Figure 4.

Comparison of data from Gemvid and from Actiwatch. A: observed data from each device is presented in blue for Gemvid and red for Actiwatch. Mobile is going at 23.8 cm · s^-1 and the mobile surface is 128 cm · s^-1. B: correlation plot between the size of the moving surface and the mean number of pixels that changed for each value of area (n = 3 for each value of area).