def main():
    """Main function for pyssim."""

    description = '\n'.join([
        'Compares an image with a list of images using the SSIM metric.',
        '  Example:',
        '    pyssim test-images/test1-1.png "test-images/*"'
    ])

    parser = argparse.ArgumentParser(
        prog='pyssim', formatter_class=argparse.RawTextHelpFormatter,
        description=description)
    parser.add_argument('--cw', help='compute the complex wavelet SSIM',
                        action='store_true')
    parser.add_argument(
        'base_image', metavar='image1.png', type=argparse.FileType('r'))
    parser.add_argument(
        'comparison_images', metavar='image path with* or image2.png')
    parser.add_argument('--width', type=int, default=None,
                        help='scales the image before computing SSIM')
    parser.add_argument('--height', type=int, default=None,
                        help='scales the image before computing SSIM')

    args = parser.parse_args()

    if args.width and args.height:
        size = (args.width, args.height)
    else:
        size = None

    if not args.cw:
        gaussian_kernel_sigma = 1.5
        gaussian_kernel_width = 11
        gaussian_kernel_1d = get_gaussian_kernel(
            gaussian_kernel_width, gaussian_kernel_sigma)

    comparison_images = glob.glob(args.comparison_images)
    is_a_single_image = len(comparison_images) == 1

    for comparison_image in comparison_images:

        if args.cw:
            ssim = SSIM(args.base_image.name, size=size)
            ssim_value = ssim.cw_ssim_value(comparison_image)
        else:
            ssim = SSIM(args.base_image.name, gaussian_kernel_1d, size=size)
            ssim_value = ssim.ssim_value(comparison_image)

        if is_a_single_image:
            sys.stdout.write('%.7g' % ssim_value)
        else:
            sys.stdout.write('%s - %s: %.7g' % (
                args.base_image.name, comparison_image, ssim_value))
        sys.stdout.write('\n')
Main function for pyssim.