# ReSTIR Validation

ReSTIR Validation is an advanced technique that helps the denoiser reject incorrect pixels during temporal and spatial filtering. It works by shooting an additional validation ray for each pixel, which comes with a performance cost.

{% hint style="info" %}
ReSTIR Validation can reliably track only screen-space lighting. Rays that fail to find on-screen hits and instead use [Fallback](/htrace-ssgi/settings-and-properties/global-settings.md#fallback) to fetch off-screen lighting cannot always be validated consistently. In practice, this means that indirect lighting from APV or Sky, as well as indirect shadows cast by objects blocking APV or Sky lighting, may benefit less from ReSTIR Validation.
{% endhint %}

## Half-Step Tracing

Reduces the [Step Count](/htrace-ssgi/settings-and-properties/tracing/tracing.md#step-count) for the validation ray by half. This leads to a bit less defined and less responsive indirect shadows and lighting but improves the performance of all validation types.

*Performance impact: beneficial, use whenever possible*

## Spatial Occlusion Validation

Mitigates spatial over-blurring and light leaks by preserving sharp details where necessary (e.g., contact shadows) while maintaining blur strength in other areas for efficient noise reduction.

*Performance impact: moderate*

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<figure><img src="/files/iT1cQqme5850E9EwHYbS" alt=""><figcaption></figcaption></figure>
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## Temporal Lighting / Occlusion Validation

* **Temporal Lighting Validation** - Increases reactivity to changing lighting conditions (e.g., lights turning on/off, changing angle, intensity, etc.). It also improves responsiveness to lighting information entering or exiting the frame, which is especially important for a screen-space solution.
* **Temporal Occlusion Validation** - Improves reactivity of indirect shadows cast by moving objects and dynamic light sources, keeping them sharp and preventing temporal artifacts.

*Performance impact: moderate*

Watch the following video to see the effect of both temporal validation types:

{% embed url="<https://files.gitbook.com/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F9GTrs62pFTw6Syf4M0nT%2Fuploads%2Frxb4HYVaPMEOXRlpywEv%2FReSTIR%20Documentation-2.mp4?alt=media&token=7851b3f8-45c1-474e-95dc-1b081be96eaf>" %}


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