void* by_number(void *arg){
    pthread_t id = pthread_self();
    for(int i = 0; i < height; i++){
        for(int j = 0; j < width; j++){
            for(int x = 0; x < thread_count; x++){
                if(pthread_equal(id,tid[x])){
                    if(can_change(x, numbers[i][j]) == 1){
                        numbers[i][j] = 255 - numbers[i][j];
                    }
                }
            }
        }
    }
}

int can_change(int thread_num, int number){
    int step = 256 / thread_count;
    if(thread_num * step <= number && number < (thread_num + 1) * step) return 1;
    return 0;
}