49 replies to this topic

[drsmith]

In my search for a suitable large screen TV over the past 6 months there has been one aspect that has ruled out most units and that is not being able to eliminate overscan on HDMI from the unit itself.

Whilst there has been extensive discussion on these forums on the pros and cons of overscan and I understand the merits of overscan for watching TV/DVD, there is a growing trend for users to attach these display devices to HTPC's and use them for PC based applications that go beyond watching TV and DVD. The advantages of no overscan for PC uses include proper display of the PC desktop and 1:1 pixel mapping.

With some units the level of overscan on HDMI is adjustable (the Sony rear pro 3LCD's for example), but there is no setting to eliminate it completely. Surely from this point it would be trivial for the manufacturers to provide the option of eliminating overscan on their TV's.

It is time the manufacturers abandoned excuses like "it's only a TV" and provided this simple option for the growing number of users that wish to use these units for a broader range of tasks than watching TV/DVD.

For units costing thousands of dollars, it's not much to ask.

[laurie]

Point is though Dr Smith how many mum & dads are affected by this   I agree totally with what you are saying by the way  

cheers laurie

[Preemo]

Dr S, which large models do support 1:1 pixel mapping ?

[Owen]

The issue of 1:1 mapping and overscan are independent on RPTV’s
All RPTV’s have overscan designed into the optics, so that when they are displaying there native resolution there is always overscan. The outer most pixels of the display are hidden behind the screen bezel and can never be visible.
The advantage of this is that no scaling is required to provide necessary overscan if the source video matches the display resolution, unlike flat panel displays which must scale to provide overscan.

There is no way to adjust out overscan in the service menu or user menu without image scaling and loosing 1:1 mapping.
The only way to address this issue directly in the display is to fit a zoom lens to the light engine or reposition the light engine closer to the mirror.

If you are using a PC, it is normally possible to use a custom resolution inside the native resolution of the display to reduce or eliminate overscan.
In this scenario the video card is outputting a standard video signal of say 1280x720 to drive the 720p display but the active area of the screen (desktop area) is reduced to say 1244x700 or whatever is required to eliminate overscan.
In this way overscan is removed and 1:1 mapping is maintained.

A small amount of overscan should be maintained to provide nice clean edges to the screen. This small amount has no affect on the usability of the Windows desktop or PC applications. People routinely overscan CRT PC monitors slightly and they don’t complain.

I don’t know if the Sony LCD accepts and displays its native resolution 1:1 mapped from a HDMI input, but the SXRD models do.

[steen]

Owen, on Oct 25 2006, 04:19 PM, said:

I don’t know if the Sony LCD accepts and displays its native resolution 1:1 mapped from a HDMI input, but the SXRD models do.

IIRC the Sony X series LCD support 1:1 pixel map via HDMI. I have not personally verified this.

[treble]

on the Bravia 3LCD via HDMI ....I think the 1:1 perfect fit desktop area is 1228 x 680. The 680 is exact and I think the width is about 1228. At 1232 it looks about 4 pixels too wide.... 2 either side

I haven't been able to drop those 4 pixels. Using my video card, the adjustment is in set increments when you click the up/down buttons. The increment is 6 pixels I think.... I am sure you can paste your exact value in but I have not tried this yet..I intended to do this tonight and see....

the TV also has a trim function which looks like just a 1 or 2 pixels adjustment... again I will be looking at this more closely tonight

treb

[RabidWolve]

Dumb question but does 1.1 pixel mapping overscan problems over hdmi only apply to pc's or will it apply to Blue Ray/PS3 also?

[Owen]

Any picture size adjustments on the TV will introduce scaling, so you will have to experiment to find the setting that provides 1:1.

RabidWolve, on Oct 25 2006, 04:44 PM, said:

Dumb question but does 1.1 pixel mapping overscan problems over hdmi only apply to pc's or will it apply to Blue Ray/PS3 also?

It applies to everything.
For display of video a little overscan is preferable, and in many cases required for clean edges.

[MLXXX]

drsmith, on Oct 25 2006, 01:47 PM, said:

Surely from this point it would be trivial for the manufacturers to provide the option of eliminating overscan on their TV's.

It is time the manufacturers abandoned excuses like "it's only a TV" and provided this simple option for the growing number of users that wish to use these units for a broader range of tasks than watching TV/DVD.

For units costing thousands of dollars, it's not much to ask.

I fully support Dr Smith's open letter.

It seems extraordinary to waste the potential resolution of an LCD or plasma display by incorporating non-defeatable overscanning that operates even when the display is sent information at its native resolution.

I have a hunch though that in some cases the option of eliminating overscan may not necessarily be as trivial to implement as one would think.  I have no real evidence.  The following dot points are just guesses:

• If a display is marketed as having 1:1 capability suitable for connection of a PC, that would require no noticeable light leakage between adjacent pixels.  Also the display driving circuitry would have to be able to have fully independent control of each pixel. Adjacent pixels would need to have closely matched intensity responses and colour responses.  Are the panels intended for TV use up to the grade for use as PC monitors?  If the same model of panel can be incorporated into either a PC monitor, or a digital TV, are only the more uniform specimens of the panel used in the more demanding role of PC monitor?  What of the non-reflective material that is laid over a TV panel? In reducing reflection of light external to the display does it slightly diffuse light emanating from the display?  Such diffusion of light could be of no consequence for real world video, but noticeably affect PC graphics.
  
  
• Some manufacturers seem bent on digitally "enhancing" the video signal.  Some of that enhancement might be permanently built in to chips used to drive the panel.  If a pristine PC graphic were fed in and the TV displayed it 1:1 but with "sharpening" or "colour enrichment" or "filtering", the result might look odd.

The second dot point could be overcome with more flexibly controllable chips.

Aspects of the first dot might be more difficult to overcome, but speaking personally, I'd prefer a slightly fuzzy 1:1 pixel mode than an even fuzzier non 1:1 mode!  Again speaking for myself, when I lash out in the next 6 months or so and spend several thousand dollars on a 1920 x 1080 display primarily for video use , I will give a wide berth to any LCD or plasma display that does not offer a 1:1 pixel mode.

Still pictures from a domestic digital camera

And I will want to display still digital photos without any last minute rescaling by the display.

If my 5 Megapixel still camera takes a picture it does so in a much higher pixel format than 1920 x 1080, which is only about 2 Megapixels.

When I display that still camera picture using my PC video card set to 1920 x 1080, on my PC CRT monitor, I can see it is a pristine image, full of detail, albeit downsampled to fit onto the 1920 x 1080 raster of the CRT monitor.  I do not want to lose that detail when I connect my PC to a large TV 1920 x 1080 display screen.

The same remarks would apply when feeding a lower resolution LCD or plasma display at its native resolution.  Why throw away some of that already limited resolution by compulsory overscanning?  It makes no sense.

Freedom of choice

I have no objection to a manufacturer making overscanning the default mode for a modern LCD or plasma television display, but please do not make it the only mode available for an external source at native resolution!

[Owen]

Over scanning does not necessarily through away any resolution, it just clips of the edge of the image. In the case of the Sony SXRD it certainly does not.

Would not you be better of with the display that gives you the best image quality, rather then the one that provides 1:1 with zero overscan.
It definitely does not follow that the displays that can be 1:1 mapped with zero overscan provide the best quality images.
You seem to have your priorities all mixed up mate.

[MLXXX]

Owen, on Oct 25 2006, 11:59 PM, said:

It definitely does not follow that the displays that can be 1:1 mapped with zero overscan provide the best quality images.
You seem to have your priorities all mixed up mate.

Cobber, I didn't say that I will buy any display that offers 1:1 mapping, regardless of quality.

What I did write, is that I'll give a wide berth to a display that doesn't offer 1:1 mapping.

[Owen]

MLXXX, on Oct 26 2006, 12:16 AM, said:

Cobber, I didn't say that I will buy any display that offers 1:1 mapping, regardless of quality.

What I did write, is that I'll give a wide berth to a display that doesn't offer 1:1 mapping.

Your loss dude.

[drsmith]

laurie, on Oct 25 2006, 02:12 PM, said:

Point is though Dr Smith how many mum & dads are affected by this   I agree totally with what you are saying by the way  

cheers laurie

Not many at the moment and this would be one reason the manufacturers are not interested. The units are selling like hot cakes, mainly because of their size.

Preemo, on Oct 25 2006, 02:16 PM, said:

Dr S, which large models do support 1:1 pixel mapping ?

Not many to my knowledge. A Pyrod 37" 1080p LCD did a few months ago but the picture quality on that unit was not the best and at 37" it's not all that big either.

Owen, on Oct 25 2006, 11:59 PM, said:

Would not you be better of with the display that gives you the best image quality, rather then the one that provides 1:1 with zero overscan.

We would be better off if we could choose between overscan and no overscan.

[MLXXX]

Owen, on Oct 26 2006, 12:19 AM, said:

Your loss dude.

I think it very unlikely I will lose out.

The panel I intend to purchase will be of very good quality and offer 1:1 pixel mapping.

I have no objection to a panel that merely clips away the outer edges of a 1:1 pixel mapped image, as that should leave the quality of what is displayed intact.  However, I would expect the clipping to be able to be disabled if desired.  For example if watching a Blu-ray or HD-DVD movie I would like to see all of the frame, at 1:1 pixel mapping.  I think it unlikely there would be objectionable spurious material at the edges.  However, if there were, an adjustable "outer edge clipping border" would serve a useful function.

[Owen]

drsmith, on Oct 26 2006, 12:33 AM, said:

We would be better off if we could choose between overscan and no overscan.

Sure it would.

[Owen]

MLXXX, on Oct 26 2006, 12:38 AM, said:

I think it very unlikely I will lose out.

You will if you chose 1:1 over picture quality.

MLXXX, on Oct 26 2006, 12:38 AM, said:

The panel I intend to purchase will be of very good quality and offer 1:1 pixel mapping.

But is it the best quality image regardless of 1:1?

MLXXX, on Oct 26 2006, 12:38 AM, said:

I have no objection to a panel that merely clips away the outer edges of a 1:1 pixel mapped image, as that should leave the quality of what is displayed intact.  However, I would expect the clipping to be able to be disabled if desired.  For example if watching a Blu-ray or HD-DVD movie I would like to see all of the frame, at 1:1 pixel mapping.  I think it unlikely there would be objectionable spurious material at the edges.  However, if there were, an adjustable "outer edge clipping border" would serve a useful function.

I don’t see why BluRay or HDDVD will be different to other 1080 content.
Most of it requires a little overscan, at least the most of the Terabyte of 1080 content I have does.

I know I come across as anti 1:1 but that is not the case at all. The truth is I have learned that it is not important, so I don’t care one way or the other.
I will always choose the best picture quality over everything else.

[treble]

I tried 2 resolutions tonight. The previous 1232x680 and I also used 1216x680. Seems I maxed the number of customs resolutions I can add. need to edit them from here...

Recap:
1232x680 is a tight fit on the vertical but overscan on horizontal

1216x680 looks like its a fit on both

I did as Owen suggestd on the #lcd thread which was to remove Noise reduction. I also found Black Corrector in Picture->Advanced Video -> Black Corrector. Those are only additional changes.

I compared a short segment from ABC. I see no huge difference, perhaps its slightly better @ 1232x680. Its like 16.3:9 aspect ratio I think. The 1216x680 is 16.1x680, so if anything that resolution should be ok. Ideally we should be looking for 1208x680 I think to get back to 16:9

at this point I can go no further I find that the ATI control will allow me to delete resolutions but not add back in. So i am down to 1 custom resolution until I can get that sorted.

treb

[MLXXX]

Owen, on Oct 26 2006, 12:57 AM, said:

I don’t see why BluRay or HDDVD will be different to other 1080 content.
Most of it requires a little overscan, at least the most of the Terabyte of 1080 content I have does.

Owen, I am interested in accessing a small sample of BluRay or HDVD content, even if only a single frame.  My internet searches to date have been unsuccessful.

I have not been all that impressed with 1080 content that is downloadable free of charge.  A lot of the WMV format samples I have seen are around 100 Megabytes and last around 100 seconds, i.e an average bit-rate of 1 Megabyte or 8 Megabits per second.  That bit rate is similar to DVDs which can operate at up to 9.8Mbps.  If all we needed for good quality 1080 content was to shift away from an MPEG2 codec to an efficient WMV or AVC codec but maintain the DVD video bit-rate why didn't that occur?  As you would know, HDDVD offers video at up to 28Mbps, with an AVC codec option.

The PQ of HDDVD and Bluray will naturally be better than the off-air Today pic crop I have posted in another thread (Real Time Video Sharpening For Hd Displays), but I suspect will not be as good as the London Tower Bridge pic I obtained here:- http://pixelmapping....pping explained

I find it difficult to discuss in meaningful detail how BluRay and HDVD will be affected by rescaling for overscanning purposes, without a sample of the video.  It is a bit surprising we have not been offered a short downloadable trailer of an HDDVD or Bluray disk.  I presume that a lot of effort will have gone into maximizing the video quality transferred to these disks.

[Owen]

I have 1080 H.264 content at 20Mbps and Mpg2 at over 30Mbps.
DVHS has been around for years and offers 28.5Mbps.
The extra bit rate does not make the kind difference you would expect.
There is less pixilation in motion, but overall image clarity is not much different to 18Mbps Mpg2.
Even 40Mbps 1080 is VERY compressed video, and to get close to lossless quality I would expect we would need over 100Mbps with any codec.
Uncompressed 1080p 24 required close to 1.5 Gigabits per second, so even 100Mbps is very compressed.

[MLXXX]

Owen, on Oct 26 2006, 02:14 AM, said:

I have 1080 H.264 content at 20Mbps and Mpg2 at over 30Mbps.

Thanks Owen.  Yes I have seen a little bit of higher bit-rate material and have to agree it is not as spectacular as one might expect.

******************************************************************************

Is Treble on the right track?  Does the Bravia 3LCD actually support 1:1 pixel mapping when connected to a PC?  I couldn't find a manual on the Sony site.  The model has a native resolution of 1280 x 720.

It is one thing to shrink the desktop size to fit it comfortably inside an LCD screen's display area.  It is an entirely separate question whether the LCD screen is displaying the desktop at 1:1 pixel mapping.

Sometimes an LCD TV is only triggered to rescale and overscan when fed an input signal with certain standard resolutions.  Changing the video card setting to a slightly less than native resolution can cause the LCD TV to drop out of rescaling mode and operate 1:1 (or not work at all!).

If a PC desktop is not being displayed in 1:1 mode, it will be somewhat blurry on the LCD TV screen.

[treble]

MLXXX these are good points. Am I on the right track. I do not think I am changing my desktop area, rather I am adjusting the HiDef monitor options in the ATI Catalyst application. I choose a HiDef resolution of 720 then adjust number of available pixels from there.... its the question tho..what is my system doing? Removing some pixels from use is what I understood but you are not running 1280x720 if you remove pixels now are you?

Given what Owen has said, i understood the set is projecting a bigger image than there is screen real estate for...hence the overscan. So am I shrinking the desktop or reducing the area that the tv is projecting onto?

and what should I be doing... apart from enjoying my tv?
treb

[MLXXX]

treb,
I see u have a rear-projection tv.  I don't know much about that technology!

As you know, with ATI Catalyst you can make small changes to desktop height, width, vertical positioning and horizontal positioning whilst operating at any given video card resolution setting.  You just click with your mouse and can make fine adjustments and observe the effects.  These adjustments do not of themselves prevent 1:1 mapping.

But you have gone further, with custom resolutions that are less than the native panel resolution of 1280 x 720.  I presume this is because there is still some overscan of the desktop, even with the Catalyst fine adjustments set for minimum desktop geometry, for a video card resolution of 1280x720.

What I don't know is whether the circuitry driving the 1280x720 LCD light source inside your rear-pro TV automatically scales up a 1280 x 720 input (and input at your lower custom resolutions) to a bigger dimensioned picture and then crops away the outer resampled pixels, so that the 1280x720 panel always receives a rescaled and cropped picture.  If the circuitry always does that, then you will not be getting 1:1 pixel mapping.

Perhaps someone else can "throw some light" *bad pun* on this.

The blurring of text should be quite noticeable if there is rescaling, just as there is if you feed a standard computer LCD monitor a non-native resolution it has to rescale.

[Owen]

When you had a HDTV connected to a PC (assuming the PC knows it is a HDTV) and adjust picture size in the Catalyst Control Centre, you are creating a desktop resolution inside a standard HDTV resolution, in this case 720p resolution.
If you where to connect the PC output to a display that does not over scan, you would see a 1280x720 image with a black border and a lower resolution desktop image in the middle 1:1 mapped. That is assuming that a 720p input is 1:1 mapped on your display in the first place, it probably is.

If you wanted to view 720p video 1:1 mapped on the reduced size desktop, you need a video playback application that allows the pixel size of the playback window to be defined, most good players allow this. The playback window can be bigger then the desktop, in this case 1280x720, so you will get an image with exactly the same overscan as you would have had if you had not created a custom desktop resolution and 1:1 mapping of the video image.
If you want a video image without overscan, the image must be scaled to fit the custom desktop resolution (visible area of the screen). No big deal either way.

[drsmith]

I cannot see how applying a custom resolution to compensate for overscan can achieve 1:1 pixel mapping.

I would have thought that the only way to achieve 1:1 pixel mapping would be to eliminate the overscan at the display level or (for those graphics cards that offer it) apply underscan that compensates exactly for the overscan on the display device.

[Owen]

Think about it a bit more mate.
The LCD panels are 1280x720 and you run them at that res.
The pixels round the edge are projected onto the screen bezel are not visible ever.
The display driver creates a 1280x720p image with a black border, and the desktop occupying only a defined centre area of the 1280x720 image.
That is what happens when you adjust the drivers to compensate for overscan with a HDTV connected to a PC.
The desktop area will be 1:1 mapped.