So I'm trying to improve the render quality in an animation of a night time, heavily overcast sky. Looking at the tgCloudDirect pass it is very clear that there are large areas in the cloud deck that are slowly changing/pulsing in light intensity. ie. The intensity of the direct light in the clouds is not consistent as you'd expect. It randomly pulses slightly brighter, darker, brighter, etc. Any ideas what may be the cause of this and how I can fix it?
Assuming you have cache files, I assume it's the blending of cache files. If you are doing a night to dark or vice versa, try just two or three cache files. One for first frame, optional middle frame, and end frame. That way the lighting falls off more gradually. I suspect TG is using too many cache files and thus inconsistencies you'd see with frame-by-frame caching are being blended between frames; thus producing a sort of pulsing glow between light cache files and darker cache files due to calculation inconsistencies.
Aren't the Cache files for GI though? ie. The indirect portion of the illumination? The pulsing is clearly happening in the tgCloudDirect pass. The tgCloudIndirect pass looks unaffected by this anomaly. For the record, I have generated only 6 cache files for a frame range of 197-779.
Pretty sure most GI takes into consideration DI to calculate GI. And with clouds the GI is very approximated from what I have seen with GI inconsistencies, and how light becomes secondaries and ambient in cloud diffusion.
If you are animating the clouds too the shadow calculation for the fractals in direct lighting could be doing it.
One thing that may help is extending your lit area. In lighting tab (can't think if field names off top of my head) change the first input to like 4, and then the second to 0.125, then apply a constant color, or scalar, to direct lighting, and set it to like 2. The clouds will have a larger glow area for overcast like IRL.
PS directly lit clouds may not be calculated like directly lit surfaces, as they are volumetrics.