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I created a C DLL out of my C++ class which uses OpenCV for image manipulations and want to use this dll in my C# application. Currently, this is how I have implemented it :

#ifdef CDLL2_EXPORTS
#define CDLL2_API __declspec(dllexport)
#else
#define CDLL2_API __declspec(dllimport)
#endif

#include "../classification.h" 
extern "C"
{
    CDLL2_API void Classify_image(unsigned char* img_pointer, unsigned int height, unsigned int width, char* out_result, int* length_of_out_result, int top_n_results = 2);
    //...
}

C# related code :DLL Import section:

//Dll import 
[DllImport(@"CDll2.dll", CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Ansi)]
static extern void Classify_Image(IntPtr img, uint height, uint width, byte[] out_result, out int out_result_length, int top_n_results = 2);

The actual function sending the image to the DLL:

//...
//main code 
private string Classify(int top_n)
{
    byte[] res = new byte[200];
    int len;
    Bitmap img = new Bitmap(txtImagePath.Text);
    BitmapData bmpData = img.LockBits(new Rectangle(0, 0, img.Width, img.Height), 
                                      ImageLockMode.ReadWrite,  
                                      PixelFormat.Format24bppRgb);
    Classify_Image(bmpData.Scan0, (uint)bmpData.Height, (uint)bmpData.Width, res, out len, top_n);
    img.UnlockBits(bmpData); //Remember to unlock!!!
    //...
}

and the C++ code in the DLL :

CDLL2_API void Classify_Image(unsigned char* img_pointer, unsigned int height, unsigned int width,
                              char* out_result, int* length_of_out_result, int top_n_results)
    {
        auto classifier = reinterpret_cast<Classifier*>(GetHandle());

        cv::Mat img = cv::Mat(height, width, CV_8UC3, (void*)img_pointer, Mat::AUTO_STEP);

        std::vector<Prediction> result = classifier->Classify(img, top_n_results);

        //...
        *length_of_out_result = ss.str().length();
    }

This works prefectly with some images but it doesnt work with others, for example when I try to imshow the image in the Classify_Image, right after being created form the data sent by C# application, I am faced with images like this : problematic example:

fine example :

Here are the original images for further investigations(may be nsfw for some people so I place the link) :
http://answers.opencv.org/upfiles/15029729463967486.jpg
http://answers.opencv.org/upfiles/15029729777606505.jpg

My own thought about the cause of the issue, is I am creating the image regardless of its true type, (setting all images to CV_8UC3 and Mat::AUTO_STEP. thats why some images are fine and some others are not. The problem is, I dont know how I'm supposed to assign the correct type to each image at creation time back in C++. (if thats the cause for such issue, if it is not then I have no idea what else could be doing this) Any help is greatly appreciated .