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    • Jean Delvare's avatar
      lavfi/delogo: avoid propagation of rounding errors in chroma planes · f0bcb13a
      Jean Delvare authored
      When operating on subsampled chroma planes, some rounding is taking
      place. The left and top borders are rounded down while the width and
      height are rounded up, so all rounding is done outward to guarantee the
      logo area is fully covered.
      
      The problem is that the width and height are counted from the
      unrounded left and top borders, respectively. So if the left or top
      border position has indeed been rounded down, and the width or height
      needs no rounding (up), the position of the the right or bottom border
      will be effectively rounded down, i.e. inward.
      
      The issue can easily be seen with a yuv240p input and
        -vf delogo=45:45:60:40:show=1 -vframes 1 delogo-bug.png
      (or virtually any logo area with odd x and y and even width and
      height.) The right and bottom chroma borders (in green) are clearly
      off.
      
      In order to fix this, the width and height must be adjusted to include
      the bits lost in the rounding of the left and top border positions,
      respectively, prior to being themselves rounded up.
      Signed-off-by: 's avatarJean Delvare <khali@linux-fr.org>
      Signed-off-by: 's avatarMichael Niedermayer <michaelni@gmx.at>
      f0bcb13a
  23. 01 Jul, 2013 1 commit
    • Jean Delvare's avatar
      lavfi/delogo: use weighted interpolation · 16fd75ce
      Jean Delvare authored
      The original delogo algorithm interpolates both horizontally and
      vertically and uses the average to compute the resulting sample. This
      works reasonably well when the logo area is almost square. However
      when the logo area is significantly larger than high or higher than
      large, the result is largely suboptimal.
      
      The issue can be clearly seen by testing the delogo filter with a fake
      logo area that is 200 pixels large and 2 pixels high. Vertical
      interpolation gives a very good result in that case, horizontal
      interpolation gives a very bad result, and the overall result is poor,
      because both are given the same weight.
      
      Even when the logo is roughly square, the current algorithm gives poor
      results on the borders of the logo area, because it always gives
      horizontal and vertical interpolations an equal weight, and this is
      suboptimal on borders. For example, in the middle of the left hand
      side border of the logo, you want to trust the left known point much
      more than the right known point (which the current algorithm already
      does) but also much more than the top and bottom known points (which
      the current algorithm doesn't do.)
      
      By properly weighting each known point when computing the value of
      each interpolated pixel, the visual result is much better, especially
      on borders and/or for high or large logo areas.
      
      The algorithm I implemented guarantees that the weight of each of the
      4 known points directly depends on its distance to the interpolated
      point. It is largely inspired from the original algorithm, the key
      difference being that it computes the relative weights globally
      instead of separating the vertical and horizontal interpolations and
      combining them afterward.
      Signed-off-by: 's avatarJean Delvare <khali@linux-fr.org>
      Signed-off-by: 's avatarStefano Sabatini <stefasab@gmail.com>
      16fd75ce
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