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I'm developing an android app in which I have to detect circle on existing image browse from gallery or capture from the camera. The browsed / captured image will be shown onto the ImageView. By the way, I'm using OpenCVAndroid Library and I compiled it properly.

Any help for my android app, I had read C, C++, or etc in detecting circles but I can't understand it 'coz its different languages for android.

Thanks.

Update

Okay ... This is how I used.

            if (requestCode == 1) { //Take Photo from Android Camera..



            File f = new File(Environment.getExternalStorageDirectory().toString());

            for (File temp : f.listFiles()) {

                if (temp.getName().equals("temp.jpg")) {

                    f = temp;

                    break;

                }

            }

            try {

                Bitmap bitmap;

                BitmapFactory.Options bitmapOptions = new BitmapFactory.Options();



                bitmap = BitmapFactory.decodeFile(f.getAbsolutePath(),

                        bitmapOptions);



                // bitmap = Bitmap.createScaledBitmap(bitmap, 70, 70, true);







                String path = android.os.Environment

                        .getExternalStorageDirectory()

                        + File.separator

                        + "Phoenix" + File.separator + "default";

                f.delete();

                OutputStream outFile = null;

                File file = new File(path, String.valueOf(System.currentTimeMillis()) + ".jpg");

                try {

                    outFile = new FileOutputStream(file);

                    bitmap.compress(Bitmap.CompressFormat.JPEG, 85, outFile);

                    outFile.flush();

                    outFile.close();

                } catch (FileNotFoundException e) {

                    e.printStackTrace();

                } catch (IOException e) {

                    e.printStackTrace();

                } catch (Exception e) {

                    e.printStackTrace();

                }



                                    /* convert bitmap to mat */

                Mat mat = new Mat(bitmap.getWidth(), bitmap.getHeight(),

                        CvType.CV_8UC1);

                Mat grayMat = new Mat(bitmap.getWidth(), bitmap.getHeight(),

                        CvType.CV_8UC1);



                Utils.bitmapToMat(bitmap, mat);



                  /* convert to grayscale */

                int colorChannels = (mat.channels() == 3) ? Imgproc.COLOR_BGR2GRAY

                        : ((mat.channels() == 4) ? Imgproc.COLOR_BGRA2GRAY : 1);



                Imgproc.cvtColor(mat, grayMat, colorChannels);



                /* reduce the noise so we avoid false circle detection */

                Imgproc.GaussianBlur(grayMat, grayMat, new Size(9, 9), 2, 2);



                // accumulator value

                double dp = 1.2d;

                // minimum distance between the center coordinates of detected circles in pixels

                double minDist = 20;



               // min and max radii (set these values as you desire)

                int minRadius = 0, maxRadius = 0;



               // param1 = gradient value used to handle edge detection

              // param2 = Accumulator threshold value for the

              // cv2.CV_HOUGH_GRADIENT method.

              // The smaller the threshold is, the more circles will be

              // detected (including false circles).

              // The larger the threshold is, the more circles will

              // potentially be returned.

                double param1 = 70, param2 = 72;



              /* create a Mat object to store the circles detected */

                Mat circles = new Mat(bitmap.getWidth(),

                        bitmap.getHeight(), CvType.CV_8UC1);



              /* find the circle in the image */

                Imgproc.HoughCircles(grayMat, circles,

                        Imgproc.CV_HOUGH_GRADIENT, dp, minDist, param1,

                        param2, minRadius, maxRadius);



              /* get the number of circles detected */

                int numberOfCircles = (circles.rows() == 0) ? 0 : circles.cols();



              /* draw the circles found on the image */

                for (int i=0; i<numberOfCircles; i++) {





              /* get the circle details, circleCoordinates[0, 1, 2] = (x,y,r)

               * (x,y) are the coordinates of the circle's center*/

                                      double circleCoordinates = circles.get(0, 0);





                    int x = (int) circleCoordinates[0], y = (int) circleCoordinates[1];



                    Point center = new Point(x, y);



                    int radius = (int) circleCoordinates[2];



/* circle's outline */

                    Core.circle(mat, center, radius, new Scalar(0,

                            255, 0), 4);



/* circle's center outline */

                    Core.rectangle(mat, new Point(x - 5, y - 5),

                            new Point(x + 5, y + 5),

                            new Scalar(0, 128, 255), -1);

                }



              /* convert back to bitmap */

                Utils.matToBitmap(mat, bitmap);

                viewImage.setImageBitmap(bitmap);

            } catch (Exception e) {

                e.printStackTrace();

            }



        }

I run my app with the code above,My Android phone is crashing after I take photo from camera and I have this errors in logcat:

          02-10 06:54:15.773    8914-8914/com.example.cloud.circle E/AndroidRuntime﹕ FATAL EXCEPTION: main



java.lang.UnsatisfiedLinkError: n_Mat

        at org.opencv.core.Mat.n_Mat(Native Method)

        at org.opencv.core.Mat.<init>(Mat.java:477)

        at com.example.cloud.circle.Image.onActivityResult(Image.java:152)

        at android.app.Activity.dispatchActivityResult(Activity.java:3908)

        at android.app.ActivityThread.deliverResults(ActivityThread.java:2532)

        at android.app.ActivityThread.handleSendResult(ActivityThread.java:2578)

        at android.app.ActivityThread.access$2000(ActivityThread.java:117)

        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:965)

        at android.os.Handler.dispatchMessage(Handler.java:99)

        at android.os.Looper.loop(Looper.java:130)

        at android.app.ActivityThread.main(ActivityThread.java:3687)

        at java.lang.reflect.Method.invokeNative(Native Method)

        at java.lang.reflect.Method.invoke(Method.java:507)

        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:867)

        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:625)

        at dalvik.system.NativeStart.main(Native Method)

Please help me. Thanks.

A detailed explanation for circle detection can be found here and here (though not in Java).

I have included a sample code snippet for circle detection below garnered from the 2 links I provided above. The code is commented, so it can be easily understood. I assume that the image bitmap bitmap already has the image you want to analyze.

/* convert bitmap to mat */

Mat mat = new Mat(bitmap.getWidth(), bitmap.getHeight(),

        CvType.CV_8UC1);

Mat grayMat = new Mat(bitmap.getWidth(), bitmap.getHeight(),

        CvType.CV_8UC1);



Utils.bitmapToMat(bitmap, mat);



/* convert to grayscale */

int colorChannels = (mat.channels() == 3) ? Imgproc.COLOR_BGR2GRAY

        : ((mat.channels() == 4) ? Imgproc.COLOR_BGRA2GRAY : 1);



Imgproc.cvtColor(mat, grayMat, colorChannels);



/* reduce the noise so we avoid false circle detection */

Imgproc.GaussianBlur(grayMat, grayMat, new Size(9, 9), 2, 2);



// accumulator value

double dp = 1.2d;

// minimum distance between the center coordinates of detected circles in pixels

double minDist = 100;



// min and max radii (set these values as you desire)

int minRadius = 0, maxRadius = 0;



// param1 = gradient value used to handle edge detection

// param2 = Accumulator threshold value for the

// cv2.CV_HOUGH_GRADIENT method.

// The smaller the threshold is, the more circles will be

// detected (including false circles).

// The larger the threshold is, the more circles will

// potentially be returned.

double param1 = 70, param2 = 72;



/* create a Mat object to store the circles detected */

Mat circles = new Mat(bitmap.getWidth(),

        bitmap.getHeight(), CvType.CV_8UC1);



/* find the circle in the image */

Imgproc.HoughCircles(grayMat, circles,

        Imgproc.CV_HOUGH_GRADIENT, dp, minDist, param1,

        param2, minRadius, maxRadius);



/* get the number of circles detected */

int numberOfCircles = (circles.rows() == 0) ? 0 : circles.cols();



/* draw the circles found on the image */

for (int i=0; i<numberOfCircles; i++) {





/* get the circle details, circleCoordinates[0, 1, 2] = (x,y,r)

 * (x,y) are the coordinates of the circle's center

 */

    double circleCoordinates = circles.get(0, i);





    int x = (int) circleCoordinates[0], y = (int) circleCoordinates[1];



    Point center = new Point(x, y);



    int radius = (int) circleCoordinates[2];



    /* circle's outline */

    Core.circle(mat, center, radius, new Scalar(0,

            255, 0), 4);



    /* circle's center outline */

    Core.rectangle(mat, new Point(x - 5, y - 5),

            new Point(x + 5, y + 5),

            new Scalar(0, 128, 255), -1);

}



/* convert back to bitmap */

Utils.matToBitmap(mat, bitmap);

Update

In order to prevent the UnsatisfiedLinkError, before using OpenCV library's functions, ensure you load the library files, as I have done below:

if (!OpenCVLoader.initDebug()) {

    Log.e(TAG, "Cannot connect to OpenCV Manager");

}