capture.py

from io import BytesIO
from time import sleep, time
from picamera import PiCamera
from PIL import Image, ImageChops
import numpy as np

def take_image(cam, stream):
    cam.capture(stream, resize=(320, 240), format='jpeg')
    # "Rewind" the stream to the beginning so we can read its content
    stream.seek(0)
    return Image.open(stream)

def get_entropy(img):
    w, h = img.size
    a = np.array(img.convert('RGB')).reshape((w*h,3))
    h, e = np.histogramdd(a, bins=(16,)*3, range=((0,256),)*3)
    prob = h/np.sum(h) # normalize
    prob = prob[prob>0] # remove zeros
    return -np.sum(prob*np.log2(prob))

if __name__ == '__main__':
    idx = 0
    streams = [BytesIO(), BytesIO()]

    with PiCamera() as cam:
        # cam.resolution = (1024, 768)

        # Camera warmup (longer => better)
        cam.start_preview()
        sleep(2)

        imgs = [take_image(cam, streams[i]) for i in range(2)]
        # TODO: stream.truncate() ?
        while True:
            diff = ImageChops.difference(imgs[0], imgs[1])
            # arr = np.array(diff)
            print(get_entropy(diff))

            sleep(1 * 60)
            streams[idx].seek(0)
            imgs[idx] = take_image(cam, streams[idx])
            idx = (idx + 1) % 2