MkI Video digitiser circuit description

Posted on Feb 6, 2014

A `video-digitiser` (also known as a `frame grabber`) captures pictures from a TV set, camera, or video recorder, etc. , and forwards them to a computer for display, storage, or general manipulation. This document describes a home-built digitiser which interfaces to an EPP (or bi-directional) parallel port on IBM PCs. This frame grabber

MkI Video digitiser circuit description
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design digitises pictures to very high quality in monochrome (8-bit black & white). Although designed for the European standard 625-line / 50Hz TV system, it should work with the American 525-line / 60Hz standard with minimal modification. Before embarking on the project, please be sure to realise that this design will not capture movies. At best, it can manage a couple of frames per second. Note also that as described, the circuit collects its picture from a succession of frames. Consequently the image must remain fairly still for the half-second or so taken to capture it. A competent constructor could purchase a larger and more expensive memory chip and modify (simplify) the circuit to overcome the latter limitation if desired (see the Mk. II Video Digitiser ). Television equipment uses a simple composite video signal which carries all the picture information. Pictures are conveyed as a continuous sequence of frames, each taking 1/25 second. Within each frame are 625 horizontal scan lines, transmitted in turn starting at the top. [To reduce flicker, each frame is actually transmitted as two consecutive fields, the first containing odd-numbered lines, and the second filling in the even numbered, a technique known as interlacing. This cunning trick ups the refresh rate to 50Hz, without increasing the signal bandwidth. ] All video recorders and many TV sets will have a composite video output, usually using a BNC or phono...

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