Overview of Illumination Techniques in Machine Vision

Illumination Techniques in Machine Vision plays a crucial role in the process of image acquisition, with the main task of enhancing the contrast between the features of the object being measured and the background. The greater the contrast, the more distinct the features of the object of interest, thus reducing the post-image processing work and improving the efficiency of the entire machine vision system. Different lighting methods can lead to astonishing differences in the observed images; therefore, understanding and selecting the appropriate illumination techniques in machine vision is crucial.

Incidence Angle and Beam Directionality

In illumination techniques in machine vision, the incidence angle is a fundamental parameter determining the effect of the light source on the object surface. Different incidence angles affect the reflection effect and image quality. Generally, machine vision lighting technologies can be divided into bright field, dark field, and backlight illumination types. Bright field illumination is the most commonly used method, with an incidence angle between 45 degrees and 90 degrees, which can produce a bright imaging effect. Dark field illumination uses an incidence angle of less than 45 degrees, highlighting the edges and scratches of the object.

Beam directionality is also a significant factor in illumination techniques in machine vision. Direct light from the same direction will produce obvious shadows, whereas scattered light from multiple directions will result in less noticeable shadows. Understanding these characteristics helps in choosing the appropriate lighting method to improve imaging quality.

Light Intensity and Uniformity

In illumination techniques in machine vision, light intensity and uniformity are two key factors affecting image quality. The illumination intensity directly influences the exposure of the camera and the signal-to-noise ratio of the image. When the light source brightness is insufficient, the image contrast decreases, noise increases, and it may not meet the visual system's requirements. Therefore, a brighter light source should be preferred when choosing a light source. However, too strong illumination can cause energy wastage and heat dissipation issues.

Uniformity is another key factor in ensuring imaging consistency. In all machine vision applications, uniform lighting is essential because the illumination intensity decreases with increasing distance and deviation from the illumination angle. Ensuring uniform illumination when handling large area objects can effectively improve image quality and avoid imaging errors caused by uneven lighting.

Applications of Bright Field and Dark Field Illumination

Bright field illumination technology is widely used in machine vision, especially for detailed observation of object surfaces. It is divided into partial bright field and full bright field illumination types, with the former using a small solid angle light source and the latter using a large solid angle diffused light source. Full bright field illumination can eliminate the effects of surface roughness, suitable for objects with high reflective and smooth surfaces.

Dark field illumination technology is suitable for occasions where fine details of the object need to be highlighted. By using low-angle incidence, dark field illumination can enhance the visibility of surface defects, helping detect minor dents and scratches. This technology has important application value in surface defect detection and quality control.

Advantages of Backlight Illumination

Backlight illumination is another common illumination techniques in machine vision, where the light source illuminates evenly from the back of the object, clearly displaying the object's outline. This illumination method is suitable for measuring object dimensions and calibrating object orientation, producing strong contrast. While using backlight technology, the surface features of the object may be hidden, but its advantages in geometric shape defect detection are indisputable.

In practical applications, the lighting technology for machine vision can be selected based on the material and characteristics of the object. For instance, in surface inspection, geometric shape defects and surface strength defects require different lighting methods to highlight features. Therefore, choosing the appropriate lighting method to suit different inspection needs is key to achieving efficient and accurate detection.

In summary, illumination techniques in machine vision has significant impacts on image quality and detection efficiency. From incidence angle, light intensity, and uniformity to different types of illumination, each factor should be carefully considered. Understanding these basic concepts will help engineers and technicians quickly select the appropriate lighting method, thereby improving the performance of machine vision systems and promoting the development of industrial automation.