问题

public void testJpegBitDepth() throws Exception {
    Path pIn = Paths.get("testing/jpg/box1.jpg"), pOut;
    BufferedImage bi;

    // *******************************************
    // Write 8 bit jpg

    // Init ImageWriter
    Iterator<ImageWriter> it = ImageIO.getImageWritersByFormatName("jpg");
    ImageWriter writer = null;
    while (it.hasNext()) {
        try {
            writer = it.next();

            // Read input
            bi = ImageIO.read(pIn.toFile());
            if (bi == null)
                throw new Exception("Failed to read input file: " + pIn);

            // Convert to gray
            bi = AWTImaging.convertToGray(bi);
            log.debug("Num bands from the image raster: " + bi.getRaster().getNumBands());

            pOut = test.outputDir.resolve("jpegBitDepth-8-"
                    + pIn.getFileName().toString() + ".jpg");

            // Init ImageTypeSpecifier
            ImageTypeSpecifier imageType = ImageTypeSpecifier.createGrayscale(
                    8,                        // 8 bits per pixel 
                    DataBuffer.TYPE_BYTE,     // stored in a byte
                    false);                   // unsigned

            // Init WriteParam
            ImageWriteParam param = writer.getDefaultWriteParam();
            param.setDestinationType(imageType);
            // Not sure if this is required or not, but the same Exception occurs either way
            // param.setSourceBands(new int[] {0});

            // Init meta
            IIOMetadata meta = writer.getDefaultImageMetadata(imageType, param);

            String metadataFormat = "javax_imageio_jpeg_image_1.0";
            IIOMetadataNode root = new IIOMetadataNode(metadataFormat);
            IIOMetadataNode jpegVariety = new IIOMetadataNode("JPEGvariety");
            IIOMetadataNode markerSequence = new IIOMetadataNode("markerSequence");

            // 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
            IIOMetadataNode app0JFIF = new IIOMetadataNode("app0JFIF");

            root.appendChild(jpegVariety);
            root.appendChild(markerSequence);
            jpegVariety.appendChild(app0JFIF);

            meta.mergeTree(metadataFormat, root);

            // Export jpg
            Files.deleteIfExists(pOut);
            ImageOutputStream ios = ImageIO.createImageOutputStream(pOut.toFile());
            writer.setOutput(ios);
            writer.write(meta, new IIOImage(bi, null, meta), param);
            log.debug("Succeeded writing jpeg with writer: " + writer.getClass().toString());
            break;
        } catch (Exception e) {
            log.error("Failed writing jpeg with writer: " + (writer != null ? writer.getClass().toString() : "null"));
            log.error("Ex: " + e);
        }
    }
}

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

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

public void testJpegBitDepth() throws Exception{
Path pIn = Paths.get("testing/jpg/box1.jpg"), pOut;
BufferedImage bi;
//*******************************************
//Write 8 bit jpg
//Init ImageWriter
Iterator<ImageWriter> it = ImageIO.getImageWritersByFormatName("jpg");
ImageWriter writer = null;
while(it.hasNext()) {
try {
writer = it.next();
//Read input
bi = ImageIO.read(pIn.toFile());
if(bi == null)
throw new Exception("Failed to read input file: " + pIn);
//Convert to gray
bi = AWTImaging.convertToGray(bi);
log.debug("Num bands from the image raster: " + bi.getRaster().getNumBands());
pOut = test.outputDir.resolve("jpegBitDepth-8-"
+ pIn.getFileName().toString() + ".jpg");
//Init ImageTypeSpecifier
ImageTypeSpecifier imageType = ImageTypeSpecifier.createGrayscale(
8,						//8 bits per pixel 
DataBuffer.TYPE_BYTE, 	//stored in a byte
false);					//unsigned
//Init WriteParam
ImageWriteParam param = writer.getDefaultWriteParam();
param.setDestinationType(imageType);
//Not sure if this is required or not, but the same Exception occurs either way
//param.setSourceBands(new int[] {0});
//Init meta
IIOMetadata meta = writer.getDefaultImageMetadata(imageType, param);
String metadataFormat = "javax_imageio_jpeg_image_1.0";
IIOMetadataNode root = new IIOMetadataNode(metadataFormat);
IIOMetadataNode jpegVariety = new IIOMetadataNode("JPEGvariety");
IIOMetadataNode markerSequence = new IIOMetadataNode("markerSequence");
//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
IIOMetadataNode app0JFIF = new IIOMetadataNode("app0JFIF");
root.appendChild(jpegVariety);
root.appendChild(markerSequence);
jpegVariety.appendChild(app0JFIF);
meta.mergeTree(metadataFormat, root);
//Export jpg
Files.deleteIfExists(pOut);
ImageOutputStream ios = ImageIO.createImageOutputStream(pOut.toFile());
writer.setOutput(ios);
writer.write(meta, new IIOImage(bi, null, meta), param);
log.debug("Succeded writing jpeg with writer: " + writer.getClass().toString());
break;
}catch(Exception e) {
log.error("Failed writing jpeg with writer: " + (writer != null ? writer.getClass().toString():"null"));
log.error("Ex: " + e);				
}
}
}

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

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：

if (bi.getSampleModel().getNumBands() != 1) {
    ColorModel colorModel = new ComponentColorModel(
        ColorSpace.getInstance(ColorSpace.CS_GRAY), false, false,
        Transparency.OPAQUE, DataBuffer.TYPE_BYTE);

    BufferedImage oneBandedImage = new BufferedImage(colorModel,
        colorModel.createCompatibleWritableRaster(
            bi.getWidth(), bi.getHeight()),
        false, new Properties());
        
    Graphics g = oneBandedImage.createGraphics();
    g.drawImage(bi, 0, 0, null);
    g.dispose();

    bi = oneBandedImage;
}

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：

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。

if (bi.getSampleModel().getNumBands() != 1) {
ColorModel colorModel = new ComponentColorModel(
ColorSpace.getInstance(ColorSpace.CS_GRAY), false, false,
Transparency.OPAQUE, DataBuffer.TYPE_BYTE);
BufferedImage oneBandedImage = new BufferedImage(colorModel,
colorModel.createCompatibleWritableRaster(
bi.getWidth(), bi.getHeight()),
false, new Properties());
Graphics g = oneBandedImage.createGraphics();
g.drawImage(bi, 0, 0, null);
g.dispose();
bi = oneBandedImage;
}

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