Why Optical Low Pass Filters Should be Avoided in Cameras for use in Industry and the Life Sciences

Digital cameras sold in the consumer market often come with optical low pass filters (Figure 1). These filters are used to remove or reduce possible Moiré effects when fixed details are captured. Fixed details could include; an urban landscape with many vertical and horizontal lines, or clothing comprising repetitive patterns.

Optical Low Pass filters are present in the vast majority of digital cameras sold within the consumer market.

Figure 1. Optical Low Pass filters are present in the vast majority of digital cameras sold within the consumer market.

Moiré Effect

Non-real patterns within an image are known as Moiré effect (Figure 2), and it is produced when the fixed, aligned grid of pixels on the sensor interfere with the object. This problem occurs on the collection side, and because of this it is difficult for the camera to eliminate the effect by post processing the data.

Example of the Moiré effect.

Figure 2. Example of the Moiré effect.

Almost all consumer cameras have a low pass filter used to fix this effect, it is made up of two crystal filters that divide the light rays onto the surrounding pixels. When the rays are split vertically and horizontally, the projected image on the sensor becomes slightly blurred, and this stops the possibility of introducing Moiré.

Optical Low Pass Filter

The optical low pass filter is a physical filter, so it cannot be easily removed or disabled. The camera avoids blurring effects, and provides sharper images by automatically applying a firmware-based sharpening filter on the image that is blurred. This results in a sharp image, but it will be very difficult to observe the original advertised resolution of the camera, making the information inaccurate.

Conclusion

Optical low pass filters are not recommended due to their inability to generate accurate images, especially when used in industrial vision and life science systems. Cameras manufactured by Lumenera are highly recommended as they do not use optical low pass filters, and they contain resolving power that is much greater than high-resolution professional and consumer cameras.

This information has been sourced, reviewed and adapted from materials provided by Lumenera Corporation.

For more information on this source, please visit Lumenera Corporation.

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