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  1. I was using yadif to deinterlace. I understand that a smart deinterlacer combines two fields to produce one full frame, which results in reducing the fps in half, but at least full vertical resolution is maintained.

    But now, I was searching for a higher quality deinterlacer, and I found QTGMC, but I'm very confused about how this deinterlacer maintains the full vertical resolution. If source is 25i and has 576px vertical resolution, and QTGMC output is 50fps, then all frames will have 288px vertical resolution upscaled and interpolated to 576px ? Or does it copy fields from other frames, for the current frame, in order to maintain 576px vertical resolution ?

    Because Yadif combines two half frames to make one full frame, and I want to make sure that, if I switch to QTGMC, vertical resolution will not be reduced. What deinterlacer will drop more from the vertical resolution, yadif or qtgmc ?
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    Originally Posted by codemaster View Post
    I was using yadif to deinterlace. I understand that a smart deinterlacer combines two fields to produce one full frame, which results in reducing the fps in half, but at least full vertical resolution is maintained.
    Incorrect. Depends on the settings. One method discard frames and maintains the same frame rate. The "usual"method doubles the number of frames and doubles the frame rate.

    Originally Posted by codemaster View Post
    But now, I was searching for a higher quality deinterlacer, and I found QTGMC, but I'm very confused about how this deinterlacer maintains the full vertical resolution. If source is 25i and has 576px vertical resolution, and QTGMC output is 50fps, then all frames will have 288px vertical resolution upscaled and interpolated to 576px ? Or does it copy fields from other frames, for the current frame, in order to maintain 576px vertical resolution ?

    Because Yadif combines two half frames to make one full frame, and I want to make sure that, if I switch to QTGMC, vertical resolution will not be reduced. What deinterlacer will drop more from the vertical resolution, yadif or qtgmc ?
    Wrong again. QTGMC works the same basic way with interlaced fields, but uses motion interpolation and more sophisticated denoising and repair techniques. By default QTGMC is a smart bobber like yadif. It doubles the number of frames and doubles the fps. You can discard Even or Odd frames to maintain the same fps, just as you can with yadif. Or you can re-interlace and have the same fps and number of frames you started with. QTGMC has more available settings to control sharpening, denoising, level of repair, etc. You can also use QTGMC in progressive mode on progressive video to clean up many artifacts and still get progressive video.

    If you're asking which of these smart bobbers usually produces higher quality output, it's QTGMC. How can you know for sure? Use it. Caution: be certain your source is interlaced, not telecined.
    Last edited by sanlyn; 25th Mar 2014 at 06:46.
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  3. Originally Posted by sanlyn View Post
    By default QTGMC is a smart bobber like yadif.
    One small correction. QTGMC is a bobber by default, yes, but Yadif is a single-rate deinterlacer at default settings. If you turn on 'Mode=1' it becomes a bobber. From the Yadif doc:
    Code:
    mode = 0 : temporal and spatial interlacing check (default).
         = 1 : double framerate (bob), temporal and spatial interlacing check.
    Use it.
    I agree. Too many questions and not enough experimentation. I think he was shown a deinterlacer comparison in a different thread.
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  4. Originally Posted by codemaster View Post
    QTGMC... I'm very confused about how this deinterlacer maintains the full vertical resolution.
    QTGMC examines multiple fields/frames to figure out what should go in the missing scan lines.

    Consider a still shot. Any two consecutive fields are complementary and can simply be woven together to make a complete frame with no loss of resolution.

    In a shot with a static background but something moving the foreground -- the background can be woven together as in a still shot. Only the moving parts of the image in the foreground need to be addressed further. With simple motions, like the object moved four pixels to the left, the scan lines can be filled by shifting the other field right by four pixels. Only with very complex motions (where QTGMC can't figure out how to use another field to fill the missing scan lines) will the filter have to resort to a technique that requires interpolation from only one field, losing resolution.
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