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6-1
6
Image Acquisition
This chapter contains information about acquiring images with the NI 17xx Smart Camera and
explains the relationships between triggering, lighting, and exposure.
Exposure
The NI 17xx Smart Camera provides control of the image sensor exposure time through
software. The exposure time is the amount of time that light is allowed to strike the sensor to
produce an image. When light strikes the surface of the sensor, it dislodges electrons. As more
light strikes the sensor, more electrons are freed, creating a charge on the sensor.
For a given amount of light, the sensor collects more charge during a longer exposure time than
a shorter exposure time. Because the charge is what is read out to produce the image, it is
important to have an optimal amount of light and exposure time for your application.
Exposing the image sensor for too short of a time relative to the amount of light in the
environment results in a dark, low contrast image. Exposing the image sensor for too long of a
time relative to the amount of light in the environment results in a bright, low contrast image.
When the image sensor is exposed for an appropriate amount of time relative to the light in the
environment, acquired images will exhibit appropriate contrast to easily distinguish both dark
and light features. Contrast is a key factor in obtaining good results from image processing
algorithms.
In applications where the object under inspection is moving, the exposure time must be carefully
considered. If the object moves significantly during the exposure, the resulting image is blurry
and unsuitable for processing.
The maximum exposure time for imaging a moving object without blurring depends on the per
pixel spatial resolution and the rate of motion of the object. The per pixel spatial resolution is the
field of view, calculated in the
, divided by the
number of pixels in the sensor. Together, this information can be used to calculate the maximum
exposure. Assuming the object is moving horizontally across the field of view, use Equation 6-1
to calculate the maximum exposure time.
Содержание NI Vision 17 Series
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