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Red vs. Blue Lasers Complicate DVD's Future
bnavarro writes: "The EE Times is reporting that the DVD Forum's Steering Committee voted this week to approve the use of low-bit-rate compression for high-definition DVD. The DVD Forum's decision, made at a meeting Tuesday (Feb. 26) in Tokyo, to stick with a red-laser-based scheme but switch to low-bit-rate compression, came only a week after nine of the world's biggest electronics companies agreed to promote a blue-laser-based format for next-generation video and computer optical disks."
the wavelengths of different color lasers are different. I believe blue and green are shorter than red and therefore would create much closer spaced pits and grooves on media. It would also therefore be able to read more data from the media.
The color.
Light's color is a function of its frequency, which is inversely proportional to its wavelength. Higher frequency lasers can read pits which are closer together on a disc substrate, allowing them to put more data in the same areal density as lower frequency lasers. Blue is better than red for this purpose.
Alas, it's also harder (read: more expensive) to make blue lasers and the industry has already spent a lot of money on reds, so a blue-laser technology would require the writeoff of existing gear AND the purchase of new. Not an easy sell these days.
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- More compression. Needs
CPU horsepower somewhere (drive? your desktop
CPU?), but CPU horsepower is dirt cheap today.
- Blue lasers. The shorter
your wavelength, the higher your recording
density. But red lasers are widespread and cheap,
while blue lasers in consumer devices are not
all that well understood and there is a very
limited supply at the moment.
If you're in the business of selling blue lasers, of course you want to promote method #2 above. But DVD companies are not in the business of selling blue lasers - they're in the business of selling content.Of course, the decision to not use blue lasers impacts those who use the disks for purposes other than what the DVD companies want. If you want to store data on the disk, the "new" DVD compression doesn't help you any. And if you want to play the new DVD's on your non-DVD-consortium-approved player, the new compression techniques will probably make your attempts more complicated (if not more illegal...)
Comparison chart
I don't see a benifit especially in storage space for the red laser format.
Anybody have a reason other than politics?
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With the wavelength of the laser, the color varies! For example red has a wavelength of 622-780 nm and blue has a wavelenngth of 455-490 nm! Red Has the longest wavelength, followeed by orange, yellow, green, blue and violet which has the shortest wavelength! ...
Refer to this document for further information
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DVD standard was never blue but people wanted it to be. Also from the beginning they supported double sided double layer. At 4.7GB per layer that is nearly 19 GB. Consumers don't like double sided media because they can't tell which side is which. Double layer is harder to verify, in fact some of the older systems could only verify the content on the first layer, to reject bad presses. Double layer is harder to pirate (via DVD-R) though, so studios are trying to go all double layer. Mpeg-4 conversions take a lot of time and CPU power, and at any decent quality they only save 1/2 to 1/4th the space over mpeg 2 compression. Blue laser will enable better quality HD when it becomes available, and will enable incredible capacity when it's finally combined with mpeg-4 compression.
Basically the mpeg-4 HD-DVD will look better on HD than normal DVDs do, but blue laser systems will look better still.
I think this HD-DVD standard in question would use bitrates equal to current MPEG2 streams but with MPEG4 content. If your DivX video seems lower quality than MPEG2 DVD it might be that your DivX video has 750kbps bitrate compared to about 5Mbps bitrate of MPEG2 video. If you compare 1600x1200@5Mbps/MPEG4 with 768x576@5Mbps/MPEG2 stream it should be clear that the former one is much better.
And what comes to "ghosts" in low light scenes it's only issue with current encoder software. Basically current encoders are using linear comparision between original and compressed instead of logarithmic and they treat 2 to 4 in intensity like 244 to 246 even though the former one has 100% increase and the latter one has 0.8% increase. Obviously you're going to notice ghosting due to this in darker scenes only.
Though, I have to admit that when you consider the CPU power needed to even decode 1600x1200 resolution MPEG4 stream it might be cheaper to jump to blue laser. Not to speak anything about real-time recording/encoding! If only they could create single RW standard this time.
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Quick corrections (I'm a laser specialist)...
Most of what you said was true a couple years ago, but it's been changing, mostly due to the entertainment industry (get to that in a second...)
Green DPSS lasers (frequency doubled solid-state, as opposed to dye or ion gas lasers) use a very powerful infra-red (either 800 nm or 1.3 um) laser diode, usually 250 mW or higher... fire that at a Yag crystal or rod. The Yag crystal absorbs the infra-red light and lases at 1048 nm. For those who don't know frequencies, 400 is a deep blue, 550 is green, and 650 is deep red. You can see a powerful enough 750 nm beam, but most of the light is invisible.
Anyways, the Yag crystal lases at 1048 and a KDP crystal in the optic resonator doubles the frequency, giving a wavelength of 524 nm. Though there are some loses in the KDP, this is more then made up for by the efficiency of the resonating cavity itself; one of the mirrors is totally reflective to 1048 nm, but totally transparent to 524 nm... any green light passes straight through it.
Most DPSS solutions these days are made for entertainment. Someone figured out that there was a way to take DPSS and make it Continuous Wave (CW), thereby making it suitable for laser light shows. This was more expensive than ion gas lasers at the time (though that's not true any more), but was still attractive because its a much simpler design, has no moving parts, does not require expensive and difficult to maintain cooling, and can be housed in a much smaller box.
As far as cost... if one looks carefully, one can usually find a 5 mW model for between $100-$200. Watts per dollar goes up sharply, I think hitting a peak at 60 mW somewhere around $400-500.
If anyone reading this wants to know more, or acquire one of these... e-mail me at merlin_jim on hotmail.
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