HD down converted to SD VS native SD

[DVdoctor]

Here is one for Alan and company

There is an ongoing debate regarding the new HD and BD players

So if you were to compare a standard dvd vs a HD or BD dvd downconverted to SD on a SD monitor would the HD originated content still have a higher perceived quality?

The issue being discussed is whether users who for instance buy a PS3 but do not have a HD display will really see a benefit from the BD content from a perceived quality standpoint?

Sharyn

[Alan Roberts]

Recording and transporting HD material and then down-sampling for the display is by far the best approach. It's a no-brain obvious one as far as I'm concerned. The technical reasons get a bit complex; they are mostly to do with the modulation transfer function of the originating material, that of the recorder, and that of the display. In simpler terms, you can regard the HD-originated/HD delivered signal as being a massively oversampled source for the display, and this satisfies John Watkinson's appeal for oversampling in transmission media.

Put simply, HD-originated material should stay HD as long as possible. Down-sample it only when you have to. The compression artefacts will relate to the resolution of the recorder and so may well be completely lost in the final down-sampling, but the display bandwidth will be gloriously filled. No contest.

[DVdoctor]

I raise the issue for a few reasons:

One is that when the Samsung BD player was released in the US, people who decided to have the player set for 720p since their display was 720p experienced that the down conversion in the player created a poor image.


The point that the BD camp is trying to make is that if you have a Bd player or for that matter a HD player and you connect it to a standard tv, that the image on your standard tv will be better than if you took a standard dvd, and played that to the same monitor. Since standard tv's typically don;t do down conversion, it raised the issue as to how good would it look in comparison.

In a sense it is realated to a broadcast question, if the broadcast is HD, but your tv is SD will your image look better, raising the point that if it does, then simply upgrading all broadcast to HD and then offering a receiver/down converter would offer the viewer a better viewing experience.

Sharyn

[Alan Roberts]

I point you back to what I said before, yes, it looks better.

This is precisely the process we're using in the UK for much drama broadcast. It's shot and edited in HD, delivered in HD, and down-converted for broadcast in SD (and simulcast in HD if it's on a BBC channel). Pictures clearly are better than if they'd been shot in SD or super16. This is old history, it's the process we've been using for years now. The business of delivery the HD further down the line can only help, provided the HD player has a decent scaler/cown-converter/down-sampler.

[DVdoctor]

Not trying to be thick but the situation is slightly different in the question, which maybe I am missing or not being clear


All the material in both cases is shot the same way, we are talking about hollywood major releases, and edited the same way, the questions is maybe better stated

IF you compress HD professionally at the hollywood studio level in mpeg2 for DVD release at SD compression levels and display it on a SD monitor, will it compare to HD professionally compressed to HD mpeg2 and then down converted for SD display on the same monitor.

Do you get better final perceived quality when you do a multipass professional compression to SD as the final resolution, or when you do a multipass professional compression to HD resolution and then on the fly down convert it to SD?

So the point is not the benefits of hd origination and editing, but I guess whether the mpeg2 compression system will do a better job if it takes the original material and compresses it based on the output level finally viewed at, or if the mpeg2 compression system does a better job if it compresses it to a HD level and then the data stream is on the fly down converted.


The point the BD camp is trying to say is that the supposed milllions of PS3 owners who have a BD drive in their system will buy BD versions of the hollywood release, even if they do not have a HD display because the BD content, played on their system will look better displayed on the owners SD monitor, vs that same user buying the DVD version of the hollywood release and viewing that version on the same monitor.

I seemed to remember that when you were looking at HD camcorders you were not impressed with the HD to SD in camera conversion on the fly.

Sharyn

[StevenBagley]

Remember the PS3 has a very very powerful processing chip in it, one which is incredibly well suited to tasks such as rescaling HD video to SD if programmed well (in fact, it is probably better suited to that than playing games). If programmed properly, then I suspect the PS3 could do downconversions that rival professional gear (at least with progressive material).

Now let's look at what is on a DVD disk -- at best, you'll have a 720x576(480) luma image and a 360x288(240) chroma image. That is as good as you can get out of it, and of course you'll get MPEG artefacts in the high frequencies (both vertically and horizontally) which will reduce the resolution some what.

Now lets consider what is on the Bluray disk, a 1920x1080 luma image coupled with a 960x540 chroma image. Now I hope you can see that we have already got more chroma pixels than we need for a 480i/p SD display and virtually enough for a 576i/p display, so you can effectively get a 4:4:4 image out rather than 4:2:0 -- there's your first benefit.

Now consider MPEG artefacts, these are still going to attack the high frequencies but these high frequencies are now well outside the SD frequency space so should be filtered out during downconversion -- which should leave an SD image that is virtually free from artefacts.

Then you'll have the advantage that the DACs on the PS3 for component output will be designed to work up to HD resolutions, and so should be pretty accurate in the SD frequency band.

Of course, whether the average TV will let you see the advantages.

Steven

[DVdoctor]

Thanks Steve
good analysis, the one minor point is that the user is at least here in the US on a DS tv likely to have s video or composite connection.

It does present from a technical stand point why someone without a HD display at this point in time (say based on the facts presented in Simonw's post) due to waiting for the displays to settle down at the level that is really needed, might still see a benefit in using BD or HD content on as SD TV

The obvious argument that is going around and around is that Sony is claiming that the installed base of PS3's is a major factor in winning the format war, and some of us in the HD camp are arguing that it really is PS3's With HD displays that represents the tru BD Video base to the Studios advantage. The gamers are agruing that they DON"t typically put the game console in the home theater, and that they keep the two independant, and that they are likely to have a smaller display for the games, since they are more likely to play on an indivudual basis or very small group, and that if they have a HD display, they are more likely to only have that attached to the Video source.


So I guess eventually it will come down to tests to see just how much this technically feasible better PQ is able to be detected on the Typical SD TV

Sharyn

[Alan Roberts]

The benefits of shooting, editing and delivering TV in HD have been very obvious in the UK for a long time. The professional kit does a better job of compressing than does consumer kit, that much is clearly obvious. But more importantly, the HD-originated material more fully fills the bandwidth of the down-converted final delivery with wanted resolution that could an SD-originated source. So it looks better. QED.

Films are a slightly different story becuase they're always progressive, and the compressor has an easier job to do than for interlaced tv. But a surprisingly large proportion of broadcast tv is already shot and delivered in progressive anyway, so the only advantage that Hollywood has over TV is that they can make their compression in non-real time, 2 pass or even hand-crafted, to get the best quality:bit-rate ratio. That option isn't available for broadcasters and never will be, that's why broadcast compressors are highly complex and expensive bits of kit.