We have observed through the glass door of the oven that the color change of roasting chickens is slow. The width of moving windows is set to 6 sample frames for computing the indicator St and the values of St (range from 0 to 1) are depicted by Eq. (19).The sample frames are attained by every two second. The recording chart of Se and St is shown in Fig. 8. These color curves matched our assumption that ‘browning color is gradually increasing. It presents from left to right that the browning color of roast chicken is more and more near dark brown. Meanwhile, results on comparison between St and Se can validate that St is smoother than Se,which is more suitable for control system design. By observing video and analysis of the proposed indicator, we found that the browning color quality nearby St of 0.7 ± 0.1 (time length 5 min) is for possible best tasty quality. Therefore, the mark of St may be regard as the ending signal of roasting.