# 电子工程代写|计算机视觉代写Computer Vision代考|CS763

## 电子工程代写|计算机视觉代写Computer Vision代考|Bulk-related properties of objects

This section deals with the various processes influencing the propagation of radiation within optical materials. The basic processes are attenuation by absorption or scattering, changes in polarization, and frequency shifts. For active emitters, radiation emitted from partially transparent sources can originate from subsurface volumes, which changès the radiance comparéd to plain surface emission. Thè most important processes for practical applications are attenuation of radiation hy absorption or scattering and luminescence. A more detailed treatment of bulk-related properties can be found in CVA1 [Chapter 3].
Attenuation of radiation. Only a few optical materials have a transmissivity of unity, which allows radiation to penetrate without attenuation. The best example is ideal crystals with homogeneous regular grid structure. Most materials are either opaque or attenuate transmitted radiation to a certain degree. Let $z$ be the direction of propagation along the optical path. Consider the medium being made up from a number of infinitesimal layers of thickness $\mathrm{d} z$ (Fig. 2.17). The fraction of radiance $\mathrm{d} L_{\lambda}=L_{\lambda}(z)-L_{\lambda}(z+\mathrm{d} z)$ removed within the layer will be proportional to both the thickness $\mathrm{d} z$ and the radiance $L_{\lambda}(z)$ incident on the layer at $z$ :
$$\mathrm{d} L_{\lambda}(z)=-\kappa(\lambda, z) L_{\lambda}(z) \mathrm{d} z$$
with the extinction coefficient or attenuation coefficient $\kappa$ of the material (in environmental sciences, $\kappa$ is sometimes referred to as turbidity). The unit of $\kappa$ is a reciprocal length, such as $\mathrm{m}^{-1}$. Solving Eq. (2.49) for $L$ and integrating over $z$ yields:
$$L_{\lambda}(z)=L_{\lambda}(0) \exp \left(-\int_{0}^{z} \kappa\left(\lambda, z^{\prime}\right) \mathrm{d} z^{\prime}\right)$$
If the medium shows homogeneous attenuation, that is, $\kappa(\lambda, z)=\kappa(\lambda)$, Eq. (2.50) reduces to
$$L_{\lambda}(z)=L_{\lambda}(0) \exp (-\kappa(\lambda) z)$$

## 电子工程代写|计算机视觉代写Computer Vision代考|Illumination techniques

In this chapter we turn to the question: How can radiation sources be used to visualize physical properties of objects? In order to set up an appropriate illumination system we have to consider the radiometric properties of the illumination sources, such as spectral characteristics, intensity distribution, radiant efficiency (Section 2.4.3), and luminous efficacy (Section 2.4.3). For practical applications we also have to carefully choose electrical properties, temporal characteristics, and package dimensions of the sources. A detailed overview of illumination sources including the relevant properties can be found in CVA1 [Chapter 6$]$

Single illumination sources alone are not the only way to illuminate a scene. There is a wealth of possibilities to arrange various sources geometrically, and eventually combine them with optical components to form an illumination setup that is suitable for different computer vision applications. In the following section we will show how this can be accomplished for some sample setups (Fig. 2.20). They are, however, only a small fraction of the almost unlimited possibilities to create problem-specific illumination setups. The importance of appropriate illumination setups cannot be overemphasized. In many cases, features of interest can be made visible by a certain geometrical arrangement or spectral characteristics of the illumination, rather than by trying to use expensive computer vision algorithms to solve the same task, sometimes in vain. Good image quality increases the performance and reliability of any computer vision algorithm.

## 电子工程代写|计算机视觉代写Computer Vision代考|Bulk-related properties of objects

$$\mathrm{d} L_{\lambda}(z)=-\kappa(\lambda, z) L_{\lambda}(z) \mathrm{d} z$$

$$L_{\lambda}(z)=L_{\lambda}(0) \exp \left(-\int_{0}^{z} \kappa\left(\lambda, z^{\prime}\right) \mathrm{d} z^{\prime}\right)$$

$$L_{\lambda}(z)=L_{\lambda}(0) \exp (-\kappa(\lambda) z)$$

## 电子工程代写|计算机视觉代写Computer Vision代考|Illumination techniques

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