NI-IMAQ Function Reference Help

Edition Date: May 2018

Part Number: 370161M-01

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A/D Analog-to-digital.
AC Alternating current.
acquisition window The image size specific to a video standard or camera resolution.
active line region The region of lines actively being stored; defined by a line start (relative to vertical sync signal) and a line count.
active pixel region The region of pixels actively being stored; defined by a pixel start (relative to the horizontal sync signal) and a pixel count.
ADC Analog-to-digital converter. An electronic device, often an integrated circuit, that converts an analog voltage to a digital number.
address Character code that identifies a specific location (or series of locations) in memory.
ANSI American National Standards Institute.
antichrominance filter Removes the color information from the video signal.
API Application programming interface.
area A rectangular portion of an acquisition window or frame that is controlled and defined by software.
array Ordered, indexed set of data elements of the same type.
ASIC Application-specific integrated circuit. A proprietary semiconductor component designed and manufactured to perform a set of specific functions for a specific customer.
aspect ratio The ratio of a picture or image's width to its height.


back porch The area of the video signal between the rising edge of the horizontal sync signal and the active video information.
Bayer encoding Method to produce color images with a single imaging sensor, as opposed to three individual sensors for the red, green, and blue components of light.
Bayer pattern Color filter array pattern that can appear in four variations, depending on the current left and top offsets of the acquisition window:
bit depth The number of bits per pixel.
black reference level The level that represents the darkest an image can get. See also white reference level.
BMP Bitmap. Image file format commonly used for 8-bit and color images (extension .bmp).
buffer Temporary storage for acquired data.
bus The group of conductors that interconnect individual circuitry in a computer, such as the PCI bus; typically the expansion vehicle to which I/O or other devices are connected.


cache High-speed processor memory that buffers commonly used instructions or data to increase processing throughput.
CCIR Comite Consultatif International des Radiocommunications. A committee that developed standards for color video signals.
chrominance The color information in a video signal.
CMOS Complementary metal-oxide semiconductor.
CompactPCI Refers to the core specification defined by the PCI Industrial Computer Manufacturer's Group (PICMG).
compiler A software utility that converts a source program in a high-level programming language, such as Basic, C, or Pascal, into an object or compiled program in machine language. Compiled programs run 10 to 1,000 times faster than interpreted programs. See also interpreter.
conversion device Device that transforms a signal from one form to another; for example, analog-to-digital converters (ADCs) for analog input and digital-to-analog converters (DACs) for analog output.
CPU Central processing unit.
CSYNC Composite sync signal. A combination of the horizontal and vertical sync pulses.


D/A Digital-to-analog.
DAC Digital-to-analog converter; an electronic device, often an integrated circuit, that converts a digital number into a corresponding analog voltage or current.
DAQ Data acquisition. (1) Collecting and measuring electrical signals from sensors, transducers, and test probes or fixtures and inputting them to a computer for processing. (2) Collecting and measuring the same kinds of electrical signals with A/D or DIO devices plugged into a computer, and possibly generating control signals with D/A and/or DIO devices in the same computer.
DC Direct current.
default setting A default parameter value recorded in the driver; in many cases, the default input of a control is a certain value (often 0) that means use the current default setting.
DIN Deutsche Industrie Norme. A format for electrical connectors.
distance calibration Determination of the physical dimensions of a pixel by defining the physical dimensions of a line in the image.
distance function Assigns to each pixel in an object a gray-level value equal to its shortest Euclidean distance from the border of the object.
DLL Dynamic link library. A software module in Microsoft Windows containing executable code and data that can be called or used by Windows applications or other DLLs; functions and data in a DLL are loaded and linked at run time when they are referenced by a Windows application or other DLLs.
DMA Direct memory access. A method by which data can be transferred to and from computer memory from and to a device or memory on the bus while the processor does something else; DMA is the fastest method of transferring data to/from computer memory.
DRAM Dynamic RAM.
driver Software that controls a specific hardware device such as an image acquisition device.
dynamic range The ratio of the largest signal level a circuit can handle to the smallest signal level it can handle (usually taken to be the noise level), normally expressed in decibels.


EEPROM Electrically erasable programmable read-only memory. ROM that can be erased with an electrical signal and reprogrammed.
external trigger A voltage pulse from an external source that triggers an event such as A/D conversion.


field For an interlaced video signal, a field is half the number of horizontal lines needed to represent a frame of video; the first field of a frame contains all of the odd-numbered lines, and the second field contains all of the even-numbered lines.
FIFO First-in first-out memory buffer. The first data stored is the first data sent to the acceptor; FIFO buffers are used on image acquisition devices to temporarily store incoming data until that data can be retrieved.
flash ADC An ADC whose output code is determined in a single step by a bank of comparators and encoding logic.
frame A complete image; in interlaced formats, a frame is composed of two fields.
front porch The area of a video signal between the start of the horizontal blank and the start of the horizontal sync.
function A set of software instructions executed by a single line of code that may have input and/or output parameters and returns a value when executed.


gain Applied value to compensate for discrepancies in the filter for a particular color.
gamma The nonlinear change in the difference between the video signal's brightness level and the voltage level needed to produce that brightness.
genlock The process of synchronizing a video source to the signal from a separate video source. The circuitry aligns the video timing signals by locking together the horizontal, vertical, and color subcarrier frequencies and phases and generates a pixel clock that clocks pixel data into memory for display or into another circuit for processing.
grab Performs an acquisition that loops continually on one buffer. You obtain a copy of the acquisition buffer by grabbing a copy to a separate buffer that can be used for analysis.
GUI Graphical user interface. An intuitive, easy-to-use means of communicating information to and from a computer program by means of graphical screen displays; GUIs can resemble the front panels of instruments or other objects associated with a computer program.


hardware The physical components of a computer system, such as the circuit boards, plug-in boards, chassis, enclosures, peripherals, cables, and so on.
HSYNC Horizontal sync signal. The synchronization pulse signal produced at the beginning of each video scan line that keeps a video monitor's horizontal scan rate in step with the transmission of each new line.
hue Represents the dominant color of a pixel. The hue function is a continuous function that covers all the possible colors generated using the R, G, and B primaries. See also RGB.


IEEE Institute of Electrical and Electronics Engineers.
INL Integral nonlinearity. A measure, in LSB, of the worst-case deviation from the ideal A/D or D/A transfer characteristic of the analog I/O circuitry.
instrument driver A set of high-level software functions, such as NI-IMAQ, that controls specific plug-in computer boards; instrument drivers are available in several forms, ranging from a function callable from a programming language to a virtual instrument (VI) in LabVIEW.
interlaced A video frame composed of two interleaved fields; the number of lines in a field are half the number of lines in an interlaced frame.
interpreter A software utility that executes source code from a high-level language, such as Java or Basic, by reading one line at a time and executing the specified operation. In contrast, a compiler converts all source code to executable machine code before execution. Compiled languages give significantly higher performance than interpreted languages. Examples of compiled languages are C, C++, and LabVIEW, while Java and Basic are generally interpreted languages. See also compiler.
interrupt A computer signal indicating that the CPU should suspend its current task to service a designated activity.
interrupt level The relative priority at which a device can interrupt.
I/O Input/output. The transfer of data to/from a computer system involving communications channels, operator interface devices, or data acquisition and control interfaces.
IRE A relative unit of measure (named for the Institute of Radio Engineers). 0 IRE corresponds to the blanking level of a video signal, 100 IRE to the white level. Note that for CIR/PAL video the black level is equal to the blanking level or 0 IRE, while for RS-170/NTSC video, the black level is at 7.5 IRE.
IRQ Interrupt request. See also interrupt.
ISO Trigger A high voltage isolated trigger.


library A file containing compiled object modules, each comprised of one or more functions, that can be linked to other object modules that make use of these functions.
line count The total number of horizontal lines in the picture.
LSB Least significant bit.
luminance The brightness information in the video picture. The luminance signal amplitude varies in proportion to the brightness of the video signal and corresponds exactly to the monochrome picture.
LUT Lookup table. Table containing values used to transform the gray-level values of an image. For each gray-level value in the image, the corresponding new value is obtained from the lookup table. Also a selection in Measurement & Automation Explorer (MAX) for Vision that contains formulas that let you implement simple imaging operations such as contrast enhancement, data inversion, gamma manipulation, or other nonlinear transfer functions.


MAX Measurement & Automation Explorer. The National Instruments Windows-based graphical configuration utility you can use to configure NI software and hardware, execute system diagnostics, add new channels and interfaces, and view the devices and instruments you have connected to your computer. MAX is installed on the desktop during the National Instruments driver software installation.
memory buffer See buffer.
memory window Continuous blocks of memory that can be accessed quickly by changing addresses on the local processor.
MSB Most significant bit.
MTBF Mean time between failure.
mux Multiplexer. A switching device with multiple inputs that selectively connects one of its inputs to its output.


NI-IMAQ Driver software for National Instruments image acquisition hardware.
noninterlaced A video frame where all the lines are scanned sequentially, rather than being divided into two frames as in an interlaced video frame.
NTSC National Television Standards Committee. The committee that developed the color video standard used primarily in North America, which uses 525 lines per frame. See also PAL.
NVRAM Nonvolatile RAM. RAM that is not erased when a device loses power or is turned off.


one-shot Applies to pulse generation and acquisitions. A one-shot pulse or acquisition happens only once.


PAL Phase Alternation Line. One of the European video color standards; uses 625 lines per frame. See also NTSC.
PCI Peripheral Component Interconnect. A high-performance expansion bus architecture originally developed by Intel to replace ISA and EISA; it is achieving widespread acceptance as a standard for PCs and workstations and offers a theoretical maximum transfer rate of 133 Mbytes/s.
PCIe PCI express. A high-performance expansion bus architecture originally developed by Intel to replace PCI. PCIe offers a theoretical maximum transfer rate that is dependent upon lane width. A x1 link theoretically provides 250 MB/s in each direction—to and from the device. Once overhead is accounted for, a x1 link can provide approximately 200 MB/s of input capability and 200 MB/s of output capability. Increasing the number of lanes in a link increases maximum throughput by approximately the same factor.
PCLK Pixel clock signal. Times the sampling of pixels on a video line.
PGIA Programmable gain instrumentation amplifier.
picture aspect ratio The ratio of the active pixel region to the active line region; for standard video signals such as RS-170 or CCIR, the full-size picture aspect ratio typically is 4/3 (1.33).
pixel Picture element. The smallest division that makes up the video scan line; for display on a computer monitor, a pixel's optimum dimension is square (aspect ratio of 1:1, or the width equal to the height).
pixel aspect ratio The ratio between the physical horizontal size and the vertical size of the region covered by the pixel. An acquired pixel should optimally be square, thus the optimal value is 1.0; however, typically it falls between 0.95 and 1.05, depending on camera quality.
pixel clock Divides the incoming horizontal video line into pixels.
pixel count The total number of pixels between two horizontal sync signals; the pixel count determines the frequency of the pixel clock.
PLL Phase-locked loop. Circuitry that provides a very stable pixel clock that is referenced to another signal, for example, an incoming horizontal sync signal.
protocol The exact sequence of bits, characters, and control codes used to transfer data between computers and peripherals through a communications channel.
PXI PCI eXtensions for Instrumentation. An open specification that builds on the CompactPCI specification by adding instrumentation-specific features.


quadrature encoderAn encoding technique for a rotating device where two tracks of information are placed on the device, with the signals on the tracks offset by 90 degrees from each other. The phase difference indicates the position and direction of rotation.


RAM Random-access memory.
real time A property of an event or system in which data is processed as it is acquired instead of being accumulated and processed at a later time.
relative accuracy A measure in LSB of the accuracy of an ADC; it includes all nonlinearity and quantization errors but does not include offset and gain errors of the circuitry feeding the ADC.
resolution (1) The number of rows and columns of pixels. An image composed of m rows and n columns has a resolution of . This image has n pixels along its horizontal axis and m pixels along its vertical axis. (2) The smallest signal increment that can be detected by a measurement system. Resolution can be expressed in bits, proportions, or a percentage of full scale. For example, a system has 12-bit resolution, one part in 4,096 resolution, and 0.0244 percent of full scale.
RGB Color encoding scheme using red, green, and blue (RGB) color information where each pixel in the color image is encoded using 32 bits: 8 bits for red, 8 bits for green, 8 bits for blue, and 8 bits for the alpha value (unused).
ribbon cable A flat cable in which the conductors are side by side.
ring Performs an acquisition that loops continually on a specified number of buffers.
ROI Region of interest. (1) An area of the image that is graphically selected from a window displaying the image. This area can be used focus further processing. (2) A hardware-programmable rectangular portion of the acquisition window.
ROM Read-only memory.
RS-170 The U.S. standard used for black-and-white television.
RTSI bus Real-Time System Integration Bus. The National Instruments timing bus that connects image acquisition and DAQ devices directly, by means of connectors on top of the devices, for precise synchronization of functions.


saturation The amount of white added to a pure color. Saturation relates to the richness of a color. A saturation of zero corresponds to a pure color with no white added. Pink is a red with low saturation.
scaling down circuitry Circuitry that scales down the resolution of a video signal.
scatter-gather DMA A type of DMA that allows the DMA controller to reconfigure on-the-fly.
sequence Performs an acquisition that acquires a specified number of buffers, then stops.
snap Acquires a single frame or field to a buffer.
SRAM Static RAM.
StillColor A post-processing algorithm that allows the acquisition of high-quality color images generated either by an RGB or composite (NTSC or PAL) camera using a monochrome video acquisition device.
sync Tells the display where to put a video picture; the horizontal sync indicates the picture's left-to-right placement and the vertical sync indicates top-to-bottom placement.
system RAM RAM installed on a personal computer and used by the operating system, as contrasted with onboard RAM.


transfer rate The rate, measured in bytes/s, at which data is moved from source to destination after software initialization and setup operations; the maximum rate at which the hardware can operate.
trigger Any event that causes or starts some form of data capture.
trigger control and mapping circuitry Circuitry that routes, monitors, and drives the external and RTSI bus trigger lines; you can configure each of these lines to start or stop acquisition on a rising or falling edge.
TTL Transistor-transistor logic. A digital circuit composed of bipolar transistors wired in a certain manner. A typical medium-speed digital technology. Nominal TTL logic levels are 0 and 5 V.


UV plane See YUV.


VCO Voltage-controlled oscillator. An oscillator that changes frequency depending on a control signal; used in a PLL to generate a stable pixel clock.
VI Virtual Instrument. (1) A combination of hardware and/or software elements, typically used with a PC, that has the functionality of a classic stand-alone instrument (2) A LabVIEW software module (VI), which consists of a front panel user interface and a block diagram program.
video line A video line consists of a horizontal sync signal, back porch, active pixel region, and a front porch.
VSYNC Vertical sync signal. The synchronization pulse generated at the beginning of each video field that tells the video monitor when to start a new field.


white reference level The level that defines what is white for a particular video system. See also black reference level.


YUV A representation of a color image used for the coding of NTSC or PAL video signals. The luminance information is called Y, while the chrominance information is represented by two components, U and V, that represent the coordinates in a color plane.


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