Human label for the pose, e.g. 'still' or 'rock -20°'.
Lit pixels (luma > LIT_THRESHOLD) on the outermost row/column.
Perimeter pixel count they were counted out of (2·w + 2·h − 4 for any real
frame; w·h for a degenerate 1-px-wide/tall one, where that formula
over-counts).
One measured pose: how much lit content sat on the frame's outermost ring.