One projector runs out of brightness and width quickly, so wide surfaces get several, overlapped by 10 to 20 percent. Edge blending ramps each unit’s output down across the overlap so summed light stays even, and the seam disappears.
Getting it right couples geometry and photometry: images aligned within a pixel across the blend zone, gamma-matched ramps, projectors of matched brightness and color. Media servers and mapping tools carry the alignment and blending machinery.
Blending is how festival stages and immersive rooms paint continuous pictures tens of meters wide, and why their rider specifies identical projector models rather than a miscellany of lumens.