Making Good with Ray Tracing
The phrase ‘Ray Tracing’ comes often hand-in-hand with any latest news about rendering techniques, so today I hope to give some clarity to myself with this terminology, and hopefully, the reader as well.
An excellent rendering engine creates a photo-realistic image from 3D geometries. This means an accurate calculation of light sources and their effects on objects, mimicking light particles hitting-reflecting-and transmitting on surfaces.
Light Sources and Effects
This may be ‘old’ knowledge for expert CG artists, but in order for beginning 3D artists to see how their light source(s) and surfaces interact to achieve a certain ambiance, it’s important to know what ray tracing actually traces.
In 3D setups, you can have one light source or multiple, but let’s start by saying there is one light source like a bulb above a table with some objects on the table. Ray Tracing will trace a light wave from your eye to a pixel point on the view plane or computer screen to the surfaces/objects and then to the light source and back, in the 3D plane. The ray tracer algorithm will first remodel out the scene and its geometric objects.
One key factor to note is whether your rendering engines use Forward Ray Tracing, Backward Ray Tracing or Hybrid Ray Tracing. You are right to think that the hybrid algorithm, as usual, is the more advanced and most accurate tracer but it is at the expense of speed since now there are more calculations involved. Hybrid tracing balances both the forward and the backward rays, biased more towards backward ray tracing.
Ray tracing works completely opposite to how our real vision works. When we see things with our naked eyes, it is a light source bouncing of objects that hit the cornea of the eyes. The algorithm of Forward Ray Tracing, in fact, does mimic this. However, the more efficient Backward Tracing does it the other way, it charts a light path from our eyes through a point on the view plane or computer screen and to the object(s), with the closest object to our view plane being seen first. The algorithm of pure forward tracing is seldom used since it is difficult to ensure that every ray of light from the objects will reach the viewer’s eyes but it creates better color calculations. So, Hybrid Ray Tracing must still sample a selective number of Forward Ray Tracing in order to achieve accurate color tones for the objects or surfaces. The Backward Ray Tracing does most of the job and also gives the artist more fine-tuning power to achieve a certain look and feel by modifying the light source and the object positioning.
Paths of Light Travel
For discussion sake, there are only two main paths of how light travels when it hits a surface – the ray is either reflected (bounces of) or transmitted (goes through the object) – transmission.
And for Reflections, there are only two types of reflective light, either ‘specular’ that is one light in and one light bounces out, or by ‘diffusion’ that is one light in and many diffused bounces of lights outwards. Specular reflections, as you may have guessed, occurs when the surface texture of an object is smoother and less rough. Diffusions occur when the surface has much roughness to it and therefore the light coming in hits at varying degrees and there is more than one angle of light bouncing back.
” The reflection of light can be roughly categorized into two types of reflection: specular reflection is defined as light reflected from a smooth surface at a definite angle, and diffuse reflection, which is produced by rough surfaces that tend to reflect light in all directions… There are far more occurrences of diffuse reflection than specular reflection in our everyday environment. ” See diagram @https://micro.magnet.fsu.edu/primer/java/reflection/specular/
So, this allows you to tweak your rendered image depending on surface roughness or material textures which you can choose in a 3D environment for a particular effect. Again, knowing the difference of material/texture types and how they interact with the light source or sources gives you the power of rendering out a medley of scenes using the same 3D model. You may access helpful rendering tutorials @ https://vimeopro.com/cebasvt/finalrender-quick-tutorials
Ray Tracing and Rendering Effects
The concern of 3D artists for interior design, architectural visualization work or animated characters and environment will always be creative look and feel. For this, you may wish to learn more about the main kinds of rendering effects with Ray Tracing:
- Shadowing
- Reflection
- Transparency
- Refraction
Referencing www.cebas.com/manual/finalRender , there are now finer tunings of Global Illumination, Ray Tracing effects combined with Scene Converters ( if you are on a different renderer ); besides supporting all standard lights in 3dsMax, cebas Visual Technology has recently incorporated Spectral Wavelength hybrid rendering (unbiased) with a unique LightCache (biased) method giving biasHybridTM.
The list is self-explanatory as we encounter these main four light effects everyday in our environment. Ray Tracing and Global Illumination are givens in a renderer. You get a different look and feel each time by adjusting the material type and placing light sources or Area Lights. Then, adding Motion Blur or Depth-of-Field again changes the creative scene. More of this later. Follow our blog https://www.cebas.org/blog/ and join in the cebasWall.
Rendering tutorial fR frameBuffer by Edwin Braun @ https://youtu.be/W7shVvWJa6U
I will not be going into details of how the rendering based on the aforementioned, desired effects will affect your scene as there are much information online. Try first at this link: https://cs.stanford.edu/people/eroberts/courses/soco/projects/1997-98/ray-tracing/effects.html
Due to the need for complex calculations, Ray Tracing is more suited to production work where complex and long rendering speeds are tolerated, such as film and television, whereas games rendering prioritizes speed and thereby does not use Ray Tracing.
For those who wishes to delve deeper into the world of Ray Tracing, see https://www.cs.cornell.edu/courses/cs4620/2013fa/lectures/22mcrt.pdf
References:
https://computergraphics.stackexchange.com/questions/337/radiosity-vs-ray-tracing
https://cs.stanford.edu/people/eroberts/courses/soco/projects/1997-98/ray-tracing/intro.html
https://www.cg.tuwien.ac.at/research/rendering/rays-radio/
https://www.scratchapixel.com/lessons/3d-basic-rendering/global-illumination-path-tracing