# 电子工程代写|计算机视觉代写Computer Vision代考|CMSC426

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

Directional illumination or specular illumination denotes a setup in which parallel light or light from a point light source is used to illuminate the object (Fig. 2.20a). This is the most simple type of illumination, as the setup basically consists of a single light source at a certain distance.

For matte (Lambertian) surfaces, directional illumination produces an irradiance, which depends on the angle of incidence of the light upon the surface. Thus, it can be used to determine the inclination of surfaces with respect to the illumination direction. At the edges of objects, directional illumination casts shadows, and does not illuminate occluded parts of objects. If the camera is observing the scene under a different angle, these shadows are visible in the image and might be confused with object borders.

For specular reflecting surfaces, directional illumination is not the appropriate illumination. These surfaces will appear black for all points where the reflection condition is not met and show specular reflexes for the remaining points.

Most surfaces are mixtures of Lambertian surfaces with additional specular reflection. Thus, object surfaces show highlights that might be confused with surface structures or object edges. Furthermore, these regions might be overexposed and do not contain structural information. On the other hand, the position of specular highlights allows determination of the direction of the surface normal in these areas, as the exact reflection condition is fulfilled. This might be important information for 3-D reconstruction of the scene. Figure $2.21$ a shows an example of a plant leaf illuminated with directional illumination. The leaf shows highlights and a shadow is cast at the lower edge.

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

If only the geometrical outline of an opaque flat object is of interest, rear illumination is the common choice of illumination (Fig. 2.20c). Opaque objects appear as black objects without any structure. More interesting features can be obtained using rear illumination for semitransparent objects. For these types of objects, the transmitted radiation exhibits the entire spectrum of bulk-related interaction of radiation with matter, such as refraction, absorption, and scatter. Local inhomogeneities in the absorptivity show up as brightness patterns, integrated over the optical path of the radiation. Prominent examples of such images are $x$-ray images of medical applications. If the absorption is spectrally selective, the spectral content of the transmitted radiation carries additional information on the internal structure of objects.
Rear illumination can be set up with both directional as well as diffuse illumination. Figure $2.21 \mathrm{~b}$ shows an example of a plant leaf illuminated by a diffuser screen behind the leaf. The background and the leaf show a well separated gray value distribution. The edge of the leaf is clearly visible. As the leaf is not totally opaque, it still shows fine structures, related to the more transparent water vessels.

Rear illumination can be considered to be a special case of light field illumination. Here a direct path exists from the light source to the camera, that is, the light source directly illuminates the sensor chip (Fig. 2.20d). As long as no object is present, the image appears bright. Any object in the light path diminishes the image irradiance by refraction, absorption, and scatter of light out of the illumination path. Thus, objects appear dark in front of a bright background. This type of illumination is commonly used to detect whether small objects (particles) are present in the volume between the illumination source and the camera (Section A13).

As opposed to light field illumination, dark field illumination inhibits a direct path between the light source and the camera (Fig. 2.20e). As long as no objects are present in the illumination path, the image appears dark. Objects in the illumination path become visible by scattering, reflecting, or refracting light into the camera. Thus, objects appear bright in front of a dark background. This type of illumination is as well used to detect small particles in the illumination path.

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

myassignments-help数学代考价格说明

1、客户需提供物理代考的网址，相关账户，以及课程名称，Textbook等相关资料~客服会根据作业数量和持续时间给您定价~使收费透明，让您清楚的知道您的钱花在什么地方。

2、数学代写一般每篇报价约为600—1000rmb，费用根据持续时间、周作业量、成绩要求有所浮动(持续时间越长约便宜、周作业量越多约贵、成绩要求越高越贵)，报价后价格觉得合适，可以先付一周的款，我们帮你试做，满意后再继续，遇到Fail全额退款。

3、myassignments-help公司所有MATH作业代写服务支持付半款，全款，周付款，周付款一方面方便大家查阅自己的分数，一方面也方便大家资金周转，注意:每周固定周一时先预付下周的定金，不付定金不予继续做。物理代写一次性付清打9.5折。

Math作业代写、数学代写常见问题

myassignments-help擅长领域包含但不是全部: