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Posted by M.I.5 on 01/18/07 15:17
"M.I.5" <no.one@no.where.NO_SPAM.co.uk> wrote in message
news:45af2b9a$1_1@glkas0286.greenlnk.net...
>
> "Barry Watzman" <WatzmanNOSPAM@neo.rr.com> wrote in message
> news:45ae3543$0$4876$4c368faf@roadrunner.com...
>> Re: "overscan is an "attribute" of CRTs"
>>
>> No, wrong. All rear projection displays overscan at least slightly, even
>> if they are digital (this includes LCD and LCoS projection, as well as
>> DMD). In fact, overscan is effectively required by law (the law doesn't
>> actually require overscan, but it does require that the picture totally
>> fill the screen. It's an artifact going back to the 1950's and the days
>> of small round picture tubes, but it's still on the books). On a rear
>> projection set, regardless of the source of the projected image, the only
>> way to assure this is to slightly overscan the screen). There is not
>> such explicit control of the optics and the magnification ratio that the
>> projected digital display can be made to just exactly fill the screen, so
>> a slight amount of overscan is used .... the entire resolution (say
>> 1920x1080) is generated, but it's projected onto the viewing screen with
>> a very slight amount of overscan so that the screen is assured to be
>> filled on every single set coming off the production line.
>>
>> [In fact, digital displays using three-element LCD and LCoS even still
>> have convergence adjustments to overlap the 3 image elements exactly.]
>>
>> The only sets that don't overscan at all are direct view digital
>> displays, e.g. direct view (not projection) LCD and plasma.
>>
>
> That's actually not quite true Barry. They actually still do lose a small
> border area (for picture type video sources such as DVD). The only time
> they don't do it, is when showing video generated by a computer.
>
> There is a very good illustration of this if you can get your hands on a
> copy of Buster Keaton's, The General in it's region 1 version. Apart from
> being a great film, if you play it on your chosen DVD video player onto a
> Plasma or LCD display, you will, well, get to watch a great film. But
> couple your PC's output to the display, and play it on the PC and repeat
> the exercise. The film material is almost wholy contained in the
> 'protected area' (because otherwise some of the subtitles would be lost) .
> The grey border is the area that is masked off when the normal video input
> is received.
>
> Other region versions are probably the same, but I haven't personally
> tried them.
>
More info at:
http://en.wikipedia.org/wiki/Display_resolution#Overscan
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