Every other phase asks whether one video is correct. This asks whether two are
different — the failure the suite could not see, since a generator that ignores
its seed passes determinism, flash safety and liveness perfectly.
Frames reduce to a structural descriptor built to be blind to the cheap axes and
sensitive to the expensive ones: standardized luma kills exposure and palette, a
Laplacian pyramid gives the radial spectrum, and the gradient-angle histogram is
carried through a DFT magnitude so a rotation shifts it without moving it.
Colour is measured and never counted; its only job is to expose the case where
two seeds differ by a palette swap and nothing else.
The score means nothing on its own, so it sits between two references the same
instrument produced: a floor of how far one video travels from itself across its
own sections, and a ceiling of the same pipeline with every layer recast at
random. Two checks gate the instrument before any number from it is trusted —
recolour must move structure ~0 while moving colour a lot, and a quarter turn
must not move it at all.
Three things this got wrong first and now does not. Averaging each video's
probes into one descriptor washed out the structure being measured and put the
floor above the ceiling; probes are matched instead, which is fair because the
track is held fixed. Cosine distance on all-positive histograms scored unrelated
scenes at 0.05, too compressed to be read; chi-square replaces it. Single-link
clustering in the library sweep chained overlapping pairs into a fourteen-scene
group that did not exist; complete-link means every pair inside a group is
really a twin.
The sweep runs against all 61 visualizations, and it finds what the per-scene
distinct gate cannot, because that one compares raw pixels and structural twins
are merely differently coloured.
Both rendered gates fail as committed. That is the point of them: separation is
0.07 against a 0.35 target, two 4-cliques of scenes are one look each, and a
third of the library is never cast. The instrument passes; the generator does
not.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
