How to make a great seamless edge blending

2019.10.08 by 

To maximize exhibit effects, large exhibit spaces, such as museums, playgrounds or convention halls, may turn to image stitching through multiple projectors to achieve a wide-screen special effect. This attracts the viewers' attention with large size, high luminance and huge pixel-count. Multi-projection is therefore a common and important topic in projector applications.

"Basic Requirements" for a good multi-projection setup

Multi-projection is made possible through two or more projectors, to achieve a display larger in size and resolution. The projection is considered good when viewers are unaware of the fact that the projection is achieved through multiple projectors. Instead, to them, it appears to come from a single projector; this is the most successful seamless edge blending

When choosing a multi-projection setup, it would be nice if the following criteria are met:

1. Same model with the same resolution, 2. Same throw ratio and lens with the same focal length range 3. Similar brightness, machines with near the same hours of use; Projection brightness will deteriorate as hours of use increases 4. Similar color parameters, pick specific configurations including color temperature and chromaticity coordinates. The best way to achieve parameter consistency such as brightness and color etc., is to choose machines from the same batch of production, with similar parameter configurations. This can be considered a priori criteria necessary for a successful multi-projection setup. With them, image blending would be much easier; conversely, it would be impossible to overcome certain issues if some of the criteria are not met, such as resolution or lens differences.

Aside from calculation for spacing between installations and projection size for stitching, there are two main factors for a successful multi-projection, the first is seamlessness (i.e. precise geometry adjustment), the second is image consistency (i.e. brightness and color consistency)

2. Image consistency (i.e. consistency of brightness and color), 2.1 Prior to image blending apply basic configurations to each projector, including setting the same picture mode, color temperature and brightness, and measures color parameters to lower the optical parameter differences between projectors.
2.2 After image blending make brightness and color adjustments, including increasing the white level of the overlapping region, decreasing the black level at the non-overlapping region as well as adjusting RGB color parameters, so that the overall projection has both even brightness and color.

Accurate geometry positioning and consistent imagery would be able to satisfy the performance requirements of multi-projection.

Compared to other (LCD) projection technologies, DLP projection can produce dark (black) levels with much lower brightness. Other technologies cannot output relatively low brightness for black images, which is already visible in a single projection setting; In a multi-projection setting, projection overlap would amplify the brightness of black images, which cause them to be visually not black enough. Since DLP projections have low brightness for black images, they can offer higher contrast in multi-projection settings.

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