ncnn::Mat opencv::Mat 互转

nihui 写的：https://github.com/Tencent/ncnn/wiki/use-ncnn-with-opencv

1、cv::Mat转ncnn::Mat

cv::Mat bgr = cv::Mat(img_h,img_w,CV_8UC3);
ncnn::Mat in = ncnn::Mat::from_pixels_resize(bgr.data, ncnn::Mat::PIXEL_BGR2RGB, img_w, img_h, w, h);

2、ncnn::Mat 转 cv::Mat

ncnn::Mat in_pad;
ncnn::copy_make_border(in, in_pad, hpad / 2, hpad - hpad / 2, wpad / 2, wpad - wpad / 2, ncnn::BORDER_CONSTANT, 114.f);

　　(1)uchar　

cv::Mat Mat1(in_pad.h, in_pad.w, CV_8UC3);
in_pad.to_pixels(Mat1.data, ncnn::Mat::PIXEL_BGR2RGB);

　　(2)float　

const float norm_vals[3] = { 1 / 255.f, 1 / 255.f, 1 / 255.f };
const float mean_vals[3] = { 0.f, 0.f, 0.f };

in_pad.substract_mean_normalize(mean_vals, norm_vals);
cv::Mat Mat2(in_pad.h, in_pad.w, CV_32FC3);
float *pMat2Data = Mat2.ptr<float>(0);
for (int c = 0; c < 3; c++) {
    int idx = 0;
    for (int i = 0; i < in_pad.h; i++)
    {
         for (int j = 0; j < in_pad.w; j++)
        {
            float t = ((float*)in_pad.data)[j + i * in_pad.w + c * in_pad.h * in_pad.w];
            *(pMat2Data+2-c+idx) = t;
            idx += 3;
        }
     }
 }

 　　（3）float，新

 cv::Mat Mat2(in.h, in.w, CV_32FC3);
 float *pMat2Data = Mat2.ptr<float>(0);
 float* inData = (float*)in.data;
 int gOffset = in.cstep;
 int rOffset = in.cstep *2;
 for (int i = 0; i < in.cstep; i++, pMat2Data+=3)
 {
     *(pMat2Data + 0) = inData[i];
     *(pMat2Data + 1) = inData[gOffset + i];
     *(pMat2Data + 2) = inData[rOffset + i];
 }