C#でPDFファイルから画像を抜き出す モノクロTIFF編 (iTextSharp)

using System;
using System.Collections.Generic;
using System.IO;
using System.Drawing;
using System.Drawing.Imaging;
using iTextSharp.text.pdf;


namespace ConsoleApplication1
{
    class Program
    {
        static void Main()
        {
            PDFtoImage(@"C:\test.pdf", @"C:\images\");
        }

        static void PDFtoImage(string pdfName, string imgFolder)
        {
            var imgName = Path.GetFileNameWithoutExtension(pdfName);

            var pdf = new PdfReader(pdfName);
            var images = new List<PdfObject>();
            int n = pdf.NumberOfPages;
            for (int i = 1; i <= n; i++)
            {
                PdfDictionary pg = pdf.GetPageN(i);
                CollectImage(pg, images);
            }

            for (int i = 0; i < images.Count; ++i)
            {
                var obj = (PRIndirectReference)images[i];
                var pfdStream = (PRStream)pdf.GetPdfObject(obj.Number);
                byte[] bytes = PdfReader.GetStreamBytesRaw(pfdStream);

                var tg = (PdfDictionary)PdfReader.GetPdfObject(images[i]);
                var filter = (PdfName)tg.Get(PdfName.FILTER);
                if (PdfName.CCITTFAXDECODE.Equals(filter))
                {
                    var wid = UInt32.Parse(tg.Get(PdfName.WIDTH).ToString());
                    var hei = UInt32.Parse(tg.Get(PdfName.HEIGHT).ToString());
                    var bpc = UInt32.Parse(tg.Get(PdfName.BITSPERCOMPONENT).ToString());
                    var cmp = Compression.CCITTFAX3;
                    var parms = (PdfDictionary)tg.Get(PdfName.DECODEPARMS);
                    var kobj = parms.Get(PdfName.K);
                    if (null != kobj)
                    {
                        if (-1 == ((PdfNumber)kobj).IntValue)
                            cmp = Compression.CCITTFAX4;
                    }

                    var name = string.Format("{0}{1}_{2}.tif", imgFolder, imgName, i);
                    Tiff tiff = Tiff.Open(name, "w");
                    tiff.SetField(TiffTag.IMAGEWIDTH, wid);
                    tiff.SetField(TiffTag.IMAGELENGTH, hei);
                    tiff.SetField(TiffTag.COMPRESSION, cmp);
                    tiff.SetField(TiffTag.BITSPERSAMPLE, bpc);
                    tiff.SetField(TiffTag.SAMPLESPERPIXEL, 1);
                    tiff.WriteRawStrip(0, bytes, bytes.Length);
                    tiff.Close();
                }
            }
        }

        static void CollectImage(PdfDictionary dic, List<PdfObject> images)
        {
            var res  = (PdfDictionary)PdfReader.GetPdfObject(dic.Get(PdfName.RESOURCES));
            var xobj = (PdfDictionary)PdfReader.GetPdfObject(res.Get(PdfName.XOBJECT));
            if (null != xobj)
            {
                foreach (PdfName name in xobj.Keys)
                {
                    PdfObject obj = xobj.Get(name);
                    if (obj.IsIndirect())
                    {
                        var tg = (PdfDictionary)PdfReader.GetPdfObject(obj);
                        var type = (PdfName)PdfReader.GetPdfObject(tg.Get(PdfName.SUBTYPE));
                        if (PdfName.IMAGE.Equals(type))
                        {
                            images.Add(obj);
                        }
                        else if (PdfName.FORM.Equals(type))
                        {
                            CollectImage(tg, images);
                        }
                        else if (PdfName.GROUP.Equals(type))
                        {
                            CollectImage(tg, images);
                        }
                    }
                }
            }
        }
    }
}