Bitmap comments = null;
            string input = "somepath";
            // Open a Stream and decode a TIFF image
            using (Stream imageStreamSource = new FileStream(input, FileMode.Open,                 FileAccess.Read, FileShare.Read))
            {
                TiffBitmapDecoder decoder = new TiffBitmapDecoder(imageStreamSource,   BitmapCreateOptions.PreservePixelFormat, BitmapCacheOption.Default);

                BitmapSource bitmapSource = decoder.Frames[0];
                using (Bitmap b = BitmapFromSource(bitmapSource))
                {
                    Rectangle cropRect = new Rectangle(169, 1092, 567, 200);
                    comments = new Bitmap(cropRect.Width, cropRect.Height);

                    //first cropping
                    using (Graphics g = Graphics.FromImage(comments))
                    {
                        g.DrawImage(b, new Rectangle(0, 0, comments.Width, comments.Height),
                                        cropRect,
                                        GraphicsUnit.Pixel);
                    }
                }
            }

http://caringprogrammer.blogspot.com/

Sample code to read tiff in C# and cropp it

How to read  tiff in C# and crop it

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C#