Path: utzoo!utgpu!jarvis.csri.toronto.edu!clyde.concordia.ca!uunet!ccavax!lmrc!hassinger From: hassinger@lmrc.uucp Newsgroups: comp.sys.amiga Subject: Re: Interlace-Flicker Message-ID: <4607@lmrc.uucp> Date: 2 Feb 90 17:53:03 GMT References: <6721@mentor.cc.purdue.edu> <2016@ultb.isc.rit.edu> <3000@d75.UUCP> <3018@d75.UUCP> Organization: Liberty Mutual Research Center, Hopkinton, MA Lines: 38 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