The diamond will be lit using the indirect light of Global Illumination and Final Gather. Before entering into the caustics, the overall lighting of the scene can be improved. Also, since raytracing is in effect, the shadow is replaced with a raytraced shadow. Light needs to enter and exit the diamond, so refractions happen twice. It's black! This is because in the Render Global Settings, Raytracing is turned on, but Refractions are set to 1. An initial render produces the following result. As the diamond is sitting in air, the Col_out and Ior_out are left at their default value for air. The IoR is simply looked up in an IoR index. It can be adjusted latter if we want add a little color to the diamond. The Phong Coefficient will take care of how sharp or blurry the light rays will appear on a surface: higher values produce sharp highlights and lower values glossy, or more blurry highlights.Ĭol is left at the default Value of 0.98. It is used to generate fake highlights of an area light source. To use the dielectric material the model normals must be oriented correctly unless the ignore_normals parameter is set to true. For a dielectric-dielectric interface the normals point into a dielectric material which is outside. For a dielectric-air interface the normals point into the air. The dielectric material will use the normals of the surface to distinguish the medium on either side of the interface. Whether a ray of light is entering or exiting an object can be determined by the direction of the object's normals. If your object is well model, Ignore_normals can be left off. If the glass object were immersed in water, the Ior_out would be changed to 1.33. For example, a glass object would have an Ior of 1.5 and an Ior_out of 1.0 because air is on the outside of the glass. When two dielectric materials are adjacent to each other then the Col_out and Ior_out are used to specify the respective values of the outside dielectric material. The Col and Ior attributes control how the light is behaving at either end of the object. Water has an IoR of 1.333 (4/3), Glass an IoR of 1.5 to 1.7, and Diamond an IoR of 2.419. IoR affectively controls the density of the medium. As light enters a medium denser than air, it bends. Ior is Index of Refraction of the dielectric material. This is where Beers law is used and affects how much light can pass through the medium. Thus 0.9 means that 10% of the light is absorbed per unit length of the material." (Maya Help manual). Col is more than just the color of the material, it also controls ".the fraction of light which is left after traversing one unit of material. There are six attributes to control the dielectric material: Col, Ior, Col_out, Ior_out, Ignore_normals and Phong_coef. So light that has entered our diamond will be less bright as it exists. Beers law states that light is absorbed exponentially as it travels through a material. Fresnel reflection controls the amount of specularity of a surface according to the camera angle: the more perpendicular the surface is to the camera the more reflective the surface becomes. Unlike a material with a high transparency setting, it also uses Fresnel reflection and Beers law of light absorption. The word dielectric refers to any material that is a poor conductor of electricity. I started by applying a dielectric material to the diamond.Ī dielectric material accurately simulates transparent objects such as glass, water and diamond. The results are convincing - it looks like a diamond - but can be improved. The diamond uses a Phong material for hard specular highlights and is set to be mostly transparent. It is lit by a high backlight casting a Depth Map Shadow onto the floor. To better appreciate the Caustics effect, the diamond is first set-up and rendered using a standard light and transparent material using Mental Ray. The diamond was modeled separately from a gem cutter diagram and then imported into a scene resembling a photographic studio - the virtual set. And just to add that touch of realism which indirect illumination creates, Global Illumination and Final Gather also need to be used. Also, to more accurately re-create the physical behavior of light in the diamond requires the use of a dielectric material. To achieve all this requires the use of Caustics to handle this refraction of light as it passes through a diamond and onto its supporting surface. Light doesn't just bounce off an object it enters it, bends, changes color, bounces back and looses intensity. Rendering a diamond as photo-realistically as possible is a 3D challenge.
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