[opendtv] Re: The Math on Screen sizes
- From: Tom Barry <trbarry@xxxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Fri, 04 Jun 2004 23:05:11 -0400
John Willkie wrote:
> B-U-L-L-S-H-I-T.
>
... and ...
> Get real.
John -
I assume from your invective that you disagreed with something I said.
IIRC there are 25.4 mm per inch, so at a .7 mm dot pitch (which seems
large) there would be 36.28 pixels / inch, or 1814 pixels on a 50"
wide screen. I remember some of my computer displays of old had dot
pitches in the range of .28 or so some time ago. I assume they would
be much better now. And of course my 55" Toshiba RPTV does not have a
grill or shadow mask and there is no sense in trying to measure it
like some camera folks do saying it takes 3 pixels of 3 colors to make
one pixel, since they overlap anyway.
And yes, no surprise, I still believe HDTV displays have much more
resolution than NTSC TV sets. Duh!
- Tom
John Willkie wrote:
> B-U-L-L-S-H-I-T.
>
> 1080 pixels across, using 0.7 mm dot pitch, requires a screen 89.29 inches
> across, with a 4:3 set having a diagonal measure of 111 inches, or a 16:9
> screen of 102 inches. How many 9 FOOT screens have you seen?
>
> And, 1080 pixels renders only 540 "lines" as that term has been used in the
> TV business since BEFORE 1939.
>
> Get real.
>
> John Willkie
>
> -----Original Message-----
> From: opendtv-bounce@xxxxxxxxxxxxx
> [mailto:opendtv-bounce@xxxxxxxxxxxxx]On Behalf Of Tom Barry
> Sent: Friday, June 04, 2004 4:28 PM
> To: opendtv@xxxxxxxxxxxxx
> Subject: [opendtv] Re: The Math on Screen sizes
>
>
> Most CRT based HDTV displays are capable of displaying 1080 lines, in
> an interlaced fashion, though if you want the proper 16:9 aspect ratio
> on a 4:3 HDTV display the CEA has decided it can still officially be
> called an HDTV set if it displays a 16:9 area using only 810 of the
> 1080 lines. However most newer CRT based 4:3 HD displays can instead
> use a squeeze function to place all 1080 lines in a 16:9 area if desired.
>
> An NTSC analog TV only displays about 480, interlaced.
>
> And as already discussed there are nuances of effective resolution,
> grill aperture, and spot beam size which detract for the stated numbers.
>
> But any HD display still displays a LOT more resolution than an NTSC
> 480i display.
>
> - Tom
>
> John Willkie wrote:
>
>>So, ONCE AGAIN, what EXACTLY is the difference between the screen
>
> resolution
>
>>of an NTSC set (440 lines?) and an 4:3 "HDTV" set capable of 810 lines?
>>
>>John Willkie
>>
>>P.S. Don't think for one second that I didn't notice you offering that
>
> one
>
>>of those 4:3 sets was "HDTV" and now you are saying that somebody else
>
> said
>
>>it. Me, I'm responsible for my words. Even erroroneous and bad ones.
>>
>>-----Original Message-----
>>From: opendtv-bounce@xxxxxxxxxxxxx
>>[mailto:opendtv-bounce@xxxxxxxxxxxxx]On Behalf Of Craig Birkmaier
>>Sent: Friday, June 04, 2004 5:40 AM
>>To: opendtv@xxxxxxxxxxxxx
>>Subject: [opendtv] Re: The Math on Screen sizes
>>
>>
>>At 6:25 PM -0700 6/3/04, John Willkie wrote:
>>
>>
>>>Please, please, somebody show me where I have gone wrong.
>>
>>
>>Nobody ever said anything about 810 samples per line being HD,
>>although most HD capable display cannot resolve much more horizontal
>>detail.
>>
>>The 810 number comes from the CEA. It is a caveat for 4:3 CRT based
>>RPTVs and relates to the number of active lines of video when a 4:3
>>HD capable display is showing 16:9 source. In essence, the display
>>scans 1080 lines (two 540 line fields, spreading the lines over the
>>entire vertical area of the 4:3 display. The alternative would be to
>>reduce the vertical drive and scan only the 16:9 portion of the
>>screen with the full 1080 lines; but many manufacturers experienced
>>differential burn in using this technique. The CEA agreed to allow
>>manufacturers to stretch the 1080 lines over the 4:3 screen, Using
>>only the central 810 lines to display 16:9 HD source. The remaining
>>lines are typically filled with grey to average out burn-in, although
>>some manufacturers do allow the unused area to be black.
>>
>>As for the actual horizontal resolution of CRT based displays, there
>>are two different issues.
>>
>>For direct view CRT displays the limiting horizontal resolution is
>>determined by the shadow mask of the CRT; the number of slits or dot
>>triads across the width of the screen; The best I have seen in and
>>consumer HD display of this type is about 850 samples per screen
>>width. I think that Princeton offered a 720P display with better
>>horizontal resolution. You don't need a spreadsheet to figure this
>>out...just count the slits (or look in the specs for the display).
>>
>>For rear projection CRT displays the situation is very different, as
>>the tubes used for these sets do not have shadow masks. Thus the
>>limiting horizontal resolution is determined by the spot size of the
>>beam and the band pass of the amps that are driving the CRTs. Again,
>>looking at the specs, you will find that most CRT based RPTVs offer
>>no more than 850 lines horizontal resolution.
>>
>>Regards
>>Craig
>>
>>
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