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 !!
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
pshen@atrp.mit.edu (Paul Shen) (07/14/89)
lars@salt.acc.com (Lars J Poulsen) writes: >(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. The simple minded, cheapest solution is three-two pull-down. Then all you need is off-shelf dual port DRAM. >(3) Interlace versus non-interlace scan. > Broadcast video is usually interlaced to reduce flicker, computer ^^^^^^^^^^^^^^ Interlace will introduce flicker. The purpose of interlace is to increase the temporal sampling rate. >(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. This can be dealt with by proper sampling rate on the AD and DA convertor. (This adjusts the spatial rate.) >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 ? With the proper design, such a stand alone system can be well below $1000. I did design one of such system, PAL-to-NTSC and NTSC-to-PAL convertor. It died in the middle stage of design, because of the limited market demand. Regards, +---------------------------------------------------------------------------+ | Email: pshen@atrp.mit.edu | Paul Shen | | Address: MIT, 36-665, Cambridge, Ma 02139 | Tel. (617) 864-3210 | +---------------------------------------------------------------------------+
sparks@corpane.UUCP (John Sparks) (07/14/89)
<2825167777@Lewis.Steinmetz> <918@anise.acc.com> Sender: Reply-To: sparks@corpane.UUCP (John Sparks) Followup-To: Distribution: Organization: Corpane Industries, Inc. Keywords: In article <918@anise.acc.com> lars@salt.acc.com (Lars J Poulsen) writes: >(3) Interlace versus non-interlace scan. > Broadcast video is usually interlaced to reduce flicker, computer Interlacing does not reduce flickering, it increases it. The interlacing is to allow higher resolution with out having to have expensive hardware. The 525 lines in NTSC are divided up into even and odd lines. The even lines are sent in one frame and the odd in the next. This increases flicker in high contrast situations and in places where some object is only one scan line thin on the screen. There are new TV's called IDTV's that de-interlace the signal and show the entire 525 lines, at 60Hz. They have less flicker than standard TV, but they suffer from motion artifacts. -- John Sparks | {rutgers|uunet}!ukma!corpane!sparks | D.I.S.K. 24hrs 1200bps ||||||||||||||| sparks@corpane.UUCP | 502/968-5401 thru -5406 As far as we know, our computer has never had an undetected error.
poynton@vector.Sun.COM (Charles A. Poynton) (08/11/89)
John Sparks <sparks@corpane.UUCP> writes: > Interlacing does not reduce flickering, it increases it. Television egineers have precise terminology for this otherwise confusing topic. Interlace improves wide-area FLICKER for a given frame rate, such as 29.97 Hz, over a non-interlaced sytstem of the same frame rate. However, this improvement comes at the expense of introducing inter-line TWITTER. Of course motion rendition is implicated in selection of a frame rate, and depends on interlace as well. Poor motion rendition can lead to JUDDER. > The even lines are sent in one frame and the odd in the next. No, the even lines are sent in one FIELD and the odd in the next. An odd field and an even field comprise a FRAME. > As far as we know, our computer has never had an undetected error. As far as we know, As far as we know, As far as we know, As far as we know, C. ----- Charles A. Poynton Sun Microsystems Inc. <poynton@sun.com> 2550 Garcia Avenue, MS 8-04 415-336-7846 Mountain View, CA 94043 -----