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The PC Technology Guide

The PC Technology Guide contains a page about video capture cards. It has a brief explanation on what they are and how they work. It also gives a brief history and some important information about applications.

The digitisation of the analogue TV signal is performed by a video capture card, which converts each frame into a series of bitmapped images to be displayed and manipulated on the PC. This takes one horizontal line at a time and, for the PAL system, splits each into 768 sections. At each of these sections, the red, green, and blue values of the signal are calculated, resulting in 768 coloured pixels per line. The 768 pixel width arises out of the 4:3 aspect ratio of a TV picture. Out of the 625 lines in a PAL signal, about 50 are used for Teletext and contain no picture information, so theyıre not digitised. To get the 4:3 ratio, 575 lines times four divided by three gives 766.7. Because computers prefer to work with whole numbers, video capture cards usually digitise 576 lines, splitting each line into 768 segments, which gives an exact 4:3 ratio.

Thus, after digitisation, a full frame is made up of 768 × 576 pixels. Each pixel requires three bytes for storing the red, green, and blue components of its colour (for 24-bit colour). Each frame, therefore, requires 768 × 576 × 3 bytes = 1.3 MB. Because the PAL system takes two passes to draw a complete frame, each pass resolving alternate scan lines, one second of video requires a massive 65 MB (1.3 × 25 fps × 2 passes). Adding a 16-bit audio track sampled at 44 kHz increases this by a further 600 KBps. In practice, however, some boards digitise fewer than 576 lines and end up with less information, and most boards make use of the YUV scheme.

For more of this article, visit The PC Technology Guide.

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Tom's Hardware

Once again, Tomıs Hardware has a great page that shows you how to set up a digital capture card in your PC and use it. Not only does he have the tutorials, he also lists some excellent pages that contain information dealing with video capture cards.

The commercials make it look easy. Get a video camera, shoot some scenes, capture the video into your computer, and with a few clicks and drags you turn those disjointed shots into a cinematic masterpiece ready to put on a CD, e-mail to grandma, or stream off your web site. No problem. But, capturing and manipulating digital video in a computer is a little trickier than that.

In part one of this two-part article, he gives you a crash course in digital video capture basics, what kinds of system issues there are, outline the types of capture hardware available (and costs), and what kinds of results you can expect. In part 2, he rolls up the sleeves and reviews and compares a number of capture systems that won't send you to the poor house.

I listed below links to these two articles:

• Building a Digital Video Capture System - Part I
• Building a Digital Video Capture System - Part II

The link I have included below will take you to a link that contains all the articles that Tomıs Hardware has ever had, containing any information about digital video:.

• Digital Video Guide

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Safe Harbor

This page from Safe Harbor allows you to compare capture cards. I found it extremely useful.

To compare, click on this link—Safe Harbor.

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Techadvice.com

This page from Tech Advice.com contains links to some of the more popular video capture cards on the market. Each link allows you to find more information about the product that you clicked on.

To check out the products, click on this link Techadvice.com.