如何在图像中设置DPI信息？ [英] How to set DPI information in an image?

问题描述

我有一个应用程序，我想导出高分辨率（或更确切地说，高像素密度？）图像进行打印 - 例如，我想要以每英寸250点（DPI）打印的图像，而不是默认值，我理解为72 DPI。

I have an application that I want to export high-resolution (or rather, high pixel density?) images for printing - for example, I want images that print at 250 dots per inch (DPI), instead of the default, which I understand to be 72 DPI.

我正在使用带有Graphics2D对象的BufferedImage来绘制图像，然后使用ImageIO.write（）来保存图像。

I'm using a BufferedImage with a Graphics2D object to draw the image, then ImageIO.write() to save the image.

我知道如何设置DPI吗？

Any idea how I can set the DPI?

推荐答案

Kurt的回答显示方式，仍然需要我相当长的时间来运行它，所以这里是保存PNG时设置DPI的代码。要获得合适的作者，还有很多工作要做...

Kurt's answer showed the way, still it took me quite some time to get it run, so here is the code that sets DPI when saving a PNG. There is a lot to do to get the proper writers and such...

 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);
 }

这篇关于如何在图像中设置DPI信息？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！