Example code for manipulating bits in a Bitmap using C# and unsafe

GDIBitManiupulation.cs

using System;
using System.Drawing;
using System.Drawing.Imaging;
using System.Windows.Forms;

namespace BitBlastBitmap
{
    static class Program
    {

        private static void Swap<T>(ref T a, ref T b)
        {
            T tmp = a;
            a = b;
            b = tmp;
        }

        /// <summary>
        /// The main entry point for the application.
        /// </summary>
        [STAThread]
        static void Main()
        {
            const int width = 800;
            const int height = 600;
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            bool appRunning = true;
            PictureBox box;
            var form = new Form
            {
                ClientSize = new Size(width, height),
                Text = "Bitmap BitBashing",
                FormBorderStyle = FormBorderStyle.FixedDialog,
                MaximizeBox = false,
            };
            form.Controls.Add(box = new PictureBox  { Dock = DockStyle.Fill});

            var buffer1 = new Bitmap(form.ClientSize.Width, form.ClientSize.Height, PixelFormat.Format32bppPArgb);
            
            using(var bg = Graphics.FromImage(buffer1)) 
                bg.Clear(Color.Black);

            var buffer2 = new Bitmap(buffer1);

            box.Paint += (sender, e) => e.Graphics.DrawImageUnscaled(buffer1, 0, 0);
            var font = new Font("Arial", 24);
            form.Show();
            form.Closing += (sender, args) => appRunning = false;
            float angle = 0f;
            float angleIncrease = (float)Math.PI/180;
            try
            {
                var sf = new StringFormat(StringFormatFlags.NoWrap)
                {
                    Alignment = StringAlignment.Center,
                    LineAlignment = StringAlignment.Center
                };
                while (appRunning)
                {
                    angle += angleIncrease;

                    ProcessBitmap(buffer1, buffer2, width, height);
                    using(var g = Graphics.FromImage(buffer2))
                    g.DrawString("Hello World!", font, Brushes.White, new PointF(width / 2 + (float)Math.Cos(angle) * 60, height / 2 + (float)Math.Sin(angle) * 60), sf);
                    Swap(ref buffer1, ref buffer2);
                    box.Invalidate();
                    Application.DoEvents();
                }
            }
            finally
            {
                buffer1.Dispose();
                buffer2.Dispose();
            }

        }

        private static readonly Random rnd = new Random();

        private static unsafe void ProcessBitmap(Bitmap buffer1, Bitmap buffer2, int width, int height)
        {
            
            var bmp1 = buffer1.LockBits(new Rectangle(0, 0, width, height), ImageLockMode.ReadWrite, PixelFormat.Format32bppPArgb);
            var bmp2 = buffer2.LockBits(new Rectangle(0, 0, width, height), ImageLockMode.ReadWrite, PixelFormat.Format32bppPArgb);
            try
            {
                var destination = (uint*)bmp2.Scan0.ToPointer();
                var source = ((uint*)bmp1.Scan0.ToPointer()) + width;

                int screenSize = width * height;
                int screenWidth = width;

                destination += screenWidth ;
                for(int i = screenWidth * 2; i < screenSize - screenWidth; i++, source++)
                {
                    *destination++ = unchecked
                        ((source[screenWidth << 1] >> 2) & 0x3F3F3F) +
                                     ((source[1] >> 2) & 0x3F3F3F) +
                                     ((source[-1] >> 2) & 0x3F3F3F) +
                                     ((source[screenWidth] >> 2) & 0x3F3F3F) | 0xff000000;
                }
            
                var bottomPointer = ((uint*) bmp2.Scan0.ToPointer()) + width * height - width;
                for (int i = 0; i < width; i++)
                {
                    var c = (uint)rnd.Next(255);
                    *bottomPointer++ = ((c) | (c << 8) | (c << 16) | unchecked (0xff000000));
                }
            }
            finally
            {
                buffer1.UnlockBits(bmp1);
                buffer2.UnlockBits(bmp2);
            }
        }

        
    }
}