mardiros@dtoa3.dt.navy.mil (Mardiros) (04/25/91)
hi, i need some advice very fast. question: What are my bennifits for buying a non-interlaced monitor versus an interlaced one? my choice: interlaced- WYSE non-interlaced - ALR Thanks, your help is appreciated. marty
bjorn@valhalla.esd.sgi.com (Bjorn Lindstrom) (04/25/91)
Interlaced monitors have a noticable "flickering" effect, particularly at the higher resolutions (greater than 800x600). Combine that with greater detail at those higher resolutions, and you have a situation that is VERY hard on the eyes. The term comes from (inter-)"lacing" the scan lines, so that every other scan line is displayed, taking two passes over the screen to display them all (taking twice as long, obviously). A non-interlaced display, on the other hand, displays all the scan lines in the same pass, creating none of the "flickering" found on interlaced displays. Good luck! Bjorn
crs@lanl.gov (Charlie Sorsby) (04/27/91)
In article <1991Apr24.230046.7851@odin.corp.sgi.com>, bjorn@valhalla.esd.sgi.com (Bjorn Lindstrom) writes: > The term comes from (inter-)"lacing" the scan lines, so > that every other scan line is displayed, taking two passes over the screen > to display them all (taking twice as long, obviously). Well, yes and no. Interlace scanning was originally used to *reduce* flicker in television displays. To understand this, one must consider global as opposed to local flicker and constraints on scanning speed. More in a moment. Cost and technical constraints *always* limit to one degree or another, the maximum video frequency that can be used. This limits the maximum horizontal scanning speed possible which, in turn, limits the maximum vertical scanning speed that will produce the required number of scanning lines per frame. > A non-interlaced display, on the other hand, displays all the scan lines in > the same pass, creating none of the "flickering" found on interlaced displays. ^^^^ ^^ ^^^ ^^^^^^^^^^^^ Not necessarily true, at least in principle. But it does depend on your definition of flickering. The reason that television uses interlace scanning is that scanning *speed* is (or was) constrained by cost and technical considerations when the standard was defined. For a given, relatively low, scanning speed, interlace scanning will produce less perceived *global* flicker. The flicker of any *single* pixel will be the same whether interlace is used or not. For given vertical and horizontal scanning speeds any specific pixel will be illuminated exactly the same number of times per second whether scanning is interlace or noninterlace. In the case of television (vertical scanning frequency is approx. 60 times per second, horizontal approx. 15,750). With this relationship between vertical and horizontal scanning periods this is possible with interlace scanning. With non-interlace scanning *and* a limit of 15,750 horizontal scans per second, *noninterlace* scanning would limit vertical scanning to approximately 30 scans per second (with the number of scanning lines needed) and the viewer would perceive global flicker. *My* interpretation of the problem with character displays as opposed to image displays is that with the former, one in concentrating intently on a small area of the screen at any one time (i.e. the area occupied by a character). With interlace scanning, vertically adjacent pixels are illuminated at significantly different times (one field period apart) and probably cause the perception of *local* flicker. I believe that, if character display monitors were constrained to the same maximum video frequency, and, therefore, the same maximum horizontal scan rate, and, therefore, the same maximum vertical scan rate, as are television displays, the apparent global flicker resulting from noninterlace scanning would be much more noticeable and annoying than the local flicker due to interlace. Once one can afford a high enough video frequency (the cost of the electronics goes up with increasing bandwidth), interlace is no longer necessary. But it isn't simply a case that interlace scanning is bad and noninterlace scanning is good. There are trade-offs that must be made. Best, Charlie Sorsby "I'm the NRA!" crs@lanl.gov