Technologies For Worship — March 2011
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Edge-Blending : The Basics

Edge-Blending by its very definition is the use of multiple projectors to project on a single screen or surface.

There is a lot going on behind the scenes of an edge-blending solution. Depending on what your individual needs are, the requirements and the functionality will change accordingly

DATA-DOUBLING AND FEATHERING

There are two different pieces to making a successful edge blend. The first is called data-doubling.When you are doing an edge blend, you have to overlap the projected images from each of the projectors onto your display surface.To simplify, we’ll just talk about edge-blending here with two projectors. In order to make a seamless image on a projection screen, you have to overlap those two images, such that the right edge of the left projector is sharing the same information as the left edge of the right projector. This shared space is typically 200 pixels or so, or anywhere from 15 - 25% of the individual projector’s horizontal resolution.

Whenever data-doubling is done, the overlapped area of the projected images, are going to be roughly twice as bright as the rest of the image given that two projectors are projecting that overlap area..

The second piece of edge-blending is “feathering” which refers to the act of feathering the edge of the images the reside in this overlapped area. This is where you taper the right edge of the left projector down to black, and vice versa for the right projector. In effect, this stitches those two images together.

Edge-Blending is challenging because you are gradually shifting from one projected image to another. The trick to doing a good edge blend is to “blur” the edge of each projected image as much as possible.

In order to determine the right calculations for edgeblending, you need to look at your screen and ask: how many pixels am I actually seeing here?

Referring to the graphics on page 16, the image is 600 pixels tall by 2000 pixels wide, even though we’re actually projecting a total of 2400 pixels. The visible pixel resolution when you compensate for the two 200 pixel edgeblends is 2000 x 600.

The math of what your resolution is going to be and how much overlap you are going to have is all based upon the resolution of each of the projectors as well as the size of the screen you are outputting to. When you know the size of the aggregate projector resolution in reference to your screen, then it is all a matter of calculation.

Before you even look at any edge blending features, you need to ensure that the individual projectors themselves are set as close as possible to the same output capabilities. You need to make sure the brightness and contrast all line up as closely as possible to ensure the best possible blended edge.

Something that will affect the brightness and contrast is if you are doing front or rear projection. DLP projectors versus LCD projectors will also affect the output. The “curve” or the drop off to black within the blend will look very different depending on all of these factors.

As you probably know, projectors, even if they are projecting black, are still projecting light. If you clear your Image and project only “black”, by virtue of the fact that you are still projecting light, you’re going to see what appears to be a lighter shade of grey where those projectors overlap. A good practice is to configure your settings to determine your minimum black level so that it remains consistent from projector to projector when you are showing “pure black”.

Edge-blending is very difficult to do with different projectors. In an ideal situation, you would have matching projectors. Even then, if you have two ‘inexpensive’ projectors with poor color balance, if will ruin the effect of your edge-blend. Even identical projectors have a different look to them. Ideally you would want to use similar projectors (all LCD for example) with similar lamp brightness.

For the calibration process, what you will generally see in many edge-blending systems is an array of color bars, or a series of grey stripes. So for example you would see a pattern of black at the bottom going through several different spans of grey to white at the top.

When you’re dealing with color in projectors it will also affect your grey and black as well. White, grey and black will all be tinged with a certain color. You’re going to use these gradient tools to make sure your color balance is right, and then you are going to use the grid to make Sure your overlap is proper between the projectors.

Edge-blending is about technology and math, but also about creativity. It can truly be a very impacting effect to use for your video systems. Once you’ve done the proper legwork and research, you may find that it adds a very unique and valuable component to your video ministry.

Brad Weston is President of Renewed Vision (makers of ProPresenter, ProVideo Player, and ProVideoSync), and has a long history of enhancing church and ministry productions.

Edge-Blending in Today’s House Of Worship

Have you ever seen the HUGE, almost wall-to-wall, screens on stage behind performers? The big image isn’t just made up of one simple video on one projector--its made up of multiple projectors being edge-blended on a screen to create a digital canvas. It’s more popular than ever before and is being used on the sets of the CBS Evening News, the NFL Today, CNN’s Wolf Blitzer set as well as churches like Northland Church outside Orlando or Hillsong in Australia. Edge blending is a great tool for churches to tell the greatest story ever told in an immersive fashion, with a “digital wallpaper”. But how do you do it? It takes three things: projectors and processing, a big screen, and great compelling content.

WHERE TO BEGIN?

First, decide how big your image needs to be--are you trying to fill the proscenium? Take over the whole stage area? Is the projection surface going to be a backdrop behind the performers, or designed to ceate a digital wallpaper behind the communicator? Get a measuring tape and take some measurements and see what size you will be happy with.

Next, before you do anything else, you’ll need to do some math to determine how much overlap each projector will have.

In this step you are determining if the size of image you want can actually be achieved by the projectors on the market. Here is a simple calculation for you: lets say you have one projector with an image size of 16’ wide by 9’ high, that’s pretty easy right? It gets more complicated when you say you want two projectors, and a blend or overlap between the two projectors at 20%. If you do the math, then you’ll find that your total canvas size is then roughly 25.6’ wide and 9’ high. This gets more mathintensive when you have more projectors!

Once you have locked in your screen size, you need to work on projectors and processing-projectors. Projectors come in all shapes and sizes. Work with a projectorpro to make sure you have projectors that have all the features for your specific application: correct input type, native pixel depth, proper lensing for your throw distance, mounting hardware etc. With processing, the more money you spend, the more features you have, the more inputs you have, the more outputs you have.

COMPELLING CONTENT

What are you going to put on this big screen? Is it graphical content? Video content? Live content like image-magnification? This determines how you are going to build the content, what the device is that gets the content to the screens, and who in your team is going to be the blending pro... the video guy or the graphics guy?Remember the blended image is like high-definition on steroids; a 45’ wide screen could easily have a pixel depth of over 5,000 native pixels wide, a native HD signal only has 1,920 pixels.

Your screen is a modern marvel of engineering.A 40’ wide rear projection screen that has no vertical bracing (otherwise you would see a shadow), that doesn’t have a visible seam is like the 8th wonder of the world. It may take eight weeks to manufacture, so be patient and have your epiphany of a big blended image on your stage with plenty of time to pull it off.

Bottom line; blended images, digital canvas, whatever you call it is an architectural piece built from technology and will be one of the definitions of your church service.Edge-blending is not for the faint of heart as it takes time every week to build custom content, big money to implement, and perhaps a totally different content work-flow than what you are using today.

But when it works...wow...I mean WOW!

I heard a layperson say the Sunday that a blended image was put on stage, “The pastor’s message today was the best I have ever heard!” I thought to myself, the pastor has been here 20 years and his teaching style probably has not changed much; I think the message today was the best not because of the pastor's teaching, but rather the 30’ digital Canvas reinforcing his sermon points throughout the lesson.

Ben Mankin is president of Mankin Media Systems with headquarters outside Nashville, TN. He grew up pulling cable at TV shoots, and professionally has worked for Fortune 50 companies and churches just like yours. Ben can be lured off a cliff with homemade ice cream. Contact Ben at ben@mankinmedia.com

Edge-Blending: Manufacturer's Outlook, Part 1

These answers provided by Scott Wellington, Product Marketing Manager for Projectors at Panasonic Solutions Company.

TFWM: What is a clear definition of edge-blending from a manufacturer's perspective?

Scott Wellington: Edge-blending is the process by which two or more projected images are overlapped and seamlessly combined to produce a custom aspect ratio
(i. e., greater than typical 4:3 or 16:9). This process makes it possible to create wider, larger and/or unique video presentations.

TFWM: What is a clear explanation of a signal chain including an edge-blend capable projector?

SW: A signal chain can be as simple as a video source, a signal splitter, cables and two edge-blend capable projectors. However, depending on application, degree of complexity and budget, an edge blend system can incorporate one or more of the following items:

A Level 3 setup might employ a video processor to combine and format various image sources into a master image to be distributed to the projectors. Blending can be done in the processor or in the projectors.If you like, a master image or program can also be produced on a choice of software platforms, and divided appropriately and recorded to PC hard drives or solid state memory players attached to each projector. (Synchronized playback must be ensured).

TFWM: How does one calculate the proper aspect ratio?

SW: To determine the aspect ratio of the image and screen needed, divide the effective width by the effective height. For example, using two 1920 x 1200 projectors with a 10% horizontal overlap, calculate as follows: 1920 x 2 = 3840 3840 - 192 (10% of 1920) = 3648 3648 / 1200 = 3.04: 1 aspect ratio

TFWM: How does content (video, still images) need to be manipulated in order to be optimized to operate with Panasonic edge-blend capable projectors, for example?

SW: Panasonic projectors can lock to a maximum input resolution of 1920 x 1200.

If the input signal is less than this, the user will need to adjust the image zoom and position function of each projector in order to position the image as needed.

If the input signal is 1920 x 1200, the projector’s scaler should be set to “through” and the division of the master image into sections and the overlap between them must be entered into the video card or the external processor.
This overlap amount must be set in the projector’s edge-blending menu to match.

TFWM: What are some rules of thumb video operators should be aware of when preparing a system to be optimized for edge-blending?

SW: Full motion video content works best because it’s more “forgiving” than graphics.

Blending static high resolution graphics such as text that will be seen close-up is the most difficult type of edge-blending.

Lenses will produce barrel distortion depending on the zoom and shift settings. Some projectors come equipped with builtin features that can be used to compensate for this distortion, as well as enabling edge-blending on a curved screen.

Periodic image “tune-ups” will be needed, depending on the application and installation.

Edge-Blending: Manufacturer’s Outlook, Part 2

These answers provided by Andrzej Lubaszka, Technical Support Engineer at Analog Way Inc.

TFWM: Are there specific screen configurations or aspect ratios that work best for edge blending?

Andrzej Lubaszka: When installing an edge blend system, your screen configuration is dependent primarily on the projectors you are using. Since projectors are the most inflexible portion of the system, your blend will be created from overlapping multiple standard projectors, which are typically 4/3 or 16/9 (1.33 or 1.78). The aspect ratio of the overall blend can be changed by adjusting the overlap (covering).

For an effective blend, let's consider the overlap to be between 10 and 50% of the screen size. Using two 4/3 projectors in a horizontal blend, you could create a screen ratio between 7.6/3 and 6/3 (2.53 to 2.00). With two 16/9 projectors blended horizontally, you can do 30.4/9 to 24/9 (3.38 to 2.67). To simplify sizing the projection screen, an aspect ratio of 3/1 (3.00) is often chosen, but by no means are you limited to choosing a nice round number.

When designing content for a blend, make sure your screen is not one of the standard aspect ratios that you find in today’s video signals (ie: 4/3 or 16/9). You will need to have a plan to be able to display sources such as cameras on the blended screen, and not have them appear distorted in any way. The most basic blend setup will simply stretch a source across the entire blend area, fitting both the horizontal and vertical dimensions to the screen.

To display your content in the intended aspect ratio, you’ll need to use a system that can display your image in a window or PIP somewhere within the blended area, or crop the image and display a portion of the aspect ratio correct image. You have the choice of fine tuning your graphics content for the unique blend aspect ratio, or letting the processor do all of the hard work.

TFWM: What are some techniques that can be used to properly calibrate the edges of one image with multiple projectors?

AL: When setting up a blend, the focus and alignment of the projectors is critical to the success of the blend. With one projector you only need to adjust the size and position of the projected image to fit the screen, and any overshoot would disappear into the black matte border surrounding the screen.

For a successful blend, the pixels from one projector must be aligned to perfectly overlap the next. A grid pattern is very useful for this alignment. You can use patterns from the projector or from the edge blend processor, but using a digital path from the test pattern to the projector will ensure that you’re aligning the actual edges of the projected image, and not a VGA source which still needs to be auto-centered.

By perfectly aligning the horizontal lines of the grid pattern, you will know that your projectors are level and aligned. Once aligned, use the blend processor to adjust the amount of overlap or covering until the covering test pattern lines converge.

Keep in mind that a successful blend is dependent on a successful projector alignment.Even if you plan on tackling the rest of a blend project in-house, it may be worthwhile to hire an experienced projectionist to help with the physical alignment.

TFWM: How can HoW staff deal with projectors of varying brightness? Does this affect the blended image, and can it be fixed?

AL: An effective blend relies on matching projectors. Using different types of projectors in the same blend could mean differences in color linearity which will allow the audience to see the seams of the blend. Since lamps tend to experience a shift in brightness and color as they age, using lamps of different ages can also make differences between projectors more obvious. Some projectors can compensate for the lamp life, but even the best compensation has its limitations.For this reason, it’s best to replace the lamps in all your blend projectors at the same time.

Once you have matched your projectors as best as possible, you can use blending equipment such as the Analog Way Di-VentiX II or Smart Edge to compensate for the brightness difference between the overlap zones where you will have the brightness of the two projectors, and the other areas where you only have the brightness of one projector.

EDGE BLENDING IN THE REAL WORLD A HOUSE OF WORSHIP PROFILE

In the Spring of 2010, Northview Church, in the northern Indianapolis suburb of Carmel, IN, completed construction of the latest addition to their sprawling 80-acre campus. Northview was growing quickly and needed a new worship center to accommodate current and future space needs.In addition, the church had been building extensive staging and set pieces for their worship services, and wanted a way to reign in some of the expenses (time, money and storage) that these sets were creating.

Under the guidance of former Disney Imagineer Lenzy Hendrix, it was decided to go with a model that would allow for the creation of “virtual” sets - a large thrust stage backed by a 30’ by 80’ screen. Jason Chapman, Northview’s Director of Production and Video, was part of the team that helped to envision and put together the new room.

“In our previous auditorium, we built a lot of stage props and backgrounds to fit the theme of a particular sermon series. The sets That used to take us weeks to build are now put together virtually in a fraction of the time.” Technical Director Shaun Miller elaborates: “One of the areas where we’ve had the most success is blurring the line where the stage and screen meet by using graphics that are scaled to the actual size of our room and people - it creates the illusion that stage actually extends beyond it’s physical limits.”

S&B Construction and ProSound worked together with several subcontractors to provide the current system and room design. Four Christie Roadster S+16K projectors, stacked in pairs, rear-project onto the screen, and are blended to create the final image (the system is set up to eventually add an additional pair of projectors). Signal is sent from the video control room below the auditorium over fiber optic cable via Magenta Infinea DVI boxes, which allow the signal to be sent up to 600 feet. The end result is a high resolution image with considerable brightness, even in a fully lit environment. Pandora’s Box by Coolux, is currently being used to scale and blend video and graphic images to the widescreen format required by the dimensions of the screen.

“Edge blending has been an ongoing challenge,” relates Lighting and Video Director Travis Carpenter. “A visible band is naturally created across the display where projected images overlap - the trick is to eliminate the band by gradually fading the edges of the images, while simultaneously fighting the creation of “hot spots” formed by the stacked projectors. These spots are areas in the center of each of the stacked pair’s projection throw where the light hits the screen directly before diffusing slightly to the sides.”

An additional, unexpected challenge was provided by the very size of the screen itself. “Because the screen is so large (roughly 30 x 80 ft.), it breathes in and out as it is impacted by the differences in air pressure between the projection room and the auditorium itself.” says Chapman. “The air pressure is often in a constant state of flux, as doors are opened at the beginning and end of services this can be a difficult issue to navigate, particularly when we’re dealing with significant temperature differences between the air in the auditorium, and the air that flows in from our atrium when the doors are opened. We have several saved blending presets within Pandora’s Box, depending on the season of the year.”

The tech and creative arts teams quickly learned that they had to be careful what goes up on the back screen. “Images with sharp or fine lines, particularly text, that flow across the blended area can sometimes call attention to a lack of perfect blending caused by the breathing of the screen.” Carpenter continues.“We’re able to get most images pretty close by projecting a grid map on the screen as we blend, but the breathing of the screen can make things rough.” Chapman adds, “It’s also critical that when making custom videos, or even simply projecting motion backgrounds, we have to be mindful of how big the screen really is. People in the services who are prone to vertigo, or who easily get dizzy, can get actually get motion sickness, so we have to be careful not to go overboard on the motion side of things. Just because something “looks cool” doesn’t necessarily mean that we should use it in church!”

One of the best practical recommendations that the Northview team has is to simply stay on top of things, and to realize that blending is an ongoing process, not something that’s done once and then forgotten about. “We’re constantly fine tuning.” concludes Miller. “We make adjustments on a weekly basis, and not just to the actual edge blending parameters. So many things can affect the image - much of it comes down to making sure that you’re taking care of equipment. Cleaning the screen itself is something we are preparing to tackle now. After nearly a year of use we are beginning to see pockets of dust showing up. Projector maintenance is also huge. When working with these high power units, we have to keep track of lamp hours and air circulation. It’s a tricky balance, but when all these things are working together, and everything is blended well, the results can be pretty incredible!”

Greg Wallace is Creative Arts Pastor of Northview Church - www.northviewchurch.us
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