How do I capture images in OpenCV and saving in pgm format?

Question

I am brand new to programming in general, and am working on a project for which I need to capture images from my webcam (possibly using OpenCV), and save the images as pgm files.

What's the simplest way to do this? Willow Garage provides this code for image capturing:

http://opencv.willowgarage.com/wiki/CameraCapture

Using this code as a base, how might I modify it to:

1. capture an image from the live cam every 2 seconds
2. save the images to a folder in pgm format

Thanks so much for any help you can provide!

Answer 1

First of all, please use newer site - opencv.org. Using outdated references leads to chain effect, when new users see old references, read old docs and post old links again.

There's actually no reason to use old C API. Instead, you can use newer C++ interface, which, among other things, handles capturing video gracefully. Here's shortened version of example from docs on VideoCapture:

#include "opencv2/opencv.hpp"

using namespace cv;

int main(int, char**)
{
    VideoCapture cap(0); // open the default camera
    if(!cap.isOpened())  // check if we succeeded
        return -1;

    for(;;)
    {
        Mat frame;
        cap >> frame; // get a new frame from camera
        // do any processing
        imwrite("path/to/image.png", frame);
        if(waitKey(30) >= 0) break;   // you can increase delay to 2 seconds here
    }
    // the camera will be deinitialized automatically in VideoCapture destructor
    return 0;
}

Also, if you are new to programming, consider using Python interface to OpenCV - cv2 module. Python is often considered simpler than C++, and using it you can play around with OpenCV functions right in an interactive console. Capturing video with cv2 looks something like this (adopted code from here):

import numpy as np
import cv2

cap = cv2.VideoCapture(0)

while(True):
    # Capture frame-by-frame
    ret, frame = cap.read()
    # do what you want with frame
    #  and then save to file
    cv2.imwrite('path/to/image.png', frame)
    if cv2.waitKey(30) & 0xFF == ord('q'): # you can increase delay to 2 seconds here
        break

# When everything done, release the capture
cap.release()
cv2.destroyAllWindows()