chris@spock (Chris Ott) (11/09/88)
Ok, since no one seems to remember the article I posted last time this question was asked, here is my input again. Let me explain now that I am speaking of the 2000 and 3000 series IRISes. I know nothing about the 4D machines, except that they have a resolution of 1280x1024, rather than 1024x768, but I would still expect this stuff to apply. For those of you who think that you can't use the whole screen when videotaping, let me confirm your suspicions. The IRIS screen's resolution is 1024x768, while NTSC's resolution is something like 500x700, if you're lucky. Also, the IRIS's video is 60Hz non-interlaced, while NTSC video is interlaced. Obviously, this requires a completely different setup to display hi-res than to display NTSC. Most IRIS systems (at least the 2000 and 3000 series) are shipped with the ability to display two of four different customer-selected video formats. The four formats are 60Hz non-interlaced, 30Hz interlaced, NTSC, and PAL. Usually, the two selected (maybe the defaults) are 60Hz and NTSC. This is the way all of our IRISes are set up. Since the video formats are different, all you can see is garbage on the 60Hz screen when the IRIS is in NTSC mode, and vice-versa. The simple solution is to get some equipment so you can see something in NTSC mode. The equipment needed is a color encoder and an NTSC format monitor. If you want _broadcast quality_ video (i.e. exact NTSC timings), you will also need a sync generator. A color encoder is used to convert the RGB signal from the IRIS to a composite video signal. Of course, for this to work, NTSC format must be selected; the color encoder will not convert 60Hz to composite video. We got a pretty cheap color encoder for about $1000. The picture is acceptable, but pretty fuzzy. The sync generator doesn't help that much, either, except to improve some of the timings. Of course, you get what you pay for. A friend of mine who works for a local television station (an NBC affiliate, if anyone cares) says they paid $6000 for their encoder. I've seen the picture, and it's flawless. Our (cheap) sync generator is also about $1000. I can't speak for other sync generators. Before I go any further, let me say that I do not recommend just shooting an NTSC video camera directly at the screen of the IRIS. The resolutions are different and the timings are different. The resulting picture will look like trash. Ever wonder why TV screens in the movies have that horizontal bar traveling from the top to the bottom of the screen? Now you know. It seems strange to me that anyone would complain about the fact that you can only display part of the screen. You can't display 1024x768 pixels on an NTSC screen, anyway. Anything over 700x500 is just a waste of pixels. It certainly doesn't give you a problem with programming, either. All you need to do is use the graphics library like so: viewport( 0,636, 0,485 ); I believe those are the correct coordinates. As far as I can remember, nothing else needs to be changed. Everything that used to take up the full 60Hz screen will now take up only the lower left-hand corner of the 60Hz screen, but it will take up the entire NTSC screen. Now, is that easy, or what? I think this was the easiest and cheapest way for SGI to do it. Conversion between two different video resolutions is _expensive_. Rather than paying $1000 for a color encoder, you'd be paying between $10000 and $20000 for a converter. So, that's how it's done. If you want any more information, like more detail, an actual working program, or some company names, let me know. Chris ------------------------------------------------------------------------------- Chris Ott Computational Fluid Mechanics Lab Just say "Whoa!!" and University of Arizona vote for Randee!! Internet: chris@spock.ame.arizona.edu UUCP: {allegra,cmcl2,hao!noao}!arizona!amethyst!spock!chris -------------------------------------------------------------------------------
henry@utzoo.uucp (Henry Spencer) (11/12/88)
In article <849@amethyst.ma.arizona.edu> chris@spock.ame.arizona.edu (Chris Ott) writes: > Before I go any further, let me say that I do not recommend just >shooting an NTSC video camera directly at the screen of the IRIS. The >resolutions are different and the timings are different. The resulting >picture will look like trash... Correction: it *may* look like trash, depending on details. It worked okay for us in the CHI+GI 87 demos track (which I ran), although the more limited resolution was a serious pain for some of the demonstrators who used a lot of fine detail. We fearlessly pointed our camera at Irises, Suns, PCs, you name it; no serious problems. This may have been an accident of our particular equipment. -- Sendmail is a bug, | Henry Spencer at U of Toronto Zoology not a feature. | uunet!attcan!utzoo!henry henry@zoo.toronto.edu
blbates@AERO4.LARC.NASA.GOV (Bates TAD/HRNAB ms294 x2601) (11/15/88)
We used a TV studio quality camera and tape machine and our results were very good. In fact some people told us it was better than using an NTSC encoder, based on the equipment they used. The process is clumsy and our technicians had to use a filter on the camera to improve the picture, but it did ok.