Accurate spectral response measurement system for digital color cameras

Abstract

In imaging systems, color plays an essential role in conveying and recording visual information from the real world. To faithfully represent colors acquired from digital cameras, a spectral responsivity measurement system is proposed for those devices in this paper. For estimating spectral responsivities of digital color cameras, a filter-based optical system is designed with proper filter selections. Since the spectral filters primarily prescribe the optical characteristics of the system, the filter consideration is important to the optical design of the system with the presence of noise. A theoretical basis is presented to confirm that sophisticated filter selections can make this system as insensitive to noise as possible. Also, we propose a filter selection method based on the orthogonal-triangular (QR) decomposition with column pivoting (QRCP). To investigate the noise effects, we assess the estimation errors between the actual and estimated spectral responsivities, with the different signal-to-noise ratio (SNR) levels of an eight-bit/channel camera. To demonstrate the effectiveness of this approach, the experimental results from the filter-based optical system with the spectral filters selected from the QRCP-based method is much less sensitive to noise than those with other filters from different selections. It is found that the measurement accuracy is fairly satisfactory.