A couple questions about overscan in analog SDTV?

[Videogamer555]

I know that a portion of the video signal is actually vertical and horizontal sync and blanking, but even all of the image portion of the video signal isn't visible on older TVs, due to an effect called overscan. So this brings me to my first question. How much of the image is typically overscan? I've heard it's something like 10%, but is it 10% on each side (top, bottom, left, and right), for a total of 20% in horizontal and vertical directions? Or is it 10% total in vertical and horizontal directions (5% on each side)?

My second question is this. Is that 720x480 standard for consumer video capture equipment, including the overscan in the captured video? Or is overscan all image content outside the 720x480 captured frame?

[Cornucopia]

We HAVE talked with you about this before...

Since analog electronics tolerances varied (especially in the early days with tubes), and physical tv monitor bezels also varied, it was a general rule that
1. "Action Safe" area excluded the outer 5% from each of the top, bottom, left and right sides, equally (percentage-wise, not pixel-wise). For a total of 10% of the total vertical and 10% of the total horizontal. It wasn't ever cut out or blanked/blacked, it was ALWAYS just ignored and allowed to be fudged (thus you might occasionally see a boom pole or electric line or fingertip accidentally if you were able to scrutinize all programs).
and
2. "Title Safe" area excluded the outer 10%, so 5% more in addition to #1's 5%, also equally from all sides for a total of 20% horizontal and 20% vertical. Good scene image is in the interim, but that inner area was where titles, credits, graphics, subtitles, etc were expected to lie so there would not be issues with edge legibility. Also, remember ESPECIALLY with all but the latest CRTs, there was curvature distortion, which was much worse toward the edges, so this minimized distortion in the lettering.

Overscan, once again, is Visible Active Picture, consisting mainly of areas outside of action safe. It is NOT Blanking (vertical or horizontal). Overscan is usually mostly obscured on CRTs, but mostly or all visible on modern screens which have no need for an inner bezel (because digital is exact, accurate). This visible active picture is 576 lines (PAL) or 480-486 lines (NTSC).


Scott

[pandy]

Wikipedia provide answers for your questions:
https://en.wikipedia.org/wiki/Safe_area_(television)?useskin=vector
https://en.wikipedia.org/wiki/Overscan?useskin=vector

As Cornucopia already wrote - overscan and associated safe area problem is outcome of technology present in past - nowadays displays are pixel based, you can explicitly activate every pixel based on its X,Y coordinates - this is standard for today TV but in past it was not possible - on both side - broadcast studio and consumer display.
Overscan was used for example to hide visibility of inaccuracies present during mixing (analog) of two sources, on consumer side after warming tubes (valves) video was able to achieve normal size (and as "scaling" was done in analog way there was no artifacts present).
Active video is 720 pixels and 480 lines and overscan sacrifice some pixels and lines so visible video is less than 720x480.