Can you say what is wrong with this code. Opencv C++ for detecting number of stars.

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1.00/5 (1 vote)

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#include "opencv2/imgcodecs.hpp"
#include "opencv2/imgproc.hpp"
#include "opencv2/highgui.hpp"
#include "opencv2/opencv.hpp"


using namespace cv;
using namespace std;


int main(int argc, char** argv)

{



	// Read image

	Mat im = imread("image1.jpg", IMREAD_GRAYSCALE);



	// Setup SimpleBlobDetector parameters.

	SimpleBlobDetector::Params params;



	// Change thresholds

	params.minThreshold = 10;

	params.maxThreshold = 200;



	// Filter by Area.

	params.filterByArea = true;

	params.minArea = 1500;



	// Filter by Circularity

	params.filterByCircularity = true;

	params.minCircularity = 0.1;



	// Filter by Convexity

	params.filterByConvexity = true;

	params.minConvexity = 0.87;



	// Filter by Inertia

	params.filterByInertia = true;

	params.minInertiaRatio = 0.01;





	// Storage for blobs

	vector<KeyPoint> keypoints;



	// Set up detector with params

	Ptr<SimpleBlobDetector> detector = SimpleBlobDetector::create(params);



	// Detect blobs

	detector->detect(im, keypoints);


	float count_keypoints;

	count_keypoints = keypoints.size();

	cout << count_keypoints;
	cout << keypoints.size();

	waitKey(0);



}

What I have tried:

No matter what I change this no output will be given.

Posted 10-Oct-17 20:53pm

Member 13458139

Updated 10-Oct-17 21:28pm

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OriginalGriff · Answer 1 · 2017-10-10T21:06:00

Compiling does not mean your code is right! :laugh:
Think of the development process as writing an email: compiling successfully means that you wrote the email in the right language - English, rather than German for example - not that the email contained the message you wanted to send.

So now you enter the second stage of development (in reality it's the fourth or fifth, but you'll come to the earlier stages later): Testing and Debugging.

Start by looking at what it does do, and how that differs from what you wanted. This is important, because it give you information as to why it's doing it. For example, if a program is intended to let the user enter a number and it doubles it and prints the answer, then if the input / output was like this:

Input   Expected output    Actual output
  1            2                 1
  2            4                 4
  3            6                 9
  4            8                16

Then it's fairly obvious that the problem is with the bit which doubles it - it's not adding itself to itself, or multiplying it by 2, it's multiplying it by itself and returning the square of the input.
So with that, you can look at the code and it's obvious that it's somewhere here:

C#

int Double(int value)
   {
   return value * value;
   }

Once you have an idea what might be going wrong, start using the debugger to find out why. Put a breakpoint on your line:

C#

Mat im = imread("image1.jpg", IMREAD_GRAYSCALE);

and run your app. Think about what each line in the code should do before you execute it, and compare that to what it actually did when you use the "Step over" button to execute each line in turn. Did it do what you expect? If so, move on to the next line.
If not, why not? How does it differ?

We have no idea what it is supposed to output, and no way to run it anyway, so it going to be down to you to find out information about what is happening, and what it does that you didn't expect or does that you didn't.

This is a skill, and it's one which is well worth developing as it helps you in the real world as well as in development. And like all skills, it only improves by use!

Jochen Arndt · Answer 2 · 2017-10-10T21:28:00

This can't be really answered without having your image. I would also expect that you got some output like "0.00" or your application terminates with an error.

You should check if loading the image was successful because you will not get a result if that fails:

Mat im = imread("image1.jpg", IMREAD_GRAYSCALE);
if (!im.data)
{
    cout << "Could not open or find the image" << std::endl;
    return -1;
}

Because you pass a file name without path, you have to ensure that the current directory is set to the directory containing your image file. While not using a file name parameter, I suggest to provide the full path.

Note also that the return type of vector::size is size_type (an unsigned integral type). While you might assign it to a float it makes no sense at all and is prone to loss of precision with large sizes.

I suggest to enable all warnings (G++: -Wall, VS: /W4 in the project settings). That should show at least two warnings: One for assigning the vector::size() return value to a float and one for the missing return statement at the end of your main function (with restrictive compiler options these may be also shown as errors).

Can you say what is wrong with this code. Opencv C++ for detecting number of stars.

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