From a169f49881fb9ce7cd55fdb654fb4b3057f8ddad Mon Sep 17 00:00:00 2001 From: Kostya Shishkov Date: Thu, 28 Aug 2008 04:53:57 +0000 Subject: Add generic IIR filter interface with Butterworth lowpass filter implementation and remove obsoleted old lowpass filter. Originally committed as revision 15005 to svn://svn.ffmpeg.org/ffmpeg/trunk --- libavcodec/iirfilter.c | 164 +++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 164 insertions(+) create mode 100644 libavcodec/iirfilter.c (limited to 'libavcodec/iirfilter.c') diff --git a/libavcodec/iirfilter.c b/libavcodec/iirfilter.c new file mode 100644 index 0000000000..bcaa021b60 --- /dev/null +++ b/libavcodec/iirfilter.c @@ -0,0 +1,164 @@ +/* + * 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 iirfilter.c + * different IIR filters implementation + */ + +#include "iirfilter.h" +#include +#include + +/** + * IIR filter global parameters + */ +typedef struct FFIIRFilterCoeffs{ + int order; + float gain; + int *cx; + float *cy; +}FFIIRFilterCoeffs; + +/** + * IIR filter state + */ +typedef struct FFIIRFilterState{ + float x[1]; +}FFIIRFilterState; + +/// maximum supported filter order +#define MAXORDER 30 + +struct FFIIRFilterCoeffs* ff_iir_filter_init_coeffs(enum IIRFilterType filt_type, + enum IIRFilterMode filt_mode, + int order, float cutoff_ratio, + float stopband, float ripple) +{ + int i, j, size; + FFIIRFilterCoeffs *c; + double wa; + complex p[MAXORDER + 1]; + + if(filt_type != FF_FILTER_TYPE_BUTTERWORTH || filt_mode != FF_FILTER_MODE_LOWPASS) + return NULL; + if(order <= 1 || (order & 1) || order > MAXORDER || cutoff_ratio >= 1.0) + return NULL; + + c = av_malloc(sizeof(FFIIRFilterCoeffs)); + c->cx = av_malloc(sizeof(c->cx[0]) * ((order >> 1) + 1)); + c->cy = av_malloc(sizeof(c->cy[0]) * order); + c->order = order; + + wa = 2 * tan(M_PI * 0.5 * cutoff_ratio); + + c->cx[0] = 1; + for(i = 1; i < (order >> 1) + 1; i++) + c->cx[i] = c->cx[i - 1] * (order - i + 1LL) / i; + + p[0] = 1.0; + for(i = 1; i <= order; i++) + p[i] = 0.0; + for(i = 0; i < order; i++){ + complex zp; + double th = (i + (order >> 1) + 0.5) * M_PI / order; + zp = cexp(I*th) * wa; + zp = (zp + 2.0) / (zp - 2.0); + + for(j = order; j >= 1; j--) + p[j] = zp*p[j] + p[j - 1]; + p[0] *= zp; + } + c->gain = creal(p[order]); + for(i = 0; i < order; i++){ + c->gain += creal(p[i]); + c->cy[i] = creal(-p[i] / p[order]); + } + c->gain /= 1 << order; + + return c; +} + +struct FFIIRFilterState* ff_iir_filter_init_state(int order) +{ + FFIIRFilterState* s = av_mallocz(sizeof(FFIIRFilterState) + sizeof(s->x[0]) * (order - 1)); + return s; +} + +#define FILTER(i0, i1, i2, i3) \ + in = *src * c->gain \ + + c->cy[0]*s->x[i0] + c->cy[1]*s->x[i1] \ + + c->cy[2]*s->x[i2] + c->cy[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_iir_filter(const struct FFIIRFilterCoeffs *c, struct FFIIRFilterState *s, int size, const int16_t *src, int sstep, int16_t *dst, int dstep) +{ + int i; + + if(c->order == 4){ + 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); + } + }else{ + for(i = 0; i < size; i++){ + int j; + float in, res; + in = *src * c->gain; + for(j = 0; j < c->order; j++) + in += c->cy[j] * s->x[j]; + res = s->x[0] + in + s->x[c->order >> 1] * c->cx[c->order >> 1]; + for(j = 1; j < c->order >> 1; j++) + res += (s->x[j] + s->x[c->order - j]) * c->cx[j]; + for(j = 0; j < c->order - 1; j++) + s->x[j] = s->x[j + 1]; + *dst = av_clip_int16(lrintf(res)); + s->x[c->order - 1] = in; + src += sstep; + dst += sstep; + } + } +} + +void ff_iir_filter_free_state(struct FFIIRFilterState *state) +{ + av_free(state); +} + +void ff_iir_filter_free_coeffs(struct FFIIRFilterCoeffs *coeffs) +{ + if(coeffs){ + av_free(coeffs->cx); + av_free(coeffs->cy); + } + av_free(coeffs); +} + -- cgit v1.2.3