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Perception
Cognachrome color-tracking system. The Cognachrome Vision System form Newton
Research Labs is a color-tracking hardware-based sensor capable of extremely fast color
tracking on a dedicated processor [162]. The system will detect color blobs based on three
user-defined colors at a rate of 60 Hz. The Cognachrome system can detect and report on a
maximum of twenty-five objects per frame, providing centroid, bounding box, area, aspect
ratio, and principal axis orientation information for each object independently.
This sensor uses a technique called constant thresholding to identify each color. In
RGB (red, green and blue) space, the user defines for each of , G , and a minimum
R
B
and maximum value. The 3D box defined by these six constraints forms a color bounding
box, and any pixel with RGB values that are all within this bounding box is identified as a
target. Target pixels are merged into larger objects that are then reported to the user.
The Cognachrome sensor achieves a position resolution of one pixel for the centroid of
each object in a field that is 200 x 250 pixels in size. The key advantage of this sensor, just
as with laser rangefinding and ultrasonics, is that there is no load on the mobile robot’s
main processor due to the sensing modality. All processing is performed on sensor-specific
hardware (i.e., a Motorola 68332 processor and a mated framegrabber). The Cognachrome
system costs several thousand dollars, but is being superseded by higher-performance hard-
ware vision processors at Newton Labs, Inc.

CMUcam robotic vision sensor. Recent advances in chip manufacturing, both in terms
of CMOS imaging sensors and high-speed, readily available microprocessors at the 50+
MHz range, have made it possible to manufacture low-overhead intelligent vision sensors
with functionality similar to Cognachrome for a fraction of the cost. The CMUcam sensor
is a recent system that mates a low-cost microprocessor with a consumer CMOS imaging
chip to yield an intelligent, self-contained vision sensor for $100, as shown in figure 4.29.
This sensor is designed to provide high-level information extracted from the camera
image to an external processor that may, for example, control a mobile robot. An external
processor configures the sensor’s streaming data mode, for instance, specifying tracking
mode for a bounded RGB or YUV value set. Then, the vision sensor processes the data in
real time and outputs high-level information to the external consumer. At less than 150 mA
of current draw, this sensor provides image color statistics and color-tracking services at
approximately twenty frames per second at a resolution of 80 x 143 [126].
Figure 4.29 demonstrates the color-based object tracking service as provided by
CMUcam once the sensor is trained on a human hand. The approximate shape of the object
is extracted as well as its bounding box and approximate center of mass.

CMVision color tracking software library. Because of the rapid speedup of processors
in recent times, there has been a trend toward executing basic vision processing on a main