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"bright" 6 Common Sensing Techniques for Reactive Robots
pastel
white
saturation

green orange
cyan red 0

magenta

hue: 0-360
(wavelength)
intensity: 0-1
(increasing
signal strength)

saturation:0-1
(decreasing whiteness)

Figure 6.13 HSV space representation.

HSV is a three-dimensional space in that it has three variables, but it is def-
initely not a cube representation, more of a cone as seen in Fig. 6.13. The hue,
or color, is measured in degrees from 0 to 360. Saturation and intensity are
real numbers between 0 and 1. These are generally scaled to 8-bit numbers.
Accordingly, red is both 0 and 255, orange is 17, green is at 85, blue is 170,
with magenta at 200.
HSV space is challenging for roboticists for many reasons. First, it re-
quires special cameras and framegrabbers to directly measure color in HSV
space. This equipment is prohibitively expensive. Second, there is a software
conversion from the RGB space measured by consumer electronics, but it is
computationally expensive and has singularities (values of RGB where the
conversion fails). These singularities occur at places where the three colors
for a pixelare thesame; theflatness of thered colorplane in CCD cameras
increases the likelihood that a singularity will occur.
An alternative color space that is currently being explored for robotics is
the Spherical Coordinate Transform (SCT). 140 That color space was designed