在 Java 中使用 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);
        }
}

与任何图像处理软件一样，我希望更改 jpeg 文件的压缩级别.但是，我正在寻找 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吗?

Can I set the compression level and how?

推荐答案

你必须使用 JPEGImageWriteParam 然后用 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，代表 100% 质量.如果我没记错的话，默认值是大约 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，您必须执行以下操作才能获得 ImageWriter 的实例.有两种方式，一种是短的，一种是长的(我都保留了，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).

捷径(由 lapo 在一条评论中建议)是:

The short way (suggested by lapo in one comment) is:

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);

或更长的路

// 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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