Part 6: EXPOSURE

Before working with exposure, let's create reference materials to gauge our exposure settings:

BP_LHT_RefExposure Blueprint: Create a Blueprint with spheres at different exposure-relevant values:

1. 18% Grey — Standard photographic middle grey (Base Color V = 0.18)
2. Pure White — Maximum reflectance (Base Color V = 1.0)
3. 90% White — Highlight reference (Base Color V = 0.9)
4. 5% Black — Shadow reference (Base Color V = 0.05)

Why these values?

• 18% Grey is the reference point for correct exposure
• If 18% grey looks correct, your exposure is properly set
• White should be bright but not clipped
• Black should have detail, not crushed

Quick access to manage all environmental lighting:

Window → Env Light Mixer

🖼️Image placeholder: Environment Light Mixer Panel

From here you can create and adjust:

• Sky Light
• Atmospheric Light (sun)
• Sky Atmosphere
• Volumetric Clouds
• Height Fog

Creates realistic atmospheric scattering:

• Blue sky during day
• Orange/red at sunset
• Works with Directional Light as "sun"

Set Atmospheric Light (sun) = 0 for indoor scenes or controlled lighting.

Adds 3D cloud rendering:

• Affected by Directional Light
• Casts shadows on ground
• Performance cost

For indoor/studio scenes: Usually disabled.

Adds atmospheric depth:

• Distant objects fade into fog
• Can be volumetric (interacts with lights)

Note: We enabled Force No Precomputed Lighting in Section 2 — this ensures all lighting is dynamic via Lumen.

Post Process is a collection of image effects and rendering configuration applied after the scene is rendered. It controls two major categories:

1. Feature Configuration

• Enabling/disabling rendering features (ray tracing, Lumen, etc.)
• Quality settings for various systems
• Bloom, motion blur, depth of field

2. Exposure & Color

• Auto exposure behavior
• Manual exposure settings
• Color grading, tone mapping

In Unreal Editor, you apply post process via a Post Process Volume:

1. Add Post Process Volume to scene
2. Enable Infinite Extent (Unbound) — affects entire level regardless of position
3. Override specific settings as needed

Cameras also have post process settings built in:

• Each Cine Camera Actor has its own post process overrides
• Camera settings override volume settings when active
• Useful for per-shot adjustments

This means post process can come from:

• Post Process Volumes (scene-wide)
• Camera actors (per-camera)
• Or both (layered)

By default, Unreal adjusts exposure automatically:

• Look at bright area → exposure darkens
• Look at dark area → exposure brightens
• Like how your eyes adapt

When this is a problem:

• Inconsistent brightness between frames
• Same scene looks different from different angles
• Cinematics, product shots, or ML training data need consistency

When auto exposure is fine:

• Games where adaptive exposure feels natural
• Dynamic environments with large brightness ranges

If using physical camera model (like real-world photography):

When to use physical camera: Cinematics where you want realistic camera behavior and depth of field.

When to skip it: Use manual exposure compensation instead for simpler, more predictable control.

After disabling auto exposure:

• Positive values = brighter
• Negative values = darker
• Adjust until your middle grey reference looks correct

Use these as starting points for different lighting conditions:

Note: EV is logarithmic — each +1 EV doubles the light, each -1 EV halves it.

Post Process Volumes also configure rendering features:

Now that we understand Post Process Volumes, here are the detailed Lumen controls:

Toggling Lumen per-area or per-level:

• Post Process Volume → Global Illumination → Method: Lumen / None

Lumen GI Quality Settings:

Console Variables (scripting/runtime):

r.Lumen.DiffuseIndirect.Allow 1    (on)
r.Lumen.DiffuseIndirect.Allow 0    (off)

Lumen can introduce:

• Frame-to-frame noise variation
• Denoising that can soften edges
• Temporal artifacts
• Unpredictable results between camera angles

Use Lumen when:

• Dynamic environments need realistic bounce light
• Games with moving lights/objects
• Architectural visualization with natural lighting

Consider disabling Lumen when:

• Consistency matters more than realism
• Cinematics with locked cameras
• Product visualization
• ML training data generation