Lighting for general purpose.
General illumination usually uses cyclic lighting and point like lighting. Ring light is a kind of general lighting way for common use, its very easy to install on camera, it can provide enough lighting for a diffuse surface.
The back lighting refers to place the light source on the back of the object facing with the camera. This kind of lighting way has very large difference with the other lighting way because that the image analyzed is the incident light but not the water glares. The back lighting has very strong contrast ratio. When applying the back light technology, the object’s surface characteristics may be lost. For example, back light technology can be applied to measure the diameter of the coins, but it can’t judge the two sides of a coin.
Coaxial illumination refers to the light which has the same direction with the axis of the camera lluminate on the surface of an object. Coaxial illumination uses a special half reflection mirror to reflect the source in the direction of the camera lens axis. Half reflection mirror only lets the light source that is reflected from the object surface and perpendicular to the lens pass through. Coaxial illumination technology is very useful for achieving the uniform lighting of the flat object with the mirror surface characteristic. In addition, the technology can also make the surface’s angular variation very bright, because the reflected light which is not perpendicular to the surface of the camera lenses will not enter the lens to cause the dark surface.
Dark-field lighting refers to provide the low angle lighting for the object surface. Use a camera to film the mirror and make it in the field of vision, if the light source can be viewed in the field of visio, it can be considered as the bright-field lighting. On the contrary, if the light source in the field of version can not be seen, it is the dark-field lighting. Therefore, whether the light source is bright-field lighting or dark-field lighting, it depends on the light source location. Typically, the dark-field lighting should be applied to the illumination of the protruding part of the surface, or the illuminance of the surface texture changes.
Structured light is a kind of geometric light(such as linear shape, roundness, square) that projected on the object surface. The typical structured light involves the optical fiber of laser. Structured light can be used to measure the distance of the camera and the light source.
In many applications, in order to make the different characteristics display the different contrast ratio in the field of view, multiple lighting technologies are needed.
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