The shadows do look extremely dark - I would say unnaturally so. This seems odd if GI was on since one of the main purposes of it is to add definition to shadowed areas. So if you want to cut down render time, and since you don't have any dense clouds here that would benefit more from the GI shading enhancements in clouds, you might just try turning GI off altogether here. A fill light setup (without shadow casting) might substitute if you even notice a difference, but I suspect you may not, and it would save a lot in render time.
The Quality setting in clouds is just another way to adjust samples; it's designed to give people a general idea of a good sample level for a given cloud setup. It is scaled relative to an approximated estimate of the number of samples needed to get acceptable cloud quality (low noise) based on several factors including cloud density and depth/height.
Detail Blending works similarly to TG 0.9's Extra Blended Detail - it blends micropolygon samples. It could be said it results in a "loss of detail", but it could also be seen the other way - that lowering it simply increases artificial sharpness, which I often find has a fairly obvious computer-generated look. Generally, as with digital photography, sharpening in post is preferred. Compensating for lowered detail blending with higher AA is probably not a good solution either. I have experimented myself with lowering detail blending and the results can be acceptable in some cases. It certainly does lower render time a lot too, but I wouldn't consider it a general solution for most scenes.
Of course everyone's preference for image sharpness varies - I find a great many TG images posted in public galleries are oversharpened for my taste. I think this corresponds with the general public's apparent preference for this level of artificial sharpness, as evidenced by digital camera maker's in-camera image processing bias of high sharpening in most cases.
- Oshyan
