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 here is an simple example

public static BufferedImage large(BufferedImage image, int n)
{

int w = n * image.getWidth();
int h = n * image.getHeight();

BufferedImage bigImage = 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 bigImage;
}