Lighting a 3D Scene Guilford County Sci Vis V part 1

Lights and Shadows in a 3D scene  Most 3D programs have some type of default lighting that can be changed to create a more realistic appearance of objects in a scene.  The standard or default lighting does not represent real world lighting, but it is simple and fast.  Numerous controls exist to modify the default settings and produce realistic images.

Four Elements of Computer Graphics ** Where in the scene the light is located (usually specified by X, Y, Z coordinates.  * Intensity of the light or how bright it is  * Color (commonly specified using RGB values)  * Angle of incidence specifies that the more a surface is angled away from a light, the darker it appears. When the angle is 90˚ to the surface, the surface is lighter.

Point Lights  Also known as Omni Lights  Shines light in all directions (much like the sun).  Good for acting as a light from a light bulb or a candle.

Spot Lights  Throw Light in a certain direction from a single point in space.  Good for headlights or spot lights on a stage.

Spot Lights  Spotlights produce a circular pattern of light known as the hotspot  The Hotspot grows elliptical in shape as the angle of the light’s centerline decreases. Hotspot Falloff

Spot Lights  The intensity of the light fades with an increase in its distance from the centerline of the cone to its edge. This fading is known as drop-off.  The width or spread of the cone can be controlled in most programs

Ambient Lights  Simulates the overall light in the world around you.  Ambient light does not come from any one point or shine in any one direction.  Good for filling the scene with overall light.  Does not cast shadows. All objects are light evenly in the scene.

Infinite or Directional Lights  Simulates the Sun by producing light rays that are parallel to each other.  All objects in the scene receive the same amount of light.  Not very effective with indoor lighting with shadows turned on.

Directional Lights

Light Icons  Lights do not have size or shape.  Only see their effects in a rendered scene.

Colored Light  *Colored lights can be used to create special effects.  *Colored lights typically are not used as general lighting within a scene, but can be used to emphasis time.  For example, use a yellow cast in a late afternoon scene, a pinkish tint to represent mornings, and white to represent noon. Longer shadows occur in the afternoon. Morning light is softer. Mid- afternoon light is hard and sharp.

Using Light to Convey Time  The color and angle of a light place a scene in time and space. For morning or evening scenes, make the sun a warm color such as yellow, orange, or red. Then place the light source at a low angle

Colored Light (cont’d)  Colored lights can be used to emphasis mood. For examples, red, orange, and yellow imply passion or anger, green implies peacefulness, and blue implies sadness or depression. Color is a visual indicator of temperature. For example, use red to represent warmth and blues to represent coolness.

Color (cont’d)  Objects in the real world derive their color, in part, from the reflections of objects around them. In computer graphics, color is pure. Blue light shining on a yellow object will cause the object to turn green. Before starting your lighting, write down how you want the scene to look when it is finished. The more lights you use, the longer the render times and the more RAM you will need.

Classic lighting  Classic lighting in 3D needs three types of lights. Key Light Fill Light Back Light

Classic Lighting Layout (3 Lights)  Remove all default lighting from the scene, the scene is now black  Key Light -The primary light source in the scene.  It is usually placed off to the side of the main feature in the scene.  It is the strongest, brightest light.  Typically it is the only light in the scene set to cast shadows.  Local lights and spotlights are often used as key lights.

The Fill Light  The real world contains a certain amount of ambient light that is always present.   In the computer scene the only light that appears is that which is inserted.  The fill light is usually 25% – 50% the strength of the key light and is used to add enough light to soften the light provided by the key and to reduce or eliminate unwanted shadows.  Place the fill light opposite the key.

Adding the Key Light  Create a spot as the Key.  In the top view, offset the Key Light degrees to the side  From a side view, raise the Key Light above the camera, so that it hits your subject from about degrees

Adding the Key Light

 Side view: The Key light is generally placed at a 45 degree angle from the subject.The angle of the Key light is determined by what kind of mood the scene needs.

 Top view: The Key light is placed next to the camera. Generally, place the Key Light at an approximately degree angle to the subject Adding the Key Light

Key Light Only in a Scene

Add The Fill Light  From the top view, a Fill Light should come from a generally opposite angle than the Key - if the Key is on the left, the Fill should be on the right - but don't make all of the lighting 100% symmetrical!  The Fill can be raised to the subject's height, but should be lower than the Key.

Add The Fill Light

 Top View: Place the Fill Light at a 90 degree angle from the Key Light

Add The Fill Light  Front View: The Fill Light is generally placed slightly higher or lower then the Key Light. Here it is on the same elevation as the Key Light

Add The Fill Light

Back Light  The Back Light (also called Rim Light) creates a "defining edge" to help visually separate the subject from the background.  Adds depth to the scene by separating the objects from the background, giving them more of a defined shape.  As the name implies the light is placed behind the objects in the scene and is about 50% – 100% the intensity of the key.

Add Back Light.  From the top view, add a spot light, and position it behind the subject, opposite from the camera.  From the right view, position the Back Light above the subject

Add Back Light.  A Back Light is not a background light - it creates a rim of light around the top or side of the subject No Back Light (left), Back Light added (right).

Add Back Light  Side View: The Back Light is pointed at a sharp angle towards the subject. Be careful here, If the light is placed too low or if the angle is set too close to 90 degrees the light will spill over onto the face or frontal areas of the subject.

Add Back Light  Top View: The Back Light is placed directly opposite the camera and behind the subject

Add Back Light

The Lighting Setup

High Key Lighting  High key lighting places the key light in front of and above the items in the scene to create interior, daylight scene.  A 50% intensity fill light is placed in front of the items and off to the side.  Place the back light at ground level at 1.5 times the key.  Cooler white lights placed at a high angle suggest the sun shining at midday. To make a midday scene more interesting, add clouds to the sky and project shadows from them  Fill lights above the ground should be blue or gray to match the sky. Fill lights below the ground should be green or brown to match the earth

Using Light for Midday

Low Key Lighting Low key lighting is a key light placed lower in the scene than in the High Key setup. The key is often placed to the side. Low key settings are used for nighttime scenes.  For night scenes, use a cool blue-white tint to suggest the light of the moon and stars.  If there is fog, streetlights create warm, hazy cones of illumination.

Using Light for Night

Frontal Lighting  Frontal lighting does what the name implies;  it places the key in front of the scene, but it also places the key high above the scene to produce an effect similar to an overhead light would produce.

Side Lighting  Side lighting places the key light at eye level and in front of the scene to produce light that simulates sunlight.

Attenuation  Attenuation simulates the diminishing (fading) of a light’s intensity over a distance.  Most computer graphics programs do not include attenuation as a default; it must be set if you want your scene to emulate natural lighting.

Attenuation (cont’d)  Decay measures the amount of fade or lessening of intensity.  Falloff describes how the light energy is dispersed. Squared falloff most closely simulates light in the real world.  Objects close to a light source appear brighter; the farther they are away from the source, the darker they should appear.

Shadows  Shadows play an important role in lighting.  Shadows add depth and realism to a scene.  The angle of your light source determines the length and size of the shadows.