将 dpi 元数据写入 Java 中的 jpeg 图像

问题描述

我试图在 Java 中以编程方式设置 jpeg 图像的 dpi 元数据.图像的来源是扫描仪，因此我从 TWAIN 获得了水平/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) 保存到 JPEG 文件，但它忽略了我通过 IIOMetadata 指定的 X/Y密度信息.任何建议我做错了什么?

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?

也欢迎任何其他解决方案(第三方库等).

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

这里没有考虑的一些问题:

Some issues that were not considered here:

1. 树没有直接映射到 IOMetaData.要应用树中的数据，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.

设置元数据为IOImage的IOMetadata.这些元数据由 JPEGImageWriter 使用.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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