如何从picamera（python，opencv）中提取数组中的图像

Question

I am quite new in picamera. Now I want to detect uncomplicated motions by camera, and I use cv2.absdiff() . However, the arrays (image1, image2) I get are the same. How can I get different arrays for abstraction or get the elements (images) in an array? Here is my code:

import sys
sys.path.append('/usr/local/lib/python2.7/site-packages')
from picamera.array import PiRGBArray
from picamara import PiCamera
import cv2
import time
import time
import numpy as np

camera = PiCamera()
camera.resolution = (640,480)
camera.framerate = 32
rawCapture = PiRGBArray(camera,size=(640,480))

time.sleep(0.1)

for frame in camera.capture_continuous(rawCapture,format="bgr",use_video_port=True):

    image1 = frame.array
    gray1 = cv2.cvtColor(image1,cv2.COLOR_BGR2GRAY)
    cv2.waitKey(33)
    image2 = frame.array
    gray2 = cv2.cvtColor(image2,cv2.COLOR_BGR2GRAY)

    diff = cv2.absdiff(gray1,gray2)
    cv2.imshow("DIFF",diff)

    key = cv2.waitKey(33)&0xFF
    rawCapture.truncate(0)
    if key == ord("q"):
        break

Answer 1

Your script is attempting to compare the same frame with itself which will obviously not show any differences.

One approach would be to take a single initial frame before starting your loop, and then compare any later frames to that, something like as follows:

import sys
#sys.path.append('/usr/local/lib/python2.7/site-packages')
from picamera.array import PiRGBArray
from picamara import PiCamera
import cv2
import time
import time
import numpy as np

camera = PiCamera()
camera.resolution = (640,480)
camera.framerate = 32
rawCapture = PiRGBArray(camera,size=(640,480))
time.sleep(0.1)
initial_frame = camera.capture(rawCapture, format="bgr", use_video_port=True):

for frame in camera.capture_continuous(rawCapture, format="bgr", use_video_port=True):
    cv2.waitKey(33)
    image2 = frame.array
    gray = cv2.cvtColor(image2, cv2.COLOR_BGR2GRAY)

    diff = cv2.absdiff(initial_frame, gray)
    cv2.imshow("DIFF", diff)

    key = cv2.waitKey(33) & 0xFF
    rawCapture.truncate(0)

    if key == ord("q"):
        break 

You could further enhance it to periodically update the initial frame to account for any long term changes to the background.