java 等比例缩略图
网上收了好几篇关于图像缩放的java文章, 都有明显的算法错误，大体思路倒是对的，细节决定成败！都是常规逻辑，根本就不考虑特殊情况，例如超扁等长条图片，明显处理都是错误的，正确的代码如下：
import java.awt.Image;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.FileOutputStream;
import javax.imageio.ImageIO;
import com.sun.image.codec.jpeg.JPEGCodec;
import com.sun.image.codec.jpeg.JPEGImageEncoder;
public class Thumbnail {
/**
* 创建图片缩略图(等比缩放)
*
* @param src
* 源图片文件完整路径
* @param dist
* 目标图片文件完整路径
* @param width
* 缩放的宽度
* @param height
* 缩放的高度
*/
public static void createThumbnail(String src, String dist, float width,
float height) {
try {
File srcfile = new File(src);
if (!srcfile.exists()) {
System.out.println("文件不存在");
return;
}
BufferedImage image = ImageIO.read(srcfile);
// 获得缩放的比例
double ratio = 1.0;
// 判断如果高、宽都不大于设定值，则不处理,按变化率大的来缩放
if (image.getHeight() > height || image.getWidth() > width)
{
double ratiox = width / image.getWidth();
double ratioy = height / image.getHeight();
if(ratiox<ratioy)
ratio = ratiox;
else
ratio = ratioy;
}
// 计算新的图面宽度和高度
int newWidth = (int) (image.getWidth() * ratio);
int newHeight = (int) (image.getHeight() * ratio);
BufferedImage bfImage = new BufferedImage(newWidth, newHeight,
BufferedImage.TYPE_INT_RGB);
bfImage.getGraphics().drawImage(
image.getScaledInstance(newWidth, newHeight,
Image.SCALE_SMOOTH), 0, 0, null);
FileOutputStream os = new FileOutputStream(dist);
JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(os);
encoder.encode(bfImage);
os.close();
System.out.println("创建缩略图成功");
} catch (Exception e) {
System.out.println("创建缩略图发生异常" + e.getMessage());
}
}
public static void main(String[] args) {
createThumbnail("D:\\My Documents\\My Pictures\\goshopping.jpg", "D:\\My Documents\\My Pictures\\a.png", 300, 400);
createThumbnail("D:\\My Documents\\My Pictures\\goshopping.jpg", "D:\\My Documents\\My Pictures\\b.png", 1400, 200);
createThumbnail("D:\\My Documents\\My Pictures\\goshopping.jpg", "D:\\My Documents\\My Pictures\\c.png", 200, 1200);
}
}