IDEC DATAVS2 Series - Manual (Page 82)

SVS2 Series Instruction Manual
77
16.10. ► Pattern match
In the pattern match method, a sample object is recognised by searching for the matching brightness
matrix in the target image.
The system stores a "pattern" of the master image and tries to find that pattern in all inspected target
images. During the search process, the pattern is made to slide over the image while brightness
differences are calculated pixel by pixel. An object is recognized when the total calculated difference is
below a preset threshold.
16.11. ► Exposure
Exposure time determines how long the image acquisition device must remain exposed to light.
Image quality depends on this parameter, that is determined based on:
• Lens aperture;
• Exposure time.
The term Lens aperture denotes the ratio of lens length to lens width. A longer lens (where light travels
a longer distance) will have a higher ratio and will provide less strength. Conversely, a shorter lens
features a lower ratio (fast lens).
The term exposure time is also known as "shutter opening time" and is directly proportional to the
quantity of light hitting the sensor: the greater the shutter opening time, the greater the quantity of
light, hence the brighter the acquired image.
A fast lens allows for shorter shutter opening time.
This is because exposure is a combination of aperture and opening time. As these are inversely
proportional, doubling aperture allows for halved opening time.
This determines correct exposure, which is the right quantity of light needed for details to be visible
both in the dark and bright areas of the image.
Underexposure will result in crushed blacks, i.e. loss of detail.
Overexposure will produce blown-out areas (bright, pale and flat).