"perfect" cut outs?

Discussion in 'Photoshop Tutorials' started by bugbear, Feb 1, 2006.

  1. bugbear

    bugbear Guest

    In films it is now routine to shoot against
    blue (or green) backgrounds, and get absolutely perfect
    cut-out masks, such that the cut
    out character can be merged into a new background
    (with no "blur", "edge" or other artefacts),
    over 100's of film frames.

    These technique
    appear to be fully automated, and not involve
    selecting, drawing, "magic wands" etc.

    Does anyone know enough about these techniques
    to apply them to a simple, single still image,
    using standard desktop apps (Gimp, Photoshop,
    ImageMagick etc).

    bugbear, Feb 1, 2006
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  2. bugbear

    Bigguy Guest

    Google for Ultimatte and Primatte

    For moving pics (video) you really need After Effects with a Matte / Keyer

    There are also many hardware solutions for matte / key / composite work.

    Bigguy, Feb 1, 2006
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  3. bugbear

    Pat Guest

    Do a google seach fore "Chromakey Photoshop" and a bunch of stuff comes
    up, including this link that explains it pretty well.


    The other place you see it every day, nearly flawlessly, is the weather
    forecast. Watch the weather guy, he isn't looking at the map, he is
    looking to the side of the map so that he can see himself in front of
    the map. He also generally has a monitor in front of him so see
    himself in front of the map. Here, you have the technique being done
    live. It is also why he doesn't wear a blue shirt or tie.
    Pat, Feb 1, 2006
  4. bugbear

    bugbear Guest

    Ouch. After googling, I'll need to pull some
    overtime :)

    I can't find any "magic" sequences that one
    could do in PhotoShop or Gimp etc.

    But there are some good algorithms
    "coming down the pike"

    "bayesian matting" shows better results
    than ultimatte (in some contexts)

    A Bayesian Approach to Digital Matting (2001)

    And this has been followed up by:
    Trimap Segmentation for Fast and User-Friendly Alpha Matting

    and something called siox is heading for the Gimp.

    bugbear, Feb 1, 2006
  5. It is an interesting use of technology to replicate a low tech
    solution. The better question is why do we need to see the weatherman
    at all? That blocks the map, just show the map and a pointer. That
    does it all in the computer much cheaper. But people like to see the

    Matt Silberstein

    Do something today about the Darfur Genocide


    "Darfur: A Genocide We can Stop"
    Matt Silberstein, Feb 1, 2006
  6. bugbear

    gpsman Guest

    Chroma-key or green screen? Select the background color using your
    preferred method of choice and delete.

    Create a New Layer and paste in your background of choice.

    In film it's sometimes referred to as A-B roll, mixing 2 sources (roll
    A & roll B) to create a composite image using the control or editing

    There's also Lumi-key, less precise but doing the same thing based on
    the luminence of the original image.
    gpsman, Feb 1, 2006
  7. bugbear

    C J Southern Guest

    Photoshop has a background eraser too that can do a reasonable job if your
    (preferably monochrome) background is well saturated and evenly lit, and
    you're prepared to be patient experimenting with the best tolerance.
    C J Southern, Feb 1, 2006
  8. bugbear

    Steve Guest

    In other words, it doesn't work that well. I often wondered why Paint
    Shop Pro's background eraser works so much better that Photoshops ...
    I'm still wondering.
    Steve, Feb 1, 2006
  9. bugbear

    C J Southern Guest

    It's proportional to the saturation of the chromakey and the evenness of the
    Can't help you there - I've never used PSP.
    C J Southern, Feb 1, 2006
  10. bugbear

    Chip Gallo Guest

    Corel KnockOut 2. I haven't used it but a friend who does a lot of
    background removal for artistic photos used the original Knockout (pre
    Corel) and swore by it.

    Chip Gallo
    Chip Gallo, Feb 2, 2006
  11. bugbear

    Stewy Guest

    Provided the thing you want to cutout is sharply focused, or has good
    contrast with the background, the magnetic lasso will work. You simply
    tidy up the few errors with an ordinary lasso adding or subtracting from
    the selection. Feathering is necessary but only with a few pixels
    otherwise you'll end up with a halo. This can be minimized with a very
    soft eraser with the opacity down to 30%. Hair (and other complicated
    outlines) is one of the biggest problems, but the clone tool or smudge
    tool can help here. Quick mask mode should give a clear indication of
    what you can expect.
    Stewy, Feb 7, 2006
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