What is an optical low-pass filter (OLPF)?
In high-quality digital imaging systems, optical low-pass filters (OLPF) are used to eliminate color Moire fringes. An OLPF cuts off the lens MTF above the sampling frequency of the image resulting an overall MTF curve that approximates a step function in spatial domain. IR cut-off function is often incorporated into OLPF as well.
An Optical Low Pass Filter (OLPF), is sometimes referred to as an Anti-Aliasing filter. The filter is built into many digital cameras and is located directly in front of the image sensor.
Digital cameras which do not have an OLPF allow high frequency image information to be recorded, this increases image sharpness. This also means that moiré and false colour may be slightly noticable according to the subject and shooting conditions. However, digital cameras are incorporating increasingly higher resolution sensors. As higher resolution sensors contain a greater number of pixels with a smaller pixel pitch, the occurrance of moiré and false colour in images is reduced. This reduction in risk increases the possibility to remove the OLPF with high resolution cameras to take advantage of the increased image sharpness.