Vector<XY> hist_data;
	for(int i=0;i<256;++i)
		hist_data << XY(i, 0);
	
	const RGBA *s = ~img;
	const RGBA *e = s + img.GetLength();
	while(s < e) {
		v_curr_value = (s->r+s->g+s->b)/3;
		hist_data[v_curr_value].y++;
		if(hist_data[v_curr_value].y>v_max_y)
			v_max_y = hist_data[v_curr_value].y;
		s++;
	}