For many years high definition television (HDTV) was held back by two factors: the sheer volume of information involved in its transmission, and the cost of manufacturing large screens capable of rendering highly-detailed images. The advent of digital encoding and data compression, and of plasma and LCD screens solved the problems, and steady progress is being made with both since HDTV started last May.
The phrase HD-ready is now well known, and any screen bearing it must comply with the minimum standard of 720-line resolution in wide aspect ratio; acceptance of 720p (progressive) or 1080i (interlaced) input signals; possession of digital and component video input ports; and HDCP copyprotection compliance.
Many screens currently available exceed this minimum display specification. Virtually all big LCD panels have a 1366×768 pixel matrix, while projectors and plasma panels vary greatly: from 852×480 through the (rectangular pixel) 1024×1024 type to the top-range 1920×1080 variants, with prices which reflect their capabilities. Progressive scanning gives a better (smoother, steadier) image than interlaced scanning, and the best screens, known as Full HD types, are capable of 1080-line progressive scanning, better than current TV transmissions can offer, but potentially available from HD discs. Examples are Pioneer PDP427XD and PDP5000EX in plasma, Sony LCD type KDL-46X2000, and projection models Epson EMPTW100 and JVC DLA-HD1. These offer the best possible pictures from any digital signal source.
The main source of HD TV pictures at present is the Sky HD offering, nine programmes in all. The possibility of eventual Freeview/terrestrial HD transmissions is in the melting pot at the time of writing, while we stand on the brink of battle between the two highdefinition optical disc formats, Bluray and HD-DVD. The cheapest entry-points into these formats are games consoles Sony PS3 and Microsoft Xbox respectively, both of which can play HD discs into suitable screens via a digital cord. Other (and less commercially significant) sources of HD pictures are highly-specified PCs and camcorders: late-model Sony cams are fitted with HDMI ports, and others will rapidly follow.
The purpose-designed high-definition AV data highway HDMI (HD Multimedia Interface) is now the de rigueur coupling system between HD screens and boxes. It scores highly over the analogue alternative, component video, by avoiding the DA and A-D conversions which degrade picture quality and introduce artefacts, especially on moving images. The current versions of HDMI in use (V1•1 and V1•2) are perfectly adequate for today’s HD systems – they can handle all the picture detail available, along with Dolby Digital 5•1 and 7•1 surround sound. The very latest equipment, however, (while using the same plug and socket type) is geared up for the latest version of the system, V1•3, starting with Sony’s PS3 games console.
Because data transmission is an allor- nothing affair, the use of 1•3- specified HDMI components will not by itself confer improved sound or vision: it’s simply that the new version is compatible with several potential improvements in the boxes it connects together. At present we use 8-bit video coding, capable of conveying 256 distinct levels of each colour. For most pictures that’s perfectly adequate, but where there are very subtle and gradual colour changes this can result in visible ‘steps’ in level, a bit like the effect of paint-by-numbers limitations. HDMI 1•3 can cope with deep colour formats with up to 16-bit coding; it also has a higher maximum data speed to afford future improvements in video and audio specification and performance – in terms of faster refresh rates and higher resolutions.
In home-entertainment applications HDMI Version 1•3 has several new and useful features. There’s support for automatic lipsync compensation to overcome one of the biggest pains which digital TV has brought; and also more sophisticated control and command systems whereby individual boxes can play the role of master or slave, governing signal routing and processing, while a single unified and auto-programmed remote control can operate everything on the network.
It’s in the audio field, perhaps, that HDMI 1•3 scores most highly: it’s compliant with the new multichannel ‘high definition’ sound systems Dolby TrueHD and DTS-HD which will come on stream from HD video discs.