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how to extract an object from the camera preview android opencv

I am trying to scan a MTG card using OpenCV on android. I have it to where I can detect the edges of the card and even draw an outline around it but am confused on how to extract just the card from the background and then exit from the camera preview. Here is my code so far:
public Mat onCameraFrame(CameraBridgeViewBase.CvCameraViewFrame inputFrame) {
Mat result = new Mat();
Mat mask = new Mat();
List<MatOfPoint> contours = new ArrayList<>();
Mat hierarchy = new Mat();
mRgba = inputFrame.rgba();
Imgproc.Canny(mRgba, result, 40, 120);
Imgproc.GaussianBlur(result, result, new Size(9,9), 2, 2);
Imgproc.findContours(result, contours, hierarchy, Imgproc.RETR_EXTERNAL, Imgproc.CHAIN_APPROX_SIMPLE, new Point(0,0));
Imgproc.drawContours(mask, contours, -1, new Scalar(0, 255, 0), 1);
hierarchy.release();
for ( int contourIdx=0; contourIdx < contours.size(); contourIdx++ )
{
// Minimum size allowed for consideration
MatOfPoint2f approxCurve = new MatOfPoint2f();
MatOfPoint2f contour2f = new MatOfPoint2f( contours.get(contourIdx).toArray() );
//Processing on mMOP2f1 which is in type MatOfPoint2f
double approxDistance = Imgproc.arcLength(contour2f, true)*0.02;
Imgproc.approxPolyDP(contour2f, approxCurve, approxDistance, true);
//Convert back to MatOfPoint
MatOfPoint points = new MatOfPoint( approxCurve.toArray() );
// Get bounding rect of contour
Rect rect = Imgproc.boundingRect(points);
Imgproc.rectangle(mRgba, new Point(rect.x, rect.y), new Point(rect.x + rect.width, rect.y + rect.height), new Scalar(255, 0, 0, 255), 3);
}
Bitmap card = Bitmap.createBitmap(result.cols(), result.rows(), Bitmap.Config.ARGB_8888);
Utils.matToBitmap(result, card);
return mRgba;
}
}
Here is an example of what it looks like when run the code. As you can see the card is outlined by a red rectangle now but how do I extract just whats in the rectangle, save it to a mat or bitmap and then exit the camera?
screenshot of outlined card

I didn't test it, but can't you just use...
return new Mat(mRgba, rect);

Segmentation number from water meter

i have a problem with character segmentation from water meter,
i have a image water meter
Then i have threshold this image after threshold
And i have get a register meter after segmentation
My problem is to get each character from register meter..
Here my code:
System.out.println("Character Segmentation the image at " + path + "... ");
// get the jpeg image from the internal resource folder
Mat image = MatImageFromPath;
// convert the image in gray scale
Imgproc.cvtColor(image, image, Imgproc.COLOR_BGR2GRAY);
// thresholding the image to make a binary image
Imgproc.threshold(image, image, 100, 255, Imgproc.THRESH_BINARY_INV);
// finding the contours
ArrayList<MatOfPoint> contours = new ArrayList<MatOfPoint>();
Mat hierarchy = new Mat();
Imgproc.findContours(image, contours, hierarchy, Imgproc.RETR_TREE, Imgproc.CHAIN_APPROX_SIMPLE);
Imgproc.drawContours(image, contours, 3, new Scalar(0, 255, 0),3);
// finding best bounding rectangle for a contour whose distance is closer to the image center that other ones
Rect rect = new Rect();
ArrayList<Rect> contourRects = new ArrayList<Rect>();
Point p1 = new Point(rect.x,rect.y);
Point p2 = new Point((rect.x+rect.width),(rect.y+rect.height));
int i=0;
for (MatOfPoint contour : contours) {
rect = Imgproc.boundingRect(contour);
contourRects.add(rect);
contour2f = new MatOfPoint2f( contours.get(i).toArray() );
i++;
}
Collections.sort(contourRects, new Comparator<Rect>(){
#Override
public int compare(Rect o1, Rect o2){
return o1.x-o2.x;
}
});
for (int j = 0; j <= contourRects.size()-1; j++) {
if ((contourRects.get(j).width >= 50 && contourRects.get(j).width <= 120) &&
(contourRects.get(j).height >= 150 && contourRects.get(j).height <= 210)) {
System.out.println(contourRects.get(j).width);
Mat result = image.submat(contourRects.get(j));
Imgcodecs.imwrite("BoundingBox/"+(j+1)+".png", result);
// write the new image on disk
path = "BoundingBox/"+(j+1)+".png";
} else {
continue;
}
}
Imgcodecs.imwrite("BoundingBox/draw.png", image);
label2.setIcon(ImageFromPath(path));
All images at : images
can anyone help my problem? Thanks in advance

how to find largest contour in java opencv

I have used find contours and boundingrect and display it at my project. then I want to find the largest contours and display it. Is this possible? I am newbie to OpenCV java lang.
heres my code so far:
#Override
public void onCameraViewStarted(int width, int height) {
mRgba = new Mat(height, width, CvType.CV_8UC4);
mHsv = new Mat(height,width,CvType.CV_8UC3);
hierarchy = new Mat();
mHsvMask = new Mat();
mDilated = new Mat();
mEroded = new Mat();
}
#Override
public void onCameraViewStopped() {
mRgba.release();
mHsv.release();
mHsvMask.release();
mDilated.release();
hierarchy.release();
}
#Override
public Mat onCameraFrame(CameraBridgeViewBase.CvCameraViewFrame inputFrame) {
mRgba =inputFrame.rgba();
contours = new ArrayList<MatOfPoint>();
hierarchy =new Mat();
mHsv = new Mat();
mHsvMask =new Mat();
Imgproc.cvtColor(mRgba, mHsv, Imgproc.COLOR_RGB2HSV);
Scalar lowerThreshold = new Scalar ( 0, 0, 0 ); // Blue color – lower hsv values
Scalar upperThreshold = new Scalar ( 179, 255, 10 ); // Blue color – higher hsv values
Core.inRange ( mHsv, lowerThreshold , upperThreshold, mHsvMask );
//just some filter
//Imgproc.dilate ( mHsvMask, mDilated, new Mat() );
//Imgproc.erode(mDilated,mEroded,new Mat());
Imgproc.findContours(mHsvMask, contours, hierarchy, Imgproc.RETR_TREE, Imgproc.CHAIN_APPROX_SIMPLE);
for ( int contourIdx=0; contourIdx < contours.size(); contourIdx++ )
{
//Minimun size allowed for consideration
MatOfPoint2f approxCurve = new MatOfPoint2f();
MatOfPoint2f contour2f = new MatOfPoint2f(contours.get(contourIdx).toArray());
//Processing on mMOP2f1 which is in type MatOfPoint2f
double approxDistance = Imgproc.arcLength(contour2f,true)*0.02;
Imgproc.approxPolyDP(contour2f,approxCurve,approxDistance,true);
//convert to MatofPoint
MatOfPoint point = new MatOfPoint(approxCurve.toArray());
//get boundingrect from contour
Rect rect = Imgproc.boundingRect(point);
Imgproc.rectangle(mRgba,new Point(rect.x, rect.y), new Point(rect.x + rect.width, rect.y + rect.height), new Scalar(255, 0, 0, 255),3);
//bisa Imgproc.rectangle(mRgba, rect.tl(), rect.br(), new Scalar(255, 0, 0),1, 8,0);
//show contour kontur
if(Imgproc.contourArea(contours.get(contourIdx))>100) {
Imgproc.drawContours(mRgba, contours, contourIdx, new Scalar(0,255,0), 5);
}
}
return mRgba;
Hopefully, someone has some experience in this. Thanks..

With function Imgproc.contourArea you can just simply find the areas of all of your contours and the contour with the largest area would simply be the largest one.
Code to draw the largest contour would be like this:
double maxVal = 0;
int maxValIdx = 0;
for (int contourIdx = 0; contourIdx < contours.size(); contourIdx++)
{
double contourArea = Imgproc.contourArea(contours.get(contourIdx));
if (maxVal < contourArea)
{
maxVal = contourArea;
maxValIdx = contourIdx;
}
}
Imgproc.drawContours(mRgba, contours, maxValIdx, new Scalar(0,255,0), 5);

OpenCV drawContours in Java

I'm trying to draw contours around object in image but i get error
OpenCV Error: Unsupported format or combination of formats ([Start]FindContours supports only CV_8UC1 images when mode != CV_RETR_FLOODFILL otherwise supports CV_32SC1 images only) in cvStartFindContours, file C:\builds\master_PackSlaveAddon-win64-vc12-static\opencv\modules\imgproc\src\contours.cpp, line 198
I tried to convert image but error is still there how to use DrawContour?
Mat imageInMat = Imgcodecs.imread("C:/Users/ja/workspace/imgtomath/bin/imgtomath/lena.png");
if(imageInMat.empty()== true)
{System.out.println("Error no image found!!");}
imageInMat.convertTo(imageInMat, CvType.CV_32SC1);
List<MatOfPoint> contours = new ArrayList<MatOfPoint>();
Mat hierarchy = new Mat();
Imgproc.findContours(imageInMat, contours, hierarchy, Imgproc.RETR_FLOODFILL, Imgproc.CHAIN_APPROX_SIMPLE);
Imgproc.drawContours(imageInMat, contours, -1, new Scalar(255,0,0));

It should work properly:
Mat image = Imgcodecs.imread("C:/Users/ja/workspace/imgtomath/bin/imgtomath/lena.png");
if(image.empty() == true) {
System.out.println("Error: no image found!");
}
List<MatOfPoint> contours = new ArrayList<MatOfPoint>();
Mat image32S = new Mat();
image.convertTo(image32S, CvType.CV_32SC1);
Imgproc.findContours(image32S, contours, new Mat(), Imgproc.RETR_FLOODFILL, Imgproc.CHAIN_APPROX_SIMPLE);
// Draw all the contours such that they are filled in.
Mat contourImg = new Mat(image32S.size(), image32S.type());
for (int i = 0; i < contours.size(); i++) {
Imgproc.drawContours(contourImg, contours, i, new Scalar(255, 255, 255), -1);
}
Highgui.imwrite("debug_image.jpg", contourImg); // DEBUG

creating HSV histogram using RGB image

Is there a way in Java or OpenCv ; preferably Java, that i can have an HSV histogram give RGB image.
I tried exploring JAI but it creates histogram for RGB image.
Thanks
Harshit

firs use cv::cvtColor to convert RGB to HSV
then use cv::calcHist to compute the histogram

Here is the pseudocode for a simple RGB to HSV converter. It will give a H of UNDEFINED if the color is a shade of gray, otherwise H is between 0 and 6.
x = min(R, G, B);
V = max(R, G, B);
if (V == x) {
H = UNDEFINED
S = 0
}
else {
if( R == x ) {
f = G - B;
i = 3;
} else if( G == x ) {
f = B - R;
i = 5;
} else {
f = R - G;
i = 1;
}
H = i - f /(V - x);
S = (V - x)/V;
}
Now you can either convert all your pixels and bin them to construct your HSV histogram, or you can convert each bin of your RGB histogram to an HSV bin.

You can use the "JavaCV" library to access OpenCV functions directly from Java:
http://code.google.com/p/javacv/
Then you can use my code for RGB to HSV that is better than OpenCV's cvConvert function:
http://www.shervinemami.co.cc/colorConversion.html
Cheers,
Shervin Emami.

Here is a code to do this:
// Assume SourceImage is a Bitmap ARGB_8888
BitmapFactory.Options options = new BitmapFactory.Options();
options.inPreferredConfig = Bitmap.Config.ARGB_8888;
Bitmap refImage = BitmapFactory.decodeFile(mBaseDir + "some_reference.jpg", options);
Mat hsvRef = new Mat();
Mat hsvSource = new Mat();
Mat srcRef = new Mat(refImage.getHeight(), refImage.getWidth(), CvType.CV_8U, new Scalar(4));
Utils.bitmapToMat(refImage, srcRef);
Mat srcSource = new Mat(SourceImage.getHeight(), SourceImage.getWidth(), CvType.CV_8U, new Scalar(4));
Utils.bitmapToMat(SourceImage, srcSource);
/// Convert to HSV
Imgproc.cvtColor(srcRef, hsvRef, Imgproc.COLOR_BGR2HSV);
Imgproc.cvtColor(srcSource, hsvSource, Imgproc.COLOR_BGR2HSV);
/// Using 50 bins for hue and 60 for saturation
int hBins = 50;
int sBins = 60;
MatOfInt histSize = new MatOfInt( hBins, sBins);
// hue varies from 0 to 179, saturation from 0 to 255
MatOfFloat ranges = new MatOfFloat( 0f,180f,0f,256f );
// we compute the histogram from the 0-th and 1-st channels
MatOfInt channels = new MatOfInt(0, 1);
Mat histRef = new Mat();
Mat histSource = new Mat();
ArrayList<Mat> histImages=new ArrayList<Mat>();
histImages.add(hsvRef);
Imgproc.calcHist(histImages,
channels,
new Mat(),
histRef,
histSize,
ranges,
false);
Core.normalize(histRef,
histRef,
0,
1,
Core.NORM_MINMAX,
-1,
new Mat());
histImages=new ArrayList<Mat>();
histImages.add(hsvSource);
Imgproc.calcHist(histImages,
channels,
new Mat(),
histSource,
histSize,
ranges,
false);
Core.normalize(histSource,
histSource,
0,
1,
Core.NORM_MINMAX,
-1,
new Mat());
double resp1 = Imgproc.compareHist(histRef, histSource, 0);
double resp2 = Imgproc.compareHist(histRef, histSource, 1);
double resp3 = Imgproc.compareHist(histRef, histSource, 2);
double resp4 = Imgproc.compareHist(histRef, histSource, 3);

First, you have to convert image to HSV using cv::cvtColor to convert RGB image into HSV image and then, you can use cv::calcHist to compute the HSV histogram.