Lec06 Lighting_2122.pdf

EIE 3101 Computer Animation Lec 06 Lighting 1 Isaac Kerlow, The art of 3D computer animation and effects, 4th ed., Hoboken, N.J.: John Wiley & Sons, 2009. Chapter 8 2021/22 sem 2 2 Content Ch8 Lighting Measuring light Types of Light Sources Basic Components of a Light Source Three-Point an...

EIE 3101 Computer Animation Lec 06 Lighting 1 Isaac Kerlow, The art of 3D computer animation and effects, 4th ed., Hoboken, N.J.: John Wiley & Sons, 2009. Chapter 8 2021/22 sem 2 2 Content Ch8 Lighting Measuring light Types of Light Sources Basic Components of a Light Source Three-Point and Four-Point Lighting Tutorial  Photometric light  Sun Positioner 3 Lighting Strategies and Mood  Lighting is an important component of the rendering process  Not only because it may contribute significantly to the overall processing time necessary to render the scene  But mostly because it reveals the 3-D world and sets the mood of the scene.  Much of the mood in any computergenerated scene is also established with the choice of lights and their arrangement.  Fig 8.1.3 4 Fig 8.1.3 5 Measuring light  f/stop is a unit to measure how much light passes through the aperture of a lens.  The aperture stop of a photographic lens can be adjusted to control the amount of light reaching the film or image sensor.  The scale of f/stops represents how traditional film reacts to light  Fig 8.1.1 f/1.4 6 Measuring light  There are a couple of additional units that are useful to measure the intensity of light—the candela and the footcandle.  The candela (cd) represents the amount of light emitted by a certain type of light, and it is a development of the standard candle, an older unit based on the amount of light created by a candle.  The footcandle (fc), and its metric system equivalent, the metercandle or lux, measures the amount of light that falls on a surface (one footcandle equals 10.764 lux).  http://help.autodesk.com/view/3DSMAX/2016/ ENU/?guid=GUID-96E37398-613E-495A-A80B9C5D398982F9 7 fc (Lumen / foot2) = 10.76 * fc http://lighttalk.via-verlag.com/wp-content/uploads/2012/11/LL3-11.jpg 8 White light vs Colored Light  Most of us assume, incorrectly, that all natural light is white.  But light, in fact, is rarely white. Light is usually tinted.  We can achieve startling lighting effects by using colored lights.  Fig 8.1.4 9 Types of Light Sources  There are several basic types of computer-generated light sources depending on the way they irradiate light.  Simulated light sources generally include point lights, spotlights, linear lights, area lights, infinite lights, and ambient lights.  Most rendering programs automatically create one or several default lights in the 3-D scene.  Fig 8.2.1 10 Types of Light Sources 1. Point Light  A point light casts light evenly in all directions  also called an omnidirectional light. 2. Spot light  Spotlights cast light in a cone shape and only in one specific direction.  Spotlights have some unique characteristics: a variable-angle cone of light, and a light fall-off factor (Fig 8.3.5)  Fig 8.2.2 11 12 Types of Light Sources 3. Infinite Light  Infinite lights are so far from the elements in the scene that their light rays reach the scene parallel to each other.  Infinite lights are also called directional lights, and they behave like stars in the sky.  Fig 8.2.3, 8.5.1 13 14 Types of Light Sources 4. Area Light  Some programs provide area lights in the form of multiple lights grouped together, or a single large area of light (Fig 8.5.3) 15 Types of Light Sources 5. Ambient Light  The light radiated by the ambient light source is distributed evenly throughout the entire scene.  Even though an ambient light source can be placed in a specific XYZ position in 3-D space, it is best to think of an ambient light as coming from all directions (Fig 8.2.4)  The ambient light source often determines the general level of illumination, or shade, of a scene and almost always there is only one ambient light source per scene. 16 17 Types of Light Sources 6. Linear Light  The light of the fluorescent tubes used to light so many public spaces can be simulated with linear lights. (Fig 8.2.5)  Linear lights have length but no width, and they can also be scaled to any size. 18 Basic Components of a Light Source  The main elements of all simulated light sources include position, color and intensity, decay and fall-off, glow, and shadows (Fig 8.3.1)  In addition, spotlights are also defined by their orientation and cone angle.  Lighting software makes it possible to edit each of the individual components of a light source separately.  A few light attributes can also be saved in a file, called a light shader. 19 Basic Components of a Light Source 1. Position and Orientation  Both the position and orientation of a light source can be controlled with the standard navigation or geometric transformation tools (translations and rotations)  In the wireframe display mode, light sources are usually represented with a variety of graphic symbols Viewport representation of a Target light with uniform spherical distribution. Viewport representation of a Target light with spotlight distribution. 20 Basic Components of a Light Source 2. Color and Intensity  Simulated light can have virtually any color.  In most rendering programs, the color of lights is usually specified using a light-based or additive color model e.g. the RGB (Red, Green, Blue) model and the HSB (Hue, Saturation, Brightness) model  Fig 8.3.2 21 Basic Components of a Light Source 3. Decay and Fall-Off  The decay value of light controls the force of a light source and, as a result, how far from the light source the light travels.  A weak light decays rapidly, while a strong light decays slowly and travels far.  In the real world, the decay of light is always linked to the intensity of the light source that created the light, but in computer simulated lighting decay it is often independent of the intensity parameter.  The light created from spot lights decays as it moves away from the light source, but also as it moves from the center of the beam cone toward the edges. This type of decay is sometimes called fall-off.  Fig 8.3.5 22 Basic Components of a Light Source 4. Beam Angle  The beam angle feature of lights is a unique characteristic of spotlights.  The cone angle of a spotlight defines the diameter of the beam of light and also the surface area covered by the light.  This parameter controls the spread of the light beam  Fig 8.3.5 23 Basic Components of a Light Source 5. Glow and Cone of Light  The glow of a light is a circle of light that forms around the light source because the light is refracted and reflected by particles in the environment—generally ice, dust, or smoke. (Fig 14.1.4)  The glow of a spotlight occurs in the form of a cone of light. (Fig 8.3.6)  Circular and conical light glows are often called volumetric lights, and they are both defined by the decay of the light source. 24 25 Basic Components of a Light Source 6. Global and Local Lights  Global light sources shine on all objects in the scene that are directly exposed to the light sources.  The light sources in a scene are global by default.  A different situation occurs with local light sources, also called linked or selective light sources.  A local light source sheds its light on the objects linked to it, and this link can be exclusive or inclusive.  An exclusive link between the light source and the objects limits the light projected by a local light source to fall only on the objects linked to it.  An inclusive link allows a local light source to always illuminate the objects linked to it as well as other objects in the scene that may be directly exposed to it. 26 Basic Components of a Light Source 7. Shadows  In principle, all light sources cast shadows.  But computer-generated shadow-casting is a feature of lights that can be turned on or off.  The final visual appearance of shadows is determined not only by the attributes of the shadow but also by the attributes of the shadow-casting object and the rendering method employed.  Shadows can be defined by several parameters, including color of the shadow, color of the penumbra, and softness of the shadow edge  The portion of a shadow that blocks direct light altogether is called umbra. It is the inner part of the shadow.  The area in the edges of the shadow that blends with other lights in the environment is called penumbra. 27 Three-Point and Four-Point Lighting  Lighting subjects in traditional portrait photography is commonly done with 3 or 4 lights.  Three-point lighting always includes a key and a fill light, and a rim light or a kick light depending on style, preference, and desired effect.  Four-point lighting include the three lights just mentioned plus a background light.  The dominant lights in both setups are the key and the fill lights, and there are multiple stylistic approaches on how to balance the lighting ratio between the two (Fig 6.1.2) 28 Three-Point and Four-Point Lighting 1. Key Lights  The key light is the dominant light on the subject or point of interest and it is also the one that sets the overall mood in a scene.  Just a single key is required when lighting a still subject, but several key lights may be needed in a shot with a moving subject or a shot with multiple subjects moving throughout the scene.  Key lights are usually positioned above the subject and at an angle, and they delineate and model the shape of the subject (Fig 8.6.6)  Shadows projected by the key lights can be softened by the fill lights. 29 Three-Point and Four-Point Lighting 2. Fill Lights  The fill light is also known as an ambient light, and its main purpose is to soften the key light.  A fill is usually positioned at the subject’s face level and on the opposite side of the subject as the key. 30 Three-Point and Four-Point Lighting 3. Kick Light and Rim Light  Both the kick and rim lights are used to accentuate and define the shape and volume of the subject or an object.  The kick light (kicker) is usually positioned to the side of the subject and above. It helps to separate the subject from the background by adding a small amount of sharp light to the front or the side of the subject.  A rim light, also called a back light, is used to sharpen the silhouette of the subject by creating an outer edge of light around some of it (Fig 4.5.6)