LockBitmap

    using System;
    using System.Drawing;
    using System.Drawing.Imaging;
    using System.Runtime.InteropServices;

    public class LockBitmap
    {
        private Bitmap source = null;
        private IntPtr Iptr = IntPtr.Zero;
        private BitmapData bitmapData = null;
        public byte[] Pixels { get; set; }
        public int Depth { get; private set; }
        public int Width { get; private set; }
        public int Height { get; private set; }

        public LockBitmap(Bitmap source)
        {
            this.source = source;
        }

        public void LockBits()
        {
            try
            {
                Width = source.Width;
                Height = source.Height;
                int PixelCount = Width * Height;
                Rectangle rect = new Rectangle(0, 0, Width, Height);
                Depth = System.Drawing.Bitmap.GetPixelFormatSize(source.PixelFormat);
                if (Depth != 8 && Depth != 24 && Depth != 32)
                    throw new ArgumentException("Only 8, 24 and 32 bpp images are supported.");
                bitmapData = source.LockBits(rect, ImageLockMode.ReadWrite, source.PixelFormat);
                int step = (int)(Depth / 8.0);
                Pixels = new byte[PixelCount * step - 1 + 1];
                Iptr = bitmapData.Scan0;
                Marshal.Copy(Iptr, Pixels, 0, Pixels.Length);
            }
            catch (Exception ex)
            {
                throw ex;
            }
        }

        public void UnlockBits()
        {
            try
            {
                Marshal.Copy(Pixels, 0, Iptr, Pixels.Length);
                source.UnlockBits(bitmapData);
            }
            catch (Exception ex)
            {
                throw ex;
            }
        }

        public Color GetPixel(int x, int y)
        {
            Color clr = Color.Empty;
            int cCount = (int)(Depth / 8.0);
            int i = ((y * Width) + x) * cCount;
            if (i > Pixels.Length - cCount)
                throw new IndexOutOfRangeException();
            if (Depth == 32)
            {
                byte b = Pixels[i];
                byte g = Pixels[i + 1];
                byte r = Pixels[i + 2];
                byte a = Pixels[i + 3];
                clr = Color.FromArgb(a, r, g, b);
            }
            if (Depth == 24)
            {
                byte b = Pixels[i];
                byte g = Pixels[i + 1];
                byte r = Pixels[i + 2];
                clr = Color.FromArgb(r, g, b);
            }
            if (Depth == 8)
            {
                byte c = Pixels[i];
                clr = Color.FromArgb(c, c, c);
            }
            return clr;
        }

        public void SetPixel(int x, int y, Color color)
        {
            int cCount = (int)(Depth / 8.0);
            int i = ((y * Width) + x) * cCount;
            if (Depth == 32)
            {
                Pixels[i] = color.B;
                Pixels[i + 1] = color.G;
                Pixels[i + 2] = color.R;
                Pixels[i + 3] = color.A;
            }
            if (Depth == 24)
            {
                Pixels[i] = color.B;
                Pixels[i + 1] = color.G;
                Pixels[i + 2] = color.R;
            }
            if (Depth == 8)
                Pixels[i] = color.B;
        }
    }