FA-79779 / Barcode symbology encoding / Member archive

Elements on the threshold are silently called wide · case 04

Borderline scans decode to wrong data instead of being retried.

Member previewVariant 4 · 3 implementations · 8 checks per implementation

Case contract

Classify measured element widths of a two-width symbology scanline (bars at even indexes, spaces at odd) into N/W. Bars and spaces are classified separately because ink spread widens bars. Within a class, if max < 1.5 * min all elements are narrow; otherwise the threshold is (min + max) / 2, elements above it are wide, below it narrow, and an element exactly on it is {"error": "ambiguous", "index": i}.

Why this case matters

Retail, logistics, pharmacy and document workflows depend on encoders that produce exactly the module pattern, code-set switches, separators and quiet zones scanners expect; one misplaced module or separator makes a label unreadable or, worse, scan as different data.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
regression: threshold tie 0	`"NWNWWNN"`	`{"error": "ambiguous", "index": 1}`	Failed

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