彩色/灰色Bmp 转单色

  Bitmap source = null;

            // If original bitmap is not already in 32 BPP, ARGB format, then convert
            if (pimage.PixelFormat != PixelFormat.Format32bppArgb)
            {
                source = new Bitmap(pimage.Width, pimage.Height, PixelFormat.Format32bppArgb);
                source.SetResolution(pimage.HorizontalResolution, pimage.VerticalResolution);
                using (Graphics g = Graphics.FromImage(source))
                {
                    g.DrawImageUnscaled(pimage, 0, 0);
                }
            }
            else
            {
                source = pimage;
            }

            // 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);

            // Dispose of source if not originally supplied bitmap
            if (source != pimage)
            {
                source.Dispose();
            }

            // Return
            return destination;