Image recovery for a direct color imaging approach using a color filter array

As an imaging scheme with a single solid-state image sensor, the direct color-imaging approach is considered promising as an acquisition scheme of color data with high spatial-resolution. The sensor has three photo-sensing layers along its depth direction. Although each pixel has three color channels, their spectral sensitivities are overlapped with each other to a considerable extent, and the direct color-imaging approach is considered to have a problem in color separation. To cope with this problem, this paper presents a hybrid color-imaging approach between the direct color-imaging approach and the color-filter-array approach. Our hybrid approach uses a direct color-imaging sensor that has three photo-sensing layers, and pastes the green and the magenta color filters on pixels' surfaces of the direct color-imaging sensor according to a checkered pattern. The use of the checkered green-magenta color-filter-array improves color separation, but the sensed reddish and the sensed bluish color channels still have somewhat different color spectra from those of the red and the blue primary color channels. In addition to it, the sensed green color channel and the sensed reddish / bluish color channels are sub-sampled in a ratio of 2 to 1 according to the checkered pattern. To recover RGB primary color images with full spatial resolution, not only the color transformation of the reddish and the bluish color channels but also the interpolation of the sensed three color channels are needed. This paper presents a method for the color transformation and a method for the interpolation. Our methods achieve high spatial resolution better than the pure color-filter-array approach, and at the same time improve color separation to some extent.