On the reference library, 631 of the faces in the tablet's snapshot
match no desktop face by box (IoU >= 0.5), so a name on them stays on
one device. Twenty of those are the same face with the box drawn
somewhere else. Whole photographs sit at IoU 0-0.48 with cosines of
0.72-0.96 between the two devices' vectors, and ten of them already
carry the same person on both sides. The merge never read the
1 KB embedding every face row carries.
match_faces now runs two passes. The box pass is unchanged except that
a pair must now be unique on both sides: a remote face with two
overlapping local faces, or a local face overlapped by two remote ones,
is no longer settled by whichever overlap is larger. Only for the
photographs where a remote face is left over, and a local face is still
free, does it read vectors: one json_each statement per side, keyed by
row id. That was 357 photographs on the reference library, not all
19 MB of vectors. A left-over face pairs with the local face it
resembles most when:
- the cosine is >= 0.7,
- the two are each other's best,
- each leads its runner-up by >= 0.2, and
- a box has not already claimed the local face.
Anything less decisive stays unmatched, so a new face stays new.
Why the threshold is safe, measured on both catalogs (w600k_mbf):
- Of 169,548 pairs of different faces in one photograph, 4 reach 0.7
(lookalikes in one frame) and the maximum is 0.82.
- At 0.6 the rule would claim two pairs that carry different people on
the two devices. At 0.7 it claims 20, none contradicted and 10
corroborated, each leading its runner-up by more than 0.5.
- It only compares faces the boxes left unmatched on both sides: 737
such pairs, so about 0.02 false pairs expected.
- A low cosine never overrules a box. About 150 box-matched pairs fall
below 0.45, because two detectors cut the same tiny face differently.
73 of them carry the same person on both devices.
- Faces are compared only within one file_id and one embedder, because
the same person in another photograph reaches cosine 1.0.
- `Embedding::cosine` refuses a comparison across models.
Before -> after on the reference pair: matched by box 18,348 -> 18,348,
by embedding 0 -> 20, unmatched 631 -> 611, ambiguous 0 -> 0. The
report counts the embedding matches. No schema change.
dtourolle
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