来自Tiff的Jpeg (jpeg压缩)

Question

如何从JPEG压缩的TIFF文件中提取图像？

我已经根据StripOffests和StripBytesCount字段读取了字节，但我无法从它们加载图像。

Answer 1

老式的TIFF-JPEG (压缩类型6)基本上是在TIFF包装器中填充一个普通的JFIF文件。较新样式的TIFF-JPEG (压缩类型7)允许将JPEG表数据(霍夫曼、量化)存储在单独的标记(0x015B JPEGTables)中。这允许您将带有SOI/EOI标记的JPEG数据条带放入文件中，而不必重复霍夫曼和量化表。这可能就是您在文件中看到的内容。单个条带以序列FFD8开始，但缺少霍夫曼和量化表。这是Photoshop产品通常写入文件的方式。

Answer 2

使用JAI：

int TAG_COMPRESSION             = 259;
int TAG_JPEG_INTERCHANGE_FORMAT = 513;

int COMP_JPEG_OLD  = 6;
int COMP_JPEG_TTN2 = 7;

SeekableStream stream = new ByteArraySeekableStream(imageData);
TIFFDirectory    tdir = new TIFFDirectory(stream, 0);
int       compression = tdir.getField(TAG_COMPRESSION).getAsInt(0);

// Decoder name
String decoder2use = "tiff";
if (compression == COMP_JPEG_OLD) { 
    // Special handling for old/unsupported JPEG-in-TIFF format:
    // {@link: http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4929147 }
    stream.seek(tdir.getField(TAG_JPEG_INTERCHANGE_FORMAT).getAsLong(0));
    decoder2use = "jpeg";
}

// Decode image
ImageDecoder  dec = ImageCodec.createImageDecoder(decoder2use, stream, null);
RenderedImage img = dec.decodeAsRenderedImage();

很好的解决方案，帮了我很多。只是补充一下，如果你在TIFF中有多个页面，你必须在TIFFDirectory对象中定义一个不同的目录号码来重复读取流，并重复上面的所有步骤。

TIFFDirectory tdir = new TIFFDirectory(stream, 1);

Answer 3

上面提到的libtiff库的问题是，它确实提取了图像，然后将其重新压缩，这意味着在jpg的情况下会出现另一种质量损失。也就是说，只要调用NET Framework的GDI+方法，我就可以在不使用第三方lib的情况下完成同样的工作。

这个线程的初始作者试图在不重新压缩的情况下获得jpeg二进制文件，这也正是我正在尝试做的。

这是一个可能的解决方案，如果你可以忍受质量损失，并且不想使用.NET库类以外的任何东西：

    public static int SplitMultiPage(string sourceFileName, string targetPath)
    {
        using (Image multipageTIFF = Image.FromFile(sourceFileName))
        { 
            int pageCount = multipageTIFF.GetFrameCount(FrameDimension.Page);

            if (pageCount > 1)
            {
                string sFileName = Path.GetFileNameWithoutExtension (sourceFileName);
                for (int i = 0; i < pageCount; i++)
                {                        
                    multipageTIFF.SelectActiveFrame(FrameDimension.Page, i);

                    // ein einzelner Frame könnte auch ein anderes Format haben, z.B. JPG, PNG, BMP, etc.
                    // Damit die Datei die korrekte Endung bekommt, holen wir uns eine Endung aus der Beschreibung des Codecs
                    // Interessanterweise liefert uns das RawFormat im Fall TIFF (der einzige Multiframefall) immer den Codec für TIFF, 
                    // statt den des Frames
                    ImageCodecInfo codec = Helpers.GetEncoder(multipageTIFF.RawFormat);
                    string sExtension = codec.FilenameExtension.Split(new char[] { ';' })[0];
                    sExtension = sExtension.Substring(sExtension.IndexOf('.') + 1);
                    string newFileName = Path.Combine(targetPath, string.Format("{0}_{1}.{2}", sFileName, i + 1, sExtension));

                    EncoderParameters encoderParams = new EncoderParameters(2);
                    encoderParams.Param[0] = new EncoderParameter(System.Drawing.Imaging.Encoder.SaveFlag, (long)EncoderValue.LastFrame);

                    // für TIF 1 Bit machen wir CompressionCCITT4 Kompression, da das die besten Ergebnisse liefert
                    switch (GetCompressionType(multipageTIFF))
                    {

                        case 1: // No compression -> BMP?
                            encoderParams.Param[1] = new EncoderParameter(System.Drawing.Imaging.Encoder.Compression, (long)EncoderValue.CompressionNone);
                            break;
                        case 2: // CCITT modified Huffman RLE 32773 = PackBits compression, aka Macintosh RLE
                            encoderParams.Param[1] = new EncoderParameter(System.Drawing.Imaging.Encoder.Compression, (long)EncoderValue.CompressionRle);
                            break;
                        case 3: // CCITT Group 3 fax encoding
                            encoderParams.Param[1] = new EncoderParameter(System.Drawing.Imaging.Encoder.Compression, (long)EncoderValue.CompressionCCITT3);
                            break;
                        case 4: // CCITT Group 4 fax encoding
                            encoderParams.Param[1] = new EncoderParameter(System.Drawing.Imaging.Encoder.Compression, (long)EncoderValue.CompressionCCITT4);
                            break;
                        case 5: // LZW
                            encoderParams.Param[1] = new EncoderParameter(System.Drawing.Imaging.Encoder.Compression, (long)EncoderValue.CompressionLZW);
                            break;
                        case 6: //JPEG ('old-style' JPEG, later overriden in Technote2)
                        case 7: // Technote2 overrides old-style JPEG compression, and defines 7 = JPEG ('new-style' JPEG)
                            {
                                codec = Helpers.GetEncoder(ImageFormat.Jpeg);
                                encoderParams.Param[1] = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, 90);
                            }
                            break;
                    }

                    multipageTIFF.Save(newFileName, codec, encoderParams);
                }
            }

            return pageCount;
        }
    }

使用的helper方法：

    public static ImageCodecInfo GetEncoder(ImageFormat format)
    {

        ImageCodecInfo[] codecs = ImageCodecInfo.GetImageDecoders();

        foreach (ImageCodecInfo codec in codecs)
        {
            if (codec.FormatID == format.Guid)
            {
                return codec;
            }
        }
        return null;
    }

读取压缩标志：

    public static int GetCompressionType(Image image)
    {
        /*  TIFF Tag Compression
            IFD     Image
            Code        259 (hex 0x0103)
            Name        Compression
            LibTiff name        TIFFTAG_COMPRESSION
            Type        SHORT
            Count       1
            Default     1 (No compression)
            Description

            Compression scheme used on the image data.

            The specification defines these values to be baseline:

            1 = No compression
            2 = CCITT modified Huffman RLE
            32773 = PackBits compression, aka Macintosh RLE

            Additionally, the specification defines these values as part of the TIFF extensions:

            3 = CCITT Group 3 fax encoding
            4 = CCITT Group 4 fax encoding
            5 = LZW
            6 = JPEG ('old-style' JPEG, later overriden in Technote2)

            Technote2 overrides old-style JPEG compression, and defines:

            7 = JPEG ('new-style' JPEG)

            Adobe later added the deflate compression scheme:

            8 = Deflate ('Adobe-style')

            The TIFF-F specification (RFC 2301) defines:

            9 = Defined by TIFF-F and TIFF-FX standard (RFC 2301) as ITU-T Rec. T.82 coding, using ITU-T Rec. T.85 (which boils down to JBIG on black and white).
            10 = Defined by TIFF-F and TIFF-FX standard (RFC 2301) as ITU-T Rec. T.82 coding, using ITU-T Rec. T.43 (which boils down to JBIG on color). 
        */
        int compressionTagIndex = Array.IndexOf(image.PropertyIdList, 0x103);

        PropertyItem compressionTag = image.PropertyItems[compressionTagIndex];

        return BitConverter.ToInt16(compressionTag.Value, 0);
    }