FA-10536 / Raster compositing / Open access
Premultiplied source over channel · case 01
Premultiplied foreground is multiplied by opacity a second time.
ROOT CAUSE
Premultiplied foreground is multiplied by opacity a second time.
THE FAILURE
Premultiplied foreground is multiplied by opacity a second time.
Unsuccessful approach: Adding channels directly fails to remove covered destination contribution.
Case contract
Source is a premultiplied channel in [0,alpha]; destination is a normalized premultiplied channel. Return source-over premultiplied channel.
Why this case matters
A deterministic software graphics stage with explicit channel and coordinate conventions; no hardware, device profile or API behavior is inferred.
1 / The failure
Exit 1"""Failure Map reference implementation. Python standard library only."""
import json
import math
N = 1
observations = []
def solve(source, alpha, destination):
return source*alpha+destination*(1-alpha)
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('fixture 1', solve(*(0.4, 0.5, 0.2)), 0.5)
check('fixture 2', solve(*(0, 0, 0.25)), 0.25)
check('fixture 3', solve(*(0.25, 1, 0.8)), 0.25)
check('fixture 4', solve(*(0.125, 0.5, 0.5)), 0.375)
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 |
|---|---|---|---|
| fixture 1 | 0.30000000000000004 | 0.5 | Failed |
| fixture 2 | 0.25 | 0.25 | Passed |
| fixture 3 | 0.25 | 0.25 | Passed |
| fixture 4 | 0.3125 | 0.375 | Failed |
SHA-256 / 725e648bd3a071ca4f76e134733654ef48191707f805d70d44e9673c7dfe143b
2 / The unsuccessful fix
Exit 1"""Failure Map reference implementation. Python standard library only."""
import json
import math
N = 1
observations = []
def solve(source, alpha, destination):
return source+destination
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('fixture 1', solve(*(0.4, 0.5, 0.2)), 0.5)
check('fixture 2', solve(*(0, 0, 0.25)), 0.25)
check('fixture 3', solve(*(0.25, 1, 0.8)), 0.25)
check('fixture 4', solve(*(0.125, 0.5, 0.5)), 0.375)
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 |
|---|---|---|---|
| fixture 1 | 0.6000000000000001 | 0.5 | Failed |
| fixture 2 | 0.25 | 0.25 | Passed |
| fixture 3 | 1.05 | 0.25 | Failed |
| fixture 4 | 0.625 | 0.375 | Failed |
SHA-256 / 6aeaf68b4d631cb42ee2a3856b2bab9ac5b4c881aee1bce6f3b788a27fefdd6d
HELD IN THE MEMBER ARCHIVE
The verified repair and its recorded checks are member-only.
This mechanism has 4 recorded checks per implementation. The open-access tier publishes the failure and the unsuccessful fix; the repaired source that passes every check, and the observations that prove it, are available to members.
Every case sharing this mechanism uses the same contract and the same repair, so this one record is held back for all of them.
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Sign in to the archive ↗Verification & scope
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 2026-09-29T14:38:39.897350+00:00.
Case digest / bf16072ba1667d4bec252d59640bbf2275c53b52ad01bd0ace4fb8d785564a87