The reflection of light from most materials consists of two major terms: the specular and the diffuse. Specular reflection may be modeled from first principles by considering a rough surface consisting of perfect reflectors, or micro-facets. Diffuse reflection is generally considered to result from multiple scattering either from a rough surface or from within a layer near the surface. Accounting for diffuse reflection by Lambert's Cosine Law, as is universally done in computer graphics, is not a physical theory based on first principles. This paper presents

Much work has been done to employ machine vision technology to sense weeds in crop fields. However, the use of machine vision weed-sensing with real-time objectives under variable outdoor lighting conditions is a relatively new area. This paper documents an effort to develop real-time weed sensing technologies using machine vision under variable lighting conditions. Images were acquired of weeds between rows of soybeans. Unsupervised learning by cluster analysis was used to classify pixels according to their color. This classified data was then used to train a Bayes classifier which was used to create a look-up table for real-time segmentation. Adaptive scanning with embedded segmentation was used to estimate weed population. These estimates were compared with manual weeds counts. The elapsed time to do this processing was measured to see if the real-time requirements were met.

Physically-based rendering methods represent the core of current realistic image synthesis frameworks. These methods, through a plausible simulation of the processes of light propagation and interaction with objects, have contributed considerably to the improvement of photorealistic rendering. The state of art research in this area includes the simulation of natural phenomena and the incorporation of biological aspects affecting light propagation in natural environments. The search for more efficient rendering solutions is also of major interest for the rendering community. In this dissertation biologically and physically-based models for light interaction with plant leaves are presented. Moreover, since the light that reach a plant leaf may be propagated directly from a light source or indirectly, due to multiple interactions with other objects in the environment, global illumination issues are also addressed, more specifically related to the radiosity method. This method is commonly...

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 1 Introduction 11 2 Selected Topics on Physically-Based Rendering 15 2.1 Optics Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 2.2 Radiometric Terms and Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 2.3 Absorption in a Homogeneous Medium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 2.4 Rendering Equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 2.5 Monte Carlo Techniques for Directional Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 2.5.1 Importance Sampling and Warping Transformations . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 2.5.2 Probability Density Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...