{"abstract":"Premultiplied foreground is multiplied by opacity a second time.","category":"Raster compositing","checks":4,"contract":"Source is a premultiplied channel in [0,alpha]; destination is a normalized premultiplied channel. Return source-over premultiplied channel.","contract_signature":"source, alpha, destination","evaluation_group":"xg-premultiplied-source-over-channel","failed_approach":"Adding channels directly fails to remove covered destination contribution.","family":"xg-premultiplied-source-over-channel","id":"FA-10536","implementations":{"attempt":{"sha256":"6aeaf68b4d631cb42ee2a3856b2bab9ac5b4c881aee1bce6f3b788a27fefdd6d","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\nimport math\nN = 1\nobservations = []\ndef solve(source, alpha, destination):\n    return source+destination\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('fixture 1', solve(*(0.4, 0.5, 0.2)), 0.5)\ncheck('fixture 2', solve(*(0, 0, 0.25)), 0.25)\ncheck('fixture 3', solve(*(0.25, 1, 0.8)), 0.25)\ncheck('fixture 4', solve(*(0.125, 0.5, 0.5)), 0.375)\nprint(json.dumps({\"observations\": observations, \"passed\": all(x[\"passed\"] for x in observations)}, ensure_ascii=False))\nraise SystemExit(0 if all(x[\"passed\"] for x in observations) else 1)\n"},"broken":{"sha256":"725e648bd3a071ca4f76e134733654ef48191707f805d70d44e9673c7dfe143b","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\nimport math\nN = 1\nobservations = []\ndef solve(source, alpha, destination):\n    return source*alpha+destination*(1-alpha)\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('fixture 1', solve(*(0.4, 0.5, 0.2)), 0.5)\ncheck('fixture 2', solve(*(0, 0, 0.25)), 0.25)\ncheck('fixture 3', solve(*(0.25, 1, 0.8)), 0.25)\ncheck('fixture 4', solve(*(0.125, 0.5, 0.5)), 0.375)\nprint(json.dumps({\"observations\": observations, \"passed\": all(x[\"passed\"] for x in observations)}, ensure_ascii=False))\nraise SystemExit(0 if all(x[\"passed\"] for x in observations) else 1)\n"}},"limitations":" 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.","method":"Deterministic executable model with adversarial boundary fixtures.","provenance":{"created_by":"Failure Map","dependencies":"Python standard library","family":"xg-premultiplied-source-over-channel","generated_at":"2026-09-29T14:38:39.897350+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"A deterministic software graphics stage with explicit channel and coordinate conventions; no hardware, device profile or API behavior is inferred.","root_cause":"Premultiplied foreground is multiplied by opacity a second time.","sha256":"bf16072ba1667d4bec252d59640bbf2275c53b52ad01bd0ace4fb8d785564a87","title":"Premultiplied source over channel · case 01","variant":1,"variant_policy":"Five numbered records share a model and may reuse boundary fixtures.","verified":true,"visibility":"public","verification":{"attempt":{"elapsed_ms":39.795,"exit_code":1,"observations":[{"actual":0.6000000000000001,"check":"fixture 1","expected":0.5,"passed":false},{"actual":0.25,"check":"fixture 2","expected":0.25,"passed":true},{"actual":1.05,"check":"fixture 3","expected":0.25,"passed":false},{"actual":0.625,"check":"fixture 4","expected":0.375,"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"fixture 1\", \"actual\": 0.6000000000000001, \"expected\": 0.5, \"passed\": false}, {\"check\": \"fixture 2\", \"actual\": 0.25, \"expected\": 0.25, \"passed\": true}, {\"check\": \"fixture 3\", \"actual\": 1.05, \"expected\": 0.25, \"passed\": false}, {\"check\": \"fixture 4\", \"actual\": 0.625, \"expected\": 0.375, \"passed\": false}], \"passed\": false}\n"},"broken":{"elapsed_ms":35.542,"exit_code":1,"observations":[{"actual":0.30000000000000004,"check":"fixture 1","expected":0.5,"passed":false},{"actual":0.25,"check":"fixture 2","expected":0.25,"passed":true},{"actual":0.25,"check":"fixture 3","expected":0.25,"passed":true},{"actual":0.3125,"check":"fixture 4","expected":0.375,"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"fixture 1\", \"actual\": 0.30000000000000004, \"expected\": 0.5, \"passed\": false}, {\"check\": \"fixture 2\", \"actual\": 0.25, \"expected\": 0.25, \"passed\": true}, {\"check\": \"fixture 3\", \"actual\": 0.25, \"expected\": 0.25, \"passed\": true}, {\"check\": \"fixture 4\", \"actual\": 0.3125, \"expected\": 0.375, \"passed\": false}], \"passed\": false}\n"}},"member_only":{"stages":["fixed"],"fields":["implementations.fixed","verification.fixed","harness","repair"],"note":"The verified repair, its recorded checks, the repair description, and the scoring harness are available to members."}}