Frame grabber
Encyclopedia
A frame grabber is an electronic device that captures individual, digital still frames from an analog video signal or a digital video stream. It is usually employed as a component of a computer vision system, in which video frames are captured in digital form and then displayed, stored or transmitted in raw or compressed digital form. Historically, frame grabbers were the predominant way to interface cameras to PC's. This has substantially changed in recent years as direct camera connections via USB, Ethernet and IEEE 1394 ("FireWire") interfaces have become prevalent.
Early frame grabbers had only enough memory to acquire (i.e., "grab") and store a single digitized video frame, hence the name. Modern frame grabbers typically can store multiple frames and compress them in real time using algorithms such as MPEG2 and JPEG
. Frame grabbers that perform compression on the video frames are referred to as "Active Frame Grabbers," while frame grabbers that simply capture raw video data are called "Passive Frame Grabbers." Technological demands in fields such as radar acquisition
, manufacturing
and remote guidance
have led to the development of frame grabbers with the ability to capture images at high frame rates and resolutions.
Digital frame grabbers, which accept and process digital video streams, include these circuits:
Circuitry common to both analog and digital frame grabbers:
and remote guidance
. In situations where an expert at another location needs to be consulted, frame grabbers capture the image or video from the appropriate medical equipment so it can be sent digitally to the distant expert.
Early frame grabbers had only enough memory to acquire (i.e., "grab") and store a single digitized video frame, hence the name. Modern frame grabbers typically can store multiple frames and compress them in real time using algorithms such as MPEG2 and JPEG
JPEG
In computing, JPEG . The degree of compression can be adjusted, allowing a selectable tradeoff between storage size and image quality. JPEG typically achieves 10:1 compression with little perceptible loss in image quality....
. Frame grabbers that perform compression on the video frames are referred to as "Active Frame Grabbers," while frame grabbers that simply capture raw video data are called "Passive Frame Grabbers." Technological demands in fields such as radar acquisition
Radar
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...
, manufacturing
Manufacturing
Manufacturing is the use of machines, tools and labor to produce goods for use or sale. The term may refer to a range of human activity, from handicraft to high tech, but is most commonly applied to industrial production, in which raw materials are transformed into finished goods on a large scale...
and remote guidance
Remote guidance
Remote guidance, in the medical context, refers to the supervision or guidance of a medical task, usually a procedures or test, from a remote location. This falls in the realm of real time telemedicine applications. By way of example, a radiologist may guide an ultrasound examination from a...
have led to the development of frame grabbers with the ability to capture images at high frame rates and resolutions.
Circuitry
Analog frame grabbers, which accept and process analog video signals, include these circuits:- An input signal conditioner to buffer the analog video input signal and protect downstream circuitry.
- A circuit to recover the horizontal and vertical synchronization pulses from the input signal.
- An analog-to-digital converterAnalog-to-digital converterAn analog-to-digital converter is a device that converts a continuous quantity to a discrete time digital representation. An ADC may also provide an isolated measurement...
. - An NTSCNTSCNTSC, named for the National Television System Committee, is the analog television system that is used in most of North America, most of South America , Burma, South Korea, Taiwan, Japan, the Philippines, and some Pacific island nations and territories .Most countries using the NTSC standard, as...
/SECAMSECAMSECAM, also written SÉCAM , is an analog color television system first used in France....
/PALPALPAL, short for Phase Alternating Line, is an analogue television colour encoding system used in broadcast television systems in many countries. Other common analogue television systems are NTSC and SECAM. This page primarily discusses the PAL colour encoding system...
decoder, a function that can also be implemented in software.
Digital frame grabbers, which accept and process digital video streams, include these circuits:
- Physical interface to the digital video source, such as Camera LinkCamera LinkCamera Link is a serial communication protocol designed for computer vision applications based on the National Semiconductor interface Channel-link. It was designed for the purpose of standardizing scientific and industrial video products including cameras, cables and frame grabbers...
, DVIDigital Visual InterfaceThe Digital Visual Interface is a video interface standard covering the transmission of video between a source device and a display device. The DVI standard has achieved widespread acceptance in the PC industry, both in desktop PCs and monitors...
, GigE VisionGigE visionGigE Vision is an interface standard introduced in 2006 for high-performance industrial cameras. It provides a framework for transmitting high-speed video and related control data over Ethernet networks. The standard was initiated by a group of 12 companies and the committee has since grown to...
, LVDS or RS-422.
Circuitry common to both analog and digital frame grabbers:
- Memory for storing the acquired image (i.e., a frame buffer).
- A bus interface through which a processor can control the acquisition and access the data.
- General purpose I/O for triggering image acquisition or controlling external equipment.
Healthcare
Frame grabbers are used in medicine for many applications including telenursingTelenursing
Telenursing refers to the use of telecommunications and information technology for providing nursing services in health care whenever a large physical distance exists between patient and nurse, or between any number of nurses...
and remote guidance
Remote guidance
Remote guidance, in the medical context, refers to the supervision or guidance of a medical task, usually a procedures or test, from a remote location. This falls in the realm of real time telemedicine applications. By way of example, a radiologist may guide an ultrasound examination from a...
. In situations where an expert at another location needs to be consulted, frame grabbers capture the image or video from the appropriate medical equipment so it can be sent digitally to the distant expert.