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Topic # 13115 23-Apr-2007 13:13
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Someone linked me this article: http://www.tvnz.tx.co.nz/planit/issue18_2007/widescreen.html

It says TVNZ are moving to widescreen for freeview and sky on the 31st july.  There is nothing on their website that I could see but if its true then - yay!




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Reply # 68188 23-Apr-2007 17:19
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While on analog it shouldn't be any different from now, right?
Are they going to broadcast any 16:9 content on analog? they don't seem to say
(it's just that I don't like seeing those dishes dangling from chimneys... )

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  Reply # 68193 23-Apr-2007 17:47
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ZiglioNZ: While on analog it shouldn't be any different from now, right?

Are they going to broadcast any 16:9 content on analog? they don't seem to say

(it's just that I don't like seeing those dishes dangling from chimneys... )


You can't broadcast 16:9 content over analogue.

I suspect TVNZ will be doing exactly the same as TV3, broadcasting 16:9 on digital and still retaining 4:3 and 14:9 broadcasts on analogue.


 
 
 
 


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  Reply # 68605 26-Apr-2007 23:18
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This may be a stupid question, but why can't you broadcast 16:9 on Analouge?

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  Reply # 68611 27-Apr-2007 00:04
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pjamieson: This may be a stupid question, but why can't you broadcast 16:9 on Analouge?

No, not a stupid question at all...

The analogue TV Broadcasting System we use in NZ is called the PAL system.  It manages to cram 625 lines of video (of which only 576 are viewable) into a 7MHz channel spacing.  This system was designed in the 1950s, well before any kind of digital video processing was feasible.

So you didn't have any MPEG compression which nowadays allows several channels to be crammed into that same 7MHz of bandwidth.

Using the maximum available Luminance (monochrome) bandwidth within that 7MHz channel just barely allows a 5MHz black-and-white image to be transmitted.  The Chroma (colour) bandwidth is far less than that, at around 1.3MHz which gives a passable picture (if you don't look too closely) because of the perception qualities of the human eye.

The point I am making here, is that the available bandwidth contained within a 7MHz VHF (or 8MHz UHF) channel is just barely adequate for an uncompressed 4:3 analogue video signal and accompanying stereo sound channels.  If you were to try and squeeze a 16:9 analogue video signal through that channel, you would end up with a noticeable lack of resolution, particularly in the Chroma area.  It would amount to a blurry mess, unpleasant to watch on all but the lowest bandwidth material.

I hope that all makes sense.

Cheers,
Grant.

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  Reply # 68612 27-Apr-2007 00:14
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Cheers Grant, nice job of making that easy to understand

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  Reply # 68640 27-Apr-2007 11:11
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There is absolutly no reason that you cannot transmit anamorphic 16:9 images through an analog network, infact this is exactly what happens. SD broadcasts only have 4:3 frames, nothing else, to transmit 16:9 anamorphic compression is applied to the 16:9 frames and inserted into a 4:3 frame. This is exactly what happens on DVD, DVB, and all other systems.

Infact in France there are were a couple of local broadcasters that transmitted full height 16:9 anamorphic movies on a regular basis on their analog transmitters.

What you cannot do without digital intervention is 4:3LB downconvertion in. If you concider a 16:9 CRT, all it does is scan the 4:3 (64uS) frame across its 16:9 tube width, and youve go 16:9. I have a 4:3 Sony 29" set, it became a 16:9 display when I reduced the vertical scan height. I set the DVD player to 16:9 and alls well. When a DVD/DVB device is set in 16:9 mode, all it does it plays out the frame without intervention. If set to 4:3LB then essentially the DVD/DVB decoder drops every 5th line and applies a vertical filter.

Technically it could be stated that a 16:9 full height anamorphic image has lower resolution than a 4:3 one, as it essentially uses rectangular pixels rather than square ones. But when you take into account the resolution enhancement when you dispense the pal encoding and composite video filter issues and use component video (as the mpeg system does) then you are still well ahead.


So just to recap, SD video has no specification for 16:9 only 4:3, therefore all 16:9 transmissions that we see today on standard def via DVD or DVB are anamorphic 16:9 frames within a 4:3 frame, thus rectangular pixels are the result. HD only specifies 16:9 frames thus square pixels. You can transmit 16:9 anamorphic over normal analog video transmisions systems, if you connect your DVD or DVB device to your TV via composite this is whats happening. There are very real resolution gains to be had by using S-Video or Component Video as mpeg is a Component video domain coding system. Without digital intervention you can not readily have a 16:9 anamorphic image displayed on a 4:3 display either in correct AR via 4:3LB or by using 4:3P&S (aka 4:3 CentreCut).


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  Reply # 68642 27-Apr-2007 11:56
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So...  just to clarify a bit more Cyril:

"The original question asked was:  Why can't you broadcast 16:9 on Analouge?"

I understand that by using S-Video or Component Video connections (which are LOCAL connections only) allied with Digital Compression it is possible to transmit 16:9 video over local analogue connections, but as the Analogue TV Broadcasting system stands in NZ:

Is it still true to say that 16:9 pictures cannot be broadcast in NZ using totally Analogue means via the existing transmitters?

I wasn't aware of the broadcasts in France, so thanks for pointing that out.

However, it seems at this late stage of the day that TVNZ would be unlikely to spend any money reconfiguring their Analogue Transmitters for 16:9 when Free-to-Air Digital Broadcasting is almost upon us.

Also, to improve the knowledge of myself and other interested people:

Could you explain a little about how Anamorphic 16:9 compression works?

Cheers,

Grant.

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  Reply # 68647 27-Apr-2007 12:29
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TVNZ and CanWest have no intention of transmitting 16:9 across their analog networks. They could nothing technical to stop them, however it would get a few folk upset for sure. The widescreen transmissions are for the digital networks only, ie Sky and Freeview (both DVB-S and DVB-T services).

As I said earlier, with SD video there is no specification for 16:9 square pixel frames, essentially 16:9 frames are anamorphically compressed into a standard 4:3 frame, the remaining video process has no idea whats happening. To check this out, if you have a 4:3 TV then select a some 16:9 material on DVD or TV3 or SkyMovies etc and configure the DVB/DVD device to 16:9 and have a look at the picture, what you will see is a tall picture, a totally standard 4:3 picture but the width of the image has been compressed inwards so everyone looks tall and skinny, the frame is a standard 15625 64uS wide image. If you were to apply this to a 16:9 CRT it would stretch the 64uS image across its entire width thus restoring aspect ratio. This is call full height anamorphic, and is the only way 16:9 images are dealt with in SD television systems. As you can see all the video processing gear has no knowledge of this, it will pass through composite, S-Video or component video.

The key feature that stopped broadcasters doing this in the past is that without digital processing in the STB you could not provide 4:3 displays with acceptable display options. With a DVB/DVD device you have the option to Letterbox the image, which involves stripping every fifth line, applying a vertical filter and placing the 16:9 image into a letterboxed 4:3 frame, or cutting a 4:3 centre out of the 16:9 frame.

Naturally modern digital panel displays can do all this to as they also have spatial scalers in them, but as most are 16:9 panels then just feed them the full 16:9 image.

By the way, most video cameras now are 16:9 capable, infact your standard Sony broadcast video camera has 16:9 pixels capability, ie in 16:9 mode will produce a 1024x576 image, which before it leaves the camera is comporess to 720x576 anamorphic. This anamorphic process is simply a horizontal scaling process.

35mm (also 4:3aspect) film as widescreen panavision or cinemascope is shot with anamorpic lenses that perform the horizontal scaling optically, in the projector a equivalent lens is used to project a wide stretched image. This only happens is standard 35mm stock is used, there are 70mm widescreen films also available.

Cyril

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  Reply # 68658 27-Apr-2007 13:19
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An awesome explanation!

Thanks for that Cyril Smile.


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  Reply # 68662 27-Apr-2007 13:49
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Wow that is comprehensive, thanks guys.  I assumed it was possible, but not worth it for the stations to make the change, which seems to be the case.  Also you'd assume most people viewing the analogue transmissions have old sets.  So it would just annoy them.

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  Reply # 68666 27-Apr-2007 14:24
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Cyril, one more question if you would be so kind...

You were saying:

cyril7: ...the frame is a standard 15625 64uS wide image.


I remember with composite video, the Active Line Period was only 52us out of the available 64us.  The other 12us was taken up with Line Sync and Colour Burst, Horizontal Blanking etc.  So, please tell me:

1)  With RGB signals am I correct in assuming that they still only use 52us out of the available 64us even though sync is either on a separate cable or multiplexed in with the Green signal?

2)  Do Component Video signals utilise the entire 64us frame?

3)  Is the 64us frame a world-wide standard i.e. do the Americans and Europeans also use it, or do they have some other standard?

Once again, thanks for sharing your knowledge, it's great Smile

Cheers,
Grant.

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  Reply # 68672 27-Apr-2007 15:18
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Yes grant you are correct, 52uS is the active frame.

The timing for digital video implementations is slightly different for older analog implementations. This is due to the 13.5MHz sampling rate used for both 50 and 60Hz digital systems.

Thus in Analog:
NTSC, 63.5uS total line length, 52.6uS active, 10.9uS blanking and sync
PAL, 64uS, 52uS, 12uS.

In the Digital realm:
NTSC, 63.56uS, 55,33uS, and 10.22uS of black samples.
PAL, 64uS, 53.33uS, 10.67uS of black samples.

In both 50Hz and 60Hz, digital standards there a 720active pixels

RGB TV signals have the identical timing to the composite they contribute to. In SCART'd systems there are infact four video circuits required, R, G, B and Composite, the latter providing sync and can be optionally used for picture.

Component video carries sync on the Y channel (as does S-Video) as if it was chromaless composite. When Component video is carried via a SCART connector (as with the Sky decoders and many DVB STBs) the G carries Y (with sync as above) the R carries Cr, and B carries Cb. The composite channel is normally also present when Component is output on a SCART connector.

Cyril

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  Reply # 68677 27-Apr-2007 15:41
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Thank you cyril7, your posts are really explanatory!

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  Reply # 68681 27-Apr-2007 15:57
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Doh

Cyril

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  Reply # 68682 27-Apr-2007 15:59
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To answer the original question will the Analog service not get 16:9, both Canwest and TVNZ (by 31July) have moved to a full 16:9 environment internally. Any 4:3 material that they recieve is immediatly converted to 16:9 via the use of pillarboxing, thus there entire workflow from that point onward is with 16:9 material, albeit that some is pillarboxed 4:3.

The entire playout area is 16:9, they dont switch or adjust AR flags at any point, its always 16:9. However the feed that drives the analog Tx service has a permanent Aspect Ratio converter taking the 16:9 feed and centre cutting it to 4:3.

Cyril

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