How to Use ProPresenter’s Alpha Keyer

Lower thirds are one of the simplest ways to make a church livestream feel polished and intentional. But if your graphics show up as big black boxes—or don’t key cleanly—you’re not alone. Learning how to use ProPresenter’s Alpha Keyer for stunning lower thirds on ATEM switchers comes down to understanding how transparency really works between ProPresenter and your switcher.

This guide explains the correct, real-world workflow churches use today—without assuming broadcast experience.

What “Alpha Keying” Actually Means (In Plain English)

Alpha keying means telling the switcher which parts of a graphic should be visible and which parts should be transparent.

In a church lower-third workflow:

The text and design should be visible
Everything else should be transparent
The live camera video shows through underneath

On ATEM switchers, this transparency is not embedded inside a single HDMI or SDI signal. Instead, it’s created using two signals working together.

The Key Concept to Understand: Fill and Key

ATEM switchers create transparency using a Fill + Key method.

What that means simply

Fill signal = the full-color lower-third graphic
Key signal = a grayscale matte that tells the switcher what is transparent

White areas = fully visible
Black areas = fully transparent
Gray areas = partially transparent

This is how professional broadcast switchers—including ATEM—handle alpha graphics.

What You Need Before You Start

Before alpha keying will work correctly, your system needs:

ProPresenter configured to output separate Fill and Key feeds (using a supported video output method)
An Blackmagic ATEM switcher with:
- Two available inputs (one for Fill, one for Key)
Lower-third graphics designed without backgrounds
A volunteer who knows which input is which

If ProPresenter only sends one output, the ATEM has no transparency information to work with.

Step 1: Configure ProPresenter for Fill and Key Output

This is the most important step.

In ProPresenter

Set one output to send the full-color lower-third graphic (Fill)
Set a second output to send the Key (grayscale transparency matte)
Confirm that:
- Visible graphic areas appear white in the key
- Background areas appear black
- Soft edges or shadows appear gray as intended

ProPresenter also allows you to choose Straight vs Premultiplied alpha output.
If edges look strange later, this setting is often the reason.

Step 2: Connect Both Outputs to the ATEM

Simple connection checklist

Connect the Fill output to one ATEM input
Connect the Key output to a second ATEM input
Label both inputs clearly (for example: “LT Fill” and “LT Key”)
Confirm both signals appear correctly on the ATEM multiview

At this point, the Fill input will still look like a normal video signal. That’s expected.

Step 3: Set Up a Linear (External) Key on the ATEM

This is where transparency actually happens.

What to do in the ATEM software

Enable a Downstream Key (DSK) or Upstream Key
Choose Linear / External Key
Assign:
- Fill source = ProPresenter Fill input
- Key source = ProPresenter Key input
Enable the key

Once enabled, the black background disappears and the lower third overlays cleanly on video.

Step 4: Check Pre-Multiplied vs Straight Key (If Needed)

If you notice:

Faint edges
Halos around text
Semi-transparent letters

The issue is usually a Straight vs Premultiplied mismatch.

Easy rule for volunteers

If the graphic looks washed out or haloed → try switching the key type
Don’t adjust gain or clip unless absolutely necessary

Most churches only need to set this once per setup.

Common Problems and Easy Fixes

Black box behind the graphic

Cause: Key not enabled or only Fill connected
Fix: Confirm both Fill and Key inputs are assigned

Text looks faint or transparent

Cause: Wrong alpha type
Fix: Switch between Straight and Premultiplied

Graphic covers the whole screen

Cause: Full-screen slide used
Fix: Use a true lower-third design with transparency

Use Lower Thirds Tastefully During Worship

Lower thirds are most effective when they’re subtle.

Good uses

Speaker names
Scripture references
Sermon titles
Brief announcements

Avoid

Leaving graphics on too long
Over-animated designs
Using during prayer or worship music

Clean, calm graphics support worship instead of distracting from it.

Final Thoughts

Learning how to use ProPresenter’s Alpha Keyer for stunning lower thirds on ATEM switchers comes down to understanding one core idea: Fill and Key working together. Once ProPresenter is outputting both signals using a supported method and the ATEM is set to a Linear (External) Key, lower thirds become reliable and repeatable. With this workflow in place, volunteers can confidently add professional overlays that enhance—not interrupt—the service.

Check out our related posts:

This post may contain affiliate links. As an Amazon Associate, I earn from qualifying purchases.