OTOY Forums

If a universal camera is used with a custom depth of field bokeh aperture texture, enabling the denoiser will cause the image to render darker than without it.

normal render denoised render c4d 2025.1.2
octane 2024.1 r3
4090 565.90

It's likely not a "darkening" issue/bug in the "pictorial exposure" sense, but simply the byproduct of denoising on "poorly sampled" output from the renderer. In other words, the rendered output requires more samples and optimizations.

A denoiser, any, relies on sampling optimization to "do its job properly", otherwise results can look unsatisfactory or "funky".

This Octane Sampling page goes in more details when it comes to kernel sampling and project file optimizations. There are some "techniques" beyond the Kernel settings.

Edit: the link with the "Custom bokeh" is sampling related. As any element during rendering is not sampled equally, some elements will be "more difficult to samples efficiently". This is why there are "best practices" when it comes to sampling optimization, i.e. as avoiding this and that (things that will be more tricky to efficiently samples).

To complement, one denoiser may "perform" better than the other in certain situations. If this was Open Image Denoise, then it would be judicious to test Octane's native denoiser.

This demo from the suggested page is the latter (Octane's)

This is unrelated to samples, the full final shots rendered here are on 8000 samples and render cleanly with no noise. They go darker. The images attached to this bug report use fewer samples to show the problem quickly.

It is literally a darkening bug caused by the denoiser.

In the absence of any further information (required for proper diagnosis), it was speculatively suggested as such (hence the "likely").
With the newly provided information, it is indeed suggesting a core bug or flaw.

However, at 8000 samples on a relatively lightweight project file, the "normal" (undenoised) render output seems more noisy than expected.
Circling back to sampling optimizations, which includes materials (e.g. gaussian spectrum instead of RGB color node), post processing, etc. or the texture bokeh file, perhaps?

As a suggestive workaround: it should be possible to reproduce (close enough) the result of that bokeh texture file via the Universal Camera, given all the options, covering a vast range of "bokeh renditions".

Thanks for the report. This issue is a bug in Octane core and will be fixed for future releases. As a workaround until then, you can use a texture where none of the pixels are pure black (e.g. very dark gray).