harald@leo.UUCP ( Harald Milne) (04/23/88)
In article <890@gethen.UUCP>, farren@gethen.UUCP (Michael J. Farren) writes: > Let me put this another way: in interlaced mode, you are trading off > the ability to update the display 60 times per second for the ability > to put more lines on the screen. Agreed. However interlaced displays have twice the number of lines, and therefore twice the amount of information. A hi-res interlaced display (640X400) versus a hi-res non-interlaced display (640X200) also takes twice the amount of memory. So from interlaced to non-interlaced, you lose half the information or more specifically pixel data. > There are 60 fields worth of information > sent to the monitor each second, in either mode, and no information is > lost. The number fields are the same, but the amount of information is not. Actually, in the context of non-interlaced displays, the term fields doesn't make sense any more. It takes 2 60hz odd/even fields to put together a 30hz NTSC RS170A video frame. In non-interlaced displays, you get two "fields" of the same information. So, in a 30hz time frame, you get the same information twice. In an interlaced display, you get two different fields. You also get these fields interspersed in such a way, they "fill" in a 30hz time period. Unfortunately, on short persistance monitors, this also creates flicker. I even get flicker watching LaserDisks on a high resolution monitor. So, it's not just an affliction unique to the Amiga. It's the NTSC standard. > Alternate half-frames are not lost, hey are simply displayed in > the same space as the other half-frames. Perhaps now I understand the problems in this terminology. We are not missing frames, just information. > > If you don't believe me, record Amiga video in Interlace and > >Non-Interlace. Interlace will look fine, where Non-Interlace will look like > >sh*t. There is information absent. > No. There is NO INFORMATION ABSENT, except for one bit - the slight > difference in timing between even and odd fields. This sounds like a timebase instability problem, due to erractic tape motion. I'm not quite sure what you are refering to here. > Vertical sync timing differs between the two, and that is the ONLY > difference. Vertical sync can't possibly be different. Look at what you said previously. 60 fields a second. These fields are separated by a vertical sync pulse. It's the only way you can start a new "field". > Perhaps some > VCRs require the timing change, but the funny thing is that my own recordings > of non-interlaced displays on a cheapo VCR look just fine. > Maybe Beta VCR's just can't hack it :-) Now that's interesting. I've never tried that on a very low resolution VCR. 8^) I believe the problem here (or the lack of one) lies in the bandwith (or resolution) of the equipment you use. If you have a REAL el cheapo VCR (like so old, it has a wired remote) you probably can't get even 240 lines of resolution. Since non-interlaced without overscan is 200 lines, you propably can't see a difference if you tried. The VCR just doesn't have the suck. NTSC is 330 lines. The Amiga is somewhere around 480 maxed out with overscan. -- Work: Computer Consoles Inc. (CCI), Advanced Development Group (ADG) Irvine, CA (RISCy business!) UUCP: uunet!ccicpg!leo!harald