tailieunhanh - Advanced Maya Texturing and Lighting- P16

Advanced Maya Texturing and Lighting- P16: I should stress that I am self-taught. In 1994, I sat down at a spare seat of Alias PowerAnimator and started hacking away. After several years and various trials by fire, 3D became a livelihood, a love, and an obsession. Along the way, I was fortunate enough to work with many talented artists at Buena Vista Visual Effects and Pacific Data Images. In 2000, I switched from PowerAnimator to Maya and have since logged tens of thousands of hours with the subject of this book | The Quality U and Quality V attributes set the size of a control texture that generates the virtual lights. For each pixel of the control texture one light is created. To make the render feasible the Samples attribute places a cap of the number of lights used. The first Samples field determines the minimum number of lights generated. The second Samples field determines the maximum number of additional lights that are randomly added to make the lighting less regular. Ultimately the Light Shader creates diffuse lighting and shadows see Figure . Since the Light Shader does not require raytracing Global Illumination or Final Gather to function it renders efficiently and quickly. However if the Quality U and Quality V attributes are raised to high values the Light Shader render will slow significantly. At the same time if the Quality U and Quality V values are set too low the render will appear grainy. Figure Left The mannequin lit with the IBL Light Shader. Raytracing is used with nonreflective surfaces. This scene is included on the CD as . Right The same scene with reflective surfaces. This scene is included on the CD as . 429 ADDING REALISM WITH HDRI Using Light Probe Images with the Env Ball Texture Light probe angular HDR images are unique in that they are created by photographing a high-reflective sphere. The sphere offers the advantage of capturing a nearly 360-degree view of an environment. The Env Ball environment texture in Maya in fact is designed to support light probe images. To create a light probe HDR image from scratch follow these basic steps 1. Digitally photograph a reflective sphere in a desired location. The example illustrated in Figure employs a 12-inch stainless steel gazing ball that is sold as a lawn ornament. Take multiple photos with different F-stops and or shutter speeds to properly expose all areas of the scene. 430 Figure Top Five exposures created by photographing a reflective .