如何在java中增加jpeg图像的ppi或dpi

Question

我正在创建一个java程序，我需要增加输入JPEG图像的PPI/DPI并将其保存为JPEG。

谁能给我一些建议，如果这是可行的?

Answer 1

你可以像在这个答案中那样做，除了你必须使用"jpeg"作为格式名称，并且你需要实现setDPI方法来处理特定于jpeg的元数据。

public static final String DENSITY_UNITS_NO_UNITS = "00";
public static final String DENSITY_UNITS_PIXELS_PER_INCH = "01";
public static final String DENSITY_UNITS_PIXELS_PER_CM = "02";
private BufferedImage gridImage;
private void saveGridImage(File output) throws IOException {
    output.delete();
    final String formatName = "jpeg";
    for (Iterator<ImageWriter> iw = ImageIO.getImageWritersByFormatName(formatName); iw.hasNext();) {
        ImageWriter writer = iw.next();
        ImageWriteParam writeParam = writer.getDefaultWriteParam();
        ImageTypeSpecifier typeSpecifier = ImageTypeSpecifier.createFromBufferedImageType(BufferedImage.TYPE_INT_RGB);
        IIOMetadata metadata = writer.getDefaultImageMetadata(typeSpecifier, writeParam);
        if (metadata.isReadOnly() || !metadata.isStandardMetadataFormatSupported()) {
            continue;
        }
        setDPI(metadata);
        final ImageOutputStream stream = ImageIO.createImageOutputStream(output);
        try {
            writer.setOutput(stream);
            writer.write(metadata, new IIOImage(gridImage, null, metadata), writeParam);
        } finally {
            stream.close();
        }
        break;
    }
}
private static void setDPI(IIOMetadata metadata) throws IIOInvalidTreeException {
    String metadataFormat = "javax_imageio_jpeg_image_1.0";
    IIOMetadataNode root = new IIOMetadataNode(metadataFormat);
    IIOMetadataNode jpegVariety = new IIOMetadataNode("JPEGvariety");
    IIOMetadataNode markerSequence = new IIOMetadataNode("markerSequence");
    IIOMetadataNode app0JFIF = new IIOMetadataNode("app0JFIF");
    app0JFIF.setAttribute("majorVersion", "1");
    app0JFIF.setAttribute("minorVersion", "2");
    app0JFIF.setAttribute("thumbWidth", "0");
    app0JFIF.setAttribute("thumbHeight", "0");
    app0JFIF.setAttribute("resUnits", DENSITY_UNITS_PIXELS_PER_INCH);
    app0JFIF.setAttribute("Xdensity", String.valueOf(300));
    app0JFIF.setAttribute("Ydensity", String.valueOf(300));
    root.appendChild(jpegVariety);
    root.appendChild(markerSequence);
    jpegVariety.appendChild(app0JFIF);
    metadata.mergeTree(metadataFormat, root);
}

此代码将PPI设置为300x300，但您可能希望将此变量设置为