Frame grabber
From Wikipedia, the free 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.
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 are typically able to store multiple frames and compress the frames in real time using algorithms such as JPEG. 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.
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[edit] 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 converter.
- An NTSC/SECAM/PAL 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 Link, GigE Vision, 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.
[edit] Applications
[edit] Manufacturing
"Pick and place" machines are often used to mount electronic components on circuit boards during the circuit board assembly process. Such machines use one or more cameras to monitor the robotics that places the components. Each camera is paired with a frame grabber that digitizes the analog video, thus converting the video to a form that can be processed by the machine software.
[edit] Network Security
Frame grabbers may be used in security applications. For example, when a potential breach of security is detected, a frame grabber captures an image or a sequence of images, and then the images are transmitted across a digital network where they are recorded and viewed by security personnel.
