使用Java中的ImageIO设置jpg压缩级别 [英] Setting jpg compression level with ImageIO in Java

问题描述

我正在使用 javax.imageio.ImageIO 将 BufferedImage 保存为jpeg文件。
特别是，我创建了以下Java函数：

I'm using javax.imageio.ImageIO to save a BufferedImage as a jpeg file. In particular, I created the following Java function:

public static void getScreenShot(BufferedImage capture, Path folder, String filename) {
        try {
            ImageIO.write(capture, "jpeg", new File(folder.toString()+"/"+filename+".jpg"));
        } catch (AWTException | IOException ex) {
            Logger.getLogger(ScreenShotMaker.class.getName()).log(Level.SEVERE, null, ex);
        }
}

同样任何图像处理软件，我希望改变jpeg文件的压缩级别。但是，我正在搜索 ImageIO 中似乎缺少的这个选项。

Likewise any image manipulation software, I wish to change the compression level of the jpeg file. However, I'm searching for this option that seems to be missing in ImageIO.

我可以设置压缩级别以及如何设置？

Can I set the compression level and how?

推荐答案

你必须使用 JPEGImageWriteParam 然后使用 ImageWriter.write（） 。在编写之前，通过 ImageWriter.setOutput 。

You have to use JPEGImageWriteParam and then save the image with ImageWriter.write(). Before to write, set the output via ImageWriter.setOutput.

设置压缩级别如下：

JPEGImageWriteParam jpegParams = new JPEGImageWriteParam(null);
jpegParams.setCompressionMode(ImageWriteParam.MODE_EXPLICIT);
jpegParams.setCompressionQuality(1f);

其中 1f 是一个浮点数100％的质量。如果我不记得错误，默认值约70％。

Where 1f is a float number that stands for 100% quality. Default value is around 70% if I don't remember wrong.

编辑

然后，您必须按照以下步骤获取 ImageWriter 的实例。有两种方式，短期和长期（我保留两种方式，以防万一）。

Then, you have to do as follows to get an instance of an ImageWriter. There are two ways, a short and a long one (I keep both, just in case).

短路（由<建议一条评论中的href =https://stackoverflow.com/users/166524/lapo> lapo 是：

final ImageWriter writer = ImageIO.getImageWritersByFormatName("jpg").next();
// specifies where the jpg image has to be written
writer.setOutput(new FileImageOutputStream(
  new File(folder.toString() + "/" + filename + ".jpg")));

// writes the file with given compression level 
// from your JPEGImageWriteParam instance
writer.write(null, new IIOImage(capture, null, null), jpegParams);

或更长的方式

// use IIORegistry to get the available services
IIORegistry registry = IIORegistry.getDefaultInstance();
// return an iterator for the available ImageWriterSpi for jpeg images
Iterator<ImageWriterSpi> services = registry.getServiceProviders(ImageWriterSpi.class,
                                                 new ServiceRegistry.Filter() {   
        @Override
        public boolean filter(Object provider) {
            if (!(provider instanceof ImageWriterSpi)) return false;

            ImageWriterSpi writerSPI = (ImageWriterSpi) provider;
            String[] formatNames = writerSPI.getFormatNames();
            for (int i = 0; i < formatNames.length; i++) {
                if (formatNames[i].equalsIgnoreCase("JPEG")) {
                    return true;
                }
            }

            return false;
        }
    },
   true);
//...assuming that servies.hasNext() == true, I get the first available service.
ImageWriterSpi writerSpi = services.next();
ImageWriter writer = writerSpi.createWriterInstance();

// specifies where the jpg image has to be written
writer.setOutput(new FileImageOutputStream(
  new File(folder.toString() + "/" + filename + ".jpg")));

// writes the file with given compression level 
// from your JPEGImageWriteParam instance
writer.write(null, new IIOImage(capture, null, null), jpegParams);

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