Applying a monotone filter to PNG for Android app icons

monotone_process.py

import os
from PIL import Image, ImageEnhance

def apply_monotone(image_path, output_path, color=(0, 0, 255)):
    """Apply a monotone filter while preserving transparency."""
    img = Image.open(image_path).convert("RGBA")  # Ensure RGBA mode
    r, g, b, alpha = img.split()  # Separate channels

    # Convert image to grayscale
    grayscale = ImageEnhance.Color(img).enhance(0)

    # Apply color overlay only to non-transparent areas
    color_layer = Image.new("RGBA", img.size, color + (255,))
    blended = Image.blend(grayscale, color_layer, alpha=0.5)  # Blend monotone color

    # Restore the original alpha channel
    blended.putalpha(alpha)

    # Save the modified image
    os.makedirs(os.path.dirname(output_path), exist_ok=True)
    blended.save(output_path)
    print(f"Processed: {output_path}")

def process_icons(input_root="res", output_root="debug_res", color=(0, 0, 255)):
    """Find all ic_launcher.png files and apply the monotone filter."""
    for root, _, files in os.walk(input_root):
        for filename in files:
            if filename == "ic_launcher.png":
                input_path = os.path.join(root, filename)
                output_path = input_path.replace(input_root, output_root, 1)
                apply_monotone(input_path, output_path, color)

# Run the script (change color for different debug colors)
process_icons(color=(0, 0, 255))  # Blue for debug build