使用 /CCITTFaxDecode 过滤器从 PDF 中提取图像

Question

我有一个通过扫描软件生成的 pdf 文件。该 pdf 每页有 1 个 TIFF 图像。我想从每个页面中提取 TIFF 图像。

我正在使用 iTextSharp，并且已成功找到图像，并且可以从 PdfReader.GetStreamBytesRaw 方法取回原始字节。问题是，正如我之前的许多人所发现的那样，iTextSharp 不包含 PdfReader.CCITTFaxDecode 方法。

我还知道什么？即使没有 iTextSharp，我也可以在记事本中打开 pdf 并使用 /Filter /CCITTFaxDecode 找到流，并且我从 /DecodeParams 知道它正在使用 CCITTFaxDecode 组 4。

有人知道吗？那里知道如何从我的 pdf 中获取 CCITTFaxDecode 过滤器图像吗？

Answer 1

实际上，vbcrlfuser的答案确实对我有帮助，但代码对于当前版本的BitMiracle.LibTiff.NET来说不太正确，因为我可以下载它。在当前版本中，等效代码如下所示：

using iTextSharp.text.pdf;
using BitMiracle.LibTiff.Classic;

...
      Tiff tiff = Tiff.Open("C:\\test.tif", "w");
      tiff.SetField(TiffTag.IMAGEWIDTH, UInt32.Parse(pd.Get(PdfName.WIDTH).ToString()));
      tiff.SetField(TiffTag.IMAGELENGTH, UInt32.Parse(pd.Get(PdfName.HEIGHT).ToString()));
      tiff.SetField(TiffTag.COMPRESSION, Compression.CCITTFAX4);
      tiff.SetField(TiffTag.BITSPERSAMPLE, UInt32.Parse(pd.Get(PdfName.BITSPERCOMPONENT).ToString()));
      tiff.SetField(TiffTag.SAMPLESPERPIXEL, 1);
      tiff.WriteRawStrip(0, raw, raw.Length);
      tiff.Close();

使用上述代码，我终于在 C:\test.tif 中获得了一个有效的 Tiff 文件。谢谢你，vbcrlfuser！

Answer 2

这个库... http://www.bitmiracle.com/libtiff/ 并且下面的示例应该让您顺利完成 99% 的任务

string filter = pd.Get(PdfName.FILTER).ToString();
string width = pd.Get(PdfName.WIDTH).ToString();
string height = pd.Get(PdfName.HEIGHT).ToString();
string bpp = pd.Get(PdfName.BITSPERCOMPONENT).ToString();

switch (filter)
{
   case "/CCITTFaxDecode":

      byte[] data = PdfReader.GetStreamBytesRaw((PRStream)pdfStream);
      int tiff = TIFFOpen("example.tif", "w");
      TIFFSetField(tiff, (uint)BitMiracle.LibTiff.Classic.TiffTag.IMAGEWIDTH,(uint)Int32.Parse(width));
      TIFFSetField(tiff, (uint)BitMiracle.LibTiff.Classic.TiffTag.IMAGEHEIGHT, (uint)Int32.Parse(height));
      TIFFSetField(tiff, (uint)BitMiarcle.LibTiff.Classic.TiffTag.COMPRESSION, (uint)BitMiracle.Libtiff.Classic.Compression.CCITTFAX4);
      TIFFSetField(tiff, (uint)BitMiracle.LibTiff.Classic.TiffTag.BITSPERSAMPLE, (uint)Int32.Parse(bpp));
      TIFFSetField(tiff, (uint)BitMiarcle.Libtiff.Classic.TiffTag.SAMPLESPERPIXEL,1 );

      IntPtr pointer = Marshal.AllocHGlobal(data.length);
      Marshal.copy(data, 0, pointer, data.length);
      TIFFWriteRawStrip(tiff, 0, pointer, data.length);
      TIFFClose(tiff);

      break;




      break;

}

Answer 3

这是Python的实现：

import PyPDF2
import struct

"""
Links:
PDF format: http://www.adobe.com/content/dam/Adobe/en/devnet/acrobat/pdfs/pdf_reference_1-7.pdf
CCITT Group 4: https://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-T.6-198811-I!!PDF-E&type=items
Extract images from pdf: http://stackoverflow.com/questions/2693820/extract-images-from-pdf-without-resampling-in-python
Extract images coded with CCITTFaxDecode in .net: http://stackoverflow.com/questions/2641770/extracting-image-from-pdf-with-ccittfaxdecode-filter
TIFF format and tags: http://www.awaresystems.be/imaging/tiff/faq.html
"""


def tiff_header_for_CCITT(width, height, img_size, CCITT_group=4):
    tiff_header_struct = '<' + '2s' + 'h' + 'l' + 'h' + 'hhll' * 8 + 'h'
    return struct.pack(tiff_header_struct,
                       b'II',  # Byte order indication: Little indian
                       42,  # Version number (always 42)
                       8,  # Offset to first IFD
                       8,  # Number of tags in IFD
                       256, 4, 1, width,  # ImageWidth, LONG, 1, width
                       257, 4, 1, height,  # ImageLength, LONG, 1, lenght
                       258, 3, 1, 1,  # BitsPerSample, SHORT, 1, 1
                       259, 3, 1, CCITT_group,  # Compression, SHORT, 1, 4 = CCITT Group 4 fax encoding
                       262, 3, 1, 0,  # Threshholding, SHORT, 1, 0 = WhiteIsZero
                       273, 4, 1, struct.calcsize(tiff_header_struct),  # StripOffsets, LONG, 1, len of header
                       278, 4, 1, height,  # RowsPerStrip, LONG, 1, lenght
                       279, 4, 1, img_size,  # StripByteCounts, LONG, 1, size of image
                       0  # last IFD
                       )

pdf_filename = 'scan.pdf'
pdf_file = open(pdf_filename, 'rb')
cond_scan_reader = PyPDF2.PdfFileReader(pdf_file)
for i in range(0, cond_scan_reader.getNumPages()):
    page = cond_scan_reader.getPage(i)
    xObject = page['/Resources']['/XObject'].getObject()
    for obj in xObject:
        if xObject[obj]['/Subtype'] == '/Image':
            """
            The  CCITTFaxDecode filter decodes image data that has been encoded using
            either Group 3 or Group 4 CCITT facsimile (fax) encoding. CCITT encoding is
            designed to achieve efficient compression of monochrome (1 bit per pixel) image
            data at relatively low resolutions, and so is useful only for bitmap image data, not
            for color images, grayscale images, or general data.

            K < 0 --- Pure two-dimensional encoding (Group 4)
            K = 0 --- Pure one-dimensional encoding (Group 3, 1-D)
            K > 0 --- Mixed one- and two-dimensional encoding (Group 3, 2-D)
            """
            if xObject[obj]['/Filter'] == '/CCITTFaxDecode':
                if xObject[obj]['/DecodeParms']['/K'] == -1:
                    CCITT_group = 4
                else:
                    CCITT_group = 3
                width = xObject[obj]['/Width']
                height = xObject[obj]['/Height']
                data = xObject[obj]._data  # sorry, getData() does not work for CCITTFaxDecode
                img_size = len(data)
                tiff_header = tiff_header_for_CCITT(width, height, img_size, CCITT_group)
                img_name = obj[1:] + '.tiff'
                with open(img_name, 'wb') as img_file:
                    img_file.write(tiff_header + data)
                #
                # import io
                # from PIL import Image
                # im = Image.open(io.BytesIO(tiff_header + data))
pdf_file.close()

Answer 4

已经为此编写了扩展 (c#)。

PdfDictionary item;
if (item.IsImage()) {
  Image image = item.ToImage();
}