海康摄像头YUV420P格式图片缩放

上面文章说过了YUV格式拼接，拼接的数据就需要提前对图像进行缩放的功能

海康摄像头获取到了图像数据解码后，分辨率随着设想头的不同，会造成YUV格式图片分辨率不同，就需要对图片进行缩放，YUV的缩放就用到LibYuv.dll动态库，动态库下提供个Scale方法，此方法为C#的导入方法

        [DllImport(_path, SetLastError = true, CallingConvention = CallingConvention.Cdecl)]
        public static extern int Scale(byte* src_y,
        byte* src_u,
        byte* src_v,
        int src_stride_y,
        int src_stride_u,
        int src_stride_v,
        int src_width,
        int src_height,
        byte* dst_y,
        byte* dst_u,
        byte* dst_v,
        int dst_stride_y,
        int dst_stride_u,
        int dst_stride_v,
        int dst_width,
        int dst_height,
        int interpolate);

C#下封装的缩放方法，缩放需要对YUV数据的分量进行分解后，获得放大或缩小后待使用YUV数据

        /// <summary>
        /// YUV缩放
        /// </summary>
        /// <param name="_syuv"></param>
        /// <param name="_dyuv"></param>
        /// <param name="_swidth"></param>
        /// <param name="_sheight"></param>
        /// <param name="_dwidth"></param>
        /// <param name="_dheight"></param>
        public void YuvScale(byte[] _syuv, ref byte[] _dyuv, int _swidth, int _sheight,
                            int _dwidth, int _dheight)
        {
            try
            {
                int s_ylen = _swidth * _sheight;
                int s_ulen = Convert.ToInt32(s_ylen * 0.25);
                int s_vlen = s_ulen;
                byte[] s_ydata = new byte[s_ylen];
                Array.ConstrainedCopy(_syuv, 0, s_ydata, 0, s_ylen);
                byte[] s_udata = new byte[s_ulen];
                Array.ConstrainedCopy(_syuv, s_ylen, s_udata, 0, s_ulen);
                byte[] s_vdata = new byte[s_vlen];
                Array.ConstrainedCopy(_syuv, s_ylen + s_ulen, s_vdata, 0, s_vlen);
                int s_ystride = _swidth;
                int s_ustride = (_swidth + 1) / 2;
                int s_vstride = s_ustride;

                int d_ylen = _dwidth * _dheight;
                int d_ulen = d_ylen / 4;
                int d_vlen = d_ulen;
                byte[] d_ydata = new byte[d_ylen];
                byte[] d_udata = new byte[d_ulen];
                byte[] d_vdata = new byte[d_vlen];
                Array.ConstrainedCopy(_syuv, s_ylen + s_ulen, s_vdata, 0, s_vlen);
                int d_ystride = _dwidth;
                int d_ustride = (_dwidth + 1) / 2;
                int d_vstride = d_ustride;
                fixed (byte* bs_ydata = s_ydata)
                fixed (byte* bs_udata = s_udata)
                fixed (byte* bs_vdata = s_vdata)
                fixed (byte* bd_ydata = d_ydata)
                fixed (byte* bd_udata = d_udata)
                fixed (byte* bd_vdata = d_vdata)
                {
                    LibYuv.Scale(bs_ydata, bs_udata, bs_vdata, s_ystride, s_ustride, s_vstride, _swidth, _sheight,
                                  bd_ydata, bd_udata, bd_vdata, d_ystride, d_ustride, d_vstride, _dwidth, _dheight, 0);
                }

                _dyuv = new byte[_dwidth * _dheight * 3 / 2];
                Array.ConstrainedCopy(d_ydata, 0, _dyuv, 0, d_ylen);
                Array.ConstrainedCopy(d_udata, 0, _dyuv, d_ylen, d_ulen);
                Array.ConstrainedCopy(d_vdata, 0, _dyuv, d_ylen + d_ulen, d_vlen);
            }
            catch (Exception ex)
            {

            }
        }