OpenCV c++ trouble while iterating over the image pixels

I tried to change colors from an image but for unknown reasons, the changes don’t apply over the entire region of the image. (I use c++ with opencv)

To test it, I tried to simply put the same color in the every pixel of the image ( (36, 81, 214) for every pixel ). For a 360 x 600 image, the color is applied to all 358 rows (because of padding – initially I tried to implement convolution transformation from scratch but this is not the point of this topic), BUT ONLY to the first 150 cols – and I don’t understand why – I added final_i and final_j to test if i,j variables values reached 358, 598 values and they reached them – then why the new color is applied only to a region of the image?

Here is the code:

Mat apply_convolution_kernel(Mat img_color, int kernel[][3], int kernel_size){
    int rows = img_color.rows;
    int cols = img_color.cols;

    Mat result = Mat(rows,cols, CV_32SC3, 0.0);
    cout<<img_color.rows<< " "<<img_color.cols<<endl;
    cout<<result.rows<< " "<<result.cols<<endl;

    int final_i = 0;
    int final_j = 0;
    // apply the kernel operator
    int aux_size = kernel_size / 2; // e.g for 3 x 3 kernel, we need [3/2] = 1 auxiliary padding
    for(int i=aux_size;i<rows - aux_size;i++){
        for(int j = aux_size;j<cols - aux_size;j++){

            Vec3b & pixel_from_res = result.at<Vec3b>(i,j);
            pixel_from_res[0] = 36;
            pixel_from_res[1] = 81;
            pixel_from_res[2] = 214;

            final_i = i;
            final_j = j;
        }
    }

    cout<<"final i: "<< final_i << " final j: "<<final_j<<endl;

    return result;
}


int main()
{
    cout << "Start" << endl;
    Mat img_color = imread("sakura.jpg", 1);
    int conv_size = 3;
    int conv_operator[3][3] = {
        {0, 1, 0},
        {1, 4, 1},
        {0, 1, 0}
        } ;
    Mat m1 =apply_convolution_kernel(img_color, conv_operator,3);
    imwrite("filter.jpg", m1);

    return 0;
}

Also, the resulted image is: (just for exemplification)

>Solution :

Type of every channel of matrix element is 32 bits integer – CV_32SC3.

If you want to read a pixel of image as structure with 3 channels, where precision of channel is int, you should use Vec3i:

Vec3i & pixel_from_res = result.at<Vec3i>(i,j);

or change a type of matrix elements to be CV_8UC3 -> for such type you can apply Vec3b.