Join Brian Bradley for an in-depth discussion in this video Generating a caustic effect, part of SketchUp: Rendering with V-Ray 3.
- [Instructor] Caustics are a lighting effect that can be seen pretty much all around us in one form or another. In fact, oftentimes they are such a familiar and expected sight that we don't always notice they are there. For instance, how many of us take time to stand and watch as focused light patterns create a dazzling display whilst we fill a bathtub, or stand by the side of a shallow stream on a bright sunny day? Of course, this naturally occurring lighting effect doesn't generally show up by default inside a CG lighting setup.
Typically speaking we have to deliberately enable caustics and then work with a unique set of controls in order to tweak and tune the effect. Which is exactly what we are going to be doing here. What we have in our scene then are the essential building blocks from which we can create a caustic lighting effect. We have a strong directional light source in the form of a V-Ray Spotlight. We have suitable geometry in the form of our shade ball and we very importantly, have a reflective, refractive material applied to it.
Which in this instance is a standard glass Shader. As things stand then, we would probably expect to see caustics generated once we enable them in the scene. Let's go ahead and do that by jumping into the Settings tab on the Asset Editor, and enabling the Caustics option. If I go ahead and hit the Render button though, we may be surprised to note that enabling caustics in the scene and then actually getting them to appear in our renders can oftentimes be two very different things.
Now don't be fooled into thinking that caustics simply aren't working here. If I save the render that we have just taken, crank the global Multiplier father caustics found in the caustics rollout up to a value of 10, and then render again. You can see, as I compare the images, that we definitely have caustic photons being generated in the scene. The problem is, that all we are currently getting from our material set up are reflective caustics rather than the perhaps more familiar and expected refracted variety.
The problem that we need to tackle then is in fact a material one. And so let's jump into the Materials tab and from the list, click to select the Glass material in order to access its properties. Down in the Refraction section, we have two options that are currently contributing quite significantly to the low kovar material. One is the Fog Color, creating the burnt orange coloration of the glass, and the other is the Affect Shadows option, that is currently causing the refractive properties of the material to create the color door transparent orange shadow effect that we are seeing.
If I turn Affect Shadows off though, and re-render, you can see that we do indeed now have refractive caustic showing up. If we wanted to brighten or darken the caustics being created in the shot, without effecting the intensity of the light being used to generate them then we could again tweak the global Multiplier option. Which in this instance I will dial down to a value of 5 and render again. Something else that we may want to do when creating a caustic effect is sharpen things up a little.
Given that the edge of the caustics here do look a little soft to me. This is a change however, that should be made quite sparingly given that we can add quite a bit extra to our overall render times if we're not careful. To show how we can sharpen up the caustics, let's jump into the Lights tab. Increase the Caustic Subdivs value on our Spotlight to about 6000 and then after saving our current image to history, take another render. If we compare our two images now we see that we're getting a much sharper cleaner look to our caustics.
Of course, we have added quite a bit to our render times and if we were in a scene with even more caustic effects going on then things would naturally slow down even more. That having been said though, seeing as we have been able to create a very nice reflective, refractive caustic effect in V-Ray, with very little effort on our part really. I would say that generally speaking, the increased render times will probably be worth the wait.
- Gamma handling in V-Ray 3 for SketchUp
- Working with interactive rendering
- V-Ray light types
- Working with irradiance mapping
- Rendering animations
- Working with the V-Ray camera
- Using the Materials UI
- V-Ray FX tools
- Stereoscopic 3D rendering
- Using V-Ray objects