java - Detecting rectangles using OpenCV -

so i'm new opencv , past 2-3 days i've searched lot how use opencv in java , android studio perform perspective correction , detect biggest rectangle in bitmaps , based on searches have done work result bitmap not correct.i'm sure i've done lot of things wrong great if me.

thanks in advance help.

public void onpicturetaken(byte[] data, camera camera) {      bitmap myimage = bitmapfactory.decodebytearray(data, 0, data.length);     mat matimage = new mat(myimage.getheight(),myimage.getwidth(), cvtype.cv_8uc3);     bitmap mybitmap32 = myimage.copy(bitmap.config.argb_8888, true);     utils.bitmaptomat(mybitmap32, matimage);      correctperspective(matimage); } 

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public static void correctperspective(mat imgsource) {      // convert image black , white (8 bit)     imgproc.canny(imgsource.clone(), imgsource, 50, 50);      // apply gaussian blur smoothen lines of dots     imgproc.gaussianblur(imgsource, imgsource, new org.opencv.core.size(5, 5), 5);      // find contours     list<matofpoint> contours = new arraylist<matofpoint>();     imgproc.findcontours(imgsource, contours, new mat(), imgproc.retr_list, imgproc.chain_approx_simple);      double maxarea = -1;     matofpoint temp_contour = contours.get(0);      // index 0 starting     // point     matofpoint2f approxcurve = new matofpoint2f();      (int idx = 0; idx < contours.size(); idx++) {         temp_contour = contours.get(idx);         double contourarea = imgproc.contourarea(temp_contour);         // compare contour previous largest contour found         if (contourarea > maxarea) {             // check if contour square             matofpoint2f new_mat = new matofpoint2f(temp_contour.toarray());             int contoursize = (int) temp_contour.total();             matofpoint2f approxcurve_temp = new matofpoint2f();             imgproc.approxpolydp(new_mat, approxcurve_temp, contoursize * 0.05, true);             if (approxcurve_temp.total() == 4) {                 maxarea = contourarea;                 approxcurve = approxcurve_temp;             }         }     }      imgproc.cvtcolor(imgsource, imgsource, imgproc.color_bayerbg2rgb);      double[] temp_double;     temp_double = approxcurve.get(0, 0);     point p1 = new point(temp_double[0], temp_double[1]);      temp_double = approxcurve.get(1, 0);     point p2 = new point(temp_double[0], temp_double[1]);      temp_double = approxcurve.get(2, 0);     point p3 = new point(temp_double[0], temp_double[1]);      temp_double = approxcurve.get(3, 0);     point p4 = new point(temp_double[0], temp_double[1]);      list<point> source = new arraylist<point>();     source.add(p1);     source.add(p2);     source.add(p3);     source.add(p4);     mat startm = converters.vector_point2f_to_mat(source);      mat result = warp(imgsource, startm);      //saving bitmap     bitmap resultbitmap = bitmap.createbitmap(result.cols(),  result.rows(),bitmap.config.argb_8888);;     mat tmp = new mat (result.cols(), result.rows(), cvtype.cv_8u, new scalar(4));     imgproc.cvtcolor(result, tmp, imgproc.color_rgb2bgra);     utils.mattobitmap(tmp, resultbitmap);  } 

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public static mat warp(mat inputmat, mat startm) {      int resultwidth = 1200;     int resultheight = 680;      point ocvpout4 = new point(0, 0);     point ocvpout1 = new point(0, resultheight);     point ocvpout2 = new point(resultwidth, resultheight);     point ocvpout3 = new point(resultwidth, 0);      if (inputmat.height() > inputmat.width())     {         ocvpout3 = new point(0, 0);         ocvpout4 = new point(0, resultheight);         ocvpout1 = new point(resultwidth, resultheight);         ocvpout2 = new point(resultwidth, 0);     }      mat outputmat = new mat(resultwidth, resultheight, cvtype.cv_8uc4);      list<point> dest = new arraylist<point>();     dest.add(ocvpout1);     dest.add(ocvpout2);     dest.add(ocvpout3);     dest.add(ocvpout4);      mat endm = converters.vector_point2f_to_mat(dest);      mat perspectivetransform = imgproc.getperspectivetransform(startm, endm);      imgproc.warpperspective(inputmat, outputmat, perspectivetransform, new size(resultwidth, resultheight), imgproc.inter_cubic);      return outputmat; }