在 Java 中使用 ImageIO 设置 jpg 压缩级别

一种更简洁的方法是直接从中获取：ImageWriterImageIO

ImageWriter jpgWriter = ImageIO.getImageWritersByFormatName("jpg").next();
ImageWriteParam jpgWriteParam = jpgWriter.getDefaultWriteParam();
jpgWriteParam.setCompressionMode(ImageWriteParam.MODE_EXPLICIT);
jpgWriteParam.setCompressionQuality(0.7f);

ImageOutputStream outputStream = createOutputStream(); // For example implementations see below
jpgWriter.setOutput(outputStream);
IIOImage outputImage = new IIOImage(image, null, null);
jpgWriter.write(null, outputImage, jpgWriteParam);
jpgWriter.dispose();

需要调用 to 才能显式设置压缩的级别（质量）。ImageWriteParam.setCompressionMode(ImageWriteParam.MODE_EXPLICIT)

In是最高质量，最小压缩，而最低质量，最大压缩。ImageWriteParam.setCompressionQuality()1.0f0.0f

ImageWriter.setOutput应该传递一个 ImageOutputStream。虽然该方法接受 ，但根据文档，它通常不受支持：Object

使用除 非 常规适用于直接与输出设备或映像协议交互的编写器。法律类集由作者的服务提供商的方法公布;大多数编写器将返回一个单元素数组，该数组仅包含以指示它们仅接受 .ObjectImageOutputStreamgetOutputTypesImageOutputStream.classImageOutputStream

大多数情况应由以下两个类处理：

• FileImageOutputStream - 将其输出直接写入 或 的实现。ImageOutputStreamFileRandomAccessFile
• MemoryCacheImageOutputStream - 将其输出写入常规 .通常与（感谢您的提示，@lmiguelmh！ImageOutputStreamOutputStreamByteArrayOutputStream

您必须使用JPEGImageWriteParam，然后使用ImageWriter.write（）保存图像。在写入之前，请通过 ImageWriter.setOutput 设置输出。

按如下方式设置压缩级别：

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

其中是代表100%质量的浮动数字。如果我不记得错误，默认值约为70%。1f

编辑

然后，您必须执行以下操作才能获得 .有两种方式，一种是短的，一种是长方法（为了以防万一，我都保留两种方法）。ImageWriter

最短的方法（由lapo在一条评论中建议）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);

或更长的路程

// 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);