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>
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