OpenMv function repeate every 5 minutes

OpenMV Boards
1

Hi!
I plan to use the frame differencing to detect bird motion. So far, I follow the OpenMv example and the frame differencing is working. I want to update the background image every 5 minutes to decrease the effect of light/shadow change. Some time functions I found are pyb.millis(), timer(), and time.time(). They look like the delay function. Is there any suggestion or examples I can use as a reference?
Thank you

1 Like
2

Um, you just use the pyb.ellapsed_millis() method to check if 5 seconds pass. Then update the FB in that case.

3

Hi! kwagyeman,
I follow your advice and build the test for pyb.ellapsed_millis(). It works if I use it directly. When I added it to the example of frame differencing, it does not refresh the image at every one second. Can you see what the problem is? I am not good at using the timer interrupt. Do you know how to handle the time overflow (after it passed 12.4 days)?

The code to test pyb.ellapsed_millis() individually:

import sensor, image, time, pyb

sensor.reset()
sensor.set_pixformat(sensor.RGB565)
sensor.set_framesize(sensor.QVGA)
sensor.skip_frames(time = 2000)

start = pyb.millis()
while (True):

if (pyb.elapsed_millis(start) == 1000):
    print('The current time is ', start)
    start = pyb.millis()

Add the pyb.elapsed_millis() to frame differencing example:
import sensor, image, pyb, os, time

TRIGGER_THRESHOLD = 5
grey_threshold = (0, 40)

sensor.reset() # Initialize the camera sensor.
sensor.set_pixformat(sensor.GRAYSCALE) # or sensor.GRAYSCALE
sensor.set_framesize(sensor.QVGA) # or sensor.QQVGA (or others)
sensor.skip_frames(time = 2000) # Let new settings take affect.
#sensor.set_auto_whitebal(False) # Turn off white balance.
clock = time.clock() # Tracks FPS.

extra_fb = sensor.alloc_extra_fb(sensor.width(), sensor.height(), sensor.GRAYSCALE)

print(“About to save background image…”)
sensor.skip_frames(time = 2000) # Give the user time to get ready.
extra_fb.replace(sensor.snapshot())
print(“Saved background image - Now frame differencing!”)

start = pyb.millis()

while(True):

if (pyb.elapsed_millis(start) == 1000):
    print("*************************************")
    print("Time to refresh the background image")
    extra_fb.replace(sensor.snapshot())
    start = pyb.millis()

clock.tick() # Track elapsed milliseconds between snapshots().
img = sensor.snapshot() # Take a picture and return the image.

# Replace the image with the "abs(NEW-OLD)" frame difference.
img.difference(extra_fb)

hist = img.get_histogram()
# This code below works by comparing the 99th percentile value (e.g. the
# non-outlier max value against the 90th percentile value (e.g. a non-max
# value. The difference between the two values will grow as the difference
# image seems more pixels change.
diff = hist.get_percentile(0.99).l_value() - hist.get_percentile(0.90).l_value()
triggered = diff > TRIGGER_THRESHOLD

blobs = img.find_blobs([grey_threshold], invert = True, merge=True, margin = 50)
if blobs:
    for b in blobs:
        img.draw_rectangle(b[0:4])
        img.draw_cross(b[5], b[6])

print(clock.fps(), triggered) # Note: Your OpenMV Cam runs about half as fast while
# connected to your computer. The FPS should increase once disconnected.

timeCounter_1
timeCounter_11678Ă—861 105 KB
timeCounter_2
timeCounter_21104Ă—850 33.1 KB

Thank you

4

Hi, please don’t post all your code, then use the code snippet butting to make your code readable.

You should not do an if comparison. Do a greater than or equal. When you reset start after the comparison passes this will prevent overflow.

1 Like
5

Hi @Alfred168 , cool use case! Have you had any success with it for detecting birds?

I was trying something similar using timers but it seems they cannot be set to non-integer frequencies, so your solution helped a lot.