Solving contrast issues on in-flight video.

Discussion in 'Professional Video Production' started by Kevin Walton, Mar 2, 2004.

  1. Kevin Walton

    Kevin Walton Guest

    Hi

    I have taken a video from a remote control airplane:

    http://mach.unseen.org/~kevin/rc/05-02-03-04/

    zagi1-original.AVI or zagi1-original-medium.wmv.

    But have a classic problem in this type of footage that the auto
    contrast on the cheap camera deals very badly with the effects of the
    sun - making the ground and trees just black for large parts of the
    clip.

    Is there an easy way of processing the video to improve the contrast,
    preferably automatically for the full video.

    Thanks in advance
    Kev


    Northamptonshire, UK
     
    Kevin Walton, Mar 2, 2004
    #1
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  2. Kevin Walton

    MSu1049321 Guest

    First try putting a small hood on the front of the lens, this will cut incident
    light from triggering the auto-iris.

    You might also ask the experts at the aerial photography group at RCgroups.com.
    They've already been where you are with this.

    Fixing this in post is going to be lots of work and take a long time, only to
    get half-decent results. Better to fix it at the camera end first.
     
    MSu1049321, Mar 2, 2004
    #2
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  3. Kevin Walton

    Toby Guest

    If I were you I would set the iris to manual so that the sky was just about
    1/2 to 1 stop overexposed, or whatever is a good compromise between the
    correct exposure for the sky and the terrain. Even if the sky is a bit
    overexposed and the land a bit underexposed it is still going to be much
    better than that terribly objectionable pumping whenever the sky comes into
    frame, and will save you the problem of blackout whenever the sun comes into
    frame, even though the video will burn out in that situation.

    Toby
     
    Toby, Mar 3, 2004
    #3
  4. What kind of camera rig are you working with?
    Is it a camcorder that has a manual/auto adjustable iris?
    Or is it a cheap pinhole camera rigged to a transmitter or recorder?
    If the camera has any kind of ND filter on board, try rolling that in. You
    just might be forcing the camera to clamp down because the iris is letting
    WAY too much light in at f.22. Or......... if the camera has a manually
    adjustable iris, do a multiple of test flights at different exposures. Keep
    accurate notes of the results.

    Your kinda against a wall Kev if it a pinhole type camera. Those cheap
    little things don't really have any kind of manual iris "control", and
    because of that, you get the clamping you speak of.
    The only thing I can think of other than buying a more sophisticated camera
    is to try a low contrast filter.......... if you can find one that will fit
    your lens. If it's a pinhole type rig you are working with you will have to
    jury rig a low con filter in front of the lens.
    Other than that you may just have to use the camera on cloudy days and/or
    re-aim the camera to more of a 'look down' position.
     
    Bill Farnsworth, Mar 3, 2004
    #4
  5. Kevin Walton

    Derry Argue Guest

    Back when I was a nipper, it used to be possible to buy neutral
    density filters in various grades in sheet form for still
    photography. You just snipped off a piece and stuck it in front
    of the lens with tape. Try a professional photo supplier and
    then experiment.

    Derry
     
    Derry Argue, Mar 3, 2004
    #5
  6. Kevin Walton

    MSu1049321 Guest

    Hey, you can get a free swatchbook of filters from Rosco. ND is in there too,
    plenty big enouh sheet for pinhole lenses...
     
    MSu1049321, Mar 3, 2004
    #6
  7. Kevin Walton

    Kevin Walton Guest

    Hi Toby

    Unfortunataly I have no control over the Iris, it's a Aiptek Mini
    Pencam. Maybe there is a mod I can do to give me manual iris control?

    Cheers
    Kev
     
    Kevin Walton, Mar 3, 2004
    #7
  8. Kevin Walton

    Kevin Walton Guest

    Cool, already have the Rosco Book, and here we have Neutral Grey.
    Will try that in combination with some down angle and trying to fly
    closer to midday so the sun is directly above and see what happens!

    Im suprised that none of the pleathur of video editing software out
    there doesn't have an auto correct feature for what must be a fairly
    common problem though? Even if it only went half way and equalised
    the contrast across the full video, rather than doing 'horizon
    detection', or am I just asking for too much :)

    Cheers
    Kev
     
    Kevin Walton, Mar 4, 2004
    #8
  9. Kevin Walton

    MSu1049321 Guest

    << Im suprised that none of the plethora of video editing software out
    there doesn't have an auto correct feature for what must be a fairly
    common problem though? Even if it only went half way and equalised
    the contrast across the full video, rather than doing 'horizon
    detection', or am I just asking for too much :) >>

    Well, it is and it isn't Kev. You can select a section of video at whatever
    length you choose and bring the peaks down and the black level up, but your
    kind of footage is so dynamic, it really requires continuous tracking and
    adjustment for best look moment to moment, and this is such a subjective thing
    it's best done manually. If you want, you could download the free versions of
    FCP or Avid DV and try their color corrector tools, which do more than just
    correct colors, but levels as well.

    good luck with the Zagi, I have one sans motor I'm going to put a hi-start
    hook on (no slopes where I live). Do go visit Rcgroups,com and try the forum on
    aerial photography if you haven't yet been there... these guys have played with
    the Aiptek and mods for it already are available.
     
    MSu1049321, Mar 5, 2004
    #9
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