March 10 2017

Remember Reflections!

TweetShareShareShare

A rendering without reflections is often lifeless and unrealistic. Especially if the image contains large water or glass areas. Handling reflections is a balance between finding the accurate beauty you seek and managing the demands on your computer - reflections can ask a lot of your graphics card!

Above: Atmospheric render with water reflections (courtesy of G.Felix)

This blog explains how to assign reflections in Lumion and can help you strike a balance between computer performance and reflective beauty.

What options are there for adding reflections in Lumion?

There are three kinds of reflection in Lumion:

1. Basic ‘cube’ reflections (Projected reflections)
   
2. Reflection planes (Planar reflections)
   
3. Speedray reflections
   

Basic ‘cube’ reflections (Projected reflections)

These are the default reflections that you see in rendered reflective surfaces in Lumion. It is the basic kind of reflection.

You can think of a 3D space as if it were a cube, which of course contains 6 surfaces: top, bottom, back, front, left and right. For any 3D scene, there is a default ‘cube’ which is used as a reference to create a reflection map of your Lumion scene. The reflection map is created using the centre of this cube and is used to simulate a reflection from any surface.

Cube-mapping has the advantage that it is very fast but has the disadvantage that reflections are often unrealistic. The results in some cases, can be pretty weird, like over-large reflections of people, cars or other objects, or even missing reflections; like trees that should be present in the reflection but aren’t.

There is an easy way to fix some of these artefacts. You can simply change the reference point of the reflection map by placing a reflection control sphere in the scene - see the tutorial below. The sphere becomes the centre of the cube which is used to create the reflection map. It is a basic fix and will not work in all circumstances but has the advantage that it demands no extra computer power and is a quick and easy fix which is good enough in many situations.

Above: Adding a reflection control sphere

Reflection planes (Planar reflections)

If you really want to get accurate reflections, then you need to assign reflection planes to particular surfaces.

Reflection planes simulate accurate mirror-like reflections, no matter where the camera viewpoint is. The drawback with adding reflection planes is computer processing time and means that rendering takes longer. The more planes assigned, the more power is needed.

As long as your computer graphics card has a good spec, this is no problem for small numbers of reflection planes. But even on high spec computers, with complex scenes, the result can be unattractive render times, if too many reflection planes are added. That’s why there is a limit of 10 reflection planes per image in Lumion.

For many animations or images, 4 or 5 reflection planes are often enough, especially if Speedray reflections (see below) are enabled.

Reflection planes and Speedray reflections are enabled using a single effect in Lumion: The reflection effect.

Above: How to add the reflection effect (Reflection planes and Speedray)

Speedray reflections

Speedray is a trademarked, Lumion-developed technology which is implemented in Lumion as a single on/off switch - see the tutorial video above. It is a neat way of creating reflections which are quite accurate - though not quite perfect - without demanding too much extra computer processing time.

Turning on Speedray when rendering doesn’t impact render time too much and improves general reflection quality. It can be used effectively on all reflective surfaces. If a surface is really prominent in the image, then it’s best also to assign a reflection plane to it.

More info

Remember also the effect of “glossiness” and “reflectivity” of your materials. If you set these values too low on a reflective material, then it won’t reflect very much. Remember to push up these sliders and switch on Speedray reflections, before assigning more reflection planes. It works very well in many situations and doesn’t tax your computer too much. 

If you want to find out more about reflections in Lumion, check out the following Lumion knowledge-base articles.

• Projected reflections
  

• Speedray reflections
  

• Planar reflections
  

In short, remember your reflections! They are essential in getting your images to look great. Use Speedray reflections almost always and add reflection planes to prominent reflective surfaces, like glass, water or wet surfaces. If you use this rule of thumb, then you will already be half way there!