使用ImageIO导出8位深度的JPEG图片。

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英文:

Exporting 8 bit-dpeth JPEG with ImageIO

问题

  1. public void testJpegBitDepth() throws Exception {
  2.     Path pIn = Paths.get("testing/jpg/box1.jpg"), pOut;
  3.     BufferedImage bi;
  5.     // *******************************************
  6.     // Write 8 bit jpg
  8.     // Init ImageWriter
  9.     Iterator<ImageWriter> it = ImageIO.getImageWritersByFormatName("jpg");
  10.     ImageWriter writer = null;
  11.     while (it.hasNext()) {
  12.         try {
  13.             writer = it.next();
  15.             // Read input
  16.             bi = ImageIO.read(pIn.toFile());
  17.             if (bi == null)
  18.                 throw new Exception("Failed to read input file: " + pIn);
  20.             // Convert to gray
  21.             bi = AWTImaging.convertToGray(bi);
  22.             log.debug("Num bands from the image raster: " + bi.getRaster().getNumBands());
  24.             pOut = test.outputDir.resolve("jpegBitDepth-8-"
  25.                     + pIn.getFileName().toString() + ".jpg");
  27.             // Init ImageTypeSpecifier
  28.             ImageTypeSpecifier imageType = ImageTypeSpecifier.createGrayscale(
  29.                     8,                        // 8 bits per pixel 
  30.                     DataBuffer.TYPE_BYTE,     // stored in a byte
  31.                     false);                   // unsigned
  33.             // Init WriteParam
  34.             ImageWriteParam param = writer.getDefaultWriteParam();
  35.             param.setDestinationType(imageType);
  36.             // Not sure if this is required or not, but the same Exception occurs either way
  37.             // param.setSourceBands(new int[] {0});
  39.             // Init meta
  40.             IIOMetadata meta = writer.getDefaultImageMetadata(imageType, param);
  42.             String metadataFormat = "javax_imageio_jpeg_image_1.0";
  43.             IIOMetadataNode root = new IIOMetadataNode(metadataFormat);
  44.             IIOMetadataNode jpegVariety = new IIOMetadataNode("JPEGvariety");
  45.             IIOMetadataNode markerSequence = new IIOMetadataNode("markerSequence");
  47.             // I think we want app0JFIF metadata here, as it can specify a grayscale image https://docs.oracle.com/javase/10/docs/api/javax/imageio/metadata/doc-files/jpeg_metadata.html
  48.             IIOMetadataNode app0JFIF = new IIOMetadataNode("app0JFIF");
  50.             root.appendChild(jpegVariety);
  51.             root.appendChild(markerSequence);
  52.             jpegVariety.appendChild(app0JFIF);
  54.             meta.mergeTree(metadataFormat, root);
  56.             // Export jpg
  57.             Files.deleteIfExists(pOut);
  58.             ImageOutputStream ios = ImageIO.createImageOutputStream(pOut.toFile());
  59.             writer.setOutput(ios);
  60.             writer.write(meta, new IIOImage(bi, null, meta), param);
  61.             log.debug("Succeeded writing jpeg with writer: " + writer.getClass().toString());
  62.             break;
  63.         } catch (Exception e) {
  64.             log.error("Failed writing jpeg with writer: " + (writer != null ? writer.getClass().toString() : "null"));
  65.             log.error("Ex: " + e);
  66.         }
  67.     }
  68. }

I'm getting an Exception thrown from JpegImageWriter, here is the relevant stack trace:

  1. Ex: javax.imageio.IIOException: Metadata components != number of destination bands
  2. File=null,Class=com.sun.imageio.plugins.jpeg.JPEGImageWriter,Method=checkSOFBands,Line=-1
  3. File=null,Class=com.sun.imageio.plugins.jpeg.JPEGImageWriter,Method=writeOnThread,Line=-1
  4. File=null,Class=com.sun.imageio.plugins.jpeg.JPEGImageWriter,Method=write,Line=-1

Also, I know that the BufferedImage is a TYPE_BYTE_BINARY, and the raster has 1 band (I printed this in a debug message above). So the Exception message would make me think that I need to define in the app0JFIF metadata that we are exporting 1 band. I don't know how to define this, though. Does anyone have any experience with this? This metadata is difficult to work with, or is it just me?

Thanks in advance.

英文:

Using Java ImageIO, is it possible to export a jpeg image that has a bit-depth of 8? How would I do this? Even when exporting a BufferedImage of TYPE_BYTE_BINARY, which is a grayscale image, the result is a JPEG with bit-depth of 24.

This is what I have so far.

  1. public void testJpegBitDepth() throws Exception{
  2. Path pIn = Paths.get(&quot;testing/jpg/box1.jpg&quot;), pOut;
  3. BufferedImage bi;
  4. //*******************************************
  5. //Write 8 bit jpg
  6. //Init ImageWriter
  7. Iterator&lt;ImageWriter&gt; it = ImageIO.getImageWritersByFormatName(&quot;jpg&quot;);
  8. ImageWriter writer = null;
  9. while(it.hasNext()) {
  10. try {
  11. writer = it.next();
  12. //Read input
  13. bi = ImageIO.read(pIn.toFile());
  14. if(bi == null)
  15. throw new Exception(&quot;Failed to read input file: &quot; + pIn);
  16. //Convert to gray
  17. bi = AWTImaging.convertToGray(bi);
  18. log.debug(&quot;Num bands from the image raster: &quot; + bi.getRaster().getNumBands());
  19. pOut = test.outputDir.resolve(&quot;jpegBitDepth-8-&quot;
  20. + pIn.getFileName().toString() + &quot;.jpg&quot;);
  21. //Init ImageTypeSpecifier
  22. ImageTypeSpecifier imageType = ImageTypeSpecifier.createGrayscale(
  23. 8,						//8 bits per pixel 
  24. DataBuffer.TYPE_BYTE, 	//stored in a byte
  25. false);					//unsigned
  26. //Init WriteParam
  27. ImageWriteParam param = writer.getDefaultWriteParam();
  28. param.setDestinationType(imageType);
  29. //Not sure if this is required or not, but the same Exception occurs either way
  30. //param.setSourceBands(new int[] {0});
  31. //Init meta
  32. IIOMetadata meta = writer.getDefaultImageMetadata(imageType, param);
  33. String metadataFormat = &quot;javax_imageio_jpeg_image_1.0&quot;;
  34. IIOMetadataNode root = new IIOMetadataNode(metadataFormat);
  35. IIOMetadataNode jpegVariety = new IIOMetadataNode(&quot;JPEGvariety&quot;);
  36. IIOMetadataNode markerSequence = new IIOMetadataNode(&quot;markerSequence&quot;);
  37. //I think we want app0JFIF metadata here, as it can specify a grayscale image https://docs.oracle.com/javase/10/docs/api/javax/imageio/metadata/doc-files/jpeg_metadata.html
  38. IIOMetadataNode app0JFIF = new IIOMetadataNode(&quot;app0JFIF&quot;);
  39. root.appendChild(jpegVariety);
  40. root.appendChild(markerSequence);
  41. jpegVariety.appendChild(app0JFIF);
  42. meta.mergeTree(metadataFormat, root);
  43. //Export jpg
  44. Files.deleteIfExists(pOut);
  45. ImageOutputStream ios = ImageIO.createImageOutputStream(pOut.toFile());
  46. writer.setOutput(ios);
  47. writer.write(meta, new IIOImage(bi, null, meta), param);
  48. log.debug(&quot;Succeded writing jpeg with writer: &quot; + writer.getClass().toString());
  49. break;
  50. }catch(Exception e) {
  51. log.error(&quot;Failed writing jpeg with writer: &quot; + (writer != null ? writer.getClass().toString():&quot;null&quot;));
  52. log.error(&quot;Ex: &quot; + e);				
  53. }
  54. }
  55. }

I'm getting an Exception thrown from JpegImageWriter, here is the relevant stack trace:

  1.     Ex: javax.imageio.IIOException: Metadata components != number of destination bands
  2. File=null,Class=com.sun.imageio.plugins.jpeg.JPEGImageWriter,Method=checkSOFBands,Line=-1
  3. File=null,Class=com.sun.imageio.plugins.jpeg.JPEGImageWriter,Method=writeOnThread,Line=-1
  4. File=null,Class=com.sun.imageio.plugins.jpeg.JPEGImageWriter,Method=write,Line=-1

Also I know that the Buffered Image is a TYPE_BYTE_BINARY, and the raster has 1 band (I printed this in a debug message above). So the Exception message would make me think that I need to define in the app0JFIF metadata that we are exporting 1 band. I don't know how to define this though, does anyone have any experience with this? This metadata is difficult to work with, or is it just me?

Thanks in advance.

答案1

得分: 0

你关于只需要一个通道是正确的。以下是我的操作方法：

  1. if (bi.getSampleModel().getNumBands() != 1) {
  2.     ColorModel colorModel = new ComponentColorModel(
  3.         ColorSpace.getInstance(ColorSpace.CS_GRAY), false, false,
  4.         Transparency.OPAQUE, DataBuffer.TYPE_BYTE);
  6.     BufferedImage oneBandedImage = new BufferedImage(colorModel,
  7.         colorModel.createCompatibleWritableRaster(
  8.             bi.getWidth(), bi.getHeight()),
  9.         false, new Properties());
  10.         
  11.     Graphics g = oneBandedImage.createGraphics();
  12.     g.drawImage(bi, 0, 0, null);
  13.     g.dispose();
  15.     bi = oneBandedImage;
  16. }

经过这样的处理，我不需要直接获取一个ImageWriter，也不需要设置任何元数据；只需要使用ImageIO.write(bi, "JPEG", file)就足够了。

我在结果上运行了/usr/bin/file，得到了以下结果：

  1. JPEG image data，JFIF standard 1.02，aspect ratio，density 1x1，segment length 16，baseline，precision 8，315x180，components 1

我认为components 1部分表示它只有一个通道。

英文:

You are correct about needing one band. Here’s how I did it:

  1. if (bi.getSampleModel().getNumBands() != 1) {
  2. ColorModel colorModel = new ComponentColorModel(
  3. ColorSpace.getInstance(ColorSpace.CS_GRAY), false, false,
  4. Transparency.OPAQUE, DataBuffer.TYPE_BYTE);
  5. BufferedImage oneBandedImage = new BufferedImage(colorModel,
  6. colorModel.createCompatibleWritableRaster(
  7. bi.getWidth(), bi.getHeight()),
  8. false, new Properties());
  9. Graphics g = oneBandedImage.createGraphics();
  10. g.drawImage(bi, 0, 0, null);
  11. g.dispose();
  12. bi = oneBandedImage;
  13. }

After doing that, I didn’t need to directly obtain an ImageWriter and I didn’t need to set any metadata; ImageIO.write(bi, &quot;JPEG&quot;, file) was sufficient.

I ran /usr/bin/file on the result, and got this:

  1. JPEG image data, JFIF standard 1.02, aspect ratio, density 1x1, segment length 16, baseline, precision 8, 315x180, components 1

I assume the components 1 part means that it has only one channel.

huangapple
  • 本文由 发表于 2020年4月11日 09:40:26
  • 转载请务必保留本文链接：https://go.coder-hub.com/61151066.html
  • grayscale
  • image
  • java
  • javax.imageio
  • jpeg
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