Under Artificial Intelligence, serious work has been done for the recreation of the human eye. Machine vision is the phenomenon that makes machines such as mobiles and computers see the surroundings and analyze them. The first step in this process is to create an image by analyzing the reflected light from the target. Since images are created when light is reflected from the object, lighting plays a crucial part in the machine vision process. It defines the ease at which the machine shall recognize the image.
Contrast is the visible ratio of different tones of light and dark in an image. Generally, a contrast image is more comfortable to analyze than an image with low contrast and uneven illumination. More effort typically results in longer processing time and incorrect image analysis. Parameters such as edges, textures, and corners are identified by focusing on the differences between light and dark areas by a machine vision system. Therefore, if the lighting is selected correctly, the images produced can be easily comprehended by the machine vision system with a high degree of reliability and efficient development time and resources.
Types of Lighting
Before jumping into selecting a lighting type for your application, you need to define the goals and focus on what is essential for the inspection. This will simplify the process of choosing the most suitable lighting technique that shall highlight the features that are required for the application.
- Coloured Light: Using the light of a particular color will help contrasting colors to separate, making them appear darker in the image. It will produce an image with a contrast based on the color hues of the object.
- Infrared Light: Infrared rays are capable of penetrating deep into the surfaces and produce images that are not visible to the human eye. Defects in solid crystals can be detected using Infrared Radiations.
- Collimated Light: It is a parallel beam of light that produces sharp images. It is useful when edge detection plays a vital role in the application.
- Diffused Light: Diffused light positively avoids glare and shadows in the image but reduces the light’s intensity.
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There are basic types of lighting techniques-
- Direct Lighting: It is a simple lighting technique that can be used for materials that are non-reflective and highly scatter the light. These are inexpensive and are used to illuminate large areas. Unwanted shadows can be avoided by a complete vertical illumination or a ring light source.
- Back Lighting: In this technique, the light is placed at the opposite end of the camera, capturing the image. This produces a silhouette of the object obscuring all the surface details. The maximum amount of contrast can be created using this technique. The contrast produced can be further enhanced by using a polarizing filter with the backlight used.
- Structured Lighting: Highly collimated light sources are used to produce a known light pattern that can be used to obtain information regarding the object’s dimensions.
- Axial Lighting: Diffuse on-axis lighting, also known as DOAL, is a uniform light that runs perpendicular to the camera axis. The camera sees through the mirror in front of the object. Since lights can lose their intensity upon reflection from the mirror, additional lighting sources should be used to improve illumination.
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There are various sources of lights available that can be used to match your lighting choice and lighting technique. Some of them are listed below-
- Halogen Lights: These can produce a high intensity of illumination but produce large amounts of heat. This problem can be solved by placing the source away from the application, which is sensitive to heat.
- Incandescent lights: These are relatively inexpensive and are readily available. But they carry the same problems as halogen lights.
- Fluorescent lights: They provide diffused lights that are extremely useful in minimizing glare. These lights can flicker due to the AC power source, and it also gets degraded over time.
- Lasers: These are collimated light sources that can be used to measure the dimensions of the object.
- LED’s (Light Emitting Diode): It is the most used lighting source in machine vision systems. They tend to last for a more extended period without any heat issues. They can also be color specific and are safe to use.
Instead of picking up different lighting sources, you can use integrated lighting sources. It comes with an added advantage of software that can control the intensity and strobing of light. Integrated Lighting is easier to install and is more cost-effective as there is no need to install any additional lighting source.
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A sound lighting system is a must to produce images of high quality. The three components of a lighting system, i.e., the lighting source, lighting technique, and the lighting source, should be used wisely to obtain a high contrast image. A proper understanding of the application and its requirements is necessary to find the perfect combination. A correct selection may significantly affect the development time and consumption of resources for your application to ensure good quality images are produced for analysis.