Graphics2D#drawImage()の挙動について

import java.awt.Color;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.awt.image.IndexColorModel;
import java.awt.image.WritableRaster;

public class DrawImageTest {
    public static void main(String[] args) {
        DrawImageTest test = new DrawImageTest();
        test.doMain();
    }
    
    private void doMain() {
        // IndexColorModelの作成
        // 0が白、1が黒のIndexColorModel
        byte[] colorArray = new byte[]{(byte)0xff, 0};
        IndexColorModel colorModel = new IndexColorModel(
                1, colorArray.length, colorArray, colorArray, colorArray);
        
        // BufferedImage作成(image1)
        BufferedImage image1 = new BufferedImage(
                16, 16, BufferedImage.TYPE_BYTE_BINARY, colorModel);
        // 白地に右上から左下に掛けて黒の線を引く。
        for (int y = 0; y < 16; y++) {
            for (int x = 0; x < 16; x++) {
                if (x == 15 - y) {
                    image1.setRGB(x, y, Color.black.getRGB());
                } else {
                    image1.setRGB(x, y, Color.white.getRGB());
                }
            }
        }
        
        // BufferedImage作成(image2)
        BufferedImage image2 = new BufferedImage(
                16, 16, BufferedImage.TYPE_BYTE_BINARY, colorModel);
        
        // image1のデータを出力
        System.out.println("image1");
        this.printElementData(image1);
        System.out.println("");
        
        // image2のデータを出力
        System.out.println("image2");
        this.printElementData(image2);
        System.out.println("");
        
        // image2からGraphics2Dを取得し、image1をdraw
        Graphics2D graphics = image2.createGraphics();
        graphics.drawImage(image1, null, 0, 0);
        
        // image2のデータを出力
        System.out.println("image2 <- image1.");
        this.printElementData(image2);
    }
    
    private void printElementData(BufferedImage image) {
        WritableRaster raster = image.getRaster();
        byte[] data = (byte[])raster.getDataElements(
                0, 0, raster.getWidth(), raster.getHeight(), null);
        System.out.println("--------------------------------");
        for (int i = 0; i < data.length; i++) {
            if (i != 0 && i % raster.getWidth() == 0) {
                // 改行
                System.out.println("");
            }
            System.out.print(data[i]);
        }
        System.out.println("");
        System.out.println("--------------------------------");
    }
}