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— Presentation at IWISS2016 —
January 12, 2017
3rd International Workshop on Image Sensors and Imaging (IWISS2016) was held in Tokyo Institute of Technology, Tamachi Campus from 17th to 18th in November, 2016. In this workshop, people from various research fields, such as image sensing, imaging systems, optics, and image processing, came together to discuss the future and frontiers of image sensor technologies. This symposium was composed of 18 invited talks and 20 poster presentation. At this symposium, Hitachi, Ltd. made a poster presentation titled "Lensless Light-field Imaging with Fresnel Zone Aperture", and a real-time imaging demonstration with a newly developed prototype.
Fig. 1 System of newly developed
lensless camera technology
Hitachi has developed a camera technology that can capture video images without using a lens and adjust focus after image capture by using a film imprinted with a concentric-circle pattern (Fresnel Zone Aperture, FZA) instead of a lens (Figure 1). This camera technology makes it possible to make a camera lighter and thinner since a lens is unnecessary and allow the camera to be more freely mounted in devices such as mobile devices and robots at arbitrary positions without imposing design restraints. Moreover, since it acquires depth information in addition to planar information, it is possible to reproduce an image at an arbitrary point of focus even after the image has been captured.
In the other research, a lensless camera which is thin and light because it has no lens has been developed. Even so, processing of images captured by the camera incurs a heavy computational load. Aiming to overcome the difficulties, Hitachi has developed a camera technology—based on the principle of Moiré fringes—that a film patterned with FZA (whose interval narrow toward the edge of the film) is positioned in front of an image sensor, and the image of a shadow formed by a light beam irradiated onto the film is captured by the image sensor. During the image processing, a virtual FZA is superimposed on the shadow and Moiré fringes with spacing dependent on the incidence angle of a light beam are formed. By utilizing the Moiré fringes, it is possible to capture images by simple and commonly used image processing called "Fourier transform" (Figure 2). This method enables the computational load incurred by image processing to be reduced to 1/300. To measure the performance of the developed technology, an experiment with a 1-cm2 image sensor and a film imprinted with a FZA positioned 1 mm from the sensor was conducted. The results of the experiment confirmed that video images could be captured at 30 frames per second when a standard laptop computer was used for image processing (Figure 3).
Photo 1 Presentation scene
Hitachi has made a press release of this camera technology on November 15th before the symposium, as the result, many people attended the symposium (Photo 1). We have had fruitful discussions with the many attendees and received the Best Poster Award. As a future work, we will study to improve the quality of the image and put it to practical use.
(By NAKAMURA Yusuke)