Point Grey Research Grasshopper Technical Reference
Appendix C: Glossary
Revised 26-Nov-10
Copyright (c) 2010 Point Grey Research Inc.
56
Grabbing Images
A commonly-used phrase to refer to the process of enabling isochronous transfers on a
camera, which allows image data to be streamed from the camera to the host system.
Hz
Hertz. A unit of frequency; one Hertz has a periodic interval of one second. Often used
interchangeably with FPS as a measure of frame rate.
Isochronous Transmission
The transfer of image data from the camera to the PC in a continual stream that is
regulated by an internal clock. Isochronous transfers on the 1394 bus guarantee timely
delivery of data. Specifically, isochronous transfers are scheduled by the bus so that they
occur once every 125µs. Each 125µs timeslot on the bus is called a frame. Isochronous
transfers, unlike asynchronous transfers, do not guarantee the integrity of data through a
transfer. No response packet is sent for an isochronous transfer. Isochronous transfers
are useful for situations that require a constant data rate but not necessarily data integrity.
Examples include video or audio data transfers. Isochronous transfers on the 1394 bus do
not target a specific node. Isochronous transfers are broadcast transfers which use
channel numbers to determine destination.
Lookup Table
A matrix of gamma functions for each color value of the current pixel encoding format.
Node
An addressable device attached to a bus. Although multiple nodes may be present within
the same physical enclosure (module), each has its own bus interface and address space
and may be reset independently of the others.
Node ID
A 16-bit number that uniquely differentiates a node from all other nodes within a group of
interconnected buses. Although the structure of the node ID is bus-dependent, it usually
consists of a bus ID portion and a local ID portion. The most significant bits of the node ID
are the same for all nodes on the same bus; this is the bus ID. The least-significant bits of
the node ID are unique for each node on the same bus; this is called the local ID. The
local ID may be assigned as a consequence of bus initialization.
One Push
For use when a control is in manual adjust mode, One Push sets a parameter to an auto-
adjusted value, then returns the control to manual adjust mode.
PHY
Physical layer. Each 1394 PHY provides the interface to the 1394 bus and performs key
functions in the communications process, such as bus configuration, speed signaling and
detecting transfer speed, 1394 bus control arbitration, and others.
Pan
A mechanism to horizontally move the current portion of the sensor that is being imaged.
In stereo and spherical cameras, Pan controls which individual sensors transmit images.
Pixel Clock
The rate at which the sensor outputs voltage signals in each pixel from the optical input.
Pixel Format
The encoding scheme by which color or greyscale images are produced from raw image
data.
Quadlet
A 4 byte (32-bit) value.
Quadlet Offset
The number of quadlets separating a base address and the desired CSR address. For
example, if the base address is 0xFFFFF0F00000 and the value of the quadlet offset is
0x100, then the actual address offset is 0x400 and the actual adress 0xFFFFF0F00400.
Register
A term used to describe quadlet-aligned addresses that may be read or written by bus
transactions.
Saturation
This is how far a color is from a gray image of the same intensity. For example, red is
highly saturated, whereas a pale pink is not.
SDK
Software Development Kit
Sharpness
This works by filtering the image to reduce blurred edges.
Shutter
A mechanism to control the length of time the sensor is exposed to light from the image
field for each frame. In milliseconds (ms), it is the amount of time that the shutter stays
open, also known as the exposure or integration time. The shutter time defines the start
and end point of when light falls on the imaging sensor. At the end of the exposure period,
all charges are simultaneously transferred to light-shielded areas of the sensor. The
charges are then shifted out of the light shielded areas of the sensor and read out.
Signal-to-Noise Ratio (dB)
The difference between the ideal signal that you expect and the real-world signal that you
actually see is usually called noise. The relationship between signal and noise is called
the signal-to-nose ratio (SNR). SNR is calculated using the general methodology outlined
in
Knowledge Base Article 142.
SXGA
1280x1024 pixel resolution
Tilt
A mechanism to vertically move the current portion of the sensor that is being imaged.
Trigger
A signal to which the acquisition of images by the camera is synchronized. Triggers can
be from an outside electrical source (external) or software-generated (internal).
UXGA
1600x1200 pixel resolution
VGA
640x480 pixel resolution
White Balance
A method to enable white areas of an image to appear correctly by modifying the gain of
red and blue channels relative to the green channel. White balance can be used to
accommodate differing lighting conditions.
XVGA
1024x768 pixel resolution
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