Niessoh's profile - activity

I also need to add that If I use larger numbers such as 640, 480, the recordings are saved, its as if opencv has issues

Why is setting frame height and width prevents saving the webcam stream to disk? Hello everyone. Excuse me for the vagu

Thank you @Tetragramm. yes part of the issue was the step size. there are still other issues for example, when I resize the image in C# and pass it to the dll, although the full image works, the resized one has scan lines in it! like an old black and white TV with vertical scan lines! (here is screeshot : http://imgur.com/a/UvkhH) if I use opencv interal resize, its fine, if I send in the full size image it works, but when I use a resized one this is what I get ) I'll dig further and if I come up with an answer i update this post. Thank you for the heads-up

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/150...
http://answers.opencv.org/upfiles/150...

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 .

@berak: you are right, I'm sorry for the trouble. I ask a new question and explain everything there

@berak: you are right, I'm sorry for the trouble. I ask a new question and explain everything there

I notriced this is caused by the sample. and if I create a black image for example and try to resize it, there would be no problem at all. though, I have no idea what specifically is wrong with sample image!

this is a follow up question from here : https://stackoverflow.com/questions/4...

I'm trying to do a simple resize using opencv which ends up crashing!
This is the example code which the access violation occurs:

void Classifier::Preprocess(const cv::Mat& img, std::vector<cv::Mat>* input_channels)
{
    /* Convert the input image to the input image format of the network. */
    cv::Mat sample;
    if (img.channels() == 3 && num_channels_ == 1)
        cv::cvtColor(img, sample, cv::COLOR_BGR2GRAY);
    else if (img.channels() == 4 && num_channels_ == 1)
        cv::cvtColor(img, sample, cv::COLOR_BGRA2GRAY);
    else if (img.channels() == 4 && num_channels_ == 3)
        cv::cvtColor(img, sample, cv::COLOR_BGRA2BGR);
    else if (img.channels() == 1 && num_channels_ == 3)
        cv::cvtColor(img, sample, cv::COLOR_GRAY2BGR);
    else
        sample = img;

    //resize image according to the input
    cv::Mat sample_resized;
    Size size(input_geometry_.width,input_geometry_.height );

    if (sample.size() != input_geometry_)
        cv::resize(sample, sample_resized, size);
    else
        sample_resized = sample;

    //...
}

This is what I get in my C# solution when debugging :

Exception thrown at 0x00007FF8C8D9AA90 (opencv_imgproc310d.dll) in Classification Using dotNet.exe: 0xC0000005: Access violation reading location 0x0000018B000F2000.

If there is a handler for this exception, the program may be safely continued.

When I debug into the opencv code, I can see that sz is a null struct(<struct at NULL>) :

template<typename _Tp> inline
Size_<_Tp>::Size_(const Size_& sz)
    : width(sz.width), height(sz.height) {}

and this clearly causes the access violation!.

What is wrong here and what should I do ?

Thanks but the standard constructor fails with error message: cant convert argument 1 uchar* to const std::allocator<_Ty>& before that I tried to convert the image to grayslcale using cv::imread(fileName, cv::IMREAD_GRAYSCALE) So it doesnt compile now

@berak: I created the whole neural networks library, its not vectorized yet and I am experimenting the differences, thats why I am not allowed to use opencvs ml algorithms at the moment. By the way doing : cv::Mat mat = cv::imread(fileName, cv::IMREAD_GRAYSCALE);

mat.convertTo(mat,CV_32F);

std::vector<float> array(mat.data);

fails as well, complains about the conversion from uchar* to const std::allocator<_Ty>&.

Hello everyone, I'm new to OpenCV , please bare with me. I am trying to train my network with different images (gray scaled) and for that I need to feed it using vectors of float values. (vector<float>). I searched and downloaded a database of images that were of type pgm and I need to load them as vectors.
I searched and came up with this code:

cv::Mat mat;
mat = cv::imread(fileName.toStdString().c_str());
cv::imshow(fileName.toStdString().c_str(),mat);
std::vector<float> array;
array.assign((float*)mat.datastart, (float*)mat.dataend);

The image dimensions are 19*19 (19 rows and 19 columns, verified it by rows and cols properties of mat), so the vector size should be 361, but it is 270! Is what I'm doing wrong here?

@StevenPuttemans: Please recover the question, Thats not the answer to my question, since if you see the question, specially the section I updated, you will notice that I had already done the suggested answer and it didn't work in qt, and the reason is explain ed at the end of the question. (I couldn't post an answer earlier, the answer to this question is know since yesterday.