使用Java将dpi元数据写入jpeg图像 [英] Write dpi metadata to a jpeg image in Java

问题描述

我正在尝试以编程方式在Java中设置jpeg图像的dpi元数据。图像的来源是扫描仪，因此我从TWAIN获得水平/垂直分辨率以及图像原始数据。我想保存此信息以获得更好的打印效果。

I am trying to programatically set the dpi metadata of an jpeg image in Java. The source of the image is a scanner, so I get the horizontal/vertical resolution from TWAIN, along with the image raw data. I'd like to save this info for better print results.

这是我到目前为止的代码。它将原始图像（byteArray）保存为JPEG文件，但忽略了我通过IIOMetadata指定的X / Ydensity信息。我有什么建议我做错了吗？

Here's the code I have so far. It saves the raw image (byteArray) to a JPEG file, but it ignores the X/Ydensity information I specify via IIOMetadata. Any advice what I'm doing wrong?

任何其他解决方案（第三方库等）也会受到欢迎。

Any other solution (third-party library, etc) would be welcome too.

import java.awt.image.BufferedImage;
import java.awt.image.WritableRaster;
import java.io.File;

import javax.imageio.IIOImage;
import javax.imageio.ImageIO;
import javax.imageio.ImageTypeSpecifier;
import javax.imageio.metadata.IIOMetadata;
import javax.imageio.plugins.jpeg.JPEGImageWriteParam;
import javax.imageio.stream.ImageOutputStream    

import org.w3c.dom.Element;    
import com.sun.imageio.plugins.jpeg.JPEGImageWriter;

public boolean saveJpeg(int[] byteArray, int width, int height, int dpi, String file)
{
    BufferedImage bufferedImage = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);

    WritableRaster wr = bufferedImage.getRaster();
    wr.setPixels(0, 0, width, height, byteArray);

    try
    {           
        // Image writer 
        JPEGImageWriter imageWriter = (JPEGImageWriter) ImageIO.getImageWritersBySuffix("jpeg").next();
        ImageOutputStream ios = ImageIO.createImageOutputStream(new File(file));
        imageWriter.setOutput(ios);

        // Compression
        JPEGImageWriteParam jpegParams = (JPEGImageWriteParam) imageWriter.getDefaultWriteParam();
        jpegParams.setCompressionMode(JPEGImageWriteParam.MODE_EXPLICIT);
        jpegParams.setCompressionQuality(0.85f);

        // Metadata (dpi)
        IIOMetadata data = imageWriter.getDefaultImageMetadata(new ImageTypeSpecifier(bufferedImage), jpegParams);
        Element tree = (Element)data.getAsTree("javax_imageio_jpeg_image_1.0");
        Element jfif = (Element)tree.getElementsByTagName("app0JFIF").item(0);
        jfif.setAttribute("Xdensity", Integer.toString(dpi));
        jfif.setAttribute("Ydensity", Integer.toString(dpi));
        jfif.setAttribute("resUnits", "1"); // density is dots per inch         

        // Write and clean up
        imageWriter.write(data, new IIOImage(bufferedImage, null, null), jpegParams);
        ios.close();
        imageWriter.dispose();
    }
    catch (Exception e)
    {
       return false;
    }

    return true;
}

谢谢！

推荐答案

此处未考虑的一些问题：

Some issues that were not considered here:

1. 树未直接映射到IOMetaData。要从树应用数据，请在设置密度和栅格参数后添加以下调用：

1. The tree is not directly mapped to the IOMetaData. To apply data from tree, add following call after setting the densities and raster parameters:

data.setFromTree("javax_imageio_jpeg_image_1.0", tree);

不要将元数据用作写入调用中的第一个参数。参见 JPEGImageWriter＃write（IIOMetaData，IIOImage，ImageWriteParam）。如果streamMetaData不为NULL，则会生成警告（WARNING_STREAM_METADATA_IGNORED）。

don't use the meta data as first parameter in the write call. See JPEGImageWriter#write(IIOMetaData, IIOImage, ImageWriteParam). If streamMetaData is not NULL, a warning (WARNING_STREAM_METADATA_IGNORED) will be generated.

将元数据设置为 IOMetadata IOImage 。 JPEGImageWriter使用这些元数据。然后正确的写调用是

set the meta data as IOMetadata of the IOImage. These meta data are used by JPEGImageWriter. The correct write call then is

imageWriter.write(null, new IIOImage(F_scaledImg, null, data), jpegParams);

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