How to apply a color cast to a video frame in OpenCV Python?

How to apply a color cast to a video frame in OpenCV Python?

By : user2172840
Date : October 22 2020, 08:10 PM
it fixes the issue I'm very new to image processing and OpenCV. I'm working on a helper-function to assist in tuning some key-frame detection parameters. , Two simple options come to mind.
Let's start with this code:
code :
import cv2
import numpy as np

frame = cv2.imread('lena3.png')
gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
result = np.zeros_like(frame)
result[...,0] = gray
cv2.imwrite('shaded_lena.png', result)
blank = np.zeros_like(gray)

shaded = [
    cv2.merge([gray, blank, blank])
    , cv2.merge([blank, gray, blank])
    , cv2.merge([blank, blank, gray])
    , cv2.merge([gray, gray, blank])
    , cv2.merge([gray, blank, gray])
    , cv2.merge([blank, gray, gray])

cv2.imwrite('shaded_lena_all.png', np.hstack(shaded))

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How to process images of a video, frame by frame, in video streaming using OpenCV and Python

How to process images of a video, frame by frame, in video streaming using OpenCV and Python

By : betul
Date : March 29 2020, 07:55 AM
fixed the issue. Will look into that further After reading the documentation of VideoCapture. I figured out that you can tell VideoCapture, which frame to process next time we call VideoCapture.read() (or VideoCapture.grab()).
The problem is that when you want to read() a frame which is not ready, the VideoCapture object stuck on that frame and never proceed. So you have to force it to start again from the previous frame.
code :
import cv2

cap = cv2.VideoCapture("./out.mp4")
while not cap.isOpened():
    cap = cv2.VideoCapture("./out.mp4")
    print "Wait for the header"

pos_frame = cap.get(cv2.cv.CV_CAP_PROP_POS_FRAMES)
while True:
    flag, frame = cap.read()
    if flag:
        # The frame is ready and already captured
        cv2.imshow('video', frame)
        pos_frame = cap.get(cv2.cv.CV_CAP_PROP_POS_FRAMES)
        print str(pos_frame)+" frames"
        # The next frame is not ready, so we try to read it again
        cap.set(cv2.cv.CV_CAP_PROP_POS_FRAMES, pos_frame-1)
        print "frame is not ready"
        # It is better to wait for a while for the next frame to be ready

    if cv2.waitKey(10) == 27:
    if cap.get(cv2.cv.CV_CAP_PROP_POS_FRAMES) == cap.get(cv2.cv.CV_CAP_PROP_FRAME_COUNT):
        # If the number of captured frames is equal to the total number of frames,
        # we stop
How to get video frame by frame from stream using openCV and python

How to get video frame by frame from stream using openCV and python

By : Dennis Preston
Date : March 29 2020, 07:55 AM
this one helps. http://answers.opencv.org/question/24154/how-to-using-opencv-api-get-web-video-stream/
You should be able to just cap = cv2.VideoCapture('yourStreamURIHere')
code :
cap = cv2.VideoCapture('http://hello:goodbye@
get frame from video with CV_CAP_PROP_POS_FRAMES in opencv python

get frame from video with CV_CAP_PROP_POS_FRAMES in opencv python

By : B4t M4n
Date : March 29 2020, 07:55 AM
I hope this helps . I am trying to detect a (photography) flash in a video using OpenCV. , From opencv-doc:
How to get frame from video by its index via OpenCV and Python?

How to get frame from video by its index via OpenCV and Python?

By : Rdy mxTrrr
Date : March 29 2020, 07:55 AM
To fix this issue Use VideoCapture::set() with CAP_PROP_POS_FRAMES property id to set the position of the frame to be read.
code :
myFrameNumber = 50
cap = cv2.VideoCapture("video.mp4")

# get total number of frames
totalFrames = cap.get(cv2.CAP_PROP_FRAME_COUNT)

# check for valid frame number
if myFrameNumber >= 0 & myFrameNumber <= totalFrames:
    # set frame position

while True:
    ret, frame = cap.read()
    cv2.imshow("Video", frame)
    if cv2.waitKey(20) & 0xFF == ord('q'):

How to get previous frame of a video in opencv python

How to get previous frame of a video in opencv python

By : Taj Sayyad
Date : March 29 2020, 07:55 AM
I hope this helps . There is no specific function in OpenCV to access the previous frame. Your problem can be solved by calling cap.read() once before entering the while loop. Use a variable prev_frame to store the previous frame just before reading the new frame. Finally, as a good practice, you should verify that the frame was properly read, before doing computations on it. Your code could look something like:
code :
import cv2
import numpy as np

cap = cv2.VideoCapture('video3.mov')
ret, frame = cap.read()

    ret, frame = cap.read()
    if ret:
        gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)

        #detect key feature points
        sift = cv2.xfeatures2d.SIFT_create()
        kp, des = sift.detectAndCompute(gray, None)

        #some magic with prev_frame

        #draw key points detected
        img=cv2.drawKeypoints(gray,kp,gray, flags=cv2.DRAW_MATCHES_FLAGS_DRAW_RICH_KEYPOINTS)

        print('Could not read frame')

    if cv2.waitKey(100) & 0xFF == ord('q'):

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