Detecting red contours

Question

I am trying to detect the largest red contour my picamera captures. The following is the code

from picamera.array import PiRGBArray
from picamera import PiCamera
import cv2 
import numpy as np

camera = PiCamera()
camera.resoultion =(640,480)
camera.framerate = 30
rawCapture = PiRGBArray(camera)


for frame in camera.capture_continuous(rawCapture, format='bgr',use_video_port=True):
image = frame.array
hsv = cv2.cvtColor(image,cv2.COLOR_BGR2HSV)

lower = np.array ([0,100,100])
upper = np.array ([18,255,255])

mask = cv2.inRange(hsv,lower,upper)
areaArray = []
count = 1

_, contours, ret = cv2.findContours(mask, cv2.RETR_TREE,cv2.CHAIN_APPROX_SIMPLE)
for i, c in enumerate(contours):
    area = cv2.contourArea(c)
    areaArray.append(area)

    sorteddata = sorted(zip(areaArray, contours), key=lambda x: x[0], reverse=True)
    largest = sorteddata[0][1]
    image = cv2.drawContours (image, largest, -1, (0,0,0), 3)
    cv2.imshow('Image',image)
    rawCapture.truncate(0)
if cv2.waitKey(1) & 0xFF == ord('q'):
    break
cv2.destroyAllWindows()

When I execute this, I get the following error message

Traceback (most recent call last):
  File "/home/pi/Downloads/detect_color.py", line 12, in <module>
    for frame in camera.capture_continuous(rawCapture, format='bgr', use_video_port=True):
  File "/usr/lib/python2.7/dist-packages/picamera/camera.py", line 1851, in capture_continuous
    if not encoder.wait(self.CAPTURE_TIMEOUT):
  File "/usr/lib/python2.7/dist-packages/picamera/encoders.py", line 850, in wait
    self.stop()
  File "/usr/lib/python2.7/dist-packages/picamera/encoders.py", line 881, in stop
    self._close_output()
  File "/usr/lib/python2.7/dist-packages/picamera/encoders.py", line 795, in _close_output
    output.flush()
  File "/usr/lib/python2.7/dist-packages/picamera/array.py", line 285, in flush
    self.array = bytes_to_rgb(self.getvalue(), self.size or self.camera.resolution)
  File "/usr/lib/python2.7/dist-packages/picamera/array.py", line 174, in bytes_to_rgb
    'Incorrect buffer length for resolution %dx%d' % (width, height))
PiCameraValueError: Incorrect buffer length for resolution 1680x1050

can anyone highlight what I could be doing wrong? Thanks :)

Answer 1

You need to "clear" the rawCapture stream each time you load the frame. (if that makes sense. Not exactly sure how to say it :))

from picamera.array import PiRGBArray
from picamera import PiCamera
import cv2 
import numpy as np

camera = PiCamera()
camera.resoultion =(640,480)
camera.framerate = 30
rawCapture = PiRGBArray(camera)


for frame in camera.capture_continuous(rawCapture, format='bgr',use_video_port=True):
image = frame.array

rawCapture.seek(0) #Added these line
rawCapture.truncate() #This too

hsv = cv2.cvtColor(image,cv2.COLOR_BGR2HSV)

lower = np.array ([0,100,100])
upper = np.array ([18,255,255])

mask = cv2.inRange(hsv,lower,upper)
areaArray = []
count = 1

_, contours, ret = cv2.findContours(mask, cv2.RETR_TREE,cv2.CHAIN_APPROX_SIMPLE)
for i, c in enumerate(contours):
    area = cv2.contourArea(c)
    areaArray.append(area)

    sorteddata = sorted(zip(areaArray, contours), key=lambda x: x[0], reverse=True)
    largest = sorteddata[0][1]
    image = cv2.drawContours (image, largest, -1, (0,0,0), 3)
    cv2.imshow('Image',image)
    rawCapture.truncate(0)
if cv2.waitKey(1) & 0xFF == ord('q'):
    break
cv2.destroyAllWindows()