Frame grabber

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The frame grabber or video grabber (to about German frame grabber ) is in the original meaning of an electronic circuit for digitizing analog video signals was used. Since almost all video cameras now digitize the signals internally and only output digital video signals , classic frame grabbers are becoming increasingly less important in video technology. Instead, digital frame grabbers are used to connect cameras to a wide variety of systems, if these do not have a common data interface such as B. USB have.

function

The task of the frame grabber is always to adapt to the data format of the camera and to pass on or save the supplied image material in the target format. Often, digital frame grabbers already allow intelligent preprocessing of the recorded image sequences, e.g. B. Brightness and contrast adjustment. In the field of industrial image processing , frame grabbers often capture the image data directly from the semiconductor image sensors and carry out complex calculations and preprocessing such as non-uniformity correction, binning and scaling.

Structure of an analog frame grabber

The frame grabber essentially consists of an analog-digital converter , which is preceded by a sample-and-hold amplifier. The analog-to-digital converter assigns a natural number to a specific voltage level at the signal input . The video signal is converted into a sequence of numbers that are stored in a memory ( random access memory ). Additional circuits determine the times of synchronization at the beginning of the image and at the beginning of the line and reconstruct the clock signal for digitization. With this information, the numerical values ​​can be arranged in an image matrix , as it is e.g. B. can be displayed on a computer screen. A technical implementation of the frame grabber can be found e.g. B. in the form of PC plug-in cards for the ISA or PCI bus as well as external video digitizer via USB for capturing old video films.

Analog frame grabbers usually capture signals of the classic analog VGA standard, analog S-Video / FBAS , analog SCART , analog RGB signal, etc.

Structure of a digital frame grabber

Digital frame grabbers either capture a standardized image format such as DVI , HDMI or Camera Link or they adapt to a manufacturer-specific, proprietary format and convert it into a target format. Digital frame grabbers exist as USB and FireWire interfaces as well as with PCIe connections, which are intended for use in PCs and PC-related applications. Furthermore, encapsulated frame grabbers are used as a module or as a circuit part in existing imaging systems such as lidar systems, radars , X-ray devices , thermal imaging cameras and the like. integrated in order to convert proprietary formats and create a connection to the outside world. Often these frame grabber modules have a standardized output such as B. CameraLink or Gigabit Ethernet ( GigE or GigE-Vision ).

Digital frame grabbers are usually equipped with programmable functions, the parameters of which can be influenced by the user. Fully programmable systems based on FPGAs also exist .

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