By Joep van Eijden, NXP Semiconductors
It is always fascinating to watch a High Definition TV demonstration. Modern HDTV panels are capable of displaying vibrant image quality and the latest wide color gamut (WCG) versions can reproduce an astounding range of colors, with contrast and brightness that even makes daylight viewing a real enjoyment.
By Joep van Eijden, NXP Semiconductors
It is always fascinating to watch a High Definition TV (HDTV) demonstration. Modern HDTV panels are capable of displaying vibrant image quality and the latest wide color gamut (WCG) versions can reproduce an astounding range of colors, with contrast and brightness that even makes daylight viewing a real enjoyment. Theoretically, at least, they can also produce ultra-sharp moving images.
However, have you ever wondered why the HDTV sets in the shops normally show slow-moving images? Moving objects present HDTV set makers with a real challenge. These objects often appear to judder across the screen instead of moving smoothly; their edges become blurred and, even worse, their edges occasionally start to get confused with the objects they are moving past.
The reason for the moving image problem is actually the 100-year old motion picture technology that’s used to produce much of the displayed content. Even blockbuster movies are typically captured at 24 frames per second (fps). It’s still the format required by most of the world’s 150,000 cinemas. However, standard definition TV sets have to display the results at 50 fps or 60 fps and new generation HDTVs typically display them at 100 fps or 120 fps. All TV formats therefore have to add extra frames to the movie’s original 24-fps sequence.
To do so, most TV broadcasters simply repeat each movie frame an appropriate number of times to get 24 fps up to 50 fps or 60 fps. In both cases, however, when your brain tries to smooth out the motion it gets confused by the repetition and what you see is motion judder.
This motion judder problem can be solved by replacing the repeated frames with new intermediate frames in which the positions of moving objects are adjusted so that your brain perceives much smoother motion. It’s a technique that is called motion estimation/compensation. The challenge for HDTV is to do it while pushing up the frame rate to 100 fps or 120 fps and at the same time handling up to five times the number of image pixels. What differentiates between high-definition LCD TV sets is how successful they are at doing it.
Most of them match pixel blocks (groups of adjacent pixels) in two successive picture frames stored in memory to determine velocity vectors for these blocks (the speed and direction in which individual blocks have moved). They then use these velocity vectors to create the new motion-compensated intermediate frames. However, calculating the correct vectors is not always easy if you only compare two frames, especially for pixel blocks situated along the edges of moving objects. It is because of errors in these vectors that many sets end up producing a visible blur around moving objects – the so-called ‘halo effect’.
NXP’s latest TV video post processor chip – the recently introduced PNX5100 – adopts a new approach. Instead of comparing two successive frames to calculate velocity vectors, it compares three successive frames. This massively increases the chances of correctly matching pixel blocks along the edges of moving objects, because edge-located blocks always appear in at least two out of the three frames. This results in a much more reliable set of motion vectors and hence a significant reduction in visible halos.
However, sophisticated motion compensation is not the only thing you need to do to get the most out of HDTV. Most TV formats don’t utilize the full range of colors that appears in nature, so to produce truly lifelike pictures you need to intelligently map and process the colors of certain features, such as blue skies, green grass and the skin-tones of human faces. Standard TV formats also fail to deliver the picture resolution and sharpness that HDTVs can display, so you need to scale up picture resolution and improve sharpness at the same time on a resolution up to 1080p at 120Hz.
As part of its Motion Accurate Picture Processing (MAPP), NXP’s new PNX5100 performs all of these motion estimation/compensation frame rate conversion and picture quality improvement operations at full 10-bit upto 17-bit accuracy. To handle the required computing load, it features three on-chip media processors plus a dedicated video back-end that performs functions such as sharpness, contrast and color enhancement as well as on-screen graphics insertion. The MAPP combination of movie judder cancellation, motion sharpness and vivid color management successfully removes visible halo and blur to deliver an enhanced viewing experience – particularly when watching fast-moving sports and action movies. The chip’s Automatic Picture Control (APC) feature dynamically adjusts the processing parameters used to obtain optimal improvement on every output frame.
The result is a straightforward add-in video post processor chip that allows set makers to produce HDTV sets that instantly stand out from the crowd, with vivid colors, smooth movement and a motion sharpness that make High-Definition really live up to its promise.
Joep van Eijden is the international product marketing manager for NXP Semiconductors’ picture quality enhancement systems including the PNX5100 product family. Joep is responsible for product definition, market analysis and contribution to the product family roadmap.
Check out NXP's product offerings for this application at NXP Semi
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