High dynamic range image acquisition method using proportion integration differentiation controller

The extensive application of surface mount technology requires various measurement methods to evaluate the printed circuit board (PCB), and visual inspection is one critical method. The local oversaturation, arising from the nonconsistent reflectivity of the PCB surface, will lead to an erroneous result. This paper presents a study on a high dynamic range image (HDRI) acquisition system which can capture HDRIs with less local oversaturation. The HDRI system is composed of the liquid crystal on silicon (LCoS) and chargecoupled diode (CCD) sensor. In this system, the LCoS uses a negative feedback to extend the dynamic range of the system, and the proportion integration differentiation (PID) theory is used to control the system for its rapidity. The input of the PID controller is images captured by the CCD sensor and the output is the LCoS mask, which controls the LCoS's reflectivity. The significant characteristics of our method are that the PID control can adjust the image brightness pixel to pixel and the feedback procedure is accomplished by the computer in less time than the traditional method. Experimental results demonstrate that the system could capture HDRIs with less local oversaturation. (C) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)