Blend Multiple Projectors

Last updated 5 May 2026

When two projectors overlap on the same surface, soft edge blending fades each projector's contribution across the overlap zone so the seam disappears. This guide covers setting up blending for a two-projector side-by-side arrangement on a flat screen.

Before you start

  • Both projectors are positioned, aimed, and geometrically calibrated in Backstage
  • The physical overlap between the two projectors is between 10-20% of the image width
  • Content is assigned to the surface and playing

Steps

1. Enable blending globally

Go to Settings → Render Group Settings → Blending and check Enable.

Set the Blending Function to Sigmoid — this produces the smoothest transition and is the recommended setting for most installations.

Leave the Algorithm at PreComputedBlendWeight (the default).

2. Set the blend curve

Still in Render Group Settings, go to the Display section and check the Global Gamma value. This controls the shape of the blend curve across the overlap zone:

Gamma

Effect

2.2

Standard — good starting point

2.5-3.0

Darker transition — use if the overlap appears brighter than the rest

1.8-2.1

Lighter transition — use if the overlap appears darker than the rest

Start at 2.2 and adjust based on what you see on the screen.

3. Set the blend limitation per projector

Each projector has a Masking section in the Inspector that defines which portion of its output participates in blending.

Select the left projector in the scene hierarchy. In Inspector → Masking, switch to Edges mode and set the right edge limit to exclude the far right of the projector's output (e.g. 80%).

Select the right projector and set its left edge limit symmetrically (e.g. 20%).

Backstage computes the blend weights automatically within the overlap zone.

4. Enable brightness correction

Two projectors illuminating the same area will be roughly twice as bright. Select each projector and enable Global Brightness Correction in the Inspector.

The Adjust Brightness slider lets you fine-tune the correction per projector. Start at 1.0 and increase slightly if the overlap seam is still brighter than the surrounding image.

5. Check the result

Project a uniform white or grey test image across the full surface. A good blend is invisible — no seam, no bright band, smooth brightness across the full width.

Symptom

Likely cause

Fix

Bright seam at the join

Gamma too low

Increase Global Gamma

Dark band at the join

Gamma too high or over-correction

Decrease Global Gamma or reduce brightness correction

Hard edge visible

Blend limitation cutting too aggressively

Widen the edge limits on each projector

Color shift in overlap

Projector colour mismatch

Use per-projector brightness adjustment to match

Common Mistakes

  • Blending configured but no visible effect — the global blend enable is off. Go to Settings → Render Group Settings → Blending and check Enable.

  • Seam still visible despite correct gamma — the two projectors have different brightness levels. Enable Global Brightness Correction per projector and adjust the Adjust Brightness slider until both sides match before tuning gamma.

  • Edge limits set but blend zone has a hard cut — the projectors are not physically overlapping enough. The blend zone must exist in the physical output — there is no software overlap to compensate for a gap between projectors.

Tips

  • The overlap width is set by physical projector positioning — move the projectors closer together to widen it, further apart to narrow it. There is no pixel-level overlap width setting in Backstage.

  • For installations requiring very precise overlap control, the Mechanical Blending option (available per output in the Outputs window) provides additional per-output fine-tuning.

  • For more than two projectors, repeat the same per-projector masking for each overlap zone — blending is computed globally across all projectors simultaneously.

Set Up a Projection Surface — single-projector setup from scratch

Set Up a Panoramic Scene — use the Projection Setup Wizard for panoramic rigs

Apply a Blend Mask to an Output — apply a greyscale blend mask to an output