The use of visual information in a presentation was once a burdensome task requiring advanced preparation of slides, overhead projector materials, and projection system availability at a venue. Not any more. The field of image projection has seen huge changes over the past few years, fueled both by the opening up of new application areas and technological developments. Foremost amongst the former has been the boom in the popularity of DVDs and the “home theater” phenomenon that has accompanied it.
As for the latter, the big development has been the emergence of digital front projectors, easy to transport and operate, capable of using electronically stored information in a variety of forms including motion-picture video, and equally suitable for use in business or home theater systems.
Modern-day projector systems work by receiving a signal (in either analogue or digital form) from a data source (such as a computer, VCR, DVD, etc.) transforming the signal into an image, and projecting the image onto a screen. The associated processing takes place in one or other of the projector’s two main sections, the video decoder and the light engine. The former is where analogue signals are converted to digital via an analogue-to-digital (ADC) signal converter. The light engine consists of the lamp, the color splitter or color wheel, and the projection optics.
The precise way in which the digital signals are processed into an image for projection depends on the type of projector – a transmissive projector shines light through the image-forming element, a reflective projector bounces light off the image-forming element – and the particular image-forming technology employed:
| Projector type | Transmissive | Reflective |
|---|---|---|
| Underlying technology | CRTsLCDs | DLPLCOS |
It used to be that three-gun, CRT projectors dominated the market and that any decision making was confined to things such as the projector’s scan rate, the size of the CRTs and the type mounting bracket. The advent of LCD projectors in the 1990s began a trend towards more compact and portable devices, a trend that was accelerated by the subsequent emergence of the, DLP chip (also known as the Digital Micromirror Device or, DMD) in 1997. Before long LCD and DLP had replaced CRT as the dominant technologies.
Both technologies have seen rapid development and improvement as they battle each other to capitalize on the burgeoning home theater market. There’s little to choose between the two. DLP projectors have a better fill factor, but are prone to rainbow effect. LCD projectors have superior light efficiency, but suffer from screen door effect. For home theater usage in particular, both technologies benefit from being used in their 3-chip variants and here, LCD projectors have a significant price advantage over their DLP counterparts.
By 2004, the longer established LCD projector accounted for the majority of the installed base, with DLP increasing its market share year-on-year and LCOS yet to break into the mainstream.
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