tiff切片、合并、转换
http://www.voidcn.com/article/p-kloikjag-bab.html
SplitTif，分割一个tif到多个tif；JoinTiffImages，合并多个图片到tif

  [Test]
        public void SplitTiff()
        {
            var targetFile = Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "黑控励志.tiff");
            var images = TiffHelper.SplitTif(targetFile, out var tempDirectory);

            var pageDirectory = Path.Combine(Path.GetDirectoryName(targetFile) ?? throw new InvalidOperationException(), Path.GetFileNameWithoutExtension(targetFile));
            if (!Directory.Exists(pageDirectory)) Directory.CreateDirectory(pageDirectory);

            var pageSize = 2;
            var pageCount = images.Count / 2 + 1;
            for (int i = 0; i < pageCount; i++)
            {
                var fileName = Path.Combine(pageDirectory, $"page_{i}.tif");
                var files = images.Skip(pageSize * i).Take(pageSize).ToList();
                TiffHelper.JoinTiffImages(files, fileName, EncoderValue.CompressionCCITT3);
            }

            //清理
            Directory.Delete(tempDirectory, true);
        }

 public class TiffHelper
    {
        /// <summary>
        /// 获取图像页数
        /// </summary>
        /// <param name="imagePath"></param>
        /// <returns></returns>
        public static int GetPageNumber(string imagePath)
        {
            using (var image = Image.FromFile(imagePath))
            {
                var objGuid = image.FrameDimensionsList[0];
                var objDimension = new FrameDimension(objGuid);

                return image.GetFrameCount(objDimension);
            }
        }


        /// <summary>
        /// 将给定的文件 拼接输出到指定的tif文件路径
        /// </summary>
        /// <param name="imageFiles">文件路径列表</param>
        /// <param name="outFile">拼接后保存的 tif文件路径</param>
        /// <param name="compressEncoder">压缩方式</param>
        public static void JoinTiffImages(List<string> imageFiles, string outFile, EncoderValue compressEncoder = EncoderValue.CompressionCCITT3)
        {
            //如果只有一个文件，直接复制到目标
            if (imageFiles.Count == 1)
            {
                File.Copy((string) imageFiles[0], outFile, true);
                return;
            }

            var enc = Encoder.SaveFlag;

            var ep = new EncoderParameters(2);
            ep.Param[0] = new EncoderParameter(enc, (long) EncoderValue.MultiFrame);
            ep.Param[1] = new EncoderParameter(Encoder.Compression, (long) compressEncoder);

            Bitmap pages = null;
            int frame = 0;
            ImageCodecInfo info = GetEncoderInfo("image/tiff");

            foreach (string strImageFile in imageFiles)
            {
                if (frame == 0)
                {
                    pages = (Bitmap) Image.FromFile(strImageFile);
                    //保存第一个tif文件 到目标处
                    pages.Save(outFile, info, ep);
                }
                else
                {
                    //保存好第一个tif文件后，其余 设置为添加一帧到 图像中
                    ep.Param[0] = new EncoderParameter(enc, (long) EncoderValue.FrameDimensionPage);

                    Bitmap bm = (Bitmap) Image.FromFile(strImageFile);
                    pages.SaveAdd(bm, ep);
                    bm.Dispose();
                }

                if (frame == imageFiles.Count - 1)
                {
                    //flush and close.
                    ep.Param[0] = new EncoderParameter(enc, (long) EncoderValue.Flush);
                    pages.SaveAdd(ep);
                }

                frame++;
            }

            pages?.Dispose(); //释放资源
        }

     
        /// <summary>
        /// 拼接两个tif文件 保存到文件2中
        /// </summary>
        /// <param name="filePath">tif文件1</param>
        /// <param name="targetFile">tif文件2</param>
        public static void AppendToTiff(string filePath, string targetFile)
        {
            var list = new List<string>(); //保存所有 tif文件路径
            list.AddRange(SplitTif(filePath, out var tempDirectory1));
            list.AddRange(SplitTif(targetFile, out var tempDirectory2));

            File.Delete(targetFile);
            JoinTiffImages(list, targetFile, EncoderValue.CompressionCCITT3);

            var di2 = new DirectoryInfo(tempDirectory2);
            di2.Delete(true);

            var di1 = new DirectoryInfo(tempDirectory1);
            di1.Delete(true);
        }

        /// <summary>
        /// 将给定文件  分割成多个tif文件 到临时目录下
        /// </summary>
        /// <param name="targetFile">目标文件</param>
        /// <param name="tempDirectory">临时目录路径，删除用</param>
        /// <returns>分割后多个文件路径集合</returns>
        public static List<string> SplitTif(string targetFile, out string tempDirectory)
        {
            var list = new List<string>();
            using (var img = Image.FromFile(targetFile))
            {
                Guid guid = img.FrameDimensionsList[0];

                var dimension = new System.Drawing.Imaging.FrameDimension(guid);

                int nTotFrame = img.GetFrameCount(dimension); //tif总页数

                int nLoop; //索引
                //生成临时目录 存放 单tif页
                tempDirectory = Path.Combine(Path.GetDirectoryName(targetFile) ?? throw new InvalidOperationException(), Guid.NewGuid().ToString());
                if (!Directory.Exists(tempDirectory))
                {
                    Directory.CreateDirectory(tempDirectory);
                }

                EncoderParameters ep = new EncoderParameters(2);
                ep.Param[0] = new EncoderParameter(Encoder.SaveFlag, (long) EncoderValue.MultiFrame);
                ep.Param[1] = new EncoderParameter(Encoder.Compression, (long) EncoderValue.CompressionCCITT3); //压缩方式  CompressionCCITT3主要用于传真

                ImageCodecInfo info = GetEncoderInfo("image/tiff");

                for (nLoop = 0; nLoop < nTotFrame; nLoop++)
                {
                    img.SelectActiveFrame(dimension, nLoop);
                    string newfilePath = Path.Combine(tempDirectory, nLoop + ".tif");
                    img.Save(newfilePath, info, ep);
                    list.Add(newfilePath);
                }
            }

            return list;
        }


        /// <summary>
        /// 获取支持的编码信息
        /// </summary>
        /// <param name="mimeType">协议描述</param>
        /// <returns>图像编码信息</returns>
        private static ImageCodecInfo GetEncoderInfo(string mimeType)
        {
            ImageCodecInfo[] encoders = ImageCodecInfo.GetImageEncoders();
            for (int j = 0; j < encoders.Length; j++)
            {
                if (encoders[j].MimeType == mimeType)
                    return encoders[j];
            }

            throw new Exception(mimeType + " mime type not found in ImageCodecInfo");
        }
    }