Sunday, 24 June 2012

3D TV: LG vs Sony

I posted on 3D TV a while ago, when I got the Sony KDL-55NX813. Now I have had a chance to compare with the LG 55LM960V. The differences are interesting. Overall the LG wins. There are lower models such as the 55LM760T for under £1,750 in Curry's at present.

When we got the Sony, it was the first LED lit LCD TV we had got. We were not impressed, especially with banding effects on dark images. The LG is also LED lit LCD, but the high end LG uses some rear LED lighting with their "Nano" technology. Overall this seems to be a better picture so far.

Like most TVs these days they both seem to come with a whole load of (IMHO) horrid image processing crap. I managed to find how to set the Sony to "full scan" but I don't think I ever managed to turn off the motion processing. The LG allows "Just scan" mode to see the picture as broadcast, and also a "game" mode that turns off the motion processing.

Personally I find it strange that now we have a standard for HD images, that TVs, by default, have modes to overscan the image (scaling up and cropping the edges). It made sense in analogue TV days, but not now. The scaling is done well without anti-aliasing effects but I simply cannot see the point. It is a digital signal, with a defined pixel array, and the TV has that exact array of display elements. As I say, both TVs let me set that, thankfully. Wikipedia article on overscan says "For 1080i/p overscan is undesirable, as it reduces picture quality and 1:1 pixel mapping is preferred." so I am clearly not alone.


As for the motion processing, whilst I can see some logic in the fact that as modern TVs can update the screen faster that the original image (e.g. 100Hz not 50Hz) then maybe they want to make intermediate frames. However, ultimately, you are not adding information. When it works, it works well, fair enough, but when it goes wrong it is really annoying. No system can be perfect. Examples of where it goes wrong are things like the slow scrolling credits at the end of films, and slowly scrolling horizontal text you get on news channels. Both can judder or do strange things, even making them unreadable. Even when not some slow scrolling text you can get odd juddering on panning shots. With the LG it looks like I have managed to turn this off. Watching the F1, all the motion was smooth except the slowed replays, but that is as broadcast. The trick in the case of the LG was to select "game" mode.

The sound is not bad, but we have a simple sound system (Sony HT-AS5) which is much better than the TV speakers on either. With the Sony TV it pretty much just works, as you would expect. TV volume control works the sound system not its own speakers, etc. It also controls power on/off. It uses Audio Return Channel (ARC) if another source is selected on the TV. It was still a tad strange on the Sony in that regardless of the audio source (even when 5.1 stereo) it only used the front speakers unless you set "Theatre" mode. This mode also adjusted the picture! The mode was forgotten every time you turned it off. Why would you ever not want the audio to work properly and use all the speakers? Mad!

Sadly the LG does not understand the sound system. Even though it, and the AV system, do ARC, the sound system produces no sound. I can turn off the TV speakers and use the AV system in-line, but that then means faffing with the audio/video sync and means no sound on other TV sources (such as digital tuner). I may go find an audio optical fibre cable and see if that will work. Who knows if it will drive all speakers?!

Anyway, lots about the TV and sound and none about 3D yet!

The LG uses circular polarized filters in front of the screen and uses passive glasses. This is a massive improvement in 3D watching. Massive! You use the same cheap glasses you get for cinema use. They are light. They do not flicker. They do not need batteries. With the Sony (and most, if not all, other 3D TVs) the glasses use LCD shutters and are heavier and flicker. The LG technology is much better - it means there is no flicker at all on the 3D. It also means the viewing angle is better (i.e. where in the room you sit) and the angle of your head is not critical (which is much nicer).

Glasses on left. Click to see fill size for detail.
There is one disadvantage in the way LG are doing it though, and this is something I do hope they fix in a later model. Essentially, as they show both images at once, you have some compromise. Without shutters (and hence flickering) you cannot show the same pixels for left and right in the same physical space (well, not yet). So they alternate which lines are left and right eye. This means that you see half the lines (540 not 1080) in each eye. There is a slight vertical offset, buyeyes can cope with that, generally. Sadly, I can notice this as it is stripy, but it is a very subtle effect, and to be honest the reduced resolution is worth it for the massively better usage that you get with the passive glasses. The fix is for them to do a 2160 line panel and have alternate lines so allowing full HD 3D with passive glasses.

Another big issue with the shutter glasses was bleed through or ghosting where you would see some of the other eye image like a sort of shadow. I see none of that on the LG. As you can see from the picture about, the filtering is perfect.

There is an irony which is that 3D is usually transmitted as left/right (at least by Sky, anyway), which reduces from 1920*1080 to 960*1080. But the LG 3D system then makes the images in each eye 960*540. If sky transmitted top/bottom, making the image 1920*540 then the LG system would not lose any more resolution. As the effect of 3D relies on very slight differences in horizontal placement, this would give a better 3D effect as it would maintain the 1920 horizontal resolution. Given Sky seem to like the LG 3D sets, it is a shame they are not switching to (or offering an option of) this mode of transmission.

They do include 4 normal glasses, one clip on set (which I can use at the cinema), and two game glasses. The game glasses are left+left and right+right which means a split screen game can be played by two players as full screen seeing only their own game. There is some input lag which is not ideal for gaming, but the effect is pretty good. Also, this does mean that for those few people who find even cinema 3D to be uncomfortable, they can watch a 3D film with the rest of the family in the cinema, in 2D, by using the gaming glasses.

So, I would recommend the LG over the Sony :-
  • No flicker at all
  • Light weight glasses - same as cinema glasses
  • Cheap glasses
  • No batteries in glasses
  • Better viewing angle in room
  • Allows head to be at different angles
  • No bleed through (seeing ghost of other eye's image)
  • Dual player game mode glasses included (left+left and right+right)
Negative points
  • Loss of vertical resolution
  • Some striping because of loss of vertical resolution if close to screen

5 comments:

  1. Curious about ghosting on active vs passive. I would have expected more ghosting on passive polarised glasses,, although I have noticed it on my Samsung active set.

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    1. All down to timing - there are settings to make the shutter gap smaller, and that helps a bit but makes it a lot darker. The polarization itself just works I think.

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    2. The problem (apparently) with the polarization scheme is that you can't lay down on the Sofa and watch the 3D output.

      A friend of mine tried in and found that lying down, his head was effectively rotated from the expected angle . So the glasses where no longer polarized 'correctly'.

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    3. Err, not quite right. My understanding is that the shutter glasses on TVs like the Sony are linear polarized and so only work in a narrow angle. This is because they are LCD shutters. However (and I just went and checked this to be sure) the circular polarization used on the LG and cinema glasses works exactly the same at all angles, even 90 degress. So lying down you still see perfectly the left eye image in the left eye and the right eye image in the right eye. The problem is that they are no longer left and right for the depth in the image as your head is on one side, and hence the 3D effect breaks totally - but this is not an issue with the polarization. i.e. if someone made a film for viewing at 90 degrees it would work on the LG (when viewed at 90 degress) but not on the Sony.

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  2. Couple of follow up points... (a) It seems the Sony sound system and sky boxes are known for not passing more than 2 channels over HDMI, d'oh, so the TV theater mode was (as I ofter suspected) just feeding the same two channels to the rear speakers. Much better now. And (b) the "game" mode disables some of the useful settings on the LG, like the black level handling, so better done with the motion handling turned off (a separate setting).

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