The Anti Aliasing Filter

The Anti Aliasing Filter

An optical filter low pass filter (OLPF), sometimes referred to as an anti-aliasing filter, a filter is present in many digital cameras (except for certain specific models, including the Nikon D810) and is located directly in front of the sensor camera. The main role of the filter OLPF (anti-aliasing) is to stop the high frequencies (we speak of waves hitting the sensor) and reduce the moire and false colors caused precisely by the high-frequency waves in the images. The Moiré pattern, remember, occurs in scenes containing repetitive details such as the tissues (especially in clothing) or in the vertical lines present, for example, in architecture. The repetitions that are in tissues or in architecture are repetitions manmade and difficult (or impossible) to find in nature, which limits the Moire effect to certain types of photography (for example, the nature is not affected) .

The anti-aliasing filter (OLPF) is generally constituted by two layers of glass and one birefringent susceptible to certain wavelengths. In the image below (taken from the website Nikon), it is seen how the light is divided when it passes through the three layers (or rather, is moved only a set of frequencies, by the central layer).

In addition, in order to improve the chromatic yield of the camera, two layers (the middle and close to the sensor) are processed in order to be, respectively, anti-reflective and absorbent Infrared.

IR coating, AR coating, and glass IR absorption are also used to obtain the best features of

Digital cameras that do not have a OLPF allow the sensor to record even the information contained in the high frequencies, which increases the sharpness of the overall image. Conversely, of course, these cameras pay something in terms of Moiré or false colors.

However, digital cameras are incorporating sensors with a resolution increasingly high. Higher resolution sensors are sensors with photodiodes smaller and smaller photodiodes are less prone to moire and false colors. In practice, the anti aliasing filter to remove a camera from high enough resolution is a relative risk that pays in terms of final image quality. The same Nikon introduced, in 2012, two versions of the D800, with and without anti aliasing filter the D800 and D800E (who has tried both realized as the difference in terms of artifacts is negligible).

Modern digital cameras are also designed to offer the best possible performance both in the sense of quality that the color fidelity. Sensors with a higher density of photodiodes, of course, also entail a greater noise modern technology, however, it is managing to compensate for this problem with the same quality

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