fc@lexicon.com (Frank Cunningham) (02/01/90)
> >scan rate is 15.75 MHz. Doubling that will give you 31.5 MHz which is > the AMI are 60 Hz. That means that the entire screen is refreshed 60 times > 15.75 [M]hz (M = Mega/Millon). If the entire screen were redrawn 15.75 million Just to get a few things straight: American NTSC TV refreshes the entire screen 29.97 times per second. Color is not exactly 30 due to some interference problem with the broadcast color subcarrier frequencies. The two interlaced fields are refreshed at 59.94 Hz. They flicker because, being interlaced, they are slightly different and are alternately refreshed at 30 Hz. A 60Hz full screen refresh does not flicker on a reasonable phosphor. The horizontal scan rate of TV is 15.75 kHz (that's kilo = 1000) or 59.94 fields / second * (~=)260 lines / field. -- -Frank Cunningham smart: fc@lexicon.com phone: (617) 891-6790 dumb: {husc6,linus,harvard,bbn}!spdcc!lexicon!fc snail: Lexicon Inc. 100 Beaver St. Waltham MA 02174 Why are viola jokes so short ? So violinists can remember them.
sparks@corpane.UUCP (John Sparks) (02/02/90)
liberato@drivax.UUCP (Jimmy Liberato) writes: >robin@sabre.uucp (Robin D. Wilson/1000000) writes: >>No, it is not an impossibility. All you have to do is increase the horizontal >>scan rate from 60hz to 120 and TAH!DAH! you have an interlaced screen that >>flickers not more than a non-interlace screen of the current variety. >Your concept is correct but the numbers are a little off. The stock horizontal >scan rate is 15.75 MHz. Doubling that will give you 31.5 MHz which is >what the IBM VGA standard is. This is the technique (in addition to buffering >the individual interlaced video frames into one) that the flickerFixer uses, >hence the requirement for a VGA or multisync monitor. The "productivity mode" >of the upcoming Enhanced Chip Set will also require a multisync monitor or >Commodore's bisync monitor. Er you are both wrong. The Horizontal Scan rate doesn't have anything to do with interlace, the Vertical refresh rate is what the first guy meant to talk about. Doubling the vertical refresh rate from 60hz to 120hz would fix the problem, but you would have a bunch of new problems, like then the Amiga wouldn't be NTSC compatible, which is the whole Idea behind the inter- lace to begin with. -- John Sparks | D.I.S.K. 24hrs 1200bps. Accessable via Starlink (Louisville KY) sparks@corpane.UUCP <><><><><><><><><><><> D.I.S.K. ph:502/968-5401 thru -5406 Don't take life too seriously. You'll never get out of it alive.
tomb@hplsla.HP.COM (Tom Bruhns) (02/03/90)
navas@cory.Berkeley.EDU (David C. Navas) writes: >In article <26360@cup.portal.com> phorgan@cup.portal.com (Patrick John Horgan) writes: >>Of course it doesn't! Your television is interlaced, and that looks quite >>nice doesn't it?...Slow scan rate means flicker:) > >Eh, my TV looks *good*? We talking about the same piece of NTSC garbage we're all >familiar with? :) :) Of course our TV has flicker -- that's why overlaid text on >Newscasts always seems to have ants in their pants... :) ... Yep. And the NTSC color standard has yet another level of interlace most folk miss: the color subcarrier is interlaced with the horizontal scan. The result is that you don't refresh the screen the same way for a whole 1/15 (nom.) of a second! So strong color borders (vertical ones) show a very obvious wave motion. At least on RGB you don't have that problem. BTW, I have seldom seen such misinformation as is woven into this thread! Megahertz vertical _or_ horizontal scan frequencies??!! C'mon. Yes, NTSC and the standard Amy screens both scan vertically at about 60 times a second. But both are interlaced, so alternate scans are slightly vertically displaced (by 1/2 the scan line spacing of a single vertical sweep, though monitors seldom put the alternate fields excatly where they belong relative to eachother). The result is that the screen is full- refreshed only 30 times a second (and as noted, NTSC color screws this up one step further :-). Can we get this right and kill the thread?
hassinger@lmrc.uucp (02/03/90)
This is all getting a bit confused I think... In article <3018@d75.UUCP>, robin@sabre.uucp (Robin D. Wilson/1000000) writes: > > I think you misunderstood. The HORIZONTAL SCAN RATE on a US television, and > the AMI are 60 Hz. That means that the entire screen is refreshed 60 times > per second. If I understand correctly, in standard (NTSC) video, the *field rate* is 60 fields per second and the *frame rate* is 30 frames per second (a frame is one 525 line picture made of of two interlaced 262.5 line fields). This can be called *vertical* scan rate. That is, the frequency at which the vertical sync fires off new vertical sweeps down the screen to form new fields and frames. > ... The Vertical sync frequency is > 15.75 [M]hz (M = Mega/Millon). ... The *horizontal* scan rate is 15,750 or 15.75K lines per second ("15.75 KHz"). Note KHz, not MHz. This comes from 30 x 525. That is the frequency or rate at which the horizontal sync fires off new horizontal sweeps across the screen to form individual scan lines (e.g. we see 15,750 lines a second less the ones lost to overscan and retrace blanking). A case of interest for the Amiga is the double rate output of the flicker fixer that is similar to many PC higher res systems that runs at a 31.5 KHz (horizontal) scan rate based on 60 full 525 line frames instead of 30. Typically special monitors that can run at these rates such as "multisync" models are used for these. The typical place one sees measures in MHz is when discussing the video and display bandwidth which ends up being largely a measure of how much detail you get in your image. Numbers like 5 MHz are common for standard broadcast NTSC. In directly connected RGB cases it can be 10, 20, 30 MHz or more, particularly in the case of higher than standard 30 frame/60 field displays. Bob Hassinger ...uunet!ccavax!lmrc!hassinger hassinger@lmrc.UUCP 508-435-9061
tomb@hplsla.HP.COM (Tom Bruhns) (02/03/90)
I wrote: >BTW, I have seldom seen such misinformation as is woven into this thread! >Megahertz vertical _or_ horizontal scan frequencies??!! C'mon. Yes, NTSC >and the standard Amy screens both scan vertically at about 60 times a >second. But both are interlaced, so alternate scans are slightly ^^^^^^^^^^^^^^^^^^^ Of course I meant that the Amy is interlaced when you put it in interlace mode ;-) -- just trying to keep the misinformation going ;-)
Jim.Priestle@afitamy.fidonet.org (Jim Priestle) (02/09/90)
Don't tell me TV doesn't ficker! That's why TV people never wear funny
clothes that make you eyes go buggy. And the Weather map on CNN Headline news
flicker quite a bit, too. The secret is to stay away from contrasting colors
on top of themselves, don't crank the contrast, and use suttle colors. -jim-
--
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Jim Priestle - via FidoNet node 1:110/300
UUCP: uunet!dayvb!afitamy!Jim.Priestle
ARPA: Jim.Priestle@afitamy.fidonet.org
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>>>> The // Air Force Institute of Technology
// Amiga Users BBS/UFGateway
\ // Dayton Ohio (513)-252-7681
\X/ 1:110/300 dan.laskowski@canremote.uucp (DAN LASKOWSKI) (02/13/90)
>From: Jim.Priestle@afitamy.fidonet.org (Jim Priestle) >Orga: AFIT Amiga Users BBS(AFITAUG), Dayton, Oh. (513) 252-7681 > >Don't tell me TV doesn't ficker! That's why TV people never wear >funny clothes that make you eyes go buggy. And the Weather map on >CNN Headline news flicker quite a bit, too. The secret is to stay >away from contrasting colors on top of themselves, don't crank the >contrast, and use suttle colors. -jim- And don't photograph close THIN horizontal lines. I was watching a movie the other day where there were window blinds in the backround. It was almost hypnotizing! In fact it would be nice if software would be written to have a minimum of 2 horizontal lines for each colour. (window borders) This would stop most of the flicker when in interlace mode! --- ~ EZ 1.24 ~ ~ QNet 2.04: NorthAmeriNet Windsor Hub ~ Windsor Spitfire BBS ~ 519-735-1504 ~
sparks@corpane.UUCP (John Sparks) (02/15/90)
dan.laskowski@canremote.uucp (DAN LASKOWSKI) writes: |In fact it would be nice if software would be written to have a minimum |of 2 horizontal lines for each colour. (window borders) |This would stop most of the flicker when in interlace mode! Er, but if you used two lines instead of one, then you might as well not even use the interlace mode, you are back to 200 lines per screen. -- John Sparks | D.I.S.K. 24hrs 1200bps. Accessable via Starlink (Louisville KY) sparks@corpane.UUCP <><><><><><><><><><><> D.I.S.K. ph:502/968-5401 thru -5406 Although the moon is smaller than the earth, it is farther away.