Global illumination model -polygon rendering
This illumination model adds to the local model the light which is reflected from the other surfaces to the current surface. This model is more comprehensive, more physically correct and generates more realistic images. This is also more computationally expensive. In a Global Illumination Model the reflection of light from a surface is modeled as in the local model along with the addition of light incident on the surface after multiple reflections among other surfaces. Though the model is computationally additionally intensive than a local model although attainment of realism via this model is fairly possible. The two main types of graphics systems which use global illumination models are Radiosity and also Ray tracing. Radiosity and Ray tracing there the dissimilarity in the simulation is the starting point: Ray tracing obeys all rays from the eye of the viewer back to the light sources. Radiosity reproduces the diffuse propagation of light beginning at the light sources. They generate extremely realistic images although are extremely computationally intensive than scan-line rendering systems that use local illumination model.