Detecting the Dominant points on an image using OpenCV

To detect the dominant points within an image first we must find the edges. In this example the edges are found using cvFindContours. The resulting contours are then processed to find the dominant points along the contour. This is done using the cvFindDominantPoints function, this function implements the IPAN99 algorithm to find the points. A small circle is then drawn at each dominant point.

#include "stdafx.h"
#include "cv.h"
#include "highgui.h"
#include "cvaux.h"

int _tmain(int argc, _TCHAR* argv[])
{
	// open and display input image  
    IplImage* input = cvLoadImage("test.jpg", CV_LOAD_IMAGE_GRAYSCALE);  
    cvNamedWindow("Input", CV_WINDOW_AUTOSIZE);  
    cvShowImage("Input", input); 

	// create gray scale image for edge detection
	IplImage* edge = cvCreateImage(cvGetSize(input), 8,1);

	// create output image
	IplImage* output = cvCreateImage(cvGetSize(input), 8,1);

	// threshold the input image
	cvThreshold(input, edge, 230,255, CV_THRESH_BINARY);
	cvNamedWindow("Threshold", CV_WINDOW_AUTOSIZE);
	cvShowImage("Threshold", edge);

	// generate the contours
	CvMemStorage* storage = cvCreateMemStorage();
	CvSeq* contours = NULL;
	int Nc = cvFindContours(edge, storage, &contours, sizeof(CvContour), CV_RETR_LIST);

	// diplay the contours
	printf("Total contours found = %d\n", Nc);
	cvDrawContours(output, contours, cvScalarAll(255),cvScalarAll(255),10); 

	// generate the dominant points
	CvMemStorage* dominantstorage = cvCreateMemStorage();
	CvSeq* dominant = cvFindDominantPoints(contours, dominantstorage, CV_DOMINANT_IPAN,5,15,5,170);

	printf("dominant total=%d\n", dominant->total);

	// display the dominant points
	int i, idx;
    CvPoint p;
	for ( i = 0; i < dominant->total; i++)
    {
        idx = *(int *) cvGetSeqElem(dominant, i);
        p = *(CvPoint *) cvGetSeqElem(contours, idx);
        cvDrawCircle( output, p , 1, CV_RGB(255,0,0) );
        printf("%d %d %d\n", idx, p.x, p.y);
    }
	
	// show output
	cvNamedWindow("Output", CV_WINDOW_AUTOSIZE);
	cvShowImage("Output", output);

	// wait for user
	cvWaitKey(0); 

	// garbage collection	
	cvReleaseImage(&input);
	cvDestroyWindow("Input");
	cvReleaseImage(&edge);
	cvDestroyWindow("Threshold");
	cvReleaseImage(&output);
	cvDestroyWindow("Output");
	return 0;
}

Input Image

threshold

After threshold

Output

5 thoughts on “Detecting the Dominant points on an image using OpenCV

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