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How to choose a visual light source?

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How to choose a visual light source?

Date:2018-05-18 Author:admin Click:

How to judge the quality of a visual light source, what aspects of knowledge do you need to know?


1.Contrast


Contrast is very important for machine vision. The most important task of lighting for machine vision applications is to maximize the contrast between the features that need to be observed and the image features that need to be ignored, so that the features can be easily distinguished. Contrast is defined as a sufficient amount of gray difference between a feature and its surrounding area. Good lighting should ensure that features that need to be detected stand out from other backgrounds.


2. Robustness


Robustness is a good adaptation to the environment. A good light source needs to have the same effect in practice as it does in the laboratory.


3.Brightness


When choosing two light sources, the best choice is to choose the brighter one. The brightness of the light source is not enough, it is necessary to increase the aperture, thereby reducing the depth of field.


4, uniformity 均匀


Uniformity is a very important technical parameter of the light source. The light source with good uniformity makes the system work stably.


5, maintainability


Maintainability mainly means that the light source is easy to install and easy to replace.


6, life and calorific value


The brightness of the light source is not easy to decay too quickly, which will affect the stability of the system and increase the cost of maintenance. Lamps with large heat generation decay quickly, and the life of the light source is also greatly affected.


视觉光源种类.jpg

Visual light source


How to rely on light sources to enhance image contrast?


1. Use the same color light or similar color light source to illuminate the illuminated part;


2. Use the light of opposite color or light source of similar color to dim the illuminated part.


3. Different wavelengths have different penetrating power (transmittance) to the substance. The longer the wavelength, the stronger the penetrating power against the object, and the shorter the wavelength, the greater the diffusivity on the surface of the substance.


Light source selection tips


1. Need more contrast between foreground and background, consider using black and white camera and color light source 彩色


2. The problem of ambient light, try using a monochromatic light source with a filter.


3. Glitter surfaces, consider using diffuse dome light


4. Flash, flat, but rough surface, try to use coaxial scatter light


5. Looking at the shape of the surface, consider using a dark field of view (low angle).


6. When testing plastic, try to use ultraviolet or infrared light.


7. Need to see the features through the reflective surface, try using a low-angle line light source (dark field)


8. Consider using a combined light source when a single light source cannot effectively solve the problem.


9. Strobe can produce 20 times stronger light than constant light


How to choose the angle of the light source


According to the desired image effect, select light sources with different incident angles. High-angle illumination, the overall image is brighter, suitable for non-reflective objects on the surface;


Low-angle illumination, the background of the image is black, and the features are white, which can highlight the changes in the contour of the measured object and the surface unevenness. Multi-angle illumination, the overall effect of the image is soft, suitable for curved object detection;


Backlight illumination, the image effect is a clear black and white outline of the measured object, which is often used for size measurement;


Coaxial light illumination, the image effect is a black feature on a bright background, and is used for the detection of flat objects with strong reflections. The schematic diagram of the light source with different angles is as follows:


光源角度选择.png


How to choose the color of the light source


Considering the color of the light source and the background, using the same color system as the measured object will make the image brighter (for example: red light makes the red object brighter); using light of the opposite color system as the measured object will make the image darker : Red light makes blue objects darker). Common visual light sources include red (R), green (G), blue (B), white (W), and ultraviolet (UV).


Example of different color light source effects:


视觉光源颜色应用.png

Light source wavelength characteristics


The longer the wavelength, the stronger the penetrating power.


The shorter the wavelength, the stronger the diffusion ability. The infrared penetrating ability is strong, suitable for detecting objects with poor light transmission, such as brown oral liquid impurities.


Ultraviolet is sensitive to the subtle features of the surface, and is suitable for detecting places where the contrast is not obvious, such as the text on an edible oil bottle.


How to choose the shape and size of the light source


The shape of the light source is mainly divided into a circle, a square and a bar. Generally, a light source with the same shape as the measured object is selected. The final light source shape is subject to the test result. The size of the light source needs to be selected to ensure uniform light in the entire field of view, which is preferably larger than the field of view.


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Phone: 183 0666 4155

Fax: 0755-2372-6873

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