Re: Why interlaced HDTV?

In article <meqng1thlul8uvp1cbma5vm7j2v90jvkik@xxxxxxx>, JC <nospam@xxxxxxxxxxx> writes

After watching an LCD i'm now like this even with some 100 Hz TVs. 

You need to eat more vegetables then, especially carrots!


I don't think it's just marketing. Some of the 100 Hz TVs have
horrible frame store artifacts (a friend has a Phillips set where you
can actually see the interlace "jaggies" on any moving image), but the
reduced flicker is noticeable.

The fact that they sell to the unwashed masses means very little in terms of image quality - slow rise time LCD panels without any colour management have been selling in volume too, but the picture quality is complete crap. 

A progressive source will in general digitally compress better than an
equivalent interlaced source in a given bandwidth.

Yes, if you ignore the fact that interlace is already 50% data compression to start with! This has been debated extensively on this group.

Coupled with
the fact that 720p has double the temporal resolution of 1080i

No it doesn't! 720p has exactly the same temporal resolution of 1080i, they both have 50Hz refresh rates. The fact is that 1080i provides additional information in that frame time, in the form of significantly enhanced horizontal resolution and additional vertical resolution through the interlace.

making
it the only real choice for any material with movement

What crap - interlace sources have been the format of choice for movement for over half a century. 

That is exactly the point: nobody would need them - if high quality
backwards compatibility were delivered.  Whilst that is certainly
possible, indeed just as simple to achieve, it isn't what most flat
panels provide.  Consequently the push for progressive standards
alienates about half a century of existing video heritage.

I don't follow this.

That is clear, from your previous posts. Perhaps you need to consider it more.

The push for progressive standards is as much
about moving forward with technology as the move to high definition.

But progressive is NOT a move forward with technology in itself. particularly when the option is between 720p and 1080i. Both formats provide similar vertical resolution in the presence of motion, but the interlaced option provides much higher horizontal resolution in all situations and much higher vertical resolution where motion is limited. Since we are already adopting a digital video coding format that drops resolution when motion is present, on the grounds that it cannot be perceived, the better system at the point of consumption is 1080i.

Since the existing systems are sadly lacking in the
temporal resolution department (25 fps really is very poor) it seems
logical to fix this at the same time.

This is a flawed logic. 25frames per second, but 50 fields per second, the temporal resolution is exactly the same as a 50 frame per second system. Yes, the full *spatial* resolution is not available simultaneously with the full vertical resolution, but that is no worse than most digital codecs, which drop horizontal and vertical resolution when full temporal resolution is required.

This no more alienates existing
video heritage than any other part of HD. HD may consign much of what
you and I are familiar with to a museum, but that's progress for you.

If it means that it cannot be rebroadcast without introduction of artefacts than it is not progress, it is anarchy.

I really agree that we should be looking to 1080p but as production is
moving in that area anyway it would appear logical to adopt the
broadcast standard that's the closest technical match.

Which is 1080i - simply drop every other line in alternate fields: no interpolative downsampling (with the consequential loss of resolution inherent in all interpolation techniques) required.

With 720p you have a down sampling of the source to from 1080 to 720
at the broadcaster

Losing vertical resolution in the process - unlike sampling a 1080i field from a 1080p frame, getting a 720p frame is not an integer spatial division!

and then this is maintained all the way through the
transmission system to the progressive TV.

That part is true: it maintains crap in crap out all the way through to the display!

With 1080i you first have to throw away half the temporal information,

Wrong - and this is the mistake that seems to underpin most of the "progressive is superior to interlace" logic! You do NOT throw away half of the temporal information. What you throw away is the information which requires *BOTH* the full temporal and the full spatial resolution. That is very much *LESS* than a quarter of the information in a real world image - and, given the temporal response of the eye, is even further reduced at the point of viewing. This is why interlace was adopted in the first place - halving the transmission bandwidth resulted in a very small amount of the perceivable information being lost.

transmit this at 1080i and then the domestic TV has to reconstruct a
1080 line progressive frame in memory from two 540 line halves of the
interlace each taken 1/50 of a second apart.


As already explained, that is trivial to accomplish if done correctly.

Since these frames may
have completely different information (depending on the amount of
movement etc) this then leads to an apparent quality reduction.

Back to your error - these frames (fields actually) do not have *completely* different information. Even in a high motion content scene, the fast majority of the information is identical in both fields.

The spatial resolution of a 1080 format is more than double that of a 720 format. Your logic appears to argue that since the temporal resolution of interlace is half that of progressive this cancels out the spatial advantage - but the temporal resolution of progressive is NOT twice that of progressive. The difference between the two lies only in the region where both the full spatial and temporal resolution is required to carry the information. At best, on a synthetic signal which fully occupies that information space, you are looking at a loss of 25% of the information in interlace compared to progressive. In practice it is *MUCH* less than that in real world images, if nothing else because the camera optics don't resolve at full contrast at full resolution.


The HD I've seen has been almost exclusively on high (and low) end
domestic equipment - native 1080 and 768 (why??) progressive LCD and
Plasma screens.

Which domestic display is currently available that has a 1080 line vertical resolution?

It's interesting what you say about the progressive DMD system and I'm
sure you're right that it and LCD/Plasma could be made to display a
native interlace cleanly. But with all the above advantages of a
progressive source would this not be the equivalent of making a wonky
road for a square wheeled car? ;-)

No, it would be the equivalent of making a vehicle that is capable of running on existing roads as well as on new roads. Just like the dimensions of the worlds most advanced transport vehicle, the space shuttle, can be traced back to the width of two horses hind quarters, even though a horse has probably never been within miles of it. Its called backwards compatibility.
--
Kennedy
Yes, Socrates himself is particularly missed;
A lovely little thinker, but a bugger when he's pissed.
Python Philosophers (replace 'nospam' with 'kennedym' when replying)
.

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