The light source is an important factor that affects the input of the machine vision system because it directly affects the quality of the input data and the effect of at least 30% of the application. Because there is no universal machine vision lighting, so for each specific application example, to choose the appropriate lighting devices, in order to achieve the best results. Many industrial machine vision systems today use visible light as a light source, primarily because of the easy availability of visible light, low cost, and ease of operation.

 

1, Brightness: The best choice when choosing between two light sources is the brighter one.

 

When the light source is not bright enough, there may be three bad situations. First, the camera's signal-to-noise ratio is not enough; because the brightness of the light source is not enough, the image contrast is inevitable, the possibility of noise in the image also increases. Second, the brightness of the light source is not enough, it is bound to increase the aperture, thereby reducing the depth of field. Third, when the brightness of the light source is not enough, natural light and other random light will have the greatest impact on the system.

 

2, light uniformity: uneven light can cause uneven reflection. Evenly related to three aspects.

 

First, for the field of vision, the field of view of the camera should be uniform. In short, the dark area in the image is the lack of reflected light, and the bright spot is that the reflection is too strong here.

 

Second, uneven light causes more light in some areas of the field of view than in other areas. Resulting in uneven reflection on the surface of the object (assuming that the reflection of light on the surface of the object is the same).

 

Third, a uniform light source will compensate for changes in the angle of the surface of the object, even if the geometry of the object surface is different, the light source in the various parts of the reflection is uniform.

 

3, spectral characteristics: the color of the light source and the color of the surface of the measured object determines the size and wavelength of light energy reflected to the camera. White light or a particular spectrum may extract more important information when extracting feature information from other colors. When analyzing multi-color features, color temperature is a more important factor when choosing a light source.

 

4, life characteristics: light sources generally need to continue to use. In order to keep the image processing consistent and accurate, the visual system must ensure a stable and consistent image for a long time.

 

5, contrast: contrast is very important for machine vision. The most important task of illumination for machine vision applications is to maximize the contrast between the features that need to be observed and those that need to be ignored, making for easy distinction of features. Contrast is defined as a sufficient gray level difference between the feature and its surrounding area. Good lighting should ensure that the features that need to be tested are highlighted in other contexts.