HDTV Overscan/Underscan discussion

Mr Latte · 5 Feb 2006 at 15:05

DO YOU KNOW YOUR HDTV IS PROBABLY HIDING VIDEO!

This is aimed more for users that can compare standard sources like DVD playback from a DVD player to the same thing on their PC connected to a HDTV display with custom resolutions.

My Sony V40 internal scaler seems to use a little too much overscan for my liking and its a little on the annoying side.

Questions
1. If possible can some others perhaps go through this process im trying on their models.
2. Is Overscan a problem with a lot of HDTVs and how common may this be?
3. Maybe its just a problem with my model/set?

Ive only really noticed this by accident during HTPC connection.
On my Sony 40" HDTV approx 3.5cm left/right and 1cm+ top/bottom is missing in the overscan process
* to confirm top/bottom size

What this means is when conneting any device to your display directly it probably goes through the same process with the overscan such as this DVD example.

One advantage or difference with PC connectivity though is i can control this loss of video with my HTPC custom resolutions so that i virtually miss nothing. Have any of you guys compared standard sources like DVD players against a PC with DVD set at 720p resolution and also custom PC resolutions like below to see what your display actually hides?

My Latest Settings on my HTPC are:
1200x700 or 1200x692 meaning you get all the video fullscreen but next to none in overscan.

Mr Latte · 5 Feb 2006 at 17:44

Right well hope this helps illustrate the problem.

Not only can HTPCs offer better quality as mentioned in the other thread but just look at the advantage custom scaling has over my HDTVs internal scaler with regards to overscan.

Stealth NTSC 2:35 Widescreen Via HTPC "Theatretek Software" @ 1200x700 Custom Resolution DVI-HDMI Nvidia 6600

Mr Latte · 5 Feb 2006 at 17:47

Stealth 2:35 Widescreen Via DVD Player 480p Component Using Tvs Scaler

The 2:35 image from DVD Player is slightly bigger in height because of the Tvs scaling but can you see whats missing?

Mr Latte · 5 Feb 2006 at 17:50

Heres the missing content highlighted, its worse than i first thought and is quite large left/right.

Mr Latte · 5 Feb 2006 at 17:53

DVD Player Closeup

*DVD Pause leaves Jaggies ignore these

HTPC Closeup

Mr Latte · 5 Feb 2006 at 17:55

DVD Player Closeup 2

*barrel distortion is from the camera

HTPC Closeup 2

Mr Latte · 5 Feb 2006 at 18:05

I havnt yet closely compared 1:85 / 16:9 ratio movies but its bound to loss information top/bottom as well although not quite as much.

Perhaps the Sony Bravia range is extra safe or its my model with regards this overscan issue but id like to here from anyone else.

Mr Latte · 5 Feb 2006 at 18:24

The first images contain the information regarding connections
DVD 480p via component Vs PC custom 720p res at 1200x700
(underscan applied to allow full video)

"Dial out" what you mean are you talking about phones now?

Please note the PC isnt the problem its the Tvs internal scaler being over-safe with overscan and its running in normal wide mode not zoomed in any way.

Call me picky but thats a lot of overscan...

Mr Latte · 5 Feb 2006 at 19:35

UPDATE:

Service menu offers nothing.

Mr Latte · 5 Feb 2006 at 20:16

Further Testing:

Tried the display at various resolutions now to emulate different "AV Seperates" sources.

1. 720x480 (HDTV 480p)
2. 1280x720 (HDTV 720p)
3. 1920x1080 (HDTV 1080i)

The reason for doing this is that its let me compare the "Overscan" for each common video source (1,2,3) and compare the "used scene above" for direct overscan comparison.

As i thought the internal scaler scales less with each higher resolution source.
Therefore DVDs will loose more (approx 3.5cm or 8%) than 720p HTDV material (approx 2.5 cm or 6%) and 1080i HDTV will loose the least (approx 1cm 2%) in overscan. These are approximations but highlight that standard defination suffers by far the worst.

It may be how the internal scaler within the current Sony Bravia range works so common gents lets here how your HDTV suffers...

Mr Latte · 5 Feb 2006 at 20:38

ripkord said:
Hmm :/ Its annoying me now. Do you own an xbox360 by any chance?

edit

- no matter, I was going to ask a daft question

Yes

I cant tell with Sky as i havnt that connected via my PC.
My DVD comparison was with both 480p and 480i with the two DVD players.

Mr Latte · 5 Feb 2006 at 20:58

ripkord said:
whats the overscan like from the 360?
shame you cant play dvds from xbox360 MCE as you have the 4 choices of screen type to choose from, if you know what I mean.

See above post i tested both 720p and 1080i resolutions from the HTPC desktop at those resolutions and compared.

Anything with those resolutions will have the same effect X360, SkyHD or DVD-HD / BLU-RAY etc

Mr Latte · 5 Feb 2006 at 21:05

ripkord said:
yeah but within MCE you can choose from 4:3, 16:9 and 2.35:1.

Isnt that some form of zoom feature though?
Im guessing as i never tried the X360 for DVDs its not used in the same room as the TV either.

Mr Latte · 5 Feb 2006 at 22:31

Users of other HDTVs?

Mr Latte · 6 Feb 2006 at 00:19

Andy firstly thanks for going to the bother.
Interesting that when you changed the upscaling from 480p - 1080i the Pioneer made no difference. Can i ask if this was done via direct connection to the display or through the media box and did you compare it each way to the other? Not sure what res you run the PC in but youll definately need a custom res to get more image. Use the underscan tool within your GFX settings in the HDTV segment.

Id say your overscan showen is consistant with my 720p overscan.
Maybe the Pioneer just handles it better.

[SIZE=-2]MY Kit Sony SKDLV40A12U / Sony DAV-DZ 700 / Sony RDR-HX 710 / Sony Sky VTX-S760U / Alphason A03 Piano Black [/SIZE]

Caged, i can live with a little overscan but i think ive showed an example that this is a tad much. I know were not talking Pan/Scan here but i want what the director intended not 8% or whatever of it missing if i can help it. By the way your link shows exactly the advantages yet you seem to think "oh nothing important is missing" * Cue Queen "I Want It All"

What may be interesting is if others compare with their sets with any material and if its possible to help them discover that perhaps a HTPC with custom res may have an advantage.

Mr Latte · 6 Feb 2006 at 12:42

Overscan has always annoyed me, my last CRT "Panasonic 36PD30" was even tweaked via the service menu.

I agree to an extent its not that big of an issue but with so much being aparent here i think its worth others checking if their a little bothered. Theirs no need for such an excessive amount as whats happening on mine, maybe the bravia is an exception.

Ive already showed the solution with custom PC res that underscans so that none of the image is missing. Having 1:1 HDTV or the display scale to its native from the custom PC res doesnt matter in this respect you still get the benifit of the tweaked "underscan" image, thats the whole point of underscan.

1:1 would be nice yes but is overrated for movies.
Go into any electrical dealer and look at a HDTV display and tell me which are 1:1 and those that arnt, imo its really only more aparent with text.

37" Plasmas 1024x768 res 50" Plasmas 1366x768 Majority of LCDs 1366x768 some LCDs 1280x720m all HDTV but can you look and tell whats what?

Mr Latte · 6 Feb 2006 at 19:17

Look forward to more tests...

QUESTIONS:
davetherave2 what Sony do you have?
attu is yours 43" or 50"?

This stuck in my head today so heres some thoughts:

Take 1280x720 thats a 720p source displayed on a 1366x768 panel which the majority of Panels are.

Lets Count:
So 720p thats 921600 Pixels that has to be filled into a 1049088 pixel area
The difference then is 127488 pixels
Taking this difference we work out the scaling required.
As a percentage of the original source this requires approx 13.5 scaled increase to fill a 1366x768 panel

Keep that thought:
Hold on that seems quite a lot requiring an approx 13.5 increase in size to fit?
Now personally id of thought "overscan" on flat display technology would have been minimal which perhaps isnt the case.

Lets take an estimated guess and say an average HDTV with 720p material
overscans 5% left/right and 3%top/bottom. Ok so thats a combined 8%

If then approx 13.5% was the scaled value required to fill the 1366x768 panel less the 8% hidden in overscan then really only approx 5% scaling is actually seen by the viewer, is this why overscan is applied so scaling doesnt look overscaled and picture quality is maintained?

Quick summary:
720p source scaled to a 1366x768 panel is approx 13.5% increase
Average HDTV (may have) 8% overall overscan
Therefore the viewed scaled area is only approx 5.5% scaled from the original 720p source

Sorry if this is going a bit far but needed to get it off my chest.
However it seems overscan & scaling go hand in hand. Its obvious a DVD requires a lot more scaling with its 720x480 to fit a 1366x768 panel and the reason why so much was lost in the overscan process.

Of course different brands and models will use different scalers and scaling techniques but none the less Sonys DVD scaling is a bit dissapointing with loosing so much on this particular model, or really is it more common than some may think?

Mr Latte · 6 Feb 2006 at 20:49

True HTPCs on HDTVs is a very large MINEFIELD.

Another problem is many models use VGA with 1:1. However id like to see these owners try HD-DVD or BLU-RAY come Vista etc. VGA is not compatible with HDCP so anyone expecting to adopt HiDef Disc formats into their HTPCs are gonna be mightly dissapointed.

Id rather have my HDMI connection with "my own overscan preferance" settling for its minor scaling to native anyday. My custom res still give me more video information with 720p and 1080i movies so overall you gain with every video source over an internal HDTV scaler, if overscan does indeed bother the person.

The Sony is one of the better recent models for HTPC although the Pioneer/Panasonic Plasmas are popular too, now i wonder how they all compare with DVD overscan, mmmm

Mr Latte · 6 Feb 2006 at 21:07

Shimmyhill said:
HDCP is irrelevant, it is almost as useful as macrovision.

The issue here is that DVI + HDMI where rushed out and do not have the flexability of VGA. Look at all the HDMI revisions and they are gradually adding missing res/refresh combo's.

Sorry youll have to re-explain what you mean.
In your opnion whats so good with VGA, heres some pointers you can answer back on.

ADV
1:1 Pixel Mapping is possible but not even always available depending on model
Every PC has one

DISADVANTAGES
Not as sharp requires a digital-analouge conversion
VGA isnt HDCP compatible nor upgradeable with upcoming DRM protected Hi-def material
PCs are converging with consumer products using HDMI connections
Windows Viista with the latest version of MCE will require HDCP compatibility. This includes 95% of TFTs they arnt HDCP compatible even though they are DVI based.

HDCP
This is fully adaptable, say a company launches a macrovision style bug blaster for HDCP. You may think you have the protection beat, but all they do is then program the digital keys that this device uses and the list of disallowed/illegal keys will be ever growing and they can be pumped down through your internet or put on each individual disc. It will then cut the digital handshake between your display as it detects the illegal keys for the now rouge device.

Who knows for sure but this is what ive read, (Engadget?) i doubt the protection will easily be beaten when its upgradable this way.

Mr Latte · 7 Feb 2006 at 00:33

Can i ask if youve tried or compared VGA to DVI-HDMI via PC connection.

You mentioned

"Eventually I stumbled on a solution by luck rather than by design of using a resolution of 1232*692 this allows me to see the whole of the desktop/movies from my htpc. "

My friend has onboard intel GFX (no HDTV modes) though i wasnt sure if the model only accepted 1024x768 as it mentioned this within the manual. Please just to confirm then that with this Sony model you have and that HDMI is best with possibly the only way of getting larger than 1024 resolution via PC?
He should be chuffed when i tell him...

On a further note have you tried a custom 1920x1080 desktop with "interlaced"