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Basic Projector Specifications

What is “Native Resolution”?

"Resolution" refers to the number of lines of picture image displayed on screen. The greater resolution, the better picture quality.

Every projector that uses microdisplays, whether they are LCD panels, or DLP or LCOS chips, has a fixed array of pixels on those microdisplays. The projector will never be able to display more actual pixels than it has on those panels or chips. That fixed array of pixels is known as the native resolution (sometimes called 'true resolution') of the projector. So native resolution is the actual, true, physical resolution of the projector. That's the maximum number of pixels it can actually project individually. For example, SVGA (800x600) projectors display a native resolution of 800 pixels horizontally by 600 pixels vertically, that means the LCD panel resolution of SVGA projectors is 800x600. So an SVGA projector can only display 480,000 pixels at a time.

This may sound like a lot, but if you take a typical projection screen of 2 metres width, each pixel is going to be a quarter of a centimetre wide, whereas with an XGA projector the image is going to be under a fifth of a centimetre wide, and over 60% more pixels are displayed. This means the image is going to be sharper and less 'blocky' when projecting with an XGA projector.

What is maximum resolution?

Well, that number has nothing to do with the projector's physical display. Instead it has to do with signal formats. Computer and video signals come in a wide variety of resolution formats. And every projector is programmed to recognize many of those different signals. Maximum resolution is the highest resolution signal that the projector has been programmed to process and display.

Converting the input signal formats to native resolution

When a projector gets a signal that does not match its native resolution, it must convert that signal to the format of its native resolution in order to display it properly. This conversion process is commonly referred to as scaling. For example, if you have a projector with a native resolution of 800x600 that is capable of displaying an 1080i signal. That means the projector's physical pixel matrix is 800 pixels wide by 600 pixels in height. However, each frame of video in 1080i signal contains 1920x1080 pixels, which is a lot more than the projector has on its physical display. So in order to display the 1080i signal the projector must compress it into 800x600 format. It can do this because it has been programmed to do the compression from 1920x1080 to 800x600. Furthermore, if 1920x1080 is the highest resolution that your projector has been programmed to recognize and compress into its native display, then 1920x1080 is known as the maximum resolution of that projector.

Sometimes the incoming signal format is smaller than the native resolution of the display. For example, let's assume you have a native XGA resolution projector, and you are displaying a standard NTSC television signal. In this case, your projector has a native 1024x768 pixel array. But a regular NTSC television signal is only 640x480 pixels. So the projector must "scale" or expand that television signal up from 640x480 pixels to 1024x768 pixels in order to display the image full frame. Conversely, in our previous example, we talked about converting a larger 1920x1080 signal into a smaller 1280x720 display. Technically speaking, that is known as compression since you are compressing the signal to fit the display. However, it is less common to use the term compression these days. In typical usage, the term scaling refers to any conversion of a data or video signal to a projector's native display format, whether it is being scaled up (expanded), or scaled down (compressed).

Brightness:

Picture Brightness is measured in ANSI lumens.

How much illumination your eyes perceive on the screen depends on two factors: (1) the light output of the projector, and (2) the reflective properties of the screen.

There are two common methods of measuring light in a home theater. One is the ANSI lumen rating of the projector. That measures the light energy being generated by the projector itself. The second is foot-Lamberts (fL), which takes the screen into account and measures the total light that is being reflected back toward the audience. Of the two, foot-Lamberts is the better method to use for setting up your home theater. However, since that number depends on your screen size and screen gain, there is no fL specification published by projector manufacturers.

So how much light do I need?

When it comes to home theater projectors, brighter is not definitely better. What you want is a projector that produces enough light to fill your screen with good contrast, but not so bright that it creates eye fatigue when viewed for any length of time.

Contrast Ratio:

Contrast Ratio refers to the difference between the brightest part of the image and the darkest. In other words, if the contrast ratio is 400:1, this means that if part of the image is at full brightness and another part is as dark as possible, the brightest part will be 400 times brighter than the darkest part.

Contrast Ratio works hand in hand with lumens. A projector with a 1000:1 contrast ratio will look brighter than one with 400:1, even though they have the same lumen rating. This is particularly true in a darkened room. Be very careful when you are comparing projectors. Picture Brightness in lumens doesn't tell the whole story until you you combine it with Contrast Ratio.

The minimum standard for electronic theatre is 300:1 contrast Ratio. The higher the Contrast Ratio, the better your movies and pictures will look. 1000:1 looks significantly sharper.

LCD Panel System:

This refers to the size, number and type of LCD panels the projector is using.

Number of Pixels:

This refers to the number of tiny squares which make up the projected image. The number is determined by the resolution and aspect ratio of the projector. For example, an XGA projector with an aspect ratio of 4:3 has 768,432 pixels per LCD panel making a total of 2,359,296 pixels.

Aspect Ratio:

Aspect ratio refers to the ratio of width to height of the projected image. Typical computer images are 4 units wide by 3 units high. This is also the ratio for standard television. Therefore for church applications, a 4:3 ratio is usually ideal. For home theatre on the other hand, the newer 16:9 ratio might be more desirable.

When choosing a projector, keep in mind that all projectors will handle all aspect ratios. The question is, which one will you usually be projecting. At this point in time, if it is primarily for computer projection, 4:3 is probably your best choice.

Image Size:

This refers to the minimum and maximum size image the projector is capable of projecting and still be in focus. It is not usually of concern when selecting projectors.

Throw Distance:

This is very similar to Image Size. It refers to the minimum and maximum distance within which the projector will focus.

Motorized Zoom & Focus:

This means that you can control the size of the image and focus it right from your remote control. If you don't have motorized zoom and focus, you need to actually go to the projector and manually adjust them. For a portable projector, this may not be a problem. For an ceiling mounted projector, once it is installed and adjusted, the focus and zoom don't need to be readjusted unless you want to change the image size on the screen. Sometimes this is desired however.

Zoom Ratio:

This refers to the amount of difference between the smallest image size and the largest, without moving the projector. A typical projector has a zoom ratio of 1:1.3. This means that if the smallest image for a given screen distance is 10 feet, the largest will be 13 feet.

Rear Screen Projection:

This is a feature which reverses (mirror image) the projection so that it can be used for Rear Screen Projection. It is simply a function on the menu which you can turn On and Off.