A Primer on DVD in a High-Def world; or How Much is that Scaler in the Window?

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PLEASE NOTE: The following is reposted by request to get it at the top of a thread. It was originally written as a reply to Texas_Longhorns who asked for a crash course on "HD DVD" and was really trying to get his head around the very confusing marketing hype currently out there regarding up-scaling DVD players, "high definition" DVD discs, digital connections, "new" HD DVD technologies and the like, and just what the heck people really meant when they bandied about the "high definition" catch phrase. He was planning on buying a DLP with 720 native resolution and was wondering just what would or would not work with that TV, and whether he had to discard his existing DVD library.
--Bob
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TL,
Your DLP (when you get it) has a fixed number of pixels that can be lit up to varying degrees of brightness to produce the color image on the screen. This is the "native" 720 resolution of your DLP. [Actually for technical reasons, the "native" resolution is more likely to be 768, but you can ignore that difference for now.]

[EDITED TO CORRECT (2/25/05): Oops! See post #146 below -- thanks to C1courtney. Although many fixed pixel technologies use actual "native" pixel counts that are influenced by what goes on in the computer world -- such as 768 or 788 line count matrices -- DLP displays do not. They use a true 720 line count matrix.]

No matter what you decide to watch, no matter what the resolution, the DLP needs to decide which pixels to light up. The circuit that does this is called a "scaler". The scaler works both ways. It can take a 480 signal or a 1080 signal and produce from it the 720 signal that it requires when lighting up the pixels. It does this using math -- more or less cleverly depending upon the quality of the electronics -- and tries to do it so well that the eye is fooled into thinking no conversion has happened. The scaler often operates even if the display is fed a 720 signal because of that 720 vs. 768 difference I mentioned [EDIT: for some display technologies].

The scaler's job is complicated by two additional factors. First, your DLP is a wide screen TV and some of the content you will be watching is recorded in the shape of a conventional TV. The various stretch and zoom modes of your DLP come into play here.

Second, a conventional TV signal is only sent half a picture at a time. One half contains all the odd numbered lines of the image and the other half all the even numbered lines. This "interlacing" of the picture is due to historical limitations on the cost of the electronics and the available bandwidth for conventional TV broadcasts. Older TVs would paint the image on the screen one half on top of the other in two passes, doing it fast enough that for the most part the eye gets fooled into thinking the whole image is there at once. But conventional TV is not all that great and the eye frequently sees the gaps between the image lines and other artifacts resulting from this 480-interlaced or 480i signal unless the set is adjusted to blur the image to conceal them.

Some years back, manufacturers decided they could sell TVs for more money if they put in circuits to try to make an interlaced signal look better, i.e., if they could do a better job of hiding the damage to the image done by interlacing than just blurring the image. The first of these were "line-doublers" that did just that -- they filled in the gaps between the lines using the data sent in each half image. That was quickly followed by "de-interlacing" circuits that stored the first half image until the second half image arrived and then constructed a FULL image from those two halves and painted the whole thing at once on the screen. The result was a "progressive scan" image which was painted progressively and smoothly from top to bottom without having to go back and do a second interlaced pass, and the resulting signal was called a 480-progressive or 480p signal. Such TVs used digital processing circuits which were just becoming cheap enough for home TV and produced a noticeably crisper image because there was no need to blur the scan lines.

"De-interlace" processing turned out to be surprisingly hard to do well. The two image halves were recorded by the video camera slightly separated in time, and thus they weren't really parts of the same picture but rather a double exposure of a slightly motion-blurred picture. And again for cost and bandwidth reasons (as well as compatibility with old black and white TV), another corner was cut in that the white to black gray scale which makes up the fine resolution detail of the picture was recorded at a higher resolution than the color data, which made it hard to figure out which color to use when reconstructing each part of the image from the two halves that were recorded slightly separated in time.

And the problem is that the math in a scaler depends upon the quality of the de-interlacing. They are both supposed to assume, and be optimized for, "natural moving images" and if the de-interlacing is faulty then the resulting artifacts in the image will mess up the result from the scaler as well.

A typical conventional TV today will also have a "native" resolution even though it doesn't have a fixed set of pixels such as your DLP. For technical reasons that will often be a 540-progressive or 540p signal. Your DLP likely has a native resolution of 768p which the marketing people will describe as being optimized for 720p because that is one of the "standard" resolutions for high definition television. [EDIT: As noted above, this last statement is not correct for DLPs although it is quite often the case for other fixed pixel display technologies.]

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Now here comes the content!

Standard definition television, whether it comes from your roof antenna, your cable service box or a satellite, is a 480i signal. This is true even if you have "digital" cable, or subscribe to satellite TV services which are inherently "digital". In fact such digital services often "compress" the signal to fit more channels into the available bandwidth which damages the signal. But since normal off air broadcasts and analog cable are subject to all sorts of other damage -- noisy signals, interference, ghosting, etc. -- the compressed digital signal still looks better which is why people pay for it. But the ORIGINAL signal is still 480i. It contains images which are the shape of a conventional TV -- a "4:3 aspect ratio".

DVDs today are ALSO recorded at 480i. ALL DVDs. Even the extra-expensive ones sold under various marketing names such as "Superbit". DVDs that say they are recorded in high definition mean that better quality equipment was used in digitizing the original film content. But the actual data that gets put on the DVD is 480i nonetheless. In fact it is "compressed" 480i like the digital cable or satellite signals. Too much compression (because the marketing guys want to save space for putting "extras" on the DVD) damages the image. The "Superbit" DVDs and their ilk use less compression -- putting a movie on 2 DVDs instead of 1 for instance -- and thus yield a less damaged image. Additional care is taken in the digitizing process as well. But the data on the DVD is still only 480i. DVDs are also designed for 4:3 shaped images. Various tricks are used to put wide screen (16:9) or "wider than wide screen" cinematic movie content on the DVDs. The most important of these is "anamorphic" enhancement which deliberately distorts the wide image so that it fits in the squarer shape without wasting pixels on the top and bottom as unused black bars. DVD players automatically sense and remove this built-in distortion and produce the original wide screen image with better fidelity because there was no such wasted resolution.

So here comes the 480i signal from your source -- complete with color data coming in at only half that resolution or less. Your DLP now wants to scale it up to 720 [EDIT: or 768p for other common fixed pixel display technologies]. First the signal goes through the de-interlacer and comes out as 480p. Then the scaler extrapolates the extra resolution it needs -- inventing the intermediate pixels by kind of averaging the real pixels around them. And then the pixels light up. If you paused that image it would not look all that great -- certainly not as good as a photograph. But here comes the next 480i frame and the next and your eye does the final bit of processing by smoothing it all together so that you see an attractive moving image. The brain is remarkably good at making a silk purse from a sow's ear here, which is a good thing since otherwise TVs would never have been cheap enough to take off in the marketplace.

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The next bit of fun and games comes when DVD player manufacturers figured out they could sell players for more money if they put a de-interlacing circuit in the players. They could then send a 480p signal to the TV. They could do this because their cronies (another division of the same company) producing the TVs set them up to take a 480p signal as input, thus by-passing the internal de-interlacing circuit. The logic behind all this was that the DVDs that were being recorded also include special information as to how to do a better job of de-interlacing which the player could see as part of it's processing to produce an analog TV image from the digital data recorded on the DVD. Thus, and this is the important bit, THE DVD PLAYER COULD DO A BETTER JOB OF DE-INTERLACING!

So now you had "progressive" DVD players that would take 480i DVDs -- the only kind that exist -- and produce 480p analog TV signals. The TVs still had their own de-interlacers to handle regular TV signals (which they needed to de-interlace to make their "line doublers" work).

So people would now pay for TWO de-interlacing circuits, plus the extra profit built into bleeding edge technology. And bleeding-edge it was. The idea was fine but the execution was often dreadful. The net result was that the de-interlacing in the DVD players was often WORSE than what the TVs could do on their own. For a variety of technical reasons, de-interlacing the wide range of DVD content out there is a tough job, and on top of that the engineering was often shoddy. So folks would spend the money for a progressive scan DVD player and then turn off the progressive option and use it like a 480i DVD player because that produced a better picture. The picture was "better" because some data was effectively being filtered out -- discarded -- and thus the TV's de-interlacer produced less noticeable glitches. In fact, many DVD players were having trouble just decoding the digital data on the DVD properly. If you'd like to see the sorts of problems that can occur, check out the remarkably detailed information in the DVD benchmarks section of the Secrets of Home Theater web site.

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Nevertheless the progressive scan DVD players had one big advantage -- they sold like hotcakes. Most buyers assumed they MUST be better and thus any problems they were seeing must be due to faulty DVD content and not the players.

They sold so well that everybody else wanted to get in on the act. So now you had cable and satellite boxes and even tape players putting out 480p progressive signals, which was kind of silly unless the de-interlacer in your TV was particularly brain-dead -- in which case your TV probably had a whole bunch of other problems as well. The "better" picture that most people saw with such boxes was almost always just a result of them switching from "channel 3/4" or "composite" video cabling to "S-video" or "component" cabling, both of which include a higher bandwidth signal -- most notably an improved color signal.

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Then came "high definition" TV.

From the standpoint of broadcast TV this was a big thing -- the real deal. This was content RECORDED in higher resolution, digital from inception, and in a wide screen aspect ratio. The industry settled on 720p and 1080i as the new broadcast standard resolutions -- not quite up to the eye-candy of the 1080p they were using for studio masters, but still looking much much better than conventional TV and at a cost the market could be made to bear.

TVs were manufactured that could handle these new signals -- originally expecting the signals to be converted to analog signals over component cables and then including true digital inputs (HDMI or DVI) and internal HDTV tuners. Of course since there was limited HDTV content out there, such sets were often used primarily to watch old, boring standard TV. So to help sell the sets, the marketing people thought up the bright idea of saying the sets would convert standard TV to high definition. This was basically a new way of marketing the old line-doubling scalers (nothing really new here) plus some real advantage arising since the display element and electronics were engineered for higher bandwidth signals in case they were ever fed a real HDTV signal -- that is the TVs were built more to studio monitor standards.

As the "HDTV" buzzword grew, DVD content producers wanted to cash in. Of course their DVDs were still only 480i, but never let the facts get in the way of a good marketing campaign. They discovered that 1080p professional digitizing equipment was being used to digitize the film content -- which was then down-scaled to 480i to be put on the DVD. And that was all they needed to know to call their new crop of DVDs "high definition" DVDs. This while they were compressing the heck out of them (damaging the image) to save space to put CD-ROM games on the same DVD. [I'm being a bit cynical here. Major studios have come a long way towards improving the transfer quality on their DVDs and are only occasionally tempted to let the movie be damaged because they know folks are more likely to buy "special" versions that include extras.]

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Still with me? OK, we've got two chapters to go.

The next big deal is the "up-scaling" or "up-converting" (a misused marketing term) DVD players. The idea is to get people to buy new DVD players for their new HDTV-ready TVs by doing the same trick they did with the progressive players. I.e., let's put the scaler in the player!

Now remember the TV still needs its own scaler for standard def TV. And fixed pixel displays need a scaler for HDTV as well because HDTV comes in different broadcast resolutions which need to be converted to the "native" resolution of the display.

But heck, if you are going to buy an HDTV-ready TV and "high definition" DVD discs, then you certainly don't want to screw up the vibe by playing them on an old "progressive" player. You want a high-tech, high definition, "up-scaling" player! Just in case you've lost track here, the content on the DVDs is *STILL* only 480i in all this.

The drooling from the hardware guys was so great that it took them a while to hear the screams from the content guys. The folks who make their money selling DVD discs don't want high-res content coming out of the players because folks will just make copies of movies and not buy their discs! The HDTV broadcast networks face the same dilemma but they are already resigned to a business model that makes money by selling commercial time and subscriptions. The DVD guys need to schlep discs.

So the boys in building "A" got together with the boys in building "B" and came up with a solution. We'll allow up-scaling DVD players but only if the high res output is limited to digital connections that we can control with a copy protection scheme. The bosses in building "C" got big grins.

Well it turns out there was a digital cabling standard already in place called DVI. It was used to connect computers to monitors and since HDTV-ready TVs now were built to the high bandwidth and sync-rates needed by computers, many already had DVI inputs so that folks could use them as computer monitors as well.

All that was needed was to clamp a copy protection boot on that DVI input. This rejoices in the name of "HDCP".

An HDCP-compliant source device will refuse to make a digital connection to a display or intervening device which is not also HDCP-compliant. Analog connections will work regardless -- but only at conventional, lower resolutions.

So voila you now had TVs with digital inputs and DVD players with fancy new, up-scaling, high-definition digital outputs. Of course there were some older TVs out there with DVI that was NOT HDCP compliant, but the industry had an answer to that. Buy a new TV. Or use your fancy new up-scaling DVD player just as if it were a previous generation progressive player by connecting it via analog cables at 480p resolution. Since it said "up-scaling" on the box the image must be better, right?

DVI had other problems as well due to it's computer-based heritage. It didn't carry audio for example. So new HDMI cabling was invented to deal with that and to remove some other confusions inherent in DVI. HDMI is, more or less, DVI plus digital audio plus HDCP and with connection standards and protocols more or less attuned to the home theater market.

But all that techy, geeky stuff aside, the big news was that these players could put out glorious 720p or 1080i signals from a DVD disc via those HDMI or DVI connections! "Glorious" here being a marketing term of art. The important thing to remember, the thing I have to keep stressing because I see that buying frenzy gleam coming into your eye again, is that THE CONTENT ON THE DVDs IS ONLY 480i AND NO SCHEME CAN INVENT DATA THAT ISN'T THERE IN THE FIRST PLACE!

The 480i data decoded from the DVD first gets de-interlaced to 480p. Then it gets scaled up either to 720p or to 1080p. If the desired output signal is 720p then you are done. If the desired output signal is 1080i then the signal gets RE-interlaced to 1080i. The TV receives a digital 720p or 1080i signal from the player and SCALES IT AGAIN to match the native resolution of the display.

Urrh why are we doing this?

As the character says in "Shakespeare in Love", strangely enough it all works out.

In fact some, by no means all but some, of these new generation "up-scaling" DVD players produce a significantly better image than the previous generation of "progressive scan" players. Why this is so is due to several factors.

First the scaler in the player may be better than the scaler in the TV. The closer the player can get the data to the native resolution of the TV the less work the TV's scaler has to do.

Second, engineering continues to advance. Other factors than scaling are likely to be better in a good "up-scaling" player than in the previous generation players.

But the most important reasons why folks get good results from some of these new players is that the data stays entirely in the digital domain.

A player connected by analog cabling, such as S-video or component cabling, has to convert the digital data present on the DVD into analog TV signals. It usually does this as the very last thing it does -- in the video output stage -- because it is so useful to keep the signal in digital form for any other processing it needs to do first. The TV set receiving that analog signal ALSO wants to do processing of various forms -- which are done more cheaply, and for the most part better, with a digital signal. So the FIRST thing the TV does is convert the analog signal BACK to digital form.

Now these dual conversions introduce their own problems, but on top of that the conversions usually involve filtering of one form or another so that the signals work well across the widest range of source content -- some of which can be pretty crappy.

But an up-scaling player sends a digital signal to the TV which just leaves it in digital form. Thus no conversion noise and no filtering.

Given all that, it would seem natural that the best arrangement would be to use a digital connection for a *480* signal, and just leave it to the TV to do whatever scaling is needed -- once. Curiously, that is not often the best way to hook things up. HDTV-ready TV's are optimized for 1080i broadcast signals because that's how they are often judged in stores. That, plus any advantage that comes from having a better scaler in the player suggests that having the player upscale the DVD data and then feed that to the TV will give a better result even though a second scaling pass may be needed. There are additional advantages if you watch movies filmed in older 4:3 shape in that the player can put pillar boxes around the movie content without loss of movie resolution because the player is sending a higher resolution signal.

The bottom line is that despite the best efforts of the marketing guys to pull a fast one here, many of the better up-scaling players DO INDEED produce a significantly better image on many HDTV-ready TVs. Some of that is due to the digital connection, but some is also due to the combination of de-interlacing and scaling technologies working well to produce a signal the TV happens to be optimized to display. Combine that with other improvements naturally occurring with each product cycle and you get a better player.

But just as with the progressive players, there are some up-scaling players out there which are nothing but hype. Engineered by the school of shoddy, they are just not worth the money. And there are undoubtedly folks who will buy up-scaling players and find they end up preferring the signal they get hooking the thing up via S-video at 480 resolution, simply because their TV does a better job doing what they paid to have the DVD player do.

For the record, I use a Pioneer Elite 59avi DVD player connected HDMI to DVI and sending a 1080i signal to a Fujitsu P50 (30 series) plasma. And I just love it. It's an up-scaling combo that rocks. [For the techy geekies, yes I meant 1080i and not 720p. Go figur...]

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And that's the world of today.

But if you are willing to hang in there for another year, or perhaps two years, the world as we know it will change.

That's because there are two competing technologies lining up to fight the battle to become the new -- TA DAH! -- high resolution DVD format. HD-DVD and Blue Ray differ from current DVD technology in that the data on the disc is actually encoded in high resolution. Such discs won't be compatible with current DVD players. You'll need to buy a new DVD player that truly deserves the moniker "high definition" -- applause from the boys in building "C".

Such a player will output a 720p or 1080i signal -- possibly even a 1080p signal -- but that signal will reflect much more what's actually on the disc and much less the art of the scaler engineer.

Those new players will undoubtedly play conventional DVD discs as well, although they may cut corners on doing that job (despite the high price of the players) since they will really be all about optimizing things so that you'll go and buy new discs.

Which you won't be able to do until there ARE new discs. It's no surprise that the major powers in the battle over which of these two formats will win are the guys who own the movies. Until a sufficient number of new discs hit the stores any such new players will be expensive curiosities.

And of course if you buy a player for the format that loses the war, then you are screwed.

But again, this is for the future. Up-scaling players for conventional DVD discs are the hot item right now. They are at price points from a few hundred bucks to a few thousand. The $1k price point is a real sweet spot right now with big news, new release players coming out closer to $2K, but you can get a fine player for a few hundred if you do your homework. You can also get some real crap, so DO please do your homework.

Hope this helps, and hope you enjoy your DLP when you get it. Just remember that 6 months from now today's electronics will be obsolete, so buy what works for you and enjoy it without angsting too much about what's around the corner.
--Bob

Trunorth,
There's no reason the player, or more normally the TV, couldn't distort the image by doing stretch/zoom processing to make a "wider than wide screen" movie fit into the 16:9 "wide screen" shape, but currently the trend is that neither players nor TVs do that with the high resolution signals sent over the digital connections. This is partly to keep the cost down and partly because marketing research believes folks viewing these high-res signals want to see the movie undistorted -- even though that means there are black letter-box bars top and bottom.

The signal coming from the player will be at most a "wide screen", 16:9 signal. The content on the DVD, even if it has been anamorphically enhanced, is also at most a 16:9 shape. That means a "wider than wide screen" movie INCLUDES black letter-box bars -- IN THE CONTENT recorded on the DVD -- fleshing it out top and bottom to a 16:9 shape.

The simplest way to make such an image fill a 16:9 screen is to "zoom" in on it -- intentionally discarding some of the image left and right and stretching the image to fill the screen top to bottom. You could also "unstretch" or "compress" the image left and right to keep from losing those parts of it off the side but that would distort the image -- i.e., circles now look like ovals. This compression could be uniform across the image or could be concentrated to the sides so that the center of the image is less distorted.

It's all just math, and basically part and parcel of what a scaler already does. And that's just what's going on if you apply stretch or zoom distortion to these images at lower resolutions or when you apply it to a 4:3 image you are trying to expand to fill a 16:9 screen.

Since there is a market out there for folks who prefer to see distorted or partially cropped movies rather than undistorted movies with letter-box or pillar-box bars, I wouldn't be surprised to eventually see upscaling players or true high definition DVD players (when they are eventually launched in a year or so) offer this -- or more likely for new HDTV-ready TVs to offer it on their digital inputs at high resolution -- but that's generally not the case today and it will add some cost when it is added. The only limiting factor is the processing power of the available scaler electronics.

Today, if you want to watch "wider than wide screen" content from an up-scaling DVD player at high resolution, you should expect to see letter-box bars top and bottom and should expect to find no option, either on the player or the TV, to distort the image so as to eliminate them. Your workaround is to switch to lower resolution -- and quite possibly also switch to analog cables -- so you can get at the scaler options (usually on the TV side) to do this distortion.
--Bob

ckelly33,
The Iscan products are widely regarded as exceptional; among the best scalers you can lay your hands on for home theater. If you shell out the bucks for one, you want to let it do almost all of the work. That means you want to send it a 480i signal from the DVD player -- i.e., bypass any de-interlacing or scaling that the player might offer -- and have it send out the true, "native" resolution of your display so that the scaler in your display has nothing to do either.

However, the industry has conspired to make this rather difficult to do. First, many HDTV-ready TVs don't actually accept their "native" resolution as an input option. You have to feed them a standard resolution such as 720p and let their internal scaler take it from there. Those that do take one of the "unusual" resolutions such as 768p as input, may only do so over their analog, component inputs -- or may treat it like a "computer" signal which means you may have problems getting blacks to work completely right (the analog black level and the analog/digital "blacker than black" data crush problems). And thus you have to expect some hassle over dealing with blacks and/or some quality loss from dual analog/digital conversions -- although less than is typically the case when you connect a typical player to a more conventionally designed TV since the Iscan does it's end well, and the TV allowing such a signal probably does a better than average job at its end.

Meanwhile you'd like to send that 480i signal from the player over a digital connection to the Iscan. Well that's a nuisance as well. DVI doesn't support 480i. The lowest it goes is 480p which means you are depending upon the de-interlacing in the player. HDMI *DOES* support 480i but this feature is often not enabled on players because marketing fears the problems people will have if they do the common connection of an HDMI output to a display's DVI input. [The Pioneer 59avi is one of the better regarded players that DOES allow 480i output via HDMI.] And to get HDMI or DVI you have to pay the premium for an upscaling player ANYWAY, which is a feature you don't intend to use.

So some folks send their players to places that open them up and do a modification to add a different type of digital output called SDI -- which is a 480i-specific digital connection that is about as close as you can get to just passing along the digital data from the DVD directly. Of course such a modification voids the warranty on your new player.

In any event, you have to decide what player to get, given that the latest and greatest stuff such as new, higher end analog video output stages and support for exotic audio discs will generally be offered on the newest up-scaling players which now populate the top end of each manufacturer's lineup of players. Or you may decide to save cash and get an older, or less adventurous, progressive design -- which might have old bugs not yet fixed or might be deliberately crippled with lower quality electronics or missing features since these are now the LOWER end of any given manufacturer's lineup, and the manufacturer needs to differentiate them from his more expensive products.

You will be primarily interested in the quality of the mechanical systems, of the MPEG decoder (the circuit that interprets the compressed digital data on the DVD), and of the video signal output stage -- particularly if you are using analog component outputs. Some older progressive players do this very well, and some have serious flaws in these. But as should be obvious, plunking down the cash for a new design is not a guarantee you won't encounter problems here either. And of course any design can have serious engineering flaws such as inadequate sized or shielded power supplies. The school of shoddy has many disciples.

And then Iscan has units that take component analog signals and SDI signals, and will soon have a unit that takes HDMI -- which I'm pretty certain will mean 480i over HDMI if your player is actually willing to send that as output. So you need to decide which way you want to hook things up.

But in doing all this you are operating on the very edge of what you can do with the 480i data that's on the DVD to begin with, and many of the refinements you will get when you fend your way through all this confusion will only really be seen if you blow up the image really really big such as with a large screen front projection system. That is, on a 45 or 50 inch display, you can go through a lot of effort for not much reward over what the scaler in your good display and/or good, up-scaling player can do for you directly. Now to be clear hear, the image really will be measurably better -- and a skilled eye will be able to see the improvement in certain areas of certain scenes -- but you may very well not see it yourself. It is, after all, only 480i data to begin with.

Heck there are plenty of folks out there happily using BROKEN progressive players who blithely ignore the problems on screen because the image looks better than their normal broadcast TV and what they might have had from older players that were, unbeknownst to them, even MORE broken.

The best thing you can do is go try some combos yourself. Borrow or buy a DVD player from a place with a liberal return policy. Take a DVD player to the store when you go look at displays. And remember that no combo of player and display is going to look its best until you learn how to adjust (calibrate) the basic levels of your display using a calibration DVD such as Avia or DVE -- and in particular how to extinguish the "torch" modes on the TV.

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I don't have any personal recommendations to offer on the less expensive players because I'm not sufficiently familiar with them. But the information you will find on this forum -- and the test results pointing out possible issues which you may or may not be sensitive to which are to be found in the DVD Benchmarks section of the Secrets of Home Theater web site -- are really your best sources of info. Among the less expensive players, a few models from Zenith, Panasonic, Denon and Sony are currently highly regarded on this forum, and I've probably left out a few. Do some Searches here and you will find lots of discussion on just this topic.

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EDIT: I should add that there is a whole forum here dedicated to the fascinating world of video processors such as the Iscan products. Technical questions and recommendations regarding such beasties are best handled over in that forum.
--Bob

Chavel,
I'm not sufficiently familiar with HTPC to help you on this. It's possible others on this forum might know the answers but you also might want to try this question over on the video processor forum here.

Of course the SDI modified side is comparatively straightforward. Your player is decoding the DVD (one possible source of errors) and then sending that digital 480i signal via SDI to your external scaler. The scaler de-interlaces that signal to 480p and scales it as instructed -- preferably all the way to the exact, native pixel count of your display. Ideally you would want the scaler to send the resulting signal by a digital connection (HDMI or DVI) to your display. The quality of the signal will be primarily the result of how good the external scaler is unless your player has one of the various MPEG decoder bugs. Your display may be doing other processing to the signal before it lights up the pixels -- color or gray level biasing or automatic adjustment, noise reduction, gamma correction, etc. Ideally you want the display to do the minimum necessary stuff to get the proper calibrated levels with a smooth gray scale ramp. You certainly do NOT want anything that adjusts colors or over-all light levels "on the fly" according to what sort of image is currently being displayed. In particular, turn off any "flesh tone correction" or "noise reduction" or "automatic gain control" stuff. These are for making crappy signals look better and you don't want them screwing up a high quality signal such as is coming from your scaler. Also be careful your display is not doing excessive Sharpness processing. You want none of this stuff to be happening on the player side as well, but depending upon where the SDI mod taps into the signal path that may be before any of that could possibly happen anyway.
--Bob

soundman11,
HDTV-ready CRT-based displays are not "fixed pixel" displays, but they generally have "preferred" resolutions anyway due to optimizations that have been made in their internal processing circuitry. Typically a current CRT-based TV design will scale 480 signals to 540p and will display HDTV signals at 1080i. It is not unusual for such CRTs to have rather strict limitations on the signals they will accept -- often limited to one of 480i, 480p, or 1080i. In particular they may require that the HDTV input signal be 1080i and not 720p. Other such TVs will accept 720p and scale it to 1080i, or may even have "computer" inputs that take other resolutions but may have problems handling black levels properly if you try to use them for home theater. The component inputs on such a TV will accept all these non-computer resolutions. The digital inputs may be limited to just the HDTV resolutions, meaning perhaps only 1080i, or may also accept 480p or 720p as well. Your user's manual should tell you what resolutions are allowed on each type of input.

So for standard definition TV you are not likely going to be able to feed the set it's preferred 540p signal since it won't accept it. Use 480i or 480p depending upon the quality of the de-interlacing in the external source device.

For high definition TV, you will likely want to feed the set it's preferred 1080i signal over either analog (component) or digital (HDMI or DVI) inputs. Your HDTV set top box will undoubtedly offer a 1080i signal on it's component outputs, and if it HAS a digital output (not all do) then that will offer 1080i as well. Your set top box would then handle the scaling to 1080i of any 480i (standard def TV) content or 720p (alternate HDTV resolution) content to 1080i before sending it out that output. Some set top boxes offer the option to pass through whatever the current broadcast resolution happens to be on any given channel. But that's only useful to you if your TV will actually accept all three -- 480i, 720p, and 1080i -- on the input you've decided to use.

If you get an upscaling DVD player, it will offer the ability to upscale the 480i DVD content to 1080i, but it will likely only output that on it's digital output. Whether that produces a better image than sending the original 480i signal from the DVD, or the de-interlaced 480p signal produced by the "progressive" circuit which is also in any upscaling player, depends on the quality of what the TV does with such a signal compared to the quality of the 1080i scaling in the player -- as described in my earlier post. But generally the digital connection helps enough that sending a digital 1080i signal is well worth trying -- and the CRT TV won't have to do any additional scaling when fed that signal -- which is a good thing.

In particular, note that HDTV-ready TVs of all flavors are often optimized in various ways for a 1080i signal since that's the signal the manufacturer expects to be used to judge the set in stores. Depending upon how many corners the manufacture cut as regards other input signal types, this could bias the set towards wanting 1080i more than just about anything else -- sometimes even including the real, "native" pixel count of a fixed pixel display. Countering that is that some TVs limit the user controls available if the signal is 1080i because the internal processing circuits aren't fast enough to do it. Thus if you like to stretch and zoom DVD content a lot, you may find it better to hook up at lower resolution so the TV can do that for you before scaling up the image.

If you only have one digital input on your TV you should first think of dedicating that to the source you want to watch most critically. For many folks that will be HDTV. For others it will be DVD movies. Keep in mind that your HDTV box *WILL* send a 1080i signal over it's analog component outputs, so if you dedicate the digital input to the upscaling DVD player then the set top box can still send HDTV via component. On the other hand if you connect your HDTV box to the digital input, the DVD player's component output will send only 480p (except for a couple very unusual players) and thus you are paying for the upscaling feature in the player and not using it.

HDMI switches are expensive but only like cables are expensive -- it's still a relatively small cost compared to what you've already spent on other gear, which is how they get away with making the price so high (extra profit) to begin with. Before shelling out for a switch, you should calibrate both styles of connection for both sources and see for yourself whether connecting both of them via the digital input is worth it in terms of a picture improvement that you, personally, can see. Keep in mind that you have to separately calibrate each combination of source, display, and choice of cables, and you should even double check the calibration is still right if you just change resolutions.

If all of this sounds complicated, well it is. There are lots of possible choices and unexpected limitations may rear up on any of them. The good thing is that trying different combinations is not hard, it just takes time.
--Bob

Superfish,
I believe your Toshiba is a CRT-based, HDTV-ready, rear projection TV. Since it is CRT based it doesn't have a fixed set of pixels and thus scaling is only done for other reasons of convenience in the electronics.

In particular, if you feed this TV a 1080i signal, it likely does no scaling on it at all. If you feed this TV a standard definition TV signal (480i, or de-interlaced to 480p as from a progressive scan DVD player), then it likely scales it to 540p -- actually a version of a de-interlacing line doubler circuit.

Essentially the set has TWO "native" resolutions.

I did some testing recently with a different Toshiba model CRT RPTV and to my eye I preferred the 1080i digital signal from a Pioneer Elite 59avi DVD player, a Denon 5900 DVD player, and the HDDirecTivo combo set top box (HR10-250). For the two DVD players the alternative is to send a 480 signal via component analog cabling, but the HDDirecTivo will also send 1080i via component.

Keep in mind that if you send a 480 DVD player signal to your set, it won't scale it up to 720p or 1080i like a flat panel would do. It will use its other "native" resolution of 540p, which can look very good. But on the testing I did, I felt the reduction in filtering of the signal that I got with a digital connection at 1080i produced better real sharpness and naturalness of the image with less sharpness enhancement needed.

As for the players that put out 1080i via analog component cabling, there are only a few models that do that and none are considered in the top tier of current DVD players (although they are by no means in the bottom tier either). But the industry is against such players so I'd be cautious. In particular, Zenith has already changed the firmware in their player to disable this "feature". Now you CAN reload the old firmware to get the feature back, but that re-introduces some bugs the new firmware fixed. And in particular, if Zenith fixes other bugs in the future, the new firmware with those fixes will likely ALSO disable component 1080i. And so you either live with the bugs or lose component 1080i.
--Bob