False colors and Moire fringes are common problems with high-resolution digital cameras. Since the colors recognized by the camera are different from the actual ones as high spatial frequency light enters a pixel. Optical low-pass filters (OLPF) are used to eliminate color Moire fringes in high-quality digital imaging systems. Nowadays, a three-layer filter is more popular and developed specifically in response to CCD/CMOS sensors. Two of the three layers are single-crystal substrates, which separate image data in horizontal and vertical directions. A phase plate, which converts linearly polarized light into circularly polarized light, has been sandwiched between these two substrates. That results in more accurate image data separation, as well as a facilitation of light reception by multiple pixels, and minimizes false colors due to finer line patterns input. In general, the optical low-pass filter is laminated together with an infrared-cut filter, which suppresses ghosts and colors overlapping caused by infrared light. This paper analyzes the contributions to MTF of optical system in detail for different F/#, orientation of single-crystal substrates and different number of layers.
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