imagescale-q-m.py

#!/usr/bin/env python3
# Copyright © 2012-13 Qtrac Ltd. All rights reserved.
# This program or module is free software: you can redistribute it
# and/or modify it under the terms of the GNU General Public License as
# published by the Free Software Foundation, either version 3 of the
# License, or (at your option) any later version. It is provided for
# educational purposes and is distributed in the hope that it will be
# useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
# General Public License for more details.

import argparse
import collections
import math
import multiprocessing
import os
import sys
import Image
import Qtrac


Result = collections.namedtuple("Result", "copied scaled name")
Summary = collections.namedtuple("Summary", "todo copied scaled canceled")


def main():
    size, smooth, source, target, concurrency = handle_commandline()
    Qtrac.report("starting...")
    summary = scale(size, smooth, source, target, concurrency)
    summarize(summary, concurrency)


def handle_commandline():
    parser = argparse.ArgumentParser()
    parser.add_argument("-c", "--concurrency", type=int,
            default=multiprocessing.cpu_count(),
            help="specify the concurrency (for debugging and "
                "timing) [default: %(default)d]")
    parser.add_argument("-s", "--size", default=400, type=int,
            help="make a scaled image that fits the given dimension "
                "[default: %(default)d]")
    parser.add_argument("-S", "--smooth", action="store_true",
            help="use smooth scaling (slow but good for text)")
    parser.add_argument("source",
            help="the directory containing the original .xpm images")
    parser.add_argument("target",
            help="the directory for the scaled .xpm images")
    args = parser.parse_args()
    source = os.path.abspath(args.source)
    target = os.path.abspath(args.target)
    if source == target:
        args.error("source and target must be different")
    if not os.path.exists(args.target):
        os.makedirs(target)
    return args.size, args.smooth, source, target, args.concurrency


def scale(size, smooth, source, target, concurrency):
    canceled = False
    jobs = multiprocessing.JoinableQueue()
    results = multiprocessing.Queue()
    create_processes(size, smooth, jobs, results, concurrency)
    todo = add_jobs(source, target, jobs)
    try:
        jobs.join()
    except KeyboardInterrupt: # May not work on Windows
        Qtrac.report("canceling...")
        canceled = True
    copied = scaled = 0
    while not results.empty(): # Safe because all jobs have finished
        result = results.get_nowait()
        copied += result.copied
        scaled += result.scaled
    return Summary(todo, copied, scaled, canceled)


def create_processes(size, smooth, jobs, results, concurrency):
    for _ in range(concurrency):
        process = multiprocessing.Process(target=worker, args=(size,
                smooth, jobs, results))
        process.daemon = True
        process.start()


def worker(size, smooth, jobs, results):
    while True:
        try:
            sourceImage, targetImage = jobs.get()
            try:
                result = scale_one(size, smooth, sourceImage, targetImage)
                Qtrac.report("{} {}".format("copied" if result.copied else
                        "scaled", os.path.basename(result.name)))
                results.put(result)
            except Image.Error as err:
                Qtrac.report(str(err), True)
        finally:
            jobs.task_done()


def add_jobs(source, target, jobs):
    for todo, name in enumerate(os.listdir(source), start=1):
        sourceImage = os.path.join(source, name)
        targetImage = os.path.join(target, name)
        jobs.put((sourceImage, targetImage))
    return todo


def scale_one(size, smooth, sourceImage, targetImage):
    oldImage = Image.from_file(sourceImage)
    if oldImage.width <= size and oldImage.height <= size:
        oldImage.save(targetImage)
        return Result(1, 0, targetImage)
    else:
        if smooth:
            scale = min(size / oldImage.width, size / oldImage.height)
            newImage = oldImage.scale(scale)
        else:
            stride = int(math.ceil(max(oldImage.width / size,
                                       oldImage.height / size)))
            newImage = oldImage.subsample(stride)
        newImage.save(targetImage)
        return Result(0, 1, targetImage)


def summarize(summary, concurrency):
    message = "copied {} scaled {} ".format(summary.copied, summary.scaled)
    difference = summary.todo - (summary.copied + summary.scaled)
    if difference:
        message += "skipped {} ".format(difference)
    message += "using {} processes".format(concurrency)
    if summary.canceled:
        message += " [canceled]"
    Qtrac.report(message)
    print()


if __name__ == "__main__":
    main()