如何在Java中增加jpeg图像的ppi或dpi? [英] How to increase jpeg image ppi or dpi in java?

问题描述

我正在创建一个Java程序，需要增加输入JPEG图像的PPI/DPI并将其另存为JPEG.

I am creating a java program which I need to increase input JPEG image's PPI/DPI and save it as JPEG.

如果可行，任何人都可以给我一些帮助吗?

Anyone can give me some hits on if this is workable?

推荐答案

您可以像在此答案中那样进行操作，除了必须使用"jpeg"作为格式名称，并且需要实现setDPI方法才能使用特定于JPEG的元数据.

You can do it like in this answer, except you have to use "jpeg" as the format name and you need to implement the setDPI method to work with JPEG-specific metadata.

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，但您可能需要设置此变量.

This code sets the PPI to 300x300 but you may want to make this variable.

这篇关于如何在Java中增加jpeg图像的ppi或dpi?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！