LCD projector glossary

Buying your first LCD projector can be a bit daunting. There is a lot of terminology to get your head around. We wrote this glossary to help those that are new to the world of LCD projectors.

480p or progressive scan or EDTV

Progressive scanning is basically drawing a picture on a TV screen 1 line at a time, 1, 2, 3, 4, 5... The difference between this and interlaced scanning is that interlacing only draws 1, 3, 5... then comes back and does 2, 4, 6... in a second pass. Interlacing (e.g. 480i) only really becomes a big problem when you have very large screens such as 50" and above. On large screens (such as one from a projector) things can easily be unwatchable when you use an interlaced signal. This is why you should always use the 480p with large screen projectors and ensure your DVD player supports a progressive scan component output.

You can however buy LCD projectors with hardware on board (e.g. deinterlacer or line doubler) that will take an interlaced signal and convert it to non interlaced so everything looks good on the screen. The more you pay the better de interlacing performance you get.

Image Quality

Resolution is given as the number of pixels that make up an image. It is measured as width by height (i.e the number of pixels along the width of the display and then the number along the side). For example, an SVGA projector is 800 pixels wide by 600 pixels high. More pixels per unit of area produce a higher resolution and create crisper images.

Brightness

Projector brightness is measured in ANSI lumens. The brightness you need depends on several factors, including image size, audience size, and amount of ambient light.

Contrast Ratio

Contrast is the ratio of whitest to blackest area within an image. Higher contrast ratios make for deeper blacks richer colors. Contrast ratios typically range from 400:1 to as high as 3000:1. Generally contrast ratios are more important than brightness in the quality of a display.

There are two methods of calculating contrast ratio used by projector manufacturers. Full On/Off contrast measures the ratio of the light output from an entirely white image (full on) versus the light output from an entirely black image (full off). ANSI contrast is measured with a pattern of 16 alternating black and white rectangles. The average light output from the white rectangles is divided by the average light output of the black rectangles to determine the ANSI contrast ratio.

No. of colors

This is the number of colors the projector is able to display. The vast majority of current projector models can display 16.7 million colors.

Aspect Ratio

These are the aspect ratios which the projector can display. The native aspect ratio is usually listed first, followed by other aspect ratios the projector can output.

Native Aspect Ratio - Because a projector is a "fixed resolution" display device, they have what is called a "native aspect ratio." The most common aspect ratios for projectors are 4:3, 5:4 and 16:9. That means that the chip (or panel) inside the projector is shaped in the specified 4:3, 5:4 or 16:9 proportions. Think of the chip as a miniature version of the image you will see on your screen. Currently the most common aspect ratio in projectors is 4:3, which is the same as most televisions and computer monitors.

Home Theater

A 16:9 native aspect ratio is designed primarily for home theater use. This is because widescreen DVD and HDTV signals are broadcast or encoded in the 16:9 format. Home theater enthusiasts tend to prefer 16:9 aspect ratios because they are closer to original 35mm film format. 4:3 projectors can also display widescreen images however, and can also be a good choice for home theater use.

Scaling

The projector's process of converting a different input format to its native output format. For example converting 1024 by 768 VGA input from a computer to a projectors's native 800 by 600 resolution.

HDTV

A type of television signal, which is scheduled by government mandate to replace the current US standard, NTSC, by the year 2006. HDTV is different from NTSC in several ways. First, HDTV is broadcast in the 16:9 aspect ratio as compared to NTSC's 4:3 aspect ratio. Second, HDTV resolutions are increased from (if expressed in computer resolution terms) 640 x 480 to either 1922 x 1080 (or 1080i) or 1280 x 720 (or 720p). Thirdly, because the signal itself is digital rather than analog, it can carry a lot of information, including full digital audio with multiple channels.

Short and Long Throw Lenses

Some projectors are designed to be mounted far back from the screen viewing surface while others can be used in closer proximity to the screen.