#include 
#include 
#include 
 
int main(int argc, char *argv[]) {
int delay = 0, key=0, i=0;
char *window_name;
CvCapture *video = NULL;
IplImage  *frame = NULL;
IplImage  *grey  = NULL;
IplImage  *edges = NULL;
 
/* check for video file passed by command line */
if (argc>1) {
video = cvCaptureFromFile(argv[1]);
} else {
printf("Usage: %s VIDEO_FILE\n", argv[0]);
return 1;
}
 
/* check file was correctly opened */
if (!video) {
printf("Unable to open \"%s\"\n", argv[1]);
return 1;
}
 
/* create a video window with same name of the video file, auto sized */
window_name = argv[1];
cvNamedWindow(window_name, CV_WINDOW_AUTOSIZE);
 
/* Get the first frame and create a edges image with the same size */
frame = cvQueryFrame(video);
grey  = cvCreateImage(cvGetSize(frame), IPL_DEPTH_8U, 1);
edges = cvCreateImage(cvGetSize(frame), IPL_DEPTH_8U, 1);
 
/* calculate the delay between each frame and display video's FPS */
printf("%2.2f FPS\n", cvGetCaptureProperty(video, CV_CAP_PROP_FPS));
delay = (int) (1000/cvGetCaptureProperty(video, CV_CAP_PROP_FPS));
 
while (frame) {
/* Edges on the input gray image (needs to be grayscale) using the Canny algorithm.
Uses two threshold and a aperture parameter for Sobel operator. */
cvCvtColor(frame, grey, CV_BGR2GRAY);
cvCanny( grey, edges, 1.0, 1.0, 3);
 
/* show loaded frame */
cvShowImage(window_name, edges);
 
/* load and check next frame*/
frame = cvQueryFrame(video);
if(!frame) {
printf("error loading frame.\n");
return 1;
}
 
/* wait delay and check for the quit key */
key = cvWaitKey(delay);
if(key=='q') break;
}
}

gcc -I/usr/include/opencv  -lopencv_core -lopencv_imgproc -lopencv_highgui -lopencv_ml -lopencv_video -lopencv_features2d -lopencv_calib3d -lopencv_objdetect -lopencv_contrib -lopencv_legacy -lopencv_flann   -o webcam_sobel webcam_sobel.c -lm