抄録
We used optical low-pass filters with solid-state imaging devices to produce images. The actual optical low-pass filter was formed by combining two types of doubly refractive crystal devices. The filters cannot sharply cut-off the high frequency components and they reduce the frequency components near the Nyquist frequency. Thus, the projected images on the surface are blurred. This paper presents a demosaicking method that restores the blur caused by optical low-pass filters. Our sharpening approach to demosaicking employs a Landweber-type iterative algorithm. For our sharpening-demosaicking approach, the Bayer's pattern of the RGB primary color filter array is not applicable. Therefore, we studied another color-filter pattern, namely the WRB filter array, which is preferable to the RGB filter array, where W-filtering means that all the visible light passes through it. Our mathematical formulations for sharpening-demosaicking are similar to the least square problem, but there are many different least square solutions. To avoid ambiguity in the spatial frequency domain, we introduced a pass-band limitation that corresponds with the sub-sampling pattern of the mosaicking of color filters into the iterative algorithm.
