Introduction
As one of my well respected colleagues' states, "De-interlacing is not a science but rather an art!" At a high-level, de-interlacing is simply doubling the amount of information or lines within an image or technically referred to as a field. At first, this seems like a simple task but in reality this is difficult to implement. What makes this relatively simple function so hard to implement in reality?
Note to the reader: This article is written with the assumption of having a basic understanding of video. For a quick tutorial, read the February issue of Digital TV Design Line how-to article called The basics of interlaced video and the techniques used in de-interlacing.
The Problem
Before we can answer the question at hand, we need to understand what we have to work with"interlaced video. Looking back when Philo T. Farnsworth invented the television one of the biggest challenges faced then and still today is the ability to send more data than the available infrastructure could handle. As a compromise, they created the first video compression scheme in the form of interlaced video.
Amazingly, people fail to appreciate interlaced video as a form of compression due to its rather simple nature. I once lectured to a group of master's and Ph.D. candidates at a local university that is globally respected for their knowledge on compression and during my presentation I brought forward the idea of interlaced video as a form of compression. Remarkably, a number of students argued against this idea. Maybe it doesn't fit well with the modern era of compression they are currently studying, but they need to learn to see the 'forest for the trees.' Let's accept interlaced video as a form of compression and move on.
Since 1930 the video we know and love has been traditionally interlaced. Interlaced video has been shown on cathode ray tubes, commonly referred to as CRT. Only in the past decade have we seen the availability of a new non-interlaced format, otherwise known as the progressive format. The progressive format captures an entire image of video 60 times every second. This format has its origins in the PC world where progressive displays were and still are the norm. Currently, progressive sources are not widely available, but this is changing very rapidly especially with the recent introductions of new gaming systems and HDTV disc players such as Blu-Ray and HD-DVD.
The need for better image quality has driven the need for progressive video. This has resulted in the tremendous growth in popularity of progressive display technologies like plasma and LCD televisions. CRT-TVs still produce the best image quality of the available technologies and relative to other technologies has a longer lifetime. Other issues related to CRTs are its weight and depth. In addition, it's becoming extremely difficult to find a good quality CRT-TV that supports the traditional interlaced format.
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