Capturing Frames from a USB Camera using OpenCV on Linux

Next step after loading image and manipulating it, I try to access a Linux-USB-registered USB Camera using a simple camera capture framework written in C with OpenCV Library. Here is the code:

/////////////////////////////////////////////////////
// trialcam1a.cpp
// A Simple Camera Capture Framework
// This program will connect to a camera then
// show the frames in a window
/////////////////////////////////////////////////////
#include <stdio.h>
#include <cv.h>
#include <highgui.h>

int main()
{
IplImage *frame = NULL; //Preparing frame pointer
int key;

//Allocates and initializes cvCapture structure
// for reading a video stream from the camera.
//Index of camera is -1 since only one camera
// connected to the computer or it does not
// matter what camera to use.
CvCapture *input_camera = cvCaptureFromCAM(-1);

//Grabs and returns a frame from camera
frame = cvQueryFrame(input_camera);

//Creates window for displaying the frames
//Flag is reset (0) --> change window size
// manually
cvNamedWindow("Capturing Image ...", 0);

//Change to the appropriate size. In GTK, the
// inappropriate size will return a segmentation
// fault. I don't know why ...
//Gets the appropriate size using cvGetCaptureProperty
// with CV_CAP_PROP_FRAME_HEIGHT and CV_CAP_PROP_FRAME_WIDTH
// as property_id
cvResizeWindow("Capturing Image ...",
(int) cvGetCaptureProperty(input_camera, CV_CAP_PROP_FRAME_HEIGHT),
(int) cvGetCaptureProperty(input_camera, CV_CAP_PROP_FRAME_WIDTH));

while(frame != NULL)
{
//Shows a frame
cvShowImage("Capturing Image ...", frame);

//Checks if ESC is pressed and gives a delay
// so that the frame can be displayed properly
key = cvWaitKey(10);
if(key == 27)
break;
//Grabs and returns the next frame
frame = cvQueryFrame(input_camera);
}

//Release cvCapture structure
cvReleaseCapture(&input_camera);

//Destroy the window
cvDestroyWindow("Capturing Image ...");

return 0;
}

Compiling (in the working directory):
$ g++ -Wall trialcam1a.cpp -o trialcam1a `pkg-config --cflags --libs opencv`

Running (in the working directory):
$ ./trialcam1a

Screenshot:


dmesg when I plugged USB Camera:
usb 3-1: new full speed USB device using uhci_hcd and address 2
usb 3-1: configuration #1 chosen from 1 choice
Linux video capture interface: v2.00
pwc: Philips webcam module version 10.0.13 loaded.
pwc: Supports Philips PCA645/646, PCVC675/680/690, PCVC720[40]/730/740/750 & PCVC830/840.
pwc: Also supports the Askey VC010, various Logitech Quickcams, Samsung MPC-C10 and MPC-C30,
pwc: the Creative WebCam 5 & Pro Ex, SOTEC Afina Eye and Visionite VCS-UC300 and VCS-UM100.
pwc: Logitech QuickCam 4000 Pro USB webcam detected.
pwc: Registered as /dev/video0.
usbcore: registered new interface driver Philips webcam
usbcore: registered new interface driver snd-usb-audio

Camera driver: pwc.
Camera interface: v4l (Video for Linux).

References:

• OpenCV wiki (http://opencvlibrary.sourceforge.net)
• Introduction to programming with OpenCV, by Gady Agam (http://www.cs.iit.edu/~agam/cs512/lect-notes/opencv-intro/opencv-intro.html)
• Linux-uvc-devel mailing list, January 2007 archieve, e-mail posting by Jose Luis Landabaso