Digital focusing and re-focusing with thin multi-aperture cameras

For small camera modules in consumer applications, such as mobile phones or webcams, size and cost are important constraints. An autofocus system increases both size and cost and can degrade optical performance by misalignment. Therefore, a monolithic optical system with a fixed focus is preferable for these applications. On the other hand, the optical system of the camera has to exhibit a very large depth of field, as it is expected to deliver sharp images for all typical working distances. The depth of field of a camera system can be increased by using a larger F-number, but this is undesirable due to light sensitivity considerations. On the other hand, it can also be increased by reducing focal length. Multi-aperture systems use multiple optical channels, each of them with a smaller focal length than a comparable single-aperture system. Accordingly, each of the channels has a large depth of field. However, as the channels are displaced laterally, parallax becomes noticeable for close objects. Therefore, the channel images have to be shifted accordingly when recombining them into a complete image. We demonstrate an algorithm that compensates for parallax as well as chromatic aberration and geometric distortion. We present a very flat camera system without moving parts that is capable of taking photos and video at a wide range of distances. On the demonstration system, object distance can be adjusted in real time from 4 mm to infinity. The focus position can be selected during capture or after the images were taken