VideoCapture doesn't open

Python
1 
import cv2

import keyboard

from time import sleep

cap = cv2.VideoCapture(2, cv2.CAP_DSHOW)

cap .set(cv2.CAP_PROP_FRAME_WIDTH, 480)

cap .set(cv2.CAP_PROP_FRAME_HEIGHT, 320)

cap2 = cv2.VideoCapture(3, cv2.CAP_DSHOW)

cap2.set(cv2.CAP_PROP_FRAME_WIDTH, 480)

cap2.set(cv2.CAP_PROP_FRAME_HEIGHT, 320)

num = 0

while cap.isOpened():

    """

    succes1, img = cap.read()

    succes2, img2 = cap2.read()

    """

    succes1 = cap.grab()

    succes1, img = cap.retrieve()

    succes2 = cap2.grab()

    succes2, img2 = cap2.retrieve()

    k = cv2.waitKey(5)

    if k == 27:

        break

    if keyboard.is_pressed('s'): # wait for 's' key to save and exit

        cv2.imwrite('images/stereoLeft/imageL' + str(num) + '.png', img)

        cv2.imwrite('images/stereoright/imageR' + str(num) + '.png', img2)

        print("images saved!")

        num += 1

        sleep(0.5)

    cv2.imshow('Img 1',img)

    cv2.imshow('Img 2',img2)

# Release and destroy all windows before termination

cap.release()

cap2.release()

cv2.destroyAllWindows()

im using the code above to get images in order to calibrate my stereo camera which uses 1 usb for both cams , however i cant have my 2nd camera have higher resolution then my first , and i cant set them both up to 720p, even tho if i open 1 on 720p here and other on windows app with 720p. Highest i can go with both of them is 480x320. Any ideas why my resolutions are stuck ?
This is the error i get :

"Traceback (most recent call last):
  File "d:\Self\cvpack\StereoVisionDepthEstimation\calibration_images.py", line 39, in <module>
    cv2.imshow('Img 2',img2)
cv2.error: OpenCV(4.5.3) C:\Users\runneradmin\AppData\Local\Temp\pip-req-build-1i5nllza\opencv\modules\imgproc\src\color.cpp:182: error: (-215:Assertion failed) !_src.empty() in function 'cv::cvtColor'"
2

please NEVER post images of code anywhere on the net …

3

fixed it or should i have opened another issue ?

1 Like
4

no, all fine, thank you !

5

img2 is None.

why? because you don’t do any error checking on your use of VideoCapture. official OpenCV tutorials show how to do that.

6

most likely, you’re saturating the usn hub.
if you have more than one, put them on different ports

7

i can open 2x 720p videos if i use ecam(a camera view app) and windows camera app at the same time , if usb was saturating i wouldnt be able to do that i think ?

8

uh no. those apps accept lossy compressed formats, which allow higher frame rates and resolutions as a tradeoff. OpenCV avoids them, as far as I know.

9

is there a way for me to make opencv accept it aswell ? image quality was decent enough ,

also another weird thing i can do 320p+720p which is around 1.075.200 pixels , but i cant do 2x 480p 614.400 pixels if i didnt calculate it wrong , shouldnt near 60% of pixels be allowed ?

10

you can try setting CAP_PROP_FOURCC like cap.set(cv.CAP_PROP_FOURCC, cv.VideoWriter_fourcc(*"MJPG"))

11

That worked , thanks a lot