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#include "ntsc.h"
#include <stdlib.h>
#include <stdint.h>
#include <stdio.h>
#include <math.h>
struct ntsc_iq {
float ei;
float eq;
};
struct biquad_filter_ctx {
float a0, a1, a2, b1, b2;
float z1, z2;
};
struct verbose_ctx {
FILE* fout;
};
struct ntsc_ctx {
struct generator_ctx {
float* sin_table;
float* cos_table;
int f;
int shift;
} generator;
uint16_t width;
struct ntsc_iq* iq;
struct biquad_filter_ctx i_filter;
struct biquad_filter_ctx q_filter;
struct verbose_ctx* verbose;
};
static void ntsc_filter_init(struct biquad_filter_ctx* filter, float fc)
{
float k = tan(M_PI * fc);
float q = 0.7;
float norm = 1 / (1 + k / q + k * k);
filter->a0 = k * k * norm;
filter->a1 = 2 * filter->a0;
filter->a2 = filter->a0;
filter->b1 = 2 * (k * k - 1) * norm;
filter->b2 = (1 - k / q + k * k) * norm;
filter->z1 = 0;
filter->z2 = 0;
}
static float ntsc_process_filter(struct biquad_filter_ctx* filter, float in)
{
float out = in * filter->a0 + filter->z1;
filter->z1 = in * filter->a1 + filter->z2 - filter->b1 * out;
filter->z2 = in * filter->a2 - filter->b2 * out;
//fprintf(stderr, "filter in: %f, out: %f\n", in, out);
return out;
}
static inline float ntsc_rgb_to_y(const float* rgb) {
return rgb[0] * 0.30 + rgb[1] * 0.59 + rgb[2] * 0.11;
}
static inline void ntsc_rgb_to_iq(const float* rgb, struct ntsc_iq* iq)
{
iq->ei = rgb[0] * 0.6 - rgb[1] * 0.28 - rgb[2] * 0.32;
iq->eq = rgb[0] * 0.21 - rgb[1] * 0.52 + rgb[2] * 0.31;
}
static inline void ntsc_iqy_to_rgb(const struct ntsc_iq* iq, float y, float* rgb)
{
rgb[0] = iq->ei * 0.96 + iq->eq * 0.62 + y;
rgb[1] = iq->ei * (-0.27) - iq->eq * 0.65 + y;
rgb[2] = iq->ei * (-1.11) + iq->eq * 1.7 + y;
}
static void ntsc_create_generator(struct ntsc_ctx* ctx)
{
int i = 0;
int n = 2 * ctx->width;
float width = ctx->width;
//TODO: tune the freq
ctx->generator.f = (int)(width / 2.5) | 0x01;
ctx->generator.sin_table = malloc(sizeof(float) * n);
ctx->generator.cos_table = malloc(sizeof(float) * n);
for (i = 0; i < n; i++) {
ctx->generator.sin_table[i] = sin(ctx->generator.f * i * M_PI/width);
ctx->generator.cos_table[i] = cos(ctx->generator.f * i * M_PI/width);
}
ctx->generator.shift = 0;
}
static void ntsc_free_generator(struct ntsc_ctx* ctx)
{
free(ctx->generator.sin_table);
free(ctx->generator.cos_table);
}
ntsc_ctx* ntsc_create_context(int width, int encode)
{
if (width >= 65535) {
return NULL;
}
ntsc_ctx* p = malloc(sizeof(ntsc_ctx));
if (!p)
return NULL;
p->width = width;
ntsc_create_generator(p);
p->iq = malloc(sizeof(struct ntsc_iq) * width);
ntsc_filter_init(&p->i_filter, 0.08);
ntsc_filter_init(&p->q_filter, 0.05);
p->verbose = NULL;
return p;
}
void ntsc_free_context(ntsc_ctx* ctx)
{
if (ctx->verbose)
free(ctx->verbose);
ntsc_free_generator(ctx);
free(ctx->iq);
free(ctx);
}
static void verbose_carrier(ntsc_ctx* ctx)
{
float t = (ctx->width * 2) / (float)ctx->generator.f;
fprintf(ctx->verbose->fout, "Width: %d pixels\n", ctx->width);
fprintf(ctx->verbose->fout, "Carrier: period is %f pixels (%f of Fmax)\n", t, 2/t);
}
void ntsc_enable_verbose(FILE* fout, ntsc_ctx* ctx)
{
ctx->verbose = malloc(sizeof(struct verbose_ctx));
ctx->verbose->fout = fout;
fprintf(ctx->verbose->fout, "Verbose output enabled\n");
verbose_carrier(ctx);
}
static void ntsc_next_line(ntsc_ctx* ctx)
{
if (ctx->generator.shift) {
ctx->generator.shift = 0;
} else {
ctx->generator.shift = 1;
}
}
static void ntsc_modulate_line(ntsc_ctx* ctx, const struct ntsc_iq* in, float* out)
{
int i;
float* sin = ctx->generator.sin_table;
float* cos = ctx->generator.cos_table;
const int chroma_shift = 3;
if (ctx->generator.shift) {
sin += ctx->width;
cos += ctx->width;
}
for (i = 0; i < chroma_shift; i++) {
const struct ntsc_iq* iq = in + i;
(void)(ntsc_process_filter(&ctx->i_filter, iq->ei * sin[i]));
(void)(ntsc_process_filter(&ctx->q_filter, iq->eq * cos[i]));
}
for (i = chroma_shift; i < ctx->width; i++) {
const struct ntsc_iq* iq = in + i;
int j = i - chroma_shift;
out[j] = ntsc_process_filter(&ctx->i_filter, iq->ei) * sin[j] + ntsc_process_filter(&ctx->q_filter, iq->eq) * cos[j];
}
for (i = 0; i < chroma_shift; i++) {
int j = i - chroma_shift + ctx->width;
out[j] = ntsc_process_filter(&ctx->i_filter, 0.0) * sin[j] + ntsc_process_filter(&ctx->q_filter, 0.0) * cos[j];
}
}
static void ntsc_demodulate_line(const float* input, ntsc_ctx* ctx)
{
int i;
float* sin = ctx->generator.sin_table;
float* cos = ctx->generator.cos_table;
// In theory we should have different delay for I and Q channel
const int chroma_shift = 3;
if (ctx->generator.shift) {
sin += ctx->width;
cos += ctx->width;
}
// Feed filter
for (i = 0; i < chroma_shift; i++) {
(void)(ntsc_process_filter(&ctx->i_filter, input[i] * sin[i]) * 2.0);
(void)(ntsc_process_filter(&ctx->q_filter, input[i] * cos[i]) * 2.0);
}
// Shift color components for chroma_shift pixels left to compensate low pass filter delay
for (i = chroma_shift; i < ctx->width; i++) {
struct ntsc_iq* iq = ctx->iq + i - chroma_shift;
iq->ei = ntsc_process_filter(&ctx->i_filter, input[i] * sin[i]) * 2.0;
iq->eq = ntsc_process_filter(&ctx->q_filter, input[i] * cos[i]) * 2.0;
}
// Drain last delayed values
for (i = 0; i < chroma_shift; i++) {
struct ntsc_iq* iq = ctx->iq + i - chroma_shift + ctx->width;
iq->ei = ntsc_process_filter(&ctx->i_filter, 0.0) * 2.0;
iq->eq = ntsc_process_filter(&ctx->q_filter, 0.0) * 2.0;
}
}
void ntsc_process_encode(const float* input, float* output, ntsc_ctx* ctx)
{
int i;
for (i = 0; i < ctx->width; i++) {
ntsc_rgb_to_iq(input + i * 3, (ctx->iq + i));
}
ntsc_modulate_line(ctx, ctx->iq, output);
for (i = 0; i < ctx->width; i++) {
output[i] += ntsc_rgb_to_y(input + i * 3);
}
ntsc_next_line(ctx);
}
void ntsc_process_decode(const float* input, float* output, ntsc_ctx* ctx)
{
int i;
ntsc_demodulate_line(input, ctx);
for (i = 0; i < ctx->width; i++) {
struct ntsc_iq* iq = ctx->iq + i;
ntsc_iqy_to_rgb(iq, input[i], output + i * 3);
}
ntsc_next_line(ctx);
}
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