import sensor, image, time
from pyb import UART
green_threshold   = (   66,   80,  -15,   0,   -6,   15)

sensor.reset() 
sensor.set_pixformat(sensor.RGB565) 
sensor.set_framesize(sensor.QQVGA) 
sensor.skip_frames(time = 2000) 
sensor.set_auto_gain(False) 
sensor.set_auto_whitebal(False)

clock = time.clock() 
uart = UART(3, 115200)
while(True):
    clock.tick() 
    img = sensor.snapshot() 
    print(type(img))
    blobs = img.find_blobs([green_threshold])
    print(blobs.corners())
    if blobs:
        for b in blobs:
            img.draw_rectangle(b[0:4]) 
            for i in range(4):
                print(b[i]) 
            img.draw_cross(b[5], b[6]) 
            uart.write("x:")
            uart.write(str(b[5]))
            uart.write("y:")
            uart.write(str(b[6]))
            uart.write("\r\n")
            print("x:"+str(b[5])+","+"y:"+str(b[6]))
    #print(clock.fps()) # 注意: 你的OpenMV连到电脑后帧率大概为原来的一半

Traceback (most recent call last):
File "", line 77, in
AttributeError: 'list' object has no attribute 'corners'
MicroPython: v1.15-r32 OpenMV: v4.0.2 HAL: v1.9.0 BOARD: OPENMV4P-STM32H743
Type "help()" for more information.

print(blobs.corners())

我这样使用就会报这样的错
主要是想问大家这个东西该怎么用