Radial distortion and reflection model

Radial distortion: the point coordinates of an image are close to and far from the image center in proportion to the radial distance, which is called barrel distortion near the image center and pillow distortion far from the image center. The reason for radial distortion is that it is difficult to ensure the uniformity of optical lens thickness in the manufacturing process. The farther away from the lens center, the greater the bending of light, resulting in radial distortion.

Reflection model: Bidirectional reflection distribution function (BRDF) is a four-dimensional function, which describes the proportion of light with a certain wavelength reflected along the incident direction and the outgoing direction. Common models can be divided into diffuse reflection model and specular reflection model.

Diffuse reflection: Diffuse reflection scatters light evenly in all directions, and the reflection ratio of each component wavelength is independent of the incident direction. However, the amount of light depends on the angle between the direction of incident light and the surface normal. Because the exposure area will increase with the inclination of the surface under a given amount of light, when the normal of the surface points away from the light, it will be completely in the shadow.

Specular reflection: Also called specular reflection, it strongly depends on the direction of the outgoing light.

Complementary color rendering: Also called Feng rendering, it is the synthesis of ambient light, diffuse reflection and specular reflection. This view points out that the light reflected from the surface of objects comes not only from point light sources, but also from ambient light, that is, mutual reflection between objects and global illumination from distant light sources, that is, ambient illumination.

Dispersive reflection model: a simplification of von model, which assumes that there is no ambient light, that is, a single point light source.

Global illumination: In reality, the light emitted by the light source may be reflected many times and blocked by blocking objects before reaching the camera. In order to solve this influence, the methods of ray tracing and radiance are proposed. Ray tracing is mainly applied to highlight the scene subject, and diffuse reflection is applied to the scene subject with uniform reflectivity.