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Thread: Retreiving the RGB values from an image

  1. #1
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    Default Retreiving the RGB values from an image


    I created an image using random numbers pixels, i.e. each pixel consists of three random numbers one for green color, another for the blue color and the last for the red color. I stored the image to a jpg file and I write a code to read and retreive the RGB values from the image, but the problem is that I retreved values that does not match the original values(when the image created). Here is the code for writing to and reading from a jpg file:

    1. Writing to an image file
    // fill the array pixels with random numbers
    // writing to a file
    private JLabel createImageLabel(int[] pixels)
     BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
     WritableRaster raster = image.getRaster(); 
     raster.setPixels(0, 0, width, height, pixels); 
          for (int i = 0; i < height; i++) {
          for (int j = 0; j < width; j++) {
            int[] data = new int[3];
            System.out.println("x,y: " + j + ", " + i);
            raster.getPixel(j, i, data);
            for (int p=0;p<=data.length-1;p++)
             System.out.println(data[p]+" ");
            } }}   
     JLabel label = new JLabel( new ImageIcon(image) );
     File f = new File("d:\\test.jpg");
     ImageIO.write(image,"jpeg",f );
     catch(IOException e){System.out.println(e);}
     return label;
    2. Reading from an image
     public ReadImage()
      BufferedImage image =             
      ImageIO.read(new File( "d:\\test.jpg" ));
      int w = image.getWidth();
      int h = image.getHeight();
      for (int i=0; i<h; i++){
       for (int j=0; j<w; j++){   
      int pixel = image.getRGB(j, i);
        int alpha = (pixel >> 24) & 0xff;
        int red = (pixel >> 16) & 0xff;
        int green = (pixel >> 8) & 0xff;
        int blue = (pixel) & 0xff;
        System.out.println("argb: " + alpha + ", " + red + ", " + green + ", " + blue);
      catch(IOException e){System.out.println(e);}
    I greately appreciate your help.

    Last edited by helloworld922; May 30th, 2011 at 08:42 AM.

  2. #2
    Super Moderator helloworld922's Avatar
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    Default Re: Retreiving the RGB values from an image

    JPEG is a lossy compression format. I'm not sure how much Java will try to compress a JPEG, but the more it does the more different your results will be. If you want an non-lossy compression format, try using the PNG format.
    Last edited by helloworld922; May 30th, 2011 at 08:49 AM.

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