From Dale Miles great web site here LearnDigital..The Imaging Chain Aug. 03
The Frame-grabber (video board)
The frame grabber (also called a video board) is probably the most important and least understood element in a digital image processing system. A frame grabber converts the captured analog, electronic signal from the sensor and converts it to a digital format for transfer as a digital image to the computer. Some frame grabbers also have technology (image processing capability) to improve the signal before displaying the image on the monitor. I believe this is termed “input signal conditioning” – some systems may have it, some may not. In addition, frame grabbers may also employ LUTs (Look Up Tables) to improve image quality prior to display. LUTs are extremely effective tools for equalizing or normalizing images captured under poor exposure conditions. I’m assuming that most digital x-ray system vendors would employ a high quality video board in their system; however, if you already have a computer with a “board” they may tell you that you can use your own. If you have a poor quality frame grabber/video board, you may not get the best image quality the system is capable of !