java图像压缩任何图像格式(jpg，PNG，gif)

Question

我正在使用下面给出的代码对 jpeg 图像进行图像压缩。

File input = new File("digital_image_processing.jpg");
BufferedImage image = ImageIO.read(input);

File compressedImageFile = new File("compress.jpg");  
OutputStream os = new FileOutputStream(compressedImageFile);

 Iterator<ImageWriter>writers = ImageIO.getImageWritersByFormatName("jpg");
 ImageWriter writer = (ImageWriter) writers.next();

 ImageOutputStream ios = ImageIO.createImageOutputStream(os);
 writer.setOutput(ios);

 ImageWriteParam param = writer.getDefaultWriteParam();

 param.setCompressionMode(ImageWriteParam.MODE_EXPLICIT);
 param.setCompressionQuality(0.05f);

 writer.write(null, new IIOImage(image, null, null), param);

但是当我尝试通过更改 ImageIO.getImageWritersByFormatName("png"); 来获取 PNG 格式时； 它给我错误，表示不支持压缩。

那么我应该如何修改上面的代码才能支持所有图像格式压缩

Answer 1

您的代码的问题是您使用了 ImageWriter.getDefaultWriteParam()。来自 ImageWriter.java 的以下引用:

public ImageWriteParam getDefaultWriteParam()

Returns a new ImageWriteParam object of the appropriate type for this file format containing default values, that is, those values that would be used if no ImageWriteParam object were specified. This is useful as a starting point for tweaking just a few parameters and otherwise leaving the default settings alone.

The default implementation constructs and returns a new ImageWriteParam object that does not allow tiling, progressive encoding, or compression, and that will be localized for the current Locale (i.e., what you would get by calling new ImageWriteParam(getLocale()).

Individual plug-ins may return an instance of ImageWriteParam with additional optional features enabled, or they may return an instance of a plug-in specific subclass of ImageWriteParam.

实际行为取决于特定 ImageWriteParam 的单独实现。我相信 JPG 图像起作用的原因是 JPG 的 ImageWriteParam 为默认 ImageWriteParam 设置了 canWriteCompressed protected 字段，但对于 PNG 图像，由于某种原因它没有这样做。

如果你查看com.sun.imageio.plugins.png.PNGImageWriteParam.java，你会发现它确实没有设置。

为了使您的代码正常工作，您可以这样做:

  File input = new File("digital_image_processing.jpg");
  BufferedImage image = ImageIO.read(input);

  File compressedImageFile = new File("compress.jpg");  
  OutputStream os = new FileOutputStream(compressedImageFile);

  Iterator<ImageWriter>writers = ImageIO.getImageWritersByFormatName("jpg");
  ImageWriter writer = (ImageWriter) writers.next();

  ImageOutputStream ios = ImageIO.createImageOutputStream(os);
  writer.setOutput(ios);

  ImageWriteParam param = writer.getDefaultWriteParam();
  // Check if canWriteCompressed is true
  if(param.canWriteCompressed()) {
     param.setCompressionMode(ImageWriteParam.MODE_EXPLICIT);
     param.setCompressionQuality(0.05f);
  }
  // End of check
  writer.write(null, new IIOImage(image, null, null), param);

更新:我试图找到一种方法让您在 ImageIO 框架内微调 PNG 图像压缩。但不幸的是，考虑到目前的实现情况，这似乎几乎是不可能的。 Java PNG writer 插件具有固定过滤 - 自适应过滤和固定放气级别 - 9，这是它能做的最好的事情。