Class for faster pixels processing

FastImage.cs

 class FastImage
        {

            Bitmap bm;
            BitmapData bmpData;
            public byte[] bytes;
            public int Width, Height;

            public FastImage(Bitmap bm)
            {
                this.bm = bm;
                Width = bm.Width;
                Height = bm.Height;

                int len = Width * Height * 4;
                bytes = new byte[len];
            }

            public FastImage(Image img) : this(new Bitmap(img)) { }


            public FastImage(int w, int h) : this(new Bitmap(w, h)) { }

            public Bitmap getBitmap()
            {
                return bm;
            }

            public Color GetPixel(int x,int y)
            {
                int i = 4 * (y * Width + x);

                return Color.FromArgb(bytes[i+3], bytes[i+2], bytes[i+1], bytes[i+0]);
            }

            public FastImage Clone()
            {
                FastImage img = new FastImage(bm);
                img.bytes = (byte[])bytes.Clone();


                return img;
            }

            public void fromBytes(byte[] b)
            {
                bytes = b;

                writeBytes();
            }

            public void SetPixel(int x,int y, Color c)
            {
                int i = 4 * (y * Width + x);

                bytes[i + 3] = c.A;
                bytes[i + 2] = c.R;
                bytes[i + 1] = c.G;
                bytes[i + 0] = c.B;
            }

             void Lock(){

                Rectangle rect = new Rectangle(0, 0, Width, Height);
                bmpData = bm.LockBits(rect, ImageLockMode.ReadWrite, bm.PixelFormat);

            }

            public byte[] readBytes()
            {
                Lock();
                System.Runtime.InteropServices.Marshal.Copy(bmpData.Scan0, bytes, 0, bytes.Length);
                Unlock();

                return bytes;
            }

            public void writeBytes()
            {
                  Lock();
                  System.Runtime.InteropServices.Marshal.Copy(bytes, 0, bmpData.Scan0, bytes.Length);
                  Unlock();
                
            }

            void Unlock()
            {
                bm.UnlockBits(bmpData);
            }
            

        }