Figure 1

The characteristic of features. (a) An input image, (b) the reference background image, (c) intensity difference image between (a) and (b), (d) thresholding of (c) with a low value (80), (e) thresholding of (c) with a middle value (100), (f) thresholding of (c) with a large value (120), (g) hue difference image between (a) and (b), (h) thresholding of (g) with a low value (80), (i) thresholding of (g) with a middle value (100), (j) thresholding of (g) with a large value (120), (k) SSIM difference image between (a) and (b), (l) thresholding of (k) with a low value (0.4), (m) thresholding of (k) with a middle value (0.5), and (n) thresholding of (k) with a large value (0.6).