BitmapData.Scan0 Property

public IntPtr Scan0 { get; }

Aurigma.GraphicsMill.BitmapData bitmapData = bitmap.LockBits();

unsafe
{
    byte* pos;
    byte* scan0 = (byte*)(bitmapData.Scan0.ToPointer());
    int stride = bitmapData.Stride;

    int widthInBytes = bitmapData.Width * bitmapData.BitsPerPixel / 8;
    int height = bitmapData.Height;

    for (int j = 0; j < height; j++)
    {
        pos = scan0 + stride * j;
        for (int i = 0; i < widthInBytes; i++)
        {
            *pos = (byte)(255 - *pos);
            pos++;
        }
    }
}

bitmap.UnlockBits(bitmapData);