How can I convert the columns, or rows of an image to vectors so that instead of going through all
the pixels in the image as in

for (unsigned int j=1;j<g_image.nj()-1; j++)
        for (unsigned int i=1; i<g_image.ni()-1; i++)
                                  {     do something with pixel(i,j)}

I can work with the vectors? (as in matlab or fortran?)
will working with such vectors  give me such a big efficiency advantage as the ones in matlab for eg?

many thanks,