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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
tags/v0.5
Kostya Shishkov 17 years ago
parent
29ca668f0a
commit
a169f49881
3 changed files with 201 additions and 146 deletions
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  1. +164
    -0
      libavcodec/iirfilter.c
  2. +37
    -17
      libavcodec/iirfilter.h
  3. +0
    -129
      libavcodec/lowpass.c

+ 164
- 0
libavcodec/iirfilter.c View File

@@ -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 <complex.h>
#include <math.h>

/**
* 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);
}


libavcodec/lowpass.h → libavcodec/iirfilter.h View File

@@ -1,5 +1,5 @@
/*
* Lowpass IIR filter
* IIR filter
* Copyright (c) 2008 Konstantin Shishkov
*
* This file is part of FFmpeg.
@@ -20,27 +20,48 @@
*/

/**
* @file lowpass.h
* lowpass filter interface
* @file iirfilter.h
* IIR filter interface
*/

#ifndef FFMPEG_LOWPASS_H
#define FFMPEG_LOWPASS_H
#ifndef FFMPEG_IIRFILTER_H
#define FFMPEG_IIRFILTER_H

#include "avcodec.h"

struct FFLPFilterCoeffs;
struct FFLPFilterState;
struct FFIIRFilterCoeffs;
struct FFIIRFilterState;

enum IIRFilterType{
FF_FILTER_TYPE_BESSEL,
FF_FILTER_TYPE_BUTTERWORTH,
FF_FILTER_TYPE_CHEBYSHEV,
FF_FILTER_TYPE_ELLIPTIC,
};

enum IIRFilterMode{
FF_FILTER_MODE_LOWPASS,
FF_FILTER_MODE_HIGHPASS,
FF_FILTER_MODE_BANDPASS,
FF_FILTER_MODE_BANDSTOP,
};

/**
* Initialize filter coefficients.
*
* @param filt_type filter type (e.g. Butterworth)
* @param filt_mode filter mode (e.g. lowpass)
* @param order filter order
* @param cutoff_ratio cutoff to input frequency ratio
* @param stopband stopband to input frequency ratio (used by bandpass and bandstop filter modes)
* @param ripple ripple factor (used only in Chebyshev filters)
*
* @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);
struct FFIIRFilterCoeffs* ff_iir_filter_init_coeffs(enum IIRFilterType filt_type,
enum IIRFilterMode filt_mode,
int order, float cutoff_ratio,
float stopband, float ripple);

/**
* Create new filter state.
@@ -49,23 +70,21 @@ const struct FFLPFilterCoeffs* ff_lowpass_filter_init_coeffs(int order, float cu
*
* @return pointer to new filter state or NULL if state creation fails
*/
struct FFLPFilterState* ff_lowpass_filter_init_state(int order);
struct FFIIRFilterState* ff_iir_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()
* @param coeffs pointer allocated with ff_iir_filter_init_coeffs()
*/
void ff_lowpass_filter_free_coeffs(struct FFLPFilterCoeffs *coeffs);
void ff_iir_filter_free_coeffs(struct FFIIRFilterCoeffs *coeffs);

/**
* Free filter state.
*
* @param state pointer allocated with ff_lowpass_filter_init_state()
* @param state pointer allocated with ff_iir_filter_init_state()
*/
void ff_lowpass_filter_free_state(struct FFLPFilterState *state);
#endif
void ff_iir_filter_free_state(struct FFIIRFilterState *state);

/**
* Perform lowpass filtering on input samples.
@@ -78,6 +97,7 @@ void ff_lowpass_filter_free_state(struct FFLPFilterState *state);
* @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);
void ff_iir_filter(const struct FFIIRFilterCoeffs *coeffs, struct FFIIRFilterState *state,
int size, const int16_t *src, int sstep, int16_t *dst, int dstep);

#endif /* FFMPEG_LOWPASS_H */
#endif /* FFMPEG_IIRFILTER_H */

+ 0
- 129
libavcodec/lowpass.c View File

@@ -1,129 +0,0 @@
/*
* 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);
}
}

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