英文:
Exporting 8 bit-dpeth JPEG with ImageIO
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.
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.
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);
}
}
}
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 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：
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。
英文:
You are correct about needing one band. Here’s how I did it:
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;
}
After doing that, I didn’t need to directly obtain an ImageWriter and I didn’t need to set any metadata; ImageIO.write(bi, "JPEG", file) was sufficient.
I ran /usr/bin/file on the result, and got this:
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.
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