TV programmes - video resolution and quality

[Dave2002]

Before we had HD TV broadcasing some propular programmes were released on DVD, which generally gave an improvement in video quality for those who wanted it. DVDs were and are capanble of better video quality than digital SD broadcasting. However, my understanding is that there are resolution limitations in DVDs which are inherent. These limitations can be overcome in distribution media by systems succh as Blu Ray, which are presumablly made with higher resolution equipment and possibly more care taken.

The BBC and other broadcasters continue to sell hard media versions of some of their output. As yet we don't have full video on demand for high quality material for some older programmes, though ITV/C4 are offering some of their earlier programmes for payment, rather than not making it available. In the case of the BBC programmes become unavailable in any quality level 30 days after the latest broadcast, though some programmes will become available again due to repeat showings. The BBC does not charge for iPlayer based streams, though further, it may be questionable whether iPlayer HD is comparable to broadcase HD video, or a Blu Ray rendition of the same programme. My personal belief is that streamed HD is less good than broadcast HD, though this may depend on the network and delivery of streamed TV programmes. It is possible that at source HD video is the same for network streaming as for broadcasting, but that the network providers reduce the quality to reduce load on the networks. On the other hand, the source providers may limit quality at source rather than relying on the network providers to change/limit quality within their networks.

Where serious effort has been put into video quality this can often best be experienced via HD or by Blu Ray discs. I don't know whether the quality of Blue Ray for TV programmes exceeds that of broadcast TV, but I would expect it to be comparable. If it exceeds broadcast HD quality, then that would imply that at the production end higher quality video is created than broadcast. Programmes which benefift from the best HD quality typically include nature programmes, such as those featuring David Attenborough.

There are some programmes which are presumably popular and may be commecially viable enough to reappear on DVD. One such is Michael Portillo's series on railway journeys. AFAIK these are not available in Blu Ray formats, but I can watch them on my HD TV. My specific question re programmes like that is whether the broadcast video quality is actually higher than the DVD for such programmes?

It may actually be difficult to assess, as perceved video quality don't just depend on resolution, but other factors, and broadcasters and programme makers are aware of that. Most viewers won't worry too much if quiz shows and such are in SD or HD, firstly because enjoyment of the programmes does not depend on very high video quality - it simply has to be adequate, and secondly because there is little detail in the video which would give "added value" in an HD version. On the other hand, some nature programmes, some sports programmes etc. do have a lot of detail in high spatial frequencies, and they are are definitely enhanced in HD formats and are easier to watch in those formats.

[Gordon]

My specific question re programmes like that is whether the broadcast video quality is actually higher than the DVD for such programmes?

There is no generic rule. Clearly HD is "better" than SD simply because there are more pixels but in my time I have seen SD that is better than HD; just because a signal is supposed to have more pixels doesn't mean it has - some "HD" is up-converted SD. We've had asimilar conversation to this some time back when we talked about conversion. An "HD Ready" TV set doesn't mean that it has full HD resolution - some TVs may well do - it just means that it has interfaces and an ability render an HD input but in its own native format which may NOT be "true" HD. Many such TVs that are now more than about 5 years old may well be of that sort.

The other factor than native resolution is how hard it may have been compressed to fit a storage medium like DVD or a rate limited real time transmission channel like Freeview, SD or HD, or streaming. DVD can use variable rate coding where tricky parts are given more bits at the expense of the easier parts of the video. Same goes for audio. Also in production of ready made material several passes of coding in non real time can be tried before settling on a final version - not really possible with live material - to tease out the difficult parts.

SDTV is based around a digital production standard set in 1981 - when PAL analogue was still being broadcast to most people - which required a resolution base of 720 x 576 pixels at a complete picture rate of 25Hz - a bit rate of 216 MBit/s. HDTV [in Europe] is supposed to be 1920 x 1080 pixels at a picture rate of 50 Hz [interlaced [I]] - or 25 Hz progressive [P] - and this is a production standard used throughout the media business even in the US. The problem is that it requires a massive bit rate: 1920 x 1080 x 25 x 30 bits per second = 1.56 GigaBits per second [0.7 TeraBYTES for an hour programme before wrapping, BluRay 25GBytes per layer wrapped], way beyond any current practical and economic consumer transmission or storage system. The images may be captured at source at this rate and stored during production but distribution pipeline bottlenecks set the need for compression in some form. Trouble is that "compression" is a variable feast and can mean anything and will compromise both Spatial and Temporal picture properties. There are several proprietary systems out there but MPEG4 or HEVC etc are open standards that broadcasters like whereas things like Blu Ray can be proprietary - a bit like Dolby Digital in audio - although BR is in fact MPEG.

Freeview HD uses a rate of around 10 MBit/s [SD less at about 2-3 MBt's] so clearly some serious high speed video processing is required to do the job well and still have little impairment to the pictures. The fact that it's done at all is the wonder. Sky's satellites have more bandwidth available compared to DTT so you'll find that their bit rates for HD are higher, especially for live sport. Streaming video does not conform generically to any particular coding standard or bit rate as is very obvious when viewing it. Typically because broadband speeds are not universally high even HD streams are not particularly high bit rate and often resort to tricks like dropping whole frames and reinserting computed ones at the receiver. That and the fact that the video and audio are contained in complex file wrappers used for transport - eg http - reduce the net bit rate available for the pictures.

So the answer to your question is that yes it can be but there are too many practical factors to be definitive. Standards are good, there are so many to choose from.

I'd agree that enjoyment of pictures can be improved with higher resolution but its the content that truly engages. A bit like HiFi perhaps!!

PS: HDTV is now old hat the industry is looking seriously at UHDTV requiring a doubling of spatial pixel densities and perhaps an increase in frame rate. More GBytes of data and more bits/second.

[Dave2002]

There is no generic rule. Clearly SD is "better" than HD simply because there are more pixels ....

I think that SD and HD have got switched in that part of the sentence.

I think your comment that there is no generic rule is probably well justified, and it would be hard to know what production teams would actually use for a particular programme. I believe we know that many "out and about" and "news/interview" sequences are now shot using equipment which is either consumer equipment, or similar. Partly this is for size and weight reasons, and partly because it is less intimidating for many of the participants - casual interviewees etc. This probably means that at present the best video quality for that kind of video recording will be HD 1080/1920, and a few years ago hand held SD or 720p equipment might have been more common. There are even higher resolution video cameras coming along, particularly for professional use, but they are perhaps not widely used yet.

Some programmes and films are still made with much larger, heavier and expensive cameras, and these are serious pieces of kit. For example, some of the shots at the Eton Dornay races at the 2012 Olympics were filmed from vehicles which drove along the side of the water, and some of the cameras used each cost in the region of £250,000, and were mounted on gyro stabilised mounts to reduce the effects of camera motion. Other cameras were mounted on towers, and on boats which proceeded in front of the racing boats, and and there were also some smaller cameras on a wire which ran along fairly high above the water. For events like that one (which was only just one part of the overall Olympic event) production companies put a lot of investment into equipment and planning in order to get an acceptable result.

Other events where large and expensive cameras might be used include some of the live opera and theatre events which are becoming more popular now. There have even been some recent events where hand held cameras have been used on stage by camera crew who blended in with the action - perhaps by an "extra" or chorus member in the case of a play or opera - I don't know the exact details.

You are right that companies are now moving on past HDTV - and some are looking at UHDTV and maybe even deploying it, and some are going for even higher potential quality/resolution than that. I don't know what is currently being used for digital cinema - perhaps it is significantly higher resolution than for TV. There seems to have been a significant jump in quality in recent years.

[Gordon]

I think that SD and HD have got switched in that part of the sentence.

Hmm, yes, finger trouble again.

Some programmes and films are still made with much larger, heavier and expensive cameras, and these are serious pieces of kit.

Yes hand held "ordinary" cameras [cam-corders actually with integral recorders, unlike professional cameras] these days are commonplace consumer grade HDTV using 1080I or P. Even my small Canon IXUS can do 720P movies but obviously compressed in real time. That means the sensor and processor devices are cheap. But the movie industry in particular still hangs on to older production methods and have DoPs that have taken ages to move to video rather than 35mm or higher image size film like 70mm. One problem is also the Aspect Ratio the ratio of the width to the height of an image - eg CinemaScope and the like which is 2.35:1. Analogue TV always used a fixed AR of 4:3 [1.33...] which gave problems showing wide AR films on TV but now uses 16:9 [or 4:3 x 4:3, 1.77..]. Increasing the image size or AR spreads a fixed number of pixels less densely and so to maintain density many more pixels are needed, in fact it's a square law with the linear dimensions if the AR is maintained. It is a rarity nowadays for a movie to be made on film and most cinemas are digital and have not seen a reel of film in a long time. These cameras are definitely not consumer models, they have bells and whistles and components - especially lenses, any camera without a decent lens is next to useless - that are professional standard and ruggedised too for use in the field. Arriflex et al are the brands to have but the real heroes are the lens makers eg Fujinon whose 4K zoom lenses can cost beyond £60K. Remember that, just like audio, in digital video there needs to be a Nyquist filter but this is BEFORE the sensor ie in the optical domain so that the filter is not electronic but made of glass. The roll off rate of an optical system is not at all fast and so oversampling is common at the sensor before rendition into the required production format. This is one reason why a consumer still camera may have a very large sensor pixel count.

You are right that companies are now moving on past HDTV - and some are looking at UHDTV and maybe even deploying it, and some are going for even higher potential quality/resolution than that. I don't know what is currently being used for digital cinema - perhaps it is significantly higher resolution than for TV. There seems to have been a significant jump in quality in recent years.

The latest in digital cinema is "4K" which is happening but the Japanese are always the ones looking for even higher resolutions. For many years specialist cameras have been used in sport where the frame rate is high in order to catch raid motion - Wimbledon this year was exceptional for capturing for Slo-Mo review fast motion in remarkable definition without the usual blur of a fast moving ball - but this challenges recording systems for reasons I gave above. The video quality at the studio end has always been good even in analogue days and the challenge to get it into the home was great with PAL but now, even with compressed digital, the gap between studio and home is much smaller - still images are perfect. Try comparing anything you have on VHS with a modern DVR. Digital processing in modern consumer displays has also helped.