noteshrink.py

#!/usr/bin/env python

'''Converts sequence of images to compact PDF while removing speckles,
bleedthrough, etc.

'''

# for some reason pylint complains about members being undefined :(
# pylint: disable=E1101

from __future__ import print_function

import sys
import os
import re
import subprocess
import shlex

from argparse import ArgumentParser

import numpy as np
from PIL import Image
from scipy.cluster.vq import kmeans, vq

######################################################################

def quantize(image, bits_per_channel=None):

    '''Reduces the number of bits per channel in the given image.'''

    if bits_per_channel is None:
        bits_per_channel = 6

    assert image.dtype == np.uint8

    shift = 8-bits_per_channel
    halfbin = (1 << shift) >> 1

    return ((image.astype(int) >> shift) << shift) + halfbin

######################################################################

def pack_rgb(rgb):

    '''Packs a 24-bit RGB triples into a single integer,
works on both arrays and tuples.'''

    orig_shape = None

    if isinstance(rgb, np.ndarray):
        assert rgb.shape[-1] == 3
        orig_shape = rgb.shape[:-1]
    else:
        assert len(rgb) == 3
        rgb = np.array(rgb)

    rgb = rgb.astype(int).reshape((-1, 3))

    packed = (rgb[:, 0] << 16 |
              rgb[:, 1] << 8 |
              rgb[:, 2])

    if orig_shape is None:
        return packed
    else:
        return packed.reshape(orig_shape)

######################################################################

def unpack_rgb(packed):

    '''Unpacks a single integer or array of integers into one or more
24-bit RGB values.

    '''

    orig_shape = None

    if isinstance(packed, np.ndarray):
        assert packed.dtype == int
        orig_shape = packed.shape
        packed = packed.reshape((-1, 1))

    rgb = ((packed >> 16) & 0xff,
           (packed >> 8) & 0xff,
           (packed) & 0xff)

    if orig_shape is None:
        return rgb
    else:
        return np.hstack(rgb).reshape(orig_shape + (3,))

######################################################################

def get_bg_color(image, bits_per_channel=None):

    '''Obtains the background color from an image or array of RGB colors
by grouping similar colors into bins and finding the most frequent
one.

    '''

    assert image.shape[-1] == 3

    quantized = quantize(image, bits_per_channel).astype(int)
    packed = pack_rgb(quantized)

    unique, counts = np.unique(packed, return_counts=True)

    packed_mode = unique[counts.argmax()]

    return unpack_rgb(packed_mode)

######################################################################

def rgb_to_sv(rgb):

    '''Convert an RGB image or array of RGB colors to saturation and
value, returning each one as a separate 32-bit floating point array or
value.

    '''

    if not isinstance(rgb, np.ndarray):
        rgb = np.array(rgb)

    axis = len(rgb.shape)-1
    cmax = rgb.max(axis=axis).astype(np.float32)
    cmin = rgb.min(axis=axis).astype(np.float32)
    delta = cmax - cmin

    saturation = delta.astype(np.float32) / cmax.astype(np.float32)
    saturation = np.where(cmax == 0, 0, saturation)

    value = cmax/255.0

    return saturation, value

######################################################################

def postprocess(output_filename, options):

    '''Runs the postprocessing command on the file provided.'''

    assert options.postprocess_cmd

    base, _ = os.path.splitext(output_filename)
    post_filename = base + options.postprocess_ext

    cmd = options.postprocess_cmd
    cmd = cmd.replace('%i', output_filename)
    cmd = cmd.replace('%o', post_filename)
    cmd = cmd.replace('%e', options.postprocess_ext)

    subprocess_args = shlex.split(cmd)

    if os.path.exists(post_filename):
        os.unlink(post_filename)

    if not options.quiet:
        print('  running "{}"...'.format(cmd), end=' ')
        sys.stdout.flush()

    try:
        result = subprocess.call(subprocess_args)
        before = os.stat(output_filename).st_size
        after = os.stat(post_filename).st_size
    except OSError:
        result = -1

    if result == 0:

        if not options.quiet:
            print('{:.1f}% reduction'.format(
                100*(1.0-float(after)/before)))

        return post_filename

    else:

        sys.stderr.write('warning: postprocessing failed!\n')
        return None

######################################################################

def percent(string):
    '''Convert a string (i.e. 85) to a fraction (i.e. .85).'''
    return float(string)/100.0

######################################################################

def get_argument_parser():

    '''Parse the command-line arguments for this program.'''

    parser = ArgumentParser(
        description='convert scanned, hand-written notes to PDF')

    show_default = ' (default %(default)s)'

    parser.add_argument('filenames', metavar='IMAGE', nargs='+',
                        help='files to convert')

    parser.add_argument('-q', dest='quiet', action='store_true',
                        default=False,
                        help='reduce program output')

    parser.add_argument('-b', dest='basename', metavar='BASENAME',
                        default='page',
                        help='output PNG filename base' + show_default)

    parser.add_argument('-o', dest='pdfname', metavar='PDF',
                        default='output.pdf',
                        help='output PDF filename' + show_default)

    parser.add_argument('-v', dest='value_threshold', metavar='PERCENT',
                        type=percent, default='25',
                        help='background value threshold %%'+show_default)

    parser.add_argument('-s', dest='sat_threshold', metavar='PERCENT',
                        type=percent, default='20',
                        help='background saturation '
                        'threshold %%'+show_default)

    parser.add_argument('-n', dest='num_colors', type=int,
                        default='8',
                        help='number of output colors '+show_default)

    parser.add_argument('-p', dest='sample_fraction',
                        metavar='PERCENT',
                        type=percent, default='5',
                        help='%% of pixels to sample' + show_default)

    parser.add_argument('-w', dest='white_bg', action='store_true',
                        default=False, help='make background white')

    parser.add_argument('-g', dest='global_palette',
                        action='store_true', default=False,
                        help='use one global palette for all pages')

    parser.add_argument('-S', dest='saturate', action='store_false',
                        default=True, help='do not saturate colors')

    parser.add_argument('-K', dest='sort_numerically',
                        action='store_false', default=True,
                        help='keep filenames ordered as specified; '
                        'use if you *really* want IMG_10.png to '
                        'precede IMG_2.png')

    parser.add_argument('-P', dest='postprocess_cmd', default=None,
                        help='set postprocessing command (see -O, -C, -Q)')

    parser.add_argument('-e', dest='postprocess_ext',
                        default='_post.png',
                        help='filename suffix/extension for '
                        'postprocessing command')

    parser.add_argument('-O', dest='postprocess_cmd',
                        action='store_const',
                        const='optipng -silent %i -out %o',
                        help='same as -P "%(const)s"')

    parser.add_argument('-C', dest='postprocess_cmd',
                        action='store_const',
                        const='pngcrush -q %i %o',
                        help='same as -P "%(const)s"')

    parser.add_argument('-Q', dest='postprocess_cmd',
                        action='store_const',
                        const='pngquant --ext %e %i',
                        help='same as -P "%(const)s"')

    parser.add_argument('-c', dest='pdf_cmd', metavar="COMMAND",
                        default='convert %i %o',
                        help='PDF command (default "%(default)s")')

    return parser

######################################################################

def get_filenames(options):

    '''Get the filenames from the command line, optionally sorted by
number, so that IMG_10.png is re-arranged to come after IMG_9.png.
This is a nice feature because some scanner programs (like Image
Capture on Mac OS X) automatically number files without leading zeros,
and this way you can supply files using a wildcard and still have the
pages ordered correctly.

    '''

    if not options.sort_numerically:
        return options.filenames

    filenames = []

    for filename in options.filenames:
        basename = os.path.basename(filename)
        root, _ = os.path.splitext(basename)
        matches = re.findall(r'[0-9]+', root)
        if matches:
            num = int(matches[-1])
        else:
            num = -1
        filenames.append((num, filename))

    return [fn for (_, fn) in sorted(filenames)]

######################################################################

def load(input_filename):

    '''Load an image with Pillow and convert it to numpy array. Also
returns the image DPI in x and y as a tuple.'''

    try:
        pil_img = Image.open(input_filename)
    except IOError:
        sys.stderr.write('warning: error opening {}\n'.format(
            input_filename))
        return None, None

    if pil_img.mode != 'RGB':
        pil_img = pil_img.convert('RGB')

    if 'dpi' in pil_img.info:
        dpi = pil_img.info['dpi']
    else:
        dpi = (300, 300)

    img = np.array(pil_img)

    return img, dpi

######################################################################

def sample_pixels(img, options):

    '''Pick a fixed percentage of pixels in the image, returned in random
order.'''

    pixels = img.reshape((-1, 3))
    num_pixels = pixels.shape[0]
    num_samples = int(num_pixels*options.sample_fraction)

    idx = np.arange(num_pixels)
    np.random.shuffle(idx)

    return pixels[idx[:num_samples]]

######################################################################

def get_fg_mask(bg_color, samples, options):

    '''Determine whether each pixel in a set of samples is foreground by
comparing it to the background color. A pixel is classified as a
foreground pixel if either its value or saturation differs from the
background by a threshold.'''

    s_bg, v_bg = rgb_to_sv(bg_color)
    s_samples, v_samples = rgb_to_sv(samples)

    s_diff = np.abs(s_bg - s_samples)
    v_diff = np.abs(v_bg - v_samples)

    return ((v_diff >= options.value_threshold) |
            (s_diff >= options.sat_threshold))

######################################################################

def get_palette(samples, options, return_mask=False, kmeans_iter=40):

    '''Extract the palette for the set of sampled RGB values. The first
palette entry is always the background color; the rest are determined
from foreground pixels by running K-means clustering. Returns the
palette, as well as a mask corresponding to the foreground pixels.

    '''

    if not options.quiet:
        print('  getting palette...')

    bg_color = get_bg_color(samples, 6)

    fg_mask = get_fg_mask(bg_color, samples, options)

    centers, _ = kmeans(samples[fg_mask].astype(np.float32),
                        options.num_colors-1,
                        iter=kmeans_iter)

    palette = np.vstack((bg_color, centers)).astype(np.uint8)

    if not return_mask:
        return palette
    else:
        return palette, fg_mask

######################################################################

def apply_palette(img, palette, options):

    '''Apply the pallete to the given image. The first step is to set all
background pixels to the background color; then, nearest-neighbor
matching is used to map each foreground color to the closest one in
the palette.

    '''

    if not options.quiet:
        print('  applying palette...')

    bg_color = palette[0]

    fg_mask = get_fg_mask(bg_color, img, options)

    orig_shape = img.shape

    pixels = img.reshape((-1, 3))
    fg_mask = fg_mask.flatten()

    num_pixels = pixels.shape[0]

    labels = np.zeros(num_pixels, dtype=np.uint8)

    labels[fg_mask], _ = vq(pixels[fg_mask], palette)

    return labels.reshape(orig_shape[:-1])

######################################################################

def save(output_filename, labels, palette, dpi, options):

    '''Save the label/palette pair out as an indexed PNG image.  This
optionally saturates the pallete by mapping the smallest color
component to zero and the largest one to 255, and also optionally sets
the background color to pure white.

    '''

    if not options.quiet:
        print('  saving {}...'.format(output_filename))

    if options.saturate:
        palette = palette.astype(np.float32)
        pmin = palette.min()
        pmax = palette.max()
        palette = 255 * (palette - pmin)/(pmax-pmin)
        palette = palette.astype(np.uint8)

    if options.white_bg:
        palette = palette.copy()
        palette[0] = (255, 255, 255)

    output_img = Image.fromarray(labels, 'P')
    output_img.putpalette(palette.flatten())
    output_img.save(output_filename, dpi=dpi)

######################################################################

def get_global_palette(filenames, options):

    '''Fetch the global palette for a series of input files by merging
their samples together into one large array.

    '''

    input_filenames = []

    all_samples = []

    if not options.quiet:
        print('building global palette...')

    for input_filename in filenames:

        img, _ = load(input_filename)
        if img is None:
            continue

        if not options.quiet:
            print('  processing {}...'.format(input_filename))

        samples = sample_pixels(img, options)
        input_filenames.append(input_filename)
        all_samples.append(samples)

    num_inputs = len(input_filenames)

    all_samples = [s[:int(round(float(s.shape[0])/num_inputs))]
                   for s in all_samples]

    all_samples = np.vstack(tuple(all_samples))

    global_palette = get_palette(all_samples, options)

    if not options.quiet:
        print('  done\n')

    return input_filenames, global_palette

######################################################################

def emit_pdf(outputs, options):

    '''Runs the PDF conversion command to generate the PDF.'''

    cmd = options.pdf_cmd
    cmd = cmd.replace('%o', options.pdfname)
    if len(outputs) > 2:
        cmd_print = cmd.replace('%i', ' '.join(outputs[:2] + ['...']))
    else:
        cmd_print = cmd.replace('%i', ' '.join(outputs))
    cmd = cmd.replace('%i', ' '.join(outputs))

    if not options.quiet:
        print('running PDF command "{}"...'.format(cmd_print))

    try:
        result = subprocess.call(shlex.split(cmd))
    except OSError:
        result = -1

    if result == 0:
        if not options.quiet:
            print('  wrote', options.pdfname)
    else:
        sys.stderr.write('warning: PDF command failed\n')

######################################################################

def notescan_main(options):

    '''Main function for this program when run as script.'''

    filenames = get_filenames(options)

    outputs = []

    do_global = options.global_palette and len(filenames) > 1

    if do_global:
        filenames, palette = get_global_palette(filenames, options)

    do_postprocess = bool(options.postprocess_cmd)

    for input_filename in filenames:

        img, dpi = load(input_filename)
        if img is None:
            continue

        output_filename = '{}{:04d}.png'.format(
            options.basename, len(outputs))

        if not options.quiet:
            print('opened', input_filename)

        if not do_global:
            samples = sample_pixels(img, options)
            palette = get_palette(samples, options)

        labels = apply_palette(img, palette, options)

        save(output_filename, labels, palette, dpi, options)

        if do_postprocess:
            post_filename = postprocess(output_filename, options)
            if post_filename:
                output_filename = post_filename
            else:
                do_postprocess = False

        outputs.append(output_filename)

        if not options.quiet:
            print('  done\n')

    emit_pdf(outputs, options)

######################################################################

def main():
    '''Parse args and call notescan_main().'''
    notescan_main(options=get_argument_parser().parse_args())

if __name__ == '__main__':
    main()