The head is now part of a store rather than a script: `finetune_identity.py --stock
stock-lopia` trains on that store's enrolled views (27 views over 7 products, 12
augmented copies each) and writes `<stock>/identity_head.pt`, which ProductGallery
loads automatically.
The first attempt exposed a trap worth recording. A discriminative head has no "none
of the above": trained with an angular margin to separate seven products, it maps
everything confidently onto those seven, including cartons it has never seen.
raw features, threshold 0.55 home shelf 78% accepted foreign shelves 5% accepted
trained head, threshold 0.40 home shelf 58% accepted foreign shelves 44% accepted
Rejection - the gallery's whole point - disappears. The fix needs no retraining: the
two mechanisms fail in opposite directions, so raw features decide *whether* to answer
(they generalise) and the head decides *what* to answer (it discriminates). Measured:
47% accepted on the home shelf, 5% on foreign ones. Lower coverage than raw-only,
which is the honest trade.
The head also needs its own threshold (0.40 against the raw 0.55): a trained head's
similarity scale is its own, and reusing the raw line rejected almost everything it
said.
175 tests pass.
Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>
Part 2 ended on the number that matters: enrolling a real shelf from itself leaves
off-the-shelf DINOv2 at ~25% top-1, because real milk cartons differ by small text
and a colour band. This trains a small projection head on frozen features - 384 -> 128,
cosine classifier, angular margin - with augmentation standing in for the second visit
we do not have, and measures it on 72 held-out facings over 8 products.
raw DINOv2 cosine top-1 2/72 (2%) balanced 1%
raw, rejecting below 0.55 top-1 2/72 (2%) balanced 1% (5% of answered right)
fine-tuned + margin top-1 28/72 (38%) balanced 73%
fine-tuned, rejecting below 0.4 top-1 17/72 (23%) balanced 58% (94% of answered right)
So fine-tuning is the difference between working and not (balanced 1% -> 73%), and
with a rejection threshold the model becomes precise - it answers 18 of 72 facings and
is right on 94% of them, which is the operating point a store wants. The raw model
cannot do that at any threshold.
Where it fails is where my labels are coarse: MEGMILK, which the contact sheet shows
is probably several products under one brand, scores 1/32 because the class is
internally inconsistent and the model correctly refuses most of it.
Honest limit, stated in the doc: enrolment and held-out facings come from one
photograph, so these are upper bounds; only a recorded second visit settles the real
number. What is settled is the mechanism - a head trained on labels the pipeline can
produce itself moves fine-grained identity from useless to usable.
175 tests pass.
Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>
