Basic knowledge of machine vision lighting technology:

1) Irradiation mode

Choosing different light sources, controlling and adjusting the direction of incident light on the object is the most basic parameter in the design of machine vision system. It depends on the type of light source and the position relative to the object. Generally speaking, there are two basic ways: direct light and diffuse light. All other ways are extended from these two methods.

Direct light: the incident light basically comes from one direction with a small angle, which can cast the shadow of the object;

Diffuse light: incident light comes from multiple directions, even all directions. It will not cast obvious shadows

2) Reflection mode

Light reflected by objects has two different reflection characteristics: direct reflection and diffuse reflection

Direct reflection: the reflection angle of light is equal to the incident angle. Direct reflection is sometimes very useful, and sometimes it may produce very strong glare. In most cases, specular reflection should be avoided.

Diffuse backscattering: light falling on an object diffuses from all directions. In most practical cases, diffuse light is formed in a certain angle range, which depends on the angle of incident light.

3) Color

A large part of the electromagnetic spectrum in the spectrum is visible to the human eye. The electromagnetic radiation in this wavelength range is called visible light, ranging from 400nm to 760nm (some people can observe 380nm-780nm), that is, from 380nm purple to 780nm red.

Color ring is to sort the colors in the visible light spectrum to form red connected to purple at the other end. The application of machine vision to color ring usually includes six different colors, which are divided into two categories: warm color and cold color. The warm color is composed of red tone, and the cold color comes from blue tone. Usually, the light with opposite color temperature is used to illuminate the image, which can achieve the highest level of contrast. The light with the same color temperature can be effectively filtered, Therefore, the flexible use of color temperature characteristics is very helpful for us to choose light sources.

4) Bright and dark fields of view

The bright field of view is the most commonly used lighting scheme, which is formed by direct light from the front, while the dark field of view is mainly formed by low angle or backlight lighting. For the detection needs of different projects, different types of lighting methods are selected. Generally speaking, the dark field of view will make the background dark and the tested object bright.

5) Light source classification

At present, there are mainly the following centralized classification methods:

a) Colour

The colors of common light sources are concentrated in the visible light range, mainly including white light (compound light), red, blue and green. In addition, infrared light is also more popular, while ultraviolet light is less used for various reasons;

b) Shape

Each manufacturer will classify according to the shape characteristics of different light sources, which is also the mainstream classification at present, such as ring light source, ring low angle light source, strip light source, dome light source (bowl light source / dome light source), area light source, etc;

c) Working principle / characteristics

Different application modes or principles are classified, mainly including shadowless light source, coaxial light source, point light source, linear light source, backlight, combined light source and structural light source.