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General HD (720 / 1080) Acquisition
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Old March 7th, 2006, 07:22 PM   #31
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Quote:
Originally Posted by Joel Aaron
"720p to 1080i is a down, not up, conversion. 1080i is actually 540 lines, not 1080..........

The conversion can look near perfect if it's done by the best broadcast quality equipment, or it can look a bit soft if it's just the cheap conversion built into a consumer CRT HD set."
A lot of these comparisons become meaningless if frame rates aren't defined. "720p" is usually taken to mean 720p/50, and "1080i" is normally taken to mean 1080i/25 in 50 Hz countries. (And using EBU nomenclature - the latter means 25 frames, 50 fields.)

In this case the two are by and large considered comparable in quality, so perhaps "cross conversion" may be a better may to describe it. But 1080 production here is not limited to 1080i/25, and most drama etc is made 1080p/25 - progressive, highest resolution, and many producers actually prefer the 25fps temporal look. Most importantly it can be transmitted as if it was 1080i/25, when it is properly described as 1080psf/25.

Conversely, "720p" can also be 720p/25, and here - provided the front end is capable of delivering - 1080p/25 must obviously be capable of better results than 720p/25. That's not to say there is anything wrong with 720p. There was never anything 'wrong' with 16mm film, but 35mm is obviously 'better'......
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Old March 7th, 2006, 08:46 PM   #32
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I can excuse profanity, but I can't excuse technical innacuracies....

720p has at least the same vertical resolution as 1080i - fact.
horizontal resolution is theoretically higher in 1080i, but in practise, you don't get very much advantage....

720p60 IMHO uprezzes to 1080p60 much better than 1080i60 does... Making it actually more futureproof, not less....

720p is NOT medium definition. To say so shows a complete lack of understanding of how interlaced video works, and it's limitations.

The RED camera is not a big IF. If you don't know that by now, which rock have you been hiding under?

It's much harder to compress an interlaced stream than a progressive one. 1080p30 is easier on the codec than 1080i60. 1080p24 is easier still.

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Old March 7th, 2006, 08:58 PM   #33
 
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Quote:
Originally Posted by Graeme Nattress
720p60 IMHO uprezzes to 1080p60 much better than 1080i60 does... Making it actually more futureproof, not less....
Can't buy that one, not even by half. Having spent a lot of time with both Qualia projectors, Qualia 70" display, and countless 1080p displays, having fed virtually every format and resolution from every HD camera currently available and some that aren't shipping yet (including ENG cams that you'll see at NAB 06') my eyes see a very different story. I'm not the only one. I've made the conversions using several tools, both hard and software.
Not digging at 720p at all. Just saying that I can't agree.
720p is a square pixel format. Compression doesn't care about square or non-square, but of course, compression cares about interlaced vs progressive. However, square pixels have to be converted to non-square pixels, lines have to be nearly doubled, so it's not a 2:1 conversion like it is with 1080i converted to 1080p 30, and same holds more or less true for 1080p 30 converted to 1080p 60.
720p to 1080p 30 requires both horizontal and vertical pixel shift, whereas 1080i does not, it's just a temporal shift.

[edit] just realized your comment about RED camera. Re-read my post before jumping on my backside. I'm well aware of the camera. My disagreement is with the comment that "most displays are 720p" That's a bogus statement from either side of the fence. I wasn't at all referring to RED.[/edit]
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Old March 8th, 2006, 03:53 AM   #34
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I think that being this discussion has been sparked by this farce interviewers statement of 720p being "medium rez" we should get away from the display arguement and focus back on the capture aspects from what the person was refering. As far as capture is concerned the differance is not 1980x1080i compared to 1280x720p but 1440x1080i compared to 1280x720p. When you calculate in the inherant resolution loss from being interlaced the two resolution become amazingly close. Uprezzing to 1980x1080p will not suddenly give more real resolution to either. If you are watching Cinealta 1980x1080 derived material, well then, but hence we are talking HDV in this forum.
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Old March 8th, 2006, 07:30 AM   #35
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Quote:
Originally Posted by Douglas Spotted Eagle
Not digging at 720p at all. Just saying that I can't agree.
720p is a square pixel format. Compression doesn't care about square or non-square, but of course, compression cares about interlaced vs progressive.
But full 1080p is als a square pixel format. HD was designed to be square pixel from the start, but then people started subsampling the raster and making a mess of that ideal. Ouch.

Quote:
Originally Posted by Douglas Spotted Eagle
However, square pixels have to be converted to non-square pixels, lines have to be nearly doubled, so it's not a 2:1 conversion like it is with 1080i converted to 1080p 30, and same holds more or less true for 1080p 30 converted to 1080p 60.
Being an exact line multiplier is not a quality factor. You have to look at many rows of pixels to re-create the new ones you're inserting, so 2:1 scaling offers no real advantage. Indeed, the complexity of doing a proper de-interlace on 1080i60 far outweighs the complexity of scaling 720p60 to 1080p60 by a vast margin. Also, scaling can be, if you want it to be a simple engineering task based upon commonly understood scaling principles - pick a polynomial function and just do it, whereas de-interlacing is, quite frankly, a black art, and much more computationally expensive.

Quote:
Originally Posted by Douglas Spotted Eagle
720p to 1080p 30 requires both horizontal and vertical pixel shift, whereas 1080i does not, it's just a temporal shift.
Scaling in two dimensions is easy, temporal stuff is very hard in comparison.

When I'm running the code I'm working on, I often use 720p footage, but displayed as 1080p - works very well in my programming environment. All you get is a slight softness, but it really passes well for the 1080p, whereas in any conversion of 1080i to 1080p you're introducing artifacts from the de-interlacing which, even with the best de-interlacers, are visible, and visible as something other than softness, so they do tend to stand out.

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Old March 8th, 2006, 08:43 AM   #36
 
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Quote:
so 2:1 scaling offers no real advantage.
I'll leave that one to the engineers to argue deeply. However Poynton, Sony, and Grass Valley's engineers have all offered different information. Poynton is the only person who I've seen lay it out clearly, and I'm terrible with math. I can follow it, but can't create it. JVC uses 2:1 scaling as part of their marketing message, but obviously, that can't be accepted any more than Panasonic's 4:2:2 HVX message either, so I'll gracefully bow out of the debate here. All I can go on is what my eyes tell me, what engineers have shown me, and by what sensibility suggests to me.
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Old March 8th, 2006, 08:58 AM   #37
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Well, all I can say is that people who make decent hardware standards converters have done superb jobs with NTSC to PAL, and that's a 1.18518518519 scaling factor - nothing nice at all. The 3/2 scaling factor for 720p to 1080p is as "nice" a number as 2/1, and although you're scaling 720p in both directions, most practical 1080i formats need scaling horizontally also, as well as de-interlacing.

Of course, shooting 1080p60 is best of all.... :-)

Although you just have 2x scaling to take 1080i60 to 1080p60, you have to have a very high quality de-interlace, and you've got to account for that interlace twitter where, if anyone has ever single field stepped through video knows, the image seems to jump up and down half a pixel as you step forwards, and to account for that in your conversion is a big challenge. It can work on general video, but if you get any sharp architectural lines, it can be very distracting indeed. You'd need to get into temporal motion vector style algorithms to account for that, and although good, are seldom perfect in a software environment, never mind a real time one.

So, the problems in de-interlacing, seperating fields and avoiding vertical twitter probably outweigh any scaling issues by a factor of about 10:1. 720p60 to 1080p60 just and only involves simple scalling. 1080i60 to 1080p60 involves scaling and de-interlacing, a significantly harder problem.

No need to debate further - what YOU see is often more important than anything else, but I would strongly suggest that a 1080i60 to 1080p60 conversion is very non-trivial compared to the simple scaling needed to get 720p60 to 1080p60.

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Old March 8th, 2006, 10:07 AM   #38
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Lets see... ten years from now the only 1080i native displays (CRT) will all be in museums. If we shoot 1080i, it MUST be converted, no matter what it is shown on. If we shoot 720p, it can be shown native on many displays, and sometimes being converted to 1080p. If we shoot 1080p, it can be shown native on many displays, and sometimes being converted to 720p.

Conversion is never a good thing!

Interlaced scanning was DESIGNED for the CRT in an analog world. Not only did it solve a flicker problem, but it provided a good compromise between spacial and temporal resolution. Today, digital processing could provide a much better methodology.
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Old March 8th, 2006, 10:12 AM   #39
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Totally agreed David - interlace is dead. Allowing HD to have interlace has a very bad move IMHO.

Graeme

Last edited by Graeme Nattress; March 8th, 2006 at 12:21 PM.
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Old March 8th, 2006, 10:22 AM   #40
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Quote:
Originally Posted by Graeme Nattress
No need to debate further - what YOU see is often more important than anything else, but I would strongly suggest that a 1080i60 to 1080p60 conversion is very non-trivial compared to the simple scaling needed to get 720p60 to 1080p60.
Right, the important thing is to do whatever conversions you need to do and assess visually how the results look. DSE has reported here that he's finding 720p HDV source material to be insufficient for customers with the best 1080p displays, but 1080i HDV source is converting nicely to 1080p30.
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Old March 8th, 2006, 10:36 AM   #41
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Ah, but converting 1080i60 to 1080p30 is quite a lot simpler than converting 1080i60 to 1080p60.

And there's no 720p60 HDV camera, but 720p30 HDV does indeed convert to 1080p30 very easily and looks great. I'd really say that if 720p30 doesn't scale well to 1080p30 on your projector, then it's scaler isn't that good.

Getting rid of interlace should have been the first step to HD, not the last!!

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Old March 8th, 2006, 10:43 AM   #42
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Graeme, that's post number 1000! do you win a prize or something?

Isn't there also the issue that interlacing leaves behind additional artefacts from the MPEG2 compression that otherwise would not be there? I've found de-interlacing Z1 footage to 25p oftenb leaves behind ugly little blotches that aren't necessarily there in CF25. I've tended to go back to CF 25 these days, despite the res drop because of this, in any "filmlook" situation.

Ironically I find the artefacts worse in plain colour areas, rather than contrasty/detailly areas.
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Old March 8th, 2006, 11:27 AM   #43
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Quote:
Originally Posted by Kevin Shaw
Right, the important thing is to do whatever conversions you need to do and assess visually how the results look. DSE has reported here that he's finding 720p HDV source material to be insufficient for customers with the best 1080p displays, but 1080i HDV source is converting nicely to 1080p30.
Considering the FX/Z1 arguably capture less detail/true resolution then the 720p HD100, then is de-interlaced for 1080p, I find the math/logic very hard to buy.
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Old March 8th, 2006, 12:13 PM   #44
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Dylan, I think I have to get to 1080p(osts) to get a prize!

MPEG2 compression is tough on interlace, but depending on the de-interlace algorithm I too find it can reveal artifacts that were less visible when interlaced - I don't think it creates them though.

Ken, agreed that the 720p from the HD100 has more real detail than you get from the Z1/FX1.

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Old March 8th, 2006, 12:24 PM   #45
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...now that's what I was hoping for when I posted that link- a real discussion. Now I can go back a reread it( the thread, except for the first page) and maybe learn something. thanks esp. to Douglas and Graeme for digging in and giving us more to think about . Kurth
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