Texture Gradient
Texture gradient is the so-called impressionism effect. It is the perception of depth based on the merging of small details as they are repeated on both the foreground and the background. The repetition of the pattern as it approaches the horizon is perceived as receding into the background. This concept is very easy to visualize if you think of a field of grain or grass that extends to the horizon. Texture gradient cues are also related to another monocular depth cue, the spatial summation cue...
Lightwave 56 or higher 1
Load the Sunlight.lws scene. Since moonlight is reflected light, we might as well start with the sunlight scene and add a few modifications. Rename Light to Moonlit and close the panel. Change the light color to This is to make it yellowish instead of pure white. Reduce the Light Intensity to 60 , Render the scene. Note the low-contrast quality of the scene and the predominance of a single hue, which is okay since it represents night. However, the flatness of the scene is not desirable Figure...
Film
Knowing about the roots of photography and understanding film and light interaction will make 3D CGI lighting easier for you, since silver gelatin-based photography is the reference point for all CGI today. Digital works are being manipulated to mimic the look of film and to blend in with the plate or live action. To understand photography, we must first grasp the concepts behind film. As discussed in Chapter 1, light is an electromagnetic vibration of which we see only a narrow portion, called...
Shiny Nonmetal Reflectors
We are all fascinated by glossy and reflective surfaces because of the movement of the reflected environment on their surfaces. Because such objects reflect their surroundings, it is not always easy to light glossy or shiny objects. Reflective objects are hard to light so that their own form and shape will be seen. This is especially tricky with light or dark back- Reflective objects are not forgiving when it comes to improper lighting, which hides them, not emphasizes them. Reflective surfaces...
Specular vs Diffuse
Real-world material properties can be broken down into two parts the specular components and the diffuse components. What this means is that the materials that we see are nothing but a balance between the specular highlight component with the diffuse reflection. Neglecting light absorption, there is always a tug of war between specular and diffuse reflection due to the finite amount of light falling on an object. If the object reflects 80 percent of the incident light as specular, 20 percent is...
The Lambertian Shading Model Revisited
As discussed, the energy flow in radiosity is conserved it goes from a hot to a cold state. Since light travels in a vacuum, it is difficult to track the light's total pathway, since it would require an enormous amount of computer memory and computation. There are two ways to solve this problem. One is to use probabilistic computations to solve the most likely light pathway in the scene. This is called the Monte Carb solution, named after a gambling mecca in Monaco. This method is similar to...
Solid vs Transmissive
The difference between objects that are solid and objects that are transmissive is quite obvious One allows light to pass through itself and the other blocks it. You cannot mistake one type of object for the other. In CG, however, it is easy to unintentionally create an object that looks transmissive, even though it was intended to be a solid object. The problem lies in the excessive use of the material properties shader's ambient term. When this shading component is abused, not only would the...
Surface Modeling vs Solid Modeling
A polygon mesh is composed of a set of points that form interconnected lines, which in turn form the surface that creates the mesh, Grasping the idea that a polygon has a surface requires understanding the two forms of model representation in 3D graphics. If the polygon's surface is shaded, meaning that the points and lines have been used to make a skin, that does not necessarily mean that the polygon is solid. Even if the object representation looks solid, it is made up of connected surfaces....
Lambertian Shading
Lambertian shading, named after Johann Heinrich Lambert, is the simulation of dull, smeared matte surfaces. It is also called ideal diffuse reflection, or cosine shading. Lambertian shading is the modeling of light falling on a subject incident light that has a constant reflection independent of the viewer's perspective. In other words, Lambertian shading assumes that the incoming light is reflected equally in all directions, without bias. The angle of the incoming light has no effect on the...
The Rods and Cones
There are two types of photosensitive receptor cells in the eye. The first are called the rods. These cells primarily provide contrast perception, which is useful in low-light situations, pattern recognition, and discrimination. Rods are also used for motion detection and analysis as well as night vision. These cells collectively function like an ultrasensitive black-and-white contrast and motion detector. Rods are uniformly distributed in the retina and are the most abundant type of...
Blinn Shading
Blinn shading, named after James Blinn, is the computer graphics application of the Torrance-Sparrow-Cook shading model, named after Kenneth F. Torrance, Ephraim M. Sparrow and Robert L. Cook, based on realistic specular-to-diffuse reflections. The Torrance-Sparrow-Cook, illumination model assumes that the surface of an object is made up of microscopic facets that are specular these facets are capable of self-shadowing. It also accounts for the edge specularity on certain materials when viewed...
The Inverse Square Law
Since light is a part of the electromagnetic spectrum, it is nothing but the emission of energy as it is transferred around and seeks a lower, more stable stage. Maxwell accounted for the existence of heat as nothing but radiation that we cannot see but only feel. Our eyes are not sensitive enough to see the extreme far red called infrared. When you approach a light source, it gets hotter as you get closer and cooler as you increase the distance. You will notice that the rate of its warmth or...
Ray Tracing
Ray tracing is the global illumination technique that uses rays or photons to keep track of the light path in a scene as it is projected on a 2D viewing plane a monitor . Therefore, the backward ray tracing from the eye is view dependent, That is, it computes the visible surfaces only from the perspective of the viewer. It ignores the surfaces that are not visible to the viewer. This is the classic backward ray-tracing technique. Backward ray tracing starts with setting up a 2D viewing plane...
The Index of Refraction
The index of refraction is the number derived when the speed of light in a vacuum is compared with the speed of light in a medium. It is really the ratio of the speed of light c divided by the speed of light in a medium v . This ratio, called the index of refraction, means that the higher the number, the slower the medium. And since light does not travel any faster than the vacuum, the number is always 1.0. In CG ray tracing, the index of refraction is always 1.0, and it never goes below it. If...
The H and D Curve
Film cannot possibly capture all the tones present in a scene, especially if the scene is taking place on a bright, sunny day. Films have a limited ability to capture different light levels. In short, film has a dynamic range. This means there is a limit to the range of brightness film can record, that there is a maximum as well as minimum illumination it can capture. Have you ever overexposed or underexposed a frame of film Most likely, you have done so using a flash or under a bright sun or...
Light Meters and EighteenPercent Gray
In talking to photographers, you often hear the phrase 18 percent gray. This is the kind of gray that a Kodak gray card gives, as well as the tonality you get if you follow the indications on your camera's light meter when you expose a pure white wall. It means that 18 percent of the light striking an object is reflected. Eighteen-percent gray is roughly the tonality you get when you mix equal amounts of white paint and black paint. In short, most light meters, especially light meters built...
Light Behavior
Since light is radiation, it obeys the rules of radiation. Radiation has properties and qualities that are quantifiable and well as predictable. Before discussing the finer points of radiation and its properties, we have to distinguish between thermal radiation and reflected radiation. Thermal radiation is the type of radiation that depends on the temperature of the object emitting it. This means that any radiation given off by an object is generated from that object itself. Sunlight and light...
The Properties of Light
Light as it interacts with matter manifests itself in a great number of ways. Since it travels in both a vacuum as well as most media, its interaction with matter is observable. Its behavior can be categorized in several ways. The observable properties of light show its wave particle duality nature. The following list presents some categories into which we can place light in terms of its behavior See Figures 1.3-1.12 Reflection. Reflection is the throwing or bouncing back of light as it hits a...
Shadow Formation
Light interacts with almost any object. It bends, is reflected, or is transmitted. Most light either passes through objects or is reflected. However, when an object obstructs the light and does not let it pass through partially or totally, it creates a shadow, A shadow is defined as the area in which there is partial or total absence of illumination due to an obstruction between the light source and the area of illumination. As you know, shadows are not uniform in shape, form, or quality....