Importance of light source in machine vision
Highlight measurement features and simplify image processing algorithms; overcome interference from ambient light and improve image signal-to-noise ratio; improve the accuracy and efficiency of the visual system.

The law of rectilinear propagation of light
Three lines are coplanar: incident light, normal line, and reflected light;
Two lines are separated: angle of incidence = angle of reflection; ‍‍‍The light path is reversible.

Specular reflection and diffuse reflection
Specular reflection: smooth surface, bright, related to angle, does not reflect color;
Diffuse reflection: rough surface, darker, not related to angle, reflects color.

Refraction of light
When light is incident obliquely from one transparent medium to another transparent medium, the propagation direction generally changes. This phenomenon is called refraction of light;
The refraction of light, like the reflection of light, occurs at the junction of two media, but the reflected light returns to the original medium, while the refracted light enters another medium.

The penetrability of light and the change of wavelength
Short wavelength: weak penetrating ability, strong scattering ability, high refractive index;
Long wavelength: strong penetrating ability, weak scattering ability, low refractive index.

Polarization characteristics of light
The polarizer is installed on the lens, and the polarizer is installed on the light source. The combination of the two can eliminate reflections or meet some special detection requirements;
Polarized light principle: In the polarized light phenomenon, mirror reflection will not change the polarization direction of light, but diffuse reflection will change the polarization direction of light.

Chromatography of light
Why we can see different colors: The colors we see are actually the corresponding colors of light reflected by the white light source after it hits the object;
Three primary colors: red, green, and blue;
Complementary colors: colors that are opposite to each other in the color wheel. Objects absorb light of wavelengths that are complementary to their colors.