使用Java中的ImageIO设置jpg压缩级别

Question

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：

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中似乎缺少的此选项。

我可以设置压缩级别以及如何设置？

Answer 1

更简洁的方法是直接从ImageWriter获取ImageIO：

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ImageWriteParam.setCompressionMode(ImageWriteParam.MODE_EXPLICIT)才能明确设置压缩级别（质量）。

在ImageWriteParam.setCompressionQuality() 1.0f中是最高质量，最低压缩，而0.0f是最低质量，最大压缩。

ImageWriter.setOutput应该传递ImageOutputStream。虽然该方法接受Object，但根据文档通常不支持：

  

使用除Object以外的通用ImageOutputStream适用于直接与输出设备或映像协议交互的编写器。法律类的集合由作者的服务提供者getOutputTypes方法公布;大多数编写器将返回仅包含ImageOutputStream.class的单元素数组，以指示它们仅接受ImageOutputStream。

大多数情况应由这两个类处理：

• FileImageOutputStream - ImageOutputStream的实施，将其输出直接写入File或RandomAccessFile。
• MemoryCacheImageOutputStream - ImageOutputStream的实现，将其输出写入常规OutputStream。通常与ByteArrayOutputStream一起使用（感谢提示，@lmiguelmh！）。

Answer 2

您必须使用JPEGImageWriteParam，然后使用ImageWriter.write()保存图像。在编写之前，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1f是一个代表100％质量的浮点数。如果我不记得错误，默认值约70％。

修改

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

简短（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);

Answer 3

更通用的方法是（来自Igor's answer）：

static void saveImage(BufferedImage image,File jpegFiletoSave,float quality) throws IOException{
    // save jpeg image with specific quality. "1f" corresponds to 100% , "0.7f" corresponds to 70%

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

        jpgWriter.setOutput(ImageIO.createImageOutputStream(jpegFiletoSave));
        IIOImage outputImage = new IIOImage(image, null, null);
        jpgWriter.write(null, outputImage, jpgWriteParam);
        jpgWriter.dispose();

    }

Answer 4

在我的古代图书馆中发现了相同的方法：

/**
 * Work method.
 * Reads the jpeg image in rendImage, compresses the image, and writes it back out to outfile.
 * JPEGQuality ranges between 0.0F and 1.0F, 0-lowest, 1-highest. ios is closed internally
 *
 * @param rendImage   [@link RenderedImage} instance with an Rendered Image
 * @param ios         {@link ImageOutputStream} instance,
 *                    note that it is disposed in this method
 * @param JPEGQuality float value for the JPEG compression quality (0..1(max))
 * @return {@code true} if image was successfully compressed
 *         else {@code false} on any error, e.g. bad (null) parameters
 */
public static boolean compressJpegFile( RenderedImage rendImage, ImageOutputStream ios, float JPEGQuality )
{
    if ( rendImage == null )
        return false;
    if ( ios == null )
        return false;
    if ( ( JPEGQuality <= 0.0F ) || ( JPEGQuality > 1.0F ) )
        return false;
    ImageWriter writer = null;
    try
    {

        // Find a jpeg writer
        Iterator iter = ImageIO.getImageWritersByFormatName( "jpg" );
        if ( iter.hasNext() )
            writer = (ImageWriter) iter.next();

        if ( writer == null )
            throw new IllegalArgumentException( "jpg writer not found by call to ImageIO.getImageWritersByFormatName( \"jpg\" )" );
        writer.setOutput( ios );

        // Set the compression quality
        ImageWriteParam iwparam = new MyImageWriteParam();
        iwparam.setCompressionMode( ImageWriteParam.MODE_EXPLICIT );
        iwparam.setCompressionQuality( JPEGQuality );
        //      float res = iwparam.getCompressionQuality();

        // Write the image
        writer.write( null, new IIOImage( rendImage, null, null ), iwparam );

        return true;
    }
    catch ( Exception e )
    {
        return false;
    }
    finally
    {
        if ( writer != null )
            writer.dispose();
        // Cleanup
        try
        {
            ios.flush();
            ios.close();
        }
        catch ( IOException e )
        {
        }
    }
}

Answer 5

如果您需要字节[]输出，请参见下面的@ user_3pij答案的修改版本：

    private static byte[] compressImageToByteArray(BufferedImage image, float quality)
        throws IOException {
    // save jpeg image with specific quality. "1f" corresponds to 100% , "0.7f" corresponds to
    // 70%

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

    ByteArrayOutputStream bos = new ByteArrayOutputStream();
    ImageOutputStream ios = ImageIO.createImageOutputStream(bos);
    jpgWriter.setOutput(ios);
    IIOImage outputImage = new IIOImage(image, null, null);
    jpgWriter.write(null, outputImage, jpgWriteParam);
    byte[] result = bos.toByteArray();
    jpgWriter.dispose();
    return result;
}