Global Illumination Model

Comparison of Local and Global Illumination in Illumination Models Illumination models represent a higher level of computer graphics that calculate how light and shadow effects should be calculated and presented in an image. Lighting is crucial for any sort of image not to exist in a vacuum and instead be part of a scene. Light must come from a clear source, create shadows and reflect on the surfaces of the objects in the scene properly, with different kinds of surfaces reacting differently to light as in real life. For example, an opaque surface should absorb some of the light and reflect the rest. If the scene is moving, illumination takes on an even greater importance. This is perhaps one of the greatest challenges in the field due to need

There are two main illumination models in the field of computer graphics: local and global illumination. Both have their unique qualities and advantages. [1] Global illumination is more expensive and more difficult to design for developers compared to local illumination. This appears to work in the favor of local illumination when choosing between the two. However, the main difference between the two models is that in local illumination, every surface is “shaded” – a technical term used to refer to the effect of lighting on surfaces – independently from each other, whereas in global illumination the light that is reflected from the other surfaces also falls on the particular surface. In general, global illumination provides effects that simulate real-world lighting more closely. This means that, overall, global lighting is more detailed, more correct and more realistic, and realism is often of utmost importance in computer graphics. These are all the factors that must be considered when making a choice between the two [2]. Considering all the aspects of the issue, global illumination clearly emerges as the better and superior choice compared to local

Photorealism is one of the goals of current efforts in the field, and achieving this absolutely needs light to be reflected in the scene in a realistic manner. This means that global illumination is the only possible choice. T. Whitted reports that realistic shading – the appearance of shadowed areas in parts of the scene – can only be achieved with the global illumination model [4]. This necessity also extends to faces. Designs of faces are reported to need lighting that simulates real world light as closely as possible in order to pass a series of face recognition tests employed to gauge the level of realism of the images. In other words, in order for a computer–generated image of a face to appear “real”, it must be lit in the scene with the global illumination model, and realistic face design in particular is a major subject in the field of computer graphics today