Glossary
GUPPY Technical Manual
V4.0.1
230
Smear
Smear is an undesirable artifact of CCDs that appears in the picture as a
vertical streak above and below a very bright object in the scene. Smear is
caused by parasitic light getting into the vertical transfer registers. It is
greatly reduced by the microlens-type of CCD used in Hyper HAD and Power
HAD sensors. Almost suppressed in FIT CCDs.
SNR
SNR =
s
ignal-to-
n
oise
r
atio
Square pixel
Pixels of the same x and y dimensions (pixel aperture ratio PAR = 1). In the
case of rectangular (non-square) pixels (usual in TV) one must maintain
the aspect ratio when measuring objects, because the dimensions of stored
frames aren't equal to true dimensions; resolutions along x and y axes
aren't the same. Use of square pixels solves such problems - picture ele-
ments are equally arrayed in both directions, and allow easy addressing.
Thus aspect ratio of the image does not require adjustment. This is needed
in image processing tasks requiring accurate image measuring.
Aspect ratio: The ratio of horizontal to vertical dimension of the illumi-
nated sensing area.
Pixel aperture dimension ratio: Defines the pixel dimension (the ratio of its
width to height). This parameter describes the resolution (granularity) and
the reproduction behavior of an image sensor area.
Aspect ratio deviation: Shows the ratio between frame store data and true
dimensions of an image.
Sub-sampling
Sub-sampling
is the process of skipping neighboring pixels (with the same
color) while being read out from the CMOS or CCD chip.
CMOS equipped MARLIN models, both color and b/w have this feature (FW
> 2.03).
Sub-sampling is used primarily for 2 reasons:
•
A reduction in the number of pixels and thus the amount of data
while retaining the original image area angle and image brightness
•
CMOS: an increase in the frame rate.
Similar to binning mode the cameras support horizontal, vertical and h+v
sub-sampling mode.
Trigger
Trigger is an input to an industrial digital camera than initiates the image
capture sequence. Otherwise, an electrical signal or set of signals used to
synchronize a camera, or cameras, to an external event.
The term
trigger
is sometimes used in the sense of a trigger shutter.
Trigger shutter
A trigger shutter is a shutter mode with random timing or even with ran-
dom shutter speed. Such randomness is controlled by the trigger signal
mentioned above.