lars@salt.acc.com (Lars J Poulsen) (07/13/89)
In article <10350003@otter.hpl.hp.com> (on rec.arts.tv.uk), Lee Carter writes: >=The problems of converting between PAL and NTSC are numerous and >=unpleasant; They use entirely different methods to encode the television >=signal Certainly the conversion requires buffering through a digital framestore. I believe that the cost of fast enough RAM used to be the driving cost factor. You probably need 24 bitplanes and about 600 x 800 resolution. But this is well within what's available in newer computer display cards, and it seems to me that several of the new display cards for the Mac-II are beginning to have framegrabbers. The idea of mixing computer graphics with video is not new. I have been told that one of the selling points of the Amiga is that it can produce NTSC video output and can overlay the graphics screen on a live video image. Anyway, video/framegrabber cards allow for video in, frame storage and video output from the frame store. It seems to me that this means we have the most expensive pieces of a scanconverter in place. This still leaves some problems: (1) 525 lines versus 625 lines. Not a big deal: Just use 600 lines. 525 line-video resides in the upper 525 lines. Or even better: set a programmable starting point so you have the choice of a window menu bar on top or a subtitle area on the bottom for 525 line video. Chop off the bottom 25 lines for 625 line video input. (2) 50 Hz vs 60 Hz scan rates. This requires the memory to be dual-ported. To reduce the effect of access collisions, you'd probably need to pre-fetch a line-buffer's worth of data on each port. (3) Interlace versus non-interlace scan. Broadcast video is usually interlaced to reduce flicker, computer displays are usually non-interlaced. This means a little extra logic, but not much. The 50 Hz interlaced video is really skipping every other line; i.e. it really is only 25 Hz. Some users might be willing to forego interlaced output (i.e. only view the euro movies on the computer screen). (4) Distortion due to 525-600-625 rate differences. Yes, it looks ugly in broadcast, but you can live with it on home viewing by fiddling with the height and/or horizontal gain. Professional systems, of course, skip/duplicate lines at even intervals in the picture. Am I the only person with family in Europe that would like to run videomovies through the computer ? Will this open up a new vertical market for Commodore, Apple or NeXT ? Followups to sci.electronics, only, please. / Lars Poulsen <lars@salt.acc.com> (800) 222-7308 or (805) 963-9431 ext 358 ACC Customer Service Affiliation stated for identification only My employer probably would not agree if he knew what I said !!
jms@tardis.Tymnet.COM (Joe Smith) (07/13/89)
[I forced this followup back to comp.sys.amiga because of the Toaster]
In article <918@anise.acc.com> lars@salt.acc.com (Lars J Poulsen) writes:
<Certainly the conversion requires buffering through a digital
<framestore. I believe that the cost of fast enough RAM used to be the
<driving cost factor. You probably need 24 bitplanes and about 600 x 800
<resolution. <This still leaves some problems:
<(1) 525 lines versus 625 lines.
<(2) 50 Hz vs 60 Hz scan rates.
<(3) Interlace versus non-interlace scan.
<(4) Distortion due to 525-600-625 rate differences. Yes, it looks ugly
You assumed two steps that you forgot to mention:
1) Convert PAL video from analog chroma/luma into digital RGB
2) Convert digital RGB to NTSC analog chroma/luma
There are a lot of frame buffers that to the latter, but very few American
ones that can do the former.
I bring this up because I talked to New Tek's Tim Jennison about that.
I asked, "since you are already converting NTSC to RGB in RAM, couldn't
you store into RAM at PAL rates and read at NTSC rates?" He said, "we
don't store RGB in RAM. That's what makes the Toaster affordable."
Apparently the signal is kept in chroma/luma form.
Also, he mentioned that the signals coming out of home VCRs do not have
the strict timing that the Toaster requires. There's supposed to be a
low-cost time base corrector in the works.
--
Joe Smith (408)922-6220 | SMTP: JMS@F74.TYMNET.COM or jms@tymix.tymnet.com
McDonnell Douglas FSCO | UUCP: ...!{ames,pyramid}!oliveb!tymix!tardis!jms
PO Box 49019, MS-D21 | PDP-10 support: My car's license plate is "POPJ P,"
San Jose, CA 95161-9019 | narrator.device: "I didn't say that, my Amiga did!"Sullivan@cup.portal.com (sullivan - segall) (07/14/89)
>In article <10350003@otter.hpl.hp.com> (on rec.arts.tv.uk), Lee Carter writes: >>=The problems of converting between PAL and NTSC are numerous and >>=unpleasant; They use entirely different methods to encode the television >>=signal > >Certainly the conversion requires buffering through a digital >framestore. I believe that the cost of fast enough RAM used to be the >driving cost factor. You probably need 24 bitplanes and about 600 x 800 >resolution. But this is well within what's available in newer computer >display cards, and it seems to me that several of the new display cards >for the Mac-II are beginning to have framegrabbers. > >/ Lars Poulsen <lars@salt.acc.com> (800) 222-7308 or (805) 963-9431 ext 358 > ACC Customer Service Affiliation stated for identification only > My employer probably would not agree if he knew what I said !! Perhaps the easiest "solution" if you just want to watch european home videos, is to get an ECS amiga, and a PAL monitor which will run on 60Hz power. (Sylvania used to make a TV set that was PAL/NTSC switchable. Too bad it never caught on.) siug -Sullivan Segall _________________________________________________________________ /V\ Sullivan was the first to learn how to jump without moving. ' Is it not proper that the student should surpass the teacher? To Quote the immortal Socrates: "I drank what?" -Sullivan _________________________________________________________________ Mail to: ...sun!portal!cup.portal.com!Sullivan or Sullivan@cup.portal.com