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"can't open camera by index" using cv2 on Linux

I am trying to make a motion detector (using the internal camera) in python(3), I am using linux (debian), and I keep getting this error
[ WARN:0#0.724] global /io/opencv/modules/videoio/src/cap_v4l.cpp (889) open VIDEOIO(V4L2:/dev/video0): can't open camera by index
here's the code I'm using
from imutils.video import VideoStream
import argparse
import datetime
import imutils
import time
import cv2
ap = argparse.ArgumentParser()
ap.add_argument("-v", "--video", help="")
ap.add_argument("-a", "--min-area", type=int, default=500, help="minimum area size")
args = vars(ap.parse_args())
if args.get("video", None) is None:
vs = VideoStream(src=0).start()
time.sleep(2.0)
else:
vs = cv2.VideoCapture(args["Video"])
firstFrame = None
while True:
frame = vs.read()
frame = frame if args.get("video", None) is None else frame[1]
text = "Muon is stuck in helium"
if frame is None:
break
frame = imutils.resize(frame, width=500)
gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
gray = cv2.GaussianBlur(gray, (21, 21), 0)
if firstFrame is None:
firstFrame = gray
continue
frameDelta = cv2.absdiff(firstFrame, gray)
thresh = cv2.threshold(frameDelta, 25, 255, cv2.THRESH_BINARY)[1]
thresh = cv2.dilate(thresh, None, iterations=2)
cnts = cv2.findContours(thresh.copy(), cv2.RETR_EXTERNAL,
cv2.CHAIN_APPROX_SIMPLE)
cnts = imutils.grab_contours(cnts)
for c in cnts:
if cv2.contourArea(c) < args["min_area"]:
continue
(x, y, w, h) = cv2.boundingRect(c)
cv2.rectangle(frame, (x, y), (x + w, y + h), (0, 255, 0), 2)
text = "Muon is fusing hydrogen"
cv2.putText(frame, "Room Status: {}".format(text), (10, 20),
cv2.FONT_HERSHEY_SIMPLEX, 0.5, (0, 0, 255), 2)
cv2.putText(frame, datetime.datetime.now().strftime("%A %d %B %Y %I:%M:%S%p"),
(10, frame.shape[0] - 10), cv2.FONT_HERSHEY_SIMPLEX, 0.35, (0, 0, 255), 1)
cv2.imshow("Security Feed", frame)
cv2.imshow("Thresh", thresh)
cv2.imshow("Frame Delta", frameDelta)
key = cv2.waitKey(1) & 0xFF
if key == ord("q"):
break
vs.stop() if args.get("video", None) is None else vs.release()
cv2.destroyAllWindows()
personally, I think that the problem is linux is having trouble using the internal camera, but I ofc have been wrong before, but if that is the problem, can somebody please help me fix it, and if it isn't, can somebody please help me out, and tell me what I need to fix please

opencv traffic light detection

import cv2
import numpy as np
import warnings
warnings.filterwarnings("ignore")
cap = cv2.VideoCapture(0)
while True :
ret ,frame = cap.read()
hsv = cv2.cvtColor(frame, cv2.COLOR_BGR2HSV)
lower_yellow = np.array([20,0,0])
upper_yellow = np.array([40,255,255])
mask = cv2.inRange(hsv, lower_yellow, upper_yellow)
res = cv2.bitwise_and(frame,frame, mask= mask)
img = cv2.medianBlur(res, 5)
ccimg = cv2.cvtColor(img, cv2.COLOR_HSV2BGR)
cimg = cv2.cvtColor(ccimg, cv2.COLOR_BGR2GRAY)
circles = cv2.HoughCircles(cimg, cv2.HOUGH_GRADIENT, 1, 20,param1=50, param2=30, minRadius=20, maxRadius=30)
if circles is not None:
print("circle is found")
circles = np.uint16(np.around(circles))
for i in circles[0, :]:
cv2.circle(cimg, (i[0], i[1]), i[2], (0, 255, 0), 2)
cv2.circle(cimg, (i[0], i[1]), 2, (0, 0, 255), 3)
cv2.imshow('detected circles', cimg)
cv2.imshow('res',res)
if cv2.waitKey(1) & 0xFF == ord("q"):
break
cv2.destroyAllWindows()
I am tring to detect trafict light by using opencv , initially i want to detect yellow color by using HSV space and then median filtering and finding the circle but it raises errors async ReadSample() call is failed with error status: -1072873821 and OnReadSample() is called with error status: -1072873821 probably errors are caused by the if state for checking if it finds any circle or not also the error is a long list but these two are repeated.

The capture device is failing to read a frame. The OnReadSample() call is failing on cap.read() and you should implement logic to handle a frame not being read. I've demonstrated this below:
import cv2
import numpy as np
import warnings
warnings.filterwarnings("ignore")
cap = cv2.VideoCapture(0)
while True:
ret, frame = cap.read()
if ret == True:
hsv = cv2.cvtColor(frame, cv2.COLOR_BGR2HSV)
lower_yellow = np.array([20, 0, 0])
upper_yellow = np.array([40, 255, 255])
mask = cv2.inRange(hsv, lower_yellow, upper_yellow)
res = cv2.bitwise_and(frame, frame, mask=mask)
img = cv2.medianBlur(res, 5)
ccimg = cv2.cvtColor(img, cv2.COLOR_HSV2BGR)
cimg = cv2.cvtColor(ccimg, cv2.COLOR_BGR2GRAY)
circles = cv2.HoughCircles(cimg, cv2.HOUGH_GRADIENT, 1, 20, param1=50, param2=30, minRadius=20, maxRadius=30)
if circles is not None:
print("circle is found")
circles = np.uint16(np.around(circles))
for i in circles[0, :]:
cv2.circle(cimg, (i[0], i[1]), i[2], (0, 255, 0), 2)
cv2.circle(cimg, (i[0], i[1]), 2, (0, 0, 255), 3)
cv2.imshow('detected circles', cimg)
cv2.imshow('res', res)
else:
print("Read Failed")
if cv2.waitKey(1) & 0xFF == ord("q"):
break
cv2.destroyAllWindows()

Save both input video and output video in Open CV python

i write a code from Open CV Document about Motion Detection .i want to save my input as a video and my output as a video but i have problems. i save video but i can just save the output video and some time the input video is the same out put video.my input video is from my computer's camera and it's like a normal video but the output is that video in addition by squares around motion objects.i need your help.
import cv2 as cv
import numpy as np
cap = cv.VideoCapture(0)
(grabbed, frame) = cap.read()
fshape = frame.shape
fheight = fshape[0]
fwidth = fshape[1]
print (fwidth , fheight)
ret, frame1 = cap.read()
ret, frame2 = cap.read()
while cap.isOpened():
diff = cv.absdiff(frame1, frame2)
gray = cv.cvtColor(diff, cv.COLOR_BGR2GRAY)
blur = cv.GaussianBlur(gray, (5, 5), 0)
_, thresh = cv.threshold(blur, 20, 255, cv.THRESH_BINARY)
dilated = cv.dilate(thresh, None, iterations=3)
contours, _ = cv.findContours(dilated, cv.RETR_TREE,
cv.CHAIN_APPROX_SIMPLE)
for contour in contours:
(x, y, w, h) = cv.boundingRect(contour)
if cv.contourArea(contour) < 100:
continue
cv.rectangle(frame1, (x, y), (x+w, y+h), (0, 0, 255), 3)
Final_Movie = cv.putText(frame1, "Status: {}".format('Movement'), (10,
20), cv.FONT_HERSHEY_DUPLEX,
1, (0, 0, 255), 3)
#cv.drawContours(frame1, contours, -1, (0, 0, 255), 3)
cv.imshow("feed", frame1)
cv.imshow("feed1", blur)
cv.imshow("feed2", gray)
cv.imshow("feed3", diff)
cv.imshow("feed4", thresh)
cv.imshow("feed5", dilated)
#cv.imshow("feed6", contours)
frame1 = frame2
ret, frame2 = cap.read()
if cv.waitKey(40) == 27:
break
cv.destroyAllWindows()
cap.release()
i tried this but it doesn't work.
import cv2 as cv
import numpy as np
cap = cv.VideoCapture(0)
(grabbed, frame) = cap.read()
fshape = frame.shape
fheight = fshape[0]
fwidth = fshape[1]
print (fwidth , fheight)
fourcc = cv.VideoWriter_fourcc(*'XVID')
out = cv.VideoWriter('output.avi', fourcc, 20.0, (fwidth, fheight))
out1 = cv.VideoWriter('input.avi', fourcc, 20.0, (fwidth, fheight))
ret, frame1 = cap.read()
ret, frame2 = cap.read()
while cap.isOpened():
diff = cv.absdiff(frame1, frame2)
gray = cv.cvtColor(diff, cv.COLOR_BGR2GRAY)
blur = cv.GaussianBlur(gray, (5, 5), 0)
_, thresh = cv.threshold(blur, 20, 255, cv.THRESH_BINARY)
dilated = cv.dilate(thresh, None, iterations=3)
contours, _ = cv.findContours(dilated, cv.RETR_TREE,
cv.CHAIN_APPROX_SIMPLE)
for contour in contours:
(x, y, w, h) = cv.boundingRect(contour)
if cv.contourArea(contour) < 100:
continue
cv.rectangle(frame1, (x, y), (x+w, y+h), (0, 0, 255), 3)
Final_Movie = cv.putText(frame1, "Status: {}".format('Movement'), (10,
20), cv.FONT_HERSHEY_DUPLEX,
1, (0, 0, 255), 3)
#cv.drawContours(frame1, contours, -1, (0, 0, 255), 3)
cv.imshow("feed", frame1)
cv.imshow("feed1", blur)
cv.imshow("feed2", gray)
cv.imshow("feed3", diff)
cv.imshow("feed4", thresh)
cv.imshow("feed5", dilated)
#cv.imshow("feed6", contours)
if ret == True:
out.write(Final_Movie)
out.write(frame2)
frame1 = frame2
ret, frame2 = cap.read()
if cv.waitKey(40) == 27:
break
cv.destroyAllWindows()
cap.release()

I am unable to download cv2, for whatever reason it does not work

from collections import deque
from imutils.video import VideoStream
import numpy as np
import argparse
import cv2
import imutils
import time
ap = argparse.ArgumentParser()
ap.add_argument("-v", "--video",
help="Users/ejr/Desktop/curry.mp4")
ap.add_argument("-b", "--buffer", type=int, default=64,
help="max buffer size")
args = vars(ap.parse_args())
greenLower = (29, 86, 6)
greenUpper = (64, 255, 255)
pts = deque(maxlen=args["buffer"])
if not args.get("video", False):
vs = VideoStream(src=0).start()
else:
vs = cv2.VideoCapture(args["video"])
time.sleep(2.0)
while True:
frame = vs.read()
frame = frame[1] if args.get("video", False) else frame
if frame is None:
break
frame = imutils.resize(frame, width=600)
blurred = cv2.GaussianBlur(frame, (11, 11), 0)
hsv = cv2.cvtColor(blurred, cv2.COLOR_BGR2HSV)
mask = cv2.inRange(hsv, greenLower, greenUpper)
mask = cv2.erode(mask, None, iterations=2)
mask = cv2.dilate(mask, None, iterations=2)
cnts = cv2.findContours(mask.copy(), cv2.RETR_EXTERNAL,
cv2.CHAIN_APPROX_SIMPLE)
cnts = imutils.grab_contours(cnts)
center = None
if len(cnts) > 0:
c = max(cnts, key=cv2.contourArea)
((x, y), radius) = cv2.minEnclosingCircle(c)
M = cv2.moments(c)
center = (int(M["m10"] / M["m00"]), int(M["m01"] / M["m00"]))
if radius > 10:
cv2.circle(frame, (int(x), int(y)), int(radius),
(0, 255, 255), 2)
cv2.circle(frame, center, 5, (0, 0, 255), -1)
pts.appendleft(center)
for i in range(1, len(pts)):
if pts[i - 1] is None or pts[i] is None:
continue
thickness = int(np.sqrt(args["buffer"] / float(i + 1)) * 2.5)
cv2.line(frame, pts[i - 1], pts[i], (0, 0, 255), thickness)
cv2.imshow("Frame", frame)
key = cv2.waitKey(1) & 0xFF
if key == ord("q"):
break
if not args.get("video", False):
vs.stop()
else:
vs.release()
cv2.destroyAllWindows()
This is my code, I have no idea why I keep getting the cv2 there is no module error when I try to pip install it. (I am on a Mac, Python 3.7.4). I am wondering what is the import error here, has the version changed, do I need to use Python 2, or is there like a newer cv that I should use

Try:
pip install opencv-python
or
pip3.7 install opencv-python
I think you are running pip install cv2, which it does not exists since the project of cv2 is: https://pypi.org/project/opencv-python/

what's rules for cv2.approxPolyDP to detect point?

I have below two input images:
First:
Second:
Now I wanna detect the square area.
And here is my code:
#!/usr/bin/env python
# coding: utf-8
import numpy as np
import cv2
import argparse
import math
import sys
ap = argparse.ArgumentParser()
ap.add_argument("-i", "--image", required=True, help="path to input image")
args = vars(ap.parse_args())
img = cv2.imread(args["image"])
# img = cv2.bitwise_not(img,img)
# gray = cv2.imread(args["image"],0)
gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
gray = cv2.GaussianBlur(gray, (5, 5), 0)
cv2.imshow('gray', gray)
cv2.waitKey(0)
gray = cv2.normalize(gray, gray, alpha=0, beta=255, norm_type=cv2.NORM_MINMAX, dtype=cv2.CV_8UC1)
cv2.imshow('normalized', gray)
cv2.waitKey(0)
# sys.exit()
ret, thresh = cv2.threshold(gray, 230, 255, cv2.THRESH_BINARY_INV)
cv2.imshow('thresh', thresh)
# cv2.imwrite('./wni230.png',thresh)
cv2.waitKey(0)
square_cnts = []
thresh = cv2.morphologyEx(thresh, cv2.MORPH_CLOSE, np.ones((5, 5), np.uint8))
cv2.imshow('dilated', thresh)
cv2.waitKey(0)
# sys.exit()
tmpimage, contours, h = cv2.findContours(thresh, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)
cnt0 = contours[0]
tmp_h = h[::-1]
for index, cnt in enumerate(contours[::-1]):
print '!!!!!!!!!!! new round !!!!!!!!!!'
print cv2.arcLength(cnt, True)
# print cnt
approx = cv2.approxPolyDP(cnt, 0.1*cv2.arcLength(cnt, True), True)
print '**********approx*****'
print approx
print len(approx)
print '**********approx end*****'
if len(approx) == 4:
print 'h[i][2]:%s' % tmp_h[0][index][2]
print 'h[i][3]:%s' % tmp_h[0][index][3]
if ret > 0.5:
print "Parallelogram"
elif 0.3 < ret < 0.5:
print "Rectangle"
elif 0 < ret < 0.3:
print "Rhombus"
else:
print "square"
print cv2.arcLength(cnt, True)
print approx
cv2.drawContours(img, [cnt], 0, (0, 0, 255), 2)
cv2.imshow('tmpsquare', img)
cv2.waitKey(0)
if int(cv2.arcLength(cnt, True)) >= 96:
x, y, w, h = cv2.boundingRect(approx)
for j in approx:
cv2.circle(img, (int(j[0][0]), int(j[0][1])), 1, (0, 255, 0), 2)
cv2.imshow('final', img[y:y+h, x:x+w])
cv2.waitKey(0)
print 'target but long squere detected...'
cv2.waitKey(0)
cv2.imshow('img', img)
cv2.imwrite('tmp.png', img)
cv2.waitKey(0)
cv2.destroyAllWindows()
So, I got the two output images:
First:
Second:
Line in red is contour, point in green is points detected by approxPolyDP.
So, the first one is what I wanna.
However, how approxPolyDP locate the up most point for the second one?
Could anyone please explain the rules?
Env:
Python: 2.7.10
Opencv: 3.2.0
Thanks.
Wesley