There's more to projecting video than just plugging in and hitting play. Choosing a projector that best suits your classroom, conference room, or auditorium can depend on a variety of issues such as price, portability concerns, weight, resolution, and brightness levels. Finding one that's also compatible with input and output connections on existing hardware (VCRs and DVD players) and computers is just as important. Here are projector facts and details to help determine which solution is right for your school or district.
LCD Projectors
The first type of computer projectors that began to replace the old, bulky CRT-based models used small, transparent LCD panels as the imaging element, and these still represent a good portion of today's projectors. Though older designs were quite often dimmer than CRT projectors, the latest designs offer very good contrast and brightness, and make excellent display systems for typical computer data.
For motion video, however, they have a couple of drawbacks, including a slower response time for pixels to change color than either CRT or DLP-based projectors, and a generally lower color depth. The slower response to changes in the image can cause streaking in motion video images, in proportion to the speed of the motion. The fastest LCD panels can alleviate most of this problem, but are not as common in LCD projectors as they have become in desktop LCD monitors. Additionally, the pattern of separate (usually rectangular) red/green/blue pixels produces video that looks more pixilated than other types of displays (the lower the color depth, the more obvious this will be). That said, these deficiencies may be more or less of an issue than those that affect the other dominant type of computer projector.
DLP Projectors
DLP projectors use an interesting type of computer chip (designed by Texas Instruments) with hundreds of thousands of miniature mirrors that can be tilted under computer control. The tilting of the mirrors changes the amount of light reflected onto the screen. These mirrors can typically be tilted faster than can the pixels in an LCD display, but this design can produce some unexpected effects on motion video.
These projectors will either use three separate DLP chips (one for each color) and a set of prisms and mirrors to combine the three sets of pixels, or just one DLP chip and a spinning color wheel with three color filters to create the same effect. In either case, the result is that each pixel is made up of only one square, since the three colors are mixed together. This produces a less pixilated image than found on an LCD projector, but the use of a spinning wheel may sometimes create a "rainbow" effect, the result of some shimmering in the image that some viewers might see as similar to a slow CRT refresh rate. (The faster the speed of the wheel, the less of a problem this will be.)
The biggest problem is that the image processing that goes on inside a DLP projector causes just enough of a delay to get the audio and video out of sync. According to Jory Olson, Principal Engineer at InFocus Corporation, future DLP projectors may have added circuitry that will delay the audio to match the processing delays in the video projection. This means that while it is possible to create just the right amount of delay between the audio and video tracks in a video editing system, doing so will make the video file incompatible with future DLP projectors (and current LCD and CRT projectors) and thus, should only be done by someone with expertise, who also knows to save another copy with a normally synchronized audio track.
Interlaced vs. Progressive
The single most important issue that will affect the quality of the video you present-regardless of whether the source is VHS, DVD, or computer video-is the nature of the video stream and how it's sent to the projector.
The vast majority of video has, and continues to be, shot in interlaced mode. Developed as a key aspect of television back in the 1940s and 50s, interlaced video captures each frame as a pair of "fields" with alternating scan lines. Interlacing video makes motion appear smoother. If you look at a single interlaced frame of video, the image looks like you put the picture through a paper shredder. A solution is to put the strips back together, and then offset every other strip by some amount.
This works somewhat well so long as the image is displayed on an interlaced display (such as televisions or the behemoth CRT-based projectors you find in larger meeting rooms and theaters), but when shown on a progressive display (including CRT computer monitors, all LCD monitors/projectors, and DLP projectors), the horizontal lines that result are obvious and, well, ugly.
The best way to avoid this is to use only progressive video sources and to use only a progressive transfer system to send the image to the projector. This is easy in theory, but hard in real life because of the limited interfaces available on most projectors and video equipment.
The two most common video ports on projectors-composite (the yellow RCA jack) and S-Video (the black 4-pin mini-DIN jack) are both analog and interlaced. If you're connecting a video tape deck to the projector, these will be your only options, unfortunately. If you're lucky, the projector will have a de-interlacer that will make some educated guesses in correcting for objects that have moved between successive interlaced fields, though these vary in the quality of the correction. The simplest ones will trade the obvious distortion for a slight amount of blurriness, while the highest-end circuits-such as Faroudja's processor-will produce a much sharper image.
If your video source is a DVD player, then the best possible connection to use is the component video interface. But this connection is not automatically progressive-only higher-end DVD players allow you to choose between interlaced and progressive (typically via a switch near the jacks) because this requires the DVD player to have its own de-interlacer, and not all DLP and LCD projectors can support the progressive input anyway. And even if both the DVD player and the projector support progressive scan component video, and you know the projector has a de-interlacer, it might be that one of the units has a higher-quality de-interlacer. Unless you have detailed specs for both units, running a comparison (using a video with motion, not a still picture!) with the DVD player set to both progressive and interlaced signals would be a good idea. Occasionally a manufacturer will choose other colors for the RCA component video ports (I have seen yellow/blue/red on Sanyo projectors), but this just confuses things even further.
All these RCA jacks, their labels, and functions can be confusing. You need to look at their colors and labels to determine what they are for. Here are the three types of connections that are dedicated to VCR, DVD, or HDTV video devices:
- A yellow RCA jack for composite video. This is always an interlaced video signal, and the lowest-quality connection you can make (other than the RF style connectors) between a video deck and projector.
- A black 4-pin mini DIN plug for S-Video. This is also always an interlaced signal, but offers a little better image quality than a composite video signal.
- Green/Blue/Red RCA jacks labeled Y/Pb/Pr (or 480i, or Y/B-Y/R-Y) are for interlaced DVD video.
- Green/Blue/Red RCA jacks labeled Y/Cb/Cr (or 480p) are for progressive DVD video and HDTV or digital cable/satellite tuners.
- Green/Blue/Red RCA jacks labeled Y-Pb/Cb-Pr/Cr with a nearby switch labeled progressive/interlaced or 480i/480p are for interlaced or progressive video, depending on the position of the switch.
Don't want to, or don't have time to do the test? Don't have the spec sheets? A rough guide will be the class of projector-one meant for home theater use will almost always have a de-interlacer, while until recently, almost no business-type projectors offered them.
Connecting Computers to Projectors
Laptops are the most common devices connected to projectors, yet getting a satisfactory display is a far more complicated task than it should be. In addition to having to choose from a plethora of connection interfaces, you must learn how your computer works when connected to an external display, and how to adjust its settings to ensure the optimum image quality.
For LCD and DLP projectors, the single most important thing you need to do is ensure that the video signal output from your computer matches the projector's resolution exactly. I don't care if your laptop screen is 1020x768, 1280x1024, or something else-if the projector's resolution is 800x600, then that is what you must set the resolution to, even if it produces a poor image on your laptop. Better that you suffer with an ugly, hard-to-read image than the entire rest of the room.
If you can set your computer to have a different resolution on the projector than the display in front of you, then by all means, do that. However, this task is so frustratingly complex (and sometimes impossible) that even this author, with over 10 years of experience as the technical editor of a computer magazine, finds it difficult (and sometimes technically impossible) to get the computer, projector, and PowerPoint or video player synchronized. Explaining how to do this would take an article longer than this one, and would have to be updated each time the graphics card vendors update their drivers.
Connecting a laptop or desktop computer (which almost always produces a progressive video signal) to a projector requires a completely different set of connectors and cables:
- A computer-style blue 15-pin VGA connector can sometimes be used as a component connection, provided the manufacturer makes a breakout cable.
- A white DVI connector for use with analog or digital computer graphics adapters. The digital connector will usually produce a better image if your graphics card or laptop supports it. A variation that uses the same connector is the flavor of DVI with copy protection used to connect HDTV receivers.
- A black M1-A connector, designed by InFocus. This looks somewhat like the DVI connector, but is actually based on the Plug & Display connector, carries USB signals, and is designed to overcome some connectivity problems inherent in the DVI specification.
- Four or five BNC connectors, which may support only the old-fashioned component video signals (requiring the color channels plus separate or combined horizontal/vertical sync signals) or the new component video, requiring just three cables (functionally the same as the three RCA green/blue/red component jacks). In this case three of the BNC connectors may be labeled R/Cr, G/Y, and B/Cb, indicating their dual role, with the other two labeled H and V (dedicated to sync).
Almost all of these connections can also be used for either interlaced or progressive DVD/HDTV video sources, so long as the source has the same connector or a breakout cable is available to convert between two different standards.
Showing Video from a Computer
Once you have the proper connection between your computer and the projector, you then have to deal with ensuring the video is presented in the best quality. This means making sure that the video clip, whether shown inside a PowerPoint slide or directly with RealPlayer or Windows Media, has been de-interlaced. Why? Because with very rare exceptions, today's computers all output progressive scan video signals only, whether the connection is analog or digital.
Not all video editing programs are capable of de-interlacing, nor can all of them do it with the same quality, but if done properly, it will make a dramatic difference in the video quality, especially since once in the computer it's almost certain to be shown on some sort of progressive display, be it your computer monitor or a computer projector. If you're playing a DVD video on your computer's DVD drive, then you will also want to make sure that the DVD playback software has a de-interlacing feature.
A quick way to check if your video file has been de-interlaced (or was shot and edited in progressive scan mode, as is possible on higher-end digital video cameras) is to find a scene with a large amount of motion and then pause the playback and look for misaligned horizontal slices or duplicate objects. If there are any aircrafts in the scene, counting the number of propeller or helicopter blades can also give you the answer-if you see twice as many as you know that model has or if they are not evenly spaced, it's a pretty good sign it is an interlaced video.
Of course, most laptops also have composite and/or S-Video outputs (sometimes only an S-Video jack is provided, along with a converter cable that allows composite output as well). Although it is possible in some cases to configure a computer to pass an interlaced video displayed via RealMedia, Windows Media, or DVD-playback software directly out the S-Video/composite port and let the projector's de-interlacer (if present) adjust it to produce a quality image, the latest video drivers on laptops typically prevent you from setting the video port to the typical video resolutions (the lowest is typically 800x600, instead of 640x480 or lower), and not all video playback software can easily be configured to show only video on this port, unencumbered by toolbars or controls.
Projection Screens
Given all of these complex technical details about how projectors work and are interfaced to computers and video decks, it is important not to forget about the one aspect of video projection that includes almost no technology-the screen.
The design and color of the screen will affect two key aspects of the image quality-brightness and contrast. A white screen-such as a white, painted wall, a whiteboard, or even white projection screens (which are typical of most modern computer projection screens), offer less contrast than a light gray screen (typical of most older movie projection screens). Though in many classrooms or meeting rooms you won't have a say in the color of the screen, if you have any choice in this matter (such as bringing your own projection screen), it can make an important difference in the quality of your presentation, particularly if your video depends on large contrast swings for artistic or other reasons.
As Senior Technical Editor of CADENCE magazine, Peter K. Sheerin heads the industry-renowned CADENCE technical lab, providing incisive reviews of the latest software and hardware products related to computer-aided design.
Projector Choices
The following is only a sample of the many portable and ultra portable projectors geared towards the education market. Many manufacturers also offer fixed installation options for higher-end use. Check company Web sites for more information and special educational pricing.
- The PowerLite S1 is part of Epson's Value Series of multimedia projectors and features 400:1 contrast ratio, SVGA (800 x 600) resolution, 1200 ANSI lumens, 4:3 and 16:9 aspect ratio, color-coded cables, and weighs seven pounds. $999.
- The new x1 multimedia projector from InFocus features 1100 lumens, SVGA resolution, a 2000:1 contrast ratio, and video compatibility (NTSC, PAL, SECAM, EDTV, HDTV). The unit weighs 6.8 pounds. $999.
- Toshiba's TLP-S10U lightweight mobile projector weighs less than five pounds and is HDTV compatible. Features include 1200 ANSI lumens, SVGA 800 x 600 resolution, integrated data, video, and audio capabilities, and a monitor output connector. $999.
- NEC's VT Series includes the LCD-based VT660. The 1800 lumens projector is HDTV compatible (1080i, 1080i/50 Hz, 720p, 480p, 480i), 800 x 600 SVGA native resolution, has automatic keystone correction, and weighs 6.6 pounds. Inputs include RGB, S-Video, and composite video. Lamp life is 3000 hours in Eco-mode and 2000 in standard. $1795.
- Canon's newest line of projectors is the LV series, including the LV-5210, LV-7210, and LV-7215. These LCD offerings combine the precision of Genuine Canon optics with high-powered light sources to bring you from 2000 to 2500 lumens and resolution that keeps images crisp and compelling. $1999, $2499 and $3499 respectively.
- Dell's 2100MP digital projector uses the latest DLP DDR projection technology to generate high resolution images at 1800:1 contrast ratio and maximum brightness of 1000 ANSI lumens. An auto-sync feature adjusts the output resolution to match that of the input device up to SXGA+ (1400x1050) for plug- and- play operation.$1299.
- Hewlett-Packard's HP digital projector vp6100 series focuses on portability, durability and ease of use. It features standard industry input and output connections for hooking up to a number of devices, such as PDAs, laptops, desktops and other video displays. The vp6110 model weighs 6.7 pounds, has 1500 lumens and an 800x600 True SVGA. $1299.
- Sharp released the Notevision B10S this fall, a 5.9-pound LCD projector offering 1200 lumens, SVGA resolution, multiple inputs, HDTV compatibility, and inputs that include RGB, composite, S-Video, and RS-232C. $1395.
- Sony's line of ultra portable projectors includes the entry level VPLEX1-XGA LCD projector. It weighs roughly five pounds, has brightness levels of 1500 lumens, 1204 X 768 XGA resolution, and a four-times digital zoom to project images up to 4x larger. The built-in scan converter allows composite video, component video or RGB video input signal. There's also a USB Input available for wireless mouse control. $2599.
- The DLP ultra lightweight XD-25m from Boxlight is about the size of a VHS tape and weighs in at less than two pounds. It has true 1024 x 768 XGA resolution, 2000:1 contrast ratio, 1100 lumens, and digital keystone adjustment. The M1-DA digital/analog input allows for direct digital-to-digital signals. $2699.
- Mitsubishi Digital's XL8 ColorView projector offers XGA resolution (1024 x 768 pixels), provides 2000 ANSI lumens, and 350:1 contrast ratio. The security feature is an on-screen numeric keypad programmed with a PIN by the projector's operator, thus deeming the projector useless if stolen. There's also the option to upgrade from the standard remote to a Learning Remote that can switch inputs from various sources simultaneously. $3495.
- Dukane's ImagePro 8039B multimedia projector weighs 5.9 pounds and comes with 1400 lumens, SVGA resolution, a 400:1 contrast ratio, keystone correction, and multiple input and output options. $3595.
- Panasonic's new portable PT-L735NTU XGA Wireless LCD Projector weighs 9.3 pounds and features 2600 lumens of brightness, HDTV compatibility, an SD Memory Card slot with 8MB SD card, 4:3 aspect ratio (16:9 capable), and Blackboard mode. $5799.
- Microtek's MVP800x multimedia projector includes XGA sharp video playback and a brightness of 650 lumens. It weighs 14.7 pounds, has a contrast ratio of 200:1, an average lamp life of 2000 hours and 1.3x manual zoom and focus. The projector ships with remote control with laser pointer and wireless mouse with case; and cables.Call company for pricing.
Read other articles from the November Issue
