Axiom Home Page Forums General Discussion Home Theater 1080 i vs 720P

I was told by a sales person in an audio store that 720 p is better quality than 1080i because 1080i represents approximately 520P.. is that true ? I know 1080p is the max and best, but between 720p and 1080i which resolution gives the better picture quality ?

thanks

1080i is 1920x1080 resolution passed in 2 consecutive frames (60/s for video and 48/s for movies). 1080p is 1920x1080 resolution passed in 1 consecutive frame (30/s for video and 24/s for movies).

One of the arguments that I heard from time to time in comparing 720p and 1080i was that 720p handled fast motion on the screen slightly better. I am not sure that was ever the case but perhaps someone out there who has made that visual comparison could comment. Either way, with normal viewing, the differences between the two are negligible.

Once again, unfortunately, you ran into another retail A/V electronics (so-called) salesperson who didn't have a clue what they were talking about. The stores are full of them.

Many video processors were overloaded with 1920x1080 resolutions so they had trouble keeping up with the decoding and de-interlacing of twice as much info. I doubt there are any TVs now with that sort of problems.

This is a Bell Express Vue HD receiver that can output a max of 1080i.. running on a brand new Panasonic 46inch Plasma 800 series. The tv has only been available in Ottawa for a few months..so it's spanking new.

I was disapointed that the Bell receiver only did 1080i, I just figured it was capable of 1080p.. ah well..

So, I've got the bell receiver set for 720p and the tv set to receive 720p. .that , whith my eyes, looks better on that tv than the 1080i...

To be honest, I'm not impressed with the PQ of the Bell HD signal.. I find that a regular DVD (animation, the incredibles)looks almost as good as the 720p or 1080i of the express vue HD.

There are broascasters that are using 720p, which then mean double conversions. I have HD-cable home and 1080i looks better (and my TV is natively 720p!), but it is so marginal that I would not be surprised if someone else in my room would prefer it the other way around.

Not sure how much the supplier and/or our choices of programming influences the final quality broadcast (I honestly don't watch much TV).

First a comment about the Bell Express Vue HD receiver. Is that like a satellite or cable box? If so, don't be upset that it can't do 1080p because there's no such thing as 1080p via broadcast. Neither from satellite nor cable, nor OTA TV. Not for a few years anyway and maybe never, so I've read. The only source for true 1080p material is from a Blu Ray DVD or from a gaming console.

I am really new to the HD world, only having had my HDTV (Samsung LED DLP 1080p) set for a couple of months. So my comments are from a newbie. But I've done *tons* of research and have spent *hours* watching HD programming both in the store and at friend's homes.

My conclusion? Well, my TV is a true 1080p set, so I have all of the options on the table. My Dish Network HD receiver can be set to send out a 480i, 480p, 720p, or 1080i signal. It does the up/down conversion automatically. I've tested them all with various content. For most content, I couldn't tell a difference between 1080i and 720p, other than the TV noting that the resolution had changed. However, I found a few programs where the 1080i did look a bit clearer or sharper. Specifically, some of the 'show-off-your-HD-eye-candy' nature type shows. Could it having nothing to do with 720p vs 1080i and just be how my TV and DishHD up/down/side conversions are working? Certainly. But since there was a difference, and the 1080i looked better in a few cases, I stick with that on the Dish receiver.

The real differences with HD content comes from the filming & broadcasting, not just the fact that it's an HD channel. Sources vary a lot. Sometimes an HD channel might broadcast 'SD' content, even though it's being piped in via HD bandwidth and recognized by your equipment as an HD show. The BravoHD channel is an example of this. While you're laughing, let me say that I don't watch it buy my wife does, and I'm usually in the same room. So occasionally I glance over the laptop screen at what's going on. Several of the shows on there, even new ones (Project Runway), are NOT really done in HD. Still 4:3 and only marginally better than normal SD quality. A show like that is a horrible demo of what HD is capable of. That signal may be broadcast in 1080i, but the picture quality is somewhere between regular TV and 480p DVD.

Then compare that to some of the jaw-dropping content on the National Geographic or DiscoveryHD Channel, and the differences become quite clear.

Another thing to keep in mind is that FOX and ABC broadcast in 720p. NBC and CBS broadcast in 1080i. So if you're watching one of those networks, that's all you're going to get.

It has been noted in many forums that most people have difficulty noticing any real difference from 1080i and 720P, just like audio it is the source material that makes the most difference. I have always felt 720P to be better as 1080i is simply 540 lines of resoltion doubled up on the screen and on smaller screens the difference is not noticeable on the larger 52" and up I have always been able to notice a difference from 1080i to 720P but only with poorer recorded material.

Native resolution of 720P is much better than 1080i. There’s a whole heck of a lot more data for a display device or video processor to work with. Depending on the VP in the display however, you may, or may not notice a difference. Also, depending on how close you sit to the image and the size of the display will also play into visual appeal of the image.

This has been answered many, many, many times with very long and informative posts. Alan also has some very good information on the topic. I’d write more but I’m too bored with this subject to do that again……

I’m going to use Randy’s line “use the search feature”.

Sorry Mdrew, did not mean to bore you.

you did however answer my question in your first sentence. Thanks

I get your point about the search feature.

my mistake


Riker out

Stephane, the sales person is wrong; 1080 resolution is by definition higher than 720 resolution. Other factors being equal(of course, many times they aren't), the higher resolution would be visible in a suitable screen size/distance scenario.

John,

I would tend to agree with you, but Mdrew stated that 720P is better than 1080i. and on the Pansonic display that I have configured, source being the Bell HD receiver (dish network hardware) the 720p setting does look better .. not by a mile, but it does look sharper, than the 1080i setting..

now if he (fajja in laa) had BD then I would agree (and hope) that 1080i would look better than 720p..but if he did have BD then we'd be looking at 1080P.

The problem is the search feature has not worked well for the last year or so whenever Axiom made changes to the forum. I have performed many basic search phrases for "subject" only and with no results. Also, the date range has been minimized to only a small 1 year window. I'm guessing this has to do with how much the DB gets taxed during a broad search.

I used to use the search a lot to pull up threads from the past, but it is just no longer user friendly or intuitive to this IT person.

In regards to the 720p or 1080i debate, I think it depends on a lot of factors. I've viewed many tv's and projectors and it is a toss up. A lot depends on the scaler.

Riker,

I’m not bored with you!! Just this subject. Sorry for sounding so harsh. I’ve just spent a lot of time answering this question. Allan Loft has a great article somewhere around this place that’s worth reading. It goes into the whole processes of cadence detection and interlacing processes which will make it very clear why NATIVE 720P is better than NATIVE 1080i.

Now…If you start out with say, a 480i source and rely on the display’s internal video processor to up scale that input – then the argument becomes nothing more than words on semantics and personal opinions debating whose display is better. It no longer is a discussion over which RESOLUTION is better, but which VP is better.

TYPICALLY – 720P, even when it’s an upscalled image, it will look better. This is very evident during panning shots.

Best regards………

I didn't know the search was goofy.... It used to be very good.

Mdrew,

Thanks for your post, No worries at all here..I do understand how you feel.. it's somewhat frustrating re-hashing old subjects and I totally get that.

You have been an invaluable source of information in another thread about projectors (anamorphic lens thread) and I truly thank you for that.

I hold you in high regards Sir.

Cheers,

Riker

Thanks you, or your talking about Mike, ar ar ar

Riker: as you have seen from this thread, there are many opinions on this subject.

However, from a theoretical standpoint, the information content is basically a function of the bandwidth. If you look at the bandwidth specs of 720P and 1080I, you will see that they are almost the same. So, it is a question of format, not which one gives more or better video.

Since many (most??) of your HDTVs convert either format to 1080P, it may be a moot point.

Bernard, good to hear from you again. What started this thread was a salesman's contention was that 1080i was about equivalent to 520(?)P, which is clearly wrong and not a matter of mere opinion. Apparently the notion was that since 1080i is transmitted in two sets of sequential frames you're only actually seeing about half of the 1080 resolution, but this isn't the way things work. Basic video principles are that 1080 resolution is higher than 720 resolution; the bandwidth required to transmit P is higher than i at a given resolution, which is why we presently don't have 1080P transmissions and may never have them. The advantage of P over i in handling fast motion(e.g., some sports)has been brought up, but this a separate matter from resolution. There are several tables and graphs of suggested resolution/screen size/viewing distance combinations(e.g., the Sound&Vision graph ), which of course combine 1080i and 1080P for evaluating resolution, since the resolution is the same and superior to 720(P).

I thought that it was true that 1080i and 1080p are identical as long as the 1080i source is deinterlaced correctly. However, many (not most) displays or receivers still don't do this correctly, so some people won't be able to see this.

- Nick

What the salesman was trying to get across is that 1080i contains only 50% native information. Why he chose to say 520P is confusing to me. He obviously doesn’t have a full understanding, but he is somewhat correct – stressing “somewhat”.

1080P is 1920 X 1080 pixels = 2,073,600 pixels of data displayed
1080i is the same resolution with the same pixel content, but missing 50% native data. (1,036,800 pixels of native data)
720P can be different resolutions, but contains 921,600 pixels of native data (IE: 1280 X 720)

The number of pixels is what we see as information on a display. Obviously, as that number increases, those little dots of information because smaller and more tightly packed onto the screen, provided the screen size remains the same.

The difference between 1080P and 720P, as being viewed by the observer, is all vertical rows of information are actual data, but the pixels are larger with the 720 display than the 1080 display (display size being equal). Depending on how close the observer is to the display, or the actual size of the display, this may be a mute point as the observer may or may not be able to see a difference. As you get closer to the display you will be able to make out actual pixels sooner with the 720 display than you will the 1080 display. – Which is why you always see charts and graphs referencing viewing distances, display size and recommended resolutions. In other words, if you sit ten feet away from a 36” display, you will not see an improvement if you go with 1080 verses 720, unless you watch TV with a pair of binoculars.

Without going into too much detail describing the interlacing possess……

Film is shot at 24 frames per second and video is shot at 30 fps (NTSC) and 25 fps (pal), all at various progressive resolutions. HD digital cameras shoot at up to 4K pixels (and maybe higher). I don’t recall what real 35mm film is in comparison to digital, but it’s significantly higher than anything we’ll ever see on a digital display. Well maybe someday, but not anytime soon….. However, 35mm film is converted to digital HD/DVD and BR content at 1080P/24. That’s as good as it gets, currently. HD/TV is broadcast at 1080i or 720P; both at 60 fps NSTC or 50 fps PAL. Each of these broadcast feeds are highly processed to convert from 1080P/24-30 to 1080i/720P – 50/60 fps. (this gets confusing real quick as film is sometimes transferred to video and you start to see 50 and 60 fps formats being referred to)

Interlaced data contain roughly half the original native data as progressive data (I say roughly because there may be some scaling going on to fit an image to a display, which is another topic). In a nutshell, to get to an interlaced resolution, vertical lines of native information in each frame (referred to as fields) are removed and replaced by digital ‘flags’ representing the deleted data. A deinterlacer then identifies these flags and attempts to reconstruct the deleted data (fields) to get a full progressive output. Unfortunately, sometimes these flags get lost in transfer or transmission and the deinterlacer can not properly reconstruct the progressive output because it looses sync with the cadence that the interlacing process used. The manor in which the interlacing process is done varies. I won’t go into that, as a quick Google search will take you to numerous web sights describing the process with graphics.

It doesn’t really matter how all this works, but it is very important to know that some video processors de-interlace better than others, or in other words, reconstruct original data better or worse than others. Then there’s film verses video which is recorded and transferred with different frame rates and interlaced with different cadences, and the deinterlacer needs to identify if it is film or video (like credits, which are video mixed in with film or video commercials mixed in with film). What makes a true native data progressive output appear smoother than an interlaced output is the fact that all data you see is real data, and not the deinterlacer’s idea of what to do to reconstruct missing data. Sometimes the video processor will screw up and drop fields or frames because it looses sync with the interlacing cadence and you see tearing, judder and artifacts. These are amplified with sports and video as there tends to be more left to right movement across a display (remember that vertical rows are eliminated and reconstructed, not horizontal).

So what’s better than relying on a VP to reconstruct deleted data? Simple, display native progressive data. It really doesn’t get any simpler than that. A display that will accept, and convert 1080P/24 to 720P will have a smoother, judder free picture without tearing and artifacts than one that displays de interlaced 1080i because it will not eliminate entire rows of native data. This however is not the general contention and source of argument, and folks need to keep the subject of the argument on track. The argument always ends up being, “my 1080i TV looks better than my uncles 720P TV or vice versa”. That is not comparing apples to apples. It’s comparing apples to bacon.

Unless I have forgotten something, this is not quite correct unless you add "in any given frame" to the end of that sentance.

Any interlaced signal should contain all the data, just spread over two frames. Deinterlacing simply takes the two frames and merges them back into one frame with all the data.

So a progressive signal gives you all the data 60 times per second, an interlaced signal gives you all the data 30 times per second, but split over alternating frames.

Good point, my statement was misleading. But even to say it with your preposition isn’t correct either as each video frame contains two fields. I was trying too hard to keep it simple and generic and avoid discussing interlacing, 2:2, 2:3 telecine pull down, reverse pull down, line doubling, 24 fps doubling….etc.

Mdrew, so much for being bored with the subject hey ? Great post, thanks so much for the explanation. This stuff can get pretty hard to understand.

So, since the broadcast signal is 1080i only, there should not be much difference between 1080i and 720p right ? because the VP is converting 1080interlaced to 720progressive. Now if the signal was 1080Progressive to start with, then 720progressive would not look as good..

That's if I understand what you are saying.

Bottom line, broacast HD signal kind of sucks either way. My older CRT display probably hides some the SD flaws so my "overall" impression of picture quality is quite good, the HD signals I have seen on my father in law new Panasonic are a bit sharper, but with a lot of noise, artifacts etc.. So, that's the main reason I'm still on standard digital signals and not hd digital signals yet.

Now, I'm sure a native Blue Ray at 1080P would be nice on his 1080P Panasonic. It might even look good on my 1080i CRT !!

Thanks again, Most informative.

Broadcast is mostly 720, no? With content coming from varying sources and being sliced, diced, and otherwise processed before reaching the viewer via any medium, I'm kinda skeptical that any de-interlacing can do much good in the general case. I also wonder how many HD-DVD and BD titles are actual HD transfers, and not rescaled SD DVD transfers. There are certainly lots of crummy DVD's out there (eg. Aliens, The Abyss) that are just VHS/LD 4:3 transfers so I have to wonder if the same laziness applies to HD media.

<--- grumbles about how his Samsung was advertised as 1080p yet can't actually take 1080p input in any useful way.

Stephane, I see that this one has new life, and yes, there's no reason to become bored with the subject as long as the technology involved isn't grasped firmly, and unfortunately some of the comments here have been as incorrect as the contention of the salesman that started this. There's no "native data" problem with respect to 1080i transmissions; all 2 million plus pixels are the original real ones. None of this is "discarded" when the two fields of the 1080i transmissions are combined into one full frame.

A CRT HD set is inherently interlaced in its operation and the persistance in the screen phosphors results in the two fields being automatically combined for viewing; no deinterlacing processing is necessary.

HD sets other than CRTs are inherently progressive in their scanning(i.e., the full frame is displayed in one swipe, not two), so when presented with an interlaced input it has to be first deinterlaced electronically to combine the two fields into one full frame. When properly deinterlaced the full 2 million plus original pixels are reproduced without loss and the 1080i material has greater resolution than 720p material, which has only 900K plus pixels. As Nick pointed out(probably he had Gary Merson's tests for HomeTheater Magazine in mind)not all sets properly deinterlace, and in that case a better picture results from having a player, receiver or separate video processor do the deinterlacing instead, as has been frequently pointed out here.

So, the botton line again is that 1080(i or p makes no difference in regard to resolution)resolution is superior in resolution to 720(rapid motion is a separate subject), as the several charts and graphs of resolution/screen size/viewing distance combinations illustrate.

Hey John, its good to be back. I've been very busy for a number of reasons.

I have not seen that specific chart before and I don't really know what factors they computed to determine those viewing distances.

I may be able to find the reference that gave the relative bandwidths of 1080I and 720P as nearly the same. I still maintain that for a fully utilized bandwidth, the data content should be the same. However, the viewing formats may be considerably different leading to different optical "visions."

Anyhow, it appears that the salesman did not correctly state what was going on.

Bernard, hope that you'll be able to participate more often now. There's no question that, as you say, the required bandwidth for transmission of 720p and 1080i are similar. Although the full 1080 frame contains over twice the pixels than does the 720 frame, 1080i is transmitted in two separate fields in sequence, so its transmission doesn't per unit of time require over twice the bandwidth, as would be required if all the pixels were transmitted simultaneously.

I used pore words and verbiage to keep an incredibly complex subject simple, which was obviously a mistake. It takes a great deal of time and effort to explain it in a way that others can understand, which is why I did not want to get into this. I do not claim to be an expert.

Seeing how I’ve dug a hole for myself with poor / incorrect verbiage, I’ll attempt to dig the hole even deeper.

In short, using the word eliminate/delete was a very poor choice of words, and as John pointed out, just wrong. Native information was also a poor descriptor. In my mind, ‘native’ means that a frame is in the original format as shot without any rearranging of pixel content in any way, shape or form. 1080P/24 is the only ‘native’ film format currently available for home entertainment that I am aware of. 1080P/30 and 1080P/25 are two ‘native’ video formats that I am familiar with. Why I chose the word eliminate is harder to describe and I’ll probability just create more confusion trying to explain my rational. It has always been a mind set of mine, and one I need to reconsider.

Per my understand………(maybe John can educate me differently)

All data that was converted from 1080p/24 is there in an interlace 1080i video stream. The data is there, but it is rearranged and also duplicated for further rearrangement during the 3:2 telecine pull down process to convert 24 fps to 25 Hz and 30 Hz video, which is further processed to get 60 Hz for NTSC and 50 Hz PAL displays (and also 72 and 120 Hz displays). Frames in an interlaced video stream are composed of two separate fields each, one field representing the odd number of horizontal lines of information, the other field representing the even number of horizontal rows of information. Some frames contain the odd and even rows from the same frame, and some frames contain fields from two separate frames. For every four frames of film, telecine conversion from film to video creates 5 frames, consisting of 10 fields for 30 Hz video. Instead of simply doubling two fields and tripling the other two fields to get the ten video fields for five frames [(A-A-A, B-B, C-C-C, D-D), which would make the video stream appear uneven (pause and hold affect)], the fields within each video frame are staggered in a sequentially reoccurring order for smoother playback (A1-A2, A1-B2, B1-C2, C1-C2, D1-C2). Legacy CRT displays would light up the fields in sequence, but not the whole frame. New digital displays light up the entire frame. When an interlaced stream is converted to a progressive stream, these fields are re-woven in an attempt to arrange them back to the original film based frame sequence. The process of reverse telecine to put all the fields back together in the proper sequence still baffles me, so I will not even try to describe it.

Digging my hole deeper, there are industry standards for the different 1080P formats which also specify different timing for each frame rate. Timing relates to the number of pixel clocks in the horizontal lines of information. [Vertical timings are standard to all 1080P formats.] In each 1080 horizontal line there are 1920 pixel clocks and also a blanking period that is composed of a front porch, a sync pulse and a back porch. Blanking is there for CRT displays to make sure each horizontal line (or field) is placed properly as it retraces across the screen from right to left. (the beam is turned off during the retracing period, which is where the term blanking came from). Pixel clocks for the sync pulse and back porch remain the same for all formats, but the front porch clocks vary from format to format. The front porch clock variation difference is for 48, 50 and 60 Hz to ensure proper sequential line placement. The sync pulse is what triggers the retrace and is towards the middle of the blanking period and the back porch is at the end of the blanking period. The front porch is at the front of the blanking period and varies in length. The back porch keeps the electron beam turned off long enough for the entire passage of the beam from right to left (maintaining proper sequential line placement timing). This blanking period no longer applies to modern digital displays, but the legacy signal / timings remain to standardize and maintain proper pixel clock timings of all the different types of display formats (1080P48/50/60/72/120 Hz).

While you’re probably thinking, “so what, how does this apply to the 1080i / 720 – 1080P comparison?”, it has to do with what you see. Timing to maintain proper horizontal interlaced line placement frequently gets out of sync. It also applies to the process converting an interlaced video stream to a progressive video stream. This is why I maintain the position that, in MY words, NATIVE 1080p/24 or any down conversion of that format will always yield a better picture than any other format, especially any interlaced video stream. Only the very best video processors can take a, in my words ‘non native’ video stream and convert it back to an original 24 fps or doubled/tripled 24 fps format, or apply progressive scanning for 60 Hz output.

DVD, HD/DVD, BR, broadcast HD, broadcast SD, video, gaming and film all vary to some degree in how these processing parameters interact and how well or poor the video processor will interpret each feed and lock onto it for proper conversion and output.

I'm putting my shovel away and warming up the back hoe......

Here ya go, Mike.



I'm a helper!

AHHHHH! duck and cover, duck and cover, the porches are coming!!

Mike, you write rather well with a shovel, I can hardly wait for the backhoe version.

I had never thought about the implications of converting a signal optimized for the analog world to the digital world. Now that we are in a world of arrays instead of beams blasting at phosphor dots you would think that getting all the data on screen properly would be simpler. Looks like we are not quite there yet.

John. You have a real tallent there: minimum words, simple explanations, maximum understanding. Not many people are able to write that effectively.

Oh cheese and rice.

It was a picture of a gigantic loader steam-shovel thing.

I'll go mind my own business now.

Very good, Mike; you can keep the back hoe put away until winter(next month for y'all). All I ever wanted to do here was to correct the salesman's notion(think he meant 540, not 520)that you only saw half of the nominal resolution in a 1080i transmission. Apparently he didn't grasp how a CRT HD set worked so that a full 1080 frame was seen, or how HD sets other than CRTs used deinterlacing to combine the two fields before they were shown.

Wow.. Thank you John and Mike.. I have created a "monster" !! but in a good way I think


Like I said before..complicated stuff for those without a broadcast / video engineering masters degree

I think part of the reason why I like my HD CRT picture quality, albeit the highest I've watched is regular DVD, might have something to do with my CRT's capabilities in black levels, maybe ?. I don't know and I don't pretend to fully understand..

All I am saying is that to my eyes, my Sony XBR 34" 1080i CRT TV looks pretty damm good for the stuff I'm watching on it.. and that I am under - impressed with the HD picture (satelite) I have seen on my father in law's brand new Panasonic 46" plasma 800 series tv..
I just expected much better PQ ..and that is a BIG reason why I have not switched to HD broadcast or replace my TV yet..

Riker, I had a Sony XBR960 34" TV and I loved the picture on it. My parents have the TV now. I sold it to them last time I moved because I didn't want to lug the thing up another flight of steps. The image on that CRT was natural and sharp.

Wise choice Riker. I held of for 4 years because of quality and pricing issues and I was watching on a 21" crt.

I expect that you will still see substantial price and image quality improvement in LCDs with an outside possibility that something like OLED technology moves far enough along the technology/development curve to deliver something even better, but don't hold your breath.