In machine vision system, it is very important to obtain a high-quality and processable image. The success of the system, first of all, to ensure that the image quality is good, the characteristics are obvious. Most of the failures of a machine vision project are caused by poor image quality and indistinct features. To ensure a good image, you must choose a suitable light source.
The basic element of light source selection:
Contrast: contrast is very important to machine vision. The most important task of illumination in machine vision applications is to make the maximum contrast between the features that need to be observed and the image features that need to be ignored, so that it is easy to distinguish features. Contrast is defined as a sufficient grey metric difference between a feature and its surrounding area. Good lighting should ensure that features that need to be detected stand out from other backgrounds.
Brightness: when you choose two light sources, the best choice is to choose the brighter one. When the light source is not bright enough, there may be three bad situations. First, the SNR of the camera is not enough, because the brightness of the light source is not enough, the contrast of the image is not enough, and the possibility of noise on the image increases. Second, the brightness of the light source is not enough, must increase the aperture, thus reducing the depth of field. In addition, when the brightness of the light source is not 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 whether the light source is least sensitive to the location of the component. When the light source is placed in different regions or angles of view of the camera, the resulting image should not change. The strong directionality of the light source increases the possibility of specular reflection in the highlight region, which is not conducive to the feature extraction.
Good light sources need to be able to make the features you need to look for very obvious. Apart from the camera being able to capture components, good light sources should be able to produce maximum contrast, brightness enough and not sensitive to changes in the parts' position. With the light source selected, the remaining work will be much easier. The specific light source selection method also lies in the practical experience of the experiment.