以最快最简单的方式扩展BufferedImage [英] Scale a BufferedImage the fastest and easiest way

问题描述

任务：
我有一些图像，我将它们缩小，然后将它们连接到一个图像。但是我对实现有一点问题：

The task: I have some images, I scale them down, and join them to one image. But I have a little problem with the implementation:

具体问题：
我想调整大小/缩放BufferedImage。 getScaledInstance方法返回一个Image对象，但我无法将其强制转换为BufferedImage：

The concrete problem: I want to resize/scale a BufferedImage. The getScaledInstance method returns an Image object, but I can't cast it to BufferedImage:

Exception in thread "main" java.lang.ClassCastException: sun.awt.image.ToolkitImage cannot be cast to java.awt.image.BufferedImage

（我不知道为什么它是ToolkitImage而不是Image ......）

(I don't know why is it a ToolkitImage instead of an Image...)

我找到了解决方案：

Image tmp = bi.getScaledInstance(SMALL_SIZE, SMALL_SIZE, BufferedImage.SCALE_FAST);
BufferedImage buffered = new BufferedImage(SMALL_SIZE,SMALL_SIZE,BufferedImage.TYPE_INT_RGB);
buffered.getGraphics().drawImage(tmp, 0, 0, null);

但它很慢，我认为应该有更好的方法。

我需要BufferedImage，因为我必须让像素加入小图像。

I need the BufferedImage, because I have to get the pixels to join the small images.

有更好的（更好/更快）的方式吗？

编辑：
如果我首先将Image转换为ToolkitImage，它有一个getBufferedImage（）方法。但它总是返回null。你知道为什么吗？

If I cast the Image first to ToolkitImage, it has a getBufferedImage() method. But it always returns null. Do you know why?

推荐答案

Graphics 对象有一个方法在执行调整大小操作的同时绘制图像：

The Graphics object has a method to draw an Image while also performing a resize operation:

Graphics.drawImage（Image，int，int，int，int，ImageObserver） 方法可用于指定绘图时的位置以及图像的大小。

Graphics.drawImage(Image, int, int, int, int, ImageObserver) method can be used to specify the location along with the size of the image when drawing.

所以，我们可以使用这样的代码：

So, we could use a piece of code like this:

BufferedImage otherImage = // .. created somehow
BufferedImage newImage = new BufferedImage(SMALL_SIZE, SMALL_SIZE, BufferedImage.TYPE_INT_RGB);

Graphics g = newImage.createGraphics();
g.drawImage(otherImage, 0, 0, SMALL_SIZE, SMALL_SIZE, null);
g.dispose();

这将花费 otherImage 并绘制它 newImage ，宽度和高度为 SMALL_SIZE 。

This will take otherImage and draw it on the newImage with the width and height of SMALL_SIZE.

或者，如果您不介意使用库，请 Thumbnailator 可以完成同样的事情：

Or, if you don't mind using a library, Thumbnailator could accomplish the same with this:

BufferedImage newImage = Thumbnails.of(otherImage)
                             .size(SMALL_SIZE, SMALL_SIZE)
                             .asBufferedImage();

Thumbnailator也会比使用 Image.getScaledInstance更快地执行调整大小操作同时还执行更高质量的调整大小操作，而不是仅使用 Graphics.drawImage 。

Thumbnailator will also perform the resize operation quicker than using Image.getScaledInstance while also performing higher quality resize operations than using only Graphics.drawImage.

免责声明：我是Thumbnailator库的维护者。

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