online photograph assessment visual acuity and contrast sensitivity?

Discussion in 'Optometry Archives' started by docmaas, Nov 10, 2008.

  1. docmaas

    docmaas Guest

    I look at quite a few images online as I am an amateur photographer.
    One thing I've noticed is that there is a pretty wide range of
    abilities in being able to discern the differences between images.

    Often people will compare two cameras on the same image. And when
    they do some people can see pretty significant differences and others
    seem to be unable to see any difference at all.

    In order to help the debates along a little I would like to find a way
    to objectively or at least quasi-objectively be able to test the
    ability to discern differences between two images.

    Here are two that are currently being discussed on www.dpreview.com in
    the sigma forum:
    http://forums.dpreview.com/forums/readflat.asp?forum=1027&thread=29963586

    The images are at:
    http://www.pbase.com/franklin/image/105711528
    http://www.pbase.com/franklin/image/105709356

    These two images are from cameras with vastly different capabilities
    and one would expect there to be differences simply base on the sensor
    size, pixel pitch and number of pixels, yet some seem to be unable to
    see the difference. Aside from the blue sky and objects in the very
    far background from around the grocery cart next to a car in the
    parking lot and further back, the remainder of the pictures shows much
    better granularity, edge sharpness and clarity in the latter image
    than in the former. It's not unexpected given the two cameras. What
    puzzles me is why some people seem unable to see these differences.

    Is there somewhere online a test that would help objectively assess
    the abilities of the participants in the convsersations so that they
    could realize their abilities or lack thereof?

    thanks,

    Mike
     
    docmaas, Nov 10, 2008
    #1
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  2. docmaas

    otisbrown Guest

    Dear Mike,

    The term "Visual Acuity" does not necessarily mean an evaluation of a
    picture -- which tends to be subjective, given color, light and many
    other factors.

    Ther is a more restrictive definition in science. And for the human
    eye, it means the ability to "resolve" to points of light to
    one minute-of-arc.

    Thus, in photographic plates in astronomy, the judgment is in
    the ability of the photograph to resolve the separation of
    stars (as a pratical matter).

    Thus in a camera, you should talk about "resolution" in those terms --
    in
    an objective manner.

    The other issues are subjective, and you can not convince a person
    that one "shading" is "better" than another -- you just
    wind up with endless arguments about which is better.

    But enjoy our conversations on this topic.
     
    otisbrown, Nov 10, 2008
    #2
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  3. docmaas

    ShadowTek Guest

    When I was a kid, I always wondered why the pictures I took looked so much
    more vibrant than in my memory. When I went to get my drivers licence for
    the first time and had to take the standard eye exam, I found out that I
    was nearsighted and needed glasses, so that explained it.
     
    ShadowTek, Nov 10, 2008
    #3
  4. docmaas

    docmaas Guest

    Yes, I know that. I had done some research prior to my post and that
    is why the "contrast sensitivity" showed up in the title as well. I
    did find an online test for that aspect of vision and it is more like
    what I am looking for.

    If you care to look at the two images I posted links for it is quite
    clear to me that the granularity of definition in one is far superior
    to that in the other. It's not a focus issue but a resolution issue.
    Some people don't seem to be able to see this and I was looking for a
    test that might help to objectify the different levels of ability to
    see these differences between observers. The test at:
    http://www.contrastsensitivity.net/cstvs2.html may help if used at
    appropriate distances. My own test results are perfect in the left
    eye and with both eyes and failure with my right eye in which I have
    amblyopia. Perhaps the fact that I have had these extremes for my
    entire life have made me more sensitive to these differences than
    others.

    Still looking for further suggestions if anyone has them.

    thanks,

    Mike
    Yes
     
    docmaas, Nov 10, 2008
    #4
  5. docmaas

    Jan Guest

    schreef:
    No.

    Jan (normally Dutch spoken)
     
    Jan, Nov 10, 2008
    #5
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