Glossary
GUPPY Technical Manual
V4.0.1
216
Dark current
Dark current is the accumulation of electrons within a CCD or CMOS image
sensor that are generated thermally rather than by light. This is a form of
noise that is most problematic in low light applications requiring long
exposure times.
Dark noise
Dark noise is the statistical variation of the dark current, equal to the
square root of the dark current. Dark current can be subtracted from an
image, while dark noise remains. Also called dark current noise.
dB
abbr. of decibel
see decibel
DCAM
DCAM =
d
igital
cam
era
s
pecification
DCAM or IIDC is a software interface standard for communicating with cam-
eras over FireWire. It is a standardized set of registers etc. If a camera is
DCAM compliant then its control registers and data structures comply with
the DCAM spec. Such a camera can be truly plug & play in a way that other
cameras are not. Recent specifications are IIDC V1.30 and IIDC V1.31.
Decibel
Decibel (abbr. dB) is a measurement unit of dynamic range.
Depth of field
Depth of field refers to the in-focus region of an imaging system. When
using a lens, especially in close proximity, objects at and near a certain
distance will be in focus whereas other objects in the field of view that are
closer or farther away will appear fuzzy, or out of focus. The depth of the
region that appears in focus is called the depth of field. Generally speak-
ing, the depth of field will be large if the lens aperture is small (large f-
number), and the depth of field will be small with a wide aperture (small
f-number).
Digital camera
A digital camera is an electronic device to transform images into electronic
data. Modern digital cameras are typically multifunctional and the same
device can take photographs, video, and/or sound.
Digital photography
Digital photography uses an electronic sensor to record the image as a
piece of electronic data.
There are two main types of sensors:
•
charge-coupled device (CCD)
•
CMOS semiconductor
There are also two main types of sensor mechanisms:
•
Area array
•
Linear array (very rare, only limited to the highest-end)
An area array sensor reads the entire image plane at once, whereas a linear
array sensor works more like a flatbed scanner.