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Freeview HD will be 1080p25 and 1080i25.

Possible good news for Freeview HD

Possible good news for Freeview HD
published on UK Free TV
BBC: We may do 1080p on Freeview HD - Crave at CNET UK is reporting that Freeview HD may use the 1080p24 line to show material sourced from movie film.

Freeview HD was thought to be a 720p/720i service, which is a resolution of 1280x720 - click here for a sample picture from BBC HD.

UK Free TV reported the original plan back in October 2007, The "secret" Ofcom plan for Freeview HDTV: DVB-T2 and whilst it was know it would be MPEG4, it was expected to be a 720-line service.

The good news is that CNet quotes the BBC saying "1080p25 uses less capacity than 1080i25 and less capacity than 1080p50 ... There is no 24p in the Freeview HD system. It's not practical to switch between 25p and 24p on programme boundaries as this would cause displays to get upset." and says that the BBC has ruled out 720p completely.

So, all programmes will be 25 frames per second, 1,920x1080-pixel, with interleaved scanning used for live and studio events and progressive used for drama and films.

This is good news, as this will double the resolution on Freeview HD to five times that of analogue and Freeview. This is a much easier sales message than 2.5 times of 720-line and puts it on par with Freesat HD.

More about frame rates, "progressive" and "interlaced" in relation to digital TV (it's not the same as analogue!) please see this excellent document - BBC R&D White Paper WHP169 - High Frame-Rate Television [pdf].

Perhaps a summary of this document would be in order...?

Additional information: Ofcom consultation on 1080p50 ... Ofcom document saying 1080p50 would delay Freeview HD start.

On the matter of 720i, that the original Ofcom consulation on DVB-T2 asked Question 17: do you agree with the proposal that HD broadcasting on the DTT platform should use the more efficient progressive format,rather than the interlaced format?, but with the annex listing 720p and 1080i.

Under the "720p 1080p 1080i" scheme, "normal telly" is 576i25, with 25 frames a second, but 50 fields of interlaced picture, effectively at 720x288.

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Thursday, 17 March 2011
Mark A.

7:17 PM
Haywards Heath

I see that Freeview HD is 720 lines per frame.
How many lines with standard definition?

I know it varies from channel to channel,
but is there a maximum and minimum Freeview SD number of lines.

Nice to also know which channels have the highest SD quality and which ones don't.

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Mark A.'s 368 posts GB
Friday, 18 March 2011
Mike Dimmick

4:01 PM

Mark A: SD signals have 576 lines per frame, interlaced.

Public Service channels - the old analogue channels - are required to use 720 pixels per line, the same as usually used on DVDs. Commercial channels are allowed to reduce this to 706 or 544 pixels per line. Many of ITV's secondary channels use the lowest pixel counts even for widescreen pictures, which were really intended for use when broadcasting 4:3 pictures (544 pixels is roughly 3/4 of 720 - a 4:3 picture is 3/4 the width of a 16:9 widescreen).

These pixels are not square. A widescreen TV has a ratio of 16:9 or 1.78:1. 720x576 is a ratio of 1.25:1. The pixels are therefore 1.42 times wider than they are tall, or 0.7 times as tall as they are wide. This is the 'Kell factor'. A 544x576 pixel widescreen picture has a 0.525 Kell factor.

Freeview HD is using 1080 lines per frame. Most broadcasters are using square pixels, 1920 pixels per line, but the BBC are sticking with a 'Kell factor' of 0.7 and using 1440x1080 (interlaced), which substantially reduces the bitrate needed.

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Mike Dimmick's 2,486 posts GB
Mark A.

6:44 PM
Haywards Heath

Mike, thank you for your reply.
The minute I posted my question I realised I said 720 when I meant 1080 for HD.
(They where talking about HD with 720 lines before using 1080)

So BBC1, BBC2, ITV1, Channel4 and Channel5 SD use 720 by 576 (576 lines)
and the other channels can be from '706 x 544' to '720 x 576'.

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Mark A.'s 368 posts GB
Mark A.

6:49 PM
Haywards Heath

So BBC1, BBC2, ITV1, Channel4 and Channel5 SD use 720 by 576 (576 lines)
and the other channels can be from '544 x 576' to '720 x 576'

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Mark A.'s 368 posts GB
Monday, 21 March 2011

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