dct 2-D not working

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please show, how you get to y_values. also, those should be cv::Mat. there is a conversion between both, but we need to see your construct there, to find the error.

also, you will probably need to convert your input to float to apply dct/dft

Hello and thanks for your quick answer. The y_values is nothing more than a vector: std::vector< std::vector<int> > y_values(height, std::vector<int>(width)); , containing values. The extraction of the pixel values has not happened with open_cv library, so i only need to implement the dct using open_cv.

ah, ok, vector<vector<int>> will not work, you need consecutive (continuous) pixel data.

try something like :

Mat ocv_y;
for (size_t i=0; i<height; i++)
    ocv_y.push_back( y_values[i] );
ocv_y.convertTo(ocv_y, CV_32F);

Mat dct_result;
dct(ocv_y, dct_result);

Seems very interesting. Even though how can i do the above with an std::vector<int> y_values (height * width); ??

yes, like:

std::vector<int> y_values (height * width); 
Mat m(y_values); // flat 1d
m = m.reshape(1,width); // back to 2d (just make a new Mat header, no pixels copied)

I am sorry but i am kinda confused. I understand that this can be implemented with a Mat. But in documentation it mentioned also std::vector. The vector mentioned above is flat (1-D). So why do we need the Mat?

you can feed a std::vector to dct(), (it will be auto-converted to a cv::Mat) but in this case, it's only 1d, it does not know the shape of your original image.

also, again, float or double data needed

Thanks again for all your time. in your first example both ocv_y and dct_result would not be 1-D?

the 1st example is pushing rows of your vector<vector<>> into a Mat, expensive copy, but retaining the shape, the 2nd example keeps a pointer to the vector data, and builds a new 2d Mat header around it

both 2d, and the result will be 2d, too.

Thanks again. One last question: At some point at my program i want to access the Mat object's specific position as in std::vector vector1[i][j]. Is that possible? I get the error: expression must have pointer to object or handle-to-C++/CLI array type