Digital Video Decoded

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The rise of digital video editing and recording has taken two parts of the high-technology world jointly. The computer geeks have found themselves reading the same catalogs as the video experts, and both are finding that their expertise in a single field doesn’t necessarily transfer to the strange hybrid world of digital video.

This article aimed at getting both groups up to date, by discussing things that computer and video experts, respectively, neglect as common knowledge. Computer folks know what resolution is. In case your monitor set to show 800 by 600 pixels, you know for a fact that that’s EXACTLY what you get.

And yes, you can indicate a single pixel, though it could take a magnifying glass to do it. Analogue video is fuzzier, in the literal as well as the conceptual sense. A better way to measure analogue video resolution has been bandwidth. Bandwidth indicated in megahertz (MHz), is how much space the video signal takes up. And then there’s vertical resolution.

The vertical resolution of the video transmission would appear to be strongly fixed – it is the amount of scan lines, full stop, right? It Is Written that NTSC video has 525 lines interlaced at 60 fields (30 frames) per second, and PAL video has 625 lines similarly interlaced at 50 areas (25 structures) per second. But, of course, it’s not that simple.

Canonically, at standard overseas, 575 lines are noticeable in PAL and 485 in NTSC; all of those other lines aren’t used for video signals. The lost lines are where closed captioning lives, for example, and a few are lost to the vertical blanking interval while the electron beam retraces to the very best of the display screen.

Of the lines that are used for video, some might not be noticeable on a given monitor clearly, you may see fewer if your vertical size control is defined high, and lines might fall sufferer to a restricted-resolution storage space format. Lines may be doubled by funky TVs also, which with digital jiggery-pokery can fool you into thinking you’re taking a look at the genuine broadcast detail, not clever interpolation.

Your average semi-professional digital video dude labors under the misconception that regular “clean VHS” quality video is 640 by 480 pixels in 24 bit color. Analogue video comes in two basic flavors – composite and component. Component video uses multiple signals to build a picture, composite rolls it all into one.

The whole notion of component video is to keep full bandwidth, so (theoretically) no fine detail is lost in storage space or transmission. No video is component, with three stations. When people talk about component video, they mean this version. The most straightforward version of three-channel component video is RGB, with separate channels for the red, the green and the blue information in the video signal. Combine red, green, and blue data in the typical additive color model and you get your color picture. In color difference component video, the first channel is luminance.

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Notated Y, the typical abbreviation for intensity, the luminance is the signal’s brightness information without color data. Y by itself gives a dark and white picture. The other two channels are called color difference signals – they’re notated R-Y and B-Y, and are the difference between red and the luminance and the difference between blue and the luminance, respectively. Prosumer Y/C video is sorta-kinda component, with two stations, but is never known as component video, for two reasons. 3000 video cameras into the golf club would cause confusion.

And two, all Y/C will be to prolong the different chrominance and luminance indicators that most low-end video types already encode into the cable connections. Every VHS VCR information video as distinct luminance and chrominance; SVHS and Hi-8 ones with Y/C output can receive and send this two-channel video without squishing it into the composite. Y/C is preferable to composite but much worse than the element still. The chrominance signal Y/C uses is NTSC-modulated, or PAL, ready for integration into a RF or amalgamated modulated signal in the correct format. This makes Y/C video inherently PAL or NTSC, while real component video is format-agnostic – it can be encoded into any format you prefer.

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