fg_rd            4139 ext/gd/gd.c    	int rd, gr, bl, fg_rd, fg_gr, fg_bl, bg_rd, bg_gr, bg_bl;
fg_rd            4175 ext/gd/gd.c    	fg_rd = gdImageRed  (bg_img, _fg);
fg_rd            4186 ext/gd/gd.c    		rd = bg_rd + (double) (fg_rd - bg_rd) / aa_steps * (i + 1);