Six lighting technologies of machine vision system:
(1) Lighting for general purposes
General lighting generally uses ring or point lighting. Annular lamps are a common general lighting method, which can be easily mounted on the lens to provide adequate illumination for diffuse surfaces.
(2) Backlight lighting
Backlighting is the placement of a light source on the back of an object relative to the camera. This lighting is very different from other lighting methods, because the image analyzes the incident light rather than the emitted light. Backlit lighting creates a strong contrast. When backlighting is applied, surface features may be lost. For example, it is possible to measure the diameter of a coin using backlight technology, but it is not possible to determine the front and back of the coin.
(3) coaxial lighting
Coaxial lighting is light shining on an object's surface in the same direction as the camera's axis. Coaxial lighting uses a special semi-reflective mirror to reflect the light source towards the lens axis of the camera. Semi-reflective mirrors allow only light sources that are reflected from the surface perpendicular to the lens to pass through. Coaxial lighting is useful for uniform illumination of flat objects with specular surfaces. It is also possible to highlight parts of the surface that vary in Angle, because the light reflected from a surface that is not perpendicular to the camera does not enter the lens, making the surface darker.
(4) continuous diffuse lighting
Continuous diffuse lighting is applied to surfaces that are reflective or have complex angles. Continuous diffuse lighting uses hemispherical uniform lighting to reduce shadow and specular reflection. This lighting method is very useful for circuit board lighting. This light source can achieve uniform illumination in the 170° solid Angle range.
(5) Dark domain lighting
Dark domain lighting is lighting at a low Angle relative to the surface of an object. Use a camera to shoot a glass mirror so that it is in its field of vision. If the light source can be seen in the field of vision, it is considered to be bright domain lighting. On the contrary, if the light source cannot be seen in the field of vision, it is dark domain lighting. Therefore, whether the light source is bright or dark lighting depends on the location of the light source. Dark domain lighting is typically used to illuminate surfaces that have protrusions or surface texture changes.
(6) structured light
Structural light is a kind of light projected on the surface of an object with a certain geometric shape (such as a line, circle, square). Typically structured light involves lasers or fiber optic sources. Structured light can be used to measure the distance from the camera to the light source.
In many applications, multiple lighting techniques are required in order to make different features in the field of view present different contrasts.