Unwrap imgage pixels into a 1-dimensional array along the Hilbert's curve, then convert it to sound using SOX

hilbert_image2audio.py

#!/usr/bin/env python
from __future__ import print_function, division
import os.path
from numpy import array, hstack, vstack, clip
from PIL import Image
import numpy as np
import subprocess # need the subprocess module
from tempfile import mkdtemp
import shutil

#SOX_EXEC = r"C:\Program Files\sox-14-4-2\sox.exe"
SOX_EXEC = r"sox"

def ilog2(x):
    log = 0
    while x > 1:
        log += 1
        x = x // 2
    return log

def hilbert_indices(N):
    m = array([[0]], dtype=np.int)
    for i in range(N):
        d = 4**i
        m1 = vstack( (hstack( (m.T, m.T[::-1, ::-1] + 3*d )),
                      hstack( (m+d, m+2*d) )
                  )
        )
        m = m1
    return m

def saveSound(sound, ofile, rate):
    if sound.dtype != np.uint8:
        sound = sound.astype(np.uint8)
    tempdir = mkdtemp()
    try:
        fname = os.path.join(tempdir, "audio.raw")
        with open(fname, "wb") as rawfile:
            sound.tofile( rawfile )
        print("saved temp file", fname)
        args = [SOX_EXEC,
                "-t", "RAW",
                '-e','signed-integer', # input encode as signed ints
                '-L',                  # input little endin
                '-c', '1',             # mono
                '-b', '8',  # input bits per sample
                '-r', str(rate),
                fname,
                ofile]
        print ("args:", " ".join(args))
        subprocess.check_call( args )
                
    finally:
        shutil.rmtree(tempdir)
        print ("Removed temp directory")
    
def hilbertImage2audio( filename, ofile, rate=44100 ):
    #load mage
    img = Image.open( filename )
    if img.mode != "L":
        raise ValueError("Image must be grayscale")
    arr = np.asarray(img)
    del img
    
    if len(arr.shape) == 3:
        w,h,chans = arr.shape
    else:
        w,h = arr.shape
        chans = 1
    if chans != 1:   raise ValueError("Image must be grayscale")
    if w!=h:         raise ValueError("Image not square")
    if (w-1)&w != 0: raise ValueError("Image sides must be powers of 2")

    arr = arr.astype(np.uint8)
    arr -= 127
    
    n= ilog2(w)

    indices = hilbert_indices( n )
    sound = np.zeros( (w*h,), dtype = np.uint8 )
    sound[ indices ] = arr
    del arr
    saveSound(sound, ofile, rate)
    
if __name__=="__main__":
    import sys
    try:
        imgfile = sys.argv[1]
        audiofile = sys.argv[2]
    except IndexError:
        print("Usage: hilbert_image2audio.py IMAGE_FILE AUDIO_FILE")
        exit(1)
    hilbertImage2audio(imgfile, audiofile)