The Selection of the Color of Machine Vision Light Sources

The visual inspection system is composed of a CCD camera, a lens, a visual light source, a software system, etc. Among them, the function of the light source is to clearly distinguish the object under test from the background and obtain high-quality images. It plays an important role in the visual recognition system, and choosing a suitable light source is a crucial step in building the visual system.

 In addition to having many types, visual light sources also come in different colors. So, how exactly should we choose?

Visual Light Sources
Currently, there are four commonly used light source colors: white light source (W), blue light source (B), red light source (R), and green light source (G).

Tips for Choosing the Color of the Light Source

In machine vision, the selection of the light source color needs to comprehensively consider factors such as the characteristics of the object, the detection task, and the characteristics of the camera. The following are some selection tips:
            According to the Color of the Object

    Contrast Principle: Select a light source color that forms a sharp contrast with the color of the object being detected. This can highlight the characteristics of the object and improve the contrast of the image. For example, for dark objects, a white or light blue light source can be chosen; for light-colored objects, a black or dark background light can be used to enhance the contrast.

    Complementary Color Principle: Utilize the complementary relationship of colors to enhance the detection effect. For example, a red object will show a large contrast under a green light source, making it easier to be recognized and detected.
According to the Detection Task

     Surface Defect Detection: Usually, it is necessary to select a light source color that can highlight the surface texture and defects. A white light source can provide uniform illumination and is suitable for most surface defect detections; for some tiny scratches or cracks, a blue or green light source can be tried because their wavelengths are shorter and can better highlight the details.

     Dimension Measurement: It is necessary to select a light source color that can provide clear edges. Generally speaking, due to its longer wavelength, the red light source has a relatively small diffraction phenomenon and can provide relatively clear object edges, making it suitable for dimension measurement tasks.

     Recognition and Classification: Select the corresponding light source color according to the color characteristics of the object to enhance the color differences between objects, facilitating recognition and classification. For example, in fruit sorting, a light source of a specific color can be used to highlight the color differences of different fruits, so as to achieve accurate sorting.
According to the Characteristics of the Camera

     Spectral Response: Different cameras have different response characteristics to light of different wavelengths. When selecting the light source color, consider the spectral response curve of the camera to make the color of the light source within the sensitive wavelength range of the camera to obtain the best imaging effect. For example, if certain cameras have high sensitivity to near-infrared light, then in detection tasks that require high resolution and low noise, a near-infrared light source can be selected.

     Color Camera and Black-and-White Camera: If a color camera is used, when selecting the light source color, consider the combination with the color of the object to accurately restore the color information of the object; for a black-and-white camera, mainly focus on the influence of the light source color on the grayscale value of the object, and improve the grayscale contrast between the object and the background by selecting an appropriate light source color.
Other Consideration Factors

     Ambient Light: Consider the color and intensity of the on-site ambient light. If the ambient light is strong and has a fixed color, a light source color different from it should be selected to avoid the interference of the ambient light on the detection results. For example, in an outdoor environment, since natural light is mainly white, a light source of a special color, such as yellow or orange, can be selected to highlight the detection object.

     Cost and Efficiency: Light sources of different colors may vary in cost, power consumption, and lifespan. On the premise of meeting the detection requirements, these factors should be comprehensively considered, and a light source color with high cost performance should be selected. For example, white LED light sources usually have a lower cost and a longer lifespan and are suitable for some general detection scenarios where the color requirements are not strict.

Color Introduction:

1. Analogous Colors，qnalogous colors refer to colors with the same hue property but different shades of chroma. They are the colors within an angle of 15° on the color wheel, such as deep red and light red, dark blue and light blue.

2. Adjacent Colors，refer to the colors adjacent to each other on the color band. For example, red and orange. On the color wheel, all colors within a range of 60 degrees belong to the range of adjacent colors.

3. Complementary Colors/Contrasting Colors,complementary colors/contrasting colors have a very strong contrast. When the color saturation is very high, many extremely stunning visual effects can be created. For example, orange and blue, red and green, yellow and purple. They are the colors opposite (180-degree diagonal) to each color on the color wheel.

4. Similar Colors,refer to three adjacent colors on the color wheel. The colors within an angle of 90 degrees on the color wheel are collectively referred to as similar colors. For example, red - red-orange - orange, yellow - yellow-green - green, cyan - cyan-purple - purple, etc. are all similar colors.