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6 Common Sensing Techniques for Reactive Robots
to transform RGB data to a color space that more closely duplicates the re-
sponse of the human eye. It is used in biomedical imaging, but has not been
widely considered for robotics. The shape of the color space is triangular,
as shown in Fig. 6.14. Initial results indicate it is much more insensitive to
changes in lighting. 74 Fig. 6.15 shows an image and the results of segmenting
a color in RGB, HSI, and SCT spaces.

6.6.3 Region segmentation

The most ubiquitous use of computer vision in reactive robotics is to identify
REGION a region in the image with a particular color, a process called region segmen-
SEGMENTATION tation. Region segmentation and color affordances are a staple perceptual
algorithm for successful entries to many different international robot com-
petitions, including the AAAI Mobile Robot Competition, RoboCup, and
MIROSOT. There are many color region segmentation algorithms available
and Newton Labs sells a Cognachrome board dedicated to the rapid extrac-
tion of colored regions. The basic concept is to identify all the pixels in an
image which are part of the region and then navigate to the region’s center
(centroid). The first step is to threshold all pixels which share the same color
(thresholding), then group those together and throw out any pixels which
don’t seem to be in the same area as the majority of the pixels (region grow-
ing).
Ch. 5 described a robot which used red to signify a red Coca-Cola can for
recycling. Ideally, the robot during the searching for the can behavior would
BINARY IMAGE see the world as a binary image (having only 2 values) consisting of red,
THRESHOLDING not-red. This partitioning of the world can be achieved by thresholding the
image and creating a binary image. A C/C++ code example is shown below:

for (i= = 0; i < numberRows; i++)
for (j= = 0; j < numberColumns; j++) {
if ((ImageIn[i][j][RED] == redValue)
&& (ImageIn[i][j][GREEN] == greenValue)
&& (ImageIn[i][I][BLUE] == blueValue)) {
ImageOut[i][j] = 255;
}
else {
ImageOut[i][j] = 0;
}
}