Glossary
GUPPY Technical Manual
V4.0.1
219
Full binning
If horizontal and vertical binning are combined, every 4 pixels are consol-
idated into a single pixel. At first, two horizontal pixels are put together
and then combined vertically.
This increases light sensitivity by a total of a factor of 4 and at the same
time signal-to-noise separation is improved by about 6 dB. Resolution is
reduced, depending on the model.
See also: horizontal binning and vertical binning
Gain
Gain is the same as the contrast control on your TV. It is a multiplication
of the signal. In math terms, it controls the slope of the exposure/time
curve. The camera should normally be operated at the lowest gain possible,
because gain not only multiplies the signal, but also multiplies the noise.
Gain comes in very handy when you require a short exposure (say, because
the object is moving and you do not want any blur), but do not have ade-
quate lighting. In this situation the gain can be increased so that the
image signal is strong.
Gamma
Gamma is the exponent in a power-law relationship between video or pixel
values and the displayed brightness.
Each pixel in a digital image has a certain level of brightness ranging from
black (0) to white (1). These pixel values serve as the input for your com-
puter monitor. Due to technical limitations, CRT monitors output these val-
ues in a nonlinear way:
Output = Input
gamma
When unadjusted, most CRT monitors have a gamma of 2.5 which means
that pixels with a brightness of 0.5, will be displayed with a brightness of
only 0.5
2.5
= 0.18 in non-colormanaged applications. LCDs, in particular
those on notebooks, tend to have rather irregularly shaped output curves.
Calibration via software and/or hardware ensures that the monitor outputs
the image based on a predetermined gamma curve, typically 2.2 for Win-
dows, which is approximately the inverse of the response of the human
vision. The sRGB and Adobe RGB color spaces are also based on a gamma
of 2.2.
A monitor with a gamma equal to 1.0 would respond in a linear way (Out-
put = Input) and images created on a system with a gamma of 2.2 would
appear flat and overly bright in non-color managed applications.
GIF
GIF =
G
raphics
I
nterchange
F
ormat
GIF is one of the most common file formats used for images in web pages.
There are two versions of the format, 87a and 89a. Version 89a supports
animations, i.e. a short sequence of images within a single GIF file. A
GIF89a can also be specified for interlaced presentation.