怎么将某块区域的灰度值统一加20

import sensor, image

sensor.reset()
sensor.set_pixformat(sensor.RGB565)
sensor.set_framesize(sensor.QQVGA) # can be QVGA on M7...
sensor.skip_frames(30)
sensor.set_auto_gain(False) # must turn this off to prevent image washout...
while(True):
    img = sensor.snapshot()
    img.lens_corr(1.8) # strength of 1.8 is good for the 2.8mm lens.

    for code in img.find_qrcodes():
        print(code)

请在这里粘贴代码