pymatting 1.1.15: estimate_alpha_rw

Clean-room public code sample — generation instructions

Write a brand-new, minimal, self-contained code sample in this clean-room directory.
Do not copy, paraphrase, or reference any existing project source. Work only from this spec.

A csx.json manifest scaffold already exists. Do not recreate it from memory. Preserve its case.goal, packages and symbols; fill its empty case.contract with exact assertions and correct its environment, commands and verifierAdapter for the files you generate.

Goal: verify pymatting.estimate_alpha_rw in pkg:pypi/pymatting@1.1.15
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:pypi/pymatting@1.1.15
Demonstrate these symbols/APIs:
  - pymatting.estimate_alpha_rw
Constraints:
  - executionContext: node
Required runtime conditions:
  - ecosystem: npm
  - language: javascript
  - moduleSystem: cjs
  - packageManager: npm@10.9.8
  - runtime: node@22.23.2

Rules:
  - One focused purpose; the smallest project that proves the goal.
  - Include a contract test (test/contract.*) that runs OFFLINE and exits 0 exactly when the goal behavior works.
  - Pin every dependency with a lockfile so resolution is reproducible.
  - No secrets, credentials, or tokens. No real URLs (only example.com or localhost). No absolute paths.
  - No personal names, emails, company names, or project identifiers of any kind.
  - No binaries and no generated output (node_modules, dist, target, venv, .git, .env).
  - Keep it under 200 files and 256KB packed.

{"case":{"caseId":"case:sha256:b779f6e1f55847768cf323f818a5728f2ed4bc537033ae5753f565dd1fa68bdd","constraints":{"executionContext":"python"},"contract":["assert estimate_alpha_rw computes random walk alpha matte bounded in [0, 1] matching trimap constraints","assert estimate_alpha_rw accepts custom laplacian_kwargs and cg_kwargs parameters","assert estimate_alpha_rw raises ValueError when trimap is missing background values"],"goal":"verify pymatting.estimate_alpha_rw in pkg:pypi/pymatting@1.1.15","kind":"HOW","packages":["pkg:pypi/pymatting@1.1.15"],"schemaVersion":1,"symbols":["pymatting.estimate_alpha_rw"]},"contractCommand":["python3","test/contract.py"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"pypi","executionContext":"python","language":"python","libc":"glibc","libcVersion":"2.39","moduleSystem":"standard","os":"linux","osVersionBucket":"24","packageManager":"pip","packageManagerVersion":"24.0","runtime":"python","runtimeVersion":"3.12","schemaVersion":1},"license":"MIT-0","packages":["pkg:pypi/pymatting@1.1.15"],"schemaVersion":1,"subject":"pkg:pypi/pymatting@1.1.15","symbols":["pymatting.estimate_alpha_rw"],"verifierAdapter":"python@1"}

[project]
name = "verify-pymatting"
version = "0.1.0"
dependencies = [
    "pymatting==1.1.15",
]

pymatting==1.1.15
numpy
scipy
pillow

{
  "schemaVersion": 1,
  "goal": "verify pymatting.estimate_alpha_rw in pkg:pypi/pymatting@1.1.15",
  "kind": "HOW",
  "packages": [
    "pkg:pypi/pymatting@1.1.15"
  ],
  "symbols": [
    "pymatting.estimate_alpha_rw"
  ],
  "constraints": {
    "executionContext": "node"
  },
  "runtimeConditions": {
    "ecosystem": "npm",
    "language": "javascript",
    "moduleSystem": "cjs",
    "packageManager": "npm@10.9.8",
    "runtime": "node@22.23.2"
  }
}

import numpy as np
from pymatting import estimate_alpha_rw


def test_estimate_alpha_rw_basic():
    h, w = 12, 12
    image = np.zeros((h, w, 3), dtype=np.float64)
    trimap = np.full((h, w), 0.5, dtype=np.float64)

    trimap[:, :4] = 0.0
    trimap[:, 8:] = 1.0

    image[:, :4] = [0.1, 0.1, 0.1]
    image[:, 8:] = [0.9, 0.9, 0.9]
    image[:, 4:8] = [0.5, 0.5, 0.5]

    alpha = estimate_alpha_rw(image, trimap)
    assert alpha.shape == (h, w)
    assert np.all(alpha >= -1e-5) and np.all(alpha <= 1.0 + 1e-5)
    assert np.all(alpha[:, :4] < 0.1)
    assert np.all(alpha[:, 8:] > 0.9)


def test_estimate_alpha_rw_custom_parameters():
    h, w = 10, 10
    image = np.zeros((h, w, 3), dtype=np.float64)
    trimap = np.full((h, w), 0.5, dtype=np.float64)

    trimap[:, :3] = 0.0
    trimap[:, 7:] = 1.0

    image[:, :3] = [0.2, 0.2, 0.2]
    image[:, 7:] = [0.8, 0.8, 0.8]
    image[:, 3:7] = [0.5, 0.5, 0.5]

    alpha = estimate_alpha_rw(
        image,
        trimap,
        laplacian_kwargs={"sigma": 0.05, "radius": 1},
        cg_kwargs={"maxiter": 100},
    )
    assert alpha.shape == (h, w)
    assert np.all(alpha >= -1e-5) and np.all(alpha <= 1.0 + 1e-5)
    assert np.all(alpha[:, :3] < 0.1)
    assert np.all(alpha[:, 7:] > 0.9)


def test_estimate_alpha_rw_invalid_trimap():
    h, w = 8, 8
    image = np.zeros((h, w, 3), dtype=np.float64)
    no_bg_trimap = np.ones((h, w), dtype=np.float64)

    try:
        estimate_alpha_rw(image, no_bg_trimap)
        assert False, "estimate_alpha_rw should raise ValueError when trimap is missing background"
    except ValueError as exc:
        assert isinstance(exc, ValueError)


def main():
    test_estimate_alpha_rw_basic()
    test_estimate_alpha_rw_custom_parameters()
    test_estimate_alpha_rw_invalid_trimap()
    print("All contract assertions passed.")


if __name__ == "__main__":
    main()