Jorijn asked whether the sample count is ours to control and whether more
samples would help. It is -- and the config dump says something more useful.
Stock enrols with 20 samples, not the 10 we had guessed, but it also sets six
keys we were leaving entirely to the trustlet's built-in defaults:
min_enrolling_coverage_threshold 70
min_enrolling_quality_threshold 20
enroll_overlap_min_area 60
enroll_overlap_max_area 80
enable_duplicated_finger_checking on
max_extral_enroll_low_quality 16
Those defaults accept anything, which is how ten quick taps in one position
became a stored template. The overlap bounds are the mechanism that matters:
a sample must overlap the previous one by 60 to 80 percent -- more means the
finger did not move, less means a gap -- so the algorithm now refuses the
same-spot sample instead of storing it. Sample count alone would have stored
twenty near-duplicates rather than ten.
Deliberately left out: min_identify_quality_threshold and
min_identify_coverage_threshold. Those gate matching rather than enrolment and
would reject exactly the landing frames the 1.5x detection threshold exists to
catch. One group of variables at a time.
fpenrol.sh grows to twenty positions, and its rejection message now says to
move rather than to press harder, because the enforcement and the guidance
finally agree on what a rejected sample means.
The threshold change is the first thing to move accuracy. Labelled protocol,
enrolled quick taps: 4 of 10, against 2 of 10 for every previous build. Seven
of fifteen presses now get two or more frames where none did before, and the
landing frames the old threshold discarded turn up in the transcript at 207,
213, 242 and 284. Wrong finger still 0 of 5.
It also explains the latency asymmetry Jorijn noticed. A match ends the loop
the moment it happens, mean 1317 ms. A no-match waits for the finger to lift,
mean 2190 ms, because a later frame in the same press may still match -- and
they do, at frames 3, 5 and 8. That is the press rule working, not a fault.
What the same run says about the template is worse than the loop ever was. One
press produced eight frames at full contact, 362 to 367, and every one
rejected; another produced six. Roughly one frame in seven matches, against the
47 to 75 percent the journal records for the template the research harness
enrolled. The first template here was ten quick taps in about one position, so
the algorithm was handed ten near-duplicate images of one spot.
fpenrol.sh enrols with a different contact position per ACCEPTED sample --
centre, left, right, tip, joint, rolled either way -- driven by
fprintd-enroll's own per-stage output rather than by counting presses. Enrol as
a SECOND finger so both templates coexist and the comparison holds the loop
constant; the trustlet reports which fid matched, and the daemon's map turns
that back into a name.
