结构相似性（SSIM）示例

import sensor, image, os, time
MIN_TRIGGER_THRESHOLD = -0.4
sensor.reset()
sensor.set_pixformat(sensor.RGB565)
sensor.set_framesize(sensor.QVGA)
sensor.skip_frames(time = 2000)
sensor.set_auto_whitebal(False)
clock = time.clock()
extra_fb = sensor.alloc_extra_fb(sensor.width(), sensor.height(), sensor.RGB565)
print("About to save background image...")
sensor.skip_frames(time = 2000)
extra_fb.replace(sensor.snapshot())
print("Saved background image!")

while(True):
clock.tick()
img = sensor.snapshot()
sim = img.get_similarity(extra_fb)
change = "- Change -" if sim.min() < MIN_TRIGGER_THRESHOLD else "- No Change -"

max_similarity，, max_location = sim.max()  # 找到最大变化图像的坐标

if max_similarity < MIN_TRIGGER_THRESHOLD:  
     x_coord, y_coord = max_location  # 获取最大变化图像的坐标
     img.draw_rectangle((x_coord-10, y_coord-10, 20, 20), color=(255, 0, 0), thickness=2)  # 绘制框
     img.draw_cross(x_coord, y_coord, color=(0, 255, 0), thickness=2)  # 绘制交叉线         
     img.show()

     print("Max change at:", x_coord, y_coord) 
print(clock.fps(), change, sim)