THRESHOLD =(1, 24, -45, 40, 74, -68) # Grayscale threshold for dark things...
import sensor, image, time
from pyb import LED
import car
from pid import PID
rho_pid = PID(p=0.4, i=0)
theta_pid = PID(p=0.001, i=0)

#LED(1).on()
#LED(2).on()
#LED(3).on()

sensor.reset()
sensor.set_vflip(True)
sensor.set_hmirror(True)
sensor.set_pixformat(sensor.RGB565)
sensor.set_framesize(sensor.QQQVGA) # 80x60 (4,800 pixels) - O(N^2) max = 2,3040,000.
#sensor.set_windowing([0,20,80,40])
sensor.skip_frames(time = 2000)     # WARNING: If you use QQVGA it may take seconds
clock = time.clock()                # to process a frame sometimes.

while(True):
    clock.tick()
    img = sensor.snapshot().binary([THRESHOLD])
    line = img.get_regression([(100, 100)], robust = True)
    print('line:',line)

按照文档说明是指想要追踪的颜色阈值，我直接用宏定义的阈值替换，程序不能正常的跑，请问这个值的设置逻辑是什么呢？