c#内存拷贝有Marshal.Copy方法，适合托管内存和非托管内存之间的拷贝。然而图像之间的内存拷贝都位于非托管内存，想用Marshal类需要先从非托管内存复制到托管内存，最后再复制到非托管内存，效率减半。最后借助win32自带的CopyMemory方法成功实现。

        [DllImport("kernel32.dll", EntryPoint = "CopyMemory")]
        public extern static void CopyMemory(IntPtr dst, IntPtr src, int length);

        /// <summary>
        /// 改变图像宽高
        /// </summary>
        public static Bitmap ReSize(Bitmap src, int w, int h)
        {
            if (src == null || w < 1 || h < 1) return null;//或者抛出异常
            var srcData = src.LockBits(new Rectangle(0, 0, src.Width, src.Height), System.Drawing.Imaging.ImageLockMode.ReadOnly, src.PixelFormat);
            var dst = new Bitmap(w, h, src.PixelFormat);
            var dstData = dst.LockBits(new Rectangle(0, 0, dst.Width, dst.Height), System.Drawing.Imaging.ImageLockMode.ReadWrite, dst.PixelFormat);
            var pSrc = srcData.Scan0;
            var pDst = dstData.Scan0;
            int wLen = w > src.Width ? srcData.Stride : dstData.Stride;//要拷贝的图像字节宽度
            int hLen = h > src.Height ? src.Height : h;//要拷贝的图像高度
            for (int i = 0; i <hLen; i++)
            {
                CopyMemory(pDst, pSrc, wLen);
                pSrc += srcData.Stride;
                pDst += dstData.Stride;
            }
            src.UnlockBits(srcData);
            dst.UnlockBits(dstData);
            return dst;
        }