Re: Software to check if images are blurred

Discussion in 'Digital Photography' started by Martin Brown, Jun 20, 2012.

  1. Martin Brown

    Martin Brown Guest

    On 19/06/2012 17:44, Alfred Molon wrote:
    > Is there a software tool which can check if images are blurred? I'd like
    > to avoid checking images one by one.


    You cannot easily tell the difference between an image with low
    information content and a blurred one. White cat in a snowstorm or black
    cat in a coal cellar would look much the same in or out of focus!

    A quick heuristic is that the JPEG size is a good indicator of in focus
    detailed images.

    --
    Regards,
    Martin Brown
     
    Martin Brown, Jun 20, 2012
    #1
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  2. Martin Brown

    Martin Brown Guest

    On 20/06/2012 21:05, Alfred Molon wrote:
    > In article<XOdEr.10757$>, Martin Brown says...
    >
    >> You cannot easily tell the difference between an image with low
    >> information content and a blurred one. White cat in a snowstorm or black
    >> cat in a coal cellar would look much the same in or out of focus!
    >>
    >> A quick heuristic is that the JPEG size is a good indicator of in focus
    >> detailed images.

    >
    > Such a heuristic fails when for instance the image is very noisy or
    > contains large blocks of blue sky.


    But it *is* good enough as a first cut. It is almost always true that
    out of focus or motion blurred images are significantly more
    compressible and smaller than their adjacent peers from the same series.

    The generic class of algorithms to decide in or out of focus use some
    variant of the absolute maximum value of del-squared in the image as a
    rough figure of merit. Registax and similar are the place to look for
    more details. Lucky imaging by shifting and adding rapidly captured
    video streams is all the rage now for planetary imaging using webcams.
    The results are way better than professional observatories were ever
    able to do with film! And have shown that Jupiter takes hits from comets
    rather more often than we realised. There are usually at least a couple
    of amateurs videoing Jupiter somewhere in the world.

    http://impact.arc.nasa.gov/news_detail.cfm?ID=182
    and
    http://jupiter.samba.org/jupiter/20100603-203129-impact/index.html

    Same very dedicated guy and another fireball.


    > I was thinking that such a tool would use a combination of spatial
    > frequency analysis (fast fourier transform the image and analyse the
    > frequency content, trying to distinguish noise from useful signal) and
    > for instance looking whether there are any straight lines and whether
    > the luminance gradient along these lines is steep. This should all be
    > easily doable by image analysis software.


    The devil is in the detail. For any algorithm you come up with I can
    devise a large number of images to fail the test you propose. There are
    plenty of high quality images where only a small part of it is in good
    focus and the background has been deliberately blurred for effect.

    Wildlife photography and some portraiture for example.
    >
    > I would think that large photo agencies such as Alamy for instance who
    > receive thousands of photo submissions per day probably have some tools
    > to pre-analyse images and detect noise levels, overall sharpness etc.
    > Would make sense.


    Yes. But it is a specialised field. Any simple algorithm will fail to
    categorise far too many otherwise good images. It is not for nothing
    that there are still requests from professional astronomers for amateurs
    to examine the bulk data and classify galaxies for them.

    The Mk1 eyeball is very hard to beat for some tasks.

    --
    Regards,
    Martin Brown
     
    Martin Brown, Jun 20, 2012
    #2
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  3. Mxsmanic <> wrote:
    > Alfred Molon writes:


    >> I would think that large photo agencies such as Alamy for instance who
    >> receive thousands of photo submissions per day probably have some tools
    >> to pre-analyse images and detect noise levels, overall sharpness etc.
    >> Would make sense.


    > No, it wouldn't. Photo agencies have to examine each photo using a human
    > being.


    Only those they accept.

    > Therefore automation serves no purpose.


    Therefore you are wrong.

    -Wolfgang
     
    Wolfgang Weisselberg, Jun 24, 2012
    #3
  4. Mxsmanic <> wrote:
    > Wolfgang Weisselberg writes:


    >> Only those they accept.


    > They decide which ones to accept by having a human being look at them.


    They decide which ones to have humans look at ...

    -Wolfgang
     
    Wolfgang Weisselberg, Jun 26, 2012
    #4
  5. Mxsmanic <> wrote:
    > Wolfgang Weisselberg writes:


    >> They decide which ones to have humans look at ...


    > How can they do that without the aid of human beings?


    By mechanical checks.

    For a very simple example even you ought to comprehend, if they
    say they need at least 6 MByte shots[1], they won't need to look
    at a 200x300 pixel shot.

    See: They can decide not to look at some images without having
    a human look at them.

    QED.


    -Wolfgang

    [1] or 10 or 20 or whatever --- point is not, if *you* feel
    that's sensible, point is they won't take it otherwise.
     
    Wolfgang Weisselberg, Jun 29, 2012
    #5
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