Apply a Blend Mask to an Output

Last updated 5 May 2026

A blend mask controls which parts of a projector's output are visible. In Backstage this is a greyscale image — white allows light through, black blocks it completely. Use a blend mask to eliminate light spill, cut an irregular output boundary, or create a soft-edge fade on a specific projector.

Before you start

Your projector output is configured and active in the Outputs window
You have an image editor (Photoshop, GIMP, or similar) to create the mask

Steps

1. Create the mask image

In your image editor, create a new image at the same resolution as your projector output (e.g. 1920x1080).

Paint the image using these rules:

Pixel value	Effect on output
White	Full light — no masking
Black	No light — fully blocked
Grey	Partial light — useful for soft edges

Save the file as PNG or JPG.

2. Load the mask in Backstage

Open the Outputs window. Select the output slot connected to the projector you want to mask.

Scroll to the Blend Mask section and click Load Blend Mask. Browse to your mask image file and open it.

3. Enable the blend mask

Check the Enable Blend Mask checkbox. The mask is applied immediately — the masked areas go dark on the physical output.

Options explained

Setting	Description	Values / Range
Enable Blend Mask	Activates or deactivates the loaded mask.	Checkbox
Blend mask is prewarped	Enable if you created the mask already aligned to the projector's warped output geometry rather than the flat image.	Checkbox
Enable debanding	Adds subtle dither noise to smooth banding artefacts along gradient edges of the mask.	Checkbox

Common Mistakes

Mask is loaded but nothing changes on the output — the Enable Blend Mask checkbox is unchecked. Check it to activate the mask.
The entire output goes black — the mask image was saved with black and white inverted, or exported in a wrong colour mode. Verify in your image editor that white areas correspond to the regions that should be visible.
Visible banding along gradient edges — enable the debanding option in the blend mask settings.

Tips

There is no limit on the shape of the mask — it can contain multiple regions, diagonal cuts, or circular holes, all defined in the image.
Each projector output has its own blend mask — configure them independently in the Outputs window.
Use the Blendmask debug view in the output test image selector to see exactly what mask is being applied.
The mask filename is saved with the project and reloaded automatically on project open.

Blend Multiple Projectors — soft edge blending between projectors

Calibration & Blending — all calibration and blending workflows