Nvidia's denoiser now counts time, not frames, and ships five breaking changes
Nvidia's real-time denoiser library has changed the thing it counts. In version 4.18.0 of NRD, published at 10:39 UTC on October 9 and read at 21:47 UTC on October 10, the REBLUR and RELAX denoisers build their history from elapsed time rather than from a frame count, and Nvidia's own wording for why is "to honor uneven frame pacing".
Denoising is the step that turns a handful of traced rays per pixel into a picture like this one. Image: Nvidia
A denoiser is what makes ray tracing affordable. A game traces a handful of rays per pixel, which on its own looks like television static, and the denoiser blends the current picture with what it accumulated over previous ones to arrive at something stable. Tie that blending to frames and it quietly assumes they arrive at a steady rate. Tie it to time and a long frame counts for more than a short one.
Not everything moved to the clock
Nvidia kept the change narrower than it sounds. The release says time-based scaling was applied "to confidence factors only" while geometry stays frame-based, and both denoisers expose a switch, named RELAX_FRAME_RATE_COMPENSATION and REBLUR_FRAME_RATE_COMPENSATION, for anyone who wants the old behaviour back.
Alongside it sits a repair that explains some of the motive. The release records fixing "a misplaced line to calculate elapsed time between frames rather than between SetCommonSettings calls", and separately notes that the internal timer now updates only when the frame index changes, so an engine calling that function more than once per frame does not skew the measured frame delta. A clock is only useful if it is reading the right interval.
Five breaking changes, counted from the release itself
The count comes from the entries Nvidia lists under BREAKING CHANGES in the release body, taken one by one rather than from any summary. CommonSettings::rectOrigin is renamed to inputRectOrigin, with the offset now applying to input resources. Custom shader resource declarations need a sixth policy argument and must invoke NRD_DECLARE_RESOURCE. Helper scripts move out of the repository root into separate Windows and Linux directories. The minimum CMake version rises from 3.22 to 3.30. And a gather-specific roughness unpacking helper that Nvidia calls ill-formed is removed outright.
Counted the same way, the release closes six issues, numbered 94, 106, 107, 108, 109 and 111, and credits six outside contributors by name.
The rest of the release, and what it is not
SIGMA, the shadow denoiser, picks up checkerboard support, a 12-tap spatial kernel and a flag to preserve darker shadows inside penumbras. The shaders gain Slang compatibility and better GLSL compatibility, and the build adds Windows ARM64 and ARM64EC continuous integration.
None of this is a driver, a game patch or a setting anyone can switch on. NRD is a library a studio integrates, and Nvidia names no title shipping any of these changes, so the practical effect depends entirely on who picks it up and when. The companion sample repository was synced the same morning.
Uneven frame intervals are ordinary in a heavily ray-traced game, between frame generation, variable refresh rates and the load itself, and Nvidia quotes its own Witcher 3 performance figures at a 6X frame generation multiplier. Version 4.18.0 leaves the old frame-counting behaviour one switch away for any integration that preferred it.
