I have a DLL in C whose function input is cv::Mat. It gives an error when I try to call this function with the frame input that I receive from opencvsharp as Mat in C#.
How do I fix this problem?
How can I match Mat in C and Mat in C# to prevent errors?
Do I need to change the C function or do I need to do something else in C# to access the data inside the Mat as input to the C function?
C function:
extern "C" __declspec(dllexport) vector<std::string> __cdecl ProcessFrame(cv::Mat image);
vector<std::string> ProcessFrame(cv::Mat image)
{
int k = 0;
cv::Mat croppedimage;
cv::Mat finalcropped;
string filename;
Mat result_image;
vector<string> listName;
Module module = torch::jit::load("D:/Project/libfacedetection/example/converted.pt");
int* pResults = NULL;
unsigned char* pBuffer = (unsigned char*)malloc(DETECT_BUFFER_SIZE);
if (!pBuffer)
{
fprintf(stderr, "Can not alloc buffer.\n");
return listName;
}
TickMeter cvtm;
cvtm.start();
pResults = facedetect_cnn(pBuffer, (unsigned char*)(image.ptr(0)), image.cols, image.rows, (int)image.step);
int face_num = (pResults ? *pResults : 0);
if (*pResults != 0)
{
result_image = image.clone();
for (int i = 0; i < face_num; i )
{
try
{
short* p = ((short*)(pResults 1)) 142 * i;
int confidence = p[0];
int x = p[1];
int y = p[2];
int w = p[3];
int h = p[4];
char sScore[256];
if (confidence >= 95)
{
//////////////////////////////////////////////////////////////////////////////
////////////// Rotate and Crop
//////////////////////////////////////////////////////////////////////////////
short angle = Face_rotate(p);
cv::Rect rc = AlignCordinates(x, y, w, h, result_image.cols, result_image.rows);
cv::Rect myroi(x, y, w, h);
cv::Rect newroi((x - rc.x) / 2, (y - rc.y) / 2, w, h);
croppedimage = result_image(rc);
//imshow("1", croppedimage);
croppedimage = croppedimage.clone();
croppedimage = rotate(croppedimage, (angle));
//imshow("Rotate", croppedimage);
croppedimage = croppedimage(newroi).clone();
finalcropped = Mat(112, 112, croppedimage.type());
//imshow("dst", croppedimage);
cv::resize(croppedimage, finalcropped, finalcropped.size());
//imshow("resize", finalcropped);
Mat flipimage;
flip(finalcropped, flipimage, 1);
torch::Tensor img_tensor = torch::from_blob(finalcropped.data, { finalcropped.rows,finalcropped.cols ,3 }, torch::kByte);
torch::Tensor img_tensor_flip = torch::from_blob(flipimage.data, { flipimage.rows, flipimage.cols, 3 }, torch::kByte);
//torch::Tensor img_tensor_final = img_tensor img_tensor_flip;
img_tensor = img_tensor.to(at::kFloat).div(255).unsqueeze(0);
img_tensor = img_tensor.sub_(0.5);
img_tensor = img_tensor.permute({ 0,3,1,2 });
img_tensor_flip = img_tensor_flip.to(at::kFloat).div(255).unsqueeze(0);
img_tensor_flip = img_tensor_flip.sub_(0.5);
img_tensor_flip = img_tensor_flip.permute({ 0,3,1,2 });
at::Tensor output_org = module.forward({ img_tensor }).toTensor();
at::Tensor output_flip = module.forward({ img_tensor_flip }).toTensor();
std::vector<double> out;
for (int i = 0; i < 512; i )
{
out.push_back(output_org[0][i].item().to<double>() output_flip[0][i].item().to<double>());
}
out = l2_norm(out);
std::ifstream file("D:/Project/libfacedetection/example/facebank.json");
json object = json::parse(file);
double min_dis = 1000;
std::string min_name;
for (auto& x : object.items()) {
auto dataSize = std::size(x.value());
std::vector<double> vec1 = x.value();
double res = cosine_similarity_vectors(vec1, out);
res = (res * -1) 1;
//double res = distance(vec1, out);
if (res <= min_dis) {
min_dis = res;
min_name = x.key();
}
}
std::cout << "One Frame " << min_name << " " << min_dis << std::endl;
if (min_dis < 0.8) {
listName.push_back(min_name);
}
else
{
listName.push_back("Unknown");
}
}
else
{
listName.push_back("conf_low");
}
}
catch (const std::exception& ex)
{
cout << "NASHOD" << endl;
//std::cout << ex.what();
}
}
}
else
{
listName.push_back("No_Body");
}
cvtm.stop();
//printf("time = %gms\n", cvtm.getTimeMilli());
//printf("%d faces detected.\n", (pResults ? *pResults : 0));
free(pBuffer);
return listName;
}
C#:
[DllImport("detect-camera.dll", CallingConvention = CallingConvention.Cdecl)]
public static extern List<string> ProcessFrame(Mat image);
private void button1_Click(object sender, EventArgs e)
{
Mat image = Cv2.ImRead("D:/c /ImportCallFunction/ImportCallFunction/123.jpg");
List<string> facelist = ProcessFrame(image);
foreach (var item in facelist)
{
listBox1.Items.Add(item);
}
Error:
System.Runtime.InteropServices.MarshalDirectiveException: 'Cannot marshal 'return value': Generic types cannot be marshaled.'
CodePudding user response：
The error that you've encountered is not related to the parameter type cv::Mat but the return type of the function which is declared as vector<std::string>.
First, a note about the parameter type: you might want to make it const cv::Mat& to avoid copying the whole matrix into the function on every frame. So it will be like:
std::vector<std::string> ProcessFrame(const cv::Mat& image)
You will also need a wrapper function that is written in C /CLI and serves as the interface between the C# code and the C code. It performs the custom marshalling required by the function both for the input argument and for the return value. Note that you should place the wrapper function in a compile unit that is compiled with /clr (to enable C /CLI). Your original (native) function doesn't need to be compiled with the /clr option. The wrapper function declaration might look like this:
System::Collections::Generic<System::String>^ ProcessFrameWrapper(
OpenCvSharp::Mat^ mat);
In the C# code, you will call the wrapper function now:
[DllImport("detect-camera.dll", CallingConvention = CallingConvention.Cdecl)]
public static extern List<string> ProcessFrameWrapper(Mat image);
// ...
List<string> facelist = ProcessFrameWrapper(image);
To summarize, you will need these files:
DetectCamera.h:
// ...
std::vector<std::string> ProcessFrame(const cv::Mat& image);
// ... other native declarations
DetectCamera.cpp:
// ...
std::vector<std::string> ProcessFrame(const cv::Mat& image)
{
// actual function implementation
}
// ... other function implementations
DetectCameraWrapper.h:
// ...
System::String^ ProcessFrameWrapper(OpenCvSharp::Mat^ mat);
// ... other wrapper functions ...
DetectCameraWrapper.cpp:
// ...
System::Collections::Generic<System::String>^ ProcessFrameWrapper(
OpenCvSharp::Mat^ mat)
{
var names = gcnew System::Collections::Generic<System::String>();
auto matNativePtr =
reinterpret_cast<cv::Mat*>(marshal_as<void*>(mat->CvPtr));
auto namesNative = ProcessFrame(*matNativePtr);
for (const auto& nameNative : namesNative)
{
names->Add(marshal_as<System::String^>(nameNative));
}
return names;
}
// ... other wrapper function implementations
DetectCamera.cs:
// ...
[DllImport("detect-camera.dll", CallingConvention = CallingConvention.Cdecl)]
public static extern List<string> ProcessFrameWrapper(Mat image);
private void button1_Click(object sender, EventArgs e)
{
Mat image = Cv2.ImRead("D:/c /ImportCallFunction/ImportCallFunction/123.jpg");
List<string> facelist = ProcessFrameWrapper(image);
foreach (var item in facelist)
{
listBox1.Items.Add(item);
}
// ...
These files can be organized in two or three separate projects:
- DetectCamera.cs is placed in a C# project - call it ProjCSharp.
- DetectCameraWrapper.cpp is placed in a C /CLI DLL project (with
/clr) - call it ProjWrapper. - DetectCamera.cpp could be placed either within the same project ProjWrapper, or in a separate native library project (.lib) - call it ProjNative. I recommend the latter. If it is placed in a separate library (ProjNative), the DLL project ProjWrapper must be linked to the library ProjNative.
The reason I recommend placing the native code inside a separate library is modularity and code reusability.
CodePudding user response：
I do not quite remember the Interop and was never an expert although I used to do pretty advanced stuff.
The advice from @misoboute is to use CLI which I have never used so I wouldn't know. It is surely possible to do that that and as he has explained, such C will understand the generic C# list and be able to marshal successfully.
But it appears to me, this is NOT your problem. You simply want to return a bunch of strings. It really does not have to be defined as List<string>. It can be defined as string[], an array of string.
So I would try
[DllImport("detect-camera.dll", CallingConvention = CallingConvention.Cdecl)]
public static extern string[] ProcessFrame(Mat image);
And then, in my C code, return an array of string by representing the vector of string as an array:
How to convert vector to array
Sorry but that is all I have for you. It is possible that after this, you will hit other problems.