... //_xi is precomputed 
for(each content1) for(each cont2){ //pseudo code, where content1 and content2 are both 1D int arrays of size width * height with each element taking value from 0 to 255.
    for(k = 0; k < width * height ; k++) { //19.39% time. where width and height are both int
      if(content1[k] == 0) l += _xi[content2[k]]; // 69.89% time, where  _xi is a 1D double array of size 256
    }
}

for(each content1) for(each cont2){
...
}

for each content1
   for(k=0;k<256;k++)
      if(content1[k] == 0)
         for each content2
            l += x[content2[k]]

... //_xi is precomputed 
size =  width * height;
for each content1
    for(k = 0; k < size ; k++) { //7.64% time
      if(content1[k] == 0) //  8.73% time
         for each content2 // 8.75% time
            tmp =  _x[content2[k]] // 18.90% time
            l += tmp // 28.53% time

Vignette_size =   Vignette::width * Vignette::height ; //24 * 24. Vignette is a class.
for(every possible tmplt){// pseduo-code, since the real code is too long. tmplt is of type Vignette*
   generate the tmplt // pseduo-code, since the real code is too long
   for(int k = 0; k < Vignette_size ; k++) { 
      if(tmplt->content[k] == 0){ // tmplt->content is a 1D int array of 24*24
          for(int i = 0; i < nb_vignettes; i++){
              double tmp = _xi[vignettes[i].content[k]]; // _xi is a 1D double array of size 256. vignettes  is of type Vignette*
              log_prob_img_t[i] += tmp;}
      }
    }
}