[Java] 製作縮圖筆記

1. package test_image; 
2.  
3. import java.awt.Graphics; 
4. import java.awt.image.BufferedImage; 
5. import java.io.File; 
6.  
7. import javax.imageio.ImageIO; 
8.  
9. public class TestImageResize { 
10.  
11.    private static int targetWidth = 120; 
12.    private static int targetHeight = 80; 
13.    private static double targetRate = (double) targetWidth / targetHeight; 
14.  
15.    public static void main(String[] args) throws Exception { 
16.  
17.        System.out.printf("Target w:%s, h:%s, r:%s\n",  
18.            targetWidth, targetHeight, targetRate); 
19.  
20.  
21.        BufferedImage image = ImageIO.read(new File("input.jpg")); 
22.  
23.        int type = image.getType(); 
24.        if(type == 0) { type = BufferedImage.TYPE_INT_ARGB; } 
25.  
26.        int width = image.getWidth(); 
27.        int height = image.getHeight(); 
28.        double rate = (double) width / height; 
29.  
30.        System.out.printf("Source w:%s, h:%s, r:%s\n", width, height, rate); 
31.  
32.  
33.  
34.        /* 等比例縮小至指定大小內 */ 
35.        int rWidth = targetWidth; 
36.        int rHeight = targetHeight; 
37.  
38.        if(width < targetWidth && height < targetHeight) { 
39.            rWidth = width; 
40.            rHeight = height; 
41.        } else if(rate > targetRate) { 
42.            rHeight = (int) (targetWidth / rate); 
43.        } else { 
44.            rWidth = (int) (targetHeight * rate); 
45.        } 
46.        System.out.printf("Resize w:%s, h:%s\n", rWidth, rHeight); 
47.  
48.        BufferedImage resize1 = new BufferedImage(rWidth, rHeight, type); 
49.        Graphics g1 = resize1.getGraphics(); 
50.        g1.drawImage(image, 0, 0, rWidth, rHeight, null); 
51.        g1.dispose(); 
52.  
53.        ImageIO.write(resize1, "jpg", new File("output_1.jpg")); 
54.  
55.  
56.  
57.  
58.        /* 等比例縮小填滿指定大小 */ 
59.        BufferedImage resize2 = new BufferedImage(targetWidth,targetHeight,type); 
60.        Graphics g2 = resize2.getGraphics(); 
61.  
62.        int startX = 0; 
63.        int startY = 0; 
64.        int size = 0; 
65.  
66.        if(rate > targetRate) { 
67.            startX = (int) (width - height * targetRate) / 2; 
68.            size = height; 
69.        } else { 
70.            startY = (int) (height - width / targetRate) / 2; 
71.            size = width; 
72.        } 
73.        System.out.printf("x:%s, y:%s, size:%s\n", startX, startY, size); 
74.  
75.        g2.drawImage( 
76.            image, 
77.            0, 0, targetWidth, targetHeight, 
78.            startX, startY, (size + startX), (size + startY), 
79.            null 
80.        ); 
81.  
82.        g2.dispose(); 
83.  
84.        ImageIO.write(resize2, "jpg", new File("output_2.jpg")); 
85.    } 
86. } 

package test_image;

import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.File;

import javax.imageio.ImageIO;

public class TestImageResize {

    private static int targetWidth = 120;
    private static int targetHeight = 80;
    private static double targetRate = (double) targetWidth / targetHeight;

    public static void main(String[] args) throws Exception {

        System.out.printf("Target w:%s, h:%s, r:%s\n", 
            targetWidth, targetHeight, targetRate);


        BufferedImage image = ImageIO.read(new File("input.jpg"));

        int type = image.getType();
        if(type == 0) { type = BufferedImage.TYPE_INT_ARGB; }

        int width = image.getWidth();
        int height = image.getHeight();
        double rate = (double) width / height;

        System.out.printf("Source w:%s, h:%s, r:%s\n", width, height, rate);



        /* 等比例縮小至指定大小內 */
        int rWidth = targetWidth;
        int rHeight = targetHeight;

        if(width < targetWidth && height < targetHeight) {
            rWidth = width;
            rHeight = height;
        } else if(rate > targetRate) {
            rHeight = (int) (targetWidth / rate);
        } else {
            rWidth = (int) (targetHeight * rate);
        }
        System.out.printf("Resize w:%s, h:%s\n", rWidth, rHeight);

        BufferedImage resize1 = new BufferedImage(rWidth, rHeight, type);
        Graphics g1 = resize1.getGraphics();
        g1.drawImage(image, 0, 0, rWidth, rHeight, null);
        g1.dispose();

        ImageIO.write(resize1, "jpg", new File("output_1.jpg"));




        /* 等比例縮小填滿指定大小 */
        BufferedImage resize2 = new BufferedImage(targetWidth,targetHeight,type);
        Graphics g2 = resize2.getGraphics();

        int startX = 0;
        int startY = 0;
        int size = 0;

        if(rate > targetRate) {
            startX = (int) (width - height * targetRate) / 2;
            size = height;
        } else {
            startY = (int) (height - width / targetRate) / 2;
            size = width;
        }
        System.out.printf("x:%s, y:%s, size:%s\n", startX, startY, size);

        g2.drawImage(
            image,
            0, 0, targetWidth, targetHeight,
            startX, startY, (size + startX), (size + startY),
            null
        );

        g2.dispose();

        ImageIO.write(resize2, "jpg", new File("output_2.jpg"));
    }
}

參考文件：
Graphics (Java 2 Platform SE 6)