Secure uplink from smartphone screen to camera communication (SCC) needs to increase the throughput and simultaneously reduce the screen luminance. To realize low-luminance wavelength division multiplexing / space division multiplexing (WDM/SDM) transmission, 2-wavelength adaptive thresholding that categorizes both inter-wavelength and spatial inter-symbol interferences (ISIs) is proposed and experimentally verified. The camera images are categorized into 3×3 cells and the symbol of the center cell is determined. The inter-wavelength ISIs are categorized by the pixel value of the center cell of the other wavelength. The spatial ISIs are categorized by the outer 8-cell symbol pattern estimated at the same wavelength.
