二值化后如何查找色块，阈值如何设置设置LAB还是其他？

[truf]

# Find Rects Example
#
# This example shows off how to find rectangles in the image using the quad threshold
# detection code from our April Tags code. The quad threshold detection algorithm
# detects rectangles in an extremely robust way and is much better than Hough
# Transform based methods. For example, it can still detect rectangles even when lens
# distortion causes those rectangles to look bent. Rounded rectangles are no problem!
# (But, given this the code will also detect small radius circles too)...

import sensor, image, time, math, pyb
from pyb import UART
import lcd

sensor.reset()
sensor.set_contrast(1)
sensor.set_brightness(1)
sensor.set_saturation(1)
sensor.set_gainceiling(16)
#sensor.set_pixformat(sensor.GRAYSCALE)
sensor.set_pixformat(sensor.RGB565) # grayscale is faster (160x120 max on OpenMV-M7)
sensor.set_framesize(sensor.QQVGA)
#sensor.set_windowing((340, 340))  #数据映射
sensor.skip_frames(time = 2000)
clock = time.clock()

uart = UART(3, 115200)

lcd.init()
led = pyb.LED(1)

#计算左右两边直线长度
def cal_line(corners):
    x1 = corners[0][0]
    y1 = corners[0][1]
    x2 = corners[1][0]
    y2 = corners[1][1]
    x3 = corners[2][0]
    y3 = corners[2][1]
    x4 = corners[3][0]
    y4 = corners[3][1]
    #计算长度
    yl1 = math.sqrt(math.pow((x1-x4),2) + math.pow((y1-y4),2))
    yl2 = math.sqrt(math.pow((x2-x3),2) + math.pow((y2-y3),2))
    return yl1,yl2

def FindMaxBlobs(BlobList):
    #寻找最大色块
    most_pixels = 0
    largest_blob = 0
    if BlobList:
        for i in range(len(BlobList)):#range()创建一个整数列表
            if BlobList[i].pixels() > most_pixels:
                most_pixels = BlobList[i].pixels()
                largest_blob = i
        return BlobList[largest_blob]
    return None

#发送uart数据
def send_uart(Type,x,y,s):
    output_str="%d,%d,%d,%d" % (Type,x,y,s)
    uart.write(output_str+'\r\n')
    print(output_str)

blank_thresholds = [(3, 35, -52, 47, -128, 126)]
red_threshold = [(19, 100, 25, 74, -128, 127)]
#blank_thresholds=[(140, 255)]
while(True):
    Type = 255
    P0 = -1
    P1 = -1
    P2 = -1
    PL1 = -1
    LP2 = -1
    clock.tick()
    img = sensor.snapshot().lens_corr(1.8)
    img.binary(red_threshold)
    #img.erode(3)
    #img.dilate(1)
    #img.erode(3)
    #img.dilate(1)
    if img.find_blobs(red_threshold,merge=True):
        led.on()
        blobs = img.find_blobs(red_threshold,pixels_threshold=3,merge=True)
        r = FindMaxBlobs(blobs)
        #for r in img.find_blobs(blank_thresholds,pixels_threshold=10,merge=True):
        img.draw_rectangle(r.rect(), color = (0, 0, 0))
        for p in r.corners(): img.draw_circle(p[0], p[1], 5, color = (0, 255, 0))
        if r.w() * r.h()>200:
            Type = 1
            P0 = r.x() + r.w()//2
            P1 = r.y() + r.h()//2
            P2 = r.w() * r.h()//100
            (PL1,PL2) = cal_line(r.corners())
            #print(PL1,PL2)
            send_uart(Type,P0,P1,P2)
        else:
            Type = 255
            send_uart(255,-1,-1,-1)
    if Type == 1:
            led.on()
    else:
        led.off()
    lcd.display(img)

使用以上代码对图片先进行二值化然后查找红色色块，二值化阈值与查找色块阈值为同一红色阈值，一开始会检测到并框出，但是莫名就不能检测了，求教

[kidswong999]

二值化之后就是黑白的了，阈值就不是红色了。是白色