What is edge blending and when do you need it?
Short answer: Edge blending is the technique of overlapping the images from two or more projectors and gradating the brightness across the overlap zone to create a single seamless wide image. It is used for large-screen events (conferences, weddings, concerts), permanent venue installs (auditoriums, temples, corporate lobbies), and simulation environments. The four steps are: physical alignment, overlap calibration, brightness and gamma matching, and software blend-curve adjustment.
How to align two projectors for edge blending — step by step
Step 1: Physical alignment — same height, same throw distance
Mount or place both projectors at exactly the same height and distance from the screen. For ceiling mounts, use a laser level to confirm both units are at the same horizontal plane. Each projector should project onto the screen at the same angle. Use lens shift (not keystone) to centre each projector's image on its half of the screen. Physical alignment before any software correction is the most important step — blending software cannot compensate for a projector that is mounted at a different height or angle than its pair. If you are using projectors with offset optics (the lens is not centred on the chassis face, as is common on Epson home theater units), check the offset specification to ensure the overlap zone is symmetrical.
Step 2: Set the overlap zone — 10 to 20 percent
Feed a test pattern (a full-field grid or a checkerboard) to both projectors and adjust the throw distance or zoom so the two images overlap by 10–20% of the total canvas width. Measure the overlap physically on the screen with a tape measure. On a 5-metre wide screen, aim for 50–100 cm of overlap. Mark the overlap edges with removable tape on the screen frame. Once the overlap is set, use warp correction in the projector OSD or blending software to geometrically align the grid lines in the overlap zone so they match perfectly between the two projectors.
Step 3: Match brightness and gamma between both projectors
Identical models from the same production batch are best. If your projectors differ in lamp age, the older lamp will be noticeably dimmer. Reduce the output of the brighter projector (via lamp brightness setting or neutral density filter) until both halves of the screen show the same brightness when displaying a full-white test field. For gamma, set both units to the same mode (typically 2.2 for events with ambient light, 2.4 for dark venues). Colour temperature must also match — set both to the same preset (Cinema / Normal / 6500K) and verify with a colourimeter if the installation is permanent.
Step 4: Apply blend curves in software or projector OSD
Most modern projectors above ₹1,20,000 have built-in edge blending menus (Epson EB series, Panasonic PT series, NEC PA series). For projectors without native blending, use software like Resolume, MadMapper, or the free Optoma Display Manager for Optoma models. The blend curve (also called the gradient or soft edge) controls how quickly the brightness ramps to zero at the edge of each projector's field. A gamma-corrected S-curve blend produces the most natural result. Start with a linear ramp and reduce the curve width until the bright band disappears. In India's event industry, professional on-site calibration visit typically costs ₹3,000–₹8,000 — see our installation and setup service for venue rates. Also useful: our keystone correction guide if individual projectors need geometry correction before blending.
When to call a technician (and what it costs in India)
When DIY ends
Call a professional if: the bright band in the overlap persists after gamma and brightness matching (indicates a lamp with unusual spectral output, often a sign of lamp degradation); geometric alignment cannot be achieved because one projector's lens has physical damage or drift; the event canvas is larger than four projectors wide (multi-projector synchronisation requires professional processors and EDID management); or the installation requires cable runs longer than 20 metres (requires fibre HDMI or signal extenders, not passive cables).
Typical setup cost in India
On-site two-projector alignment and calibration: ₹3,000–₹8,000. Permanent venue install with custom mounting and cable routing: ₹15,000–₹50,000 depending on site. Projector rental for events: contact us for current rates. Doorstep service for projector faults: ₹149 visit.
A note from the PRW Engineer Team
The most common edge-blending failure we see at Indian events is two projectors with mismatched lamp hours — one fresh, one 1,500 hours old. The older lamp's colour has shifted yellow and its brightness has dropped, making a seamless blend impossible regardless of software settings. For high-visibility events, both projectors should either be matched for lamp age or both given fresh OEM lamps before the show.