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475b11b2e0
This is a complete rewrite of the math in swscale/utils.c initFilter(), using floating point math and with a bit more polished UI and internals. I have also included a substantial number of improvements, including a method to numerically compute the true filter support size from the parameters, and a more robust logic for the edge conditions. The upshot of these changes is that the filter weight computation is now much simpler and faster, and with fewer edge cases. I copy/pasted the actual underlying kernel functions from libplacebo, so this math is already quite battle-tested. I made some adjustments to the defaults to align with the existing defaults in libswscale, for backwards compatibility. Note that this commit introduces a lot more filter kernels than what we actually expose; but they are cheap to carry around, don't take up binary space, and will probably save some poor soul from incorrectly reimplementing them in the future. Plus, I have plans to expand the list of functions down the line, so it makes sense to just define them all, even if we don't necessarily use them yet. Sponsored-by: Sovereign Tech Fund Signed-off-by: Niklas Haas <git@haasn.dev>
114 lines
3.8 KiB
C
114 lines
3.8 KiB
C
/*
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* Copyright (C) 2026 Niklas Haas
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*
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* This file is part of FFmpeg.
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*
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* FFmpeg is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* FFmpeg is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with FFmpeg; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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#ifndef SWSCALE_FILTERS_H
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#define SWSCALE_FILTERS_H
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#include <libavutil/refstruct.h>
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#include "swscale.h"
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/* Design constants of the filtering subsystem */
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enum {
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/**
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* 14-bit coefficients are picked to fit comfortably within int16_t
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* for efficient SIMD processing (e.g. pmaddwd on x86). Conversely, this
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* limits the maximum filter size to 256, to avoid excessive precision
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* loss. (Consider that 14 - 8 = 6 bit effective weight resolution)
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*
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* Note that this limitation would not apply to floating-point filters,
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* and in a future update to this code, we could gain the ability to
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* generate unbounded floating point filters directly.
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*/
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SWS_FILTER_SCALE = (1 << 14),
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SWS_FILTER_SIZE_MAX = 256,
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};
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/* Parameters for filter generation. */
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typedef struct SwsFilterParams {
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/**
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* The filter kernel and parameters to use.
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*/
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SwsScaler scaler;
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double scaler_params[SWS_NUM_SCALER_PARAMS];
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/**
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* The relative sizes of the input and output images. Used to determine
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* the number of rows in the output, as well as the fractional offsets of
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* the samples in each row.
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*/
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int src_size;
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int dst_size;
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} SwsFilterParams;
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/**
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* Represents a computed filter kernel.
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*/
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typedef struct SwsFilterWeights {
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/**
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* The number of source texels to convolve over for each row.
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*/
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int filter_size;
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/**
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* The computed look-up table (LUT). This is interpreted as a 2D array with
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* dimensions [dst_height][row_size]. The inner rows contain the `row_size`
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* samples to convolve with the corresponding input pixels. The outer
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* coordinate is indexed by the position of the sample to reconstruct.
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*/
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int *weights; /* refstruct */
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size_t num_weights;
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/**
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* The computed source pixel positions for each row of the filter. This
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* indexes into the source image, and gives the position of the first
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* source pixel to convolve with for each entry.
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*/
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int *offsets; /* refstruct */
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/**
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* Copy of the parameters used to generate this filter, for reference.
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*/
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int src_size;
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int dst_size;
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/**
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* Extra metadata about the filter, used to inform the optimizer / range
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* tracker about the filter's behavior.
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*/
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char name[16]; /* name of the configured filter kernel */
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int sum_positive; /* (maximum) sum of all positive weights */
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int sum_negative; /* (minimum) sum of all negative weights */
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} SwsFilterWeights;
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/**
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* Generate a filter kernel for the given parameters. The generated filter is
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* allocated as a refstruct and must be unref'd by the caller.
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*
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* Returns 0 or a negative error code. In particular, this may return:
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* - AVERROR(ENOMEM) if memory allocation fails.
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* - AVERROR(EINVAL) if the provided parameters are invalid (e.g. out of range).
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* - AVERROR(ENOTSUP) if the generated filter would exceed SWS_FILTER_SIZE_MAX.
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**/
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int ff_sws_filter_generate(void *log_ctx, const SwsFilterParams *params,
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SwsFilterWeights **out);
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#endif /* SWSCALE_FILTERS_H */
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