Art Tips from a Graphics Programmer 1, FRESNEL!
This funny word is responsible for creating many of those sweet, sweet rim lighting effects we know & love. Understanding it will really help you up to the believability & pop factor of your rendering & lighting!
(THREAD)
This funny word is responsible for creating many of those sweet, sweet rim lighting effects we know & love. Understanding it will really help you up to the believability & pop factor of your rendering & lighting!
(THREAD)
The Fresnel effect is actually very simple at its core, and is one of the basic principles of how *ANY* object is lit.
The basic idea is this: the greater the ANGLE of reflection of a ray of light off a surface, the more energy (brightness) that ray will carry!
The basic idea is this: the greater the ANGLE of reflection of a ray of light off a surface, the more energy (brightness) that ray will carry!
So, let's explore that image above a little more. We have a light shining onto a surface which reflects the light back at several different angles. Depending on how glossy the surface is, some directions will have more or less rays, and some will end up at the viewer.
Let's look at a few points on the plane.
At each, we can take the ANGLE between the incoming and outgoing ray, and this will tell us how bright the outgoing ray will be in relation to the incoming one!
The greater the angle, the higher the percentage of light reflected!!
At each, we can take the ANGLE between the incoming and outgoing ray, and this will tell us how bright the outgoing ray will be in relation to the incoming one!
The greater the angle, the higher the percentage of light reflected!!
This means that light at those "grazing angles" where both the light and the viewer are almost perpendicular to the surface will create the brightest reflections.
A good example of this is a lake! Notice how close up, the water is transparent, but far away it's reflective.
A good example of this is a lake! Notice how close up, the water is transparent, but far away it's reflective.
However, fresnel is also visible in MANY other things besides water & one area it's important for is LARGE LIGHT SOURCES, like the sky!
So, let's take a look at that. This time we have a sphere, lit by a sky-like light above a large portion of it.
So, let's take a look at that. This time we have a sphere, lit by a sky-like light above a large portion of it.
Now let's look at a couple different points on the sphere. In this first one, a large portion of the sky light is still hitting it, but the *maximum & average angle* of the sky light rays bouncing to the viewer is quite low, so the light will end up quite dim after bouncing!
But at this other point, a "grazing angle" is created where the average angle of the sky light to the camera is much higher, with some even reaching fully to 180 degrees!
As such, there will be a much more obvious reflection here! You can see this exemplified IRL in the third.
As such, there will be a much more obvious reflection here! You can see this exemplified IRL in the third.
Another example. This time let's say we have a dark colored sphere inside a bright box, and then the camera is placed inside (not really a common scenario, but good to illustrate the principle, and it's similar to something like an overcast day!)
With no fresnel, the entire sphere is lit evenly since it's receiving the same light from every direction & just looks like a circle. But, when we take into account the position of the CAMERA and the fresnel effect, we can add a much more lifelike reflection around the edges!
One more slightly contrived example to illustrate what's going on is in the case of a polished floor or table with an object on it. The illustrations below are from Dorien Iten's awesome article on fresnel, here: dorian-iten.com/fresnel/
Finally, let's look at a non-contrived example of what the fresnel effect will mean in an actual complex scene. This is a scene from Guardians of the Galaxy 2.
If you pay attention to the right side plane of Groot's face here, you'll notice that there's a soft fill light coming in from the right/behind, which right now is quite subtle and just "fills" the shadow slightly.
However, as the camera moves around to the left, we can see that the right side of his face gets lit up really brightly, almost like a new light is there! But there is no new light: instead, we are seeing how at this new grazing angle, the fresnel effect means that the reflection
is now much stronger, and is creating a really awesome rim/"kicker" light that highlights the side of his face and really shows the contour and 3d form of the awesome model!
Side note, you can see fresnel effect in action on several other parts of Groot here too, and in the BG!
Side note, you can see fresnel effect in action on several other parts of Groot here too, and in the BG!
Alright, that's all for today. There's more we could dive into with fresnel, but this is I think the most important parts.
I hope you learned something, and if you did and are interested in seeing more, drop a follow and I'll be making more of these kinds of tips in the future!
I hope you learned something, and if you did and are interested in seeing more, drop a follow and I'll be making more of these kinds of tips in the future!
Also, if you're interested, I'm currently looking for part-time (20hrs~/wk) or freelance work! More info here:
