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Creating Light

Creating photo-realistic computer generated imagery.

Charlie G

on 21 April 2010

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Transcript of Creating Light

Shading Rendering Flat shading is the simplest of all the shading algorithms and is therefore the fastest. It simply calculates the sum of the distances from the polygon to any light sources and draws the colour of the polygon accordingly. This method is the least realistic, and sees very little use in photorealistic rendering.

Non-biased rendering algorithms perfectly adhere to the rendering equation. For example, if the algorithm is to run for an infinitely long period of time (and calculate an infinite number of bounces for any ray of light) the result would perfectly satisfy the rendering equation. (Shirley, Wang, 2008) Therefore, these renderers are perfectly accurate and will produce photorealistic results under all conditions and include effects such as caustics, global illumination, colour bleeding, and etcetera. The only drawback is that the solution will take a very long time to compute, even on the world’s most powerful computers (typically, the algorithm runs until further iterations do not change the rendered image). However, recent unbiased approaches have drastically reduced rendering times and have made the concept much more accessible. (Veach, Guibas, 1997) Biased renderers are more commonly used in today’s 3D programs because of their speed. Biased renderers also attempt to solve the rendering equation, but will never produce the actual result, even if the algorithm runs for an infinite number of iterations. This is because biased renderers try to emulate the result of the rendering equation rather than solve it. For example, caustics are simulated by a “photon map” of the scene (Jensen, 1999), which varies in density across the scene according to scene complexity, while caustics would be produced by a uniform spread of light rays in an unbiased renderer. The results produced by a biased renderer under the direction of a skilled artist would be indistinguishable from the result of an unbiased renderer. (Autodesk, 2007) The Lambert shading algorithm was one of the earliest known methods of smoothing. The main concept behind Lambert shaders is that all perfectly matte surfaces emit light at equal intensity in all directions and that intensity is independent of viewing angle. Therefore, the apparent intensity can be calculated using Lambert’s Cosine Law, which states the apparent intensity equals the intensity when illuminated at a perfectly perpendicular angle multiplied by the cosine of the angle to the light source. (Lambert, 1760) However, the main drawback is that this shader only applies to perfect Lambertian radiators, which do not actually exist in real life. Nonetheless, this concept has been the core of many modern physically-based shaders. The Oren-Nayar shader is one example of a shader based on the Lambert model. The most visible improvement is the addition of a roughness coefficient. The roughness coefficient affects the influence of Lambert’s cosine law at very high angles, creating a much more natural and plausible effect. (Oren, Nayar, 1994)

The Phong algorithm is another improvement over the Lambertian model, which adds a diffuse value and a specular value to the calculation light intensity. This allows the shading of reflective surfaces such as hardwood and ceramic. (Phong, 1975)
The most recent and most widely used model to date is the Blinn model, which is actually based on the Phong shader. It is a slight variation which allows for more accurate and customizable specular highlights (Blinn, 1977).

Another very important type of shader is the reflection/refraction shader. As its name suggests, these shaders accurately represent materials which reflect or refract light. These shaders all take Fresnel reflection into consideration and calculated reflection and refraction based on Snell’s Law. Modeling Creating Light Gouraud shading is a natural extension of the flat shading method. Instead of using polygons to calculate brightness, it uses the vertexes, and linearly interpolates the gradients across polygons using the intensities of its vertexes. This produces a much smoother effect, but requires a very dense model to achieve any realism. (Gouraud, 1971) The most common modeling approach is polygonal modeling. For example, the artist would first create a cylinder to make a wheel. To morph the cylinder into a wheel, the artist would edit the vertices, edges, and faces of the model by translation, rotation, and scaling. NURBs (Non-uniform rational B-spline) modeling creates complex, organic models using simple lines and points. The modeling program interpolates the model to an infinite resolution, unlike traditional vertex modeling. This makes it ideal for creating exact, smooth surfaces such as car bodies or boat hulls. A recent entry into the field of 3D modeling is the sculpting technique. This approach simulates the sculpting of clay or other soft materials by allowing the artist to push, pull and manipulate the surface of 3D models. Although this technology is present in many 3D modeling suites, its most notable application is ZBrush, which very closely mimics the feel of sculpting in real life. Another way of creating 3D models is by scanning 3D objects using a 3D scanner. This method usually produces very accurate models, but requires very expensive equipment. Other means of acquiring 3D models have been explored, such as using stereoscopic camera setups and webcams. However, these approaches are not nearly accurate or robust enough to be used commercially. ...is the process of creating a 3D model in a virtual environment. ... is the process of declaring how a virtual 3D object is to be represented visually. ... is the process of converting a virtual 3D environment into an image. THE PROCESS THE APPLICATIONS http://www.mentalimages.com/fileadmin/user_upload/gallery/esterno_01_sm.jpg http://www.mentalimages.com/fileadmin/user_upload/gallery/archimation_NatoHQ_03_Aerial_sm.jpg http://www.mentalimages.com/fileadmin/user_upload/gallery/019CLS_04.jpg http://media.artstorm.net/content/2008/08/male-head-zbrush-steps.jpg http://www.pixologic.com/zbrush/gallery/375254 http://upload.wikimedia.org/wikipedia/commons/c/ce/LaserPrinciple.png http://upload.wikimedia.org/wikipedia/commons/e/ea/NURBS_3-D_surface.gif http://www.maxwellrender.com/gallery/index.php?album=technical&image=018.jpg&p=*full-image http://www.maxwellrender.com/gallery/index.php?album=architecture&image=001.jpg&p=*full-image http://familyrights.us/how_to/balance_scale.gif The architectural industry would not be what it is today if not for modern 3D visualization technologies. Practical applications of Snell’s Law translate into photorealistic reflections in the windows of skyscrapers and applications of Lambert’s reflectance model are unilaterally used for creating concrete walls and cloth curtains. In fact, there are several software packages specifically aimed at the architecture industry, with pre-installed libraries containing pre-designed doors, windows, and all other basic elements of building design. Almost every mass-produced consumer product sold today has, at some point, used the modeling, shading, and rendering techniques stated above. In fact, in most cases, the 3D software is not just used to create photorealistic images of the product, but rather better-than-photorealistic images. Specular maps can be used to finely control how the glossy display on a Mac reflects the light, and complex NURBs can be used to model the ergonomic curves of an Xbox controller. The control and flexibility which 3D design suites allow the artist far surpasses traditional prototyping techniques. The entertainment industry has perhaps seen the most use of photorealistic rendering technology. The ability to virtually create any setting, character, or special effect has lifted almost all restrictions on the creative process. In fact, many productions now favour producing imagery which is purposely unreal, such as the popular animated film, UP, which purposefully caricaturizes characters’ main features, to create a stronger emotional attachment. An excellent example of the practical applications of this technology is cinema. Photorealistic virtual imagery has been an indispensible tool in the film industry for several decades. Nowadays, it is nearly impossible to differentiate what is shot with a camera and what is virtually rendered. This has increased society’s awareness of everything from how a microscopic blood cell carries oxygen to how a galaxy is formed. The simple concepts of Lambert’s Law and Snell’s Law has allowed more and more people to understand what would have been regarded as science as advanced as quantum physics. However, this is just the tip of the iceberg. Photorealistic imagery has become even more real through the use of 3D viewing technology. It is now common for films to be shot in 3D, and viewed thorough specialized equipment. This was the logical next step after motion pictures, and computer-generated photorealistic imagery is what allowed society to take that step. This is the pinnacle of the advancement of human technology for the masses, and a sign of what is to come. The next logical step is augmented reality. This adds an element of interaction, which is essential in establishing the vital connection between the medium and the audience. This “gimmick” keeps the audience interested while delivering the intended content. The final frontier is complete virtual reality. This technology is truly in its infancy, but early prototypes have already made its potential clear. This technology will eventually allow society to take the next step in its evolution by allowing humans to exist in a world which they themselves can fully control. http://corthodoxy.files.wordpress.com/2010/01/avatar-floating-mountains.jpg http://cdn1.slashgear.com/wp-content/uploads/2009/02/psp2_concept_render-480x327.jpg http://weblogs.wgntv.com/news/wgn-news-blog/pixar%20up%20balloons.jpg http://thefutureofthings.com/upload/items_icons/VirtuSphere_large.jpg
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