process_source.py

#!/usr/bin/env python3

# crops a series of screenshots, splits them based on vertical blackspace (i.e.
# completely black scanlines), then aligns and merges them by y-concatenation.
# if a piece can't be y-catted to the previous one, a new file is created for
# it. this has the use of ripping ebooks that have been pirated from temporary
# views via screenshots, such as those lent out by archive.org.

import os
from os.path import join
import sys
import numpy as np
from PIL import Image

SOURCE_PATH = 'source/'
OUT_PATH = 'images/'
CROPBOX = (538, 186, 1369, 1046)
MIN_HEIGHT = 830
EXTENSION = 'jpg'

def is_black(im):
    x, y = im.size
    return (x*y, (0, 0, 0)) in im.getcolors(x*y)

def is_same(im_1, im_2):
    return (np.asarray(im_1) == np.asarray(im_2)).all()

def scanline(im, i):
    return im.crop((0, i, im.size[0], i+1))

def scanlines(im):
    return (scanline(im, i) for i in range(im.size[1]))

def vcat(im_1, im_2):
    return Image.fromarray(np.vstack((np.asarray(im_1), np.asarray(im_2))))

def align_and_merge(im_1, im_2):
    width = im_1.size[0]
    assert width == im_2.size[0]
    offset = None
    first_line = scanline(im_2, 0)
    for y, line in enumerate(scanlines(im_1)):
        if is_same(line, first_line):
            offset = y
    if offset == None:
        raise ValueError('Images don\'t overlap.')
    return vcat(im_1, im_2.crop((0, im_1.size[1]-offset, *im_2.size)))

def parts_from_path(path, source_im=None):
    im = Image.open(path)
    im = im.crop(CROPBOX)
    parts = []
    black = True
    source_i = None
    for i in range(im.size[1]):
        line = scanline(im, i)
        if is_black(line):
            black = True
            continue
        if black or not parts:
            black = False
            parts.append(line)
            continue
        parts[-1] = vcat(parts[-1], line)
    if source_im is not None:
        try:
            parts[0] = align_and_merge(source_im, parts[0])
        except ValueError:
            parts.insert(0, source_im)
    return parts

def output():
    global last_part
    global parts
    global name_i

    for i, im in enumerate(parts[:-1]):
        if im.size[1] >= MIN_HEIGHT:
            im.save(join(OUT_PATH, '.'.join((str(name_i+i), EXTENSION.lower()))))
    last_part = parts[-1]
    name_i = name_i + len(parts) - 1

if __name__ == '__main__':
    paths = os.listdir(SOURCE_PATH)
    paths.sort()

    last_part = None
    name_i = 0
    for path in paths:
        path = join(SOURCE_PATH, path)
        parts = parts_from_path(path, last_part)
        for i, im in enumerate(parts[:-1]):
            if im.size[1] >= MIN_HEIGHT:
                im.save(join(OUT_PATH,
                             '.'.join((str(name_i+i), EXTENSION.lower()))))
        last_part = parts[-1]
        name_i = name_i + len(parts) - 1