写PNG文件与更少的磁盘大小在Java中

Question

我有一个BufferedImage:

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

我已经使用以下代码将此图像保存为PNG文件:

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);
    }

当代码执行时，它创建一个PNG文件与400 DPI和磁盘大小168 MB;这太过分了。

是否有任何方法或参数我可以用来保存较小的PNG?

以前，我有一个1.20 GB的TIFF文件，当我使用imagemagick以400 DPI将其转换为PNG时，生成的文件大小仅为700 KB。

所以，我想我可以把上面的文件保存得更小。

pngj可以帮我吗?因为我现在有了一个png文件可以在pngj库中读取

Answer 1

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(不太重要的)PNG压缩参数或多或少地压缩。

当我使用imagemic转换为PNG使用400 DPI生成的文件大小只有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)你是说你得到一个14400x14400 ARGB的700KB吗?这将代表1/1000的压缩，很难相信，除非图像实际上是平坦的。你应该首先了解这里发生了什么。

无论如何，这里有一个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();
}

Answer 2

我将尝试修改您正在创建的writeParam对象的设置。目前你正在调用getDefaultWriteParam();，它给你一个基本的writeParam对象。我猜默认是NO压缩。

这样做之后，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);

见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)

Answer 3

PNGJ的示例代码，适用于2。X版本的leonbloy的PNGJ库

      /** writes a BufferedImage of type TYPE_INT_ARGB to PNG using PNGJ */
  public static void writePNGJARGB(BufferedImage bi, /*OutputStream os, */File file) {
      
      System.out.println(".....entering PNGj alternative image file save mode....." );
        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(file, imi, false);
                // PngWriter pngw = new PngWriter(file,imginfo,overwrite); //params
         pngw.setCompLevel(7); // tuning compression, not critical usually
         pngw.setFilterType(FilterType.FILTER_PAETH); // tuning, see what you prefer here
                System.out.println("..... PNGj metadata = "+pngw.getMetadata() );
        DataBufferInt db =((DataBufferInt) bi.getRaster().getDataBuffer());
        if(db.getNumBanks()!=1) {
                    throw new PngjException("This method expects one bank");
                }
        SinglePixelPackedSampleModel samplemodel =  (SinglePixelPackedSampleModel) bi.getSampleModel();
        ImageLineInt line = new ImageLineInt(imi);
        int[] dbbuf = db.getData();
        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 = dbbuf[elem++];
                                line.getScanline()[j++] =  (sample & 0xFF0000)>>16; // R
                                line.getScanline()[j++] =  (sample & 0xFF00)>>8; // G
                                line.getScanline()[j++] =  (sample & 0xFF); // B
                                line.getScanline()[j++] =  (((sample & 0xFF000000)>>24)&0xFF); // A
                        }
                      //pngw.writeRow(line, /*imi.rows*/);
                        pngw.writeRow(line);  
                }
                pngw.end();
    }