Monocular Optical Flow For Real-Time Vision Systems
Graduate Student - Master's
See full image of optical flow field of moving hand.
See full image of optical flow field magnitude and
While laser rangefinders offer high resolution depth maps, the apparatus is
sometimes too expensive for the needs of smaller industry groups. A low -
cost alternative is to produce lower-resolution depth maps using a structure -
from - motion algorithm with a common video camera and digitizing hardware.
An efficient scheme would involve an operator who would present the target
object to the video camera and move the object under the computer's
suggestions for new views. While the operator manipulates the object, the
computer would automatically track the target and produce new pose estimates
and depth maps at near real - time. These coarse depth maps can be processed
by generalized view integration algorithms to fuse the data into more detailed
Shown here is live video (1.4 FPS) overlaid with a red flow field, surrounded
by a green tracking window. The magnitude of the flow vectors is rendered at
left, brighter pixels indicate faster motion, black indicates no motion. The
green blob indicates the result of figure / ground separation.
For our experiments, we used off-the-shelf components on a 100 MHz SGI INDY
workstation. The video framegrabber is built-in, and the camera perched above
the monitor is inexpensive. Although the hardware can accomodate 640x480
8-bit video at 30 frames per second, our software was very demanding. We used
video images of 320x240 pixels, and the software grabs the images when it
finishes processing frame pairs, typically around 2 FPS. But when tracking is
enabled, the software predicts where the object moves, and will limit its
attention to that region, ignoring the background. With this strategy, we
have sustained 5 FPS.
See full image of hardware setup.
Our philosophy is to use commonly-available, low-cost approaches on
workstations. Investing in custom computing power does not always pay
off, since the desktop processing power rapidly obsoletes the
hand-made machines, and are more maintainable.
- 100 MHz SGI INDY
- MIPS R4600 CPU with MIPS R4610 FPU
- 32 Mbytes main memory
- built-in frame-grabber
- pre-installed frame-grabber drivers
- Irix 5.2 Operating System