User's Manual
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6-
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6.5 Glossary of Imaging Terms
CCD:
Charge Coupled Device.
CCD Element:
Each CCD element or pixel is a single photodetector capable of
detecting light and converting and storing the information in an
electronic form.
CCD Array:
A CCD array can be visualized as a periodic grid array of individual
CCD elements, (analogous to buckets of water). When the shutter is
open, photons of light (analogous to drops of rain) fall into the photo
detectors (buckets of water).
Integration:
When the camera shutter is open and the CCD is exposed to light.
Thermoelectric A
thermoelectric cooler (TEC) that pulls heat away from the CCD.
Cooler:
The heat is then transferred to the camera body, which is cooled by
forced air.
Dark Current:
Dark current arises from the creation of electrons generated through
the process of thermal emission within the silicon layers comprising
the CCD. Dark current noise is the square root of the number of dark
current electrons. The presence of dark current is an additional
concern in low light level applications. It is important to ensure that
dark current noise does not exceed read noise from the signal even
when long integration times are used
Signal to Noise: Signal to noise ratio (SNR) is the measure of the signal quality at a
given pixel. It is the ratio of the measured signal to the overall
measured noise at that pixel.
Dynamic Range: Dynamic range of a CCD is simply defined as the ratio of CCD
saturation to the read noise. It is the ability to quantitatively detect
very dim and very bright pixels within a single image.
Quantum
Quantum efficiency is the measure of the effectiveness of an imaging
Efficiency:
device to produce electronic charge from incident photons. This is an
especially important property when performing very low light level
imaging.
Dead Pixels:
There are a variety of different grades of CCD chips. Each grade has
some percentage of dead or bad pixels. These are typically displayed
as white or dark lines on the image. Most CCD systems correct for
dead pixels.
Image
Image resolution refers to the spacing of pixels in the image and is
Resolution:
measured in pixels per inch (ppi). If an image has a resolution of 72
ppi this means that it contains 5182 pixels (72 x 72) in a square inch.
Monitor
Monitor resolution defines the number of dots or pixels per unit length of
Resolution:
output. It is commonly measured in dots per inch (dpi). The monitor
resolution determines the size of the displayed image and should not
be confused with image resolution, which reflects the spacing of
pixels in the image.
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