Realistic outdoor animations in VUE
This section sums up the 2009 work in VUE for animations. There were some exciting projects early this year on professional post production level, some of them resulting in good VUE renders for composites or just stand alone renders. During the process of rendering animations for these projects we ran into several problems, the most severe of all being indirect lighting flickering (a.k.a `GI flicker´ in software like maya etc).
The focus at the end of the year was therefore on realistic animations and how to get them flicker free. This is a much avoided frontier in VUE and people rather prefer spending time on artistic still pictures. The reason is that several techniques for realistic stills in VUE do not work for animations since they cause a number of flickering noises. For example the `picture of the year´ runner up on the other page would never work in animation.
Here is why
- Global radiosity, the indirect lighting technique in VUE, does not work because it does not allow you to store the indirect lighting solution for animations (‘AO’ and ‘GI’ in VUE are no indirect lighting techniques: AO - occlusion based, GI - I think shadow map based). The result is either heavy GI flickering or unrealistic long render times with global radiosity. Vue lacks a feature like the fly-trough/light cache mode in Vray for example, where the indirect lighting solution is stored and can be re-used as long as only the camera is moving. Vue does feature a setting called reduced pulsation though, but the heavy increase in render time and the final quality make it a bit useless. An alternative is illumination baking, but it takes very long and additionally is unstable from my experience.
There is one animation render with indirect lighting (global radiosity/reduced pulsation) in the reel below (the very first scene). Due to the heavy render time though, only this light-weight foreground intended for a composite was possible. If this was a full scene, it would probably still be rendering. The rock in the scene is the only element exposed to indirect lighting (trees/grass only with direct lighting).
GI flickering is resolvable to some extent by retreating to direct lighting (means no light bounces; ‘global ambience‘ in VUE) and by careful matching the colours/materials in a scene to get a realistic picture. Matching the colours within the scene is the most important part, as the eye picks immediately on something that looks unnatural. The good thing is that the colour of every component (trees, sky, ground, ...) can be adjusted separately, which gives large space for optimisation. This has been done for everything shown on this page. The results are of course not as good as with indirect lighting, especially in shadow areas, but they are not bad.
- Procedural terrains, the most realistic terrain models, do not work in animation either.
This is mainly because of the fine features, which tend to flicker and require unrealistic render times. But converting procedurals to heightmap terrains and a quality material/shader (but without displacement for render time reasons) save the day. The winter scene for example uses a really simple and height map based standard terrain (the inset), and the features are only brought in via bump mapping and realistic slope/height distributions of the stone and snow. There is no displacement map or procedural terrain at work here, thus the low render time.
- Very high anti aliasing settings in general do not work because the render time explodes, especially with the relatively slow VUE render engine (no mental ray or Vray support yet). In terms of render time, my limit is 40mins/frame at 1280x720 on a quadcore Q6600. All work shown in the reel on this page is within this limit and most is well below. The need for a low render time also prohibits any use of spectral clouds or complex atmospheres. In fact, coming up with a realistic atmosphere that renders fast is challenging, but achievable. Fancy effects can then be included in the final composite, although I am aware that rendering them all in one go is preferable.
- Another flickering source which seems like the final show stopper for winter scenes is texture filtering flicker. It means that the anti aliasing is destroyed by the mandatory texture filtering in VUE if an object is rendered against a white background (snow). This heavy flickering messed up my otherwise optimised winter scene in animation and it seems that there is no workaround.
So all in all, going for realistic animations in VUE is tricky business. Considering all the points above and still getting a realistic picture basically requires a good terrain with realistic geological features, realistic ecosystems and materials/colours that look real and are matched (eg sky colour and ground colour). By doing so, the eye is drawn away from the fact that the lighting is only the direct global ambience lighting, which especially shows in shadow areas on most materials.
Figuring out and following all those guidelines can be difficult. Vue users could argue that life can be a lot easier if you just render stills with lots of sunsets, funny god rays and spectral clouds filling half the frame. But then, rendering such stills that can not be used in animations is really boring and the imagination only really takes off once you can let the camera fly. I think VUE can be really good with direct lighting outdoor animations and that this is the way to go for VUE. No other application knocks off huge outdoor scenes like in the reel with so much ease. Although Vray Scatter for 3dsmax looks also nice, but I have not tested it yet. Fact is that Vray handles all the flickering noises much better than VUE.
The stills and the reel on this page show what I came up with following the rules on top of this page. Taking it from here, a few things could be (or should be) optimized for a post production scene: the terrain sculpting, the camera path, ecosystem variety on a large scale and the saturation of some of the colours for the trees. Also some of the ground materials are only demo materials. Doing so is eventually just a matter of spending more time on a scene or doing the test renders on a small farm. (everything displayed here was rendered on one quadcore Q6600/2.4GHz)
Frame blending (AE pixel motion, 200% stretch: 12fps to 24fps) was also applied to scenes where only background is on screen and it is marked in the subtitles. This very fast technique works surprisingly well if no foreground or midground is on screen and the camera is slow. The result is almost identical to a raw VUE render at 24fps, because VUE´s multi frame anti aliasing for animations and frame blending in After Effects are somehow similar.
Unrelated to the VUE work, I would also like to recommend this book here to understand rendering better. It is remarkable how close computer science, maths and physics work together in this area on a pretty high level. Even psychology plays a role for perception issues and so on.
It even comes with a fully functional render engine.
The video file is quite big, but streaming is fast and the reel shows a lot of different renders.