My Oppo 970HD front projector says that it can accept input signals up to 1080p/24. The 24 Hz rate is much lower than the 50 or 60 Hz of 720p, but it's still comparable to film, so I guess it should look good, right?

Here's what I'd like to know: is this the standard rate for 1080p, or are there higher rates used as well?

thanks,
Bruce

1080p can be any refresh rate. We're used to 60Hz because that's what our TV's operate at. Our TV's are that way because our electrical service operates at in North America. In Europe, electricity is distributed at 50Hz, which is why PAL video is based on 50Hz refresh rates. Film is shot and projected at 24 frames per second. HD-DVD and Blu-ray video is being encoded at 1080p/24, if I remember correctly, although players that support output at 1080p/24 have been hard to find (if they offer 1080p, they generally force a 3-2 pulldown to get the video to 1080p/60). You may be hard pressed to find a source that will provide 1080p/24.

What projector are you using?

Ha ha! I identified my DVD player for you didn't I? I forget which is which sometimes! My projector is the Panasonic PT-AE900U. I never paid attention to its 1080p capability because I didn't expect to have a 1080p source any time soon. But now that I've seen some 1080p Blu-Ray and HD-DVD players' output ... whoo ... that's pretty tempting!

I take it those players I've seen were probably putting out 1080p/60? Seems odd that they'd use 3:2 pull-down if the native encoding was already at a 24fps rate and there are devices that can handle that. Wouldn't the best image come from projecting at the same rate at which the content was encoded?

Yep - oddly enough, the HD-DVD and Blu-ray players (those that offer 1080p of any sort) have generally only been doing 1080p/60 even though the source material is 1080p/24. Since most of the displays we're using are built to operate at 60fps anyway it makes a certain sense, but it is odd that there isn't at least an option for it. I suspect that later generations will start to offer this.

1080P is aweome. I will be buying the Sony KDS55a2000 1080p LCOS HDTV hopefully soon. This is a full 1080P HDTV. I have the Denon 3930CI DVD with the aweome video chip that upconverts DVD to 1080P.

IMHO, 1080p looks good, but only if the screen size/viewing distance ratio is correct. We recently compared the 50" Pioneer Elite 1080p plasma to the 42" 720p Elite display, and found that we could not notice much difference at our viewing distance of about 7-8 feet. The retailer also felt that unless you have a larger sized display, 1080p's detail would be lost at normal viewing distances.

Display size has a lot to do with it. When I was deciding which Oppo model to purchase they recommended the 1080i model for screen sizes under 50".

I was reading an article on the subject of 1080p just this morning. It was posted on Secrets in the last day or so: 1080p: Why You Should Be Concerned . The basic premise is interesting. First, HD video is shot at 1080p/24 (either as film at 24fps with the individual frames subsequently scanned in or as digital video done at 1080p/24 to match film), which can be converted to 1080i/60 for broadcast very simply. They present the case that our 1080i HD broadcasts are technically 1080p/24 (with only an "easy" deinterlacing step required to get that 1080p/24 back), and since the only displays that can natively display interlaced video are CRT's (which the article declares dead technology, and even though I was watching an HD CRT just last night I have to say they're right) it makes sense to opt for 1080p where possible. Not such a concern for me, since my display won't accept higher than 1080i and actually operates "natively" at that resolution, but it's definitely an interesting read.

Gonk -- Thanks for the link; very interesting reading. What I found most interesting was that after spending so much time arguing the importance of 1080p, Secrets says in the end, "Of course, you don't need to have a 1080p display to have a great image. In fact, we're happy to concede that in most cases, with most material, there are many variables, starting from basic calibration, the environment (your room), yada yada, that are far more important than having a real 1080p display." I guess I come down to own a set whose picture and features you enjoy, since you will go broke trying to keep up with every change in technology.

BTW, besides our plasma, we also have an HD CRT (Sony XBR700) that we plan on using for many more years, so in our household CRT is not yet dead, either.

Hi Gonk:

First thanks for your intro to HT on your webpage. It's the best I have found on the net and reference often when I need to brushup on the terms. I do have a few questions?

>480i: 480 lines, interlaced. This is the resolution used by most standard definition television. It is also the native video resolution for DVD. >

Why was 480i picked as the number of lines? Was it the best they could do at the time? Why did they decide on Interlace and not pregessive, again was this just a technical problem?

>Converting between film's 24 frames per second and the 60 frames per second of progressive scan video introduces an odd issue:<
I am surprised that film has not adapted a higher frames per second rate? Why didn't film use a 30 Frames per sec like TV did at the time?

Does a CRT TV actually use all 480 lines of resolution? I thought I read somewhere that SD analog TV singnal would use less then 480 where as a standard DVD would use more of the 480 lines. The VHS format somewhere in between??

>720p: 720 lines, progressive scan. Now we are at HD resolution. 720p is the threshold for HDTV.<
How do lines translate to pixels. For example, can the height of one line on an LCD TV be composed of more then 1 Pixel?

Even though a LCD excepts a 1080I input, does it refresh it on the screen painting the Odd lines and then the Even lines or is it done all at once?

Thanks Bob

It's good to hear that my intro page is getting used!
The DVD format was developed in the mid-90's (actual development probably goes back a fair bit farther than that), and at the time there was no way to display more than 480i in the home environment. Therefore it made perfect sense to develop along those lines.

The infrastructure for film is getting close to a century old now, and the 24fps speed still works well - moving to 30fps would be a 25% increase in the amount of film used (with costs across the board - particularly film stock, developing, and distribution) and would require the retrofitting or replacement of an insanely high number of cameras. It's just not practical to do so.

A CRT television (standard definition) can use all 480 lines, although not all sources offer that many lines. I believe that standard VHS lands around 250 or so, for example, with S-VHS going up to the full 480.

You actually touched on one of the principal points of the new Secrets 1080p article: a fixed-pixel display device like DLP or LCD is inherently de-interlaced. Plasma's the same way, for that matter, as I understand it. It can't display interlaced source material without de-interlacing it first. All of the pixels (or mirrors, in DLP) get refreshed at once every 1/60th of a second. If an LCD display with 720 lines of resolution gets a 1080i input, it has to both scale and deinterlace the input before it can display it (usually by deinterlacing first and then scaling the 1080p signal).

>The infrastructure for film is getting close to a century old now, and the 24fps speed still works well<
Ok, how about a news room camera or a network camera covering a basketball game. Is that shooting in 24fps?

Thanks again

Bob

If it's a live broadcast, they aren't using film - they'd be recording either to analog videotape or (more and more often these days) to a digital medium of some sort, which either way will be 60 cycles per second.

This actually brings up one of the long-standing challenges encountered by progressive scan DVD players when deinterlacing - some material started life at 24fps and some (such as many, but not all, TV shows on DVD) started life at 60fps. The DVD format provides flags for identifying the video's origin, but the flags aren't always right (hence problems with "flag-reading" progressive scan players).

Gonk,

>This actually brings up one of the long-standing challenges encountered by progressive scan DVD players >

That was going to be my next question. Would this be a problem just for progressive scan, what about the first generation players? A 480I player would not have to deinterlace but it would still have to do the 3:2 pull down??

Bob

A player outputting 480i doesn't run into this problem because 3:2 pulldown is only an issue when deinterlacing film material, so there's no need to worry about 3:2 pulldown with 480i output. When you play back a 480i source at 480i to a display that operates at 480i (as would be the case with a DVD player used with a standard definition TV), none of this is an issue.

This discussion has reminded me of a project I started last summer - a general-purpose guide to home theater that would fill in the blanks inevitably left by user's manuals, similar in content to my Home Theater Basics page but organized differently. The idea came from conversations with UMtiger and his wife when they were trying out the Model 990, with a bit of inspiration from Outlaw's SMS-1 Guide tossed into the mix. I got a pretty decent draft of the document pulled together by last September, but then got buried in work - plus I didn't know quite what I'd do with it once it was done anyway (some folks suggested publication, but I was even thinking of offering it as a PDF download for a small PayPal fee). It's been sitting around untouched for six months now. Anybody interested in seeing what I was thinking of?

>A player outputting 480i doesn't run into this problem because 3:2 pulldown is only>

Why is this, you still have 24fms, don't you have to deal with that since the "clock" on the TV is still working at 60Hz? I must be missing something. Bob

Keep in mind that the migration from 24fps film to 60cps video has already happened when the DVD is produced. When the DVD master is created from that 24fps film source, part of the process involves developing 10 interlaced frames of video from every four frames of film. (There's an example of this near the middle of this Secrets article .) As far as the DVD player is concerned, every disc it gets is 480i at 60 cycles per second (or 30 complete frames, more or less). When the video output is kept at 480i, that initial "trick" of video mastering performed before the DVD was created will remain unaltered and the player has nothing to do. It's not the best solution, of course, but it's the only one that works reasonably with 480i/60 from a 24fps source.

When we give the player a chance to generate a 480p signal, we are offering the player a chance to correct some of the limitations imposed by going from 24fps to 480i/60 - which is both blessing (improved picture quality) and curse (opportunity to screw up that improvement). The player is going attempt to create 60 complete video frames, using alternately three and two copies of each original film frame (10 complete frames for each 4 originals).

>When we give the player a chance to generate a 480p signal, we are offering the player a chance to correct some of the limitations imposed by going from 24fps to 480i/60<
Just so I understand you, even with a progressive scan player, when it looks at the DVD the migration from 24-30fms has already taken place?

>using alternately three and two copies of each original film frame (10 complete frames for each 4 originals).<
When you say orginal frames here, you mean the migrated frames on the DVD which are at 30Fps?

Bob

No matter what video processing the DVD player offers, the source material on the disc is already 480i/60 (30 frames per second, interlaced). That is inherent in the DVD format - there's no way around it.

I mean original film frames (of which there were 24 per second before the film was transferred to video). In other words, the player is working backwards to piece those original frames back together while taking into account the "p24"-to-"i60" conversion process that took place during the DVD mastering process.

This is exactly why deinterlacing is hard, and why "cadence" based deinterlacers often have better luck. Deinterlacing has to be done differently for sources that were originally 24fps film or 30fps interlaced video. After all, if the DVD is taken from a TV show that was shot on video tape, there was never a 3:2 pulldown performed and the deinterlacing simply needs to combine every two interlaced frames - doing a 3:2 pulldown as part of the deinterlacing process would actually mess things up. A flag-based deinterlacer trusts the person who mastered the disc to flag the video data properly ("this is taken from film" or "this is taken from video"), and if the flags are set wrong the deinterlacer is out of luck. A cadence-based deinterlacer looks at the patterns of the individual interlaced frames and tries to recognize when a 24-to-30 conversion (3:2 pulldown) has taken place in the creation of that video transfer, then behaves accordingly.

Thanks and hope you don't mine all the questions. I think I have it now but I want to back up to one question:

>This actually brings up one of the long-standing challenges encountered by progressive scan DVD players when deinterlacing - some material started life at 24fps and some (such as many, but not all, TV shows on DVD) started life at 60fps.>

Do some TV shows do use 24fps cameras? I wonder how they decide if this is the case?

Bob

Some TV shows have been shot on film over the years rather than video, generally for creative reasons (preferred the look of film over video) or because they pre-dated video tape (the original Star Trek was shot on film, for example).

(preferred the look of film over video)

Can you see a differnce, I have alwasy noticed something differnet about TV shows during outside shots?

Bob

It is possible to shoot video in 1080/24p, and it is certainlly possible to shoot on film and transfer it that way.

PodBoy's right, of course, although in the past (even just a few years ago) it was not possible to achieve 1080p/24 with video.

Video is going to be cheaper and easier to work with as a general rule, but until recent improvements in video technology it came at the expense of resolution and picture quality. That didn't matter in the days of smaller TV screens and analog video delivery (over-the-air or cable), when the delivery method itself leveled the playing field to a great degree, but digital delivery, bigger screens, and especially HD have changed all that.

Thanks gonk for all the insight. Bob

Okay, my turn, now!

I don't understand why pixel-based displays can't display interlaced images. Say I have a 1080X1920 display - can't it display 540 even lines, with "blacked out" odd lines, and then 1/60 of a second later display 540 odd lines, with "blacked out" even lines? Isn't that essentially what a CRT does?

Bruce,

The CRT takes advantage of the fact that the phosphors on the inside of the tube take a while to fade out -- the unpainted line will continue to glow while the other lines are being painted.

Obviously, LCDs don't do that. You must supply voltage to them constantly.

B