The appearance of false colors — colors not found in the actual subject — and moiré patterns are phenomena specific to digital cameras. They occur when light of high spatial frequency (typically in fine patterns or boundaries between light and dark areas) enters only a single pixel, causing the light to be perceived as a color different from the original color.

The optical low-pass filter, located directly in front of the CMOS sensor, is designed to reduce these problems. Canon developed a new three-layered optical low-pass filter in response to increasing CMOS pixel counts. Two of the three layers are single-crystal substrates that separate the image data into horizontal and vertical directions. To preserve image sharpness while cutting the high-spatial-frequency component of the image that causes false colors and color moirés, a phase plate designed to apply circular polarization to light is sandwiched between these substrates and the image data is accurately separated. Additionally, this optical low-pass filter features a hybrid structure that incorporates an infrared-cut filter to suppress ghosting and color fogging.

Structure of Low-Pass Filter