FA-79061 / Image orientation metadata / Open access

Lossless mirror pads the width instead of trimming it · case 01

Mirrored JPEGs gain a strip of garbage pixels on the left edge.

Verified by executionVariant 1 · 8 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The width is rounded up to the next MCU boundary, which exposes padding rather than dropping the partial block.

VERIFIED REPAIR

Round the width down to a multiple of the MCU width when the transform flips horizontally.

Unsuccessful approach: Trimming the width with the MCU height is wrong whenever the MCU is not square.

Case contract

Input [w, h, tag, sampling]. A lossless JPEG transform that bakes the orientation can only move whole MCUs (444: 8x8, 422: 16 wide x 8 high, 420: 16x16, 440: 8 wide x 16 high), so any partial MCU column or row that would move to the leading edge is trimmed. The tag decomposes into stored-space flips (fx, fy) followed by an optional transpose; fx trims the width and fy trims the height to a multiple of the MCU size. Invalid tags are treated as 1. Return the displayed [width, height], "refuse" when a trimmed side becomes 0, or "unknown-sampling".

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.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(x):
    w, h, tag, sampling = x
    mcu = {'444': (8, 8), '422': (16, 8), '420': (16, 16), '440': (8, 16)}
    if sampling not in mcu:
        return 'unknown-sampling'
    mw, mh = mcu[sampling]
    flips = {1: (0, 0, 0), 2: (1, 0, 0), 3: (1, 1, 0), 4: (0, 1, 0), 5: (0, 0, 1), 6: (0, 1, 1), 7: (1, 1, 1), 8: (1, 0, 1)}
    fx, fy, tr = flips.get(tag, (0, 0, 0))
    tw = w + (-w) % mw if fx else w
    th = h - h % mh if fy else h
    if tw == 0 or th == 0:
        return 'refuse'
    if tr:
        tw, th = th, tw
    return [tw, th]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[[[8, 24, 3, '422'], 'refuse'], [[12, 29, 3, '422'], 'refuse'], [[24, 12, 0, '440'], [24, 12]], [[2969, 96, 1, '422'], [2969, 96]], [[24, 16, 5, '422'], [16, 24]], [[40, 2600, 0, '440'], [40, 2600]], [[24, 20, 0, '444'], [24, 20]], [[12, 16, 7, '420'], 'refuse']], [[[8, 2948, 7, '422'], 'refuse'], [[24, 24, 2, '440'], [24, 24]], [[40, 8, 2, '422'], [32, 8]], [[12, 1946, 4, '420'], [12, 1936]], [[8, 12, 1, '411'], 'unknown-sampling'], [[24, 24, 0, '422'], [24, 24]], [[16, 16, 6, '444'], [16, 16]], [[71, 24, 8, '440'], [24, 64]]], [[[8, 12, 8, '420'], 'refuse'], [[8, 16, 8, '422'], 'refuse'], [[24, 20, 8, '422'], [20, 16]], [[24, 12, 6, '422'], [8, 24]], [[8, 8, 6, '440'], 'refuse'], [[24, 8, 4, '444'], [24, 8]], [[12, 12, 3, '420'], 'refuse'], [[8, 8, 8, '422'], 'refuse']], [[[2979, 24, 2, '422'], [2976, 24]], [[40, 58, 8, '422'], [58, 32]], [[12, 20, 2, '440'], [8, 20]], [[24, 12, 6, '420'], 'refuse'], [[40, 8, 5, '440'], [8, 40]], [[16, 272, 4, '422'], [16, 272]], [[24, 16, 6, '440'], [16, 24]], [[8, 71, 8, '420'], 'refuse']], [[[24, 12, 8, '420'], [12, 16]], [[12, 16, 8, '422'], 'refuse'], [[12, 20, 8, '422'], 'refuse'], [[8, 67, 7, '444'], [64, 8]], [[16, 24, 2, '411'], 'unknown-sampling'], [[40, 18, 1, '420'], [40, 18]], [[16, 74, 7, '422'], [72, 16]], [[8, 688, 2, '420'], 'refuse']]]
labels = ["regression: partial MCU trimming direction", "repair trap", "combined fault", "control", "control", "boundary", "boundary", "control"]
for i, (args, expected) in enumerate(fixtures[N-1]):
    check("%s %d" % (labels[i % len(labels)], i), solve(args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
regression: partial MCU trimming direction 0	`[16, 24]`	`refuse`	Failed
repair trap 1	`[16, 24]`	`refuse`	Failed
combined fault 2	`[24, 12]`	`[24, 12]`	Passed
control 3	`[2969, 96]`	`[2969, 96]`	Passed
control 4	`[16, 24]`	`[16, 24]`	Passed
boundary 5	`[40, 2600]`	`[40, 2600]`	Passed
boundary 6	`[24, 20]`	`[24, 20]`	Passed
control 7	`[16, 16]`	`refuse`	Failed

SHA-256 / 20e4cf2a43b2996bde3ba0926e0043eb76eccbb9a1486841cd212c8cdb67992a

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(x):
    w, h, tag, sampling = x
    mcu = {'444': (8, 8), '422': (16, 8), '420': (16, 16), '440': (8, 16)}
    if sampling not in mcu:
        return 'unknown-sampling'
    mw, mh = mcu[sampling]
    flips = {1: (0, 0, 0), 2: (1, 0, 0), 3: (1, 1, 0), 4: (0, 1, 0), 5: (0, 0, 1), 6: (0, 1, 1), 7: (1, 1, 1), 8: (1, 0, 1)}
    fx, fy, tr = flips.get(tag, (0, 0, 0))
    tw = w - w % mh if fx else w
    th = h - h % mh if fy else h
    if tw == 0 or th == 0:
        return 'refuse'
    if tr:
        tw, th = th, tw
    return [tw, th]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[[[8, 24, 3, '422'], 'refuse'], [[12, 29, 3, '422'], 'refuse'], [[24, 12, 0, '440'], [24, 12]], [[2969, 96, 1, '422'], [2969, 96]], [[24, 16, 5, '422'], [16, 24]], [[40, 2600, 0, '440'], [40, 2600]], [[24, 20, 0, '444'], [24, 20]], [[12, 16, 7, '420'], 'refuse']], [[[8, 2948, 7, '422'], 'refuse'], [[24, 24, 2, '440'], [24, 24]], [[40, 8, 2, '422'], [32, 8]], [[12, 1946, 4, '420'], [12, 1936]], [[8, 12, 1, '411'], 'unknown-sampling'], [[24, 24, 0, '422'], [24, 24]], [[16, 16, 6, '444'], [16, 16]], [[71, 24, 8, '440'], [24, 64]]], [[[8, 12, 8, '420'], 'refuse'], [[8, 16, 8, '422'], 'refuse'], [[24, 20, 8, '422'], [20, 16]], [[24, 12, 6, '422'], [8, 24]], [[8, 8, 6, '440'], 'refuse'], [[24, 8, 4, '444'], [24, 8]], [[12, 12, 3, '420'], 'refuse'], [[8, 8, 8, '422'], 'refuse']], [[[2979, 24, 2, '422'], [2976, 24]], [[40, 58, 8, '422'], [58, 32]], [[12, 20, 2, '440'], [8, 20]], [[24, 12, 6, '420'], 'refuse'], [[40, 8, 5, '440'], [8, 40]], [[16, 272, 4, '422'], [16, 272]], [[24, 16, 6, '440'], [16, 24]], [[8, 71, 8, '420'], 'refuse']], [[[24, 12, 8, '420'], [12, 16]], [[12, 16, 8, '422'], 'refuse'], [[12, 20, 8, '422'], 'refuse'], [[8, 67, 7, '444'], [64, 8]], [[16, 24, 2, '411'], 'unknown-sampling'], [[40, 18, 1, '420'], [40, 18]], [[16, 74, 7, '422'], [72, 16]], [[8, 688, 2, '420'], 'refuse']]]
labels = ["regression: partial MCU trimming direction", "repair trap", "combined fault", "control", "control", "boundary", "boundary", "control"]
for i, (args, expected) in enumerate(fixtures[N-1]):
    check("%s %d" % (labels[i % len(labels)], i), solve(args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
regression: partial MCU trimming direction 0	`[8, 24]`	`refuse`	Failed
repair trap 1	`[8, 24]`	`refuse`	Failed
combined fault 2	`[24, 12]`	`[24, 12]`	Passed
control 3	`[2969, 96]`	`[2969, 96]`	Passed
control 4	`[16, 24]`	`[16, 24]`	Passed
boundary 5	`[40, 2600]`	`[40, 2600]`	Passed
boundary 6	`[24, 20]`	`[24, 20]`	Passed
control 7	`refuse`	`refuse`	Passed

SHA-256 / 1159451ea28c363f92c3e874a447f813601894f1038e682f5d99aa4c1c252bad

3 / The verified repair

Exit 0

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(x):
    w, h, tag, sampling = x
    mcu = {'444': (8, 8), '422': (16, 8), '420': (16, 16), '440': (8, 16)}
    if sampling not in mcu:
        return 'unknown-sampling'
    mw, mh = mcu[sampling]
    flips = {1: (0, 0, 0), 2: (1, 0, 0), 3: (1, 1, 0), 4: (0, 1, 0), 5: (0, 0, 1), 6: (0, 1, 1), 7: (1, 1, 1), 8: (1, 0, 1)}
    fx, fy, tr = flips.get(tag, (0, 0, 0))
    tw = w - w % mw if fx else w
    th = h - h % mh if fy else h
    if tw == 0 or th == 0:
        return 'refuse'
    if tr:
        tw, th = th, tw
    return [tw, th]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[[[8, 24, 3, '422'], 'refuse'], [[12, 29, 3, '422'], 'refuse'], [[24, 12, 0, '440'], [24, 12]], [[2969, 96, 1, '422'], [2969, 96]], [[24, 16, 5, '422'], [16, 24]], [[40, 2600, 0, '440'], [40, 2600]], [[24, 20, 0, '444'], [24, 20]], [[12, 16, 7, '420'], 'refuse']], [[[8, 2948, 7, '422'], 'refuse'], [[24, 24, 2, '440'], [24, 24]], [[40, 8, 2, '422'], [32, 8]], [[12, 1946, 4, '420'], [12, 1936]], [[8, 12, 1, '411'], 'unknown-sampling'], [[24, 24, 0, '422'], [24, 24]], [[16, 16, 6, '444'], [16, 16]], [[71, 24, 8, '440'], [24, 64]]], [[[8, 12, 8, '420'], 'refuse'], [[8, 16, 8, '422'], 'refuse'], [[24, 20, 8, '422'], [20, 16]], [[24, 12, 6, '422'], [8, 24]], [[8, 8, 6, '440'], 'refuse'], [[24, 8, 4, '444'], [24, 8]], [[12, 12, 3, '420'], 'refuse'], [[8, 8, 8, '422'], 'refuse']], [[[2979, 24, 2, '422'], [2976, 24]], [[40, 58, 8, '422'], [58, 32]], [[12, 20, 2, '440'], [8, 20]], [[24, 12, 6, '420'], 'refuse'], [[40, 8, 5, '440'], [8, 40]], [[16, 272, 4, '422'], [16, 272]], [[24, 16, 6, '440'], [16, 24]], [[8, 71, 8, '420'], 'refuse']], [[[24, 12, 8, '420'], [12, 16]], [[12, 16, 8, '422'], 'refuse'], [[12, 20, 8, '422'], 'refuse'], [[8, 67, 7, '444'], [64, 8]], [[16, 24, 2, '411'], 'unknown-sampling'], [[40, 18, 1, '420'], [40, 18]], [[16, 74, 7, '422'], [72, 16]], [[8, 688, 2, '420'], 'refuse']]]
labels = ["regression: partial MCU trimming direction", "repair trap", "combined fault", "control", "control", "boundary", "boundary", "control"]
for i, (args, expected) in enumerate(fixtures[N-1]):
    check("%s %d" % (labels[i % len(labels)], i), solve(args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
regression: partial MCU trimming direction 0	`refuse`	`refuse`	Passed
repair trap 1	`refuse`	`refuse`	Passed
combined fault 2	`[24, 12]`	`[24, 12]`	Passed
control 3	`[2969, 96]`	`[2969, 96]`	Passed
control 4	`[16, 24]`	`[16, 24]`	Passed
boundary 5	`[40, 2600]`	`[40, 2600]`	Passed
boundary 6	`[24, 20]`	`[24, 20]`	Passed
control 7	`refuse`	`refuse`	Passed

SHA-256 / 5a9c4ca3b3bd8a610732569890aed5afe87755d811721b432c01ef586edb10ea

Verification & scope

A deterministic bounded teaching model with a stipulated contract; it makes no claim of conformance to any published specification. This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.

Observations recorded using Python 3.12.14 at 2026-09-29T14:49:41.125712+00:00.

Case digest / 37aee6c646c7f87c755959bdd1896316fddd630216a836229a9c60b839fdee82