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,但是我无法从中加载图像。
旧式的TIFF-JPEG压缩类型6基本上是将正常的JFIF文件嵌套在TIFF包装器中。新式的TIFF-JPEG(压缩类型7)允许将JPEG表数据(霍夫曼,量化)存储在单独的标签中(0x015B JPEGTables)。这使您可以将带有SOI / EOI标记的JPEG数据条带放入文件中,而无需重复Huffman和Quantization表格。这可能是您所看到的文件。单个条带以序列FFD8开头,但缺少Huffman和量化表格。这通常是Photoshop产品写入文件的方式。
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();
很棒的解决方案,对我帮助很大。
补充一点,如果您有多个TIFF页面,您需要重复使用TIFFDirectory
对象定义不同的目录号来读取流并重复上述所有步骤。
TIFFDirectory tdir = new TIFFDirectory(stream, 1);
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;
}
}
使用的辅助方法:
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);
}
如果您正在尝试从TIFF、JPEG或其他格式中提取实际图像,最好使用类库(例如libtiff)来完成此操作。 TIFF是一个非常复杂的规范,虽然您可能能够自行完成并获得一两类图像,但往往会遇到其他频繁出现的情况,特别是“旧式”的JPEG,这是一种被强加给TIFF并不适合整体的子格式。
我的公司Atalasoft为.NET产品提供了非常好的TIFF编解码器。如果您只需要处理单页图像,我们的免费产品就可以完美地满足您的需求。
在.NET领域中,您还可以查看Bit Miracle的管理版本的libtiff。这是该库的相当不错的移植版。