Display Guide

01 Defining Your System

Clearly identifying your goals will help you define the attributes of the system most useful to you. There are many trade-offs to consider — many attributes are, to some degree, at odds with others. As an example, high brightness and quality night scenes often force a trade-off. By narrowing your goals and focusing on your critical needs, a clear solution will emerge.

First, you need to consider the purpose of the display:

• To be used for simulation training, entertainment, visualization, or education?
• One or more than one person involved in the experience?
• Looking straight on, or at various angles?
• The relative closeness of the viewer.
• Daytime or mostly nighttime scene.
• Night vision apparatus.
• Stereo 3D.
• Portability requirements.

02 Content — Planar Images vs. Real World & 3D Stereo

Generally, content comes in two types: planar and material meant for curved screens. Examples of planar content include movies, games, and presentations; immersive content includes simulation, VR, or visualization.

Both types may be curved, but planar images are better represented where the horizontal field of view is less than 180 degrees. Distortion increases as the field of view widens — parts of the image drawn to be in front of the viewer end up at the sides. Material meant for curved screens has no theoretical field-of-view limitation. Given enough projectors and computers, they can fill an entire sphere for complete immersion.

03 Projection System Budget

One of the first items people wrestle with is cost. With today's modern software warping and blending tools, the majority of the cost is spread between the projectors and the screen. Projectors range from $500 to as much as $500,000. Screens can be home-made or cost many thousands of dollars.

All of the attributes below will affect your budget and system capability. Decide which attributes are most important to you and concentrate spending there — compromising on items of lesser importance to achieve your goals.

04 How Big Should Your Projection Screen Be?

Generally speaking, it doesn't cost much to make a projected display larger — just move the projectors back (though there are trade-offs in brightness and spatial resolution). A display is often defined by the space available. However, this should be informed by field-of-view requirements.

The question is: "How much of the participant's view needs to be filled with the image?" For immersion purposes, the greater the field of view, the better. Field of view is governed by the size of the display and the radius of curvature. Generally, the larger the screen and tighter the radius, the more immersive the experience. Larger systems maintaining brightness and spatial resolution usually require more projectors — and subsequently more budget.

05 Optimum Screen Shape

When people talk about curved displays, they generally refer to cylindrical screens — constant curvature in one axis. While this presents a good immersive experience, a sphere or partial sphere does a much better job. Spheres are curved both vertically and horizontally, making the participant feel more enveloped and part of the scene — but they are harder to build and considerably more expensive.

Other screen shapes are possible. Conical screens are often used in air traffic control simulators where participants look at the airfield below. Advertisers sometimes use screens shaped like products or abstract forms.

06 Front Projection or Rear Projection

Most curved screens are front-projected for two primary reasons. First, front projection screens are less expensive. Second, front projection designs use less overall space — projectors occupy the same space as the viewer(s), while rear projection requires space behind the screen for both the projector and the throw distance needed.

Mirrors can mitigate rear projection space requirements and are often a good choice, but create design challenges of their own. Additional considerations: anomalies tolerable in front-projected images are not acceptable in rear projection. Rear projection is harder to blend, prone to hot spotting, and requires better lenses with longer throw ratios.

07 Spatial Resolution

Projector resolution and spatial resolution are two very different things. Projector resolution refers only to the number of pixels and aspect ratio. Spatial resolution is governed by the pixel pitch of the projector, the lens configuration, the distance from the screen, and the projector spacing. In short: if you make a larger picture, it will be a grainier image.

08 Processing Power

To create higher pixel count displays, pay close attention to processing and graphics performance. Using HD (1920×1080) projectors, your graphics card must draw 2 million pixels every 1/60 of a second. A 4K display requires nearly 9,000,000 pixels every 1/60 of a second. The increase in processing power required to drive higher resolutions increases costs significantly. Be sure there is a real advantage before embracing higher pixel counts.

09 Projector Contrast vs. Apparent Contrast

Contrast is the most under-appreciated aspect of display devices. Customers always speak of brightness and resolution, but almost never contrast. Contrast is the apparent difference in brightness between light and dark pixels — how black the black pixels are — the "pop" in a picture and a major contributor to vibrancy.

In immersive displays, you can affect contrast by choosing high-contrast devices, controlling ambient light, and/or using a lower-gain screen. Limit field of view to what is needed. Do not use projectors brighter than necessary.

10 Projectors — What's Best in a Multi-Projector System?

Projectors are not created equally. Consumer-grade office projectors will not do justice to most immersive material. Color saturation, brightness roll-off, and contrast are all lacking. These problems worsen as the picture gets bigger, and they are designed for short usage cycles — not the extended duty cycles of simulation and immersive environments.

Single-chip vs. Multi-chip Projectors

Most DLP projectors use a single chip and a color wheel producing red, green, and blue pixels in succession. This works well for most people, but some viewers — especially in rapidly-changing scenes like flight simulation — may notice a rainbow sparkle effect. Three-chip projectors avoid this entirely. There is a substantial cost difference, but in high-end trainers, 3-chip projectors are used nearly exclusively.

11 Lenses for Curved Screens

Throw Ratio is defined as the distance from the screen compared to the horizontal size of the image. A ratio of 1:1 means the image will be as wide as the projector is back from the screen. Most curved screen displays call for short throw lenses — less than 1.2:1 — to avoid shadows and conserve space.

Depth of Field is a measure of how much of the image remains in focus when deviating from the optimal focus distance. This is critical for highly curved screens where the surface curves toward the projector, or where the projector must be mounted at an angle.

Generally, a short throw lens reduces shadows from objects in the theater. Longer throw lenses have a wider depth of field for better focus across varying screen distances, and often more even light distribution. Anamorphic (pre-curved) lenses are very expensive, support only a single screen geometry, and are a poor choice where spatial resolution is important.

12 Projector Brightness in Curved Screen Displays

Is brighter better? Not always. In projected displays, contrast is always an issue. Some of the light from white pixels always adversely affects black pixels — due to stray light in the light engine, screen reflectance, and light reflected off the screen from adjacent channels. The greater the field of view, the more likely light will reflect from one side of the screen to the other, reducing effective contrast.

13 Projector Resolution Requirements in Simulation

Resolution is something people focus on — and rightly so. Smooth color transitions and reduced grain are hallmarks of high-resolution displays. But there is a diminishing return argument. A human can only see a certain level of detail, which diminishes as you move back from the screen.

A choice to upgrade a customer to better optics, improved color saturation, or better contrast can often be money better spent than adding pixels. The perceived difference is much greater. That is not to say you won't notice the difference when increasing from XGA to WQXGA — you will — but other factors are just as important.

14 IR Capable Light Engines

LED and Laser light engines are especially capable for night-vision enabled simulators. While you can use night vision goggles in most simulators, having a separate IR light source in the projector uncouples the visible light spectrum from the IR spectrum.

Using a standard projector, one must show visible light to excite the goggles — creating an unrealistic situation. Adding a separate IR source allows you to excite the goggles while turning down visible light to imperceptible levels, creating a far more realistic scenario.

We offer several projector types to meet our customers' needs. We would be happy to help you find the right product for your project.

15 Front Projected Screen Types & Considerations

Screen gain, the amount of light reflected back to the viewer, and surface texture are also of concern in immersive displays. We would be happy to help you find the right screen product for your project.

16 Geometry Correction

There are essentially 3 types of geometry correction on the market today: software-based, hardware-based, and camera-based semi-automatic. Each has its advantages and disadvantages.

Geometry Correction Features to Consider

• Intuitive real-time geometry correction
• Simple and easy-to-use edge blending
• Color correction
• Gamma adjustment
• Masking
• Scaling (for overlap in non-multi-projector-aware systems)
• Black level adjustment (for improved night scenes)
• Support for simultaneous wrapped and unwrapped output
• Test patterns