How to Fix Gray/Blue Artifacts on Wall Edges During Fast Camera Rotation in UEFN

If you are developing a map in Unreal Editor for Fortnite (UEFN), you may notice a distracting visual bug: gray or blueish streaks, shimmering, or "ghosting" appearing on the edges of walls and props when the camera rotates quickly. While these artifacts disappear when the camera is static, they can break immersion in high-action games. These issues are almost always tied to Temporal Accumulation—the way Unreal Engine 5 combines previous frames to create a final image.

1. The Primary Culprit: Temporal Super Resolution (TSR)

UEFN defaults to using Temporal Super Resolution (TSR), a high-quality upscaler. TSR uses information from previous frames to fill in details. However, during rapid camera rotation, the "history" of the wall edge doesn't align perfectly with the new frame, leading to "ghosting" or blueish trailing artifacts.

• The Fix: In your Fortnite Game Settings (or your project's Scalability settings), try switching the Anti-Aliasing method. While TSR provides the sharpest image, FXAA or TAA may reduce these specific trailing artifacts, though at the cost of some overall clarity.

2. Lumen Global Illumination and Ghosting

UEFN utilizes Lumen for real-time lighting and reflections. Lumen relies on "Screen Probe Gather," which accumulates lighting data over time. When you rotate the camera fast, the indirect lighting (especially in interior spaces or near dark wall edges) cannot update as fast as the camera moves, resulting in a gray or blueish "lag" in the lighting.

Ways to mitigate Lumen artifacts:

• Increase Light Source Radius: Sharp, tiny light sources often cause more flickering and ghosting. Using larger, softer light sources helps the temporal denoiser converge faster.
• Avoid Thin Walls: Ensure your walls have actual thickness (at least 10–20cm). Single-sided planes often cause "light leaking" and artifacts at the edges when the camera shifts perspective.

3. Motion Blur Mismatches

Even if you have Motion Blur disabled, some temporal effects still calculate "Motion Vectors." If a prop has a complex material or uses World Position Offset (WPO), it might output incorrect velocity data.

• Check your Post Process Volume settings. Even if global motion blur is off, ensure the "Target" and "Amount" are set to 0.
• If you are using custom materials, ensure "Output Velocity" is enabled in the material details to help the engine track the edges correctly during movement.

4. Screen Percentage and Resolution Scale

Artifacts are significantly more visible when the Screen Percentage is low (e.g., below 70%). When the engine has to upscale from a very low resolution, the "guesswork" it does at the edges of geometry becomes much more apparent as blue or gray noise.

Recommendation: Test your map at 100% Screen Percentage. If the artifacts disappear, you know the issue is related to the upscaling algorithm (TSR) struggling with your specific geometry or lighting setup.

5. Troubleshooting Checklist

1. Disable Global Illumination: Temporarily set GI to "None" in a Post Process Volume to see if Lumen is the cause.
2. Check Anti-Aliasing: Toggle between TSR and off/FXAA.
3. Material Check: Look for "Translucent" materials or "World Position Offset" on the affected walls, as these are known to cause heavy ghosting.
4. Fortnite Settings: Ensure your "Rendering Mode" in the Fortnite client (DirectX 12 vs Performance Mode) isn't the primary driver of the visual noise.

Summary

Gray and blue artifacts on wall edges in UEFN are typically the result of Temporal Super Resolution (TSR) or Lumen failing to update as fast as the camera rotates. By adjusting your Anti-Aliasing settings, ensuring proper mesh thickness, and optimizing your lighting density, you can significantly reduce these visual "ghosts" and provide a smoother experience for your players.