Point Grey Research Grasshopper Technical Reference
Appendix C: Glossary
Revised 26-Nov-10
Copyright (c) 2010 Point Grey Research Inc.
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Appendix C: Glossary
Term Definition
1394a
An Institute of Electrical and Electronics Engineers (IEEE) interface standard capable of
transferring data at a rate of 400Mbit per second.
1394b
An IEEE interface standard capable of transferring data at a rate of 800Mbit per second.
Absolute Values
Real-world values, such as milliseconds (ms), decibels (dB) or percent (%). Using the
absolute values is easier and more efficient than applying complex conversion formulas to
integer values.
Analog-to-Digital Converter
Often abbreviated as ADC or A/D converted, it is a device that converts a voltage to a
digital number.
API
Application Programming Interface. Essentially a library of software functions.
Asynchronous Transmission
The transfer of image data from the camera to the PC that is regulated by an external
signal, such as a trigger. Asynchronous transfers do not guarantee when data will be
transferred. However, they do guarantee that data will arrive as sent. Asynchronous
transfers may be used when data integrity is a higher priority than speed. An example
might be an image data transfer to a printer, where speed is less critical than getting the
image pixels correct. Asynchronous transfers are initiated from a single node, designated
the ‘requestor’, to or from the address space of another node, designated the ‘responder’.
Asynchronous requests are packet-based. The requestor node generates a request
packet that the 1394 bus sends to the responder node. The responder node is
responsible for handling the request packet and creating a response packet that is sent
back to the requestor node to complete a single transfer. There are three types of 1394
asynchronous transfers: Read, Write and Lock.
BPP
Bytes per packet. An image is broken into multiple packets of data, which are then
streamed isochronously to the host system. Each packet is made up of multiple bytes of
data.
Brightness (%)
This is essentially the level of black in an image. A high brightness will result in a low
amount of black in the image. In the absence of noise, the minimum pixel value in an
image acquired with a brightness setting of 1% should be 1% of the A/D converter’s
minimum value.
Config ROM
Configuration read-only memory. A section of memory dedicated to describing low-level
device characteristics such as Model and Vendor ID, IEEE-1394 version compliance,
base address quadlet offsets, etc.
Color Processing
Also known as ‘interpolation,’ an algorithm for converting raw Bayer-tiled image data into
full color images. Depending on camera model, this process takes place either on-camera
or on the PC. For more information, refer to
Knowledge Base Article 33.
DCAM Abbreviation for the IIDC 1394-based Digital Camera (DCAM) Specification, which is the
standard used for building FireWire-based cameras.
Dynamic Range
The difference between the maximum and minimum amounts of light that a sensor can
measure. This is bounded on the upper end by the maximum charge that any pixel can
contain (sensor full well depth) and at the lower end by the small charge that every sensor
spontaneously generates (read noise).
Exposure (EV)
This is the average intensity of the image. It will use other available (non-manually
adjustable) controls to adjust the image.
Firmware
Programming that is inserted into programmable read-only memory, thus becoming a
permanent part of a computing device. Firmware is created and tested like software and
can be loaded onto the camera.
Format_7
Encompasses partial or custom image video formats and modes, such as region of
interest of pixel binned modes. Format_7 modes and frame rates are defined by the
camera manufacturer, as opposed to the DCAM specification.
FPS
Frames Per Second.
Frame Rate
Often defined in terms of number of frames per second (FPS) or frequency (Hz). This is
the speed at which the camera is streaming images to the host system. It basically
defines the interval between consecutive image transfers.
Gain (dB)
The amount of amplification that is applied to a pixel by the A/D converter. An increase in
gain can result in a brighter image and an increase in noise.
Gamma
Gamma defines the function between incoming light level and output picture level.
Gamma can also be useful in emphasizing details in the darkest and/or brightest regions
of the image.
GPIO
General Purpose Input/Output.
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