Unable to save background subtracted video Python openCV

Question

I have a input text file which contains the names of the images which I have to put together into a video and then apply background subtraction on the video and then save the output.

I tried this:

# convert images to video
f = open('files_harsha.txt','r+')
fourcc = cv2.VideoWriter_fourcc(*'DIVX')
out = cv2.VideoWriter('harsha_output.avi',fourcc, 10.0, (1344,1024))
for line in f:
    frame=cv2.imread(line.strip())
    out.write(frame)
#    cv2.imshow('1',frame)
#    cv2.waitKey(0)

out.release()

The above snippet works correctly, saving the video. Then I perform the background subtraction and try to save the output, as shown below:

capture = cv2.VideoCapture('harsha_output.avi')
size = (int(capture.get(cv2.CAP_PROP_FRAME_WIDTH)),
int(capture.get(cv2.CAP_PROP_FRAME_HEIGHT)))
fourcc = cv2.VideoWriter_fourcc(*'DIVX')
video = cv2.VideoWriter('harsha_subtractor.avi', fourcc, 10.0,size)
fgbg= cv2.createBackgroundSubtractorMOG2(varThreshold=50,history=4)

while (1):
    ret, img = capture.read()
    if ret==True:
        fgmask = fgbg.apply(img)
        video.write(fgmask)
        #cv2.imshow('forehead',fgmask)

    else:
        capture.release()
        video.release()
        break

    k = cv2.waitKey(30) & 0xff
    if k == 27:
        break

cv2.destroyAllWindows()

I am able to see the background subtracted video but I am unable to save the file. Why am I having this issue?

I am using Python 2.7 within the Anaconda IDE (Spyder) and am using openCV 3.x

Answer 1

Just for the record. As suggested by dan-mašek , the fgmask is a 1-channel image, thus the VideoWriter fails showing the following error: (-215) scn==2 & (scn == 3 || scn == 4) . I solved passing the isColor=False argument to VideoWriter .

Answer 2

I was facing similar problem. Add isColor=False argument to the VideoWriter .

Change certain portion of your code accordingly as shown:

video = cv2.VideoWriter('harsha_subtractor.avi', fourcc, 10.0, size, 
isColor=False)