ossrules.md

imagegen Skill

Generate or edit raster images when the task benefits from AI-created bitmap visuals such as photos, illustrations, textures, sprites, mockups, or transparent-background cutouts. Use when Codex should create a brand-new image, transform an existing image, or derive visual variants from references, and the output should be a bitmap asset rather than repo-native code or vector. Do not use when the task is better handled by editing existing SVG/vector/code-native assets, extending an established icon or logo system, or building the visual directly in HTML/CSS/canvas.

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npx skills add 'https://github.com/openai/codex/tree/main/codex-rs/skills/src/assets/samples/imagegen'
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scripts/remove_chroma_key.py

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#!/usr/bin/env python3"""Remove a solid chroma-key background from an image. This helper supports the imagegen skill's built-in-first transparent workflow:generate an image on a flat key color, then convert that key color to alpha.""" from __future__ import annotations import argparsefrom io import BytesIOfrom pathlib import Pathimport refrom statistics import medianimport sysfrom typing import Tuple  Color = Tuple[int, int, int]KEY_DOMINANCE_THRESHOLD = 16.0ALPHA_NOISE_FLOOR = 8  def _die(message: str, code: int = 1) -> None:    print(f"Error: {message}", file=sys.stderr)    raise SystemExit(code)  def _dependency_hint(package: str) -> str:    return (        "Activate the repo-selected environment first, then install it with "        f"`uv pip install {package}`. If this repo uses a local virtualenv, start with "        "`source .venv/bin/activate`; otherwise use this repo's configured shared fallback "        "environment."    )  def _load_pillow():    try:        from PIL import Image, ImageFilter    except ImportError:        _die(f"Pillow is required for chroma-key removal. {_dependency_hint('pillow')}")    return Image, ImageFilter  def _parse_key_color(raw: str) -> Color:    value = raw.strip()    match = re.fullmatch(r"#?([0-9a-fA-F]{6})", value)    if not match:        _die("key color must be a hex RGB value like #00ff00.")    hex_value = match.group(1)    return (        int(hex_value[0:2], 16),        int(hex_value[2:4], 16),        int(hex_value[4:6], 16),    )  def _validate_args(args: argparse.Namespace) -> None:    if args.tolerance < 0 or args.tolerance > 255:        _die("--tolerance must be between 0 and 255.")    if args.transparent_threshold < 0 or args.transparent_threshold > 255:        _die("--transparent-threshold must be between 0 and 255.")    if args.opaque_threshold < 0 or args.opaque_threshold > 255:        _die("--opaque-threshold must be between 0 and 255.")    if args.soft_matte and args.transparent_threshold >= args.opaque_threshold:        _die("--transparent-threshold must be lower than --opaque-threshold.")    if args.edge_feather < 0 or args.edge_feather > 64:        _die("--edge-feather must be between 0 and 64.")    if args.edge_contract < 0 or args.edge_contract > 16:        _die("--edge-contract must be between 0 and 16.")     src = Path(args.input)    if not src.exists():        _die(f"Input image not found: {src}")     out = Path(args.out)    if out.exists() and not args.force:        _die(f"Output already exists: {out} (use --force to overwrite)")     if out.suffix.lower() not in {".png", ".webp"}:        _die("--out must end in .png or .webp so the alpha channel is preserved.")  def _channel_distance(a: Color, b: Color) -> int:    return max(abs(a[0] - b[0]), abs(a[1] - b[1]), abs(a[2] - b[2]))  def _clamp_channel(value: float) -> int:    return max(0, min(255, int(round(value))))  def _smoothstep(value: float) -> float:    value = max(0.0, min(1.0, value))    return value * value * (3.0 - 2.0 * value)  def _soft_alpha(    distance: int, transparent_threshold: float, opaque_threshold: float) -> int:    if distance <= transparent_threshold:        return 0    if distance >= opaque_threshold:        return 255    ratio = (float(distance) - transparent_threshold) / (        opaque_threshold - transparent_threshold    )    return _clamp_channel(255.0 * _smoothstep(ratio))  def _dominance_alpha(rgb: Color, key: Color) -> int:    spill_channels = _spill_channels(key)    if not spill_channels:        return 255     channels = [float(value) for value in rgb]    non_spill = [idx for idx in range(3) if idx not in spill_channels]    key_strength = (        min(channels[idx] for idx in spill_channels)        if len(spill_channels) > 1        else channels[spill_channels[0]]    )    non_key_strength = max((channels[idx] for idx in non_spill), default=0.0)    dominance = key_strength - non_key_strength    if dominance <= 0:        return 255     denominator = max(1.0, float(max(key)) - non_key_strength)    alpha = 1.0 - min(1.0, dominance / denominator)    return _clamp_channel(alpha * 255.0)  def _spill_channels(key: Color) -> list[int]:    key_max = max(key)    if key_max < 128:        return []    return [        idx for idx, value in enumerate(key) if value >= key_max - 16 and value >= 128    ]  def _key_channel_dominance(rgb: Color, key: Color) -> float:    spill_channels = _spill_channels(key)    if not spill_channels:        return 0.0     channels = [float(value) for value in rgb]    non_spill = [idx for idx in range(3) if idx not in spill_channels]    key_strength = (        min(channels[idx] for idx in spill_channels)        if len(spill_channels) > 1        else channels[spill_channels[0]]    )    non_key_strength = max((channels[idx] for idx in non_spill), default=0.0)    return key_strength - non_key_strength  def _looks_key_colored(rgb: Color, key: Color, distance: int) -> bool:    if distance <= 32:        return True     spill_channels = _spill_channels(key)    if not spill_channels:        return True     return _key_channel_dominance(rgb, key) >= KEY_DOMINANCE_THRESHOLD  def _cleanup_spill(rgb: Color, key: Color, alpha: int = 255) -> Color:    if alpha >= 252:        return rgb     spill_channels = _spill_channels(key)    if not spill_channels:        return rgb     channels = [float(value) for value in rgb]    non_spill = [idx for idx in range(3) if idx not in spill_channels]    if non_spill:        anchor = max(channels[idx] for idx in non_spill)        cap = max(0.0, anchor - 1.0)        for idx in spill_channels:            if channels[idx] > cap:                channels[idx] = cap     return (        _clamp_channel(channels[0]),        _clamp_channel(channels[1]),        _clamp_channel(channels[2]),    )  def _apply_alpha_to_image(    image,    *,    key: Color,    tolerance: int,    spill_cleanup: bool,    soft_matte: bool,    transparent_threshold: float,    opaque_threshold: float,) -> int:    pixels = image.load()    width, height = image.size    transparent = 0     for y in range(height):        for x in range(width):            red, green, blue, alpha = pixels[x, y]            rgb = (red, green, blue)            distance = _channel_distance(rgb, key)            key_like = _looks_key_colored(rgb, key, distance)            output_alpha = (                min(                    _soft_alpha(distance, transparent_threshold, opaque_threshold),                    _dominance_alpha(rgb, key),                )                if soft_matte and key_like                else (0 if distance <= tolerance else 255)            )            output_alpha = int(round(output_alpha * (alpha / 255.0)))            if 0 < output_alpha <= ALPHA_NOISE_FLOOR:                output_alpha = 0             if output_alpha == 0:                pixels[x, y] = (0, 0, 0, 0)                transparent += 1                continue             if spill_cleanup and key_like:                red, green, blue = _cleanup_spill(rgb, key, output_alpha)            pixels[x, y] = (red, green, blue, output_alpha)     return transparent  def _contract_alpha(image, pixels: int):    if pixels == 0:        return image     _, ImageFilter = _load_pillow()    alpha = image.getchannel("A")    for _ in range(pixels):        alpha = alpha.filter(ImageFilter.MinFilter(3))    image.putalpha(alpha)    return image  def _apply_edge_feather(image, radius: float):    if radius == 0:        return image     _, ImageFilter = _load_pillow()    alpha = image.getchannel("A")    alpha = alpha.filter(ImageFilter.GaussianBlur(radius=radius))    image.putalpha(alpha)    return image  def _encode_image(image, output_format: str) -> bytes:    out = BytesIO()    image.save(out, format=output_format.upper())    return out.getvalue()  def _alpha_counts(image) -> tuple[int, int, int]:    pixels = image.load()    width, height = image.size    total = 0    transparent = 0    partial = 0     for y in range(height):        for x in range(width):            alpha = pixels[x, y][3]            total += 1            if alpha == 0:                transparent += 1            elif alpha < 255:                partial += 1     return total, transparent, partial  def _sample_border_key(image, mode: str) -> Color:    width, height = image.size    pixels = image.load()    samples: list[Color] = []     if mode == "corners":        patch = max(1, min(width, height, 12))        boxes = [            (0, 0, patch, patch),            (width - patch, 0, width, patch),            (0, height - patch, patch, height),            (width - patch, height - patch, width, height),        ]        for left, top, right, bottom in boxes:            for y in range(top, bottom):                for x in range(left, right):                    red, green, blue = pixels[x, y][:3]                    samples.append((red, green, blue))    else:        band = max(1, min(width, height, 6))        step = max(1, min(width, height) // 256)        for x in range(0, width, step):            for y in range(band):                red, green, blue = pixels[x, y][:3]                samples.append((red, green, blue))                red, green, blue = pixels[x, height - 1 - y][:3]                samples.append((red, green, blue))        for y in range(0, height, step):            for x in range(band):                red, green, blue = pixels[x, y][:3]                samples.append((red, green, blue))                red, green, blue = pixels[width - 1 - x, y][:3]                samples.append((red, green, blue))     if not samples:        _die("Could not sample background key color from image border.")     return (        int(round(median(sample[0] for sample in samples))),        int(round(median(sample[1] for sample in samples))),        int(round(median(sample[2] for sample in samples))),    )  def _remove_chroma_key(args: argparse.Namespace) -> None:    Image, _ = _load_pillow()    src = Path(args.input)    out = Path(args.out)     with Image.open(src) as image:        rgba = image.convert("RGBA")    key = (        _sample_border_key(rgba, args.auto_key)        if args.auto_key != "none"        else _parse_key_color(args.key_color)    )     transparent = _apply_alpha_to_image(        rgba,        key=key,        tolerance=args.tolerance,        spill_cleanup=args.spill_cleanup,        soft_matte=args.soft_matte,        transparent_threshold=args.transparent_threshold,        opaque_threshold=args.opaque_threshold,    )    rgba = _contract_alpha(rgba, args.edge_contract)    rgba = _apply_edge_feather(rgba, args.edge_feather)     total, transparent_after, partial_after = _alpha_counts(rgba)     out.parent.mkdir(parents=True, exist_ok=True)    output_format = "PNG" if out.suffix.lower() == ".png" else "WEBP"    out.write_bytes(_encode_image(rgba, output_format))     print(f"Wrote {out}")    print(f"Key color: #{key[0]:02x}{key[1]:02x}{key[2]:02x}")    print(f"Transparent pixels: {transparent_after}/{total}")    print(f"Partially transparent pixels: {partial_after}/{total}")    if transparent == 0:        print(            "Warning: no pixels matched the key color before feathering.",            file=sys.stderr,        )  def _build_parser() -> argparse.ArgumentParser:    parser = argparse.ArgumentParser(        description="Remove a solid chroma-key background and write an image with alpha."    )    parser.add_argument("--input", required=True, help="Input image path.")    parser.add_argument("--out", required=True, help="Output .png or .webp path.")    parser.add_argument(        "--key-color",        default="#00ff00",        help="Hex RGB key color to remove, for example #00ff00.",    )    parser.add_argument(        "--tolerance",        type=int,        default=12,        help="Hard-key per-channel tolerance for matching the key color, 0-255.",    )    parser.add_argument(        "--auto-key",        choices=["none", "corners", "border"],        default="none",        help="Sample the key color from image corners or border instead of --key-color.",    )    parser.add_argument(        "--soft-matte",        action="store_true",        help="Use a smooth alpha ramp between transparent and opaque thresholds.",    )    parser.add_argument(        "--transparent-threshold",        type=float,        default=12.0,        help="Soft-matte distance at or below which pixels become fully transparent.",    )    parser.add_argument(        "--opaque-threshold",        type=float,        default=96.0,        help="Soft-matte distance at or above which pixels become fully opaque.",    )    parser.add_argument(        "--edge-feather",        type=float,        default=0.0,        help="Optional alpha blur radius for softened edges, 0-64.",    )    parser.add_argument(        "--edge-contract",        type=int,        default=0,        help="Shrink the visible alpha matte by this many pixels before feathering.",    )    parser.add_argument(        "--spill-cleanup",        dest="spill_cleanup",        action="store_true",        help="Reduce obvious key-color spill on opaque pixels.",    )    parser.add_argument(        "--despill",        dest="spill_cleanup",        action="store_true",        help="Alias for --spill-cleanup; decontaminate key-color edge spill.",    )    parser.add_argument(        "--force", action="store_true", help="Overwrite an existing output file."    )    return parser  def main() -> None:    parser = _build_parser()    args = parser.parse_args()    _validate_args(args)    _remove_chroma_key(args)  if __name__ == "__main__":    main()
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