LED lighting system design in color vision measurement

1 Introduction

At the heart of visual measurement is image acquisition and processing. All information is derived from images. In addition to the quality of the image itself, the spectral distribution of the source is another important factor affecting the image quality of the vision system. Color vision measurement is different from gray-scale visual measurement, which enriches one-dimensional information of simple gray-scale changes into color three-dimensional information. The spectral characteristics of the light source emission and the surface reflection of the measured object determine the spectral distribution of the light energy collected by the visual measurement system. Even if the light source has the same structure and illumination mode, the image will be greatly different due to the different luminescence spectra. Therefore, a full-spectrum light source or a light source of a specific spectrum plays an important role in extracting characteristic information such as color and contour of a target. How to use the color characteristics of the light source to get the best contrast effect.

Image has always been an important direction for the development of color vision measurement lighting systems. Monochromatic LEDs have the advantages of small size, easy integration, simple driving, good monochromaticity compared with ordinary light sources, etc. In recent years, performance in luminous intensity, peak wavelength, half-wave bandwidth, etc. Both have been greatly improved. In view of the special requirements of color vision measurement system, combined with the advantages of red, green and blue LEDs, this paper designs and produces an LED light source with multi-color features, adjustable brightness and uniform irradiation.

2 LED light source system

2.1 Design principle and structure analysis

According to the four basic laws of color and light mixing: continuous color change law, complementary color rate, intermediate color law and replacement rate, using red, green and blue primary color LEDs with good monochromaticity, by independently controlling the luminous intensity independently, it can simulate A variety of uniform and stable colors. When selecting the LED band, the wavelengths of the three colors should be matched to the peaks of the three spectral lines of the camera.

To achieve the required light source system, forward illumination technology should be adopted, that is, the light source is irradiated on the target object, and the camera on the same side of the light source receives the light reflected by the object, which is most advantageous for extracting the color information and surface detail features of the measured object. In order to solve the projection problem and the uniformity of the irradiation, we use the scattered light illumination, that is, the light of the three colors is diffusely reflected in a hemispherical reflector, and the secondary illumination is realized by the reflected light.