Expand image's canvas to Power of 2.

pot_images.py

#!/usr/bin/env python

from PIL import Image
import math
import os
from glob import glob


allowed_sizes = [2, 4, 8, 16, 64, 128, 256, 512, 1024, 2048]


def resize():
    
    cwd = os.getcwd()

    result = [y for x in os.walk(cwd) for y in glob(os.path.join(x[0], '*.png'))]
    for filepath in result:
        im = Image.open(filepath)
        image_width, image_height = im.size;
        if not is_pot(image_width, image_height):
            generate_pot_image(filepath)

    result = [y for x in os.walk(cwd) for y in glob(os.path.join(x[0], '*.jpg'))]
    for filepath in result:
        im = Image.open(filepath)
        image_width, image_height = im.size;
        if not is_pot(image_width, image_height):
            generate_pot_image(filepath)


def generate_pot_image(filepath):
    im = Image.open(filepath)
    image_width, image_height = im.size;

    if image_width > image_height:
        image_size = image_width
    else:
        image_size = image_height

    # Find POT size which fit for image.
    canvas_size = 0
    for size in allowed_sizes:
        if size > image_size:
            canvas_size = size
            break

    if canvas_size > 0:
        destination_filepath = os.path.splitext(filepath)[0] + '.png';

        # Center the image
        x = int(math.floor((canvas_size - image_width) / 2))
        y = int(math.floor((canvas_size - image_height) / 2))

        # Create POT canvas.
        newImage = Image.new('RGBA', (canvas_size, canvas_size), 255)
        newImage.paste(im, (x, y, x + image_width, y + image_height))
        newImage.save(destination_filepath)

        print destination_filepath
        
        if os.path.splitext(filepath)[-1] == '.jpg':
            # Delete original JPG file.
            os.remove(filepath)

            # Remove meta file to keep reference.
            jpg_meta_filepath = filepath + '.meta'
            png_meta_filepath = os.path.splitext(filepath)[0] + '.png.meta'
            if os.path.isfile(jpg_meta_filepath):
                os.rename(jpg_meta_filepath, png_meta_filepath)


def is_pot(width, height):
    if (width != height): return False
    return width > 0 and ((width & (width - 1)) == 0)


resize()

# How to use
# python pot_images.py /path/to/images/