在C++中将pytorch张量转换为opencv mat，反之亦然 [英] Convert pytorch tensor to opencv mat and vice versa in C++

问题描述

我想在 C++ 中将 pytorch 张量转换为 opencv mat，反之亦然.我有这两个功能:

I want to convert pytorch tensors to opencv mat and vice versa in C++. I have these two functions:

cv::Mat TensorToCVMat(torch::Tensor tensor)
{
    std::cout << "converting tensor to cvmat\n";
    tensor = tensor.squeeze().detach().permute({1, 2, 0});
    tensor = tensor.mul(255).clamp(0, 255).to(torch::kU8);
    tensor = tensor.to(torch::kCPU);
    int64_t height = tensor.size(0);
    int64_t width = tensor.size(1);
    cv::Mat mat(width, height, CV_8UC3);
    std::memcpy((void *)mat.data, tensor.data_ptr(), sizeof(torch::kU8) * tensor.numel());
    return mat.clone();
}

torch::Tensor CVMatToTensor(cv::Mat mat)
{
    std::cout << "converting cvmat to tensor\n";
    cv::cvtColor(mat, mat, cv::COLOR_BGR2RGB);
    cv::Mat matFloat;
    mat.convertTo(matFloat, CV_32F, 1.0 / 255);
    auto size = matFloat.size();
    auto nChannels = matFloat.channels();
    auto tensor = torch::from_blob(matFloat.data, {1, size.height, size.width, nChannels});
    return tensor.permute({0, 3, 1, 2});
}

在我的代码中，我加载了两个图像(image1 和 image2)，我想将它们转换为 pytorch 张量，然后返回到 opencv mat 以检查它是否有效.问题是我在第一次调用 TensorToCVMat 时遇到内存访问错误，我无法弄清楚出了什么问题，因为我对 C++ 编程没有太多经验.

In my code I load two images (image1 and image2) and I want to convert them to pytorch tensors and then back to opencv mat to check if it works. The problem is that I get an memory access error on the first call of TensorToCVMat and I cant figure out whats wrong as I do not have much experience with C++ programming.

cv::Mat image1;
image1 = cv::imread(argv[1]);
if (!image1.data)
{
    std::cout << "no image data\n";
    return -1;
}
cv::Mat image2;
image2 = cv::imread(argv[2]);
if (!image2.data)
{
    std::cout << "no image data\n";
    return -1;
}

torch::Tensor tensor1 = CVMatToTensor(image1);
cv::Mat new_image1 = TensorToCVMat(tensor1); // <<< this is where the memory access error is thrown
torch::Tensor tensor2 = CVMatToTensor(image2);
cv::Mat new_image2 = TensorToCVMat(tensor2);

如果你能给我提示或解释来解决这个问题，那就太好了.

It would be great if you could give me hints or an explanation to solve this problem.

推荐答案

我正在使用 torch>=1.7.0.

I am using torch>=1.7.0.

对于 dtype=float 和大小 [1, 3, height, width] 的张量这对我有用

For a tensor of dtype=float and size [1, 3, height, width] this is what worked for me

cv::Mat torchTensortoCVMat(torch::Tensor& tensor)
    {
        tensor = tensor.squeeze().detach();
        tensor = tensor.permute({1, 2, 0}).contiguous();
        tensor = tensor.mul(255).clamp(0, 255).to(torch::kU8);
        tensor = tensor.to(torch::kCPU);
        int64_t height = tensor.size(0);
        int64_t width = tensor.size(1);
        cv::Mat mat = cv::Mat(cv::Size(width, height), CV_8UC3, tensor.data_ptr<uchar>());
        return mat.clone();
    }

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