by admin on December 6, 2009
A nice feature of Vue is the possibility to add dispersion effects for materials with a non-zero refraction index. Dispersion is the result of the fact that the refraction index of a material is dependent on the wavelength of the light.
We all know this effect from a prism where white light is dispersed into rainbow colors, but also the sparkling of diamonds is caused by dispersion.
In real life, what is usually called white light is a continuos spectrum of all wavelengths depending on the properties of the emitter. This is called black body radiation in physics. The perceived color varies with the temperature of the radiation and the properties of the sensor. Bright sunlight appears white to us and corresponds to a temperature of about 5500 K.
Now you might think that the “spectral” atmosphere settings of Vue will reflect the physical properties of sunlight. But if you create a scen with a prism, you will notice that white light (and all other colors) in Vue is treated as a mixture of red, green and blue light, as represented by the RGB values you can set in the options dialog for the light source. So in a way, the “spectral” name for atmosheric effects is a bit misleading.
The type of the light source does not matter for this effect. A spotlight acts the same as the sun or a point light. Thes types only differ in the way shadows are created. The special feature of the sunlight only is that it influences the sky and cloud colors, but the calculations for these effects also rely on the RGB values instead of a black body spectrum.
For most purposes, this “fake dispersion” does not really do any harm, as the spectrum usually is squeezed together so much that the RGB nature of the light can’t be detected. But if you want to do closeup renders of optical effects, you will hit the limit of realism that can be achieved with Vue.
by admin on November 26, 2009
This is a followup to my comparison of Vue lighting models for an outdoor scene. Because lighting for indoor scenes is much different from outdoors, I am covering this topic in a dedicated post.
I set up a simple indoor scene, just an empty box with a few geometric primitives in one corner. Walls and floor are flat white, the ceiling is blue. Just as in the outdoor series, I made two variations of the scene. Again, all renders were made at a 640 x 480 resoulution on “Final” render level
1. Closed Box With a Single Point Light
Closed Box - Standard Model
Closed Box - Radiosity Without Boost
Closed Box - Radiosity boost 4.0
For a closed box, Global Ambience, Ambient Occlusion and Global Illumination models are useless because they involve the influence of the sky on the objects.
You can easily see that Global Radiosity is a must for indoor renders. It is also advisable to make use of the boost slider as the results will look even more convincing.
2. Box with Indirect Sunlight Through a Window
Indirect Sunlight - Standard Model
Indirect Sunlight - Global Ambience
Indirect Sunlight - Ambient Occlusion
Indirect Sunlight - Global Illumination
Indirect Sunlight - Radiosity Without Boost
Indirect Sunlight - Radiosity Boost 4.0
The first noteworthy result is that Global Illumination works far worse here than Ambient Occlusion although it is supposed to be superior. And it beomes very obvious that even with Global Radiosity Vue has significant problems handling tricky light situations like this one. Even with a 4.0 boost setting there are obvious light leaks around some edges. I also played around a bit with the advanced indirect lighting and photon map settings within the render options dialog, but was not able to get much better results.
For lighting situations like this one, Vue is significantly inferior to unbiased renderers like LuxRender or Yafaray.
If you want to test render settings for this scene, here is the scene file as download:
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download: Indoor Test Scene (318.34KB)
added: 28/11/2009
clicks: 343
description: Indoor scene for testing lighting models
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But beware, the user settings are set to extreme values, so the render time will be long, if you don’t change the settings.
by admin on November 22, 2009
In the atmosphere editor of Vue you can choose among five different lighting models. They differ in how the effects of indirect lighting is calculated. I will compare the effects of these models on a sample scene. But first here is what each mode does:
- Standard Model
A uniform ambient light of pre-defined color is adde to the scene. You can choose how much will come from the sky and how much will come from all directions. Horizontal surfaces will be brightened more by light from the sky
- Global Ambience
This takes into account the color variations of the sky. A surface facing a blue part of the sky will receive a little blue light, surfaces facing clouds will receive white or grey light.
- Ambient Occlusion
Every point in the sky acts like a tiny light source. An point on an object receives a bit of shadow if another object is occluding the path to the sky. Only objects within a pre-defined range will cast these shadows. If the path is free, the point receives light from the sky.
- Global Illumination
This is basically the same as ambient occlusion, but there is no range limit. So all objects influence each other.
- Global Radiosity
Instead of calculating shadows as in the AO and GI models, the radiosity models asumes that any obect that recieves light will reemit a bit of it according to its physical properties. This light affects the surrounding objects. This is done recursively. Vue includes an option to “optimize for outdoor rendering”. This effectively cuts down the number of indirect contributions because usually in outdoor scenes this effect is less relevant.
Comparision of the Lighting Models
To compare the different lighting models I used a simple nature scene with a basic grassland terrain and an ecosytem of red maple trees. I used two different atmospheres for the test: “Default” for a clear sky and “Glasgow” for bad weather. No other settings were changed. The images are 640×480 renders on “Final” setting with Vue 8 Complete.
Default Atmosphere – Clear Sky
Standard Model
Global Ambience
Ambient Occlusion
Global Illumination
Global Radiosity with outdoor optimization
Global Radiosity without outdoor optimization
The standard model is easily recognised by its uniformly bright coloration. In GA the shadows within the leaves of the background trees are very dark. They lighten up with AO and even more with GI which is unusal according to the manual. GR is almost as bright as the standard model, but the coloring of the leaves is much better differentiated. Optimized GR is a bit darker than standard GR
“Glasgow” Atmosphere – Bad Weather
Standard Model
Global Ambience
Ambient Occlusion
Global Illumination
Global Radiosity with outdoor optimization
Global Radiosity without outdoor optimization
The results here are slightly different than with the default atmosphere. Global Illumination is now noticeably darker than Ambient Occlusion and outdoor optimization for radiosity results in a significantly brighter picture.
Conclusion
The standard model should only be used if render times would get too long otherwise. All other models give significantly better results. Where there is no sunlight, Global Illumination will darken the picture as compared to Ambient Occlusion, with much sunlight it seems to brighten the shadows more than AO. Global Ambience is a good and reasonably fast alternative for scenes without much direct light. Global Radiosity works best in all atmospheres, but I would recommend it only for detailled scenes where objects are close to each other. I don’t think that vast open landscapes will profit much from radiosity. Regarding the difference beween the two radiosity variants, I think it is up to personal taste which version looks nicer. I couldn’t honesttly say that I would prefer one over the other.
For a comparison of lighting models for indoor scenes look here.
