[图像处理]在.net cf 下面使用LockBits仍不够快

想在.net cf 的winform程序里做半透明的控件,实时使用LockBits直接进行内存运算,但是效果不好,运算一个30*30的图像都需要140-160ms之间,若我们N个这样的按扭,那程序就很慢了,请问,有没有更快的方法?或是别的实现半透明按扭的方法?谢谢!{            Rectangle rect = new Rectangle(0, 0, img.Width, img.Height);
            BitmapData bd =
            img.LockBits(rect, ImageLockMode.ReadOnly,
                         pxf);            m_Image = (Bitmap)m_TmpImg.Clone();
            BitmapData bkBD = m_Image.LockBits(new Rectangle(0, 0, Width, Height), ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);
            unsafe
            {
                byte* pbd = (byte*)bd.Scan0.ToPointer() + bd.Stride * Top + Left * 3;
                byte* pbk = (byte*)bkBD.Scan0.ToPointer();
                for (int h = 0; h < Height; h++)
                {
                    for (int w = 0; w < Width; w++)
                    {
                        if (pbk[0] != 0 && pbk[1] != 0 && pbk[2] != 0)
                        {
                            pbk[0] = (byte)((pbd[0] + pbk[0]) >> 1);
                            pbk[1] = (byte)((pbd[1] + pbk[1]) >> 1);
                            pbk[2] = (byte)((pbd[2] + pbk[2]) >> 1);
                        }
                        else
                        {
                            pbk[0] = pbd[0];
                            pbk[1] = pbd[1];
                            pbk[2] = pbd[2];
                        }
                        pbk += 3;
                        pbd += 3;
                    }
                    pbk += bkBD.Stride - Width * 3;
                    pbd += bd.Stride - Width * 3;
                }
            }
            img.UnlockBits(bd);
            m_Image.UnlockBits(bkBD);