120hz versus 240hz
in [Repair]
|
Prev: mp3 player will not play songs
Next: Gale turntable
From: Dave Plowman (News) on 1 Mar 2010 10:50 In article <4b8bb33b$0$14745$c3e8da3(a)news.astraweb.com>, Sylvia Else <sylvia(a)not.at.this.address> wrote: > On 1/03/2010 11:13 PM, William Sommerwerck wrote: > >> Lots of tricks have been used over the years to take advantage > >> of the limitations of the "equipment" and the process. For example, > >> anything faster than 24 frames a second is not perceived as being > >> discrete images, but one smooth image. > > > > Actually, it's 16 frames a second. However, that rate is not fast > > enough to prevent flicker -- which is why silent films were sometimes > > called "flickers". This is one of the reasons the frame rate was > > increased to 24 with the introduction of sound. > > > > > >> The 50 and 60 fields per second (a field being half an interlaced > >> frame) were chosen not because they needed to be that fast (48 would > >> have done), but to eliminate interefence effects from electrical > >> lights. > > > > That's new to me. > Well, the story I heard way back when is that it was to synchronise the > picture's vertical frequency with the mains frequency, so that > inadequacies in power smoothing produced static distortions in the > picture rather than much more noticable rolling distortions. UK TV went off mains lock many many years ago. Something like the early '60s, - before colour arrived here. When sets were still valve. -- *Always drink upstream from the herd * Dave Plowman dave(a)davenoise.co.uk London SW To e-mail, change noise into sound.
From: Michael A. Terrell on 1 Mar 2010 11:17 William Sommerwerck wrote: > > >>> The 50 and 60 fields per second (a field being half an interlaced frame) > >>> were chosen not because they needed to be that fast (48 would have > >>> done), but to eliminate interefence effects from electrical lights. > > >> That's new to me. > > > Well, the story I heard way back when is that it was to synchronise > > the picture's vertical frequency with the mains frequency, so that > > inadequacies in power smoothing produced static distortions in the > > picture rather than much more noticable rolling distortions. > > That's what I heard, too. But that's not "interefence effects from > electrical lights". 60 Hz ws used in the US to prevent hum bars from rolling up or down the screen due to the difference in the line & scan frequencies. A faint bar would be hard to spot if it was not moving, but very annoying if it did. People have to remember that the standards were set when Electronics was fairly new, and rather crude designs were used. -- Greed is the root of all eBay.
From: Mark Zenier on 28 Feb 2010 12:29 In article <PrNhn.74162$_W6.55448(a)newsfe30.ams2>, Arfa Daily <arfa.daily(a)ntlworld.com> wrote: >You should also be aware that there are several 'resolutions' of screen and >drive to take into consideration. Almost all TV showrooms both here and in >the US, tend to have the sets running on at least an HD picture, and often a >BluRay picture. This makes them look very good at first glance. Problem is >that in normal day to day use when you get it back home, you are going to be >watching standard resolution terrestrial broadcasts on it, and on many sets, >these look pretty dreadful, and it is the reason that so many people are >disappointed with their purchase when they get it home, and think that it is >not what they saw in the store. At least in my area (Seattle), all the mainstream over the air stations are HD, now. (Each station has its own transmitter, so they don't have shared "multiplexes" like in the UK). The typical situation is an HD subchannel with the main program and one SD subchannel with some secondary service (sports, weather, old movies, old TV show, or an SD copy of the main signal to feed analog cable). There's a smaller number of stations that trade selection for resolution, running four or five SD subchannels. Christian broadcasting and speciality stuff like the secondary channels on the other stations. The only way you'd get stuck with standard definition on the national networks is to still be using analog cable. (I'm not familiar with what you get with the two (subscription only) national direct broadcast satellite providers). Mark Zenier mzenier(a)eskimo.com Googleproofaddress(account:mzenier provider:eskimo domain:com)
From: Phil Allison on 1 Mar 2010 22:31 "Geoffrey S. Mendelson" > > The 50 and 60 fields per second (a field being half an interlaced frame) > were > chosen not because they needed to be that fast (48 would have done), but > to > eliminate interefence effects from electrical lights. ** But the lights concerned were those being used to illuminate the TV studio. When frame rates are not locked to the AC supply frequency, faint shadows can be seen moving up or down studio images on a monitor or home TV set - due to the twice per cycle dip in brightness of incandescent lamps. Other fixes include using lamps with sufficient thermal inertia or groups of lamps on different phases to eliminate the light modulation. ...... Phil
From: Dave Plowman (News) on 2 Mar 2010 04:54
In article <td_in.163148$Dy7.138444(a)newsfe26.ams2>, Arfa Daily <arfa.daily(a)ntlworld.com> wrote: > The digital terrestrial TV being provided here in the UK now, currently > carries no HD content, despite ongoing promises. Not so. BBC HD is transmitted on FreeView as is ITV HD. CH4 and 5 will be added shortly. This is from the London transmitter. Not sure about everywhere. -- *Who are these kids and why are they calling me Mom? Dave Plowman dave(a)davenoise.co.uk London SW To e-mail, change noise into sound. |