Radiosity in Bryce 4

Forget high end applications. With a bit of planning and thought you can easily achieve Radiosity effects in Bryce.

 
But what is Radiosity? Well Radiosity is the reflected or bounced light that is thrown off by almost all surfaces. I say almost all as only the most matt of surfaces have no reflective effect whatsoever. However in most cases the amount of reflected light (Radiosity) given off by most surfaces is so small as not to be worth simulating.
 
So where and when do we need Radiosity?

Radiosity is most noticeable where reflective coloured objects are places in close proximity to other objects and should ideally be kept for enhancing key items within your scene.

Consider the following two images, both are of a gold sphere lit from above by a white light. The image on the left (fig 1) is s straight forward image whilst the image on the right (fig 2) has had a Radiosity effect added. I think you will agree that the image on the right is far more convincing.

 

fig 1
fig 2

What first? The first thing to do is to build and light your scene just like normal. Then do a test render to see where Radiosity will be needed, it is almost impossible to pre guess where your scene will benefit from Radiosity without actually rendering it. You will now have your basic image like (fig 1, above).

Take a good look at your scene and try to find the sort of surfaces that will be reflecting light. In our scene above the gold sphere is an obvious candidate.
 

I have my objects? The trick to adding Radiosity in Bryce is a simple one and relies on the fact that light in Bryce is only blocked by surface normals facing the ray of light. 
  
What does this mean? Well think of it like a one way mirror. Light can pass through but only from one side, usually the inside. Surface normals are a residual of model geometry that allow a rendering program to only compute surface effects for the outside of objects, thus saving lots of rendering time by ignoring things that can't be seen. For our purposes we can use this to hide one or more additional radial lights inside our objects to simulate light reflected from the surface.


fig 3

Where do I put the lights? Positioning of the lights is an important aspect of achieving a good Radiosity effect. For the best results a small radial light should be placed on the direct light path from the emitter light source and as near to the outer edge of the object as possible. Consider the two examples below.
 

fig 4

fig 6
fig 5

fig 7

In the image on the left (fig 4) the Radiosity light has been placed correctly (fig 6) whilst in the image on the right I have deliberately placed it to low and off line with the emitters lightpath (fig 7). If you compare the two images you will see that in the incorrect image (fig 5) only one wall has received any Radiated light and the plinth base which should be in shadow is now lit up.
 
What light settings should I use? Just as important as light placement is the light settings. Remember what I said back at the beginning, that Radiosity is the light that bounces off of a surface. The radiated light will therefore be a mixture of the diffuse colour of the object and the colour of the emitter light.

To get the accurate colour of our object Alt+click on the colour icon for the diffuse channel in the Material Lab. This will bring up the colour pallet showing the RGB values, in this case 244.212.0.

Now do the same to get the emitter lights colour. In our example the light was white so only the objects diffuse colour will be used for setting the Radiosity light. However if our emitter light had been 255.100.0 for example, then we would have used the mix of the two colours, 244.100.0, for our Radiosity light.

For the Radiosity light settings I set Edge Softness to the maximum and Intensity to 500. I then set Falloff to Ranged and reduced the range down to 20. (You will need the 4.01 patch for this). This has the effect of producing an intense soft light that quickly fades to nothing. You will have to play around with the Intensity and Range to get the result that looks right in your scene. If for example the object reflecting the light is dull then the Intensity will be less, just use what looks right.

Colour = R:244, G:212, B:0
Edge Softness = 100
Intensity = 500
Ranged Falloff = 20

Any other hints? Don't overuse Radiosity, it should be used where it is needed to enhance your scene.

Watch the render times. Radiosity is adding lights so your render times will suffer.

Time spent experimenting with the light values and spray rendering is time well spent.

 
Well I hope you enjoyed this tutorial and found it useful. If it inspires you to do anything wonderful with Radiosity please tell me and happy rendering.

Jarec   (jarec@tarran.co.uk)

 

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