两个色块颜色一样但大小不一样，一个大一个小，我该如何去识别小的色块，请大佬求教

[dehi]

import sensor, image, time
thresholds = [(9, 89, 103, -114, -117, -36)] 
sensor.reset()
sensor.set_pixformat(sensor.RGB565)
sensor.set_framesize(sensor.QVGA)
sensor.skip_frames(time = 2000)
sensor.set_auto_gain(False) 
sensor.set_auto_whitebal(False) 
clock = time.clock()


def find_small(blobs):
    max_size=0
    for blob in blobs:
        if blob[4] < 5000:
            small_blob=blob
    return small_blob
    

while(True):
    clock.tick()
    img = sensor.snapshot()
    blobs = img.find_blobs(thresholds,pixels_threshold=3500, area_threshold=3500,merge=True)
    if blobs:
        small_blob = find_small(blobs)
        img.draw_rectangle(small_blob.rect()) # rect
        img.draw_cross(small_blob.cx(), small_blob.cy()) # cx, cy
    print(clock.fps())

以上是我的源代码。
我曾尝试用blob.pixels小于某个值实现，但出现了报错，下面是报错的提示，提示错的代码行是 return small_blob
不知道错在哪里了，向大佬求教。

[dehi]

[kidswong999]

def find_small(blobs):
    max_size=0
    small_blob=None
    for blob in blobs:
        if blob[4] < 5000:
            small_blob=blob
    return small_blob

[dehi]

@kidswong999
大佬按照你的提示，自己又修改了一下代码，代码如下
import sensor, image, time
thresholds = [(79, 39, 100, 31, -1, -96)]
sensor.reset()
sensor.set_pixformat(sensor.RGB565)
sensor.set_framesize(sensor.QVGA)
sensor.skip_frames(time = 2000)
sensor.set_auto_gain(False)
sensor.set_auto_whitebal(False)
clock = time.clock()

def find_small(blobs):
max_size=0
small_blob=None
for blob in blobs:
if (blob[2]*blob[3] > max_size) and (blob[4] < 5000):
small_blob=blob
return small_blob

while(True):
clock.tick()
img = sensor.snapshot()
blobs = img.find_blobs(thresholds,pixels_threshold=3500, area_threshold=3500,merge=True)
if blobs:
small_blob = find_small(blobs)
img.draw_rectangle(small_blob.rect())
img.draw_cross(small_blob.cx(), small_blob.cy()) # cx, cy
print(clock.fps())
但是又出现了下面这个错误，不知道怎么办，请教一下大佬

[kidswong999]

@dehi 如果没找到色块呢？你要处理一下。

[dehi]

@kidswong999
好的大佬，我明白了