Selecting different light sources, controlling and adjusting the direction of the incident light on the object are the most basic parameters of machine vision system planning. It depends on the type of light source and the orientation relative to the object. Generally speaking, there are two most basic parameters. The method: direct light and diffused light. All other approaches extend from these two approaches.
Direct light: The incident light basically comes from one direction, and the angle of incidence is small, it can cast shadows on objects;
Diffuse light: Incident light comes from many directions, even all directions, and it does not cast a noticeable shadow.
Objects reflect light with two different reflection properties: direct reflection and diffuse reflection.
Direct reflection: The angle of reflection of light is equal to the angle of incidence. Direct reflections are sometimes very useful, and sometimes they can be extremely dazzling. Specular reflections should be avoided in most cases.
Diffuse reflection: Light hitting an object is diffused in all directions. In most practical situations, diffuse light is formed within a certain angular range and depends on the angle of the incident light.
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, and the range is between 400nm and 760nm (some people can observe 380nm-780nm), that is, from violet 380nm to red 780nm.
The color circle is the sorting of colors in the visible light spectrum, forming red connected to purple at the other end. The color circle used in machine vision generally contains 6 different colors, which are divided into two categories: warm colors and cool colors. Warm colors are composed of red colors, cool colors come from blue tones.
Generally, when the light with opposite color temperature is used, the image can achieve the highest contrast, and the light with the same color temperature can be effectively filtered out. Therefore, the flexible use of color temperature characteristics is very helpful for the selection of light sources.
Bright field is the most commonly used lighting scheme, which is composed of direct light from the front, while dark field is mainly composed of low-angle or backlight lighting. For different project detection requirements, different types of lighting methods are selected. Generally, a dark field will make the set appear dark and the object under inspection appear bright.
1. Color. Commonly used light source colors are concentrated in the visible light range, mainly white light (composite light), red, blue, green, and other infrared light is also more common. And ultraviolet light is less used due to various reasons;
2. Appearance. Each manufacturer will classify according to the shape characteristics of different light sources, which is also the current mainstream classification, such as square ring light source, annular low-angle light source, strip light source, dome light source, surface light source, etc.
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