Dalsa MotionVision CA-D6-0256W-ECEW, User Manual

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CA-D6-xxxxW User’s Manual
03-32-00225-06 DALSA INC.
1.4 CCD Camera Primer
How CCD Image Sensors Work
In a CCD camera such as the CA-D6-xxxxW, a CCD image sensor converts
photons (light) into electrons (electricity). When photons hit an image sensor, an
electron is released, and the sensor adds this electric charge to the charge it has
already collected. This is called charge integration. The brighter your light
source, the more photons available for the sensor to integrate, and the smaller
the amount of time required to collect a given amount of charge.
The way photosensitive elements (pixels)
on CCD image sensors collect charge has
often been compared to buckets filling
with water. From this analogy comes the
term “full-well capacity,” meaning the
maximum charge (number of electrons) a
pixel can hold without “spilling” charge
onto adjacent pixels.
As light energy hits an array of pixels, the pixels collect charge. At certain
intervals, a frame transfer sensor such as the IA-D6 transfers its collected charge
from the active, photosensitive region to a light-shielded storage region. Then it
transfers the charge, line by line, to one or more readout registers, which feed
each pixel’s charge from the image sensor into an output node that converts the
charges into voltages.
After this transfer and
conversion, the
voltages are amplified
to become the camera’s
analog output. In
digital output cameras,
the camera’s analog-to-
digital (A/D) board
converts voltages to
digital numbers (0-255
for 8-bit cameras).
These digital numbers
are what the camera
outputs as data to a framegrabber.
For more information on terms and concepts from the digital imaging industry, see
DALSA’s current Databook Glossary, CCD Technology Primer, and Application Notes.