You enable several post-processing effects: Bloom, Color Grading, Vignette, maybe a Depth of Field. In the Editor everything looks fine. But when you run the game, some effects appear too strong, colors clip, or you see strange flickering and banding. Some effects seem to override others unexpectedly.

This is often called the “Post-Processing stacking bug.” In most cases, Unity is not broken — this happens due to the way multiple post-processing volumes interact and how the stack order affects rendering.

Understanding Post-Processing Stacking

Unity Post-Processing (both the old stack and URP/HDRP Volume system) uses a priority-based system. Volumes with higher priority override lower ones. When multiple volumes overlap, the final effect is a blend depending on their weights.

Common problems occur when:

• Multiple overlapping volumes affect the same effect
• Weights are set incorrectly
• Global vs Local volume conflicts
• Camera layering conflicts with volume layer masks

Step 1: Check Volume Priority

Select your Post-Processing Volumes and inspect the Priority field.

• Higher priority volumes override lower ones
• Conflicting effects may occur if priorities are not set thoughtfully

Rule of thumb: give local volumes affecting small areas a slightly lower priority than global volumes that affect the entire scene.

Step 2: Inspect Volume Weight

Volume weight controls blending:

• Weight 1 = full effect
• Weight 0 = no effect
• Intermediate = blended effect

Accidental overlapping volumes with weight 1 can result in “double” application of effects like Bloom or Color Grading, creating clipping or color artifacts.

Step 3: Check Layer Masks

Volumes use Layer Masks to determine which cameras they affect.

Make sure:

• The camera is on the correct layer
• Volumes do not unintentionally overlap the same camera if not desired

Mismatched layers often create unexpected stacking behavior.

Step 4: Watch Effect-Specific Conflicts

Some post-processing effects interact poorly when applied multiple times:

• Bloom: Multiple volumes with Bloom can increase brightness dramatically
• Color Grading: Can saturate or clip colors if stacked
• Vignette: Two overlapping vignette effects darken the edges too much

Solution: Avoid duplicating the same effect across multiple overlapping volumes. Keep one global effect for consistent look and use local volumes only for subtle changes.

Step 5: URP vs HDRP Differences

URP and HDRP handle post-processing differently:

• URP uses a single volume stack per camera
• HDRP uses a more complex volume blending system

Artifacts may appear if mixing URP post-processing assets with old Post-Processing Stack v2 assets.

Step 6: Avoid Runtime Volume Creation Without Control

If you spawn volumes at runtime without adjusting priority or weight, they can unintentionally override existing volumes and cause visual artifacts.

Always initialize runtime volumes carefully and test how they blend with existing volumes.

Step 7: Test in Both Scene View and Game View

Some artifacts only appear in Game View because Scene View sometimes ignores weight blending or global volume overrides.

Always validate your post-processing setup in Game View and on the target platform.

Quick Debug Checklist

• Check volume priorities and weights
• Ensure camera layer matches intended volumes
• Do not duplicate the same effect in overlapping volumes
• Test both URP and HDRP settings depending on your pipeline
• Check runtime volumes for unintended overrides
• Always validate in Game View on target hardware

Is This a Unity Bug?

Not really. Post-processing artifacts usually result from misconfiguration or misunderstanding of the volume system. Unity blends overlapping volumes intentionally; unexpected visual results often come from multiple overlapping effects rather than engine faults.

Final Thoughts

Post-processing stacking requires careful management of volume priority, weight, and camera layers. By structuring your global and local volumes properly and avoiding duplicated effects, you can eliminate flickering, clipping, and other visual artifacts.

Once volumes are organized, post-processing looks consistent and professional across all scenes and devices.