FA-10606 / Color encoding / Open access

Normalized channel to byte half up · case 01

Truncating scaled color introduces a downward quantization bias.

Verified by executionVariant 1 · 5 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

Truncating scaled color introduces a downward quantization bias.

THE FAILURE

Truncating scaled color introduces a downward quantization bias.

Unsuccessful approach: Banker rounding changes even-integer midpoint ties from half-up behavior.

Case contract

Clamp a finite normalized channel to byte range and round the scaled value to nearest with half-up ties.

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(value):
    return int(value*255)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('fixture 1', solve(*(0.5,)), 128)
check('fixture 2', solve(*(0.3,)), 77)
check('fixture 3', solve(*(-0.5,)), 0)
check('fixture 4', solve(*(1.5,)), 255)
check('fixture 5', solve(*(0,)), 0)
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	`127`	`128`	Failed
fixture 2	`76`	`77`	Failed
fixture 3	`-127`	`0`	Failed
fixture 4	`382`	`255`	Failed
fixture 5	`0`	`0`	Passed

SHA-256 / d25b1c15899371953e3351874644468bf1d7beb93b0772834575404d59dce1b0

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import math
N = 1
observations = []
def solve(value):
    return min(255,max(0,round(value*255)))
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('fixture 1', solve(*(0.5,)), 128)
check('fixture 2', solve(*(0.3,)), 77)
check('fixture 3', solve(*(-0.5,)), 0)
check('fixture 4', solve(*(1.5,)), 255)
check('fixture 5', solve(*(0,)), 0)
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	`128`	`128`	Passed
fixture 2	`76`	`77`	Failed
fixture 3	`0`	`0`	Passed
fixture 4	`255`	`255`	Passed
fixture 5	`0`	`0`	Passed

SHA-256 / 7294d8570de62ff4b1be61f00236d047340e3202ad4f535b39eac5f1c498761e

HELD IN THE MEMBER ARCHIVE

The verified repair and its recorded checks are member-only.

This mechanism has 5 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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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 2026-09-29T14:38:40.547767+00:00.

Case digest / c4e72d74f3c3d84d6fd13e57ffa2ca931067ec14f6497db710c6cbde5b960e5d