What you'll learn:
- Why bloom is independent of your lighting systems
- How to control bloom settings in Project Settings and Post Process Volumes
Section 51: Bloom Project Settings & Post Process (10 min)
Bloom is a post-process effect that adds glow around bright areas. It simulates how real cameras and eyes perceive very bright light sources — the light "bleeds" into surrounding areas.
Key insight: Bloom works on the rendered image, not the 3D scene. It only sees pixel colors in the frame buffer.
| Aspect | Lighting | Bloom |
|---|---|---|
| When applied | During rendering | After rendering |
| Affects geometry | Yes — shadows, reflections | No — image only |
| Physically based | Often (Lumen, ray tracing) | Artistic approximation |
Let's prove bloom works on the frame buffer, not the lighting system.
Setup:
- In your GI demo room from Part 10, make sure the emissive sphere has
MI_LHT_GI_Emissiveapplied - Set EmissiveIntensity = 100+ so the sphere is bright
- Disable or delete all lights in the scene — no Directional Light, no Sky Light
- The scene should be mostly dark, with only the emissive sphere glowing
Toggle Bloom in Project Settings:
In Part 2: Project Setup, we disabled Bloom so we could see pure lighting. Now let's enable it:
Project Settings > Engine > Rendering > Default Settings:
Bloom: ✓ On
Result: Bloom appears around the emissive sphere — even with no lights in the scene.
This proves bloom doesn't care about your lighting setup. It only sees bright pixels in the frame buffer. The emissive material outputs bright values, bloom detects them and adds glow.
TODO: Screenshot - Emissive sphere with bloom ON, no lights in scene
TODO: Screenshot - Same scene with bloom OFF
Section 52: Bloom Settings in Post Process Volumes (8 min)
With your Post Process Volume selected, navigate to:
Details Panel → Lens → Bloom
Check the checkbox next to settings to override the project defaults.
TODO: Screenshot - Post Process Volume showing Lens > Bloom expanded
| Setting | What It Does |
|---|---|
| Intensity | How strong the glow is (0 = off, 1 = default, 2+ = exaggerated) |
| Threshold | Brightness required to trigger bloom (-1 = everything, 1+ = only bright pixels) |
| Method | Standard (fast) or Convolution (realistic, expensive) |
Intensity controls glow strength. Threshold controls what triggers bloom.
For realism:
- Keep Intensity around 0.5 - 0.8
- Keep Threshold at 1.0+
- Only the brightest sources should bloom
For stylized looks:
- Increase Intensity (1.0 - 2.0)
- Lower Threshold (0.0 or negative)
Section 53: Preparing for Exposure (2 min)
Before moving to Exposure, let's disable bloom so we can see pure brightness without the glow effect:
Project Settings > Engine > Rendering > Default Settings:
Bloom: ✗ Off
Or in your Post Process Volume, set Bloom Intensity = 0.
This lets us focus on exposure and brightness control without bloom affecting our perception.
Note: You can re-enable bloom after learning exposure. Many projects use both — exposure for correct brightness, bloom for visual polish.
Key Points:
- Bloom is a post-process effect — it works on the frame buffer, not the 3D scene
- Bloom is independent of lighting systems — it only cares about bright pixels
- Control bloom globally in Project Settings or per-scene in Post Process Volumes
- Disable bloom before learning exposure for clearer results
In Part 15: Cameras, we'll explore how physical cameras work — the relationship between sensor, shutter, aperture, and ISO — and how these concepts translate to Unreal's camera systems.