Extract area detected by color using OpenCV in Android

问题

The sample project named "color-blob-detection" that comes with the openCV SDK for android can be used to identify an area of a particular color. What I require is to extract that area and save it into the phone memory as a bitmap.

This is what I have understood so far:

There is a list of contours:

List<MatOfPoint> contours = new ArrayList<MatOfPoint>();

Contours are found using:

Imgproc.findContours(mDilatedMask, contours, mHierarchy, Imgproc.RETR_EXTERNAL, Imgproc.CHAIN_APPROX_SIMPLE);

This finds the max contour area:

double maxArea = 0;
        Iterator<MatOfPoint> each = contours.iterator();
        while (each.hasNext()) {
            MatOfPoint wrapper = each.next();
            double area = Imgproc.contourArea(wrapper);
            if (area > maxArea)
                maxArea = area;
        }

I would like to know how this largest area can be saved into the sdcard as a bitmap. Any help is greatly appreciated!

//////EDIT

This is used to draw Contours. I am not sure whether this is the correct way:

 Imgproc.cvtColor(mDilatedMask, mDilatedMask, Imgproc.COLOR_GRAY2BGR);
            Imgproc.drawContours(mDilatedMask, contours, -1, new Scalar(0, 255, 0), 1);
Toast.LENGTH_LONG).show();
            Bitmap bmpOut = Bitmap.createBitmap(mDilatedMask.cols(), mDilatedMask.rows(), Bitmap.Config.ARGB_8888);

            Utils.matToBitmap(mDilatedMask, bmpOut);

            try {
                bmpOut.compress(CompressFormat.JPEG, 100, new FileOutputStream("/sdcard/mediaAppPhotos/bigrect.jpg"));
            } catch (FileNotFoundException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

回答1:

Here is the code that implemented in C++ to find largest contour and draw it as an image, I am not familiar with OpenCV JAVA but you can have something like similar in JAVA.

#include <iostream>
#include "opencv2\highgui\highgui.hpp"
#include "opencv\cv.h"

using namespace cv;
using namespace std;
int main()
{
 int largest_area=0;
 int largest_contour_index=0;
 Rect bounding_rect;

 Mat src = imread("src.jpg"); //Load source image
 Mat thr(src.rows,src.cols,CV_8UC1);
 Mat dst(src.rows,src.cols,CV_8UC1,Scalar::all(0));
 cvtColor(src,thr,CV_BGR2GRAY); //Convert to gray
 threshold(thr, thr,25, 255,THRESH_BINARY); //Threshold the gray

    vector<vector<Point>> contours; // Vector for storing contour
    vector<Vec4i> hierarchy;

    findContours( thr, contours, hierarchy,CV_RETR_CCOMP, CV_CHAIN_APPROX_SIMPLE ); // Find the contours in the image

     for( int i = 0; i< contours.size(); i++ ) // iterate through each contour.
      {
       double a=contourArea( contours[i],false);  //  Find the area of contour
       if(a>largest_area){
       largest_area=a;
       largest_contour_index=i;                //Store the index of largest contour
       bounding_rect=boundingRect(contours[i]); // Find the bounding rectangle for biggest contour
       }

      }

 Scalar color( 255,255,255);
 drawContours( dst, contours,largest_contour_index, color, CV_FILLED, 8, hierarchy ); // Draw the largest contour using previously stored index.
 rectangle(src, bounding_rect,  Scalar(0,255,0),1, 8,0); 
 imshow( "src", src );
 imshow( "largest Contour", dst );
 waitKey(0);
}

Hope these help....

来源：https://stackoverflow.com/questions/18853838/extract-area-detected-by-color-using-opencv-in-android

标签

android

OpenCV

bitmap

area

contour