I am a complete beginner with coding and needed to code a few lines of code for getting pictures from a USB camera for a research project that i am responsible for. admittingly i took help of a few source codes from a few blogs online, they did show a couple of errors but most of them were resolved except this one that keeps popping up no matter what i do. does anyone have any idea where exactly the problem could be arising from? all the errors in the previous lines of code seem to be dealt with. I really need to get this right as this project decides my bacheklor thesis
the following was the code that i used, even though i am really really dumb with this stuff:
`
#new camera code
import cv2
import imutils
import time
#loop for taking picture and saving
cap = cv2.VideoCapture(0)
frame = cap.read()
def takePicture():
global showimg
(frame) = cap.read()
showimg=frame
return image
cv2.imshow('image', img)
cv2.imshow('img1',showimg) # display the captured image
cv2.waitKey(1)
time.sleep(0.3) # Wait 300 miliseconds
image ='C:/Users/whale/Desktop/REMOVE/capture.png'
cv2.imwrite(image, frame)
img = cv2.imread('no-such-file.jpg', 0)
cap.release()
print(takePicture())
`
There are a few issues with your code:
The takePicture() function is not returning anything. It needs to return showimg instead of image.
The line global showimg (frame) = cap.read() should be changed to global showimg, frame; frame = cap.read().
The line img = cv2.imread('no-such-file.jpg', 0) should be removed as it is not being used and it may cause confusion.
The line print(takePicture()) should be changed to takePicture() as the function already displays the image.
Here's the correct code:
#new camera code
import cv2
import imutils
import time
#loop for taking picture and saving
cap = cv2.VideoCapture(0)
def takePicture():
global showimg, frame
frame = cap.read()
showimg = frame
cv2.imshow('image', showimg) # display the captured image
cv2.waitKey(1)
time.sleep(0.3) # Wait 300 miliseconds
image ='C:/Users/whale/Desktop/REMOVE/capture.png'
cv2.imwrite(image, frame)
return showimg
takePicture()
cap.release()
I'm using OpenCV with USB camera on a Raspberry Pi4. I have activated an external trigger by RPI's GPIO pin. I wrote a short Python code to test the trigger and made sure it worked. Then I wrote another Python program to save a single image captured by the camera. Here is the code:
import time
import cv2
import smbus
from gpiozero import LED
TRIG_ADDR = 17
def setup_trigger_control_gpio(pin):
trigger = LED(pin)
return trigger
def setup_camera(frame_width, frame_height, fps):
cap = cv2.VideoCapture(0, cv2.CAP_ANY)
cap.set(cv2.CAP_PROP_FRAME_WIDTH, frame_width)
cap.set(cv2.CAP_PROP_FRAME_HEIGHT, frame_height)
cap.set(cv2.CAP_PROP_FPS, fps)
cap.set(cv2.CAP_PROP_BUFFERSIZE, 1)
cap.set(cv2.CAP_PROP_FOURCC, cv2.VideoWriter_fourcc('M', 'J', 'P', 'G'))
if cap.isOpened() is not True:
print ("Cannot open camera. Exiting.")
quit()
else:
return cap
trigger = setup_trigger_control_gpio(TRIG_ADDR)
cap = setup_camera(640, 480, 120)
trigger.on()
ret, frame = cap.read()
if ret:
frame = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
cv2.imwrite("images/frame.pgm", frame)
trigger.off()
cap.release()
I set the buffersize to 1, since I'm using a trigger to capture the frame exactly when I need to. The program however gets stuck on the cap.read() line as if it did not receive the trigger. When I ran the program after that I ran the short program for the trigger only, it has finished successfully. Sometimes I had to run the trigger program more than once for the main program to finish, which I find a bit scary, because of the inconsistency.
I tried to set the buffersize to 10, which seemingly worked, however the saved image was empty(all black). I have also tried to "flush" the buffer by reading the first 10 empty frames, which worked and I have finally saved a proper image. The real problems occur when I try to process real time video this way, as even after flushing the buffer, the images do not correspond to the point in time when they should've been taken. Therefor I would love to use the feature of setting the buffersize to one, so that I would know exactly which frame is being processed. I will be thankful for any ideas.
I'm using an ONVIF IP security camera with the python-onvif-zeep library https://github.com/FalkTannhaeuser/python-onvif-zeep. Can anybody please provide a short, simple, and concise example that shows how to grab a frame?
The readme and the examples https://github.com/FalkTannhaeuser/python-onvif-zeep/tree/zeep/examples show how to set camera properties and some other things, but I can't find a working example that shows how to grab a frame.
For example, this is the simplest possible OpenCV program that grabs frames from the 1st attached webcam and shows them:
import cv2
def main():
vidCap = cv2.VideoCapture(0)
while True:
frameGrabSuccessful, openCvImage = vidCap.read()
cv2.imshow('openCvImage', openCvImage)
keyPress = cv2.waitKey(1)
if keyPress == 27 or keyPress == ord('q'):
break
# end if
# end while
# end function
if __name__ == '__main__':
main()
Can somebody please provide an equivalent example for the python-onvif-zeep library? i.e.:
from onvif import ONVIFCamera
def main():
camera = ONVIFCamera('192.168.1.100', 80, 'username', 'pass')
# what goes here ??
while True:
# what goes here ??
# end while
# end function
if __name__ == '__main__':
main()
Upon further investigation it seems python-onvif-zeep cannot be used for grabbing frames. It's necessary to use RTSP for that, see Access IP Camera in Python OpenCV
The code
import cv
capture = cv.CaptureFromFile("a.avi")
while True:
frame = cv.QueryFrame(capture)
cv.ShowImage("a',frame)
Shows the same initial frame from the video repeatedly (QueryFrame is not advancing the video and grabbing the next frame). It works fine if the video is captured from a webcam.
Any ideas?
I see the same mistakes over and over again, so this is probably the last time I'll address them. Hopefully people will start using the search box in the future and dig a little deeper.
Call cv.WaitKey() after displaying the frame. If don't have a delay between displaying the frames some problems could happen. I believe this the problem.
Code defensively: if you are calling a function/method that can fail, believe in Murphy, and add the appropriate check to verify it doesn't:
import cv
capture = cv.CaptureFromFile("a.avi")
if not capture :
print "Error loading video file"
# Should exit the application
while True:
frame = cv.QueryFrame(capture)
if not frame:
print "Could not retrieve frame"
cv.ShowImage("a", frame)
k = cv.WaitKey(10)
if k == 27:
break # ESC key was pressed
My program generates a series of windows using the following code:
def display(img, name, fun):
global clicked
cv.NamedWindow(name, 1)
cv.ShowImage(name, img)
cv.SetMouseCallback(name, fun, img)
while cv.WaitKey(33) == -1:
if clicked == 1:
clicked = 0
cv.ShowImage(name, img)
cv.DestroyWindow(name)
I press "q" within the gui window to close it. However, the code continues to the next call of the display function and displays a second gui window while not closing the first. I'm using a Mac with OpenCV 2.1, running the program in Terminal. How can I close the gui windows? Thanks.
You need to run cv.startWindowThread() after opening the window.
I had the same issue and now this works for me.
Hope this helps for future readers. And there is also a cv2 binding (I advise to use that instead of cv).
This code works for me:
import cv2 as cv
import time
WINDOW_NAME = "win"
image = cv.imread("ela.jpg", cv.CV_LOAD_IMAGE_COLOR)
cv.namedWindow(WINDOW_NAME, cv.CV_WINDOW_AUTOSIZE)
initialtime = time.time()
cv.startWindowThread()
while (time.time() - initialtime < 5):
print "in first while"
cv.imshow(WINDOW_NAME, image)
cv.waitKey(1000)
cv.waitKey(1)
cv.destroyAllWindows()
cv.waitKey(1)
initialtime = time.time()
while (time.time() - initialtime < 6):
print "in second while"
The same issue happens with the C++ version, on Linux:
Trying to close OpenCV window has no effect
There are a few peculiarities with the GUI in OpenCV. The destroyImage call fails to close a window (atleast under Linux, where the default backend was Gtk+ until 2.1.0) unless waitKey was called to pump the events. Adding a waitKey(1) call right after destroyWindow may work.
Even so, closing is not guaranteed; the the waitKey function is only intercepted if a window has focus, and so if the window didn't have focus at the time you invoked destroyWindow, chances are it'll stay visible till the next destroyWindow call.
I'm assuming this is a behaviour that stems from Gtk+; the function didn't give me any trouble when I used it under Windows.
Sayem2603
I tried your solution and it worked for me - thanks! I did some trial and error and discovered that looping 4 times did the trick for me... or posting the same code 4 times just the same..
Further, I drilled down to:
cv2.destroyAllWindows()
cv2.waitKey(1)
cv2.waitKey(1)
cv2.waitKey(1)
cv2.waitKey(1)
or simply calling DestroyAllWindows and then looping the waitKey() code 4 times:
cv2.destroyAllWindows()
for i in range (1,5):
cv2.waitKey(1)
Worked as well. I am not savvy enough to know why this works exactly, though I assume it has something to do with the interruption and delay created by looping that code(?)
Matthäus Brandl said, above, that the third waitKey() worked for him, so perhaps it is slightly different on each system? (I am running Linux Mint with 3.16.1 kernel and python 2.7)
The delay, alone, doesn't explain it, as simply increasing the delay time on the waitKey() does not do the trick. (Also looped print("Hello") 1000 times instead of using wiatKey() just to see if the delay that created helped any - it did not.) Must have something more to do with how waitKey() interacts with window events.
OpenCV Docs say: "This function is the only method in HighGUI that can fetch and handle events, so it needs to be called periodically for normal event processing unless HighGUI is used within an environment that takes care of event processing."
Perhaps it creates an interrupt of sorts in the GUI display that allows the destroyAllWindows() action to process?
J
Here is what worked for me:
cv2.namedWindow("image")
cv2.imshow('image', img)
cv2.waitKey(0) # close window when a key press is detected
cv2.destroyWindow('image')
cv2.waitKey(1)
This solution works for me (under Ubuntu 12.04 with python open in the shell):
Re-invoke cv.ShowImage after the window is 'destroyed'.
If you are using Spyder ( Anaconda Package ) there is the problem.
None of the solutions worked for me.
I discovered that the problem wasn't the functions, but a problem on Spyder really. Try to use a texteditor plus running on terminal and you be fine using simply:
WINDOW_NAME = "win"
image = cv.imread("foto.jpg", 0)
cv.namedWindow(WINDOW_NAME, cv.CV_WINDOW_AUTOSIZE)
cv.startWindowThread()
cv.imshow(WINDOW_NAME, image)
cv.waitKey()
cv.destroyAllWindows()
I solved the problem by calling cv2.waitKey(1) in a for loop, I don't know why it worked but gets my job done, so I didn't bother myself further.
for i in range(1,10):
cv2.destroyAllWindows()
cv2.waitkey(1)
you are welcome to explain.
It seems that none of the above solutions worked for me if I run it on Jupyter Notebook (the window hangs when closing and you need to force quit Python to close the window).
I am on macOS High Sierra 10.13.4, Python 3.6.5, OpenCV 3.4.1.
The below code works if you run it as a .py file (source: https://www.learnopencv.com/read-write-and-display-a-video-using-opencv-cpp-python/). It opens the camera, records the video, closes the window successfully upon pressing 'q', and saves the video in .avi format.
import cv2
import numpy as np
# Create a VideoCapture object
cap = cv2.VideoCapture(0)
# Check if camera opened successfully
if (cap.isOpened() == False):
print("Unable to read camera feed")
# Default resolutions of the frame are obtained.The default resolutions are system dependent.
# We convert the resolutions from float to integer.
frame_width = int(cap.get(3))
frame_height = int(cap.get(4))
# Define the codec and create VideoWriter object.The output is stored in 'outpy.avi' file.
out = cv2.VideoWriter('outpy.avi',cv2.VideoWriter_fourcc('M','J','P','G'), 10, (frame_width,frame_height))
while(True):
ret, frame = cap.read()
if ret == True:
# Write the frame into the file 'output.avi'
out.write(frame)
# Display the resulting frame
cv2.imshow('frame',frame)
# Press Q on keyboard to stop recording
if cv2.waitKey(1) & 0xFF == ord('q'):
break
# Break the loop
else:
break
# When everything done, release the video capture and video write objects
cap.release()
out.release()
# Closes all the frames
cv2.destroyAllWindows()
Fiddling around with this issue in the python console I observed the following behavior:
issuing a cv2.imshow after cv2.destroyWindow sometimes closes the window. Albeit the old window pops up again with the next highgui call, e.g., cv2.namedWindow
the third call of cv2.waitKey after cv2.destroyWindow closed the window every time I tried. Additionally the closed window remained closed, even when using cv2.namedWindow afterwards
Hope this helps somebody.
(I used Ubuntu 12.10 with python 2.7.3 but OpenCV 2.4.2 from the 13.04 repos)
After searching aroung for some time, none of the solutions provided worked for me so since there's a bug in this function and I did not have time to fix it, I did not have to use the cv2 window to show the frames. Once a few frames have been saved, you can open the file in a different viewer, like VLC or MoviePlayer ( for linux ).
Here's how i did mine.
import cv2
threadDie = True # change this to false elsewhere to stop getting the video
def getVideo(Message):
print Message
print "Opening url"
video = cv2.VideoCapture("rtsp://username:passwordp#IpAddress:554/axis-media/media.amp")
print "Opened url"
fourcc = cv2.cv.CV_FOURCC('X','V','I','D')
fps = 25.0 # or 30.0 for a better quality stream
writer = cv2.VideoWriter('out.avi', fourcc,fps, (640,480),1)
i = 0
print "Reading frames "
while threadDie:
ret, img = video.read()
print "frame number: ",i
i=i+1
writer.write(img)
del(video)
print "Finished capturing video"
Then open the file with a different viewer, prabably in a nother function, like if you like vlc, you can start it and pass the saved file as a parameter. On the terminal, i would do this
vlc out.avi #out.avi is my video file being saved by the function above.
This worked for me on arch linux.
I had the same issue. The problem is that while(cap.isOpened()): loop does not finish so that I added below structure. When video has no frame in the following part, it returns ret values as False. Normally, I put destroyAllWindows command out of loop but I moved it into the loop. It works in my code properly.
while(cap.isOpened()):
ret, frame = cap.read()
if ret == False:
cap.release()
cv2.waitKey(1)
cv2.destroyAllWindows()
cv2.waitKey(1)
This worked for me in spyder :
import cv2 as cv
cv.namedWindow("image")
img = cv.imread("image_name.jpg")
cv.imshow("image",img)
cv.waitKey(5000) # 5 sec delay before image window closes
cv.destroyWindow("image")
Remember use only cv.waitKey(positive Integer) for this to work
cv2.imshow("the image I want to show ",img)
cv2.waitKey(0)
cv2.destroyAllWindows()
cv2.waitKey(1) # to close the window.
The above code worked well for me.
I'm using Mac and python 3.7 .
Close the terminal, later close the window, it worked for me in Visual Studio Code in Windows; I made a task to compile and run the executable in the terminal, the program used my webcam to capture video and display it in a QT window, when I clicked the close button it didn't close, it reopened itself again and continued with the program until I closed the terminal and later could close the program window without it reopening again.