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Techie Stuff

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Native Aspect Ratio

Projectors are fixed resolution display devices. As such, they have what is referred to as a native aspect ratio. The native aspect ratio is determined by the shape of the chip inside the projector. For example, if the native aspect ratio of a projector is 4:3, it means that the chip inside is shaped in the specified 4:3 proportion.

With that being said, many people assume that they absolutely must have a projector with a native aspect ratio of 16:9 in order to obtain the best image quality and that if a projector has a native aspect ratio of 16:9, then the projector must be top of the line. This is not necessarily the case. Not all 16:9 projectors are created equal. The cheaper 16:9 native aspect ratio projectors use SVGA resolution, which means that they aren’t going to perform as well as the higher-end home theater projectors with the same native aspect ratio.

What does this mean to you? Let’s say you get a projector for home theater use and that projector has a native aspect ratio of 16:9 but has SVGA resolution. This means when you watch a 16:9 aspect ratio image on the projector, your vertical resolution is going to drop to 450 lines. On the other hand, if you were to watch the image with a 4:3 projector, you would have 600 lines of vertical resolution. This goes to show you that the high-end 4:3 projectors may very well outperform the low-end 16:9 projectors.

When shopping for a projector, never look at just one spec when making your decision. Native aspect ratio must be considered along with other things like contrast, brightness and resolution. All of these things will affect your picture quality.

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Lamp Life

The lamp life of projectors is given in hours, but that doesn’t often tell a person exactly how long a projector lamp will last. For a long time, projector lamps were able to last only 3,000 hours (and that was in eco-mode). Today’s projector lamps are lasting much, much longer. If you estimate that a projector has a lamp life of 5,000 hours in eco-mode and the average projector that is used in home theaters is run for 8 hours a week, the lamp will last approximately 12 years if run in eco-mode at all times.

The exact life of a lamp in years will depend on the lamp life of the projector and the number of hours per week it is run. To estimate the life of your projector lamp, take the lamp life (5,000 hours in eco-mode as an example) divided by the number of hours used per week (8 hours as an example) divided by 52 (the number of weeks in a year). This will tell you how long your projector lamp will last.

Remember, when looking at projectors, make sure you know exactly what mode the company is quoting you when they tell you the lamp life of the product. You need to make sure you are comparing apples to apples. If two projectors are quoting lamp lives of 5,000 hours and one of them is much more expensive than the other, it could be due to the fact that the hours aren’t being quoted in the same operating mode.

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Throw Distance

The throw distance of a projector is how far the image can be projected from where the projector stands to the intended placement of the screen. This distance is calculated by measuring the distance from the projector’s lens to the projection screen that the image will be cast on to. A common standard for throw distance is one foot of projection width for every two feet between the projector’s lens and the screen. A smaller throw distance means that the distance the image can be projected will be smaller, whereas a higher throw distance allows you to project the image further.

Since projectors have zoom lenses, they usually have a range of throw distance ratios. When you know your screen size and the projector’s throw ratio, you should be able to figure out how far back to place the projector. For example, if the screen width is 8 feet and the projector’s throw ratio is 2.0-2.4, the projector should be located 16 to 19.2 feet from the screen. You can also determine the size of screen to get when you know the projector’s throw ratio and the distance you have to work with. Using the same example, if the maximum distance is 12 feet instead, a screen of 6 feet wide will work for your projector.

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Keystone Correction

Keystone correction occurs when a projector is not aligned perpendicularly to the screen or when the projection screen has an angled surface. The result is a distorted image. This can be addressed with keystone correction. While many of today’s projectors have keystone correction features, earlier projectors did not.

To perform keystone correction manually, you physically adjust the lens of the projector so that it projects at an angle that is higher or lower than it would be if it were on a flat surface. While this works for vertical keystoning, it does not help for horizontal keystone correction.

Today’s projectors are digital display devices. By adding an algorithm to the scaling, the new projectors are able to alter the image being projected onto the screen before it even reaches the projector’s projection lens. This results in an image that shows no distortion, even if the projection is at an angle.

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Light Source

Today’s projectors come in a variety of light sources including DLP, LCD and LED.

DLP projectors obtain their light source from a DLP lamp. The DLP chip, which may be one of the world’s most advanced light switches, is reflective and made up of thousands of tiny mirrors with each mirror representing a single pixel. A DLP chip can contain up to two million of these microscopic mirrors, each measuring less than one-fifth of the width of a strand of human hair. The light from the projector’s lamp is directed onto the surface of the DLP chip and the tiny mirrors move back and forth to direct light either into or away from the lens path. The DLP chip combined with the components that surround it produce images that are crisp, clear and of theater-like quality.

LCD projectors contain three separate LCD glass panels and as light passes through the panels, individual pixels can be opened to allow light to pass or closed to block the light. The biggest advantage to LCD projector lamps is that they are readily available and can be purchased from a number of suppliers, which means that competition can drive the price down. The fact that many LCD projector lamps can be obtained from third-party manufacturers also lowers the cost of these lamps. LCD projector lamps also tend to have a longer life span than DLP projector lamps, which can reduce the cost of ownership.

LED technology is more energy efficient as the light source is the LED lights that are installed in the projector rather than a traditional lamp. Instead of having a traditional lamp, the projector’s light source is created directly by the LEDs that are inside the projector. Like LCD projectors, LED projectors project the light from the LEDs through three LCD panels. Since there is no lamp to replace and the projector uses less power, the cost of ownership is reduced. It is the best choice for going green.

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DEEP Color

The HDMI consortium released a new standard in 2008 that supports what is referred to as DEEP Color. In the past, HDMI cables were only able to support 8-bit color. DEEP Color cables, however, support 10, 12 and 16 bit colors. This technology allows the number of shades of each color to be increased, which eliminates banding. If you want a DEEP Color image, look for a projector model that says it supports DEEP Color or that says it is HDMI 1.3a (or higher) compliant.

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Frame Interpolation

The average movie is shot at a rate of 24 frames per second. This is slow when compared to the average television show (which is usually shot in 30p) or something that has been shot in 1080i HDTV (which is 60p). There are times, however, when these speeds will not be fast enough to create a fluid image. This is especially true when you are viewing something on the large viewing area that is used by the projector. To make up for this, new home theater projectors use something called frame interpolation or frame creation. The projectors that use this technology analyze the differences between frames and then insert new frames in between them. These new frames adjust the image and make moving images look as though they are moving more fluidly across the larger display.

Not all frame interpolation systems are created equally. Some projectors generate more created frames than others. Frame interpolation is not always desirable either. There are complaints that it creates a digital video effect, which makes a film look too smooth with a little lesser amount of the surreal and sensual quality. However, if you are using the projector to watch an animated film or a concert, frame interpolation actually enhances the viewing experience.

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Picture in Picture Support

Some of today’s projectors have picture-in-picture (PIP) and POP technology. With PIP technology, the projector can display two images at the same time on a single screen. One of the images is a smaller image displayed within the larger image on the screen. With POP, the projector is able to display two images of the same size at the same time. With built-in switchers, it makes source switching seamless. Some projectors also offer special transition effects to choose from when utilizing the feature.

The only problem with PIP and POP is that both images cannot be active at the same time. That does not mean however, that you cannot go to the “inactive” image to update it or go back and forth between the two images that you have put up.

Another issue that consumers may run into is that many projectors only have one HDMI port, so if you are going to be using PIP or POP through multiple devices, one of the devices will have to be fed in through an analog connection. This is not usually of most concern for businesses but for home theater users it’s important to remember that you will only be able to have one device hooked up to the projector’s HDMI port.

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Many manufacturers do not discuss the issue of uniformity in their specs, but it is an important aspect when it comes to brightness consistency. The term “uniformity” refers to the consistency of the brightness over an entire image. For example, if a projector has a uniformity of 95 percent, then if that projector is projecting a single color image on an entire screen, there will be a variation of no more than 5 percent in intensity across the screen. The higher the uniformity percentage, the better the image quality will be.

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Dot Clock

Dot Clock is a term that is used to refer to the speed at which the information is processed to make up an image in 1/60 of a second. The spec actually comes from the video card of a computer connected to the projector, but the projector has to have the ability to match the speed of the computer video. The higher the resolution of a projector, the better the chance that it will be able to meet the Dot Clock of the connected device. It is important to note that Dot Clock is downward compatible. If the projector’s speed is higher than that of the connected device, it will work just fine. If, however, the speed of the projector is slower than the Dot Clock of the connected device, there could be problems.

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