How to crop image using contour not in Rectangle shape in OpenCV Java? -


i learn opencv 2 weeks ago , planning use on spring project java wrapper. want crop image based on shape , embed pure white background. tried several method internet (hsv average comparison, cropping using standard roi, masking, etc) , decided use these steps got forum :

  1. convert img grayscale
  2. threshold binary image
  3. use findcontours actual outline
  4. crop image based on contour result

i hope can me on matter or maybe guide using method, thank much.

example image source : image source

current extracted result using rectangle roi (the code not contain on below section because i'm trying change method) : cropped image

here tried (using opencv 3.2.0) : 

system.loadlibrary(core.native_library_name);  // reading image file , storing in matrix object string file ="c:/examples/opencv/smartphone.jpg"; mat src = imgcodecs.imread(file);   mat srcclone = new mat(); // clone won't affect original image imgproc.cvtcolor(src, srcclone, imgproc.color_bgr2gray); // convert color gray  double threshold =  imgproc.threshold(srcclone, srcclone, 50, 255, imgproc.thresh_binary);  // add gaussian blur effect reduce noises imgproc.gaussianblur(srcclone, srcclone, new size(5,5), 0);  //find edges using canny mat edges = new mat(); imgproc.canny(srcclone, edges, 100, 200);  //find contour based on canny result list<matofpoint> contours = new arraylist<matofpoint>(); final mat hierarchy = new mat(); imgproc.findcontours(edges, contours, hierarchy, imgproc.retr_external , imgproc.chain_approx_simple);  //don't know next step if not using rectangle roi ...


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