Machine Vision Light Source Selection

In machine vision systems, it is crucial to obtain a high-quality processable image. The success of the system depends on ensuring good image quality and clear features. Most of the failures of a machine vision project are caused by poor image quality and unclear features. To ensure a good image, a suitable light source must be selected.

Basic elements of light source selection:

Contrast: Contrast is very important for machine vision. The most important task of lighting in machine vision applications is to create the greatest contrast between the features to be observed and the image features to be ignored, so that the features can be easily distinguished. Contrast is defined as the difference in grayscale between the feature and the area around it. Good lighting should ensure that the features to be detected stand out from the background.

Brightness: When choosing between two light sources, the best choice is to choose the brighter one. When the light source is not bright enough, three bad situations may occur. First, the camera's signal-to-noise ratio is not enough; since the light source is not bright enough, the image contrast is necessarily insufficient, and the possibility of noise appearing in the image also increases. Second, if the light source is not bright enough, the aperture must be increased, thereby reducing the depth of field. In addition, when the light source is not bright enough, random light such as natural light will have the greatest impact on the system.

Robustness: Another way to test a good light source is to see if it is minimally sensitive to the position of the part. When the light source is placed in different areas or at different angles in the camera's field of view, the resulting image should not change accordingly. A light source with strong directional characteristics increases the likelihood of specular reflections in bright areas, which is not conducive to subsequent feature extraction.

A good light source needs to be able to make the features you need to find very obvious. In addition to the camera being able to capture the parts, a good light source should be able to produce the greatest contrast, have sufficient brightness, and be insensitive to changes in the position of the parts. Once the light source is selected, the rest of the work will be much easier. The specific method of selecting a light source depends on practical experience in the experiment.