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