Scalers, what are they good for?

Devices to expand the resolution of video images by creating new lines and columns of data, commonly referred to as video scalers, were first launched over a decade ago and found great success in delivering enhanced images from standard definition sources. Steve Montgomery explores how things have moved on.

Up until this point most of the processing in a scaler has been performed in the digital domain, both source and display devices has been analogue, which means that there have been several stages of analogue to digital and digital conversion in the picture path.  More recently, the widespread use of digital HD devices at both ends of the chain has potentially obviated the need to insert a scaling device.  Where standard definition content is desired, most displays, whether LCD, plasma or projector will upscale the image internally.
So are external scalers still necessary?  Are they still in demand and are manufacturers still designing and launching new models?  Robert Drake, technical director of TVOne confirms that they are: “Video scaling, which nowadays encompasses all forms of conversion between video formats; including up, down and cross conversion is still a growing business.  The C2-2355 for example, offers bi-directional conversion with auto sizing and screen positioning between a wide variety of analogue and digital inputs and outputs and is one of our best selling products into various market sectors including broadcast, pro AV and store systems.”
He cites flexibility as a key feature of this type of device: “Many applications, such as presentation rooms and videoconferencing suites still have a wide variety of formats that need to be handled and displayed on a single screen.  Collecting these together and reformatting them at a single switching unit and then connecting the output over a single cable is often much more convenient and economical.”
Ali Haghjoo, CEO of Hall Research concurs: “Although displays have multiple inputs, if you have multiple sources with different formats, including composite, S-video, component, VGA, DVI and others, scalers are invaluable in converting all these sources to one common format that can then be switched and distributed. The connection to each display will be the same.  An example is the use of a scaler to convert everything into RGBHV with a cost effective and easy-to-install VGA switching and distribution matrix switch as our VSM-A-16-JA16 over Cat5 cable.”
Another market sector that still requires video scaling capability is broadcast. Franck Facon, world wide marketing & communication director of Analog Way offers an explanation: “A vast amount of television content is still in SD, and TV channels need to broadcast higher quality.  In this kind of applications, scalers are used to enhance the quality and in converting SD into HDTV format.  For this application, we have the Optimizer HD, which converts any SDTV, HD-YUV or PC signals into SD-HDI signals. This type of solution is attractive to TV stations since it allows them to display high quality content with SD sources instead of having to work only with HD sources that are much more expensive.”
Another distinct advantage lies in the quality of video processing.  Scaling in any direction is not a simple task, requiring complex algorithms and high levels of processing to achieve acceptable quality on the largest display devices.  Tim Brooksbank, Chairman of Calibre UK: “It is true that most displays nowadays do include scaling, but the quality varies a lot between models.  Bear in mind that in a $2,000 top of the line screen the manufacturer has probably budgeted somewhere between $5 and $20 for the scaler within it.  You're not going to get the best at that price point.  The scaler is an afterthought for the screen manufacturer, it's an enabler because without it their product won't sell, but it doesn't earn them extra revenue so they spend as little as possible.  Next time you look at a screen data sheet, check whether it mentions scaling or de-interlacing.  It will tell you the brightness, contrast ratio, response time but most won't make any claims about video processing or scaling.  HD has helped, but a lot of content is still SD.  Also, even HD signals often have noise and a lack of definition; few internal scalers can fix this.  HD noise reduction in particular requires a lot of processing power if it's to be done without losing detail or causing smearing and for that you need a premium professional video processor.”
Mike Child Sales Manger of AV installation company AV Department offers a user’s point-of-view: “Scaler-switchers are invaluable when you need to deal with a range of sources on a single projector and need to be able to control and switch them instantly without producing glitches or switch-to-black on the live screen.”
Similarly Frank Sheehan, Director of Technology Visual Acuity: “We spend our days designing large systems where a client will have a requirement for a more creative display system than you would typically find in a standard presentation environment or a video conferencing room.  A typical display could well be a multi-projector immersive environment such as a planetarium or virtual environments such as those used in oil and gas, automotive research & design and research academia.  These applications require high pixel count displays with very specific requirements that require careful pixel management across their displays and often have a centralised equipment room some distance away, with the display connected to the rack room via a single point of connection rather than multiple video sources, therefore all potential sources of signals to be shown on a display will be processed, scaled and then switched back at the rack room before being sent to the display end.  Scalers can play an important role in that part.”
Whilst one normally thinks of scaling as a function to increase the resolution of picture content (up-scaling) the reverse process is just as important. Downscaling is a different technique and many LED screen users make the mistake of not realising this, resulting in a poor image on their hugely expensive LED screen. To successfully downscale to an arbitrary image size requires a very large scaling filter which is able to analyse and process a large area of incoming pixels for every output pixel it generates.
Most scalers can't do this since it requires a very powerful video processor with massive memory bandwidth.  That impacts on cost and just isn't relevant for consumer grade screens or projectors. FPGA-based scalers also struggle since implementing a very large scaling filter requires a powerful FPGA with resulting high cost. Another example is the display of very latest formats such as 3G-SDI which most screens and projectors can't support directly.
Pure video scalers are becoming a little less common as this function is combined with others to produce generic products with enhanced operation and functionality.  Extron’s new DVS304DVI is a typical example. Rainer Stiehl, Extron’s VP of Marketing explains the philosophy behind  the design: “This is a straightforward, four input video and RGB scaler which offers high performance scaling for a wide variety of analogue video input sources, and provides high resolution DVI and analogue video outputs.
“It is ideally suited for AV presentations using the latest projectors or flat panel monitors, as well as centralised system integration with high quality source switching, automatic input format detection, and other capabilities.  A key element is Automatic Input Format Detection that allows it to accept and automatically detect any video format. This provides the ability to deliver multiple signal types to the DVS 304 DVI via a single cable using an external switcher, such as an Extron CrossPoint matrix switcher. The result is a streamlined system that provides significant cost savings, since fewer outputs are required on the matrix switcher.”
Manufacturers are working extremely hard to incorporate additional features to differentiate their product from the competition.  Robert Drake: “Picture-in-picture and derivatives such as side-by-side image display are extremely popular for videoconferencing and training set-ups, allowing disparate formats to be shown together, for example Powerpoints alongside live demonstrations or videoconference inputs.”
Image enhancements are also possible and included in external scalers: functions including noise reduction and real-time un-sharp mask on up-scaled content; a process which typically takes several seconds on a PC running an application such as Photoshop but which seriously powerful professional scalers can run in real time.  They are also finding application with more esoteric applications; Frank Sheehan : “A client may add additional layers to the imagery, for example, they may have some kind of PC based display management device using a frame grabber.  Frame grabbing multiple sources of different nature can sometimes lead to strange results, so including a scaler in the system can provide the level of stability needed to provide a seamless result and maximising the grabber’s performance”
Video scaling is far from becoming a redundant technology, continuing to be used in standalone products, generic switching, scaling and mixing devices and as predicted by Frank Facon: “Video resolutions and formats are not frozen and will evolve further in the future.  3D applications will have an impact on future scalers with need to increase the display frequency in order to operate two displays at 60Hz for compatibility with stereoscopy applications. Video scalers still have plenty of potential in years to come.”

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