FA-79313 / Image orientation metadata / Member archive

Canonical restore tag treats quarter turns as self-inverse · case 03

Restoring a deduplicated photo turns it a half turn away from the upload.

Member previewVariant 3 · 3 implementations · 8 checks per implementation

Case contract

For duplicate detection, bring a pixel grid into a canonical orientation: of the eight orientations (tags 1..8, same pixel mapping as EXIF baking), pick the one whose key (height, width, row-major pixels) is smallest; ties go to the lowest tag. Return [tag, inverse_tag, canonical_grid] where the inverse tag restores the original (6 and 8 are mutual inverses, every other tag is self-inverse).

Why this case matters

Camera, phone and scanner images carry an orientation hint separately from the stored pixels; galleries, thumbnailers, editors and upload pipelines must interpret it consistently or photos appear sideways, mirrored or doubly rotated.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
regression: restoring inverse tag 0	`[6, 6, [[2, 7, 4]]]`	`[6, 8, [[2, 7, 4]]]`	Failed

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