Calculate offsets for scrolling piano sheet music

partoche_calc_offsets.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-

from __future__ import print_function, absolute_import, division
import itertools
import json
from PIL import Image, ImageFilter


def pairwise(iterable):
    "s -> (s0,s1), (s1,s2), (s2, s3), ..."
    a, b = itertools.tee(iterable)
    next(b, None)
    return zip(a, b)


def calc_offsets(image_path):
    im = Image.open(image_path)

    # binarize and transpose the image, so that columns in the original become rows
    imgbin = im.convert("1")
    imgbin_rotated = imgbin.transpose(Image.ROTATE_90)
    width, height = imgbin_rotated.size

    imgdata = list(imgbin_rotated.getdata())


    def getrow(row):
        start = row * width
        end = start + width
        return imgdata[start:end]


    # find the line in the middle...
    middle_row = getrow(height // 2)

    # find all the points where the color changes...
    changes = [i for i, (b, a) in enumerate(pairwise(middle_row)) if b != a]
    # TODO: we probably will want to do some filtering here to ignore short
    # changes among a lot of white

    # guesstimate a minimum for the minimum amount of whitespace between the parts
    staff_distance_min = width / 20

    # calculate offsets based on the above guesstimate...
    offsets = [a - (a - b)//2 for b, a in pairwise(changes) if a - b > staff_distance_min]

    # print the offsets
    return [0] + offsets


def run(args):
    print(json.dumps([calc_offsets(path) for path in args.image_paths], indent=2))


if '__main__' == __name__:
    import argparse
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument('image_paths', nargs='+')

    args = parser.parse_args()
    run(args)