Articles and whitepapers

The Need for Video Scalers (1/11/2004)

By Udo Ratai, cinemateq

How good is the picture quality of your home cinema? Is digital best? And what will be the effect of HDTV? Another typical question concerning projectors and digital displays is 'which component is ultimately responsible for the picture quality on the projection screen?' If the eye detects an error, which component is to blame? Is it the video source, the displaying device or the video processor in between? In a test environment, many devices, cables and interfaces in the long chain from the video source to the projection screen, must be coordinated with each other. Finding the setup with the best possible picture quality, has been a central task in my working life for years.

In the past, I have always used professional video scalers in order to fully test components, but using the highest quality signals often resulted in only being able to work with a handful of good devices. Attempts using native-resolution or HDTV pictures at 50Hz, which we will soon have in Europe, caused problems more than once.

DVI (Digital Visual Interface) has been a quantum leap for digital display technologies, but using this for 50Hz PAL picture distribution only works in some cases. We therefore need to tread with caution when using technologies that have been predominantly developed in NTSC countries.

Scalers, HDTV and current issues

The number of projectors and/or displays compatible with European HDTV signals is constantly growing, and HDTV scalers conceived for this purpose will finally be able to prove what experts have been saying for some time: that the line doubler or video scaler will define the picture quality of home cinema.

cinemateq picture optimizer plus II

In addition to its originally-intended tasks, the professional video scaler can serve as a tool and working device for testing video interfaces in the home cinema using HDTV 50Hz signals.

With the arrival of European HDTV, the professional scaler can help avoid a number of problems. The worst case is where incompatible displays stay dark and are unable to offer the fascinating quality of HDTV pictures. Hardly better is the case where devices recognise an HDTV picture, but show unacceptable artefacts in moving scenes such as 'motion judder' (internal 60Hz rendering), 'tearing' (crosswise flashing edges in moving scenes) or the wrong picture position and geometry.

HDTV compatibility

Given the announcement by ASTRA and some cable providers to start broadcasting high-resolution HDTV content from January 2005 onwards, both broadcasters and manufacturers are under pressure to bring to market HDTV content and/or HDTV-enabled devices. In the run up to the World Soccer Championship in 2006, there will be a true HDTV boom in Europe, so it is essential that testing is carried out now.

Not only will future HDTV-compatible home cinemas benefit from the new broadcasts, but current TV and/or DVD applications can also take advantage of the conversion of PAL pictures into HDTV resolution.

There is one clear conclusion to be drawn. To be future proof, a modern home cinema must be based both on components with HDTV-enabled interfaces and displays with high resolutions far beyond conventional PAL. A home cinema that supports HDTV signals today will avoid conversion difficulties in future.

Interfaces are the key

For many years, both plasma and LCD displays and LCD, DLP or LCOS projectors, have been available - all of which are digital technologies. DVD players, DVB (Digital Video Broadcast) via satellite or DVB-T (terrestrial) transmit digital video signals. So why on earth we are still communicating between these digital worlds using analogue interfaces?

The result of multiple D/A and A/D conversions affects picture quality, so if you want to experience a convincing home cinema picture, it is best to buy or install digital home cinema components that have professional digital interfaces such as SDI, DVI and HDMI (High Definition Multimedia Interface).

SDI interface and DVI interface

While this is great in theory, interfaces for digital HDTV signals must also work in practice. Many plasma displays only accept doubling (PAL/NTSC), some do not recognise 50Hz video pictures via DVI at all, and some show 'motion judder.' For modern HDTV projectors however, full HDTV compatibility (DVI and YUV) has almost become standard at HDTV 720p using 1280x720 pixels - even for cheaper LCD devices costing less than 2000 Euros. Moreover, thanks to so-called 'auto input receivers' some PC monitors work with true HDTV signals via DVI without displaying errors - making them the least expensive digital HDTV displays currently available.

It is incredible that an SXGA monitor costing less than 400 Euros can offer an error-free picture with HDTV 720p/50Hz, while a plasma display costing 20 times as much, might not. The lack of 50Hz-compatible DVI inputs could be overcome by converting PAL material to 60Hz, but in the long run, this will not help, since a PAL 60Hz rendition always leads to motion judder.

No video scaler in the world can work at its best with some incompatible displays, but it is often difficult to get people to admit that the fault lies with their particular plasma display or expensive projector. In such cases, we need to proceed systematically, and double check the real signal quality delivered by the scaler with an analogue CRT monitor or another compatible device. Analogue CRT monitors are well-suited to this purpose, as they hardly alter the video signal and do not produce motion judder errors.

Many of the latest generation projectors and plasma displays offer HDTV-compatible YUV and DVI interfaces, and adapters from DVI to HDMI can be used to connect displays with HDMI-only interfaces. Thus we move ever closer to a 'perfect HDTV world.' In order to be sure that devices are future-proof however, we need to check our home cinema components with HDTV signals using professional video scalers.

Scaler requirements

Of course it is essential that the video scaler itself delivers a signal that complies with current standards. The cinemateq picture optimizer plus II SDI for example, adheres to the latest SMPTE and/or VESA standards. Considering the variety of different output signals possible, including DVI, RGB,HV, RGBS and RGsB/YUV with bi-level or tri-level-sync, this is a demanding requirement. Moreover, the picture optimizer plus II SDI also delivers video signals for all possible panel resolutions. Twenty-two formats from 'doubling' to 'quadrupling,' VGA to UXGA, HDTV 720p and HDTV 1080i/1080p are predefined and can be easily accessed at any time.

As opposed to American HDTV formats that have been defined by SMPTE (Society of Motion Picture and Television Engineers) for some time now, HDTV formats using 50Hz have only been available for a short time in Europe. This is why settings sometimes differ, especially with older devices. It may therefore be necessary to generate different HDTV settings or settings that may refer to the 'old' SMPTE standard. For this purpose, the picture optimizer plus II SDI for example, offers four custom resolutions for individual fine adjustment.

The way to a perfect home cinema

The core component of a future proof home cinema is a digital video scaler that integrates digital inputs (SDI) and digital outputs (DVI). Interfaces to the analogue world should also be available in the best possible quality, although they can never match the quality of the loss-free signal transfer of digital interfaces.

Perfect picture sharpness thanks to a digital chain (One Night at Mc Cool's)

Ideally, there should only be one DVI cable leading from the output of the scaler to the modern projector or flat screen. This is the easiest and technically cleanest solution - not only for projectors mounted to the ceiling, but for flat screens where we want to avoid having many cables leading to different connected devices. In terms of cables, ceiling-mounted projectors can, in most cases, be connected via DVI cables up to 10m long without any problems.

cinemateq DVI-Link optical DVI cable (30m)

Should higher cable lengths be necessary, fibre optic DVI cables are ideal. These can securely cover distances in excess of 100m without any loss in quality, and thanks to detachable DVI connectors, can fit through narrow cable channels. Using the cinemateq picture optimizer plus II SDI video scaler for example, you can also pass through two analogue PC or HDTV signals (5xBNC/ 1x15PIN) per bypass function to your projector. It is therefore worth considering analogue signal connections (YUV / RGB,HV) which may be needed for future HDTV receivers. For purely digital HDTV signals however, there are also flexible solutions and applications. cinemateq for example, offers DVI switchers in all variants, so a projector can be switched to up to four external digital HDTV signals, and if necessary, DVI signals can be distributed in up to five rooms at a time with a DVI amplifier.

For the home cinema devotee who wants to push their large CRT projector to the limit, the picture optimizer plus II SDI supports 1920x1080p. Indeed the first digital HDTV devices with 1920x1080 pixel resolution - designated to professional cinema applications (Digital Cinema) - are already being tested in European home cinemas by a selected group of enthusiasts.

Conclusion

HDTV may be reality in Europe in a few months, and the advantage of a home cinema setup that includes a professional video scaler is that you do not need to change its installation and wiring for years to come. You can sit back and wait until 1920x1080 pixel HDTV projectors are readily available and perhaps reach affordable prices similar to current 720p projectors.

Udo Ratai is the Product Manager for cinemateq, specialist in video optimisation for home cinema and the presentation sector.

www.cinemateq.com