Resize the image to given size. Don't strech images, crop and center instead.

crop-resize.py

#!/usr/bin/env python
"""Resize the image to given size.

Don't strech images, crop and center instead.
"""
import os
import sys
from argparse import ArgumentParser, ArgumentDefaultsHelpFormatter
from fractions import Fraction
from functools import partial
from multiprocessing import Pool

from PIL import Image # $ sudo apt-get install python-imaging

def crop_resize(image, size, ratio):
    # crop to ratio, center
    w, h = image.size
    if w > ratio * h: # width is larger then necessary
        x, y = (w - ratio * h) // 2, 0
    else: # ratio*height >= width (height is larger)
        x, y = 0, (h - w / ratio) // 2
    image = image.crop((x, y, w - x, h - y))

    # resize
    if image.size > size: # don't stretch smaller images
        image.thumbnail(size, Image.ANTIALIAS)
    return image

def crop_resize_mp(input_filename, outputdir, size, ratio):
    try:
        image = crop_resize(Image.open(input_filename), size, ratio)

        # save resized image
        basename, ext = os.path.splitext(os.path.basename(input_filename))
        output_basename = basename + ("_%dx%d" % tuple(size)) + ext
        output_filename = os.path.join(outputdir, output_basename)
        image.save(output_filename)

        return (input_filename, output_filename), None
    except Exception as e:
        return (input_filename, None), e

def main():
    # parse command-line arguments
    parser = ArgumentParser(description=__doc__,
        formatter_class=ArgumentDefaultsHelpFormatter)
    parser.add_argument('-s', '--size', type=int, nargs=2,
                        default=[120, 80], metavar='N',
                        help='new image size')
    parser.add_argument('-q', '--quiet', action='store_true')
    parser.add_argument('--outputdir', default=os.curdir, metavar='DIR',
                        help='directory where to save resized images')
    parser.add_argument('files', nargs='+',
                        help='image filenames to process')
    args = parser.parse_args()

    # crop, resize using multiple processes
    error_count = 0
    f = partial(crop_resize_mp, outputdir=args.outputdir, size=args.size,
                ratio=Fraction(*args.size))
    pool = Pool() # use all available cpus
    for (infile, outfile), error in pool.imap_unordered(f, args.files):
        if error is not None:
            error_count += 1
            sys.stderr.write("error: %s: %s\n" % (infile, error))
        elif not args.quiet:
            print("%s -> %s" % (infile, outfile))
    sys.exit(error_count != 0)

if __name__ == "__main__":
    main()