FA-78946 / Image orientation metadata / Open access
Flipping a rotated photo keeps its rotation count · case 01
Mirroring a portrait photo in the editor leaves it lying on its side.
ROOT CAUSE
A display-space mirror applied after a rotation reverses the rotation direction, but the code keeps k unchanged.
VERIFIED REPAIR
Negate the quarter-turn count modulo 4 when toggling the mirror bit for flip_h.
Unsuccessful approach: Adding a half turn is only right when the current rotation is a quarter turn.
Case contract
A photo editor rotates and flips losslessly by rewriting only the orientation tag. An orientation is modelled as (k, m): mirror horizontally m times, then rotate k quarter turns clockwise (tag table 1:(0,0) 2:(0,1) 3:(2,0) 4:(2,1) 5:(3,1) 6:(1,0) 7:(1,1) 8:(3,0)). Editor operations act on the displayed image: cw, ccw, r180, flip_h (mirror left-right) and flip_v (mirror top-bottom). Invalid starting tags count as 1; an unknown operation returns {"error": "unknown-op", "op": op}. Return the final tag.
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(tag, ops):
to_km = {1: (0, 0), 2: (0, 1), 3: (2, 0), 4: (2, 1), 5: (3, 1), 6: (1, 0), 7: (1, 1), 8: (3, 0)}
from_km = {v: t for t, v in to_km.items()}
if tag not in to_km:
tag = 1
k, m = to_km[tag]
for op in ops:
if op == 'cw':
k = (k + 1) % 4
elif op == 'ccw':
k = (k + 3) % 4
elif op == 'r180':
k = (k + 2) % 4
elif op == 'flip_h':
k, m = k, 1 - m
elif op == 'flip_v':
k, m = (2 - k) % 4, 1 - m
else:
return {'error': 'unknown-op', 'op': op}
return from_km[(k, m)]
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[[(4, ['cw', 'cw', 'ccw', 'flip_h']), 6], [(8, ['ccw', 'flip_h', 'ccw']), 7], [(0, ['flip_h', 'ccw', 'flip_h', 'flip_v']), 7], [(7, ['flip_v', 'ccw', 'r180']), 3], [(8, ['ccw', 'cw']), 8], [(3, ['rotate']), {'error': 'unknown-op', 'op': 'rotate'}], [(1, ['cw', 'ccw', 'r180', 'cw']), 8], [(2, ['ccw', 'flip_h', 'r180', 'ccw']), 3]], [[(11, ['flip_v', 'ccw', 'flip_h', 'flip_v']), 5], [(7, ['cw', 'r180', 'flip_h']), 1], [(8, ['ccw', 'flip_h', 'ccw', 'flip_h']), 8], [(0, []), 1], [(8, ['ccw', 'r180']), 1], [(4, ['mirror', 'flip_v', 'cw', 'r180']), {'error': 'unknown-op', 'op': 'mirror'}], [(2, ['flip_v', 'ccw', 'cw']), 3], [(7, ['flip_h', 'flip_v']), 5]], [[(5, ['flip_h']), 6], [(11, ['flip_h']), 2], [(4, ['flip_h', 'ccw', 'flip_h']), 5], [(1, ['ccw', 'ccw', 'r180']), 1], [(11, ['r180', 'cw', 'flip_v', 'cw']), 2], [(2, ['flip_v', 'cw', 'cw']), 1], [(6, ['r180', 'flip_v', 'ccw']), 4], [(11, ['cw', 'flip_v', 'flip_h']), 8]], [[(5, ['flip_h', 'flip_v', 'r180']), 5], [(8, ['ccw', 'flip_h']), 4], [(1, ['flip_h', 'ccw', 'r180', 'flip_h']), 8], [(4, ['ccw']), 7], [(8, ['rotate']), {'error': 'unknown-op', 'op': 'rotate'}], [(4, ['ccw', 'ccw', 'flip_v', 'ccw']), 6], [(11, ['r180']), 3], [(2, ['ccw', 'r180', 'flip_h', 'flip_v']), 5]], [[(4, ['cw', 'flip_h']), 6], [(0, ['flip_h', 'r180', 'flip_v']), 1], [(3, ['r180', 'flip_h', 'ccw', 'flip_h']), 6], [(1, []), 1], [(11, ['cw', 'cw', 'ccw']), 6], [(5, ['r180']), 7], [(6, ['ccw']), 1], [(7, ['flip_h']), 8]]]
labels = ["regression: horizontal flip of a rotated view", "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: horizontal flip of a rotated view 0 | 8 | 6 | Failed |
| repair trap 1 | 7 | 7 | Passed |
| combined fault 2 | 5 | 7 | Failed |
| control 3 | 3 | 3 | Passed |
| control 4 | 8 | 8 | Passed |
| boundary 5 | {'error': 'unknown-op', 'op': 'rotate'} | {'error': 'unknown-op', 'op': 'rotate'} | Passed |
| boundary 6 | 8 | 8 | Passed |
| control 7 | 1 | 3 | Failed |
SHA-256 / 2d4f57000ce366ab66a2f841d0d4ea42a67f8d1028119061d7f559bd6a5a37a4
2 / The unsuccessful fix
Exit 1"""Failure Map reference implementation. Python standard library only."""
import json
N = 1
observations = []
def solve(tag, ops):
to_km = {1: (0, 0), 2: (0, 1), 3: (2, 0), 4: (2, 1), 5: (3, 1), 6: (1, 0), 7: (1, 1), 8: (3, 0)}
from_km = {v: t for t, v in to_km.items()}
if tag not in to_km:
tag = 1
k, m = to_km[tag]
for op in ops:
if op == 'cw':
k = (k + 1) % 4
elif op == 'ccw':
k = (k + 3) % 4
elif op == 'r180':
k = (k + 2) % 4
elif op == 'flip_h':
k, m = (k + 2) % 4, 1 - m
elif op == 'flip_v':
k, m = (2 - k) % 4, 1 - m
else:
return {'error': 'unknown-op', 'op': op}
return from_km[(k, m)]
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[[(4, ['cw', 'cw', 'ccw', 'flip_h']), 6], [(8, ['ccw', 'flip_h', 'ccw']), 7], [(0, ['flip_h', 'ccw', 'flip_h', 'flip_v']), 7], [(7, ['flip_v', 'ccw', 'r180']), 3], [(8, ['ccw', 'cw']), 8], [(3, ['rotate']), {'error': 'unknown-op', 'op': 'rotate'}], [(1, ['cw', 'ccw', 'r180', 'cw']), 8], [(2, ['ccw', 'flip_h', 'r180', 'ccw']), 3]], [[(11, ['flip_v', 'ccw', 'flip_h', 'flip_v']), 5], [(7, ['cw', 'r180', 'flip_h']), 1], [(8, ['ccw', 'flip_h', 'ccw', 'flip_h']), 8], [(0, []), 1], [(8, ['ccw', 'r180']), 1], [(4, ['mirror', 'flip_v', 'cw', 'r180']), {'error': 'unknown-op', 'op': 'mirror'}], [(2, ['flip_v', 'ccw', 'cw']), 3], [(7, ['flip_h', 'flip_v']), 5]], [[(5, ['flip_h']), 6], [(11, ['flip_h']), 2], [(4, ['flip_h', 'ccw', 'flip_h']), 5], [(1, ['ccw', 'ccw', 'r180']), 1], [(11, ['r180', 'cw', 'flip_v', 'cw']), 2], [(2, ['flip_v', 'cw', 'cw']), 1], [(6, ['r180', 'flip_v', 'ccw']), 4], [(11, ['cw', 'flip_v', 'flip_h']), 8]], [[(5, ['flip_h', 'flip_v', 'r180']), 5], [(8, ['ccw', 'flip_h']), 4], [(1, ['flip_h', 'ccw', 'r180', 'flip_h']), 8], [(4, ['ccw']), 7], [(8, ['rotate']), {'error': 'unknown-op', 'op': 'rotate'}], [(4, ['ccw', 'ccw', 'flip_v', 'ccw']), 6], [(11, ['r180']), 3], [(2, ['ccw', 'r180', 'flip_h', 'flip_v']), 5]], [[(4, ['cw', 'flip_h']), 6], [(0, ['flip_h', 'r180', 'flip_v']), 1], [(3, ['r180', 'flip_h', 'ccw', 'flip_h']), 6], [(1, []), 1], [(11, ['cw', 'cw', 'ccw']), 6], [(5, ['r180']), 7], [(6, ['ccw']), 1], [(7, ['flip_h']), 8]]]
labels = ["regression: horizontal flip of a rotated view", "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: horizontal flip of a rotated view 0 | 6 | 6 | Passed |
| repair trap 1 | 5 | 7 | Failed |
| combined fault 2 | 5 | 7 | Failed |
| control 3 | 3 | 3 | Passed |
| control 4 | 8 | 8 | Passed |
| boundary 5 | {'error': 'unknown-op', 'op': 'rotate'} | {'error': 'unknown-op', 'op': 'rotate'} | Passed |
| boundary 6 | 8 | 8 | Passed |
| control 7 | 3 | 3 | Passed |
SHA-256 / a9d8f0c4d857fda8590cd34c99866e1fb0ac6e1c2f3b74997fd101d1169eed2c
3 / The verified repair
Exit 0"""Failure Map reference implementation. Python standard library only."""
import json
N = 1
observations = []
def solve(tag, ops):
to_km = {1: (0, 0), 2: (0, 1), 3: (2, 0), 4: (2, 1), 5: (3, 1), 6: (1, 0), 7: (1, 1), 8: (3, 0)}
from_km = {v: t for t, v in to_km.items()}
if tag not in to_km:
tag = 1
k, m = to_km[tag]
for op in ops:
if op == 'cw':
k = (k + 1) % 4
elif op == 'ccw':
k = (k + 3) % 4
elif op == 'r180':
k = (k + 2) % 4
elif op == 'flip_h':
k, m = (-k) % 4, 1 - m
elif op == 'flip_v':
k, m = (2 - k) % 4, 1 - m
else:
return {'error': 'unknown-op', 'op': op}
return from_km[(k, m)]
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[[(4, ['cw', 'cw', 'ccw', 'flip_h']), 6], [(8, ['ccw', 'flip_h', 'ccw']), 7], [(0, ['flip_h', 'ccw', 'flip_h', 'flip_v']), 7], [(7, ['flip_v', 'ccw', 'r180']), 3], [(8, ['ccw', 'cw']), 8], [(3, ['rotate']), {'error': 'unknown-op', 'op': 'rotate'}], [(1, ['cw', 'ccw', 'r180', 'cw']), 8], [(2, ['ccw', 'flip_h', 'r180', 'ccw']), 3]], [[(11, ['flip_v', 'ccw', 'flip_h', 'flip_v']), 5], [(7, ['cw', 'r180', 'flip_h']), 1], [(8, ['ccw', 'flip_h', 'ccw', 'flip_h']), 8], [(0, []), 1], [(8, ['ccw', 'r180']), 1], [(4, ['mirror', 'flip_v', 'cw', 'r180']), {'error': 'unknown-op', 'op': 'mirror'}], [(2, ['flip_v', 'ccw', 'cw']), 3], [(7, ['flip_h', 'flip_v']), 5]], [[(5, ['flip_h']), 6], [(11, ['flip_h']), 2], [(4, ['flip_h', 'ccw', 'flip_h']), 5], [(1, ['ccw', 'ccw', 'r180']), 1], [(11, ['r180', 'cw', 'flip_v', 'cw']), 2], [(2, ['flip_v', 'cw', 'cw']), 1], [(6, ['r180', 'flip_v', 'ccw']), 4], [(11, ['cw', 'flip_v', 'flip_h']), 8]], [[(5, ['flip_h', 'flip_v', 'r180']), 5], [(8, ['ccw', 'flip_h']), 4], [(1, ['flip_h', 'ccw', 'r180', 'flip_h']), 8], [(4, ['ccw']), 7], [(8, ['rotate']), {'error': 'unknown-op', 'op': 'rotate'}], [(4, ['ccw', 'ccw', 'flip_v', 'ccw']), 6], [(11, ['r180']), 3], [(2, ['ccw', 'r180', 'flip_h', 'flip_v']), 5]], [[(4, ['cw', 'flip_h']), 6], [(0, ['flip_h', 'r180', 'flip_v']), 1], [(3, ['r180', 'flip_h', 'ccw', 'flip_h']), 6], [(1, []), 1], [(11, ['cw', 'cw', 'ccw']), 6], [(5, ['r180']), 7], [(6, ['ccw']), 1], [(7, ['flip_h']), 8]]]
labels = ["regression: horizontal flip of a rotated view", "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: horizontal flip of a rotated view 0 | 6 | 6 | Passed |
| repair trap 1 | 7 | 7 | Passed |
| combined fault 2 | 7 | 7 | Passed |
| control 3 | 3 | 3 | Passed |
| control 4 | 8 | 8 | Passed |
| boundary 5 | {'error': 'unknown-op', 'op': 'rotate'} | {'error': 'unknown-op', 'op': 'rotate'} | Passed |
| boundary 6 | 8 | 8 | Passed |
| control 7 | 3 | 3 | Passed |
SHA-256 / bf141fda52073ffe1d7443b23d08a4d31ee9aebdd55bae03c80597396ead28b5
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 2026-09-29T14:49:39.881078+00:00.
Case digest / 4bc5860aa236c9c7c8b65983b15a432cc6c1b79f660ab0974a321dff5c0717b8