static void AssignSegments(VP8Encoder* const enc,
const int alphas[MAX_ALPHA + 1]) {
const int nb = enc->segment_hdr_.num_segments_;
int centers[NUM_MB_SEGMENTS];
int weighted_average = 0;
int map[MAX_ALPHA + 1];
int a, n, k;
int min_a = 0, max_a = MAX_ALPHA, range_a;
// 'int' type is ok for histo, and won't overflow
int accum[NUM_MB_SEGMENTS], dist_accum[NUM_MB_SEGMENTS];
// bracket the input
for (n = 0; n <= MAX_ALPHA && alphas[n] == 0; ++n) {}
min_a = n;
for (n = MAX_ALPHA; n > min_a && alphas[n] == 0; --n) {}
max_a = n;
range_a = max_a - min_a;
// Spread initial centers evenly
for (n = 1, k = 0; n < 2 * nb; n += 2) {
centers[k++] = min_a + (n * range_a) / (2 * nb);
}
for (k = 0; k < MAX_ITERS_K_MEANS; ++k) { // few iters are enough
int total_weight;
int displaced;
// Reset stats
for (n = 0; n < nb; ++n) {
accum[n] = 0;
dist_accum[n] = 0;
}
// Assign nearest center for each 'a'
n = 0; // track the nearest center for current 'a'
for (a = min_a; a <= max_a; ++a) {
if (alphas[a]) {
while (n < nb - 1 && abs(a - centers[n + 1]) < abs(a - centers[n])) {
n++;
}
map[a] = n;
// accumulate contribution into best centroid
dist_accum[n] += a * alphas[a];
accum[n] += alphas[a];
}
}
// All point are classified. Move the centroids to the
// center of their respective cloud.
displaced = 0;
weighted_average = 0;
total_weight = 0;
for (n = 0; n < nb; ++n) {
if (accum[n]) {
const int new_center = (dist_accum[n] + accum[n] / 2) / accum[n];
displaced += abs(centers[n] - new_center);
centers[n] = new_center;
weighted_average += new_center * accum[n];
total_weight += accum[n];
}
}
weighted_average = (weighted_average + total_weight / 2) / total_weight;
if (displaced < 5) break; // no need to keep on looping...
}
// Map each original value to the closest centroid
for (n = 0; n < enc->mb_w_ * enc->mb_h_; ++n) {
VP8MBInfo* const mb = &enc->mb_info_[n];
const int alpha = mb->alpha_;
mb->segment_ = map[alpha];
mb->alpha_ = centers[map[alpha]]; // for the record.
}
if (nb > 1) {
const int smooth = (enc->config_->preprocessing & 1);
if (smooth) SmoothSegmentMap(enc);
}
SetSegmentAlphas(enc, centers, weighted_average); // pick some alphas.
}
static void AssignSegments(VP8Encoder* const enc,
const int alphas[MAX_ALPHA + 1]) {
const int nb = enc->segment_hdr_.num_segments_;
int centers[NUM_MB_SEGMENTS];
int weighted_average = 0;
int map[MAX_ALPHA + 1];
int a, n, k;
int min_a = 0, max_a = MAX_ALPHA, range_a;
int accum[NUM_MB_SEGMENTS], dist_accum[NUM_MB_SEGMENTS];
for (n = 0; n <= MAX_ALPHA && alphas[n] == 0; ++n) {}
min_a = n;
for (n = MAX_ALPHA; n > min_a && alphas[n] == 0; --n) {}
max_a = n;
range_a = max_a - min_a;
for (n = 1, k = 0; n < 2 * nb; n += 2) {
centers[k++] = min_a + (n * range_a) / (2 * nb);
}
for (k = 0; k < MAX_ITERS_K_MEANS; ++k) {
int total_weight;
int displaced;
for (n = 0; n < nb; ++n) {
accum[n] = 0;
dist_accum[n] = 0;
}
n = 0;
for (a = min_a; a <= max_a; ++a) {
if (alphas[a]) {
while (n < nb - 1 && abs(a - centers[n + 1]) < abs(a - centers[n])) {
n++;
}
map[a] = n;
dist_accum[n] += a * alphas[a];
accum[n] += alphas[a];
}
}
displaced = 0;
weighted_average = 0;
total_weight = 0;
for (n = 0; n < nb; ++n) {
if (accum[n]) {
const int new_center = (dist_accum[n] + accum[n] / 2) / accum[n];
displaced += abs(centers[n] - new_center);
centers[n] = new_center;
weighted_average += new_center * accum[n];
total_weight += accum[n];
}
}
weighted_average = (weighted_average + total_weight / 2) / total_weight;
if (displaced < 5) break;
}
for (n = 0; n < enc->mb_w_ * enc->mb_h_; ++n) {
VP8MBInfo* const mb = &enc->mb_info_[n];
const int alpha = mb->alpha_;
mb->segment_ = map[alpha];
mb->alpha_ = centers[map[alpha]];
}
if (nb > 1) {
const int smooth = (enc->config_->preprocessing & 1);
if (smooth) SmoothSegmentMap(enc);
}
SetSegmentAlphas(enc, centers, weighted_average);
}
