[FFmpeg-devel] [PATCH] lavfi/delogo: avoid propagation of rounding errors in chroma planes

[Michael Niedermayer]

On Tue, Jul 02, 2013 at 01:50:02PM +0200, Jean Delvare wrote:
> 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: Jean Delvare <khali at linux-fr.org>
> ---
>  libavfilter/vf_delogo.c      |    6 -
>  tests/ref/fate/filter-delogo |  218 +++++++++++++++++++++----------------------
>  2 files changed, 113 insertions(+), 111 deletions(-)

applied

thanks

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

it is not once nor twice but times without number that the same ideas make
their appearance in the world. -- Aristotle
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