This scene was inspired by a "20 megabyte" challenge in which the entire packed .blend file for a scene is supposed to stay under 20 megabytes (maybe that was self explanatory). While the version of the scene I used for these two renders is closer to a gigabyte, the final scene for the challenge was about 16 megabytes (I swapped out the JPEG compressed textures for the original full-resolution TIFF).
I was inspired to add bubbles to the scene later, as a test of Luxrender's support of thin film interference. In Luxrender, I used the glass node with 256mm thin film, multiplied by distorted noise to add variance to the thickness. In LuxCoreRender, I created Gaussian pattern color noise in Photoshop, then used various blurs and hue adjustments to create a texture, which was mapped to the glass reflection color. The texture I created to add color can be seen below.
The result of the two scenes is very similar. Here is a comparison between the two, rendered for 1 hour and 15 minutes each. The first image is Luxrender SPPM with 4 million photons per pass, recursion depth of 48 for eye and 48 for light. The second is LuxCore BiDir, with recursion depth of 48 for eye and 48 for light as well. Both use a Mitchell filter with X and Y width set to 3.30. Unfortunately I could not figure out how to add more saturation to the reflection color, so the bubbles are less "brilliant" in the LuxCore scene.
Finally here is a comparison of the two scenes mostly converged. The Luxrender scene ran for about 12 hours on an old machine with 2x Xeon X5690s (12 cores, 24 threads, ~3.5 GHz), the LuxCore scene ran for 1 hour on the same machine then was cleaned up by OIDN. Unfortunately a direct comparison (not using OIDN) was not possible, as the number of fireflies increased over time using LuxCore (I will have to play with the clamp settings in the future). Both were developed from OpenEXR in Luminance HDR using the exact same settings. SPPM is the top image, LuxCore BiDir is the bottom image.
Interesting for sure, and the differences are mainly in the brightness and quantity of reflections and refractions. Overall, there is a certain charm to letting something render for 12 hours, only to find it is still noisy
