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| author | Gerion Entrup <gerion.entrup@flump.de> | 2024-06-02 14:02:53 +0200 |
|---|---|---|
| committer | Michael Niedermayer <michael@niedermayer.cc> | 2024-06-07 21:42:23 +0200 |
| commit | 300df41c30c7767729e51be1d09cda02901f9b16 (patch) | |
| tree | 2d56d91d4f19fba1bfc5eec4bc5211718e7a3549 | |
| parent | 3152c684cb59e929ed572039ad9cdb3dde273dc3 (diff) | |
| download | ffmpeg-300df41c30c7767729e51be1d09cda02901f9b16.tar.gz | |
libavfilter/signature_lookup: fix jaccard distance
Actually, the jaccard distance is defined as D = 1 - intersect / union.
Additionally, the distance value is compared against a constant that
must be between 0 and 1, which is not the case here. Both facts together
has led to the fact, that the function always returned a matching course
signature. To leave the constant intact and to avoid floating point
computation, this commit multiplies with 1 << 16 making the constant
effectively 9000 / (1<<16) =~ 0.14.
Reported-by: Sachin Tilloo <sachin.tilloo@gmail.com>
Reviewed-by: Sachin Tilloo <sachin.tilloo@gmail.com>
Tested-by: Sachin Tilloo <sachin.tilloo@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
| -rw-r--r-- | libavfilter/signature_lookup.c | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/libavfilter/signature_lookup.c b/libavfilter/signature_lookup.c index a0ca818a9b..46602874de 100644 --- a/libavfilter/signature_lookup.c +++ b/libavfilter/signature_lookup.c @@ -127,9 +127,10 @@ static int get_jaccarddist(SignatureContext *sc, CoarseSignature *first, CoarseS { int jaccarddist, i, composdist = 0, cwthcount = 0; for (i = 0; i < 5; i++) { - if ((jaccarddist = intersection_word(first->data[i], second->data[i])) > 0) { + if ((jaccarddist = (1 << 16) * intersection_word(first->data[i], second->data[i])) > 0) { jaccarddist /= union_word(first->data[i], second->data[i]); } + jaccarddist = (1 << 16) - jaccarddist; if (jaccarddist >= sc->thworddist) { if (++cwthcount > 2) { /* more than half (5/2) of distances are too wide */ |