LCD Resolution & 720P/1080i

acfoster

Hi all,

I have been a round a few shops and am getting some weird conflicting answers from salespersons so I would appreciate it if you could help me.

I’m trying to understand the difference between 1080i and 720p by looking at them on different 40” LCDs to help me decide what to buy and what suits my needs best.

Okay I know there are two broadcast formats:

1080i is represented by 1920 vertical pixels by 1080 horizontal pixels interlaced
720p is represented by 1,280 vertical pixels by 720 horizontal pixels progressive scan

I also know a 1080i LCD or 720p LCD can show both formats by converting the signal as needed to the native resolution.

However where I get confused and so do the sales assistants is when we start talking about what is the native resolution for an LCD actually is

The 1920X1080 resolution LCDs are easy to spot as unless they have a 3000+ price tag are going to support 1080i native and convert 720P to 1080i

The complexity comes on the LCDs that are 1280x768 or 1280x720. What is their native resolution in terms of 720P signals? Do they:

a) show a 720p source natively as 720p as the LCD is progress by nature
b) show a 720p source as 1280x768 or 1280x720 but interlace it
c) convert 1080i source to 720p
d) convert 1080i source to 1280x768 or 1280x720 but interlaced

I really get confused here can you help? How do you detect that the LCD shows true 720p?

As a side point I generally watch a lot of DVD films and sports and will be looking at an LCD of size 40 to 42inch.

Do you have any recommendations by the way of what I should go for?

Regards

Andy

ah802

Here's my attempt to help... adding to the confusion do check-out the article http://blog.hometheatermag.com/geoffreymorrison/

Native resolution: the actual 'pixels' on screen represented by little boxes.. if you use a jewellers loop pressed against the screen you should see them. eg. 1920x1080=2073600 boxes. When the sales guy tells you all his panels to 1080p, tell him you'll count the boxes and if he's wrong you'll make him pay

Most panels have a fast transforming chip, that will convert any signal to fit the native panel. Now it's possible to massage the signal to the correct size before it goes into the panel... but most likely it still will go through the transforming chip.. some chips work better than others of course and the transforming circuit in some are smarter and that's we have this High Def Forum to discuss which is better.

When displaying movie broadcasts, overscan is usually considered to hide non visual content and the image area is stretched to fit all the pixels and goes through the transforming circuit. This would apply to any signal (1080i or 720p) and how well this works depends on the design of the circuit (again some are better than others). So whatever the native display... almost all are transforming the signal and the native display resolution is more of a guide of PQ capability.

Having your display 1080i or 720p is more of a refresh question on LCD panels.. the 1080i image could look sharper (when it's deinterlaced over the two interlaced frames) but the 720p will look better with faster moving images, or so I'm told... I only get 1080i signals OTA were I'm at. But again.. the signal goes through the transformation circuit.. and will always appear on the panel as native to that panel and manufacturers are not all ways clear about native and price is no guide. Almost all plasmas are not 1080p (there's about 3) and only recently have there been LCD TV's with 1080p native. Yet when you ask a native at BB they will tell you they all handle 1080p native.

Working with my PC as my source display device, I can send a signal that is exactly native (In my case it's 1280x720) and the panel excepts it as 1:1 aspect (each pixel can be directly addressed) bypassing the transforming chip.. not all panels have this. For watching content on the PC, The PC handles the transformation (my PC is not fast enough for 1080p content.. ugh).. but I can switch to the transformation chip in the display device to allow overscan, but the images becomes a bit more fuzzy.

Guess this throws a bit of mud into it.. but you have to get a bit dirty to have any fun.

dontknowjack

You know I asked that same question to so many different people and never got a straight answer. If TV's native resolution is 720(768) than how can they say it can do 1080i? What I found more perplexing was the fact that they went from 720p native resolution Television to 1080p native resolution. They bypassed 1080i native resolution altogether. Go to your local circuitcity or best buy stores and check it out. Most TVs they sell still have native resolution of 1280x720. Yet industry says these TVs still do 1080i. This is so confusing it will drive you nuts!

BobY

Don't let them mislead you by misusing terms.

"Native resolution" refers *only* to the number of physical pixels on a display (1920 x 1080, 1366 x 768, 1280 x 720, 1024 x 768, etc.). It has nothing to do with what input signals a display can receive.

Any HD display will accept 480i, 480p, 720p or 1080i input signals (some will also accept 1080p signals), the important point is how it actually displays a signal.

LCD displays are the easiest to talk about as they are *all* progressive. They never display an image as interlaced. If you feed them a progressive signal (480p, 720p, 1080p) they will scale the image to the native resolution of the panel directly. If you feed them an interlaced signal (480i, 1080i), they will de-interlace the signal to progressive, then scale the image to the native resolution of the panel.

Scaling involves a mathematical operation called interpolation, which creates a digital simulation of what an image at a given resolution would look like if it were a different resolution.

If you are displaying a 720p signal on an LCD with a native resolution of 1280 x 720, no scaling will occur.
If you are displaying a 720p signal on an LCD with a native resolution of 1920 x 1080, the image will be upscaled from 1280 x 720 to 1920 x 1080.
If you are displaying a 1080i signal on an LCD with a native resolution of 1280 x 720, the signal will be de-interlaced, then downscaled from 1920 x 1080 to 1280 x 720.
If you are displaying a 1080i signal on an LCD with a native resolution of 1920 x 1080, the signal will be de-interlaced and no scaling will occur.
Any signal displayed on an LCD with a native resolution of 1366 x 768 will be scaled, as 1366 x 768 is not a standard HD signal format. 1080i will be de-interlaced and downscaled, 720p will be upscaled.

I don't like the convention of referring to certain displays as 720p or 1080i or 1080p, as it confuses the input signals with how images are shown on the display. I think it's more clear to refer to displays as being either interlaced or progressive, with a particular native resolution. Referring to a progressive display with a native resolution of 1920 x 1080 as a "1080p display" can be confusing as it would apply to displays that did not accept a 1080p input, only a 1080i input, but it would also be incorrect to refer to such displays as a "1080i display" since the image is progressive. A progressive display with a native resolution of 1366 x 768 would be called a "768p display", which is confusing as there is no 768p HD signal format in use.

Usually it is best to display a particular resolution signal on a display with the same resolution. A 720p signal will look best on a progressive display with a native resolution of 1280 x 720. You can view it on a progressive display with a native resolution of 1920 x 1080 and you won't lose any information, but the interpolation process can result in a less sharp picture. A 720p signal will not look very good on an interlaced display as the smooth, fast motion response of the progressive signal will be corrupted by interlacing it for display at a lower frame rate. Information is lost when a 1080i signal is de-interlaced and downscaled for viewing on a progressive display with a native resolution of 1280 x 720 (or 1366 x 768), however a 1080i signal downscaled may still look sharper than a 720p signal upscaled, as downscaling will still preserve some of the details of the higher-resolution image, but upscaling cannot add details that were never there to start with.

acfoster

Thanks for all this it really helps. So if I have understood the points above I can summarise by saying:

* 720p , 1080i etc - These are signals and you just need to make sure your lcd can accept them and convert/deinterlace them to native resolution

* Native Resolution - This is the resolution of the screen 1920x1080, 1280x720 or 1366x769

* All LCD displays are progressive in nature. Non of them are interlaced and it will always deinterlace a 1080i signal before rendering it on the screen.

So even though an lcd has native resolution of 1920x1080 it still displays/renders screen progressive it just has to deinterlace the 1080i first in to a single progressive frame. The difference between the £1500 and £3000 priced 1920x1080 lcds are that the expensive ones can now handle an input signal of 1080p. Hence you could say that a 1080i and 1080p signal look no different on a 1920x1080 lcd as long as the 1080i deinterlace algorithum does its job properly.

So my important decision is not about signal and the old 1080i v 720p debate at all it is on what native resolution I opt for as this implies the conversion that is required to be done to the input signal:

A 1920x1080 is always going to show 1080i signals the best and 720p signals a little less sharper
A 1280x720 has to only to convert 1080i signals down but will show a better image than upscaling 720 to a 1920x1080 display
A 1366x769 has to convert all signals

Is this all correct?

------------------------------------------------------------------------
So I would say I spend my time as follows:

50% DVD Movies and HD when I buy the hardware in the future
25% Normal cable
20% Watching sports again in HD when I buy the hardware
5% Video Games may increase if I buy a PS3

The $100 Question is what resolution is best for this spread given movies tend to be broadcast using 1080i and sport 720p?

Using the info above then would I be correct in saying that the 1920x1080 lcd is best choice for myself as I tend to watch more movies hence less conversion is going to be required to the 1080i and just accept that the 720p signals may look a little less sharp and that I doubt I will be able to notice it anyway on a 40 or 42 inch LCD. Also if I get a PS3 then the 1920x1080 resolution would better meet the consoles output format of 1080p.

Nevada_MO_Guy

Welcome to HDF

Remember it is 1920 or 1280 horizontal and 1080 or 720 vertical.

Should equal a 16:9 ratio for widescreen. 16/9 = 1.7777 (1.778). So 1080 x 1.778 = 1920'ish

ah802

Quote :"1080i and 1080p signal look no different on a 1920x1080 lcd as long as the 1080i deinterlace algorithum does its job properly."

There can be more information in the 1080p signal (e.g. camera) or other source.

I'll step out a bit and say every input signal is going to go through the transforming circuit even if it's native.. (overscan).

If you shop for specs... you may be disappointed, let your eyes be the final arbitrator.

acfoster

Thanks I am planning to let my eyes be the arbetrator just trying to work out whether to go 1920x1080 lcd or for a 720 lcd at the moment

rbinck

If you can afford it, I'd recommend the 1920x1080. For your stated use, it wouldn't need to be able to handle 1080p input, but things change and, again, if you can afford it get one that will handle 1080p input.

__________________
www.highdefinitionblog.com
www.BlogOfHawaii.com

BobY

If you can afford it, definitely get a progressive display with a native resolution of 1920 x 1080. That's the highest resolution we're going to see in consumer HD for many years, so you won't need anything better. If you really want to be future-proof, get a display with a 1080p input, as there will be more products coming in the future with 1080p output and if you really want the ultimate, get one that can either support both 60 Hz and 72 Hz refresh rates, or a 120Hz refresh rate. This will insure the smoothest possible motion response from both video (30/60 Frames-per-second) and movies (24 Frames-per-second).

Not all upscalers soften the image, it depends on the sophistication of the scaler.

A 1080p input shouldn't really add much cost to a display (it's just a different data format--1080p/30 is the same bandwidth as 1080i/30 and 1080p/24 is less bandwidth than 1080i/30. There are no 1080p/60 sources, although I've seen pre-release info on Sony's Blu-Ray player that claims it will support 1080p/60 output--but there's no 1080p/60 content). The difference in cost between two displays of the same resolution might be a result of many things--better black level, faster response time, better scaler, better de-interlacer, superior backlight spectrum, etc.

Personally I think 720p is on the way out. There are only a few HD networks broadcasting in 720p and few if any new HD stations are going to be broadcasting in 720p. The 720p mode on HD DVD players uses an inferior method of scaling that degrades the picture, so they should only be used at 1080i (or hopefully 1080p someday).

The only reason 1280 x 720 displays were made was because 1920 x 1080 displays were cost prohibitive. LCD's are a lot like semiconductor memory and follow the same general technology curve--they will continue to increase in density and decrease in cost. Since HD doesn't need higher density than 1920 x 1080, they will concentrate on getting the cost down. The single largest raw cost component of an LCD is the panel itself, which costs about the same for a given size regardless of the resolution. The biggest factor that affects the final cost is the yield of good displays (the more pixels in the display, the more likely there are to be bad pixels). Once they tweak the manufacturing process so that yields of 1920 x 1080 panels are close to that of 1280 x 720 panels, most manufacturers will switch over to producing only 1920 x 1080 displays as 1280 x 720 displays won't be significantly cheaper and will be perceived as inferior in the marketplace.

At that point, 1280 x 720 displays will get blown out at retail and the only new 1280 x 720 displays will be at the rock bottom from manufacturers who make enough money at the low end that it isn't worth it to upgrade their production lines.

With smaller screen sizes, you may not notice much difference at normal viewing distances. It's like digital photography--if you're making 3" x 5" prints, you probably won't see much of a difference between a 1 Mpixel, 2 Mpixel or 4 Mpixel image, but if you make larger prints you will notice, and at some size you will have a perfectly fine picture at 2 Mpixels that is noticeably pixelated at 1 Mpixels.

Finally, I have to remind you that, as you noted, there are some displays (including many 1280 x 720 displays) that do not de-interlace 1080i properly and instead of downscaling each 1920 x 1080 frame to 1280 x 720, instead upscale each 1920 x 540 field to 1280 x 720. That's a cheat and really isn't even HD anymore...

acfoster

You have all helped me so much and I want to thank you all.

I'm going to hold tight till January next year I think and see if the 1080p LCDs drop into my budget of max 2000 pounds otherwise i will get a standard 1920x1080 at that time that will give me the best picture quality.

Cheers all.

davethedude

As a directv customer, I FINALLY feel I am getting my moneys worth after buying HD tv's. I have a samsung 1080P & a Hitachi 720P. after viewing both for a couple of months now, all I can say is "DO NOT WASTE YOUR MONEY ON A 720P HD TV!!!!!!

Codes20

Thanks for reviving a thread that is over a year old.