Why is 1080p "harder" for devices than 1080i ?

[rohan]

I must be overlooking a fundamental aspect of the whole interlaced vs progressive issue.

I can't figure out why progressive should be any more taxing for devices to playback than interlaced.

-- 1080i --
With 1080i, you're getting 60 "half frames" every second. So essentially you're outputting 540 lines (that are 1920 pixels wide), 60 times per second.

-- 1080p --
With 1080p, you're getting 30 "full frames" every second. So you're outputting 1080 lines (that are 1920 pixels wide), 30 times per second.

It would seem that in either case, you're displaying about 62 million pixels every second. The only different being that 1080 INTERLACED does half the work, twice as frequently...

Why is that harder?

(and it apparently is, since stuff frequently supports 1080i, and not 1080p)

[BHK]

It really isn't about the extra work, its the adding of the hardware to deinterlace the signal i believe

[rohan]

That doesn't make sense -

If that were the case, 1080p should be EASIER because it wouldn't require any de-interlacing hardware.

[The_Keymaker]

It has to do with bandwidth. 1080i is putting HALF the information per unit time than 1080p.

Greater bandwidth means more expensive hardware....

[zambelli]

I believe 1080p implies 60 fps, not 30 fps. Therefore, it would require twice the bandwidth of 1080i to transfer.

[Shinigami-Sama]

I think it may also has to do with the way the bitstream is decoded, I remember reading that somewhere interlaced was geared to easier decoding for broadcasts to keep end devices' hardware requirements low

Don't quote me though I've been wrong before

[Jay Bee]

At the same framerate interlaced is harder to decode because of the deinterlacing. I think 1080p capable screens need to be able to handle 60 fps though which is even harder.

[DarkZell666]

Just read this : http://en.wikipedia.org/wiki/1080i

The article doesn't give too much hints as to why 1080i is easier to decode than 1080p. The only rule that comes out is : the lower the fps, the easier :)

Also, the majority of consumer televisions offered for sale are currently not equipped to receive or decode a 1080p signal at any frequency. It is less bandwidth-intensive to broadcast a film at 1080p24 than 1080i30, since 20% less data would be transferred.

Wierdly enough, it only seems devices aren't "equiped" for 1080p (ie: not designed for it). After all, TV has been traditionnally interlaced for so long ... but yeah, mathematically, it's completely stupid to say : 30 * 1080 > 60 * 540.

[bobololo]

Actually it's a matter of ambiguity of the used terms.

- 1080i refers to 1920x1080i60 which represents 60 fields (1920x540) per second.
- 1080p refers to 1920x1080p60 which represents 60 frames (1920x1080) per second.

That explains why 1080p (ie 1080p60) bandwidth is higher than 1080i's.

Beside, there is another thing that could bring some confusions. It's common to convey progressive video into interlaced signal transport channel like SDI (by splitting the progressive data over the 2 corresponding fields). In such case, the progressive video matches the bandwidth of its interlaced counterpart. This is referred as "PsF". For instance you may have 1080PsF30 which represents 30 frames (1920x1080) per second.

[DarkZell666]

Actually it's a matter of ambiguity of the used terms.

- 1080i refers to 1920x1080i60 which represents 60 fields (1920x540) per second.
- 1080p refers to 1920x1080p60 which represents 60 frames (1920x1080) per second.


OMG, how could it have been so simple and I didn't think about it !

So in terms of bandwidth, 1080i60 is equivalent to 1080p30.

This makes me think (and I'm feeling really stupid now :p) : so PAL DVD's actually are something that "could" be called "576i50" ? 50 fields/s to represent 25 frames/s ? (*realises he was ignorant from the beginning xD*)

[DarkNite]

Yeah, if only your source and display would allow a change to 24Hz you could watch film based material with no impedence to the hardware concerned. You might have a migraine, and/or a siezure, long before your movie got to "the good part" though.

Flicker or judder are generally easier to deal with than convulsions or delirium. You don't need a leather wallet between your teeth, or a half dozen Tylenol to watch something at 60Hz-100Hz.

In that perspective working with 60Hz as a display standard makes perfect sense. Staring at a screen at 24Hz, or even 30Hz for the entire Lord of the Rings trilogy would not. Leather wallets aren't cheap, and Tylenol ruins your liver.

[vlada]

Being from Europe I don't understand one thing: Almost all movies are made 24p. For PAL countries it is sped up to 25p. For NTSC it is telecined to 30i (29,97i respectively).

But AFAIK I know, the NTSC movies (both DVD and HD) are encoded as 24p and there some flags which tell the player how to do the telecine. Am I right? So most NTSC movies are in fact 24p. But why isn't it the possible to ignore the telecine flags and simply output the 24p video? Why do we have to use inverse telecine filters? Could somebody please explain this to me?

[reepa]

Yeah, if only your source and display would allow a change to 24Hz you could watch film based material with no impedence to the hardware concerned. You might have a migraine, and/or a siezure, long before your movie got to "the good part" though.

Depends on the type of display. LCDs are constantly "on", they wouldn't flicker if the input was 10Hz. Besides, with digital connections there's no need to transmit video at anything else except its original frame rate. If the display needs to refresh more often, it can just repeat the frame from a buffer. Even ATSC has support for progressive 1920x1080 at 23.976, 24, and 30 fps.

[foxyshadis]

Being from Europe I don't understand one thing: Almost all movies are made 24p. For PAL countries it is sped up to 25p. For NTSC it is telecined to 30i (29,97i respectively).

But AFAIK I know, the NTSC movies (both DVD and HD) are encoded as 24p and there some flags which tell the player how to do the telecine. Am I right? So most NTSC movies are in fact 24p. But why isn't it the possible to ignore the telecine flags and simply output the 24p video? Why do we have to use inverse telecine filters? Could somebody please explain this to me?

That's how so-called progressive scan DVD players and TVs work. It works best with LCD TVs that can set their refresh rate to 24fps.

[zambelli]

That's how so-called progressive scan DVD players and TVs work. It works best with LCD TVs that can set their refresh rate to 24fps.
That's not how progressive scan players work, or at least I'm not aware of any that output 24 Hz. They output 60p video. For this reason they require at least component connections to the display - a composite or S-video connection couldn't carry a 60p signal, it wasn't designed for it.
The MPEG-2 decoder in a prog scan DVD player is still outputting interlaced video, but the integrated deinterlacer performs IVTC (if it's film-based) and then creates a progressive 3:2 pulldown pattern instead. True interlaced video gets bobbed to 60p.

[MuttLover]

Yeah, if only your source and display would allow a change to 24Hz you could watch film based material with no impedence to the hardware concerned. You might have a migraine, and/or a siezure, long before your movie got to "the good part" though.

Flicker or judder are generally easier to deal with than convulsions or delirium. You don't need a leather wallet between your teeth, or a half dozen Tylenol to watch something at 60Hz-100Hz.

In that perspective working with 60Hz as a display standard makes perfect sense. Staring at a screen at 24Hz, or even 30Hz for the entire Lord of the Rings trilogy would not. Leather wallets aren't cheap, and Tylenol ruins your liver.

I've been interested in all of this for quite some time and I thank all the contributors to this thread. After reading this thread and following some basic links at Wiki, I learned that the shutter speed of a projector @ 24fps is designed to interrupt the light 2 or 3 times per frame ( see http://en.wikipedia.org/wiki/Frame_rate ) for the flicker-fusion frequency.

To my understanding, 1080i@60hz would be 60 fields per second. 1080p@60hz would be 60 frames per second.

What's not plain is what does a modern TV do with the interlaced signal?
a) buffer field 1 and combine with field2 to output a full frame 30 times per second
b) line-double field 1 then line-double field 2
c) ??? not sure.

So I agree with whomever said that 1080i is half the bandwidth of 1080p. I also think Wiki is getting a bit outdated in that now, 1080p capability is being used as a selling point for newer HiDef TVs and they currently more prominent.

It gets more complicated to me when you introduct the 1080@24p "film" frame rate. If your hi-def DVD player outputs 1080@24p, there will still be the need for the displayed image to reach the flicker/fusion threshold for human viewing. So I am wondering if a true 24hz output is a practical reality in modern TV/DVD. I'm thinking not, and I'm thinking that modern 1080p HD DVD players are increasing the 24hz to 60hz, or if passing to the TV, the TV is doing the job.

In the US broadcast hi-def is 720p or 1080i. From what I've studied, the progressive is better in high-action viewing such as sporting events.

[rohan]

By a modern TV, you're talking about a plasma or LCD right?

I would imagine (nothing to back this up) that it treats the interlaced video much like a regular TV does. If the LCD runs at 60hz, then in cycle one it outputs the EVEN lines keeping them up during the next cycle when it outputs the ODD lines, after which it then changes the EVEN lines again (while keeping the ODD lines constant), then etc etc etc.

Look at this:

Field 1 X-X-X-X-
Field 2 -X-X-X-X

Assume that "X" means output the field during this cycle, and "-" means hold the field constant for this cyle (ie. don't change it)

With 60 cycles per second, this would give you 30 FPS. The example above gives you 4 frames, and accounts for 8 of the 60 cycles.

In fact, now that I think of it, the 1080p content I've seen from Blu-Ray and HD DVD discs - Isn't 60 frames per second, it's 30 (or really 29.97). So I'm not sure we're correct about this assumption that 1080p means 60 frames per second.

[Jay Bee]

What's not plain is what does a modern TV do with the interlaced signal?
a) buffer field 1 and combine with field2 to output a full frame 30 times per second
b) line-double field 1 then line-double field 2
c) Use advanced deinterlacing algorithms (motion compensation etc.) that adapt to the type of content you are watching, thus keeping the spatial resolution of film and the temporal resolution of video unharmed.


... :)

[rohan]

Except that I'm not sure it's really "Advanced" - basically, it would just do exactly the same thing a tube TV does... odd then even then odd then even then odd then even.

The difference being that instead of letting the diminishing fluorescence created by the electron collision dictate the timing, the LCD's circuits merely keep the fields constantly active until it's their turn to change.

(my guess)

[MuttLover]

@rohan:

Yes -- a bit more research turns up

All 1080p content currently (as of March 2007) distributed on the Internet has frame rate of either 24, 25 or 30 frames per second.


Also...

where 24 fps film-based material is concerned, a 1080i encoded/transmitted stream can become a true "1080p" signal during playback by deinterlacing to re-combine the split field pairs into progressive film-scanned frames. Regarding 24 fps film-source material presented in conventional 1080i60 form, the deinterlacing process that achieves this goal is usually referred to as "3:2 pulldown reversal" [also known as "inverse telecine"]. The importance of this is that, where film-based content is concerned, all 1080-interlaced signals are potentially 1080p signals given the proper deinterlacing.

From wiki article @ http://en.wikipedia.org/wiki/1080p

[Jay Bee]

Don't assume that all content starts it's life as 24 fps film.