こんばんは、
　魔界の仮面弁士様の紹介していた
　　https://dobon.net/vb/dotnet/graphics/createmultitiff.htmlに載っていた
　　https://www.codeproject.com/Articles/16904/Save-images-into-a-multi-page-TIFF-file-or-add-imaをフォームアプリケーションのクラスライブラリにしてみました
　　文字数が多いので分けます
　　

using System;

using System.Drawing;

using System.Drawing.Imaging;

using System.Runtime.InteropServices;

using System.IO;



namespace WindowsFormsAppTiffTo1L_CL

{

    [Guid(TiffTo1L.ClassId)]

    public class  TiffTo1L

    {

        //  COM用のGUID値

        public const string ClassId = "14BC0BB5-22E6-45C8-8656-45D84E25F60D";



        //https://www.codeproject.com/Articles/16904/Save-images-into-a-multi-page-TIFF-file-or-add-ima

        //This function can save newly scanned images on existing single page or multipage file

        public String OriginDest(string fileName, string type,long col,string orig,float dpi)

        {

            Image origionalFile = null;

            FileStream fr = File.Open(fileName, FileMode.Open, FileAccess.ReadWrite);

            origionalFile = Image.FromStream(fr);

            int PageNumber = getPageNumber(origionalFile);



            if (PageNumber > 1)//Existing File is multi page tiff file

            {

                saveImageExistingMultiplePage(origionalFile, type, PageNumber, orig, col,dpi);

            }

            else if (PageNumber == 1)//Existing file is single page file

            {

                saveImageExistingSinglePage(origionalFile, type, orig, col,dpi);

            }

            fr.Flush();

            fr.Close();

           // System.IO.File.Replace("shreeTemp.tif", fileName, "Backup.tif", true);

            return "ok";

        }



        public ImageCodecInfo getCodecForstring(string type)

        {

            ImageCodecInfo[] info = ImageCodecInfo.GetImageEncoders();



            for (int i = 0; i < info.Length; i++)

            {

                string EnumName = type.ToString();

                if (info[i].FormatDescription.Equals(EnumName))

                {

                    return info[i];

                }

            }

            return null;



        }

    

        public void saveImageExistingSinglePage(Image origionalFile, string type, string location,long col1,float dpi)

        {

            //Now load the Codecs 

            ImageCodecInfo codecInfo = getCodecForstring(type);



            EncoderParameter SaveEncodeParam;

            EncoderParameter CompressionEncodeParam;

            EncoderParameters EncoderParams = new EncoderParameters(3);

            EncoderParameter ColorEncodeParam;



            // Save the first page (frame).

            SaveEncodeParam = new EncoderParameter(System.Drawing.Imaging.Encoder.SaveFlag, (long)EncoderValue.MultiFrame);

            CompressionEncodeParam = new EncoderParameter(System.Drawing.Imaging.Encoder.Compression, (long)EncoderValue.CompressionNone);

            // Save the image with a color depth of 24 bits per pixel.

            ColorEncodeParam = new EncoderParameter(System.Drawing.Imaging.Encoder.ColorDepth,col1);

            EncoderParams.Param[0] = CompressionEncodeParam;

            EncoderParams.Param[1] = SaveEncodeParam;

            EncoderParams.Param[2] = ColorEncodeParam;



            origionalFile = ConvertToBitonal((Bitmap)origionalFile,dpi);

            origionalFile.Save(location, codecInfo, EncoderParams);



            SaveEncodeParam = new EncoderParameter(System.Drawing.Imaging.Encoder.SaveFlag, (long)EncoderValue.Flush);

            EncoderParams.Param[0] = SaveEncodeParam;

            origionalFile.SaveAdd(EncoderParams);

        }