Upscaling

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We sold a modestly priced DVD player a couple of weeks ago, and were surprised when it was indignantly returned, with a demand for an instant refund. The reason? It degraded the picture, we were told, and therefore must be faulty. We gave the man another identical model to try, but results, he said, were the same. So we refunded his money – after getting from him a full description of the alleged fault. With the new player set to upscale the image and pipe it along an HDMI link, the image was inferior (“lacking in detail and texture”) to that obtained from this and his previous player when coupled via an analogue RGB link. But there was no fault in either the player or the TV….

Picture conversion

Scaling is the process of converting an image from one form of pixel matrix to another, usually to match an incoming video stream to the structure of a thinscreen display system. First the picture, if it is in analogue form, is digitised by sampling and quantisation, then de-interlaced and fed into a frame-store memory. Each pixel’s brightness is defined as an (e.g.) 8-bit word, with luminance (detail) and colour separately registered. Readout from the memory is at a different rate, to suit the display in use.

Thus, in the most common conversion, upscaling, ‘extra’ pixels are generated, and can be made up in various ways: clones of adjacent pixels; interpolations from adjacent pixels; and others which enhance the reproduced image in various ways. Edge-enhancement (‘crispening’, sharpening) is achieved by detecting sudden brightness changes in vertical and horizontal planes, and giving emphasis to the transition, while noise reduction is achieved by averaging successive frames, whose picture content is similar, but whose noise component is random, though the process must be governed by movement in the picture; and so on. Different rates of readout, and selection of the memory area read from, give zoom, picture-in-picture, flicker removal and other effects. These processes form the heart of the various ‘engines’ competitively featured by manufacturers: Bravia, Motionflow, Dynapix, Intelligent Frame Creation, Twin XD, Resolution Plus, etc. Every TV contains a scaler, whose output matches the basic structure, native resolution, of the screen it partners, and whose input is adaptable to whatever it sees coming in, typically a 480i (625/50) SD analogue image.

Disc players

Inside an upscaling video disc player the same process takes place, but here there is no analogue to digital conversion, little or no control over the upscaling process, and a choice of output standards, selected by the user in a pre-set menu. The advantage of upscaling in the disc player is that at no stage does the signal appear in analogue form: the off-disc data is digital and it remains so all the way to the display screen. This avoids, then, the degenerative processes of D-A and A-D conversion – carried out just to pass the signal along a metre of cable – which can cause picture artefacts, especially on fast-moving images.

Even when upscaled in the player, the data must undergo another stage of processing within the thinscreen TV to facilitate all those ‘engine’ features the set boasts. Two lots of digital manipulation, then, to avoid the analogue bridging stage. Now digital processing technology is continually evolving and improving, but performance still depends on the price paid for it.

Mix and match

Thus it can be that the upscaling system of the disc player is inferior to that of the TV, as with our customer and his Pioneer plasma set. In this case, and especially with relatively slow-moving pictures, using the player’s upscaling facility can actually degrade the image. Conversely, with a basic TV and a good-quality upscaling disc player the picture can be greatly enhanced. Toshiba has achieved an excellent performance in its XD-E (eXtended Detail Enhancement) range of DVD decks. Once an exotic rarity, upscaling DVD players are now available throughout the price range: I saw one on sale in a supermarket for less than £35.

In all cases, the best result is likely when the upscaler’s output format is set to match the TV’s native screen resolution, avoiding a second scaling process. Take care not to select a format which is outside the TV’s specification or you’ll get a blank screen.

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