Reprinted from the June 2009 issue of Church Production Magazine
Mike Cruser, Southbrook Church
Edgeblending, Matrix of Choices
Panoramic video backdrops are the hottest new visual effects for churches. Edge-blending techniques using video projectors are becoming affordable, and church creativity is blooming.
Last fall, Southbrook Church in North Carolina was opening a new campus in Weddington, about 20 miles from Charlotte. Pastor Mike Cruser was busy: In addition to juggling the tasks that typically attend the launch of a new worship facility he was overseeing the integration of a 3x1 matrix of projectors. (He's both the worship and production pastor at Southbrook.) The end result would be a stunning super-wide visual backdrop for the new sanctuary, which seats about 1,250. The projected image would be processed and fed by a Vista Spyder unit and beamed through three Panasonic PT-D12000U projectors with onboard soft edge-blending capabilities.
Cruser had researched the video system himself, and now was collaborating directly with Vista Systems engineers and corresponding with Panasonic engineers in Japan. "We wanted to go with an integrator, but the price of the integrator was fairly expensive," he says. But with the pastor leading the integration, nothing would stop the Weddington campus of Southbrook Church from getting its ultra-widescreen projected image.
In the course of his do-it-himself foray into systems integration, Cruser has encountered most of the problems that still confront a church attempting to set up a matrix of projectors that's designed to display a singular image. For Southbrook's Weddington campus, all was certainly not for naught. Pastor Mike's efforts have resulted in a 70- by 20-foot image that's seamless---almost. "The only time we see a little bit of a problem is when there are really dark colors," he says. "Sometimes there's just a little variation that you'll see right on those blend lines. But for the most part you can't even tell."
Even for the most sophisticated soft edge-blended projection systems, variations in brightness are inevitable in areas of projector overlap that contain extreme black or extreme white imagery. Though it may always be slightly out of reach, how does a church go about striving toward edge-blended perfection?
Step by Step
The general steps toward devising a soft edge-blended projector matrix display are as follows. First, an appropriately proportioned image signal is repeated --- or "split" --- enough times to feed a certain number of projectors. A splitter---either outboard or integrated into a switcher or other image processor---handles this step.
Second, the image needs to be cut into pieces before its parts are assigned to each projector in the matrix. Some projectors contain the onboard processing power to perform this slicing and dicing --- really just "zooming into" a specific part of the unit --- but outboard units such at TV One's C2-1250 and others, can also do the job. You'll need a separate image processor, or an individual output on a processor with multiple outputs, for each projector. The image slice will need to include an area of overlap; this is the edge to be blended. For example, in a 2x2 projector matrix, the left-upper projector will display the left-upper quadrant of the original image, plus 10 to 20 percent extra on its right and bottom edges.
Third, the projectors' intensity within the overlap areas needs to be adjusted so that the edges appear seamless. This modification often involves some sort of gamma and black-level fade from 100 percent at the beginning of the overlap out to zero percent at the last pixel, and the fade is reversed starting at the near edge of the neighboring projector's image. This is the essence of edge blending, and as with image processing, both projectors and outboard processors can handle the step.
Finally, there's the fine calibration of the projectors' outputs in terms of color and brightness, and positioning to the pixel. This is where test patterns come into play. They're typically generated by image processors and projectors with edge-blending features, but also available on DVD and as computer image files.
Traditionally, soft edge-blended display systems relied solely on projectors with xenon lamps. Today, image processors are more powerful and can accommodate less-expensive projectors, which typically use UHP lamps. But it's a difficult step in the calibration process. "Color matching is the biggest gotcha," says Mark Holt, vice president and general manager for Sanyo's presentation technologies division. "It's not difficult to do the edge blending itself; color matching is the issue and part of that is because of [UHP] lamps." That's because UHP lamps lose their color properties as they age, while the more expensive xenon lamps do not. "But they're much more expensive than the UHPs, and they die in half the time," says Holt. "So pick your poison."
With UHP-style lamps, your edge-blended display system needs to be recalibrated with some frequency to match the projectors' colors. What's usually more "set and forget" is the physical alignment of the multiple projectors. When the system is being integrated, the projectors' positioning needs to be locked in so that their images' physical overlap matches to the pixel the area that the image processor has assigned for the blended edge.
Of course, sometimes projectors move ever so slightly, and the blended image's edges become a blurry mess. Pastor Mike Cruser discovered this problem on a few hot and humid days, when the warehouse in which Southbrook Church's Weddington campus resides tends to expand. "I don't know what forces are pulling on what, where," he says, "but we have noticed that we've had to go in and do just a little bit of lens shifting, just to line things up a little bit." Whether it's the sun or a volunteer's errant elbow, outside forces can conspire to physically move your projectors. For this reason, it seems crucial to select a projector model with lens-shift technology, which enables the fine mechanical adjustment of the lens in order to tweak the projected image's horizontal and vertical positioning. Some projectors have mounting plates that allow similar tweaking.
Projector Types
Now that you have a basic understanding of the technical process of blending projected images' edges to form a matrix, it's time to assess projector choices. Technically it's possible to do edge blending with the cheapest of projectors, but it's not advisable; lower-end business projectors tend to exhibit image fall-off around their edges, which is exactly where you want the brightness and colors to be uniform if you're blending edges. You'll see the seam. So the first requirement is to select a projector with a relatively uniform image from the center to the corners.
The first real dilemma, of course, is whether or not to select a projector with integrated edge-blending capabilities. "Soft edge-blending technology can be provided by the projector itself, by software applications, by external boxes, or by a seamless switcher," says Ludovic Mellot, vice president of Analog Way, which offers many lines of seamless switchers with edge-blending mode. "Using the projector itself or software has limitations, especially in terms of the use of different and numerous sources and multiple layers."
Creating a vast palette of pixels, any edge-blended matrix of projectors will display multiple sources well. Even a 2x1 matrix will allow you to display two video or computer sources at full resolution, for instance, the IMAG shot of your pastor and song lyrics. If you need a video system that displays multiple sources simultaneously, you're already in the market for some sort of image processor. And these units usually --- but not always --- offer edge blending as a feature. So perhaps onboard edge blending isn't a required feature for your projector.
If, however, your church is simply looking to create a huge image based on the content of one computer's display output or a single video source, integrated edge blending might be key. If the congregation will view video and song lyrics via a computer desktop, your media department might consider a multi-display device that expands the display output of your computer to match your edge-blended matrix. A Matrox TripleHead2Go, for instance, can triple your computer's desktop real estate to feed a 3x1 projector matrix properly. Then with a beefy graphics card (from Nvidia, perhaps) and software like Renewed Vision's ProPresenter, which can fill an extra-wide desktop, you're ready to feed content to your projectors. In this case, a projector model with integrated edge blending would obviate the need for another outboard image-processing unit.
Of course, image processors don't have to cost five figures. In the example above, with a TripleHead2Go card and ProPresenter software, each of the three projectors could be driven by a single image processor (about $1,500) to bring edge-blending capabilities to your system for not a whole lot of money.
I've already discussed the advantages and disadvantages of UHP vs. xenon lamps. Your projector choice will, as always, also be complicated by the pros and cons of competing projector imaging technologies: LCoS vs. DLP vs. LCD and three-chip vs. single-chip. (Three-chip technology assigns the red, green, and blue color elements each to a single imaging chip; single-chip technology utilizes a color wheel to route all colors through one imager.) There are no single-chip LCD projectors in the professional market, so you're essentially deciding among three-chip LCD, three-chip LCoS, single-chip DLP, and three-chip DLP.
Three-chip DLP technology sits at the highest end of the market and is typically associated with xenon lamps, whose color properties do not change as their bulbs diminish over time. For an edge-blended projector system, "It doesn't need to be three-DLP," says Chuck Collins of Digital Projection Inc., which manufactures both single- and three-chip DLP models. "You get better contrast historically and better control over the light engine with DLP because it's reflective rather than transmissive." Those two elements of image control play heavily into edge blending.
Another advantage of single-DLP over three-LCD is that there's only a single imaging device in each projector, which makes alignment easier. With three imagers, there's the possibility that internally, there will be imperfect alignment among the three chips.
But are there any advantages to three-LCD over single-DLP? (These competing technologies tend to carry similar price tags.) In terms of pure color, Mark Holt of Sanyo says yes, and his company now integrates edge blending into both types of projectors. Compared to single-DLP technology that utilizes a single color wheel, "LCD has always had more vibrant, warm colors, and if you color map it it's always had a significant advantage in red and green," he says. But DLP models with dual color wheels and six segments widen the color spectrum to approach that of three-LCD. "The drawback there is you lose about 30 percent of your light output," he says, comparing dual-color-wheel DLP models to single-color-wheel DLP, which outputs pure light through a clear color wheel section.
Option Matrix
To create a soft-edge-blended matrix of projected images, you've clearly got a matrix of choices. Higher-end options involve more sophisticated algorithms for matching projectors' gamma and color; they also typically can handle many video effects beyond the edge-blending steps I described in the "Step-by-Step" section. "All-in-one" solutions offer convenience --- at a price, of course. A Vista Spyder unit, for instance, could take a live video feed of your pastor, make it a picture-in-picture against a graphical background, and simultaneously display song lyrics --- all while blending edges, splitting and processing images before they reach the projectors.
Green Hippo's Hippotizer, distributed in the U.S. by TMB, performs similar functions. Folsom division of Barco is all about image processing; its Encore Presentation System might be comparable to Vista's Spyder. Christie offers add-in cards (such as the Twist) for many of its projectors to enable edge-blending and image-warping functions. Projector manufacturer Digital Projection Inc. has introduced the rack-mountable Mercator 3, an "edge-blending/warp engine," according to Collins. The company also is set to integrate edge blending into its Titan line of three-DLP models. Then, of course, other external units feather the edges of individual projectors. Some are more feature-limited than the higher-end solutions, but depending on your church's specific needs, they could certainly fit the bill.
Then, of course, many manufacturers offer projectors with edge blending and some form of image processing built in. These start in the five-figure range, but the ground floor is a lot lower than it used to be. Sanyo, for instance, is introducing the PT-DHT100L, a dual-color-wheel, single-DLP model that starts at $21,995 (without a lens). Panasonic's PT-D5700U goes for $11,500. No one said it would be cheap, but devising a matrix of projectors that display a single, oversized, edge-blended image isn't the six-figure proposition it very recently was.
Trevor Boyer is a freelance writer living in Brooklyn, New York. He likes to write professional A/V and video production stories (like this one) that can be reported via subway travel.