public Bitmap ConvertToBitonal(Bitmap original,float dpi)

        {

            Bitmap source = null;



            // If original bitmap is not already in 32 BPP, ARGB format, then convert

            if (original.PixelFormat != PixelFormat.Format32bppArgb)

            {

                source = new Bitmap(original.Width, original.Height, PixelFormat.Format32bppArgb);

                source.SetResolution(original.HorizontalResolution, original.VerticalResolution);



                //   source.SetResolution(dpi, dpi );



                using (Graphics g = Graphics.FromImage(source))

                {

                    g.DrawImageUnscaled(original, 0, 0);

                }

            }

            else

            {

                source = original;

            }



            // Lock source bitmap in memory

            BitmapData sourceData = source.LockBits(new Rectangle(0, 0, source.Width, source.Height), ImageLockMode.ReadOnly, PixelFormat.Format32bppArgb);



            // Copy image data to binary array

            int imageSize = sourceData.Stride * sourceData.Height;

            byte[] sourceBuffer = new byte[imageSize];

            Marshal.Copy(sourceData.Scan0, sourceBuffer, 0, imageSize);



            // Unlock source bitmap

            source.UnlockBits(sourceData);



            // Create destination bitmap

            Bitmap destination = new Bitmap(source.Width, source.Height, PixelFormat.Format1bppIndexed);



            // Lock destination bitmap in memory

            BitmapData destinationData = destination.LockBits(new Rectangle(0, 0, destination.Width, destination.Height), ImageLockMode.WriteOnly, PixelFormat.Format1bppIndexed);



            // Create destination buffer

            imageSize = destinationData.Stride * destinationData.Height;

            byte[] destinationBuffer = new byte[imageSize];



            int sourceIndex = 0;

            int destinationIndex = 0;

            int pixelTotal = 0;

            byte destinationValue = 0;

            int pixelValue = 128;

            int height = source.Height;

            int width = source.Width;

            int threshold = 500;



            // Iterate lines

            for (int y = 0; y < height; y++)

            {

                sourceIndex = y * sourceData.Stride;

                destinationIndex = y * destinationData.Stride;

                destinationValue = 0;

                pixelValue = 128;



                // Iterate pixels

                for (int x = 0; x < width; x++)

                {

                    // Compute pixel brightness (i.e. total of Red, Green, and Blue values)

                    pixelTotal = sourceBuffer[sourceIndex + 1] + sourceBuffer[sourceIndex + 2] + sourceBuffer[sourceIndex + 3];

                    if (pixelTotal > threshold)

                    {

                        destinationValue += (byte)pixelValue;

                    }

                    if (pixelValue == 1)

                    {

                        destinationBuffer[destinationIndex] = destinationValue;

                        destinationIndex++;

                        destinationValue = 0;

                        pixelValue = 128;

                    }

                    else

                    {

                        pixelValue >>= 1;

                    }

                    sourceIndex += 4;

                }

                if (pixelValue != 128)

                {

                    destinationBuffer[destinationIndex] = destinationValue;

                }

            }



            // Copy binary image data to destination bitmap

            Marshal.Copy(destinationBuffer, 0, destinationData.Scan0, imageSize);



            // Unlock destination bitmap

            destination.UnlockBits(destinationData);



            // Return

            return destination;

        }

    }

}