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je280
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Post subject: Re: Why wasn't dual layer laserdisc not developed? Posted: 17 Jan 2016, 19:29 |
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Joined: 13 Sep 2012, 23:14 Posts: 1199 Location: United Kingdom Has thanked: 265 times Been thanked: 259 times
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substance wrote: maybe because they barely made single layer efficiently produced. Fair shout there. By the time the pressing plants got everything sorted (mostly) any real future development had all but stopped by Pioneer & no one else was going to take up the cudgel on it as it was clear that the format had a rather limited lifespan by then therefore no money in it so it would have made no commercial sense. Might have been an interesting development exercise though.
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substance
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Post subject: Re: Why wasn't dual layer laserdisc not developed? Posted: 18 Jan 2016, 00:49 |
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Joined: 16 May 2009, 18:05 Posts: 3592 Location: California, USA Has thanked: 28 times Been thanked: 328 times
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Digital laserdisc didn't happen because affordable, smaller than toaster size microprocessors became available only in 1990s. They could use a room size computer to encode the mpeg compression for the master but then you would need similarly sized and mega expensive computer in your LD player to decode it.
When small and cheap microprocessors became available, narrower lasers also became available, they saw no reason to keep the size at 12", a 6" disc could hold over two hours video with higher signal ratio, twice the color and a 100 lines bump in luma resolution.
Dual layer indeed needs narrower laser, in analog domain, it could cause crosstalk. Larger surfaces are more difficult to deal with in clean room environment. Smaller discs also gave this advantage.
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muzer
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Post subject: Re: Why wasn't dual layer laserdisc not developed? Posted: 18 Jan 2016, 02:33 |
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Joined: 02 Sep 2015, 00:03 Posts: 173 Location: United Kingdom Has thanked: 3 times Been thanked: 24 times
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blam1 wrote: Personally, I would have been much more accepting of a Digital LaserDisc and the huge storage capacity available over the DVD with it's limited bandwidth, resulting use of the horrible MPEG2 codec. To be fair, though, they get around that by using high bitrates on DVDs that make MPEG2 compression artefacts not really a problem. I'm not really sure LaserDisc could have done any better, given the limitations available at the time, as you say. I mean, now we can look back and say that MPEG2 is pretty primitive (though modern compressors are pretty good by now), but at the time it was state-of-the-art.
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blam1
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Post subject: Re: Why wasn't dual layer laserdisc not developed? Posted: 18 Jan 2016, 18:08 |
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muzer wrote: blam1 wrote: Personally, I would have been much more accepting of a Digital LaserDisc and the huge storage capacity available over the DVD with it's limited bandwidth, resulting use of the horrible MPEG2 codec. To be fair, though, they get around that by using high bitrates on DVDs that make MPEG2 compression artefacts not really a problem. I'm not really sure LaserDisc could have done any better, given the limitations available at the time, as you say. I mean, now we can look back and say that MPEG2 is pretty primitive (though modern compressors are pretty good by now), but at the time it was state-of-the-art. I'll give you this, but I will add that I went into DVD kicking and screaming. I have always seen the compression artifacts, even in Sony's "Superbit" releases. I would personally much prefer the "limitations" of LaserDisc than watching the wood grain on a kitchen cupboard crawl with compression artifacts, or watch a cloud of fog either disolve into a complete blur or look like it is "alive". I only purchased DVD because Image abandoned LaserDisc. On one hand, they promised to continue to release title on the format for 5 years, and 18 months later, they were done. Compression is certainly better than it used to be, but for god's sake, don't stand to close to the screen during a credits scrawl with white credits on a black screen. That kind of stuff will make your eyes hurt. I embrace Blu-ray completely, but until they find a way to perform lossless compression on the video like they've gone through great pains to do with audio, I will still miss LaserDisc to some degree. And as for the upcoming Ultra HD 4K stuff... encoding 60fps isn't necessarily the answer. Encode at 24 frames lossless and then we'll be going somewhere.
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jjrclassic88
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Post subject: Re: Why wasn't dual layer laserdisc not developed? Posted: 14 May 2022, 16:29 |
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Joined: 13 May 2022, 14:50 Posts: 2 Location: United States Has thanked: 0 time Been thanked: 3 times
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Apologies for replying in a thread that's been dormant for 4 years. The dual-layer concept on a Laserdisc is something I've questioned before as well, since the idea for dual-layered discs had already existed in the late 60s early 70s. 1.) David Paul Gregg (a.k.a. the father of optical discs) briefly mentioned this principle in his 'transparent optical disc' patent from 1967 (the same patent that MCA purchased to develop their DiscoVision discs with Phillips): https://patents.google.com/patent/US3430966A/enTowards the bottom of the page, he states the feasibility of controlling a dual-sided transparent disc via the focus of the light lenses: "In order to prevent the modulation of the light source by the recorded information on the side nearest the light source, the optical lenses of the light source are constructed so as to produce a cone of light rays converging on the bottom side of the recorded information nearest the reproducing transducer. In this manner, many bits of information are encompassed on the side nearest the light source, none are resolved, and the light intensity reaching the side to be reproduced is diminished only by an average amount equal to a large area of the lighted side, taken as a whole, together with the light attenuation provided by the diffusing layer." He basically says that the lenses could be set in a certain position so that the data on one side of the transparent disc is read (while the other side is ignored). However he does not talk about automatically *re-positioning* the lens to read the data on the other side (like that of DVDs). 2.) Four years later in 1971, Phillips finished where Gregg left off when they filed a patent for the 'Apparatus for playing a transparent optically encoded multilayer information carrying disc': https://patents.google.com/patent/US3999009A/en"An apparatus for reading the information carrier is disclosed which there is inserted in the path of the read beam radiation from a source of radiation to a radiation-sensitive detection system an optical system for selectively converging the read beam on each track, whereby the tracks may be read without turning over the information carrier." If you look at the second patent photo in the link (see below), there's a section view of a disc with each side containing two sandwiched layers of data (four layers total). Yes, the same basic design principles (later used in dual-layer DVDs), were being imagined by Phillips engineers in 1971... I don't know what happened behind the scenes during the developmental stages of the Laserdisc. I suspect that early on, MCA/Phillips did attempt to produce a true dual-layer disc prototype with a refocusing lens, but unfortunately were not successful. Of course, it wasn't until 1997 when the DVD finally turned that concept into a reality, despite technical problems early in their introduction...
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admin
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Post subject: Re: Why wasn't dual layer laserdisc not developed? Posted: 15 May 2022, 21:18 |
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lonerangerface wrote: From what I understand, CAV LD (30 min.) is equivalent to the single-layer DVD (4.7 GB), whereas CLV LD is equivalent to the dual-layer DVD (8.5 GB). I am not sure what you mean by "equivalent" but data storage version did exist and they were FAR from DVD specs. LV-ROM (CAV) could store up to 324MB of digital information. LD-ROM (CLV) could store up to 540MB. It was more similar to a CD-ROM. Julien
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jesuslovesgood
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Post subject: Re: Why wasn't dual layer laserdisc not developed? Posted: 17 May 2022, 08:39 |
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admin wrote: lonerangerface wrote: From what I understand, CAV LD (30 min.) is equivalent to the single-layer DVD (4.7 GB), whereas CLV LD is equivalent to the dual-layer DVD (8.5 GB). I am not sure what you mean by "equivalent" but data storage version did exist and they were FAR from DVD specs. LV-ROM (CAV) could store up to 324MB of digital information. LD-ROM (CLV) could store up to 540MB. It was more similar to a CD-ROM. Julien Pretty good Picture Quality for CLV and CAV for not a lot of MBs. I think these look like 4:3 dvds.
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