ken@wybbs.mi.org (Ken) (01/24/91)
This weeks Engineering times has an article on something I have been
waiting for a long time: Competition for the cable companies!!!
Starting this summer, a company called Sky Pix (Kent, WA) will be
selling a direct broadcast dish system for the home. Dishes have
been around for a long time, but check out these details:
o The dish size in most of the US is 24 or 30 inches. East and West
coasters may have to go to 36 inches.
o The dish is a sealed unit that looks like a gooseneck desk lamp
pointed at the sky. It is a window mount unit and will be aimed
at Hughes SBS-6.
o Initial capacity is 80 channels, expandable to 250 when future
satellites are launched.
o Dolby Stereo Sound, 480 lines resolution.
o Pay per View prices: $1-$2 for older films, $3-$4 for new releases.
o Basic service will include typical basic cable channels and will
be priced at $10-$13 a month.
o Videotape inhibit circuit will prevent home taping unless premium
charge is paid.
o The unit will be available at Macys, Wards, Dayton Hudson, etc.
Except for the last item, I think it's about time TCI and the others had
some competition. Since they own many of the basic cable channels, I'll
bet they'll fight tooth and nail to keep from supplying Sky Pix. Still,
the competition will be great for the consumer. Europe has had similar
systems for a while now (BSB and Sky), but they had a very limited
number of channels (around 6, I think).
Sales should start in the spring with full promotions in the summer.
Considering that Sky Pix is half of what the local cable channel charges
for "basic" non-service, they should do very well.
--
Ken Jongsma ken@wybbs.mi.org
Smiths Industries ken%wybbs@sharkey.umich.edu
Grand Rapids, Michigan ..sharkey.cc.umich.edu!wybbs!ken ken@wybbs.mi.org (Ken) (01/24/91)
Whoops! I meant except for the video tape inhibit, Sky Pix looked very good.... -- Ken Jongsma ken@wybbs.mi.org Smiths Industries ken%wybbs@sharkey.umich.edu Grand Rapids, Michigan ..sharkey.cc.umich.edu!wybbs!ken
dennett@acadia.Kodak.COM (Charlie Dennett) (01/25/91)
In article <620@wybbs.mi.org>, ken@wybbs.mi.org (Ken) writes: |> This weeks Engineering times has an article on something I have been |> waiting for a long time: Competition for the cable companies!!! |> |> Starting this summer, a company called Sky Pix (Kent, WA) will be |> selling a direct broadcast dish system for the home. Dishes have |> been around for a long time, but check out these details: |> |> o Videotape inhibit circuit will prevent home taping unless premium |> charge is paid. |> This may not be the correct newsgroup for this question but I'll ask anyways. How does this videotape inhibit work. It would seem to me that the signal can "tell" that it is bing recorded. How can it do this? Is there some component of the signal that is missing that is required by the recorder and not the TV? Charlie Dennett | Rochester Distributed Computer Services Mail Stop 01816 | Internet: dennett@Kodak.COM Eastman Kodak Company | Rochester, NY 14650-1816 |
mas35638@uxa.cso.uiuc.edu (Odin) (01/26/91)
> 480 lines 525 is standard. You're talking about a picture which is not as good as normal tv broadcasts. |~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~|~~~~~~~~~~~~~~| | | Mike Stangel | | Intentionally blank .sig | m-stangel@ | | | uiuc.edu | `~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~'
amichiel@rodan.acs.syr.edu (Allen J Michielsen) (01/26/91)
In article <620@wybbs.mi.org> ken@wybbs.mi.org (Ken) writes: >This weeks Engineering times has an article on something I have been >Starting this summer, a company called Sky Pix (Kent, WA) will be >selling a direct broadcast dish system for the home. Dishes have >been around for a long time, but check out these details: Pretty good description, but sorry. All of this was available in the 30 largest us cities more than 5 years ago. The single difference was that the antenna pointed to the tallest building downtown for it's 'sat' signal, and downtown, the 'sat' sales company used down link dishes to create the artificial sat. In short, except for a very few locations (maybe zero). They've all gone bankrupt in short order. They discovered a lot of things, one of which was that you can't compete with the costs for most cable companies, and people that are willing to are willing to spend the money for a real dish. The costs of launching the sat and cost for the startup are so astronomical that unless the government foot the bill and holds everybody's hand, it a belly up deal. al -- Al. Michielsen, Mechanical & Aerospace Engineering, Syracuse University InterNet: amichiel@rodan.acs.syr.edu amichiel@sunrise.acs.syr.edu Bitnet: AMICHIEL@SUNRISE
gwangung@milton.u.washington.edu (Roger Tang) (01/26/91)
In article <1991Jan25.165057.671@ux1.cso.uiuc.edu> mas35638@uxa.cso.uiuc.edu (Odin) writes: >> 480 lines > >525 is standard. You're talking about a picture which is not as >good as normal tv broadcasts. ???? Last time I heard, broadcast quality was nowhere near 525 and, in fact, many midline TVs don't get this even from direct video connections. Clarifications?
larry@syscon%nstar.rn.com (Larry Snyder) (01/26/91)
ken@wybbs.mi.org (Ken) writes: >Whoops! I meant except for the video tape inhibit, Sky Pix looked >very good.... how much for installation and setup? -- Larry Snyder larry@nstar.rn.com larry%nstar@iuvax.cs.indiana.edu
ken@uswat.uswest.com (Kenny Chaffin) (01/26/91)
In article <1991Jan25.183121.9017@rodan.acs.syr.edu-> amichiel@rodan.acs.syr.edu (Allen J Michielsen) writes: ->In article <620@wybbs.mi.org> ken@wybbs.mi.org (Ken) writes: ->>This weeks Engineering times has an article on something I have been -> ->>Starting this summer, a company called Sky Pix (Kent, WA) will be ->>selling a direct broadcast dish system for the home. Dishes have ->>been around for a long time, but check out these details: -> Pretty good description, but sorry. All of this was available in the ->30 largest us cities more than 5 years ago. The single difference was that ->the antenna pointed to the tallest building downtown for it's 'sat' signal, ->and downtown, the 'sat' sales company used down link dishes to create the ->artificial sat. -> In short, except for a very few locations (maybe zero). They've all gone ->bankrupt in short order. They discovered a lot of things, one of which was ->that you can't compete with the costs for most cable companies, and people that ->are willing to are willing to spend the money for a real dish. The costs of ->launching the sat and cost for the startup are so astronomical that unless the ->government foot the bill and holds everybody's hand, it a belly up deal. -> ->al -> -> ->-- ->Al. Michielsen, Mechanical & Aerospace Engineering, Syracuse University -> InterNet: amichiel@rodan.acs.syr.edu amichiel@sunrise.acs.syr.edu -> Bitnet: AMICHIEL@SUNRISE Yeah, But... There are considerable differences. One the downlink is actually owned and operated by the user-- that eliminates considerable cost. The other is that things have changed considerably in the past 5 years satellite time is much cheaper and more efficient. The Japanese and others are going all out for direct broadcast HDTV, and I believe some places in Europe also. There is always a risk in any business but I would hope that the japanese and this new company here in the U S are aware of history and still see it as a positive proposition. In any case, we'll watch and see what happens. KAC "Anybody want a drink before the war?" Sinead O'Connor >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> Kenny A. Chaffin {...boulder}!uswat!ken U S WEST Advanced Technologies (303) 930-5356 6200 South Quebec Englewood, CO 80111 <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
tmkk@ux1.cso.uiuc.edu (Scott Coleman) (01/26/91)
In article <1991Jan25.165057.671@ux1.cso.uiuc.edu> mas35638@uxa.cso.uiuc.edu (Odin) writes: >> 480 lines > >525 is standard. You're talking about a picture which is not as >good as normal tv broadcasts. He's talking about 480 HORIZONTAL lines, not vertical lines. This is considerably BETTER than broadcast (which is ~330 or so). This DBS sounds like a great idea, but that "video tape inhibit" "feature" scares me a bit. This great new DBS service won't be much good if the price of basic + "record de-inhibit" together cost the same as or more than hardwired cable (unless, of course, the wired cable companies decide to lower their price to keep people from switching). -- Scott Coleman tmkk@uiuc.edu "Unisys has demonstrated the power of two. That's their stock price today." - Scott McNealy on the history of mergers in the computer industry.
roger@wrq.com (Roger Fulton) (01/26/91)
In article <1991Jan25.183121.9017@rodan.acs.syr.edu> amichiel@rodan.acs.syr.edu (Allen J Michielsen) writes: >In article <620@wybbs.mi.org> ken@wybbs.mi.org (Ken) writes: >>This weeks Engineering times has an article on something I have been > >>Starting this summer, a company called Sky Pix (Kent, WA) will be >>selling a direct broadcast dish system for the home. Dishes have >>been around for a long time, but check out these details: > Pretty good description, but sorry. All of this was available in the >30 largest us cities more than 5 years ago. The single difference was that ^^^^^^^^^^^^^^^^^^^^ Well, gee, not all of us live in or near "the 30 largest us (sic) cities." I read an extensive article a few weeks ago in the Seattle Times about this system, and I very much look forward to getting it. I will soon live in a rural area which will probably NEVER get cable, and the cost of a standard large satellite dish is beyond my budget. However, I recall from the Times article that the installation cost and montly fees seemed quite reasonable, compared to either a large dish system or cable. The Times article made no mention of the "defeat video taping 'feature'." This "feature" does not make me happy. I wonder if a basic video "enhancer/stabilizer" (the kind you use when taping from one VCR to another) would defeat this. Roger Fulton roger@wrq.com
ken@wybbs.mi.org (Ken) (01/26/91)
I believe you are confusing horizontal and vertical resolution. -- Ken Jongsma ken@wybbs.mi.org Smiths Industries ken%wybbs@sharkey.umich.edu Grand Rapids, Michigan ..sharkey.cc.umich.edu!wybbs!ken
chittamu@pogo.cs.umass.edu (Satish Chittamuru) (01/27/91)
In article <1991Jan26.013437.25836@ux1.cso.uiuc.edu> tmkk@ux1.cso.uiuc.edu (Scott Coleman) writes: > > In article <1991Jan25.165057.671@ux1.cso.uiuc.edu> mas35638@uxa.cso.uiuc.edu (Odin) writes: > >> 480 lines > > > >525 is standard. You're talking about a picture which is not as > >good as normal tv broadcasts. > > > He's talking about 480 HORIZONTAL lines, not vertical lines. This is > considerably BETTER than broadcast (which is ~330 or so). A small correction folks. 525 line *IS* the number of horizontal lines is an NTSC television signal. But the fact is not all the lines are display lines. 480 lines are displayed on the screen and the remaining lines are blanked out while the vertical retrace occurs i.e. while the elctron beam is moving from the bottom right of the screen to top left. Now broadcast TV has a channel size of 6 MHz which is the full channel size of an NTSC signal (part of this is an audio signal band, about 300 KHz for FM transmission. Video is AM transmission). So broadcast TV does indeed have a vertical display resolution of 480 lines. Now cable signals do not have such a wide bandwith. Stuff like capacitive/inductive losses on the coaxial cable cause it to have a vertical display resolution of 330 lines. A normal VCR is even worse. The magnetic tape used in regular VCR cannot record a signal of that large a bandwith. The Video signal has a band of about 2.7-3 MHz on the tape. This translates to about 240 lines of vertical resolution. Now the SuperVHS VCRs, by some method (I don't know the technology used there) increase the recorded bandwith and thus are able to give a resolution that is equal to or better than a Cable signal. So, if the satellite system does have 480 line of display resolution, it is technically superior to your Cable system. > Scott Coleman tmkk@uiuc.edu -- -Satish K. Chittamuru chittamu@cs.umass.edu Software Development Lab. chittamu@umass.bitnet Dept. of Computer & Info. Sciences University of Massachusetts Amherst, MA 01002 === Theory of Objectivity: E=MC++
berger@atropa (Dire Wolf) (01/27/91)
ken@wybbs.mi.org (Ken) writes: >Starting this summer, a company called Sky Pix (Kent, WA) will be >selling a direct broadcast dish system for the home. Dishes have >been around for a long time, but check out these details: *---- If the system is as described, I doubt that it will be successful. First, many people video tape for time-shifting purposes. Having to pay extra for that feature means that many people will not even get the "basic" service they are paying for. Secondly, with my conventional cable service, I can run as many cable-ready TV's and VCR's as I want, each on their own channel. Will you be able to do that with this system? -- Mike Berger Department of Statistics, University of Illinois AT&TNET 217-244-6067 Internet berger@atropa.stat.uiuc.edu
Ordania-DM@cup.portal.com (Charles K Hughes) (01/27/91)
Charlie writes: >In article <620@wybbs.mi.org>, ken@wybbs.mi.org (Ken) writes: >|> o Videotape inhibit circuit will prevent home taping unless premium >|> charge is paid. >|> > >This may not be the correct newsgroup for this question but I'll >ask anyways. How does this videotape inhibit work. It would seem >to me that the signal can "tell" that it is bing recorded. How >can it do this? Is there some component of the signal that is >missing that is required by the recorder and not the TV? It's probably a version of Macrovision - screws up the VCR but doesn't bother the TV. (A few tapes that I've used with my VCR - originals no less - were protected and screwed up my TV anyway. Nice copy protection - it fucks with everybody.) > >Charlie Dennett | Rochester Distributed Computer Services Charles_K_Hughes@cup.portal.com
kludge@grissom.larc.nasa.gov ( Scott Dorsey) (01/28/91)
In article <1991Jan25.165057.671@ux1.cso.uiuc.edu> mas35638@uxa.cso.uiuc.edu (Odin) writes: >> 480 lines > >525 is standard. You're talking about a picture which is not as >good as normal tv broadcasts. Yes, but of those 525 lines, many of them carry vertical synch information. Most TV broadcasts use about 480 lines vertically. For those who don't know, 16mm Kodachrome 25 has about 12,000 lines of resolution. Personally I'll avoid HDTV and stay with film for a while.
bixenman@scr1.ocpt.ccur.com (michael bixenman <bixenman>) (01/29/91)
In article <1991Jan25.165057.671@ux1.cso.uiuc.edu> mas35638@uxa.cso.uiuc.edu (Odin) writes: >> 480 lines >525 is standard. You're talking about a picture which is not as >good as normal tv broadcasts. Your VIEWED picture is not 525 lines. What you see is alot less. 8^) ------------------------------------------------------------------------------- Mike Bixenman bixenman@scr1.ocpt.ccur.com Concurrent Computer Corp. "Opinions are sacred, mine are Oceanport, NJ (908)870-5875 cows, so this must be a cow!" -------------------------------------------------------------------------------
myers@hpfcdj.HP.COM (Bob Myers) (01/29/91)
>>> 480 lines >> >>525 is standard. You're talking about a picture which is not as >>good as normal tv broadcasts. > > >He's talking about 480 HORIZONTAL lines, not vertical lines. This is >considerably BETTER than broadcast (which is ~330 or so). This DBS sounds Actually, no, he IS talking about vertical lines, not horizontal. (Think about it: the horizontal resolution is the number of *vertical* lines which can be resolved). And we should also point out that when we talk about lines of *resolution*, this is actually (usually) referring to line *pairs*. Speaking of "330 lines" resolution actually means something roughly equivalent to a display with 660 *pixels* in each horizontal line. (Broadcast TV being an analog medium, the idea of "pixels" did not originate there and is somewhat of a foreign idea, if you consider the language that's typically used.) And to get back to the original point, yes, a resolution of 480 lines *is* better than what we're normally used to in broadcast television. Bob Myers KC0EW HP Graphics Tech. Div.| Opinions expressed here are not Ft. Collins, Colorado | those of my employer or any other myers@fc.hp.com | sentient life-form on this planet.
f@Alliant.COM (Bill Freeman) (01/29/91)
In article <1991Jan26.013437.25836@ux1.cso.uiuc.edu>, tmkk@ux1.cso.uiuc.edu (Scott Coleman) writes: > In article <1991Jan25.165057.671@ux1.cso.uiuc.edu> mas35638@uxa.cso.uiuc.edu (Odin) writes: > >> 480 lines > > > >525 is standard. You're talking about a picture which is not as > >good as normal tv broadcasts. > > > He's talking about 480 HORIZONTAL lines, not vertical lines. This is > considerably BETTER than broadcast (which is ~330 or so). This DBS sounds > ... NTSC and RS-170 video standards specify 525 horizontal scan times per frame (262.5 per field since it is interleaved 2:1), each with horizontal sync (either straight or the effective half of the equalizer pulses). These are called lines even though they are not all intended to display as such (like when the beam is in vertical retrace). The standards specify a minimum for the duration of vertical blanking, which while not specified directly in terms of lines, wind up requiring you to blank 19 lines per field, or 38 per frame, assuming that you don't want to count fractional lines. 525 - 38 = 487. I'm not sure what standard broadcast practice is in terms of any additional lines considered part of the "vertical interval", but we are certainly within spitting distance of 480. So the 480 may well be the number of displayed horizontal lines, and would not represent a degraded picture. You will not find a significant fraction of TV sets that don't lose more than that in overscan (the degree to which the picture is displayed larger than the face of the tube. A very good broadcast color television receiver might get 3.5 MHz of effective bandwidth in the luminance signal (or maybe 4.25 MHz for a monochrome broadcast). This is a basic fact of NTSC encoding life. The allowable unblanked portion of a horizontal scan time is about 50 microseconds. You can get 175 cycles of 3.5 MHz in during that 50 us. If you count both the dark lines and the light lines that separate them (peaks and valleys of the luminance signal), that gives you 350 "lines" of horizontal resolution as an absolute maximum for color on a standard set. The only way that 480 lines could be the horizontal resolution is if these guys provide RGB outputs for use with an RGB monitor. I get the impression that this is a commercial venture, so to have any hope, they are providing something that hooks to the two "VHF" screws on your Emerson. (Of course they could provide both, or if they just do RGB and the monitor you are not going to find a VCR to record it at K-mart, but I'd be surprised if there is anything other than "VHF".) I suspect that the number is vertical resolution, provided in response to the question of a "journalist" who suffers from HDTV sexual fixation. (Can someone give me examples of programming whose content justifies even standard broadcast resolution?) -- -- ...!{decvax!linus,mit-eddie}!alliant!f Bill Freeman KE1G alliant!f@eddie.mit.edu PP-SMEL
ken@wybbs.mi.org (Ken) (01/29/91)
The article did not say how much installation and setup would be. Since the antenna itself is very small, I would assume you could just aim it yourself until the picture came in. Then again... -- Ken Jongsma ken@wybbs.mi.org Smiths Industries ken%wybbs@sharkey.umich.edu Grand Rapids, Michigan ..sharkey.cc.umich.edu!wybbs!ken
lmb@sat.uucp (Larry Blair) (01/29/91)
In article <15129@milton.u.washington.edu> gwangung@milton.u.washington.edu (Roger Tang) writes: =In article <1991Jan25.165057.671@ux1.cso.uiuc.edu> mas35638@uxa.cso.uiuc.edu (Odin) writes: =>> 480 lines => =>525 is standard. You're talking about a picture which is not as =>good as normal tv broadcasts. = = ???? = = Last time I heard, broadcast quality was nowhere near 525 and, in fact, =many midline TVs don't get this even from direct video connections. The actual video in an NTSC signal consists of 485 lines (actually 484 plus two half lines). The entire signal is 525, so there are 2 ways to look at it. While most sets won't display all 485 lines, they sure as hell have to handle them, since they're going to have a horizontal sync pulse coming at them for each of those 525 lines. -- Larry Blair apple!sat!lmb lmb%sat@apple.com
poynton@vector.Eng.Sun.COM (Charles A. Poynton) (01/29/91)
Speculation abounds in Sci.electronics concerning television resolution.
Here's a note that I wrote ages ago in response to a similar thread on
Rec.video to explain television resolution. Pardon the stuff at the end
about storage capacity, it's not relevant to this discussion but I'll
leave it in anyway. Followups to Rec.video, but take care introducing
this subject over there!
The quick story? In television, one measures horizontal resolution in
units of one equivalent vertical "TV line", which is half of a black-white
line pair (cycle). There are 79 TVL of resolution per MHz of luminance
bandwidth. Over-the-airwaves NTSC has 525 raster lines, 480 picture
lines, and is strictly limited to about 330 lines of resolution.
C.
p.s. Great .sig, Scott Coleman!
-----
Charles A. Poynton Sun Microsystems Inc.
vox 415-336-7846 2550 Garcia Avenue, MTV21-10
fax 415-969-9131 Mountain View, CA 94043
<poynton@sun.com> U.S.A.
-----
TELEVISION RESOLUTION
SCOPE
This is a tutorial that describes how television resolution is measured,
how television signals are represented digitally, and how much memory is
needed for a television frame in various digital representations.
This discussion is limited to 525-line television, but the concepts apply
to other CRT display systems. The S-VHS interface is explained briefly.
SUMMARY
In television, one measures horizontal resolution in units of one
equivalent vertical "TV line", which is half of a black-white line pair
(cycle). There are 79 TVL of resolution per MHz of luminance bandwidth.
Over-the-airwaves NTSC is strictly limited to about 350 lines.
RASTER AND THEORETICAL RESOLUTION
There are 525 total scan lines per frame in North American television.
29.97 frames are transmitted per second. The fact that the total number
of raster lines is odd means that a vertical field retrace occurs once
every 262-and-one-half lines; it is this relationship that causes the 2:1
interlace and the separation of each transmitted frame into two fields.
Television old-timers think of each field as comprising 262 1/2 lines,
but in digital systems it is easier to think of field one as being 263
lines and field two as 262 lines. Of the 525 total raster lines, 483
contain picture information. [Closed captioning, if present, takes two
lines which would otherwise contain picture.] The remainder comprise
vertical scanning overhead.
Television system engineers measure vertical resolution in units of
"cycles per picture height" (C/PH), where a cycle comprises a white
element and a black element. C/PH is entirely comparable to the unit
which is used to describe film resolution: line pairs per millimetre
(often contracted to "lines/mm"). The maximum theoretical vertical
resolution contained in the 480 picture scan lines of television is 240
C/PH, corresponding to Nyquist's principle that at least two samples [in
this case, scan lines] are required to convey each cycle.
ACTUAL RESOLUTION
But just because you've got the samples doesn't mean that the full
theoretical reolution is being conveyed. In the early days of television
a typical picture tube could resolve at best about two thirds (the "Kell"
factor) of the maximum theoretical vertical resolution, or about 160
C/PH. This does not indicate that fewer lines are transmitted; rather, in
such a reduced-resolution system, the signal content of each scan line is
not completely independent, but is to some extent related to the content
of adjacent lines. Also, not all of this theoretical resolution is
necessarily delivered to the face of the CRT: a transmitted or recorded
signal may contain a pattern of say 160 cycles vertically, but a
particular picture tube (CRT) which has poor focus or poor convergence may
blend these variations into invisibility, to result in an actual vertical
resolution less than 160 C/PH.
The aspect ratio of a 525-line television picture is 4:3, so equal
vertical and horizontal resolution are obtained (assuming a Kell factor of
2/3) at a horizontal resolution of 160 times 4/3, or 213 C/PW. Multiply
this by 1.2 to accommodate horizontal scanning overhead to get 256, the
minimum number of cycles which must be conveyed per total line time to
obtain equal vertical and horizontal resolution. Multiply this by the
horizontal (line) scanning rate of 15.734 kHz to get a bandwidth for video
of about 4 MHz. This reasoning, combined with the monochrome television
channel spacing of 6 MHz, led the NTSC to choose a bandwidth of 4.2 MHz.
This will remain forever the limit for any over-the-airwaves NTSC signal.
Consumer equipment which exceeds this bandwidth is feasible but not yet
available. Remember that this calculation assumes a Kell factor of 2/3;
this may no longer be an appropriate assumption.
"TELEVISION LINES"
Just like television markete(e)rs decided early on to exaggerate picture
size by stating the diagonal dimension of the screen rather than its width
or height, they state "resolution" in terms of equivalent television scan
lines, denoted by the abbreviation TVL ("television lines") rather than
C/PH. There are two TVL per cycle: think of a cycle as a white element
and a black element. If a signal is sampled and represented digitally,
then each "TVL" is equivalent to one sample, so television system
engineers sometimes use the terms "samples per picture height" or
"samples per picture width".
Actual resolution is measured optically by a calibrated wedge pattern of
black and white lines. It is desirable that the same pattern, and the
same resolution number, apply to both the vertical and horizontal
directions. Therefore, the TVL unit is used to measure horizontal
resolution as well. Since the picture aspect ratio is 4:3, the
theoretical maximum 480 TVL of vertical resolution would be matched
horizontally by 640 samples.
One cycle per picture width consumes a time which is one total line time
[572/9 us], minus the FCC minimum blanking time [10.9 us]. This is the
duration in us corresponding to the picture width, and this is equivalent
to the number of cycles per picture width in the first 1 MHz of video
bandwidth. Double this to get samples per picture width, and divide by
the picture aspect ratio to express this in units of [vertical] TVL.
Hence:
((572/9)-10.9)*2*3/4
or about 79, is the number of TVL per MHz of bandwidth.
LIMITING RESOLUTION
The amplitude response of any electronic system generally falls off
gradually as a function of frequency. The term "bandwidth" refers to the
frequency at which the signal amplitude has fallen to 50% ("-3 dB") of its
reference amplitude. "Limiting resolution" in television is defined as
10% of the reference amplitude. Limiting resolution is typically reached
at perhaps 1.2 times the 3 dB bandwidth. Your factor may vary.
NTSC has a 3 dB bandwidth of 4.2 MHz, for a resolution (at 50%) of 332
TVL. It could be argued that 10% limiting resolution could be a little
higher than this, but the in NTSC the sound subcarrier is at 4.5 MHz so it
is absolutely guaranteed that no resolution above 355 TVL is possible
over-the-airwaves.
"Advanced" or "improved" television technology, in particular frame rate
doubling (de-interlacing) at the display, can achieve very close to the
theoretical 480 TVL of vertical resolution (i.e. a Kell factor of unity),
and would benefit from horizontal resolution up to perhaps 700 TVL for
non-broadcast signals. Broadcast studio equipment typically samples at
13.5 MHz, with 720 samples per picture width. Baseband analog signals in
the studio typically have a bandwidth of 5.5 MHz, and the best 525-line
studio monitors are quoted as having 900 TVL of resolution at the centre
of the tube.
YUV REPRESENTATION (3 wires)
Studio equipment typically maintains colour signals in three components
YUV, which are easily derived from RGB. The Y channel contains the
luminance (black-and-white) content of the image, and is computed as:
Y = 0.299 R + 0.587 G + 0.114 B
"Colour difference" signals U and V are scaled versions of B-Y and R-Y
respectively; these vanish for monochrome (grey) signals. The human
visual system has much less acuity for spatial variation of colour than
for luminance, and the advantage of U and V components is that each can be
conveyed with substantially less bandwidth than luminance, R or G or B.
In analog YUV studio systems, U and V each have a bandwidth of 1.5 MHz.
In digital systems, U and V are each horizontally subsampled by a factor
of two (i.e. conveyed at half the rate of Y).
Y/C REPRESENTATION (2 wires)
U and V can be combined easily into a "chroma" signal which is conveyed as
modulation of a continuous 3.58 MHz sine-wave subcarrier. [This frequency
is exactly 455/2 times the line rate of 9/.572 kHz.] The phase of the
chroma signal conveys a quantity related to hue, and its amplitude conveys
a quantity related to colour saturation (purity). [Phase is decoded with
reference to a "burst" of the 3.58 MHz continuous-wave subcarrier which is
transmitted during the horizontal blanking interval.] The "S" connector
simply carries Y and C on separate wires. This coding is easily decoded
without artifacts. Current S-VHS equipment conveys chroma with severely
limited bandwidth, about 300 kHz (which is just 16 cycles of U or V
per picture width). Consumer VCR equipment has always recorded the
luminance and chroma components separately on tape, but only with the
introduction of the S-connector in S-VHS and ED-Beta equipment was the
consumer able to take advantage of this capability.
NTSC REPRESENTATION (1 wire)
The NTSC system mixes Y and C together and conveys the result on one piece
of wire. The result of this addition operation is not theoretically
reversible: the process of separating luminance and colour often confuses
one for the other. Cross-colour artifacts result from luminance patterns
which happen to generate signals near the 3.58 MHz colour subcarrier.
Such information may be decoded as swirling colour rainbows.
Cross-luminance artifacts result if modulated colour information is
incorrectly decoded as crawling or hanging luminance dots. It is these
artifacts which can be avoided by using the S-connector interface. In
general, once the NTSC footprint is impressed on a signal, it persists
even if subsequent processing is performed in RGB or YUV components.
Encoded NTSC signals can be sampled into a stream of 8-bit bytes. Such
"composite digital" systems have the advantage of using slightly less
memory than component systems, at the expense of the dreaded NTSC
artifacts. Manipulation of such composite signals to perform operations
such as shrinking the picture is difficult or impossible, because if the
colour subcarrier frequency is altered the colour information in the
signal is destroyed. Therefore, these operations are performed in the
component domain.
MEMORY REQUIREMENTS
[Nomenclature: k=kilo=1000, K=2^10=1024, b=bit, B=Byte.]
About 210 KB (480-by-430), or 1.6 Mb, is sufficient to store composite
NTSC at a horizontal resolution of 320 TVL. Y/C components can be stored
at S-VHS colour resolution in 256 KB (2 Mb). Consumer equipment uses as
few as six bits for Y, U, or V.
Composite NTSC digital studio equipment typically stores a frame as
768-by-480 samples of 8 bits each, for about 384 KB (3 Mb) per frame.
Component digital equipment stores YUV components at 720-by-480 samples of
16 bits each for about 675 KB (5.4 Mb) per frame: 8-bit U and V colour
components are horizontally subsampled by a factor of two with respect to
luminance.
-----
Charles A. Poynton Sun Microsystems Inc.
<poynton@sun.com> 2550 Garcia Avenue, MS 8-04
415-336-7846 Mountain View, CA 94043
-----rrw@naucse.cse.nau.edu (Robert Wier) (01/30/91)
Another real interesting question would be whether current
dish owners could install a system putting in only the receiver
(and if so, how much cheaper would it be?). A 10' dish (assuming
it functions acceptably at KU band freqs) should provide outstanding
signal strength (maybe too much!).
- Bob Wier
-------------- insert favorite standard disclaimers here ----------
College of Engineering
Northern Arizona University / Flagstaff, Arizona
Internet: rrw@naucse.cse.nau.edu | BITNET: WIER@NAUVAX | WB5KXH
or uucp: ...arizona!naucse!rrwbill@bilver.uucp (Bill Vermillion) (02/01/91)
In article <1991Jan28.150552.3082@news.larc.nasa.gov> kludge@grissom.larc.nasa.gov ( Scott Dorsey) writes: >In article <1991Jan25.165057.671@ux1.cso.uiuc.edu> mas35638@uxa.cso.uiuc.edu (Odin) writes: >>> 480 lines >> >>525 is standard. You're talking about a picture which is not as >>good as normal tv broadcasts. > >Yes, but of those 525 lines, many of them carry vertical synch information. >Most TV broadcasts use about 480 lines vertically. > Display lines DON'T equal resolution. The 480 lines displayed will give 240 lines resolution. It takes two lines (or a pair) to resolve 1 line. THink of it this way. If you had 480 horizontal lines and put them on video, the screen would be all white or all black as there is nothing to separate the lines. TV pictures are 4 units wide and 3 units high. Take the approx 240, and divided by 3 and multiply by 4. You get 320. That is the horizontal resolution spec. This gives approximately equal horizontal and vertical resolution. When you have a higher bandwidth, you can turn the horizontal trace on and off faster. Doing this increases the amount of vertical line pairs you can display. There is a limit to the amount of apparent resolution you increase because the resolution limit by the NUMBER of horizontal trace lines will fool the brain so it won't see the resolution increased by the number of TIMES the horizontal trace line is turned on/off. (eg, how small the dots are going left to right). -- Bill Vermillion - UUCP: uunet!tarpit!bilver!bill : bill@bilver.UUCP