I'm using a camera to store raw data in a numpy array, but I don't know What does mean a colon before a number in numpy array?
import numpy as np
import picamera
camera = picamera.PiCamera()
camera.resolution = (128, 112)
data = np.empty((128, 112, 3), dtype=np.uint8)
camera.capture(data, 'rgb')
data = data[:128, :112]