MediaPipe normalises x by image WIDTH and y by image HEIGHT, so for a 1080x1920
clip one unit of x is 1080px and one unit of y is 1920px. makeXform applied a
single scale to both, stretching everything horizontally by H/W - 1.78x on this
footage. The photo underlay looked equally squashed because frameAffine divided
x by imgW, matching the equally wrong vector shapes rather than disagreeing
with them.
Fixed at ingest: landmarks convert to an isotropic space whose unit is one image
height (x *= W/H), so equal numbers mean equal pixels everywhere downstream.
Pixel mapping follows - both axes divide by imgH.
This also silently fixes head roll. fitSimilarity was fitting a rotation in a
sheared space, so the "similarity" it recovered was not one, and stabilisation
of rolled heads was subtly wrong.
selftest: a shape circular in pixel space must stay circular in raster space,
checked at 1080x1920, 1920x1080 and 640x640. Fails at ratio 1.78 without the
conversion.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
The generated face oval was never going to be good enough to draw from:
MediaPipe's face oval is the FACE boundary, cut at the hairline and excluding
hair, ears, jaw and neck, so it is an egg by construction. Segmentation would
give a real head outline but costs a 16MB model and per-frame inference for a
shape that gets replaced by a drawing anyway.
So the plate layer becomes switchable, and the useful modes are photographic:
the source frame mapped into raster space through the same transform chain the
contours go through. Registration is the whole point - the head sits still and
a drawing traced from the underlay is already aligned to the mouth. An
unregistered underlay would be decoration.
- underlay.js: pixel->raster affine (a general affine, since MediaPipe
normalises x by width and y by height), registered draw, palette posterise
- plate modes: photo / photo dim / posterized / oval / oval+photo / none, B cycles
- worksheet cells are registered composites rather than raw crops
- Save frame 4x writes a 1280x800 PNG to draw on
- selftest: FACE_OVAL simplicity, which was never asserted; a wrong ordering
there reads as a lumpy plate rather than an obvious bowtie
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
