Gpu is working slower than Cpu(General Filters)

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I am working on a barcode recognition project that includes filtration,Image geometric transformation and CNN implementation.

I wrote the code working on cpu and gpu correctly and created same filtration in cuda(using cuda namespace) and core(cpu).According the performance criteria of my project, The code is working x2 or x3 times faster in Cpu than Gpu.I searched all relativity between Cpu and Gpu memory and created two different program.

According to my research, I checked all implementation for splitting image memory to gpu and the reason where the GPU runs slowly.They directed me to run it in high resolution to see if Gpu runs faster than Cpu.But unfortunately Gpu was still working x2 slower than cpu.I would like to share part of the code here with same filtration on gpu and cpu.Therfore you can direct me right.I just would like to raise performance of my program using Gpu implementation.

IDE : Visual Studio 2015(x64), release mode in 64 bit

Nvdia Graphic Card : Nvdia Geforce gtx 550m , fermi

Cuda version : Cuda8 , compatible with given graphic card

I showed you part of sobel filtration function in Gpu and Cpu but it also includes Gaussianblur, Geometric transformation and Morphology filters in both gpu and cpu side.

Thank you in advance,

Sample Cpu Sobel filtration code;

Mat Morphology::Sobel_operations(Mat& gray_image){//directly change vector with using only struct(future operations)

    vector<Sobel_variables> sobel_variables(1);
    //Sobel_variables sobel_variables;
    sobel_variables[0].alpha = 1;

    sobel_variables[0].beta = 0.9;


    Sobel(gray_image, sobel_variables[0].Gradx, sobel_variables[0].ddepth, 1, 0, 3);
    Sobel(gray_image, sobel_variables[0].Grady, sobel_variables[0].ddepth, 0, 1, 3);

    subtract(sobel_variables[0].Gradx, sobel_variables[0].Grady, sobel_variables[0].Gradient);

    //normalize(sobel_variables[0].Gradient, sobel_variables[0].Gradient, 1, 0, NORM_MINMAX);
    //convertScaleAbs(sobel_variables[0].Gradient, sobel_variables[0].Gradient);


    add(sobel_variables[0].Grady, sobel_variables[0].Gradx, sobel_variables[0].Gradient1);


    //convertScaleAbs(sobel_variables[0].Gradient1, sobel_variables[0].Gradient1);//It can be used but not necessary

    addWeighted(sobel_variables[0].Gradient, sobel_variables[0].alpha, sobel_variables[0].Gradient1, sobel_variables[0].beta, 0, sobel_variables[0].Out_Image);



    imshow("Sobel_operations", sobel_variables[0].Out_Image);

    //------free memory of all unnecessarry images--------------------------
    sobel_variables[0].Gradx.release();
    sobel_variables[0].Grady.release();
    gray_image.release();
    sobel_variables[0].Gradient.release();
    sobel_variables[0].Gradient1.release();

    return sobel_variables[0].Out_Image;
}

The output result

Aproximately 110 ms with cpu in high resolution

Same sobel filtration with GPU;

Ptr<cuda::Filter> filter;
cuda::GpuMat Morphology::Sobel_operations(cuda::GpuMat& gray_image){//directly change vector with using only struct(future operations)

    vector<Sobel_variables> sobel_variables(1);
    //Sobel_variables sobel_variables;
    sobel_variables[0].alpha = 1;

    sobel_variables[0].beta = 0.9;

    //Apply sobel filter to x for cuda
    filter=cuda::createSobelFilter(gray_image.type(), sobel_variables[0].ddepth, 1, 0, 3);
    filter->apply(gray_image, sobel_variables[0].Gradx);

    //Apply sobel filter to y cuda
    filter = cuda::createSobelFilter(gray_image.type(),sobel_variables[0].ddepth, 0, 1, 3);
    filter->apply(gray_image, sobel_variables[0].Grady);

    cuda::subtract(sobel_variables[0].Gradx, sobel_variables[0].Grady, sobel_variables[0].Gradient);

    //normalize(sobel_variables[0].Gradient, sobel_variables[0].Gradient, 1, 0, NORM_MINMAX);
    //convertScaleAbs(sobel_variables[0].Gradient, sobel_variables[0].Gradient);


    cuda::add(sobel_variables[0].Grady, sobel_variables ...