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Thread: Problem with image crop and pixel comparison code

  1. #1
    Junior Member
    Join Date
    Jun 2012
    Thanked 0 Times in 0 Posts

    Default Problem with image crop and pixel comparison code

    I have got some code to read in an image, crop a region from the image and compare with a reference image.
    It seems to compile and work ok until the line
    data1 = (int[]) grab1.getPixels();
    at which point it crashes
    when i run the code. I do previously use pdftk and convert (in Ubuntu) to extract .png images from a pdf file so maybe it is a problem with the output .png?


      if(NAME.endsWith("_1.1.1.png")) {
    	println("first filename:");
            String curDir = System.getProperty("user.dir");
    	println("current directory:");
      	int flag = 111;
    	System.out.format("flag = %d%n", flag);
    	BufferedImage image = null;
            try {
    	    // Read from a first image file  
    		//hardcoded right now!
              // File file = new File(".../image/2cm.png");
      File file = new File(".../s123456TTT2012-06-2_1.1.1.png"); 
    	      //File file = new File(curDir, '/', NAME); 
                image = ImageIO.read(file);  
    	   // crop and save output image
    	image = image.getSubimage(100, 40, 100, 100);
     	ImageIO.write(image, "png",new File(".../image/out.png"));
            } catch (IOException e) {
    	// compare the cropped image with the reference image (for 2 cm scale)
    	String file1 = ".../image/ref.png";
    	String file2 = ".../image/out.png";
    	Image image1 = Toolkit.getDefaultToolkit().getImage(file1);
    	Image image2 = Toolkit.getDefaultToolkit().getImage(file2);
    	try {
    	PixelGrabber grab1 =new PixelGrabber(image1, 0, 0, -1, -1, false);
    	PixelGrabber grab2 =new PixelGrabber(image2, 0, 0, -1, -1, false);
    	int[] data1 = null;
    	if (grab1.grabPixels()) {
    	int width = grab1.getWidth();
    	int height = grab1.getHeight();
    	data1 = new int[width * height];
    	data1 = (int[]) grab1.getPixels();
    	int[] data2 = null;
    	if (grab2.grabPixels()) {
    	int width = grab2.getWidth();
    	int height = grab2.getHeight();
    	data2 = new int[width * height];
    	data2 = (int[]) grab2.getPixels();
    	System.out.println("The Calypso data has a 2 cm scale: " + java.util.Arrays.equals(data1, data2));
    	} catch (InterruptedException e1) {


    Now running java PNG to ASCII code...
    first filename:
    current directory:
    flag = 111
    Exception in thread "Animation Thread" java.lang.ClassCastException: [B cannot be cast to [I
    	at CalypsoAnalysis.setup(CalypsoAnalysis.java:104)
    	at processing.core.PApplet.handleDraw(Unknown Source)
    	at processing.core.PApplet.run(Unknown Source)
    	at java.lang.Thread.run(Thread.java:636)


  2. #2
    Junior Member
    Join Date
    Jun 2012
    Thanked 0 Times in 0 Posts

    Default Re: Problem with image crop and pixel comparison code

    i figured it out. I perform two Linux 'convert' commands on the original PNG image. this somehow corrupts the data. I have modified my code to crop from the image output after the initial 'convert' and the pixel comparison works ok.

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