replacements.py

import pymatting
import numpy as np
from PIL import Image
import random
from pathlib import Path

def get_foreground_estimation(image, alpha):
    # Downscale the input image to match predicted_alpha
    h, w = alpha.shape
    downscaled_image = image.resize((w, h), Image.Resampling.LANCZOS)

    # Normalize the image to [0, 1] range
    normalized_image = np.array(downscaled_image) / 255.0

    # Invert the alpha mask since the pymatting library expects the sky to be the background
    inverted_alpha = 1 - alpha

    return pymatting.estimate_foreground_ml(image=normalized_image, alpha=inverted_alpha)


def sky_replacement(foreground, alpha_mask):
    new_sky_path = Path(__file__).parent / "assets/skies/francesco-ungaro-i75WTJn-RBY-unsplash.jpg"
    new_sky_img = Image.open(new_sky_path).convert("RGB")

    # Get the target size from the foreground image
    h, w = foreground.shape[:2]

    # Check the size of the sky image
    sky_width, sky_height = new_sky_img.size

    # If the sky image is smaller than the target size
    if sky_width < w or sky_height < h:
        scale = max(w / sky_width, h / sky_height)
        new_size = (int(sky_width * scale), int(sky_height * scale))
        new_sky_img = new_sky_img.resize(new_size, resample=Image.Resampling.LANCZOS)
        sky_width, sky_height = new_sky_img.size

    # Determine the maximum possible top-left coordinates for the crop
    max_left = sky_width - w
    max_top = sky_height - h

    # Choose random offsets for left and top within the valid range
    left = random.randint(a=0, b=max_left) if max_left > 0 else 0
    top = random.randint(a=0, b=max_top) if max_top > 0 else 0

    # Crop the sky image to the target size using the random offsets
    new_sky_img = new_sky_img.crop((left, top, left + w, top + h))

    new_sky = np.asarray(new_sky_img).astype(np.float32) / 255.0
    if foreground.dtype != np.float32:
        foreground = foreground.astype(np.float32) / 255.0
    if foreground.shape[2] == 4:
        foreground = foreground[:, :, :3]

    # Ensure that the alpha mask values are within the range [0, 1]
    alpha_mask = np.clip(alpha_mask, a_min=0, a_max=1)

    # Blend the foreground with the new sky using the alpha mask
    return (1 - alpha_mask[:, :, None]) * foreground + alpha_mask[:, :, None] * new_sky