CurtPalme.com Home Theater Forum

[greg_mitch]

Help me understand something here.

I have seen several people say that 1080i is the same as 1080p.

I know that film based material is either shot digital at 1080/24p or scanned into 1080/24p and this will fit nicely into a 1080i60 carrier using the 2:3 method.

Are there any sources that are shot or scanned at 1080/60p?

Does the blanket statement that 1080i = 1080p with a good deinterlacer always true?

It seems that it is only true with film based material and a great deinterlacer.

[ecrabb]

[ecrabb]

Oh, one other thing... Nobody shoots 1080/60p for broadcast - it can't be broadcast. There is some equipment that allows a production to shoot 1080p/60 and capture it to "over-crank" the camera for .5x slo-mo, or to go into a production pipeline for broadcast flexibility (i.e., it can easily be down-converted for broadcast either at 720p/60 or 1080i/60). Since the conversion from 720p to 1080i sucks, and the conversion from 1080i to 720p sucks, it's handy to capture 1080p/60 for ATSC broadcast.

SC

[GEBrown]

[dbaisey]

http://www.hometheatermag.com/gearworks/1106gear/

[greg_mitch]

watch this video (if you can stand the cheesy water background and the headset microphone!).

http://www.youtube.com/watch?v=Z-JXfyvlPh0

In it he keeps saying that at any moment in time, 1080i only has half of the information and in essence is only displaying 540 lines of information.

I thought that at any moment in time all 1080 lines are there but at every 1/60th of a time every other field is updated. so I guess at any moment in time only every other line is accurate but ALL 1080 lines are present.

Its not like there are blank lines every 1/60th of a second, right? the even field stays while the odd is updated and vice versa, right?

I was watching that and it made we questions what I thought I knew.

One a pause of a screen shot between 1080i and 1080p (if not a motion shot) they should look identical, correct?

[garyfritz]

If you have some kind of processor that deinterlaces the signal and outputs 1080p, yes. It takes the alternate 540-line fields, assembles them into a consistent 1080-line image, and passes that to the projector. The projector sees 1080 lines so it displays 1080 lines.

If you just feed 1080i straight into your pj, nothing does that deinterlacing and assembly operation. You're only giving the pj 540 lines at a time, so it only displays 540 lines at a time. You're relying on persistence of vision to do the "filling in" and "deinterlacing" for you.

This is why I've always preferred 720p to 1080i. I seem to see a lot of "twitter" in 1080i signals, which I believe is caused by thin horizontal lines being alternately displayed and skipped. Am I misunderstanding?

Would be lovely if there was a really good and really cheap "deinterlacer" box that would accept 1080i in and output a good 1080p signal. But most of our projectors can't really handle 1080p at 60 or 72Hz anyway.

[ecrabb]

The YouTube guy is both right and wrong... The things is that it's a very complicated subject. How this stuff "looks" depends on the display technology and format, the source format, and the content. Even the viewer's perception is a wildcard. You can see why it's just too complex to put into some sound bites or a 3 minute YouTube vid, and you're probably getting by now that's too complicated to get it all by reading a couple of forum posts.

It is true that at any given moment, a 1080i display will be scanning only one field. It's not necessarily true however, that the other field is just all black... It depends on the phosphor's decay rate, scan frequency, and the viewer's sensitivity to flicker. It's not persistence of vision that prevents us from seeing flicker, it's phoshpor decay time and our flicker fusion threshold.

The thing that bugged me the most about that piece was that they put 1080i "over" 720p. I would put them next to each other as neither is better or worse than the other in all regards. They each have their advantages and disadvantages.

Here are some of the pros and cons. If you guys think of some more, I'll update this.

720p
+ Progressive, no interlaced motion artifacts
+ 60hz, good temporal resolution
- Judders more noticeably with film source
- Always < 1 megapixel of spatial information

1080i
+ 50% more horizontal resolution
+ Lower bandwidth than 720p (less compression in same
+ 50% more vertical resolution on stationery/slow objects/shots
- 25% less vertical resolution on fast-moving objects/shots
- Interlaced motion artifacts (reduced temporal/spatial resolution depending on motion)
+ Slightly smoother motion (reduced judder) on film sources

SC

[ecrabb]

[greg_mitch]

I thought we had a thread about the phospher decay rate somewhere (I suppose I should at least try to search!).

Does the phospher decay faster than 1/60th of a second? If it doesnt then all lines would be on essentially all the time right?

How do you expect me to explain this to anyone in my family, lol. I guess I have to start somewhere...

[greg_mitch]

Ok, I hate to do this but I need some back up in this thread.

http://www.avsforum.com/avs-vb/showthread.php?t=939069

Caspian is already over there but trying not to stir the pot. Let's go over and straighten it up without causing a CRT vs digital cat fight plz.

Before I feel like I don't know squat again....when a CRT displays 720p it is actually displaying 720p on the phospher right? I mean, each line of resolution is being updated every 1/60 of a second?

[ecrabb]

A couple of those posters are what started to really bug me about AVS - especially in certain... forums. Cough cough... digital. I've been around computers, computer graphics and video my whole life. When I hit AVS, it was at least a couple of years before I did anything but ask the occasional question. The rest of the time, I read, read, and read some more. Some of these guys, though - they apparently think that just because they work in IT and bought a little DLP projector and read a couple of magazine articles and have been a member of AVS for a year, they know enough about home theater and video to answer any possible question.

I don't understand some people. When I don't have a REALLY firm grasp on a concept, and I'm not at least quite confident I can add good solid information to the discussion, I either keep my mouth shut - or if I'm interested in learning about the subject - ask more questions. Otherwise, I sit and read... and learn.

SC

[garyfritz]

[WanMan]

I do not think this i vs P for 1080 discussion is of much importance to digital-heads. The more important question is what their digital displays are doing with the interlaced signal to begin with. I've always feared they simply throw away one field and double the remaining field to get a progress signal to the imager, and in some cases this is even what the cheapest processors did.

Then again, how many people get their eye sight check and corrected enough to even see half the resolution they are aspiring to, and insure their image-to-eyes relation will afford them the ability to benefit from resolution? I find it amusing seeing someone spend their life savings on a 1080P display that is 47-52" diagonal, and then sit 15 feet from the display. You can have 2-/20 vision and sitting that far back from that small of a display will make it a moot point to have 1080P in the home.

[greg_mitch]

Thank you SC. Well put.

[WanMan]

And this is only for material via pre-recorded methods and not through cable or DBS.