Automatic light control of an arbitrary color source for AMOLED inspection using random-search method

Illumination is one of the important factors in machine-vision systems, and optimization of illumination is essential to acquire high-quality images during an inspection process. This paper proposes optimization process of the light color and intensity for inspection of active matrix organic light emitting diode (AMOLED) panels using a random-search method. The raw image acquired by a line scan camera had low luminance uniformity due to the surface condition of the AMOLED. The brightness deviation of the image was corrected to increase uniformity. The image quality after the correction was evaluated using a kind of image index, namely Tenenbaum gradient. The random-search method switched the dimming levels of the color source until a better image index was obtained. The random search was formulated for a multi-dimensional vector to be used in an arbitrary number of color sources. The random value in this study was generated using Gaussian random method, and was terminated when the size of a random vector became sufficiently smaller. The random-search method for automatic light control of AMOLED inspection showed 0.6% difference in the image index between the equal-step search and the proposed method. However the number of iterations in the proposed method was 22 but that of the combinations was 20484.