Convert a PDF file to black&white and display it

bw.py

#!/usr/bin/env python
"""
Convert a PDF file to black&white and display it.
Run as: python bw.py input.pdf
"""

viewer = 'evince'

from contextlib import contextmanager
import tempfile
import shutil
import os
import subprocess
import argparse

## emulate Python 3.2's tempfile.TemporaryDirectory()
@contextmanager
def TemporaryDirectory():
    name = tempfile.mkdtemp()
    try:
        yield name
    finally:
        shutil.rmtree(name)


def _parser():
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument('input', help='The input PDF file')
    parser.add_argument('-s', default=False, action='store_true',
                        help='Save the output PDF as input-bw.pdf')
    return parser.parse_args()


if __name__ == '__main__':
    args = _parser()

    assert args.input.endswith('.pdf'), 'Input file must have .pdf extension'

    with TemporaryDirectory() as tmpdirname:
        # print('created temporary directory', tmpdirname)
        output = os.path.join(tmpdirname, 'output.pdf')

        cmd = ['gs',
               '-q',
               '-sOutputFile=%s' % output,
               '-sDEVICE=pdfwrite',
               '-sColorConversionStrategy=Gray',
               '-dProcessColorModel=/DeviceGray',
               '-dCompatibilityLevel=1.4',
               '-dNOPAUSE',
               '-dBATCH',
               args.input,
               ]

        subprocess.call(cmd)

        subprocess.call([viewer, output])

        if args.s:
            # saving output
            savefile = '-bw'.join(os.path.splitext(args.input))
            print('Saving B&W PDF to %s' % savefile)
            shutil.copy2(output, savefile)