In machine vision system applications, the choice of source is very important, it will directly affect the quality and application of the input data. A suitable light source will provide a stable, high contrast image for the image acquisition mechanism. So how to choose a suitable machine vision light source, and how to evaluate the quality of a light source? Here are some answers for you.
1, contrastContrast is very important for machine vision. The most important task of illumination for machine vision applications is to create maximum contrast between features that need to be observed and image features that need to be ignored, thereby facilitating the differentiation of features. Contrast is defined as having a sufficient amount of grayscale difference between the feature and the area around it. Good lighting should be able to ensure that features that need to be detected stand out from other backgrounds.
2, robustnessRobustness is a good adaptation to the environment. A good light source needs to have the same effect as it does in the lab in practice.
3, brightnessWhen choosing two sources, the best option is to choose the brighter one. When the light source is not bright enough, there may be three bad conditions. First, the camera's signal-to-noise ratio 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. Secondly, the brightness of the light source is not enough, and the aperture must be increased, thereby reducing the depth of field. In addition, when the brightness of the light source is insufficient, the random light such as natural light will have the greatest influence on the system.
4, the light source can be predictedWhen the light source is incident on the surface of the object, the reflection of the light source is predictable. The light source may be absorbed or reflected. Light may be completely absorbed (black metal material, the surface is difficult to illuminate) or partially absorbed (causing a difference in color and brightness). Light that is not absorbed is reflected, and the angle of the incident light is equal to the angle of the reflected light. This scientific law greatly simplifies the machine vision light source, because the ideal effect can be achieved by controlling the light source.
5, uniformityUniformity is a very important technical parameter of the light source. A light source with good uniformity stabilizes the system.
6, maintainabilityMaintainability mainly means that the light source is easy to install and easy to replace.
7, life and heatThe brightness of the light source is not easily attenuated too fast, which will affect the stability of the system and increase the cost of maintenance. The brightness of a lamp with a large amount of heat is quickly attenuated, and the life of the light source is also greatly affected.
How to rely on the light source to enhance image contrast?Illuminating the illuminated portion with light of the same color or a source of similar color;
Irradiation with a source of opposite color or a source of similar color can darken the illuminated portion.
Different wavelengths have different penetrating power (penetration rate) to the substance. The longer the wavelength, the stronger the penetrating power to the object, and the shorter the wavelength, the greater the diffusion rate to the surface of the material.
Some tips for choosing a light sourceNeed a greater contrast between the foreground and the background, consider a black and white camera and a color light source;
For ambient light problems, try using a monochromatic light source with a filter;
Flash surface, consider using diffuse dome light;
Flash, flat, but rough surface, try to use coaxially scattered light;
Look at the shape of the surface, consider using a dark field (low angle);
When testing plastics, try using ultraviolet or infrared light;
Need to look at the features through the reflective surface, try to use a low angle line source (dark field of view);
A combined light source is considered when a single light source cannot effectively solve the problem;
Strobe can produce light 20 times stronger than constant illumination;
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