Soft Edge Blending in the world of projection refers to 2 or more projectors being used to display a section of the same video image. If is often used when a very wide image needs to be displayed. If we take a 3:1 image for example:
If we were to use a 16:9 (1.78:1) projector to show the whole image, the image would be “letter-boxed”, only filling the centre of the frame. This means that both resolution and brightness are lost. With a 4:3 (1.33:1) projector this is even more apparent. By blending together either two 16:9 projectors or three 4:3 projectors we are able to use the full brightness of the projectors and also increase the horizontal resolution.
Soft edge blending of projectors can be accomplished with either facilities built into projectors themselves or external video processors. Like the phrase suggests, the edges of the two projects to be blended together are softened along a smooth curve towards the edge. The projectors are also colour balanced to make them match as closely as possible.
In large scale situations such as outdoor building projections, projector blending is often used simply because the surface to project onto is larger than a single projector is capable of filling.