DOF - TAA pass ghosting when using r.DOF.TAA.CoCBilateralFilterStrength

In Unreal 5.6, there's a new CVar:* r.DOF.TAA.CoCBilateralFilterStrength, *which should help with ghosting artifacts introduced by TAA in DOF passes. However, it doesn't work as expected since many ghosting artifacts are still visible even with filter strength set to 1.

Looking at the implementation (TemporalAA.usf), it looks like that CVar enables an additional filtering on history data based on CoC radius (proportional to depth/viewZ) differences. However, I suspect that comparing the current frame data CoC radius with neighborhood clamped history data may decrease the effectiveness of the filtering when it comes to reducing ghosting. (see WithClampedHistory.gif)

TemporalAA.usf - line 2262: float BilateralWeight = ComputeBilateralWeight(IntermediaryResult.Filtered.CocRadius, History.CocRadius);

Here, History is already clamped, so large CocRadius deltas between current and history data are lost (or at least greatly reduced).

Solution:

1. Edit TemporalAA.usf, line 2262: replace float BilateralWeight = ComputeBilateralWeight(IntermediaryResult.Filtered.CocRadius, History.CocRadius); *with float *BilateralWeight = ComputeBilateralWeight(IntermediaryResult.Filtered.CocRadius, PreClampingHistoryColor.CocRadius); and save the changes.

2. Enter console command RecompileShaders changed or restart the editor.

3. The ghosting issue is solved.

(see WithUnclampedHistory.gif)

The effect of using unclamped history can be clearly seen in the attached image (DOF's TAA output UAV texture)

Steps to Reproduce

1. Open the attached project (AntighostCocRadius)

2. Open the Level /Game/NewWorld (should be the startup level)

3. Start PIE

4. Enter console command t.MaxFPS 15 to make ghosting artifacts more obvious

5. Enter console command r.DOF.TAA.CoCBilateralFilterStrength 1 to enable CoC Radius filtering for DOF's TAA pass.

6. The actor in the foregroung ghosts on the blurred bg.

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