Photorealism

Photorealism is an artistic style characterized by the highly detailed depiction of ordinary life withthe impersonality of a photograph; creating an accurate representation using traditional artpractices such as painting or using computer visual effects.

Throughout this research project I plan to analyse and document a variety of design techniquesthat aid the development of computer generated images that appear photorealistic to the humaneye.

Evolving from the pop-art and art movements of the 1960's and 70's in east coast America,photorealism has expanded into a variety of different sub-genres such as hyper and superrealism and with the advance of computer technology and media production, photorealism hasbecome a focal area within visual effects.

To understand the advanced techniques used to compose a photorealistic scene a basicunderstanding of colour, light and physical form must be developed as they are the baseattributes when creating a computer generated environment.

Colour is a characteristic of light; the difference between light and other types of radiation isdefined by their wavelength, energy and frequency. Radiation is energy that travels anddissipates as it moves, whether it is x-ray or light waves, together they all form theelectromagnetic spectrum.

The visible section of the spectrum consists of violet, blue, green,yellow, orange and red before encountering infrared that weinterpret as heat. Humans have the ability to see objectssurrounding them by light being emitted from a source, thesewaves are absorbed by the object and the remaining waves arereflected into the viewer's eyes and processed by our brain toconstruct an image, this is a known subtractive colour.It is not practical to digitally reproduce ‘nature's way' of creatingcolours instead we use the additive colour method, a processusing the primary colours of light consisting of red, green and blueand when mixed together they make white, similar to the reverseof a light hitting a prism.

In the 19th century, physicist Lord William Thompson Kelvin discovered the Kelvin scale ofprecise temperature measurement; carbon would emit different colours depending on the heatapplied to it. Based on this research the modern day colour temperature scale was establishedwhich is often used in real world lighting architecture.

Colour temperatures applied to different lights are not the actual physical temperature of thesource but the description of the light's colour when being compared to the heated carbon.The Kelvin Colour Temperature scale is very beneficial to the development of photorealisticimage as it allows digital artists to illuminate a scene with accurate real-world lighting colours andalter the effect with detailed precision.

Light

Light is as essential to computer graphics as it is to reality. We are accustomed to light and theambient properties that help illuminate our environment but it controls many atmosphericconditions with the ability to adjust our mood and alter how we observe world.The exact physical description of the interaction of light with an object is very complicated andphysicists have spent centuries studying the topic. A lot of the real-world physics do not apply ina digital scene but they are still important to understand how light behaves.As computers do not use subtractive lighting, arrays of mathematical equations are used tosubstitute the properties of natural light.

1. Diffuse Lightrepresents the colour of any light that is cast after leaving an illuminated object;this property controls parameters like tint, intensity and texture of the model's surface.

2. Specular Lightrefers to how “shiny” the surface is, often perceived by a white highlight.Specularity in real-world physics explains how reflective a surface is but in computer imageryspecularity only characterises brightness.

3. Reflectivityin the digital scene specifically handles reflection of the surrounding environmentin the object's surface.As well as being one of the major aesthetic considerations, shadows are considered one of themost important technical aspects of lighting. Many people perceive shadows as space for objectsto get lost in, but they provide cues for such attributes as location of the light source, how faraway an object is positioned and an assurance that objects share the same space.There are two main categories when discussing lighting algorithms; direct illumination and globalillumination.

Direct Illuminationis best defined as a scenecomposed of lights and objects. It calculates the lightcast directly onto the objects from the primary lightsource and not the light that bounces off the floor andother surfaces in the scene. If a secondary object ispresent then algorithm will cast shadows, but these willbe solid black shadows as there is no ambient light.Global Illuminationmodels the direct light producedbut also attempts to interpret the indirect light emittedfrom the objects in a scene. It processes this informationfrom the ambient and diffuse light components, addingcolour and depth to shadows by calculating the bouncesof light around the scene from the different light sourcesbut does not affect the intensity of light within the scene.

Physical Form

Around 300 BC, Greek mathematician Euclid studied the relationships between distances andangles documenting the notion of “Euclidean Space” or “Cartesian Space”, the theory thatdefines the geometry occupied by an object via calculating the flatness of its mesh; this is thebasis of polygon modelling and the x, y and z values in found in 3D design applications.In modern day mathematics and computer graphics, this poses some disadvantages. If allobjects are constructed of straight lines then it becomes impossible to precisely represent acurve, meaning a large number of polygons are needed to calculate these shapes in anappealing aesthetic manner, this process in return increases the rendering time and reducesreal-time speed within the engine.

To create a computer generated scene, extremeley powerful software is used known as agraphics engine such as 3D Studio Max, an industry standard software package used in gamesdevelopment, film and television. Within these engines artists and designers have the ability toconstruct detailed scenes and perform advanced calculations with minimal effort.One of the preferred methods of creating objects within a graphics engine is known as polygonmodelling. A polygon is a n-sided shape constructed of vertices, a vertex is a independent coordinatethat defines a three-dimensional point within the evironment. This is a preferred methodas it is faster to implement and render than other techniques, a benefit for real-time computergraphics.

Although there is a lot of mathematics involved with photorealismin computer arts, traditional art practices are still important. Rulessuch as, an average mature human is the equivalent height to 7½ heads and the distance from head to toe is equivalent to thespace between fingertip to fingertip. These ratios are veryimportant when attempting to imitate a real-world subject, ashumans have an extraordinary ability to notice if something isincorrect although unaware of what specific element is absent.