Page 411 - Mechatronics with Experiments

October 9, 2014 8:1
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JWST499-Cetinkunt
JWST499-c06
SENSORS 397 254mm×178mm
are set to one fixed low value, and all pixel values above that value are set to a high
value (i.e., black value). This turns the image into a binary image. Various detection
algorithms can be run quickly on such an image, such as the edge detection algorith.
2. Edge detection of an object: an edge is detected when a sharp change occurs from
one pixel to another in the gray scale value of the image. Once such a transition is
detected between two pixels in a search direction on the image array, then all the
pixels around the transition pixel are searched to determine the edge boundary.
3. Color or gray scale distribution (also called the histogram of image): this is a plot of
the gray scale distribution of the image, that is how many pixels (y-axis) has a given
gray scale (x-axis).
4. Connectivity of the object (detect discontinuities).
5. Image comparison with a reference image in memory (also called template matching),
that is image system may store a set of “good part” images. A real-time image is
compared to the stored images to determine whether it matches one of the template
images or not.
6. Position and orientation of an object relative to another reference.
7. Dimensions (length, area) of an image: once the boundaries of a part or parts in an
image are detemined, the dimensions and area information can be easily calculated.
8. Character recognition, that is recognizing letters and numerals.
9. Geometric image transformations, that is mathematical operations on the matrix data
of the image to move, rotate, stretch the image.

Example Consider a vision system with 1024 × 1024 pixel resolution. The camera
processes 60 frames per second. The resolution of the the A/D converter system is 8-bit.
What is the amount of data (bytes) processed per second? If the camera is focused into an
surface with 10 cm × 10 cm dimensions, what is the spatial resolution in measurement?
Each pixel holds one byte of data since the ADC converter has 8-bit resolution. The
number of bytes processed per second is equal to the number of data bytes per frame times
the number of frames per second,

N = 1024 × 1024 × 60 (6.190)
= 62 914 560 bytes∕s (6.191)
≈ 63 MB∕s (6.192)

Clearly, the amount of data processed per second is very large in a high resolution camera.
The smallest distances in x and y directions the system can measure are
10 cm
Δx = = 0.00976 cm = 0.0976 mm (6.193)
f
1024
10 cm
Δy = = 0.00976 cm = 0.0976 mm (6.194)
f
1024
which indicates that the vision system can measure dimensions in x and y coordinates with
about 0.1 mm accuracy.

6.13 GPS: GLOBAL POSITIONING SYSTEM

The global positioning system (GPS) is a location measurement system on Earth, based
on signals received from a group of satellites (about 24 satellites) orbiting the Earth at an