From 2e0b635a57c39ca0ff968904370fc1a7b2cb7a2a Mon Sep 17 00:00:00 2001 From: Kostya Shishkov Date: Sat, 23 Aug 2008 15:49:58 +0000 Subject: Simple lowpass filter implementation. Originally committed as revision 14921 to svn://svn.ffmpeg.org/ffmpeg/trunk --- libavcodec/lowpass.c | 129 +++++++++++++++++++++++++++++++++++++++++++++++++++ libavcodec/lowpass.h | 83 +++++++++++++++++++++++++++++++++ 2 files changed, 212 insertions(+) create mode 100644 libavcodec/lowpass.c create mode 100644 libavcodec/lowpass.h diff --git a/libavcodec/lowpass.c b/libavcodec/lowpass.c new file mode 100644 index 0000000000..7159a1ee02 --- /dev/null +++ b/libavcodec/lowpass.c @@ -0,0 +1,129 @@ +/* + * Lowpass IIR filter + * Copyright (c) 2008 Konstantin Shishkov + * + * This file is part of FFmpeg. + * + * FFmpeg is free software; you can redistribute it and/or + * modify it under the terms of the GNU Lesser General Public + * License as published by the Free Software Foundation; either + * version 2.1 of the License, or (at your option) any later version. + * + * FFmpeg is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + * Lesser General Public License for more details. + * + * You should have received a copy of the GNU Lesser General Public + * License along with FFmpeg; if not, write to the Free Software + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA + */ + +/** + * @file lowpass.c + * lowpass filter implementation + */ + +#include "lowpass.h" + +/********************** + * TODO: + * support filters with order != 4 + * calculate coefficients for filter instead of taking approximate ones from the table + *********************/ + +/** filter order */ +#define LOWPASS_FILTER_ORDER 4 + +/** + * IIR filter global parameters + */ +typedef struct FFLPFilterCoeffs{ + float gain; + float c[LOWPASS_FILTER_ORDER]; +}FFLPFilterCoeffs; + +/** + * filter data for 4th order IIR lowpass Butterworth filter + */ +static const FFLPFilterCoeffs lp_filter_coeffs[] = { + { 9.398085e-01, { -0.0176648009, 0.0000000000, -0.4860288221, 0.0000000000 } }, + { 6.816645e-01, { -0.4646665999, -2.2127207402, -3.9912017501, -3.2380429984 } }, + { 4.998150e-01, { -0.2498216698, -1.3392807613, -2.7693097862, -2.6386277439 } }, + { 3.103469e-01, { -0.0965076902, -0.5977763360, -1.4972580903, -1.7740085241 } }, + { 2.346995e-01, { -0.0557639007, -0.3623690447, -1.0304538354, -1.3066051440 } }, + { 1.528432e-01, { -0.0261686639, -0.1473794606, -0.6204721225, -0.6514716536 } }, + { 6.917529e-02, { -0.0202414073, 0.0780167640, -0.5277442247, 0.3631641670 } }, + { 6.178391e-02, { -0.0223681543, 0.1069446609, -0.5615167033, 0.4883976841 } }, + { 5.298685e-02, { -0.0261686639, 0.1473794606, -0.6204721225, 0.6514716536 } }, + { 2.229030e-02, { -0.0647354087, 0.4172275190, -1.1412129810, 1.4320761385 } }, + { 1.693903e-02, { -0.0823177861, 0.5192354923, -1.3444768251, 1.6365345642 } }, + { 7.374053e-03, { -0.1481421788, 0.8650973862, -1.9894244796, 2.1544844308 } }, + { 5.541768e-03, { -0.1742301048, 0.9921936565, -2.2090801108, 2.3024482658 } }, +}; + +/** cutoff ratios for lp_filter_data[] */ +static const float lp_cutoff_ratios[] = { + 0.5000000000, 0.4535147392, 0.4166666667, 0.3628117914, + 0.3333333333, 0.2916666667, 0.2267573696, 0.2187500000, + 0.2083333333, 0.1587301587, 0.1458333333, 0.1133786848, + 0.1041666667, +}; + +/** + * IIR filter state + */ +typedef struct FFLPFilterState{ + float x[LOWPASS_FILTER_ORDER]; +}FFLPFilterState; + +const struct FFLPFilterCoeffs* ff_lowpass_filter_init_coeffs(int order, float cutoff_ratio) +{ + int i, size; + + //we can create only order-4 filters with cutoff ratio <= 0.5 for now + if(order != LOWPASS_FILTER_ORDER) return NULL; + + size = sizeof(lp_cutoff_ratios) / sizeof(lp_cutoff_ratios[0]); + if(cutoff_ratio > lp_cutoff_ratios[0]) + return NULL; + for(i = 0; i < size; i++){ + if(cutoff_ratio >= lp_cutoff_ratios[i]) + break; + } + if(i == size) + i = size - 1; + return &lp_filter_coeffs[i]; +} + +struct FFLPFilterState* ff_lowpass_filter_init_state(int order) +{ + if(order != LOWPASS_FILTER_ORDER) return NULL; + return av_mallocz(sizeof(FFLPFilterState)); +} + +#define FILTER(i0, i1, i2, i3) \ + in = *src * c->gain \ + + c->c[0]*s->x[i0] + c->c[1]*s->x[i1] \ + + c->c[2]*s->x[i2] + c->c[3]*s->x[i3]; \ + res = (s->x[i0] + in )*1 \ + + (s->x[i1] + s->x[i3])*4 \ + + s->x[i2] *6; \ + *dst = av_clip_int16(lrintf(res)); \ + s->x[i0] = in; \ + src += sstep; \ + dst += dstep; \ + +void ff_lowpass_filter(const struct FFLPFilterCoeffs *c, struct FFLPFilterState *s, int size, int16_t *src, int sstep, int16_t *dst, int dstep) +{ + int i; + + for(i = 0; i < size; i += 4){ + float in, res; + + FILTER(0, 1, 2, 3); + FILTER(1, 2, 3, 0); + FILTER(2, 3, 0, 1); + FILTER(3, 0, 1, 2); + } +} diff --git a/libavcodec/lowpass.h b/libavcodec/lowpass.h new file mode 100644 index 0000000000..6a77907746 --- /dev/null +++ b/libavcodec/lowpass.h @@ -0,0 +1,83 @@ +/* + * Lowpass IIR filter + * Copyright (c) 2008 Konstantin Shishkov + * + * This file is part of FFmpeg. + * + * FFmpeg is free software; you can redistribute it and/or + * modify it under the terms of the GNU Lesser General Public + * License as published by the Free Software Foundation; either + * version 2.1 of the License, or (at your option) any later version. + * + * FFmpeg is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + * Lesser General Public License for more details. + * + * You should have received a copy of the GNU Lesser General Public + * License along with FFmpeg; if not, write to the Free Software + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA + */ + +/** + * @file lowpass.h + * lowpass filter interface + */ + +#ifndef FFMPEG_LOWPASS_H +#define FFMPEG_LOWPASS_H + +#include "avcodec.h" + +struct FFLPFilterCoeffs; +struct FFLPFilterState; + +/** + * Initialize filter coefficients. + * + * @param order filter order + * @param cutoff_ratio cutoff to input frequency ratio + * + * @return pointer to filter coefficients structure or NULL if filter cannot be created + */ +const struct FFLPFilterCoeffs* ff_lowpass_filter_init_coeffs(int order, float cutoff_ratio); + +/** + * Create new filter state. + * + * @param order filter order + * + * @return pointer to new filter state or NULL if state creation fails + */ +struct FFLPFilterState* ff_lowpass_filter_init_state(int order); + +#if 0 //enable with arbitrary order filter implementation, use av_free() for filter state only for now +/** + * Free filter coefficients. + * + * @param coeffs pointer allocated with ff_lowpass_filter_init_coeffs() + */ +void ff_lowpass_filter_free_coeffs(struct FFLPFilterCoeffs *coeffs); + +/** + * Free filter state. + * + * @param state pointer allocated with ff_lowpass_filter_init_state() + */ +void ff_lowpass_filter_free_state(struct FFLPFilterState *state); +#endif + +/** + * Perform lowpass filtering on input samples. + * + * @param coeffs pointer to filter coefficients + * @param state pointer to filter state + * @param size input length + * @param src source samples + * @param sstep source stride + * @param dst filtered samples (destination may be the same as input) + * @param dstep destination stride + */ +void ff_lowpass_filter(const struct FFLPFilterCoeffs *coeffs, struct FFLPFilterState *state, int size, int16_t *src, int sstep, int16_t *dst, int dstep); + +#endif /* FFMPEG_LOWPASS_H */ -- cgit v1.2.3