Wednesday, April 2, 2014

How to Convert Mat to BufferedImage & Vice Versa

How to Convert Mat to BufferedImage & Vice Versa 

Introduction

In this tip, we see how to do the conversion between Mat and BufferedImageMat is a data structure from OpenCV to process image. BufferedImage is a data structure from Java to store images.

Using the Code

Convert Mat to BufferedImage

Mat data structure has image data, image type (GRAY, BGR), Height, Width. In mat2Img, the following function extracts meta data from Mat data structure and gets assigned to BufferedImage. This way, Mat is assigned toBufferedImage.

public static BufferedImage mat2Img(Mat in)
    {
        BufferedImage out;
        byte[] data = new byte[320 * 240 * (int)in.elemSize()];
        int type;
        in.get(0, 0, data);

        if(in.channels() == 1)
            type = BufferedImage.TYPE_BYTE_GRAY;
        else
            type = BufferedImage.TYPE_3BYTE_BGR;

        out = new BufferedImage(320, 240, type);

        out.getRaster().setDataElements(0, 0, 320, 240, data);
        return out;
    } 

Convert BufferedImage to Mat

img2Mat function accepts BufferedImage object as parameter and returns the Mat object. Mat Object is created with 320 width and 240 height, then extract RGB values from BufferedImage object and assigned to databuffwhich is a one dimensional int array. databuff is right shifted to 16 , 8, 0 gets ANDED with 0XFF, then assigned toMat object.

public static Mat img2Mat(BufferedImage in)
    {
          Mat out;
          byte[] data;
          int r, g, b;

          if(in.getType() == BufferedImage.TYPE_INT_RGB)
          {
              out = new Mat(240, 320, CvType.CV_8UC3);
              data = new byte[320 * 240 * (int)out.elemSize()];
              int[] dataBuff = in.getRGB(0, 0, 320, 240, null, 0, 320);
              for(int i = 0; i < dataBuff.length; i++)
              {
                  data[i*3] = (byte) ((dataBuff[i] >> 16) & 0xFF);
                  data[i*3 + 1] = (byte) ((dataBuff[i] >> 8) & 0xFF);
                  data[i*3 + 2] = (byte) ((dataBuff[i] >> 0) & 0xFF);
              }
          }
          else
          {
              out = new Mat(240, 320, CvType.CV_8UC1);
              data = new byte[320 * 240 * (int)out.elemSize()];
              int[] dataBuff = in.getRGB(0, 0, 320, 240, null, 0, 320);
              for(int i = 0; i < dataBuff.length; i++)
              {
                r = (byte) ((dataBuff[i] >> 16) & 0xFF);
                g = (byte) ((dataBuff[i] >> 8) & 0xFF);
                b = (byte) ((dataBuff[i] >> 0) & 0xFF);
                data[i] = (byte)((0.21 * r) + (0.71 * g) + (0.07 * b)); //luminosity
              }
           }
           out.put(0, 0, data);
           return out;
     } 

Points of Interest

  • Learn how to convert Mat to BufferedImage.
  • Learn how to convert BufferedImage to Mat.

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