Figure 4.

Statistical relationship between the luminance boundaries in the projected images and the corresponding physical sources in 3D space. (A) Example of straight-line segments (shown in red) extracted from a scene in the database. The images were converted to gray scale from true color before the extraction of contours. (B) The normalized mean of the physical-to-projected length ratio (λ; in meters/pixel) plotted as a function of θ of luminance contours in the image plane (bin width of θ = 1°). The data obtained from this analysis, which represent a small subset of the data shown in Fig. 3, show the same peaks approximately 20–30° from the vertical and the same trough at 90°. The variation from the minimum to the maximum of this function is greater compared with the function in Fig. 3C. This greater variation arises because the extracted line segments tend to be in the ground plane (see Fig. 6 B and C for the effect of the ground plane) or in the more rectilinear components of the scenes (see A).