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commit dae77f2d458b6d47ed903dabd05f2bbbeb194e6b Author: Niklas Haas <[email protected]> AuthorDate: Tue Sep 1 21:29:41 2026 +0200 Commit: Niklas Haas <[email protected]> CommitDate: Sun Nov 8 00:36:29 2026 +0000 swscale/filters: properly handle filter tails When the filter overlaps an image boundary, we need to add all the weights past the edge to the appropriate edge weight. Apart from generating correct filtering behavior near boundaries, this also fixes an edge case where the `wsum < 0` guard could fire, as well as some examples of catastrophic filter overshoot. Signed-off-by: Niklas Haas <[email protected]> --- libswscale/filters.c | 34 ++++++++++++++++++++++------------ 1 file changed, 22 insertions(+), 12 deletions(-) diff --git a/libswscale/filters.c b/libswscale/filters.c index 3073ed8cdc..811c5729ec 100644 --- a/libswscale/filters.c +++ b/libswscale/filters.c @@ -82,13 +82,11 @@ static void compute_row(SwsFilterWeights *f, const SwsFilterFunction *fun, return; } - /* First pixel that is actually within the filter envelope */ - const double start_pos = src_pos - radius; - int64_t start_idx = ceil(start_pos); - start_idx = FFMAX(start_idx, 0); /* edge clamping */ - start_idx = FFMIN(start_idx, f->src_size - f->filter_size); - const double offset = start_idx - src_pos; - *pos = start_idx; + /* First and last pixels that are actually within the filter envelope */ + const int start = ceil (src_pos - radius); + const int stop = floor(src_pos + radius); + const int clamped = av_clip(start, 0, f->src_size - f->filter_size); + *pos = clamped; /** * Generate raw filter weights with maximum precision. Sum the positive @@ -96,14 +94,26 @@ static void compute_row(SwsFilterWeights *f, const SwsFilterFunction *fun, * summation order should already give the best precision because abs(w) * is monotonically decreasing */ - const double base = stretch_inv * offset; + const double base = stretch_inv * (clamped - src_pos); double wsum_pos = 0.0, wsum_neg = 0.0; for (int i = 0; i < f->filter_size; i++) { - tmp[i] = scaler_sample(fun, base + stretch_inv * i); - if (tmp[i] >= 0) - wsum_pos += tmp[i]; + /* Fold extra edge weights into the first/last weight in case the + * filter got truncated; loop over all needed samples */ + int i0 = i, i1 = i; + if (i == 0) + i0 = start - clamped; + if (i == f->filter_size - 1) + i1 = stop - clamped; + + double w = 0.0; + for (int k = i0; k <= i1; k++) + w += scaler_sample(fun, base + stretch_inv * k); + + if (w >= 0) + wsum_pos += w; else - wsum_neg += tmp[i]; + wsum_neg += w; + tmp[i] = w; } const double wsum = wsum_pos + wsum_neg; -- To stop receiving notification emails like this one, please contact [email protected]. _______________________________________________ ffmpeg-cvslog mailing list -- [email protected] To unsubscribe send an email to [email protected]
