Develop Reference

OpenCV, Android: remove background lines draw only object

I'm trying to only detect, draw & fill/color the battery black while filling everything else white, but I'm getting other lines from the background as well. How do i go about fixing this?
Note: I cannot change the background of the input image.
Below is the output of an image i got after drawing the contours of everything that's black using the following code:
if(getIntent().hasExtra("byteArray")) {
b = BitmapFactory.decodeByteArray(getIntent().getByteArrayExtra("byteArray"),0,getIntent().getByteArrayExtra("byteArray").length);
contours = new ArrayList<>();
srcMat= new Mat();
gray = new Mat();
matHSV = new Mat();
Utils.bitmapToMat(b,srcMat);
Imgproc.cvtColor(srcMat, gray, Imgproc.COLOR_RGBA2GRAY);
Imgproc.Canny(gray, gray, 20, 20*3, 3, true);
Mat hierarchy = new Mat();
Imgproc.findContours(gray,contours,hierarchy,Imgproc.RETR_EXTERNAL, Imgproc.CHAIN_APPROX_SIMPLE);
for (int contourIdx = 0; contourIdx < contours.size(); contourIdx++) {
Imgproc.drawContours(srcMat, contours, contourIdx, new Scalar(0, 0, 255), -1);
}
mask = new Mat(new Size(srcMat.cols(), srcMat.rows() ), CvType.CV_8UC1);
mask.setTo(new Scalar(255));
black = new Scalar(0,0,0);
Imgproc.drawContours(mask, contours, -1, black, 10);
for (MatOfPoint contour: contours) {
Imgproc.fillPoly(mask, Arrays.asList(contour), black);
}
Mat masked = new Mat();
srcMat.copyTo(masked, mask);
Utils.matToBitmap(mask, b);
imgR.setImageBitmap(b);
}
Output:
Input:

Android, OpenCV: Detect color & Draw Contours

How do i draw contours on only black object, and filling everything else in the background white?
My code currently is able to draw contours on an image:
Bitmap b = BitmapFactory.decodeByteArray(getIntent().getByteArrayExtra("byteArray"),0,getIntent().getByteArrayExtra("byteArray").length);
srcMat= new Mat();
Utils.bitmapToMat(b,srcMat);
Mat gray = new Mat();
Imgproc.cvtColor(srcMat, gray, Imgproc.COLOR_RGBA2GRAY);
Imgproc.Canny(gray, gray, 20, 20*3, 3, true);
List<MatOfPoint> contours = new ArrayList<>();
Mat hierarchy = new Mat();
Imgproc.findContours(gray,contours,hierarchy,Imgproc.RETR_EXTERNAL, Imgproc.CHAIN_APPROX_SIMPLE);
for (int contourIdx = 0; contourIdx < contours.size(); contourIdx++) {
Imgproc.drawContours(srcMat, contours, contourIdx, new Scalar(0, 0, 255), -1);
}
Utils.matToBitmap(gray, b);
imgR.setImageBitmap(b);

You should create and apply mask, like in answer to this question. You can do this, for example, by this way (insert code below after Your Imgproc.findContours() call instead of for (int contourIdx = ...:
// create Mat for mask
Mat mask = new Mat(new Size(srcMat.cols(), srcMat.rows() ), CvType.CV_8UC1);
mask.setTo(new Scalar(0.0));
// create Scalar for color of mask objects
Scalar white = new Scalar(255, 255, 255);
// draw contours border and fill them
Imgproc.drawContours(mask, contours, -1, white, 10);
for (MatOfPoint contour: contours) {
Imgproc.fillPoly(mask, Arrays.asList(contour), white);
}
// create mat foe masked image
Mat masked = new Mat();
// apply mask to srcMat and set result to masked
srcMat.copyTo(masked, mask);
Then change gray mat in Utils.matToBitmap() call to masked:
Utils.matToBitmap(masked, b);
imgR.setImageBitmap(b);

finding edges and drawing contours with OpenCV on Android

I want to find the edges of image that I have used in basic image processing methods(blurring,sharpening..etc).I don't get any errors, but it isn't working.The program stops when it comes to on the Imgproc.Canny or Imgproc.findContours method with Debugging.
As a last resort, I wrote native code to find the edges, but I could not run it.
That is my code to call finding contours and execute it:
{
Mat rawImageMatGray = new Mat();
Imgproc.cvtColor(this.rawImageMat, rawImageMatGray, Imgproc.COLOR_BGR2GRAY);
Imgproc.adaptiveThreshold(rawImageMatGray, rawImageMatGray, 255, Imgproc.ADAPTIVE_THRESH_MEAN_C, Imgproc.THRESH_BINARY, 55, 15);
Bitmap segmentImage = Bitmap.createBitmap(rawImageMatGray.cols(), rawImageMatGray.rows(), Bitmap.Config.ARGB_8888);
Utils.matToBitmap(rawImageMatGray, segmentImage);
segmentImage = Contours(segmentImage);
return segmentImage;
}
private Bitmap Contours(Bitmap cannyImage) {
Mat cannyImageMat = new Mat();
Mat cannyImageMat2 = new Mat();
Utils.bitmapToMat(cannyImage, cannyImageMat);
Mat cannyEdges = new Mat();
Mat hierarchy = new Mat();
List<MatOfPoint> contourList = new ArrayList<MatOfPoint>();
//A list to store all the contours
//Converting the image to grayscale
//Imgproc.cvtColor(originalMat,grayMat,Imgproc.COLOR_BGR2GRAY);
Imgproc.Canny(cannyImageMat, cannyEdges, 80, 100);
//finding contours
Imgproc.findContours(cannyEdges, contourList, hierarchy, Imgproc.RETR_LIST, Imgproc.CHAIN_APPROX_SIMPLE);
//Drawing contours on a new image
Mat contours = new Mat();
contours.create(cannyEdges.rows(), cannyEdges.cols(), CvType.CV_8UC3);
Random r = new Random();
for (int i = 0; i < contourList.size(); i++) {
Imgproc.drawContours(contours, contourList, i, new Scalar(r.nextInt(255), r.nextInt(255), r.nextInt(255)), -1);
}
//Converting Mat back to Bitmap
Bitmap cannyImage2 = Bitmap.createBitmap(cannyImageMat2.cols(),cannyImageMat2.rows(), Bitmap.Config.ARGB_8888);
Utils.matToBitmap(cannyImageMat2, cannyImage);
Utils.matToBitmap(contours, cannyImage2);
return cannyImage2;
}

Opencv contour rectangle on musical notations

I am trying to draw the contour of every element in a picture with separated musical notations.
This is the code that I am running in android/java:
public static Bitmap findNotationContours(Bitmap inputImage) {
Mat inputImageMat = new Mat();
Utils.bitmapToMat(inputImage, inputImageMat);
Imgproc.cvtColor(inputImageMat, inputImageMat, Imgproc.COLOR_BGR2GRAY);
Imgproc.GaussianBlur(inputImageMat, inputImageMat, new Size(5, 5), 0);
Imgproc.adaptiveThreshold(inputImageMat, inputImageMat, 255, 1, 1, 11, 2);
List<MatOfPoint> contours = new ArrayList<>();
Mat hierarchy = new Mat();
Imgproc.findContours(inputImageMat, contours, hierarchy, Imgproc.RETR_LIST, Imgproc.CHAIN_APPROX_SIMPLE);
int contourColor = android.R.color.holo_red_dark;
Scalar contourScalar = new Scalar(Color.red(contourColor), Color.green(contourColor), Color.blue(contourColor));
for (int i = 0; i < contours.size(); i++) {
Rect rect = Imgproc.boundingRect(contours.get(i));
Imgproc.rectangle(inputImageMat,
new Point(rect.x, rect.y),
new Point(rect.x + rect.width, rect.y + rect.height),
contourScalar, 3);
}
Utils.matToBitmap(inputImageMat, inputImage);
return inputImage;
}
The result I am getting is:
If you zoom in enough you can see that the contour for the notations are there, but I need to keep the original picture with just a rectangle contour around each of them, so I can save those as a pattern.
Can you please tell me what I am doing wrong?

With the crucial information from #Dan Mašek the problem was fixed, I will add the revised code that needs no explanation, just that we keep a Mat with the initial 3-channel image which we use to draw the contour rectangles on.
public static Bitmap findNotationContours(Bitmap inputImage) {
Mat inputImageMat = new Mat();
Mat resultImageMat = new Mat();
Utils.bitmapToMat(inputImage, inputImageMat);
Utils.bitmapToMat(inputImage, resultImageMat);
Imgproc.cvtColor(inputImageMat, inputImageMat, Imgproc.COLOR_BGR2GRAY);
Imgproc.GaussianBlur(inputImageMat, inputImageMat, new Size(5, 5), 0);
Imgproc.adaptiveThreshold(inputImageMat, inputImageMat, 255, 1, 1, 11, 2);
List<MatOfPoint> contours = new ArrayList<>();
Mat hierarchy = new Mat();
Imgproc.findContours(inputImageMat, contours, hierarchy, Imgproc.RETR_LIST, Imgproc.CHAIN_APPROX_SIMPLE);
Scalar contourScalar = new Scalar(255,0,0);
for (int i = 0; i < contours.size(); i++) {
Rect rect = Imgproc.boundingRect(contours.get(i));
Imgproc.rectangle(resultImageMat,
new Point(rect.x, rect.y),
new Point(rect.x + rect.width, rect.y + rect.height),
contourScalar, 3);
Log.i("contour", "contour" + i + " x:" + rect.x + " y:" + rect.y);
}
Utils.matToBitmap(resultImageMat, inputImage);
return inputImage;
}
final result

OpenCV, Java compareHist() returns same value

In openCV I want to compare two histograms. First I transform Bitmap to Mat:
Bitmap puzzleBmp = BitmapFactory.decodeFile(photoPath, options)
mat = new Mat(puzzleBmp.getHeight(), puzzleBmp.getWidth(), CvType.CV_8U, new Scalar(4));
Utils.bitmapToMat(puzzleBmp, mat);
Next I want to create histogram of this image:
Mat mRgba = new Mat();
Imgproc.cvtColor(mat, mRgba, Imgproc.COLOR_RGBA2RGB);
Imgproc.GaussianBlur(mRgba, mRgba, new Size(5, 5), 0, Imgproc.BORDER_DEFAULT);
Mat mHSV = new Mat();
Imgproc.cvtColor(mRgba, mHSV, Imgproc.COLOR_RGB2HSV_FULL);
Mat hist = new Mat();
int h_bins = 30;
int s_bins = 32;
MatOfInt mHistSize = new MatOfInt (h_bins, s_bins);
MatOfFloat mRanges = new MatOfFloat(0, 179, 0, 255);
MatOfInt mChannels = new MatOfInt(0, 1);
List<Mat> lHSV = Arrays.asList(mHSV);
Mat mask2 = new Mat();
mask2 = Mat.zeros( mRgba.rows() + 2, mRgba.cols() + 2, CvType.CV_8UC1 );
Range rowRange = new Range( 1, mask2.rows() - 1 );
Range colRange = new Range( 1, mask2.cols() - 1 );
Mat mask = new Mat();
mask = mask2.submat(rowRange, colRange);
boolean accumulate = false;
Imgproc.calcHist(lHSV, mChannels, mask, hist, mHistSize, mRanges, accumulate);
Core.normalize(hist, hist, 0, 255, Core.NORM_MINMAX, -1, new Mat());
From this part I get hist. But when I make these transformations with two different images i always get from method Imgproc.compareHist() same values, which means they are the same pictures.