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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. In addition to video, associated audio can be captured at the same time if the hardware device is so equipped. Some cards have multiple inputs of the same or different signal type that can capture concurrently.
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, CoaXPress, DVI, 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.
Frame grabbers are used in medicine for many applications including telenursing 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.
"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.
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.
In recent years with the rise of personal video recorders like camcorders, mobile phones,etc. video and photo applications have gained ascending prominence. Frame grabbing is becoming very popular on these devices.
Astronomy & Astrophotography
Amateur astronomers and astrophotographers use frame grabbers when using analog "low light" cameras for live image display and internet video broadcasting of celestial objects. Frame grabbers are essential to connect the analog cameras used in this application to the computers that store or process the images. Day/night security cameras are popular in this field.
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