Sharpening-demosaicking method with a total-variation-based superresolution technique
Takahiro Saito, Takashi Komatsu · Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 2005
As an optical low-pass filter, a doubly refractive crystal device is used. The filter reduces frequency components lower than the Nyquist frequency, and images are blurred. We previously presented a demosaicking method that simultaneously removes blurs caused by the optical low-pass filter. For the sharpening-demosaicking approach, the Bayer’s RGB color filter array is not necessarily proper, and we studied another color-filter array, namely the WRB filter array, where the W-filtering means that all the visible light passes through it. Our prototypal sharpening-demosaicking method employed the iterative algorithm, and restored only spatial frequency components of color signals lower than the Nyquist frequency corresponding to the mosaicking pattern of the W filters. However, the same recovery problem is solved by a non-iterative method in the Discrete Fourier Transform domain. Moreover, our prototypal method often produced ringing artifacts near sharp color edges. To suppress those artifacts, we introduce the TV-based super-resolution into the sharpening-demosaicking approach. This super-resolution approach restores spatial frequency components higher than the Nyquist frequency from observed blurry spatial frequency components so that without producing ringing artifacts it can enlarge and sharpen images while preserving 1D image structures that intensity values are almost constant along the edge direction.