Class Objectives
• Review how color is represented and can be segmented in a computer image
• Introduction to basic Motion Planning for a mobile robot
Supporting References
• Color Segmentation
– CVOnline “Color Image Processing” Lecture Notes
– Poynton's Color FAQ
• Motion Planning
– “Motion Planning Using Potential Fields”, R. Beard & T. McClain, BYU, 2003
Color Segmentation Motivation
• Computationally inexpensive (relative to other features)
• “Contrived” colors are easy to track
• Combines with other features for robust tracking
What is Color?
• Color is the perception of light in the visible region of the spectrum
• Wavelengths between 400nm - 700nm
• Imagers
– Retina (humans)
– CCD/CMOS (cameras)
RGB Color Space• Motivated by human visual system
– 3 color receptor cells (rods) in the retina with different spectral response curves
• Used in color monitors and most video cameras
YCbCr (YUV/YIQ) Color Space
“Greyscale”Y= 0.30*R+0.59*G+0.11*B
B
G
R
V
U
Y
081.0419.0500.0
500.0331.0169.0
114.0587.0299.0
• Separates luma (“brightness”) from the chroma (“color”) channels:
Y = 0.30*R+0.59*G+0.11*B, Cb = B-Y, Cr=R-Y
• YUV/YIQ are similar variants based upon NTSC/PAL television signals
Simple RGB Color Segmentation
)1.1,5.254( )8.14,6.103( )07.6,1.45(
256),(251 yxIR 135),(73 yxIG 58),(32 yxIB
& &
Red Green Blue
SegmentedColor Image
Again the Issue of
Thresholding!