Getting single frames from video with python

asked 2012-07-25 04:19:00 -0600

Kea
36 ●1 ●1 ●4

updated 2012-09-25 10:39:30 -0600

2792 ●13 ●25 ●52

I am just getting started on using OpenCV using Python, and I will work with video. I have established connection to the web camera, using the script below. Now I would like to take out a couple of frames that can be analyzed. Is there some one who can help me get started on that?

I have the following code:

import cv2.cv as cv
import time
from scipy import *
import numpy
import sys, os, random, hashlib
from math import *

cv.NamedWindow("camera", 1)
capture = cv.CaptureFromCAM(0)

while True:
    img = cv.QueryFrame(capture)
    cv.ShowImage("camera", img)
    if cv.WaitKey(10) == 27:
        break

cv.DestroyAllWindows()

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answered 2012-07-25 19:31:00 -0600

Martin Peris
1742 ●10 ●23 http://blog.martinperi...

Hi Kea,

well, on each iteration the current frame captured from the camera is stored in the variable img. After the call to:

img = cv.QueryFrame(capture)

you can do whatever you want with img: Store it to disk, modify it in some way, detect objects... anything.

All the awesomeness is documented here

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if you're going to store or modify the Mat (frame) provided by VideoCapture, you need to do it with its clone (use Mat::clone()) - because the returned frame refers to some internal VideCaptures's buffer that can be overwritten by the next requested frame.

Andrey Pavlenko ( 2012-07-26 01:30:27 -0600 )edit

1

Thank you!

Kea ( 2012-07-26 02:53:26 -0600 )edit

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answered 2012-07-26 02:44:05 -0600

Kirill Kornyakov

2792 ●13 ●25 ●52

I suggest you to carefully read all the existing python samples: http://code.opencv.org/projects/opencv/repository/revisions/master/show/samples/python2. There are a lot of interesting use cases.

You could also study all the questions with the python tag here.

@Abid Rahman K has very interesting blog on the subject: http://www.opencvpython.blogspot.com/

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Thank you!

Kea ( 2012-07-26 02:53:09 -0600 )edit

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answered 2012-07-26 02:49:24 -0600

Kea
36 ●1 ●1 ●4

updated 2012-07-26 02:55:00 -0600

Kirill Kornyakov

2792 ●13 ●25 ●52

Thanks a lot. That cleared up something. The following code will take a snapshot with the web cam and save it in the directory of the code:

import cv2.cv as cv
import time

cv.NamedWindow("camera", 1)
capture = cv.CaptureFromCAM(0)

while True:
    img = cv.QueryFrame(capture)
    # cv.ShowImage("camera", img)

    cv.SaveImage('test1.jpg', img)

    if cv.WaitKey(10) == 27:
        break
cv.DestroyAllWindows()

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Hi Instead of opening a new question i would like to ask the same how to accomplish the same task capture snapshot using opencv 3.0 ?. Please point me to some examples or tutorials.

Thanks, krishna

vkichu ( 2016-01-19 18:11:50 -0600 )edit

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