Front Projection Television

There are three grades of CRT projectors, each determined by their horizontal scan rates (the number of lines the projector can draw across the screen in one second). Video grade projectors scan at 15.75kHz and are the least expensive CRT models. Data grade projectors scan at 31.5kHz and above, and can be used with a line doubler (see next paragraph). Graphics grade models are the highest quality projectors, and can scan at 63kHz and above. These projectors can be used with either a line doubler or a line quadrupler. The numbers of pixels determines the quality of an LCD projector: the higher the better.

A line doubler significantly improves picture quality from conventional interlaced video sources. A television picture is made up of horizontal lines. One field contains the even numbered lines and the other field contains the odd number lines. This process is called interlace scan. A line doubler doubles the number of lines present at any one time. The line doubler holds one field in memory and then spits it out at the same time as the next field. This is called progressive scan and is used in computer monitors. The horizontal scan lines disappear and the picture looks more film-like.