CODEWITHSUNDEEP
python-3.xopencv
Puspam
Puspam

Reputation: 2777

Cannot save modified frames with Python OpenCV

I wrote this code to take a video file as input from my local storage, then display it and re-encode the frames in grayscale and save it to an output file. Here is my code:

import cv2 as cv

fourcc = cv.VideoWriter_fourcc(*'XVID')
out = cv.VideoWriter('output.avi', fourcc, 25.0, (640,  480))
cap = cv.VideoCapture(input())
if not cap.isOpened():
    print("Error opening video file")
    exit()
while cap.isOpened():
    ret, frame = cap.read()
    if not ret:
        print("Can't receive frame. Exiting ...")
        break

    frame = cv.cvtColor(frame, cv.COLOR_BGR2GRAY) #This line is causing the problem
    out.write(frame)
    cv.imshow('frame', frame)
    if cv.waitKey(1) == ord('q'):
        break

cap.release()
out.release()
cv.destroyAllWindows()

With this code, I can see the video file being played, but the output file appears blank. It works if I write the original frame object into the output file. But, whenever I use frame = cv.cvtColor(frame, cv.COLOR_BGR2GRAY) to convert the frame into grayscale, it does not work and I get a blank output file. What mistake am I doing?

Upvotes: 1

Views: 204

Answers (1)

soumith
soumith

Reputation: 606

From the cv docs, here the signature of VideoWriter constructor is

VideoWriter (const String &filename, int fourcc, double fps, Size frameSize, bool isColor=true)

i.e. if you're writing a grayscale image, you need to set the isColor param to false since it's true by default. Replace the line with this,

out = cv.VideoWriter('output.avi', fourcc, 25.0, (640,  480), 0)

Upvotes: 2

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