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Comparing images with opencv c++

YikUTM (19)
opencv beginner here... I came across this example code in the opencv folder. The instruction for the usage of this program is matcher_simple <image1> <image2>. I am quite sure that that is instruction for image loading but I don't know how to use this. Can somebody explain to me?

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  #include <stdio.h>
#include <opencv2/core/core.hpp>
#include <opencv2/features2d/features2d.hpp>
#include <opencv2/highgui/highgui.hpp>

using namespace cv;

void help()
{
	printf("\nThis program demonstrates using features2d detector, descriptor extractor and simple matcher\n"
			"Using the SURF desriptor:\n"
			"\n"
			"Usage:\n#include <stdio.h>
#include <opencv2/core/core.hpp>
#include <opencv2/features2d/features2d.hpp>
#include <opencv2/highgui/highgui.hpp>

using namespace cv;

void help()
{
	printf("\nThis program demonstrates using features2d detector, descriptor extractor and simple matcher\n"
			"Using the SURF desriptor:\n"
			"\n"
			"Usage:\n matcher_simple <image1> <image2>\n");
}

int main(int argc, char** argv)
{
	if(argc != 3)
	{
		help();
		return -1;
	}

	Mat img1 = imread(argv[1], CV_LOAD_IMAGE_GRAYSCALE);
	Mat img2 = imread(argv[2], CV_LOAD_IMAGE_GRAYSCALE);
	if(img1.empty() || img2.empty())
	{
		printf("Can't read one of the images\n");
		return -1;
	}

	// detecting keypoints
	SurfFeatureDetector detector(400);
	vector<KeyPoint> keypoints1, keypoints2;
	detector.detect(img1, keypoints1);
	detector.detect(img2, keypoints2);

	// computing descriptors
	SurfDescriptorExtractor extractor;
	Mat descriptors1, descriptors2;
	extractor.compute(img1, keypoints1, descriptors1);
	extractor.compute(img2, keypoints2, descriptors2);

	// matching descriptors
	BruteForceMatcher<L2<float> > matcher;
    vector<DMatch> matches;
    matcher.match(descriptors1, descriptors2, matches);

	// drawing the results
	namedWindow("matches", 1);
	Mat img_matches;
	drawMatches(img1, keypoints1, img2, keypoints2, matches, img_matches);
	imshow("matches", img_matches);
	waitKey(0);

	return 0;
}\n");
}

int main(int argc, char** argv)
{
	if(argc != 3)
	{
		help();
		return -1;
	}

	Mat img1 = imread(argv[1], CV_LOAD_IMAGE_GRAYSCALE);
	Mat img2 = imread(argv[2], CV_LOAD_IMAGE_GRAYSCALE);
	if(img1.empty() || img2.empty())
	{
		printf("Can't read one of the images\n");
		return -1;
	}

	// detecting keypoints
	SurfFeatureDetector detector(400);
	vector<KeyPoint> keypoints1, keypoints2;
	detector.detect(img1, keypoints1);
	detector.detect(img2, keypoints2);

	// computing descriptors
	SurfDescriptorExtractor extractor;
	Mat descriptors1, descriptors2;
	extractor.compute(img1, keypoints1, descriptors1);
	extractor.compute(img2, keypoints2, descriptors2);

	// matching descriptors
	BruteForceMatcher<L2<float> > matcher;
    vector<DMatch> matches;
    matcher.match(descriptors1, descriptors2, matches);

	// drawing the results
	namedWindow("matches", 1);
	Mat img_matches;
	drawMatches(img1, keypoints1, img2, keypoints2, matches, img_matches);
	imshow("matches", img_matches);
	waitKey(0);

	return 0;
}
tpb (1495)
You should check your posts afterwards to see if you screwed something up. Here's a proper repost of your code.
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#include <stdio.h>
#include <opencv2/core/core.hpp>
#include <opencv2/features2d/features2d.hpp>
#include <opencv2/highgui/highgui.hpp>

using namespace cv;

void help()
{
    printf("\nThis program demonstrates using features2d detector, "
           "descriptor extractor and simple matcher\n"
           "Using the SURF desriptor:\n\n"
           "Usage:\n matcher_simple <image1> <image2>\n");
}

int main(int argc, char** argv)
{
    if(argc != 3)
    {
        help();
        return -1;
    }

    Mat img1 = imread(argv[1], CV_LOAD_IMAGE_GRAYSCALE);
    Mat img2 = imread(argv[2], CV_LOAD_IMAGE_GRAYSCALE);
    if(img1.empty() || img2.empty())
    {
        printf("Can't read one of the images\n");
        return -1;
    }

    // detecting keypoints
    SurfFeatureDetector detector(400);
    vector<KeyPoint> keypoints1, keypoints2;
    detector.detect(img1, keypoints1);
    detector.detect(img2, keypoints2);

    // computing descriptors
    SurfDescriptorExtractor extractor;
    Mat descriptors1, descriptors2;
    extractor.compute(img1, keypoints1, descriptors1);
    extractor.compute(img2, keypoints2, descriptors2);

    // matching descriptors
    BruteForceMatcher<L2<float> > matcher;
    vector<DMatch> matches;
    matcher.match(descriptors1, descriptors2, matches);

    // drawing the results
    namedWindow("matches", 1);
    Mat img_matches;
    drawMatches(img1, keypoints1, img2, keypoints2, matches, img_matches);
    imshow("matches", img_matches);
    waitKey(0);

    return 0;
}


Your question almost sounds like you don't know how to use the command line. Are you using an IDE? The instructions are telling you to run it from the command line, type the name of the program followed by the two file names and then hit enter.
Last edited on
jonnin (11429)
in windows I know for sure that a single arg can be dropped onto the program via drag and drop mechanics. I *think* you can simply use the mouse to highlight 2 files and drop both on the executable for a 2 arg program, but I am not 100% sure. You can try it to see if it works. This saves firing up the command line and makes actually USING a program you wrote easier, but I prefer to run from the prompt when debugging it so I can see messages when it chokes.

you can also set up a batch file to run it if you need to run it a bunch of times with the same inputs while testing.
Last edited on
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