java设置图像dpi

 

private BufferedImage gridImage;
 ...

 private void saveGridImage(File output) throws IOException {
    output.delete();

    final String formatName = "png";

    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 void setDPI(IIOMetadata metadata) throws IIOInvalidTreeException {

    // for PMG, it's dots per millimeter
    double dotsPerMilli = 1.0 * DPI / 10 / INCH_2_CM;

    IIOMetadataNode horiz = new IIOMetadataNode("HorizontalPixelSize");
    horiz.setAttribute("value", Double.toString(dotsPerMilli));

    IIOMetadataNode vert = new IIOMetadataNode("VerticalPixelSize");
    vert.setAttribute("value", Double.toString(dotsPerMilli));

    IIOMetadataNode dim = new IIOMetadataNode("Dimension");
    dim.appendChild(horiz);
    dim.appendChild(vert);

    IIOMetadataNode root = new IIOMetadataNode("javax_imageio_1.0");
    root.appendChild(dim);

    metadata.mergeTree("javax_imageio_1.0", root);
 }

 

 

代码来源：http://*.com/questions/321736/how-to-set-dpi-information-in-an-image

其中DPI就是你要设置的值，java中默认是72，如果需要打印图片，可能就要设置为300

INCH_2_CM表示1英寸等于多少厘米，这里就是2.54