What Light Color Should a White-Light-Scanner Use?

Publication Details

Abstract

This article addresses some aspects of the question, “Why and when should a fringe-projection system for 3D scanning use a particular color of light?” This is opposed to a white-light system, which has been the standard approach for the past decade. We will demonstrate the effect of changing the color of the illumination source by explaining the working principle of a state-of-the-art fringe-projection system, as well as the limitations of these techniques when it comes to transparent, translucent, or shiny objects. The pros and cons of white-light illumination (the full spectrum) will be contrasted with the use of selected component colors that comprise white light. The choice of illumination colors (wavelengths) can range from infrared (IR) to ultraviolet (UV), including the visible “rainbow” spectra. Different wavelength bands can uniquely benefit different application categories, e.g., the use of IR is beneficial for cultural heritage and biometric scanning. Real-world examples in which certain wavelengths make particular sense (such as blue for skin scanning) are highlighted, and we will outline the problem when it comes to objects with complementary colors to the projected color. The effect of different colors on shiny object surfaces will also be assessed. The main benefit of monochromatic light is that it enables the use of filters in front of camera lenses to suppress ambient light. The color of the ambient light (for example, fluorescent light) plays an important role when considering monochromatic light for scanning. Last but not least, we will demonstrate how the sensitivity of current camera technologies is highly dependent on different light wavelengths. As these factors make clear, the answer to the question raised in the headline of this article rests on a series of complex considerations. We will provide many examples of these issues, and will suggest that a multi-color approach, including white light, provides the user with a necessary and flexible approach to the problem.