Color Segmentation & Introduction to Motion Planning

CSE350/450-01111 Sep 03

Administration

• Questions?

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

Representing Colors in an RGB Image

Red Green Blue

How do we segment a “single” color?

Sample set for orange hat

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!

Color Tracking Demo

Motion Planning

The Basic Motion Planning Problem

Given an initial robot position and orientation in a potentially cluttered workspace, how should the robot move in order to reach an objective pose?