convert image to weezer collage

	from argparse import ArgumentParser
	from pathlib import Path

	import cv2
	import numpy as np
	import numpy.typing as npt


	def generate_collage(
	image: npt.NDArray,
	red: npt.NDArray,
	green: npt.NDArray,
	blue: npt.NDArray,
	tile_size: int,
	upscale: int,
	) -> npt.NDArray:
	scale = (tile_size, tile_size)
	image = cv2.resize(
	image,
	(np.array(image.shape[:2][::-1]) * upscale // tile_size).tolist(),
	interpolation=cv2.INTER_AREA,
	)
	red_small = cv2.resize(red, scale)
	green_small = cv2.resize(green, scale)
	blue_small = cv2.resize(blue, scale)

	red_average = np.mean(red, axis=(0, 1))
	green_average = np.mean(green, axis=(0, 1))
	blue_average = np.mean(blue, axis=(0, 1))

	mat = np.column_stack([red_average, green_average, blue_average])
	inv = np.linalg.inv(mat)
	weights = np.clip(np.einsum("ij,klj->kli", inv, image), 0, 1)

	tiles = np.einsum(
	"ijk,lmnk->iljmn",
	weights,
	np.stack([red_small, green_small, blue_small], axis=-1),
	)

	return (
	tiles.reshape((*np.multiply(image.shape[:2], scale), 3))
	.clip(0, 255)
	.astype(np.uint8)
	)


	def validate_input_image(filename: str, name: str) -> npt.NDArray:
	path = Path(filename)

	if not path.exists():
	raise FileNotFoundError(f"File for {name} does not exist")
	elif not path.is_file():
	raise OSError(f"Path for {name} is not a file")

	ret = cv2.imread(path, cv2.IMREAD_COLOR_RGB)
	if ret is None:
	raise OSError(f"Could not read image file for {name}")
	return ret


	if __name__ == "__main__":
	parser = ArgumentParser("Generates Weezer collage from input image")
	# you'll have to download the album cover images yourself first
	parser.add_argument("--red", default="red.png", help="Red Album cover image path")
	parser.add_argument(
	"--green", default="green.png", help="Green Album cover image path"
	)
	parser.add_argument(
	"--blue", default="blue.png", help="Blue Album cover image path"
	)
	parser.add_argument("-i", "--input", help="input image path")
	parser.add_argument("-o", "--output", help="output image path")
	parser.add_argument(
	"--tile-size", default=100, type=int, help="size of individual tiles"
	)
	parser.add_argument("--upscale", default=4, type=int, help="upscale factor")
	args = parser.parse_args()

	output_path = Path(args.output)
	if output_path.exists() and not output_path.is_file():
	raise OSError("Output path is not a file")
	output_path.parent.mkdir(parents=True, exist_ok=True)

	red = validate_input_image(args.red, "Red Album cover")
	green = validate_input_image(args.green, "Green Album cover")
	blue = validate_input_image(args.blue, "Blue Album cover")
	image = validate_input_image(args.input, "input")

	collage = generate_collage(image, red, green, blue, args.tile_size, args.upscale)
	cv2.imwrite(output_path, collage[..., ::-1])

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