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Use min_cluster_pixels for early gradient cluster rejection #433

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Use min_cluster_pixels for early gradient cluster rejection #433

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10 changes: 6 additions & 4 deletions apriltag_quad_thresh.c
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Original file line number Diff line number Diff line change
Expand Up @@ -102,6 +102,7 @@ struct cluster_task
int w;
int s;
int nclustermap;
int min_cluster_pixels;
unionfind_t* uf;
image_u8_t* im;
zarray_t* clusters;
Expand Down Expand Up @@ -1557,7 +1558,7 @@ unionfind_t* connected_components(apriltag_detector_t *td, image_u8_t* threshim,
return uf;
}

zarray_t* do_gradient_clusters(image_u8_t* threshim, int ts, int y0, int y1, int w, int nclustermap, unionfind_t* uf, zarray_t* clusters) {
zarray_t* do_gradient_clusters(image_u8_t* threshim, int ts, int y0, int y1, int w, int nclustermap, int min_cluster_pixels, unionfind_t* uf, zarray_t* clusters) {
struct uint64_zarray_entry **clustermap = calloc(nclustermap, sizeof(struct uint64_zarray_entry*));

int mem_chunk_size = 2048;
Expand All @@ -1578,7 +1579,7 @@ zarray_t* do_gradient_clusters(image_u8_t* threshim, int ts, int y0, int y1, int

// XXX don't query this until we know we need it?
uint64_t rep0 = unionfind_get_representative(uf, y*w + x);
if (unionfind_get_set_size(uf, rep0) < 25) {
if ((int)unionfind_get_set_size(uf, rep0) < min_cluster_pixels) {
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@bouk bouk Mar 26, 2026

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Should this be < min_cluster_pixels - 1? To match the old behavior when min_cluster_pixels = 24 (the default)

connected_last = false;
continue;
}
Expand Down Expand Up @@ -1610,7 +1611,7 @@ zarray_t* do_gradient_clusters(image_u8_t* threshim, int ts, int y0, int y1, int
\
if (v0 + v1 == 255) { \
uint64_t rep1 = unionfind_get_representative(uf, (y + dy)*w + x + dx); \
if (unionfind_get_set_size(uf, rep1) > 24) { \
if ((int)unionfind_get_set_size(uf, rep1) >= min_cluster_pixels) { \
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@bouk bouk Mar 26, 2026 •
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same as above, should this be > min_cluster_pixels? This version makes more sense to me

uint64_t clusterid; \
if (rep0 < rep1) \
clusterid = (rep1 << 32) + rep0; \
Expand Down Expand Up @@ -1705,7 +1706,7 @@ static void do_cluster_task(void *p)
{
struct cluster_task *task = (struct cluster_task*) p;

do_gradient_clusters(task->im, task->s, task->y0, task->y1, task->w, task->nclustermap, task->uf, task->clusters);
do_gradient_clusters(task->im, task->s, task->y0, task->y1, task->w, task->nclustermap, task->min_cluster_pixels, task->uf, task->clusters);
}

zarray_t* merge_clusters(zarray_t* c1, zarray_t* c2) {
Expand Down Expand Up @@ -1768,6 +1769,7 @@ zarray_t* gradient_clusters(apriltag_detector_t *td, image_u8_t* threshim, int w
tasks[ntasks].uf = uf;
tasks[ntasks].im = threshim;
tasks[ntasks].nclustermap = nclustermap/(sz / chunksize + 1);
tasks[ntasks].min_cluster_pixels = td->qtp.min_cluster_pixels;
tasks[ntasks].clusters = zarray_create(sizeof(struct cluster_hash*));

workerpool_add_task(td->wp, do_cluster_task, &tasks[ntasks]);
Expand Down
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