, Martin Brown says...
    >> If you can characterise the exact point spread function *and* it in
    >> invariant across the field of view then astronomical deconvolution codes
    >> will do a better job but at a cost of some artefacts.

    >
    > Has anybody done this for a not so sharp lens or a slightly defocused
    > image?


    Pretty much routine these days for certain types of forensics where the
    original photograph is important critical evidence and blurred.

    A very old example: http://www.maxent.co.uk/example_1.htm
    (done in the 1980's)

    Computational cost is about 200x normal linear inverse methods so it is
    still time consuming even today. But it can be done.

    You can get roughly 3x the raw image resolution on a good day with a
    trailing wind on the highlights and with sufficient signal to noise. The
    catch is that resolution then depends on local signal to noise.

    --
    Regards,
    Martin Brown
    Martin Brown, Mar 23, 2013
    #2
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