The following Java method takes a BufferedImage object and returns its enlarged version. The parameter n specifies the enlargement factor.

To enlarge an image by an integer factor n, we will replicate pixels such that each pixel in the input image becomes an n x n block of identical pixels in the output image.

 public static BufferedImage enlarge(BufferedImage image, int n) {
        
        int w = n * image.getWidth();
        int h = n * image.getHeight();
        
        BufferedImage enlargedImage =
                new BufferedImage(w, h, image.getType());
        
        for (int y=0; y < h; ++y)
            for (int x=0; x < w; ++x)
                enlargedImage.setRGB(x, y, image.getRGB(x/n, y/n));
        
        return enlargedImage;
    }