初识Java ImageIO - 居中生成文字图片

import java.awt.Color;
import java.awt.Font;
import java.awt.FontMetrics;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.FileInputStream;
import java.util.Iterator;

import javax.imageio.ImageIO;
import javax.imageio.ImageReader;
import javax.imageio.stream.ImageInputStream;

public class TestImage {

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

        // 测试图片类型（不支持 tif 格式）
        String[] imgFiles = new String[] { "C:/1/1.bmp", "C:/1/1.gif",
                "C:/1/1.jpg", "C:/1/1.png", "C:/1/1.tif" };
        for (String file : imgFiles) {
            System.out.println(file + " - " + getImageType(new File(file)));
        }

        // 生成居中的文字图片
        String rootDir = "C:/tmp";
        generateImages(rootDir);
    }

    public static String getImageType(File file) throws Exception {
        ImageInputStream iin = ImageIO
                .createImageInputStream(new FileInputStream(file));
        Iterator<ImageReader> it = ImageIO.getImageReaders(iin);
        if (it.hasNext()) {
            return it.next().getFormatName();
        }
        return null;

    }

    public static void generateImages(String rootDir) throws Exception {
        File dir = new File(rootDir, "trainingImg");
        dir.mkdirs();
        Font font = new Font("Courier New", Font.PLAIN, 72);
        // Font font = new Font("宋体", Font.PLAIN, 72);
        for (char c = 'a'; c < 'z'; c++) {
            String str = Character.toString(c);
            File file = new File(dir, str + ".png");
            generateImage(str, file, font, 72, 72);
        }
        for (char c = 'A'; c < 'Z'; c++) {
            String str = Character.toString(c);
            File file = new File(dir, "_" + str + ".png");
            generateImage(str, file, font, 72, 72);
        }
        for (char c = '0'; c < '9'; c++) {
            String str = Character.toString(c);
            File file = new File(dir, "_" + str + ".png");
            generateImage(str, file, font, 72, 72);
        }
    }

    public static void generateImage(String str, File file, Font font,
            int height, int width) throws Exception {
        BufferedImage bi = new BufferedImage(width, height,
                BufferedImage.TYPE_INT_BGR);
        Graphics2D g = bi.createGraphics();
        g.setColor(Color.WHITE);
        g.fillRect(0, 0, width, height);
        g.setFont(font);
        g.setColor(Color.BLACK);

        FontMetrics fm = g.getFontMetrics(font);
        java.awt.geom.Rectangle2D rect = fm.getStringBounds(str, g);
        int textWidth = (int) (rect.getWidth());
        int textHeight = (int) (rect.getHeight());

        int x = (width - textWidth) / 2;
        int y = (height - textHeight) / 2 + fm.getAscent();

        g.drawString(str, x, y);
        g.dispose();
        ImageIO.write(bi, "png", file);
    }
}

// ref:

import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;

import javax.imageio.ImageIO;

public class A {
    public static void main(String[] args) throws IOException {

        // 将彩色图片转为黑白二值图片
        BufferedImage input = ImageIO.read(new File("C:/b1.jpg"));
        BufferedImage im = new BufferedImage(input.getWidth(), input
                .getHeight(), BufferedImage.TYPE_BYTE_BINARY);
        Graphics2D g2d = im.createGraphics();
        g2d.drawImage(input, 0, 0, null);
        ImageIO.write(im, "jpg", new File("C:/b2.jpg"));

        // 将彩色图片转为灰度图片
        im = new BufferedImage(input.getWidth(), input.getHeight(),
                BufferedImage.TYPE_BYTE_GRAY);
        g2d = im.createGraphics();
        g2d.drawImage(input, 0, 0, null);
        ImageIO.write(im, "jpg", new File("C:/b3.jpg"));
    }
}