Color and brightness appearance issues in tiled displays

Large-format displays created by tiling multiple, projected images have been used for decades in flight simulators and entertainment and are commercially available in a variety of forms. More recently, various research organizations have built custom display walls out of commodity projectors to support research in visualization, large-format display, and interaction. In these settings, making the display appear as a single, seamless surface has proven challenging. Where tiles overlap, they create bright seams. The tiles vary in color and brightness, not only from tile to tile, but within each tile. Each projector has a slightly different color gamut, caused by variations in the bulb, color filters, and digital processing (contrast, brightness, and gamma) for the projector. The spatial variation in brightness has two causes. First, the light from a projection system doesn't uniformly illuminate the screen. Second, the light doesn't scatter uniformly out of the front of the screen, making the perceived brightness depend on the viewing angle. In some projectors, the projected light's color also varies across the tile's face, resulting in unwanted tints in the images. I describe what causes these variations and what can be done about them.