Edge Blending and Projection Mapping: Projector Requirements for Large Venues

Edge blending joins several projectors into one seamless image by overlapping them by about 15–25% and fading the overlap; projection mapping warps that image onto stages, buildings and objects. Success depends on matched projectors, enough lumens for the canvas area, careful black-level control and a proper test session. This guide covers the calculations and the checklist.

What edge blending and mapping are

Edge blending joins two or more projected images into one seamless canvas. The images overlap, and in the overlap each projector fades out gradually so the combined brightness stays even. Projection mapping goes further: the image is warped to fit buildings, sculptures, stages or domes, often combining blending, stacking and masking.

How much overlap to plan

A blend zone of 15–25% of the image width is typical; 20% is a common starting point. Wider blends hide small brightness differences better; narrower blends keep more pixels for the canvas. Very narrow blends (under about 10%) make the seam harder to hide.

Canvas resolution formula

Blended width = n × native width − (n − 1) × overlap. With WUXGA projectors (1920 pixels wide) and 20% overlap (384 pixels):

WUXGA, 20% overlap. Rotate projectors to portrait for tall canvases.

Brightness, stacking and black level

• Brightness per area — work out lumens from the total canvas area and the ambient light, exactly as in the lumens guide. Each projector lights its own share plus the overlap.
• Stacking — two projectors on the same image roughly double brightness; it is the standard way to reach outdoor levels and adds redundancy.
• Black level — in the overlap, the 'black' of two projectors adds up and appears as a lighter band. Black-level compensation raises the rest of the image to match; it is easier with high native contrast.
• Headroom — run projectors below maximum so they can be balanced to the dimmest unit.

Worked example: a three-projector conference stage

A conference stage needs a 12 m × 3 m wide screen (4:1). Three WUXGA projectors side by side with 20% overlap give a 4,992 × 1,200-pixel canvas (≈ 4.2:1) — a close match, with the small difference masked at the top and bottom.

1. Each projector covers 12 ÷ (3 − 2 × 0.2) ≈ 4.6 m of width; the image is about 2.9 m high at 16:10, and the extra height is masked.
2. With a 1.5:1 lens the projectors sit about 6.9 m from the screen.
3. The screen area is 36 m². In a dimmed hall with about 20 lux on the screen and a 15:1 target, the formula from the lumens guide gives roughly 10,000 lumens in total — about 3,400 per projector before overlap and headroom, so 10,000-lumen units leave ample margin for a brighter hall or video lighting.
4. Projectors are rigged on a truss with identical lenses and aligned with lens shift before the blend is set.

Matching projectors and lenses

1. Use the same model, firmware and, ideally, production batch for every projector in a blend.
2. Prefer laser light sources — they drift far less than lamps, so a blend stays matched for longer.
3. Use the same lens type and similar zoom positions so brightness and focus behave alike.
4. Use lens shift to align images optically before any digital warping.
5. Colour-match on site with test patterns, then save and back up the settings.

Curved screens and domes

Curved screens and domes need warping as well as blending: each projector's image is pre-distorted so that it lands correctly on the curved surface. Camera-based auto-alignment tools speed this up for many projectors. Plan more overlap on strongly curved surfaces, and check that the chosen lens keeps focus across the whole curved area.

Warping and the signal chain

Simple flat blends can be done inside projectors with built-in warping and blending, such as on the PSP-12000. Complex surfaces, many projectors or show control usually move the warping into a media server or image processor. Either way, plan synchronised outputs, consistent resolution per output and signal redundancy for live shows.

Outdoor and building mapping checklist

• Survey the surface: dimensions, material, colour and texture; light façades reflect far more than dark stone.
• Measure ambient light at show time — streetlights and illuminated signs nearby matter.
• Plan projector positions, throw distances and lenses (long-throw lenses for distant towers) — see the throw distance guide.
• Protect equipment: weatherproof enclosures, ventilation, power stability and secure rigging.
• Choose sealed optical engines (IP5X) for dusty or humid outdoor sites.
• Schedule a full test night before the show for alignment, blending and colour.

Projector features to require

Our engineering projectors — PSP-10000 and PSP-12000 — are specified for this work, with pre-sale throw and blend calculations.

Maintenance and recalibration

• Recheck alignment after any rigging change, transport or significant temperature swing.
• Re-balance brightness and colour periodically on permanent installs — laser sources drift slowly, but not identically.
• Keep a backup of projector settings and warp/blend files with the date and firmware version.
• Clean vents and filters on a schedule; dust raises temperature and changes brightness.

Frequently asked questions