3

I have a BufferedImage: 

BufferedImage bi = new BufferedImage(14400, 14400, BufferedImage.TYPE_INT_ARGB);

I have saved this image to a PNG file using the following code:

public static void saveGridImage(BufferedImage sourceImage, int DPI,
            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, DPI);

            final ImageOutputStream stream = ImageIO
                    .createImageOutputStream(output);
            try {
                writer.setOutput(stream);
                writer.write(metadata,
                        new IIOImage(sourceImage, null, metadata), writeParam);
            } finally {
                stream.close();
            }
            break;
        }
    }

    public static void setDPI(IIOMetadata metadata, int DPI)
            throws IIOInvalidTreeException {

        double INCH_2_CM = 2.54;

        // for PNG, 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);
    }

When the code executes it creates an PNG file with 400 DPI and Disk Size of 168 MB; this is too much.

Is there any way or parameters I can use to save a smaller PNG?

Before, I had a 1.20 GB TIFF file, and when I converted it to PNG using imagemagick at 400 DPI, the resulting file size was only 700 KB.

So, I think I might be able to save the above file smaller.

Can pngj help me? Because I now have a png file which I can read in pngj library.

4

2 回答 2

2

14400x14400 ARGB8 图像的原始（未压缩）大小为 791MB。它将根据其性质（具有均匀或平滑的区域）和根据（不太重要的）PNG 压缩参数或多或少地进行压缩。

当我使用 imagemagic 将其转换为使用 400 DPI 的 PNG 时，生成的文件大小仅为 700 KB。

（我不明白你为什么说 DPI，这无关紧要，重要的是像素大小）你是说你得到 700KB 的 14400x14400 ARGB？这将代表 1/1000 的压缩，除非图像实际上是平坦的，否则很难相信。您应该首先了解这里发生了什么。

无论如何，这是一个使用 PNGJ 的示例代码

/** writes a BufferedImage of type TYPE_INT_ARGB to PNG using PNGJ */
public static void writeARGB(BufferedImage bi, OutputStream os) {
    if(bi.getType() != BufferedImage.TYPE_INT_ARGB) 
       throw new PngjException("This method expects  BufferedImage.TYPE_INT_ARGB" );
    ImageInfo imi = new ImageInfo(bi.getWidth(), bi.getHeight(), 8, true);
    PngWriter pngw = new PngWriter(os, imi);
    pngw.setCompLevel(9);// maximum compression, not critical usually
    pngw.setFilterType(FilterType.FILTER_AGGRESSIVE); // see what you prefer here
    DataBufferInt db =((DataBufferInt) bi.getRaster().getDataBuffer());
    SinglePixelPackedSampleModel samplemodel =  (SinglePixelPackedSampleModel) bi.getSampleModel();
    if(db.getNumBanks()!=1) 
        throw new PngjException("This method expects one bank");
    ImageLine line = new ImageLine(imi);
    for (int row = 0; row < imi.rows; row++) {
        int elem=samplemodel.getOffset(0,row);
        for (int col = 0,j=0; col < imi.cols; col++) {
            int sample = db.getElem(elem++);
            line.scanline[j++] =  (sample & 0xFF0000)>>16; // R
            line.scanline[j++] =  (sample & 0xFF00)>>8; // G
            line.scanline[j++] =  (sample & 0xFF); // B
            line.scanline[j++] =  (((sample & 0xFF000000)>>24)&0xFF); // A
        }
        pngw.writeRow(line, row);
    }
    pngw.end();
}
于 2013-03-24T15:11:39.300 回答
1

我会尝试摆弄您正在创建的 writeParam 对象的设置。目前您正在调用getDefaultWriteParam();它，它为您提供了一个基本的 writeParam 对象。我的猜测是默认为无压缩。

之后，您可能可以设置一些压缩模式来减小文件大小。

writeParam.setCompressionMode(int mode);
writeParam.setCompressionQuality(float quality);
writeParam.setCompressionType(String compressionType);

请参阅http://docs.oracle.com/javase/6/docs/api/javax/imageio/ImageWriteParam.html 特别是http://docs.oracle.com/javase/6/docs/api/javax/imageio/ ImageWriteParam.html#setCompressionMode(int)

于 2013-03-24T13:24:23.690 回答