VIDEO CAPTURE BOARD: This special purpose add-in board allows direct input of composite or S-Video component signals to the computer. Some video capture boards incorporate graphic accelerator and display driver functions. Others are independent of the video graphics board which drives the computer monitor. These devices range from inexpensive, parallel port external units (~$100<) which capture only still images through more costly, broadcast-quality internal PCI cards (`$1,000 - $5,000) which capture broadcast-quality motion video.
The analog video signal is converted to digital bitmap which can be frozen, captured, edited and stored as a file in a variety of computer graphic formats. Multi-function capture boards can combine into a single computer PCI slot:
Another desireable feature is an external analog VIDEO output to allow computer-stored images to be reprinted on a VIDEO printer. The most efficient storage format is .jp[e]g (journalists picture [expert] group) which can compress a 900 kbyte, full frame 640 X 480 pixel bit mapped VO S-video image into a 15 - 25 kbyte .jpg file with no significant loss of resolution. For clinical purposes, NTSC video images can be captured in a 1/2 frame format of 320 X 240 pixels. The resulting file size in bit-mapped (*.dib or *.bmp) format will be on the order of 225kBytes. When saved in *.jpg file format at a compression factor of 50, a pair of 1/2 frame right and left ear images can be stored in as little as 12k bytes of hard disk space. This extrapolates to more than 80 patient right/left ear VO records per megabyte.
Roy F. Sullivan, Ph.D.