Line Doublers & 480P(30) Content

[rlabarge]

I have been trying to push the DVD-Video format to its limit as far as video quality is concerned. Many people know that DVD-Video supports progressive scan video from film - called 480P(24). However DVD also supports progressive scan video at a higher frame rate - called 480P(30).

I have completed work on several DVD titles that use 480P(30) video and have found the spatial and temporal resolution of the video to be excellent, particularly when displayed on wide screen progressive scan monitors.

During my testing I uncovered a problem that needs more investigation. It appears that some line doublers can not correctly handle 480P(30) video. These line doublers recognize that the video is progressive scan and then perform a 3:2 pull down to reduce the video to 24 frames per second.

If the video was 480P(24) this would be fine, but since it is 480P(30) the net effect is to make the video look pretty bad. In fact the video looks better with the line doubler bypassed, so in effect the line doubler is reducing the video quality level, rather than enhancing it.

I am looking for some HT Guide volunteers who have line doublers. I would like to send you one of my 480P(30) titles and have you test it on your home theatre system with, and without, your line doubler in the signal path. Then I can collect some real data on which line doublers have this problem, and contact the manufacturers to see if they can correct the problem with a firmware update.

I may be the only DVD Producer crazy enough to try to release DVD titles with 480P(30) video, but I suspect in the next few years we will see a lot more of this. There are a number of new DV cameras coming on the market that can shoot in the 480P(30) format. So this is a problem that needs to be addressed.

If you are interested in helping out please let me know.

Thanks




Ralph LaBarge
Managing Partner, Alpha DVD
Author, "DVD Authoring & Production"
rlabarge@alphadvd.com

[Lex]

Wow Ralph, pushing the envelope! I like it! Hope you find some worthy guinuea pigs.

I would guess we do have a few here that might be able to test this.

Lex

[Kevin P]

Can you better explain 480p(30) vs. 480p(24) to those of us who are under-educated in such matters?

I always thought the MPEG decoders on DVD players outputted an interlaced signal (regardless of the DVD's encoding), and then the doubler (deinterlacer) converts it to progressive, either performing 3:2 pulldown reversal (for 24 fps encoded material) or 30 fps deinterlacing (for 30 fps video material). Flags in the bitstream, or educated guessing by the deinterlacer, is used to decide whether to perform 3:2 pulldown reversal or not.

So, does 480p(24) imply material encoded with 3:2 pulldown, and (30) imply 30 fps video (no 3:2)? Or is the encoding such that the MPEG decoder outputs a 480p signal? How would an interlaced DVD player handle this (it would have to be interlaced after the fact).

Are these doublers that have troubles with your 480p(30) disc the doublers in HDTV sets, or the deinterlacers in progressive scan DVD players? If it's progressive DVD players incorrectly performing 3:2 pulldown reversal, perhaps the bitstream flags are set incorrectly on the DVD. Does disabling "film" mode (3:2 pulldown) on the PS DVD player or line doubler fix the problem?

BTW, I have a Sony DVP-S9000ES progressive DVD player connected to a Mitsubishi 46805 HDTV. The 9000ES does 3:2 in progressive mode, but the 46805's doubler does not. The 46805's doubler is only in effect when fed an interlaced signal. Would my configuration be suitable for a guinea pig test?

KJP




Official Computer Geek and Techno-Wiz Guru of HTGuide - Visit Tower of Power
My HT Site

[rlabarge]

480P(24) starts out as film at 24 frames per second, is then encoded at a resolution of 720x480 pixels per frame, and the MPEG-2 flags are set to indicate progressive scan content.

480i(30) starts out as video at 60 fields per second (interlaced), is then encoded at a resolution of 720x480 pixels per frame, and the MPEG-2 flags are set to indicate interlaced content.

480P(30) starts out as video at 30 frames per second (non-interlaced), is then encoded at a resolution of 720x480 pixels per frame, and the MPEG-2 flags are set to indicate progressive content.

All NTSC DVD-Video players can create an interlaced signal from either 480P(24), 480i(30) or 480P(30) MPEG-2 streams. Some DVD-Video players also support a component Y-Pr-Pb progressive scan output which is created from the same MPEG-2 stream. There are even some DVD-Video players that support a progressive scan SDI output.

Line doublers that I am seeing the problem on are not limited to HDTV systems, but in some cases are just standard off-the-shelf equipment used to improve the picture on large screen televisions.

There is a subtle yet important difference between the 480i(30) and 480P(30) formats. 480i(30) is what the vast majority of video programs are created in. This is essentially a standard NTSC signal with 60 fields per second.

480P(30) is created either using computer animation or progressive scan cameras that dont record in NTSC, but rather in a progressive scan format with 30 full frames per second of content.

In theory the best looking video that a DVD-Video player can put out is 480P(30). This video will have the highest spatial resolution - 480 pixels per line, and the highest temporal resolution - 30 progressive frames per second. Film based content, which is 480P(24) has the same spatial resolution, but with only 24 frames per second it has about 20% less temporal resolution.

I hope I am making sense.

If you are willing I would like to test out your system with some 480P(30) content. I know the discs are encoded correctly and all the flags are set right. I have narrowed the problem down to line doublers that are trying to force a 3:2 pull down onto a signal that does not need it.

If you can send my your mailing address (offline to my email address) I will send you one of the 480P(30) production discs already on the market. Please send email to rlabarge@alphadvd.com

Thanks




Ralph LaBarge
Managing Partner, Alpha DVD
Author, "DVD Authoring & Production"
rlabarge@alphadvd.com

[Kevin P]

Is this an issue you're seeing with the doublers built into progressive scan DVD players, or do you see it with interlaced players when fed through an external doubler (e.g. DVDO iScan) or the doubler built into a SDTV/HDTV?

An external doubler, fed an interlaced signal from a DVD player, shouldn't see any difference between 480p(30) and 480i(30), unless the MPEG decoder does funky stuff to the video. All the doubler is doing is converting the interlaced to progressive, and (hopefully) performing 3:2 pulldown reversal when it's needed and skipping it when it's not.

KJP




Official Computer Geek and Techno-Wiz Guru of HTGuide - Visit Tower of Power
My HT Site

[rlabarge]

That is one of the questions I would like to have answered by testing on a variety of home theatre systems. All the line doublers I have tested so far are connected via component (Y, Pr, Pb) video to the DVD player, which I think will be in progressive format, rather than interlaced.

I have primarily seen the problem when using an external line doubler that is connected to the DVD player as well as the TV.




Ralph LaBarge
Managing Partner, Alpha DVD
Author, "DVD Authoring & Production"
rlabarge@alphadvd.com

[Pat]

Ralph, I'd try but I don't think I have the proper connections
Everything goes through my iScan.
I don't have a 30' s-video cable.
The video inputs haven't even been setup, no convergence, size, color, etc.
I can't bypass the iScan.




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