In Depth: Everything you need to know about upscaling
TechRadar - 30 November 2008 - 8:00am
You’ve heard of high definition, you know about standard definition, but what about ‘near HD’?
It’s a term coined by manufacturers of systems designed to increase the quality of SD images to make them look closer to hi-def. Fans of near high definition say it really can improve the viewing experience, but can you make standard-definition pictures look so good, and why are some manufacturers pushing this quality?
The answer lies in something called the content gap. HD Ready TVs have been flying out of stores and into our homes at a super-fast rate. But the amount of HD content has been struggling to catch up.
Make the most of HD Ready TVs
You can watch HD quality broadcasts from services such as Sky and Freesat and the number of programmes is growing almost on a weekly basis. But a quick glance at a TV listing guide shows that HD broadcasts are but a small fraction of the total television output.
The same goes for Blu-ray titles, which are vastly outnumbered by the number of DVDs on offer.
So, the argument goes, if you want to make the most of your HD Ready set (and don’t want to buy your movie collection all over again on Blu-ray), you need near HD.
Pixels, lines and frames
To understand how near HD works, we need to delve a little into the workings of TV technology. Most of Europe uses the PAL standard, with each picture or frame composed of 625 lines (although only 575 of them actually make up the content).
Each frame is split into two halves called fields and displayed at the rate of 50 images per second (50Hz) to reduce flicker. On screen, two fields are combined or interlaced to form a complete frame. Each picture line consists of a series of picture elements or pixels, which are like the dots that make up a photograph.
In a PAL display, there are 720 pixels on each picture line, so the total number of pixels displayed is 720 x 575, or a little over 400,000 pixels. As a rule of thumb, the more lines and pixels a display has, the sharper the image.
Many HD Ready sets have panels composed of 1,920 x 1,080 pixels, which means they can display around five times more picture information than a standard-definition set. That’s why HD pictures look so stunning.
So with all this in mind, what technical tricks are used for creating near HD images, and can you really make the televisual equivalent of a silk purse out of a sow’s ear?
Upscaling TVs
The answer lies in the upscaling process (also known as upconverting). Let’s go back to our HD Ready telly with a 1,920 x 1,080-pixel display. If you connect a DVD player or feed an analogue or Freeview signal, it will receive a standard-definition signal, with each interlaced picture composed of just 720 x 575 pixels.
If this was displayed on an HD Ready screen, there would be large areas of black, because many of the screen pixels wouldn’t be used for the smaller-sized image. HD Ready sets, therefore, have a video processing chip, which is used for upscaling the image. Upscaling simply means matching the incoming picture signal with the native resolution of the display.
The video processing chip does two things. First, it deinterlaces the picture so that it can be processed, and then the upscaler gets to work, using smart algorithms and filters to add pixels and lines so that the output matches the resolution of the TV. The algorithms analyse the standard-definition image and then use a process called interpolation to generate extra lines and pixels.
So does this mean we can get high-definition images from standard-definition signals? Sadly not, because upscaling cannot add detail that wasn’t there in the first place.
What’s more, the effectiveness of the upscaling depends on many variables, including the quality of the signal source, the quality of the processing chip and the ability of the set to handle upscaled material; some TVs are better at displaying upscaled pictures than others.
Upscaling technologies
Many manufacturers have their own technologies which claim to greatly improve standard-definition picture quality. Toshiba, for example, has introduced Resolution+ in its Regza ZF series of televisions.
This is based on the company’s Cell processor technology used in its laptop PCs. Resolution+ TVs and Qosimios share the same upscaling algorithms, but whereas the laptops have a quad core HD processor, Resolution+ sets use a different chip.
The latter analyses three picture elements: texture, flat areas and edges and uses this information to detect which areas should be sharpened and where edge enhancement is required.
The technology works by comparing adjacent images and then combining pixel detail to add definition to the overall image. Edges are sharpened and texture is improved by increasing focus and sharpness. However, flat areas are left untouched.
Toshiba is first to admit that Resolution+ doesn’t offer true HD images as a result of all this processing, but it does claim to be a leap forward in television upscaling technology. Of course, the proof of the pudding is in the viewing.
We’ve yet to get our hands on a Resolution+ set and give it a good workout in our test lab, but demonstrations of the technology suggest that the technology can make a difference to the subjective picture resolution. Watch this space for an in-depth investigation.
DVD Upscalers
DVD players can also upscale standard-definition images, but these shouldn’t be confused with players that offer progressive scan output. These models convert interlaced images into full frames to improve motion and remove artefacts created by interlacing, such as flickering between picture lines. What they don’t do is use algorithms to generate extra lines or pixels and thus improve subjective picture resolution.
An upscaling DVD player matches the output signal with the screen resolution so when you connect it to an HD Ready set, pictures should look better. In order to use this, both devices need to be connected via an HDMI cable.
Toshiba backed the now-defunct HD DVD format, and rather than offer Blu-ray Disc players, has developed a DVD upscaling technology called XDE (eXtended Detail Enhancement) found on its new player, the XD-E500.
Toshiba says that XDE is different from other DVD upscalers because it upconverts standard 576-line DVD images up to 1080p images, and then uses three additional video processes designed improve image detail, colour and contrast.
After the 1080p upconversion stage, XDE technology analyses the picture and adds enhancements where needed. There are three user selectable enhancements: Sharp enhances the edge detail of areas in the image and this setting is always on by default (although it can be switched off via a menu).
The Colour setting boosts the levels of blues and greens, while Contrast enhancement boosts the contrast in parts of the image that are normally too dark or where it is hard to make out detail.
Is near HD worth it?
Let’s get one thing straight ? near HD is no substitute for the real thing. But that said, the technology can help you squeeze a little more out of standard-definition pictures.
When you first watch a near HD picture, you’re unlikely to experience a ‘wow’ factor, but you should notice some improvements, even though many of them are more subtle than spectacular. If you’re in the market for a new DVD player and don’t anticipate imminently upgrading your HD Ready TV, it’s well worth investigating an upscaling model.
There’s a lot of hype surrounding near HD, but there’s also a lot of snobbishness from some, who dismiss the concept as a bit of a gimmick. Our advice is: trust your own eyes and you might well be pleasantly surprised.
First published in What Video magazine, Issue 341
