And the final result, with the original 8spp noisy image for reference again.

Pixel peepers will see all sorts of problems with the filtered result, and the edge stopping function could be improved using tricks from the SVGF paper. Still, it's better than waiting for an 2048 spp image to converge 😄

The biggest difference is that the À-trous algorithm is run iteratively, with the previous c' being used as input for the next run. Each iteration, the gap between neighboring pixels q doubles. The linked paper used 5 iterations.

Finally, moving to the À-trous wavelet algorithm yields still better results. The filter looks similar to the previous one, with the spatial Gaussian replaced with a cubic B-spline.

This particular filter is inspired by a bilateral filter (course notes: people.csail.mit.edu/sparis/bf_co...), as well as the edge stopping function from the À-Trous wavelet filter paper (jo.dreggn.org/home/2010_at...)

The edges are now preserved, but the spatial blur is still not sufficient for removing the noise.

The Gaussian blur can be improved by applying an edge stopping function. It's a Gaussian blur with extra weight multipliers controlling for color and normals, not just distance from the center pixel.

This results in a blurred image, which is a start!

First, ran the image through a Gaussian blur. The new color c' is the average over neighboring pixels.

The new model gives the transmittance at any point in the sky, so the sun turns convincingly red as it approaches the horizon🌗

At a quick glance I thought you had gone down some kind of hardcore atmospheric rendering rabbit hole 😁

The sky is an implementation of Hillaire's model: sebh.github.io/publications...

The atmosphere is rendered into a small 2D angular coordinate lookup table using raymarching integrators from section 3. The LUT is small enough that it can be updated in real-time on the CPU.

The images show a 2D look-up table of scattered light.

The sun position and camera altitude can be played around with in real time. But zooming to space and back just looks so good 😄

Mandatory view of the scene in the #raytracing mode ✨