Lighting & 3D Graphics. Images from 3D Creative Magazine

Transcription

1 Lighting & 3D Graphics Images from 3D Creative Magazine

2 Contents Introduction Definitions 3D Lighting Basics 3D Light Sources Lighting Controls & Effects Brightness & Colour Shadows Hotspot And Falloff Include And Exclude Projection Mapping Volume Lighting Default Lighting Global Illumination High Dynamic Range Imaging Colour Bleeding Caustics Lighting Arrangements Lighting Methodology Reference

3 Introduction Computer displays use an additive light model (light made up of amounts of red, green & blue) rather than in real life where light is produced by the reflection of light off objects. Equal amounts of red, green & blue at full intensity result in white light. Variations result in different colours.

4 Definitions Colour Temperature: A scale used to differentiate between different near-white spectrums of light. Measured in degrees Kelvin. In a practical sense it shows the warmth or coolness of the light in terms of its colour. Cool (fluorescent) lights have a high value & warm (yellowish) light has a low value. Intensity: The brightness of the light source or reflection. Angle Of Incidence: The angle at which a light ray strikes a surface. Affects how brightly an object appears to be illuminated. Radiosity: Light reflecting off an object that illuminates another object (also known as global illumination).

5 Definitions Ambient Light: The combined effect of all the light bouncing of all objects in an area. Attenuation: The property of light where it appears to become weaker over distance. Occurs because particles in the atmosphere blocks and reflects light rays. Smoke and fog dramatically increase the effect.

6 3D Lighting Basics 3D programs seek to copy the behaviour of light in the real world. Three main types of lighting; key, fill & ambient. Key Lighting: The main illumination source in a scene and one that casts the most apparent shadows. In an outdoor scene the key light is the sun. In an indoors scene it may be light through a window, a nearby lamp or camera flash. Fill Lighting: Fills in dark shadows cast by the key light. Ambient Light: In the context of 3D light, not really a light source but the light from key and fill lights bouncing off walls and objects. In global illumination rendering, ambient light is simulated by light interacting with the reflective properties of all object material surfaces in a scene.

7 3D Lighting Basics The Three Main Types Of Lighting. Key Light: the main source of illumination. Fill Light: to bring out details from the shadows. Ambient Light: that surrounding the object.

8 3D Light Sources To imitate the three types of light, 3D programs use four basic main light sources; omni or point lights, directional or distant lights, spotlights, and ambient or global light. Basic 3D Light Sources Omni or Point Light: casts light in all directions. Directional Light: casts parallel light along a single axis. Spot Light: casts a cone or pyramid of light.

9 3D Light Sources Omni Or Point Light: Casts light in all directions. Used to simulate non-directional light source. May or may not be capable of casting shadows depending on program. Can cast light through objects in some programs. Omni-directional Light Source Characteristics. (a) Omni light source positioned in centre of scene casts light in all directions. (b) In some programs omni lights cannot cast shadows.

10 3D Light Sources Directional Or Distant Light: Projects light along one axis only. All beams are parallel & good for distant light sources such as the sun or the moon. Directional Light Characteristics. (a) A directional light source, which casts parallel light rays, aimed down a sphere. (b) The resulting shadows are also parallel.

11 3D Light Sources Spotlights: A directional light source that radiates out from a single point into a cone or pyramid that the user can define the size and shape. Usually, have a target connected to the source to show where the beam is pointing. Can be used in almost any situation. Can also be used for adding small highlights and accent lighting and for adding drama and realism. Spotlight Characteristics. (a) A spotlight source projects a cone of light at a sphere. (b) Shadows created by a spotlight radiate way from the source.

12 Photometric Lights Photometric lights use light energy values that enable you to more accurately define lights as they would be in the real world. You can create lights with various shadow casting patterns and colour characteristics, or import specific photometric files available from lighting manufacturers where the shadow patterns and colours are defined.

13 Lighting Controls & Effects Most 3D software have a standard set of controls for lighting and many have additional features. These controls and effects can be: Brightness & colour Shadows Hotspot and falloff Include and exclude Projection mapping

14 Brightness & Colour There are a number of controls for light brightness & colour. Intensity: The brightness level of the light source. Multiplier: The ability of some programs to exceed a brightness of 255 white. Attenuation: The natural reduction of light over distance. Allows control of light over both distance and amount. Invert Light: Offered by some software to make a light shine darkness to darken corners or other areas. Colour: Controlled by RGB or HSV sliders. Can vary colour to simulate plastic gels over photographic lights, give a theatrical flair, add extra interest by blending light colours, simulate different types of light bulbs.

15 Shadows Shadow Mapped Shadows: Work by creating a grayscale texture map based on the lighting & mesh in a scene and applies it to the objects at render time. Creates soft edged and more natural shadows than ray traced shadows but can tend to be blocky. This can be fixed by increasing the shadow mapped size setting. Position of shadow can be adjusted with a map bias setting. Shadow Types. (a) Shadow mapping produces natural-looking soft-edged shadows (b) Ray-traced shadows are sharper and more precise.

16 Shadows Ray Traced Shadows: Defined using ray-tracing rendering techniques. Ray traced shadows often have a hard edge that is very accurate and precise. They are especially good for sharp dramatic shadows such as space scenes or strong sunlit scenes. Position of shadow can also be adjusted with a bias setting. Effects of Shadow Map Size. (a) Blockiness & smearing with a 256K map size. (b) Increasing the map size to 1024K reduces the problem but slows rendering time.

17 Hotspot And Falloff Most spotlights and directional lights have controls to adjust the concentration of light & is represented by two cones or pyramids. Hotspot: Defines the inner angle of the beam of light at the current intensity for that light.. Falloff: Defines the outer perimeter of the light beam indicating where the intensity has dropped to zero.

18 Hotspot And Falloff Effects Of Hotspot And Falloff Sizes. (a) When hotspot and falloff settings are close together, the beam appears focused. (b) Widening the difference between settings makes the beam more diffuse looking.

19 Include And Exclude Include & exclude allows you to set up lights that only affect objects you identify. Include: Enables the selection of a list of objects a light affects Exclude: The opposite where you select objects a light doesn t affect. Can be used to fine tune complex lighting and achieve special lighting effects.

20 Projection Mapping This is the process of using a spotlight as a projector by adding a map to the light to change it s shape or cast a pattern onto objects. In traditional film making & photography metal plates called gobos are used. Projection maps are the virtual gobos of 3D programs. Projection Map Samples. (a) Star shaped gobo. (b) Venetian blinds. (c) Tree branches. (d) Full colour or grayscale maps can also be used.

21 Volume Lighting Volumetric Light: Is an adjustable 3D volume associated with a light to simulate natural light behaviour in an atmosphere. Volumetric light can be simulated using a conical mesh and extend it further than the edge of where it is lighting and apply a translucent (semi-transparent) map set to the following suggested parameters Colour adjusted to desired colour temperature of source Self Illumination: maximum Transparency level: 75-90% Transparency type: additive Transparency falloff: inward.

22 Volume Lighting Volumetric Lights Have an adjustable 3D volume that can simulate the effect of the beam shining through mist or smoke.

23 Default Lighting Default Lighting: Many programs provide a base light set up to allow shaded mode models and basic renders. Usually automatically turns off when user defines a light source. A good tip is to use default lighting or a base set of shadowless lights for the modelling process and do lighting at the end. Base Default Lighting Usually consists of two or three non-shadow-casting omni or directional lights arranged around the 3D universe or the default ambient light value.

24 Global Illumination Global illumination are algorithms used in 3D computer graphics so that when determining the light falling on a surface, it takes into account not only the light which has taken a path directly from a light source (direct illumination), but also light which has undergone reflection from other surfaces in the scene (indirect illumination). Images rendered this way are more photorealistic. However, they are more computationally intensive. A common approach is to compute the global illumination of a scene and store that information with the geometry (e.g. final gather & photon mapping in Mental Ray ). That stored data can then be used to generate images from different viewpoints for generating walkthroughs of a scene without having to go through expensive lighting calculations.

25 Global Illumination Rendering without Global Illumination. Global illumination rendering demonstrating how light is reflected by surfaces.

26 HDRI (High Dynamic Range Imaging) A High Dynamic Range Image (HDRI) is an image file that is capable of displaying more exposure information than is visible within a displayed image. The main uses of HDRI images are as an image format that can be manipulated and adjusted as a post rendering process. They also provide lighting source data for Image Based Lighting (IBL). IBL is a process that that surrounds a scene with a giant sphere. This projects an image inward from the sphere, so the colours and tones from the image are added as light to a scene.

27 HDRI (High Dynamic Range Imaging) A scene rendered to a High Dynamic Range Image file can be displayed at different exposures without having to relight and re-render the scene.

28 HDRI (High Dynamic Range Imaging) Animation by Paul Debevec, the pioneer of HDRI ( illustrating use of HDRI as light sources. Animation by Paul Debevec ( illustrating use of Image Based Lighting (IBL)

29 Colour Bleeding Colour bleeding is the natural transfer of colour between objects that are near to each other. It is the effect of light bouncing off one surface indirectly illuminating the other. Can be faked using coloured light sources or using a renderer with Global Illumination capabilities (e.g. Mental Ray, VRay, Maxwell). The purpose is to make images appear more realistic, add variety to surfaces and add visual clues when two surfaces are close together. However, it takes much longer to render, is not suited for stylised colour schemes and not suitable for composited shots with live action plates, miniatures or matte paintings.

30 Colour Bleeding In scenes with Radiosity or Global Illumination, the hue (colour) of objects naturally spreads over other nearby surfaces. Colour bleeding can be faked by adding coloured lights, for example, below the ant to create the reddish glow of the skin on the surface.

31 Caustics Caustics are similar to colour bleeding but describe light effects from reflections off surfaces such as a body of water or the surface of a mirror. That is, it simulates glints of light focused through glass or lenses and light reflecting off metal, mirror or water. Examples of caustic light effects are: Light reflected from a rectangular mirror that throws a rectangle of reflected light onto the floor Light refracted through a glass to cast a pattern on the table below it. Light concentrated or focused by passing through a lens or reflected off a curved surface. Shimmering light that reflects or refracts off water

32 Caustics Caustic effects can create interesting patterns of light bouncing off water. A caustic effect rendering illustrating the reflected rectangle of light on the floor from the mirror surface.

33 Lighting Methodology In general, use as few lights as possible. Get core lighting right first and then work on any accents or highlights. Shadow casting spotlights make the best key lights and is often the first light to be set up. The key light is the most important light and all other lights work with it. Add fill lights to areas that are too dark, use extra spot or omni lights. Fill light is not often a recognisable light source so needs to be subtle in use.

34 Lighting Methodology Use attenuation, include/exclude and turn off/on shadows & use backlighting in fill lighting to add highlights. Add accent lights to represent practical but minor light sources such as indicator lamps or to highlight particular objects in a scene. Accent lighting can make good use of include/exclude lighting to create particular highlights.

35 Reference Source data & cover images from 3D Graphics & Animation by Mark Giambruno. New Techniques in 3D Lighting & Rendering (3D World Issue 33) by Jeremy Birn. Additional information from 3D Studio MAX user manual