Lifespan characteristics: Light sources generally need to be used continuously. To ensure consistent accuracy in image processing, the vision system must guarantee the acquisition of stable and consistent images over long periods.
Contrast: Contrast is crucial for machine vision . The most important task of illumination in machine vision applications is to create maximum contrast between the features to be observed and those to be ignored in the image, thus facilitating feature differentiation. Contrast is defined as a sufficient grayscale difference between a feature and its surrounding area. Good illumination should ensure that the features to be detected stand out from the background.
Spectral characteristics: The color of the light source and the color of the object being measured determine the amount and wavelength of light reflected to the camera. White light or a specific spectrum may be a significant factor when extracting feature information for other colors. When analyzing multi-color features, color temperature is a crucial factor when selecting a light source.
Brightness: When choosing between two light sources, the best choice is the brighter one. Insufficient light can lead to three problems. First, the camera's signal-to-noise ratio will be low; insufficient brightness will result in insufficient image contrast and a higher likelihood of noise. Second, insufficient brightness necessitates a larger aperture, reducing depth of field. Third, when the light source is insufficient, random light, such as natural light, will have the greatest impact on the system.
Light source uniformity: Uneven light causes uneven reflection. Uniformity relates to three aspects: ① For the field of view, the light should be uniform within the camera's field of view. Simply put, dark areas in an image lack reflected light, while bright areas reflect too much light. ② Uneven light will cause some areas within the field of view to receive more light than others, resulting in uneven reflection from the object's surface (assuming the object's surface reflects light uniformly). ③ A uniform light source compensates for changes in the object's surface angle; even if the object's surface geometry is different, the reflection of light from the light source will be uniform across all parts.
