Statistics
| Branch: | Revision:

ffmpeg / libavcodec / iirfilter.c @ fcdf0a43

History | View | Annotate | Download (10.7 KB)

1
/*
2
 * IIR filter
3
 * Copyright (c) 2008 Konstantin Shishkov
4
 *
5
 * This file is part of FFmpeg.
6
 *
7
 * FFmpeg is free software; you can redistribute it and/or
8
 * modify it under the terms of the GNU Lesser General Public
9
 * License as published by the Free Software Foundation; either
10
 * version 2.1 of the License, or (at your option) any later version.
11
 *
12
 * FFmpeg is distributed in the hope that it will be useful,
13
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
15
 * Lesser General Public License for more details.
16
 *
17
 * You should have received a copy of the GNU Lesser General Public
18
 * License along with FFmpeg; if not, write to the Free Software
19
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
20
 */
21

    
22
/**
23
 * @file
24
 * different IIR filters implementation
25
 */
26

    
27
#include "iirfilter.h"
28
#include <math.h>
29

    
30
/**
31
 * IIR filter global parameters
32
 */
33
typedef struct FFIIRFilterCoeffs{
34
    int   order;
35
    float gain;
36
    int   *cx;
37
    float *cy;
38
}FFIIRFilterCoeffs;
39

    
40
/**
41
 * IIR filter state
42
 */
43
typedef struct FFIIRFilterState{
44
    float x[1];
45
}FFIIRFilterState;
46

    
47
/// maximum supported filter order
48
#define MAXORDER 30
49

    
50
static int butterworth_init_coeffs(void *avc, struct FFIIRFilterCoeffs *c,
51
                                   enum IIRFilterMode filt_mode,
52
                                   int order, float cutoff_ratio,
53
                                   float stopband)
54
{
55
    int i, j;
56
    double wa;
57
    double p[MAXORDER + 1][2];
58

    
59
    if (filt_mode != FF_FILTER_MODE_LOWPASS) {
60
        av_log(avc, AV_LOG_ERROR, "Butterworth filter currently only supports "
61
               "low-pass filter mode\n");
62
        return -1;
63
    }
64
    if (order & 1) {
65
        av_log(avc, AV_LOG_ERROR, "Butterworth filter currently only supports "
66
               "even filter orders\n");
67
        return -1;
68
    }
69

    
70
    wa = 2 * tan(M_PI * 0.5 * cutoff_ratio);
71

    
72
    c->cx[0] = 1;
73
    for(i = 1; i < (order >> 1) + 1; i++)
74
        c->cx[i] = c->cx[i - 1] * (order - i + 1LL) / i;
75

    
76
    p[0][0] = 1.0;
77
    p[0][1] = 0.0;
78
    for(i = 1; i <= order; i++)
79
        p[i][0] = p[i][1] = 0.0;
80
    for(i = 0; i < order; i++){
81
        double zp[2];
82
        double th = (i + (order >> 1) + 0.5) * M_PI / order;
83
        double a_re, a_im, c_re, c_im;
84
        zp[0] = cos(th) * wa;
85
        zp[1] = sin(th) * wa;
86
        a_re = zp[0] + 2.0;
87
        c_re = zp[0] - 2.0;
88
        a_im =
89
        c_im = zp[1];
90
        zp[0] = (a_re * c_re + a_im * c_im) / (c_re * c_re + c_im * c_im);
91
        zp[1] = (a_im * c_re - a_re * c_im) / (c_re * c_re + c_im * c_im);
92

    
93
        for(j = order; j >= 1; j--)
94
        {
95
            a_re = p[j][0];
96
            a_im = p[j][1];
97
            p[j][0] = a_re*zp[0] - a_im*zp[1] + p[j-1][0];
98
            p[j][1] = a_re*zp[1] + a_im*zp[0] + p[j-1][1];
99
        }
100
        a_re    = p[0][0]*zp[0] - p[0][1]*zp[1];
101
        p[0][1] = p[0][0]*zp[1] + p[0][1]*zp[0];
102
        p[0][0] = a_re;
103
    }
104
    c->gain = p[order][0];
105
    for(i = 0; i < order; i++){
106
        c->gain += p[i][0];
107
        c->cy[i] = (-p[i][0] * p[order][0] + -p[i][1] * p[order][1]) /
108
                   (p[order][0] * p[order][0] + p[order][1] * p[order][1]);
109
    }
110
    c->gain /= 1 << order;
111

    
112
    return 0;
113
}
114

    
115
static int biquad_init_coeffs(void *avc, struct FFIIRFilterCoeffs *c,
116
                              enum IIRFilterMode filt_mode, int order,
117
                              float cutoff_ratio, float stopband)
118
{
119
    double cos_w0, sin_w0;
120
    double a0, x0, x1;
121

    
122
    if (filt_mode != FF_FILTER_MODE_HIGHPASS &&
123
        filt_mode != FF_FILTER_MODE_LOWPASS) {
124
        av_log(avc, AV_LOG_ERROR, "Biquad filter currently only supports "
125
               "high-pass and low-pass filter modes\n");
126
        return -1;
127
    }
128
    if (order != 2) {
129
        av_log(avc, AV_LOG_ERROR, "Biquad filter must have order of 2\n");
130
        return -1;
131
    }
132

    
133
    cos_w0 = cos(M_PI * cutoff_ratio);
134
    sin_w0 = sin(M_PI * cutoff_ratio);
135

    
136
    a0 = 1.0 + (sin_w0 / 2.0);
137

    
138
    if (filt_mode == FF_FILTER_MODE_HIGHPASS) {
139
        c->gain  =  ((1.0 + cos_w0) / 2.0)  / a0;
140
        x0       = (-(1.0 + cos_w0))        / a0;
141
        x1       =  ((1.0 + cos_w0) / 2.0)  / a0;
142
    } else { // FF_FILTER_MODE_LOWPASS
143
        c->gain  =  ((1.0 - cos_w0) / 2.0)  / a0;
144
        x0       =   (1.0 - cos_w0)         / a0;
145
        x1       =  ((1.0 - cos_w0) / 2.0)  / a0;
146
    }
147
    c->cy[0] =  (2.0 *  cos_w0)        / a0;
148
    c->cy[1] = (-1.0 + (sin_w0 / 2.0)) / a0;
149

    
150
    // divide by gain to make the x coeffs integers.
151
    // during filtering, the delay state will include the gain multiplication
152
    c->cx[0] = lrintf(x0 / c->gain);
153
    c->cx[1] = lrintf(x1 / c->gain);
154
    c->cy[0] /= c->gain;
155
    c->cy[1] /= c->gain;
156

    
157
    return 0;
158
}
159

    
160
av_cold struct FFIIRFilterCoeffs* ff_iir_filter_init_coeffs(void *avc,
161
                                                enum IIRFilterType filt_type,
162
                                                enum IIRFilterMode filt_mode,
163
                                                int order, float cutoff_ratio,
164
                                                float stopband, float ripple)
165
{
166
    FFIIRFilterCoeffs *c;
167

    
168
    if (order <= 0 || order > MAXORDER || cutoff_ratio >= 1.0)
169
        return NULL;
170

    
171
    FF_ALLOCZ_OR_GOTO(avc, c,     sizeof(FFIIRFilterCoeffs),
172
                      init_fail);
173
    FF_ALLOC_OR_GOTO (avc, c->cx, sizeof(c->cx[0]) * ((order >> 1) + 1),
174
                      init_fail);
175
    FF_ALLOC_OR_GOTO (avc, c->cy, sizeof(c->cy[0]) * order,
176
                      init_fail);
177
    c->order = order;
178

    
179
    if (filt_type == FF_FILTER_TYPE_BUTTERWORTH) {
180
        if (butterworth_init_coeffs(avc, c, filt_mode, order, cutoff_ratio,
181
            stopband)) {
182
            goto init_fail;
183
        }
184
    } else if (filt_type == FF_FILTER_TYPE_BIQUAD) {
185
        if (biquad_init_coeffs(avc, c, filt_mode, order, cutoff_ratio,
186
            stopband)) {
187
            goto init_fail;
188
        }
189
    } else {
190
        av_log(avc, AV_LOG_ERROR, "filter type is not currently implemented\n");
191
        goto init_fail;
192
    }
193

    
194
    return c;
195

    
196
init_fail:
197
    ff_iir_filter_free_coeffs(c);
198
    return NULL;
199
}
200

    
201
av_cold struct FFIIRFilterState* ff_iir_filter_init_state(int order)
202
{
203
    FFIIRFilterState* s = av_mallocz(sizeof(FFIIRFilterState) + sizeof(s->x[0]) * (order - 1));
204
    return s;
205
}
206

    
207
#define CONV_S16(dest, source) dest = av_clip_int16(lrintf(source));
208

    
209
#define CONV_FLT(dest, source) dest = source;
210

    
211
#define FILTER_BW_O4_1(i0, i1, i2, i3, fmt)         \
212
    in = *src0 * c->gain                            \
213
         + c->cy[0]*s->x[i0] + c->cy[1]*s->x[i1]    \
214
         + c->cy[2]*s->x[i2] + c->cy[3]*s->x[i3];   \
215
    res =  (s->x[i0] + in      )*1                  \
216
         + (s->x[i1] + s->x[i3])*4                  \
217
         +  s->x[i2]            *6;                 \
218
    CONV_##fmt(*dst0, res)                          \
219
    s->x[i0] = in;                                  \
220
    src0 += sstep;                                  \
221
    dst0 += dstep;
222

    
223
#define FILTER_BW_O4(type, fmt) {           \
224
    int i;                                  \
225
    const type *src0 = src;                 \
226
    type       *dst0 = dst;                 \
227
    for (i = 0; i < size; i += 4) {         \
228
        float in, res;                      \
229
        FILTER_BW_O4_1(0, 1, 2, 3, fmt);    \
230
        FILTER_BW_O4_1(1, 2, 3, 0, fmt);    \
231
        FILTER_BW_O4_1(2, 3, 0, 1, fmt);    \
232
        FILTER_BW_O4_1(3, 0, 1, 2, fmt);    \
233
    }                                       \
234
}
235

    
236
#define FILTER_DIRECT_FORM_II(type, fmt) {                                  \
237
    int i;                                                                  \
238
    const type *src0 = src;                                                 \
239
    type       *dst0 = dst;                                                 \
240
    for (i = 0; i < size; i++) {                                            \
241
        int j;                                                              \
242
        float in, res;                                                      \
243
        in = *src0 * c->gain;                                               \
244
        for(j = 0; j < c->order; j++)                                       \
245
            in += c->cy[j] * s->x[j];                                       \
246
        res = s->x[0] + in + s->x[c->order >> 1] * c->cx[c->order >> 1];    \
247
        for(j = 1; j < c->order >> 1; j++)                                  \
248
            res += (s->x[j] + s->x[c->order - j]) * c->cx[j];               \
249
        for(j = 0; j < c->order - 1; j++)                                   \
250
            s->x[j] = s->x[j + 1];                                          \
251
        CONV_##fmt(*dst0, res)                                              \
252
        s->x[c->order - 1] = in;                                            \
253
        src0 += sstep;                                                      \
254
        dst0 += dstep;                                                      \
255
    }                                                                       \
256
}
257

    
258
void ff_iir_filter(const struct FFIIRFilterCoeffs *c,
259
                   struct FFIIRFilterState *s, int size,
260
                   const int16_t *src, int sstep, int16_t *dst, int dstep)
261
{
262
    if (c->order == 4) {
263
        FILTER_BW_O4(int16_t, S16)
264
    } else {
265
        FILTER_DIRECT_FORM_II(int16_t, S16)
266
    }
267
}
268

    
269
void ff_iir_filter_flt(const struct FFIIRFilterCoeffs *c,
270
                       struct FFIIRFilterState *s, int size,
271
                       const float *src, int sstep, void *dst, int dstep)
272
{
273
    if (c->order == 4) {
274
        FILTER_BW_O4(float, FLT)
275
    } else {
276
        FILTER_DIRECT_FORM_II(float, FLT)
277
    }
278
}
279

    
280
av_cold void ff_iir_filter_free_state(struct FFIIRFilterState *state)
281
{
282
    av_free(state);
283
}
284

    
285
av_cold void ff_iir_filter_free_coeffs(struct FFIIRFilterCoeffs *coeffs)
286
{
287
    if(coeffs){
288
        av_free(coeffs->cx);
289
        av_free(coeffs->cy);
290
    }
291
    av_free(coeffs);
292
}
293

    
294
#ifdef TEST
295
#define FILT_ORDER 4
296
#define SIZE 1024
297
int main(void)
298
{
299
    struct FFIIRFilterCoeffs *fcoeffs = NULL;
300
    struct FFIIRFilterState  *fstate  = NULL;
301
    float cutoff_coeff = 0.4;
302
    int16_t x[SIZE], y[SIZE];
303
    int i;
304
    FILE* fd;
305

    
306
    fcoeffs = ff_iir_filter_init_coeffs(FF_FILTER_TYPE_BUTTERWORTH,
307
                                        FF_FILTER_MODE_LOWPASS, FILT_ORDER,
308
                                        cutoff_coeff, 0.0, 0.0);
309
    fstate  = ff_iir_filter_init_state(FILT_ORDER);
310

    
311
    for (i = 0; i < SIZE; i++) {
312
        x[i] = lrint(0.75 * INT16_MAX * sin(0.5*M_PI*i*i/SIZE));
313
    }
314

    
315
    ff_iir_filter(fcoeffs, fstate, SIZE, x, 1, y, 1);
316

    
317
    fd = fopen("in.bin", "w");
318
    fwrite(x, sizeof(x[0]), SIZE, fd);
319
    fclose(fd);
320

    
321
    fd = fopen("out.bin", "w");
322
    fwrite(y, sizeof(y[0]), SIZE, fd);
323
    fclose(fd);
324

    
325
    ff_iir_filter_free_coeffs(fcoeffs);
326
    ff_iir_filter_free_state(fstate);
327
    return 0;
328
}
329
#endif /* TEST */