如何用Java中的JPEG创建缩略图？ [英] How do you create a thumbnail image out of a JPEG in Java?

问题描述

有人可以帮助我们帮助创建一些用Java创建JPEG缩略图的代码。

Can someone please help with some code for creating a thumbnail for a JPEG in Java.

我是新手，所以一步一步的解释是赞。

I'm new at this, so a step by step explanation would be appreciated.

推荐答案

Image img = ImageIO.read(new File("test.jpg")).getScaledInstance(100, 100, BufferedImage.SCALE_SMOOTH);

这将创建一个100x100像素的缩略图作为Image对象。如果你想把它写回磁盘，只需将代码转换为：

This will create a 100x100 pixels thumbnail as an Image object. If you want to write it back to disk simply convert the code to this:

BufferedImage img = new BufferedImage(100, 100, BufferedImage.TYPE_INT_RGB);
img.createGraphics().drawImage(ImageIO.read(new File("test.jpg")).getScaledInstance(100, 100, Image.SCALE_SMOOTH),0,0,null);
ImageIO.write(img, "jpg", new File("test_thumb.jpg"));

此外，如果您担心速度问题（如果您想扩展，上述方法相当慢许多图片）使用这些方法和以下声明：

Also if you are concerned about speed issues (the method described above is rather slow if you want to scale many images) use these methods and the following declaration :

private BufferedImage scale(BufferedImage source,double ratio) {
  int w = (int) (source.getWidth() * ratio);
  int h = (int) (source.getHeight() * ratio);
  BufferedImage bi = getCompatibleImage(w, h);
  Graphics2D g2d = bi.createGraphics();
  double xScale = (double) w / source.getWidth();
  double yScale = (double) h / source.getHeight();
  AffineTransform at = AffineTransform.getScaleInstance(xScale,yScale);
  g2d.drawRenderedImage(source, at);
  g2d.dispose();
  return bi;
}

private BufferedImage getCompatibleImage(int w, int h) {
  GraphicsEnvironment ge = GraphicsEnvironment.getLocalGraphicsEnvironment();
  GraphicsDevice gd = ge.getDefaultScreenDevice();
  GraphicsConfiguration gc = gd.getDefaultConfiguration();
  BufferedImage image = gc.createCompatibleImage(w, h);
  return image;
}

然后致电：

BufferedImage scaled = scale(img,0.5);

其中0.5是比例，img是包含正常大小图像的BufferedImage。

where 0.5 is the scale ratio and img is a BufferedImage containing the normal-sized image.

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