Difference Between Bright Field Illumination and Dark Field Illumination in Visual Light Sources




In machine vision systems, the importance of the light source cannot be ignored.Light sources can affect image quality and recognition results, so choosing the right type of illumination is critical.Common lighting methods can be categorized as backlighting, bright field lighting, and dark field lighting.


The backlighting is from the bottom of the object and is very effective for edge detection.


Brightfield lighting refers to a vision light source that shines directly on a photographed object, giving the surface of the object a bright appearance.Outlines and details of objects can be clearly displayed.Depending on the directionality of the beam it can be categorized into full bright field and partial bright field.


A full bright field is a light source shining from multiple directions, allowing small bumps and breaks on the surface of an object to be seen clearly.Large 3D angle light sources such as coaxial diffuse light sources and surface light sources are available for full brightfield illumination.



Partial brightfield is where the light source shines from an angle, allowing the surface of the object to be illuminated, while the damage to the surface can be rendered in more shadow, achieving a contrast between the damage and the background.Ordinary ring light sources, strip light sources and point light sources can achieve partial bright field illumination.


Bright field illumination is an excellent choice when information such as surface defects and color of an object needs to be detected.However, mirrored objects are less suitable because this light source shines directly on the surface of the object and receives a lot of reflected light in the lens.


Dark field illumination is the use of shadows to emphasize the bumpy texture and form of an object's surface.It is possible to make the bumps on the surface of an object produce bright reflections, while the recessed parts are in shadow.This approach makes the details of the object's surface clearer and also emphasizes the three-dimensionality of the object.Therefore, dark field illumination is a very good choice when information such as defects and shapes on the surface of an object need to be detected.


Both bright field lighting and dark field lighting have their own advantages and can be selected according to specific application scenarios.But no matter which type of lighting is used, the importance of the light source cannot be ignored.Factors such as the stability, brightness, and color of the light source affect image quality and recognition results.Therefore, when performing machine vision applications, you need to choose the right light source and fine-tune it to achieve the best results.



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