@Override
public int[] getPixels(Image img, int x, int y, int w, int h)
{
    int[] pixels = new int[w * h];

    PixelReader reader = img.getPixelReader();

    PixelFormat.Type type =  reader.getPixelFormat().getType();

    WritablePixelFormat<IntBuffer> format = null;

    if(type == PixelFormat.Type.INT_ARGB_PRE)
    {
        format = PixelFormat.getIntArgbPreInstance();
    }
    else
    {
        format = PixelFormat.getIntArgbInstance();
    }

    reader.getPixels(x, y, w, h, format, pixels, 0, w);

    return pixels;
}
 

/**
 * Determine the appropriate {@link WritablePixelFormat} type that can be
 * used to transfer data into the indicated BufferedImage.
 * 
 * @param bimg
 *            the BufferedImage that will be used as a destination for a
 *            {@code PixelReader<IntBuffer>#getPixels()} operation.
 * @return
 */
private static WritablePixelFormat<IntBuffer> getAssociatedPixelFormat(BufferedImage bimg) {
	switch (bimg.getType()) {
	// We lie here for xRGB, but we vetted that the src data was opaque
	// so we can ignore the alpha. We use ArgbPre instead of Argb
	// just to get a loop that does not have divides in it if the
	// PixelReader happens to not know the data is opaque.
	case BufferedImage.TYPE_INT_RGB:
	case BufferedImage.TYPE_INT_ARGB_PRE:
		return PixelFormat.getIntArgbPreInstance();

	case BufferedImage.TYPE_INT_ARGB:
		return PixelFormat.getIntArgbInstance();

	default:
		// Should not happen...
		throw new InternalError("Failed to validate BufferedImage type");
	}
}
 

/**
 * Return OpenCV MAT in CvType.CV_8UC4
 */
public static Mat imageToMat(Image image) {
   int width = (int) image.getWidth();
   int height = (int) image.getHeight();
   byte[] buffer = new byte[width * height * 4];

   PixelReader reader = image.getPixelReader();
   WritablePixelFormat<ByteBuffer> format = WritablePixelFormat.getByteBgraInstance();
   reader.getPixels(0, 0, width, height, format, buffer, 0, width * 4);

   Mat mat = new Mat(height, width, CvType.CV_8UC4);
   mat.put(0, 0, buffer);
   return mat;
}