tailieunhanh - Capturing light

Radiometry, solid angle, radiometry of thin lenses, from light rays to pixel values, the interaction of light and surfaces,. is the main content of the lecture "Capturing light". Invite you to consult the detailed content lectures to capture details. | Capturing light Source: A. Efros Radiometry What determines the brightness of an image pixel? Light source properties Surface shape and orientation Surface reflectance properties Optics Sensor characteristics Slide by L. Fei-Fei Exposure Radiometry Radiance: energy carried by a ray Power per unit area perpendicular to the direction of travel, per unit solid angle Units: Watts per square meter per steradian (W m-2 sr-1) dω dA Solid Angle By analogy with angle (in radians), the solid angle subtended by a region at a point is the area projected on a unit sphere centered at that point The solid angle dw subtended by a patch of area dA is given by: A dA projected onto surface of the sphere of radius r: dA cos theta Ratio of surface areas of spheres of radii 1 and r: 4 pi / (4 pi r^2) = 1/r^2 dA Radiometry Radiance (L): energy carried by a ray Power per unit area perpendicular to the direction of travel, per unit solid angle Units: Watts per square meter per steradian . | Capturing light Source: A. Efros Radiometry What determines the brightness of an image pixel? Light source properties Surface shape and orientation Surface reflectance properties Optics Sensor characteristics Slide by L. Fei-Fei Exposure Radiometry Radiance: energy carried by a ray Power per unit area perpendicular to the direction of travel, per unit solid angle Units: Watts per square meter per steradian (W m-2 sr-1) dω dA Solid Angle By analogy with angle (in radians), the solid angle subtended by a region at a point is the area projected on a unit sphere centered at that point The solid angle dw subtended by a patch of area dA is given by: A dA projected onto surface of the sphere of radius r: dA cos theta Ratio of surface areas of spheres of radii 1 and r: 4 pi / (4 pi r^2) = 1/r^2 dA Radiometry Radiance (L): energy carried by a ray Power per unit area perpendicular to the direction of travel, per unit solid angle Units: Watts per square meter per steradian (W m-2 sr-1) Irradiance (E): energy arriving at a surface Incident power per unit area not foreshortened Units: W m-2 For a surface receiving radiance L coming in from dw the corresponding irradiance is n θ dω Radiometry of thin lenses L: Radiance emitted from P toward P’ E: Irradiance falling on P’ from the lens What is the relationship between E and L? Forsyth & Ponce, Sec. Radiometry of thin lenses o dA dA’ Area of the lens: The power δP received by the lens from P is The irradiance received at P’ is The radiance emitted from the lens towards dA’ is Solid angle subtended by the lens at P’ Radiometry of thin lenses Image irradiance is linearly related to scene radiance Irradiance is proportional to the area of the lens and inversely proportional to the squared distance between the lens and the image plane The irradiance falls off as the angle between the viewing ray and the optical axis increases Forsyth & Ponce, Sec. Radiometry of thin lenses .

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