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3D Lighting Theory

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Lighting Theory

Studio lighting is a lighting concept created by sitcom television to standardize and simplify the work of lighting technicians for high-paced productions.  Film lighting, however needs to go a step further in customizing the light for every shot and make the scene look 'film special', as if every frame was photographically perfect on its own.  This is done using variants of the 3 point lighting theory.

Lights should be set up in this order: the key, fill and back light.  This setup maximizes zones of dark and shadows on the subject to consistently creates a well lit subject.  Lighting has to follow the rules below, even if it means cheating some shots, to make it 'visually matching' rather than 'consistently placed'.

 

1. Key Light

The key light represents the main light source of the scene: the sun, the moon or the strongest artificial lighting for indoors scenes.  It is almost always the strongest light in the scene and it is positionned on the sides of the subject camera to bring out the shapes of 3D models.   It should be positionned a little in front of the subject, but some directors will prefer a backlit key light.  A fully front lighting will flatten the look of your scene and models, and is to be avoided at all times.

 

2. Fill Light

The fill light serves to 'fill in' the dark areas not lit by the key light.  Indeed, a 3D scene is completely black at the begining of the lighting process.  Because of  that, anything that is not lit by other lights will be completely black.  In order to bring out some details from those areas, the fill light bring the base luminosity level just a little bit.  This will maximise the possibilities when it comes to compositing.

 

3. Back Light

The back light will be positionned in the back of the subject, on the opposite side to the key light.  This light will be used to create a thin line on the edge of the character, separating it from the background.  It can be positionned slightly upwards, to make a halo in the hairs of the characters.  It is said that Marlene Dietrich always asked for a strong backlight in her hair to recreate her iconic look with her blonde hair on black and white film.

 

Light Color

Light color does not have to be determined before rendering.  It can be set in compositing, and should ideally be done there to maximise the flexibility of editing the look, without re-rendering.  However, the render engine or lighting passes must supports a way to isolate different lightsources on different render layers or render passes. The ideal is to use AOV lightsources to separate lights, or in different render layers, grouped

If the color is set in the 3D scene itself, instead of the compositing software, light colors have to be very subtle to be realistic.  Saturation values above 30% are likely to look unrealistic, even for cartoon-styled scenes.

 

Ray-Casting Light Models

Standard

The standard lighting model is the base concept for lighting a scene in 3D.  It is only the process of lighting a scene using standard lights, like point lights, spotlights, ambiant lights and directional lights.  Light hits the surface of the object and it stops there.  Any bounce of light has to be simulated.

 

Ambiant Occlusion

Ambiant occlusion is a lighting model that recreates natural zones of shadows according to the shape of the 3D model.  In any lighting situations, creases and folds receive less light than other areas, because they are hidden from light sources from most angles.  This is can create a similar shadow effect as the global illumination model.

 

Global Illumination

Global illumination is a lighting model that creates a uniform lighting on objects, from lightsource coming from everywhere from the top of the sky.

 

(Global) Radiosity

Radiosity Models are models that calculate light bounces on surfaces, after the first contact between light rays and a surface.  For example, a red shirt lit near a white wall would splash the wall with red light from the secondary bounce of its light source.  It has different names in different 3D software, for example 'Final Gathering' in Maya. It is extremely time-consuming at rendertime, so it can be simulated otherwise by experienced lighting artists.  The technique is to recreate a 'faked bounce' using a secondary (and softer) light source, instead of asking the renderer to bounce everything on all the surfaces multiple times, until there is no more luminosity to distribute.

 

Volumetric Model

The volumetric lighting model is made to create a light rays, as if in a fog for every light in a scene.  It is very time-consuming, and generally unnecessary, as you can always cast volumetric rays and shadows on individual lights for quicker results.  Rarely do you need to cast shadows with a directional sunlight everywhere in a scene, unless it is to make 'godrays'.  Even then, it can be fakes in other quicker ways, if you know what look you want to create.

 

HDR

HDR, for High Dynamic Range, is a type of image that can contain all the different exposure levels of an image at once.  It is often used for background images, or as a contextual fill-light.

 

Light Types

Diegetic vs non-Diegetic Lights

Light sources in films can either be diegetic or non-diegetic, just like sounds.  A diegetic element in a movie means that it is part of the story and visible in the set, like a ceiling lamp in a dining room.  A non-diegetic source, on the other hand, is a light source that is added for aesthetics, but that does not actually have a real correspondance in the filmed set.

 

Natural vs Artificial Lighting

Artificial lighting is usually for inside scenes, but street lamps also enter this category.  Theses are lights that are man-made and they are usually a warm color, because of the habits of the incandescent lightbulb.  'Cool' light bulbs are now also possible for interior lighting, which creates more of a gloomy or space-like atmosphere.

Natural lighting on the other hand, is any light source that comes naturally without human intervention.  There can only be two types: the sun (warm) or the moon (cool).

 

Light Sources

Ambiant Lights

Ambian lights are lights that do not have a specific source.  They heighten the base level of luminosity in the scene, mostly to create some details in shadow areas.

 

Point Lights

Point lights are light sources that emit in every direction, like a lightbulb.  They are usually used when no special effect is required.

 

Spot Lights

Spot lights are directionnally controllable light sources.  They can be used for theater lights, volumetrics, and most studio lighting techniques.  Real live cinema uses only this type of light as non-diegetic lights.

 

SkyDome

A skydome is a sphere with  an image that creates light onto the scene.

 

Directional Lights

Directionnal lights are infinitely directional lights.  Unlike spot lights, there is no widening of the cone angle.  It comes from the same direction and lights evenly throughout the whole scene.

 

Physical / Natural Sunlight

Physical natural sunlight is light created from a directional light, ambiant light, a global illumination and radiosity model.  The sun is directional in nature, but it also creates an indirect ambiant of blue from the sky and a bounce that requires radiosity.

 

Mesh Lights

Mesh Lights are lights that emanate from a 3D mesh surface.  For example, a neon light would be a mesh light, as we can see a volume to it's lighting surface.  A bulb would usually not require such an light type, unless it was a close up of it's filament.

Photographic Lighting

Recommended Lighting Books

Color Scripts Examples from Pixar first 25 years

 


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