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commit f6a2d41fe2f3316b05dffdce96f867a0b9bf88cd Author: Niklas Haas <[email protected]> AuthorDate: Fri Mar 27 19:18:43 2026 +0100 Commit: Niklas Haas <[email protected]> CommitDate: Sun Mar 29 12:13:11 2026 +0200 swscale/ops: keep track of correct dither min/max Mostly, this just affects the metadata in benign ways, e.g.: rgb24 -> yuv444p: [ u8 +++X] SWS_OP_READ : 3 elem(s) packed >> 0 min: {0, 0, 0, _}, max: {255, 255, 255, _} [ u8 +++X] SWS_OP_CONVERT : u8 -> f32 min: {0, 0, 0, _}, max: {255, 255, 255, _} [f32 ...X] SWS_OP_LINEAR : matrix3+off3 [...] min: {16, 16, 16, _}, max: {235, 240, 240, _} [f32 ...X] SWS_OP_DITHER : 16x16 matrix + {0 3 2 -1} - min: {33/2, 33/2, 33/2, _}, max: {471/2, 481/2, 481/2, _} + min: {16.001953, 16.001953, 16.001953, _}, max: {235.998047, 240.998047, 240.998047, _} [f32 +++X] SWS_OP_CONVERT : f32 -> u8 min: {16, 16, 16, _}, max: {235, 240, 240, _} [ u8 XXXX] SWS_OP_WRITE : 3 elem(s) planar >> 0 (X = unused, z = byteswapped, + = exact, 0 = zero) However, it surprisingly actually includes a semantic change, whenever converting from limited range to monob or monow: yuv444p -> monow: [ u8 +XXX] SWS_OP_READ : 1 elem(s) planar >> 0 min: {0, _, _, _}, max: {255, _, _, _} [ u8 +XXX] SWS_OP_CONVERT : u8 -> f32 min: {0, _, _, _}, max: {255, _, _, _} [f32 .XXX] SWS_OP_LINEAR : luma [...] min: {-20/219, _, _, _}, max: {235/219, _, _, _} [f32 .XXX] SWS_OP_DITHER : 16x16 matrix + {0 -1 -1 -1} - min: {179/438, _, _, _}, max: {689/438, _, _, _} + min: {-0.089371, _, _, _}, max: {2.071106, _, _, _} + [f32 .XXX] SWS_OP_MAX : {0 0 0 0} <= x + min: {0, _, _, _}, max: {2.071106, _, _, _} [f32 .XXX] SWS_OP_MIN : x <= {1 _ _ _} - min: {179/438, _, _, _}, max: {1, _, _, _} + min: {0, _, _, _}, max: {1, _, _, _} [f32 +XXX] SWS_OP_CONVERT : f32 -> u8 min: {0, _, _, _}, max: {1, _, _, _} [ u8 XXXX] SWS_OP_WRITE : 1 elem(s) planar >> 3 (X = unused, z = byteswapped, + = exact, 0 = zero) Note the presence of an extra SWS_OP_MAX, to correctly clamp sub-blacks (values below 16) to 0.0, rather than underflowing. This was previously undetected because the dither was modelled as adding 0.5 to every pixel value, but that's only true on average - not always. Signed-off-by: Niklas Haas <[email protected]> --- libswscale/ops.c | 5 +++++ tests/ref/fate/sws-ops-list | 2 +- 2 files changed, 6 insertions(+), 1 deletion(-) diff --git a/libswscale/ops.c b/libswscale/ops.c index c281305766..896b0564ec 100644 --- a/libswscale/ops.c +++ b/libswscale/ops.c @@ -304,6 +304,7 @@ void ff_sws_op_list_update_comps(SwsOpList *ops) switch (op->op) { case SWS_OP_READ: case SWS_OP_LINEAR: + case SWS_OP_DITHER: case SWS_OP_SWAP_BYTES: case SWS_OP_UNPACK: case SWS_OP_FILTER_H: @@ -364,9 +365,13 @@ void ff_sws_op_list_update_comps(SwsOpList *ops) case SWS_OP_DITHER: /* Strip zero flag because of the nonzero dithering offset */ for (int i = 0; i < 4; i++) { + op->comps.min[i] = prev.min[i]; + op->comps.max[i] = prev.max[i]; if (op->dither.y_offset[i] < 0) continue; op->comps.flags[i] = prev.flags[i] & ~SWS_COMP_ZERO; + op->comps.min[i] = av_add_q(op->comps.min[i], op->dither.min); + op->comps.max[i] = av_add_q(op->comps.max[i], op->dither.max); } break; case SWS_OP_UNPACK: diff --git a/tests/ref/fate/sws-ops-list b/tests/ref/fate/sws-ops-list index f24c95f388..0dc23800a6 100644 --- a/tests/ref/fate/sws-ops-list +++ b/tests/ref/fate/sws-ops-list @@ -1 +1 @@ -a2ed0581163448a2c398ee9992e8eaf6 +374319dfd2b74cb5b69dac68b627fa9b _______________________________________________ ffmpeg-cvslog mailing list -- [email protected] To unsubscribe send an email to [email protected]
