720p vs. 1080i

GRN

I might be wrong on this, but hear me out; It's agreed upon that when you have a program in 480i, that's one sweep of 240 lines and then another sweep of 240 lines. When you have 480p, that's all 480 lines of resolution in one sweep. If you have 720p. that's all 720 lines of resolution in one sweep. So if you have 1080i, wouldn't that then be 540 lines in one sweep, and then the next 540 lines in another sweep?

I get the logic behind the idea of using 720p for sporting events (less flicker and artifacting) and using 1080i for television shows (better on stationary images), but wouldn't 720p be a superior format to 1080i (which in essence is 540p)?

ja2935

I would think not as 1080I has 1080 lines of unique information, even though it take two scans to put all 1080 lines on the screen. 720p, whilst it only takes one scan to paint the entire picture, only has 720 lines of information. As you say, 720P may well be better for fast action as the picture refresh rate is twice that of 1080I.

rbinck

It is difficult to compare the two on horizontal lines alone.

Let's look at some numbers. At 1920 x 540 pixels per scan that is a total of 1,036,800 pixels. The two scans ends up with 1920 x 1080 or 2,073,600 pixels. Now you compare that with 1280 x 720 which is 921,600 pixels. Even each 540 lines that make up the half frame has more pixels than the 720p format.

The only case for 720p is the motion blur case, which is valid when you compare 480i with 480p when both of them have the same number of horizontal pixels. It is much less valid when you compare 1080i against 720p, but we humans tend to discount this. Consider the motion blur of interlaced scan vs the pixel straddling blur of object edges occuring between pixels. This can and is as bad or worse as the motion blur and it happens in both directions. The more pixels the less this blur is.

GRN

Thanks for the great answers! That's always been something that I wanted clarification on.....

ja2935

I have a Toshiba 34hf84. The viewing options are 540p or 1080i. The motion argument suggests that for viewing fast action DVDs, which are after all only 480 lines, the 540p setting should produce less blurr than 1080i. So far I have only compared the two settings at freeze frame and didn't notice any difference - I will do the test with fast action......

Lanny

All current DVDs are 480i. No amount of downstream processing can completely eliminate motion distortion caused by the original material being in an interlaced format. Depending on your DVD player and its setup, the DVD content is either being deinterlaced in the DVD player or your TV. 720p programming, from ABC, ESPN, and Fox is currently the only progressive source material, other than computer media files, available.

IMHO: Although many people seem to be content on waiting for the availability of 1080p programming before upgrading to HD, they're in for a long wait, as in years. No one has any definite plans to offer 1080p broadcasting in the near future, and when they do take that step, they'll have to deal with all of the current HD TVs not being able to handle the signals. The current standards for broadcasting and cable don't have enough bandwidth to handle 1080p unless a new compression scheme is implemented. And, as you may have noticed, most broadcasters, satellite and cable providers are having a hard enough time just providing acceptable bandwidth for the current 720p and 1080i standards.

Don't get me wrong, 1080 60p will come some day, but in my opinion, it won't be in the next couple of years.

borromini

That's actually incorrect and commonly misunderstood. All studio-issued movie DVDs and similarly all professionally produced DVD titles are digital 480p source materials. On the other hand, people who have burned their home videos on DVDs probably have produced a disc with 480i source material. If you take any DVD movie title disc and place it in a PC-DVD drive and use software that analyzes the disc's data, you'll always note that the video source is listed as 480p. If you play that disc on a regular DVD player with any type of connection to an analog/CRT based display, a D/A conversion takes place and the resulting display is 480i. If you play the disc on a progressive-scan DVD player and use a progressive component-video connection to any HDTV or EDTV display, there's still a D/A conversion that takes place but the deinterlacing hardware on the player will output the video as 480p. Finally if you play the disc on a progressive-scan or upconverting DVD player using a DVI or HDMI connection to a digitial display like a DLP or LCD TV, then there is no D/A conversion taking place because the 480p digital video signal can be sent straight to the digital display. And in the case of the upconverting DVD players, that 480p digital video can be scaled up to 720p or 1080i.

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Lanny

Actually, that's incorrect, and commonly misunderstood.

The reason it shows up as 480p in your computer is because your computer is deinterlacing it.

AACrestron

Semi-right.

The only reason DVD's arent being sold in high definition formats are because the film companies have not agreed upon a common format.

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borromini

Hate to keep the tag line circulating but I've read that article when first posted and it's actually incorrect and perpetuates the misunderstanding. There are articles that say otherwise. Review this:

http://www.cnet.com/4520-7874_1-5107912-1.html

The current DVD standard specification used by studios calls for an encoding of the video source as 480p on the disc. The disc contains a digital version of the movie that's in a native progressive format (single-field scan). What is commonly misunderstood is that 480i is the resulting image when that native 480p video has to go thru the DAC chip that exists on all standard and progressive-scan DVD players and becomes an analog interlaced signal that can now be sent thru the player's various analog connections (component, s-video and composite) and then on to an analog TV. The purpose of progressive-scan DVD players is to allow folks who own an EDTV or HDTV display to see a 480p image, but this image is the result of a deinterlacing that takes place after the signal has already passed thru the DAC and is then sent thru a component-video connection that supports a deinterlaced analog signal similar to the way a PC's VGA connection is capable of. In other words, all DVD players that only have analog connections (component, s-video and composite) are designed with a DAC chip that is located in the pipeline roughly between the laser head and output connection. A progressive-scan DVD player simply adds a deinterlacing chip between the DAC chip and component-video output connection. It may seem silly that the digital progressive source goes thru the DAC where it becomes interlaced only to go back to a progressive format when passing thru the deinterlacing chip. But this is because the digital source has to be converted to analog in order for those output connections to work and has to be interlaced for s-video and composite to work so the deinterlacing can be viewed as a post-process and the DAC as a pre-process. DVD players that utilize digital output connections like HDMI/DVI (Blu-ray, HD-DVD and upconverting players) have their pipeline designed in a sort of "dual" channel configuration whereby the laser head scans the DVD's digital, progressive-format video data and sends that signal thru the DAC and simultaneously direct to the HDMI/DVI port. So with a digital display that has DVI/HDMI input, that DVD's digital-progressive data is received without any D/A conversion or deinterlacing processes.

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Thanks for including this link. It explains all on DVDs in the HI-DEF world. It explained a lot about the new up scaling DVD players and worth the read.

ja2935

To 'progress' the topic further, try this link

http://www.hometheaterhifi.com/volum...e-10-2000.html

It's all very interesting but go down to the section "How Progressive Players Work", 'How the Information is stored on Disc'

borromini

That article was written in 2000 and is a very good one. Many DVD titles produced from 1997 thru 2002 would have been interlaced source materials (480i). However, with the arrival of DVI/HDMI connections, more DVD authoring companies contracted with the studios now produce 480p discs so that you don't have to uneccesarily use a TV's deinterlacer when connecting via digital ports.

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ja2935

So there are both formats available - presumably the DVD player identifies which is on the disc and processes it accordingly - perhaps this explains some player/disc incompatibilities.

Lanny

Are you assuming that all TVs have deinterlacing circuits, including old analog ones? Are you assuming that cheap DVD players have deinterlacing circuits so that 480p material can be sent to older analog TVs through composite video connections?

The reason DVDs are in 480i is because most of the TVs in the U.S. are still only capable of using 480i. In accordance with your statements, a cheap DVD player could produce 480p, be a progressive player, with just the addition of a set of component connectors, that no additional circuitry would be necessay, because it's included in all DVD players. A DAC is a digital to analog converter, it doesn’t interlace or deinterlace signals.