In recent years, along with the higher luminance of LED light sources, fluorescent lamps, incandescent bulbs, and other light sources used in illumination lights, headlights of automobile, signal lights, etc. up until now have been gradually replaced by LEDs. When further increasing the luminance and light emission efficiency of LEDs in the future, it is predicted that all types of surrounding light sources will be replaced by LEDs.
On the other hand, considering this future situation, there has been attempted to utilize these LED light sources not only for merely illumination light or merely alarm light, but also as high speed communicating means ranking with wireless communications etc. Researches etc. are being conducted to develop optical wireless use high speed vision chips which are light receiving devices assuming such communicating means. Further, visible ray communication consortiums etc. aimed at the spread of these communication systems have been already formed.
Further, camera systems and applications, using blinking of such LEDs for communications, have been proposed (see for example Patent Document 1). This relates to a camera system. This camera system has the function of acquiring an ordinary image and discriminating a blinking pattern of the LEDs and other light sources, which is coded according some sort of information. When such light sources are set as a variety of objects in real space, it becomes possible to simultaneously acquire images of those objects and information accompanying those.
A variety of applications can be considered for such a system. For example, by emitting a network ID as the information, it is possible to form a means for establishing a communication connection between the object and a terminal mounting a camera thereon and to utilize the same in a navigation system providing positional information, advertising means. etc.
As an imaging means for realizing such a camera system, there is one holding frame memories and comparators within the pixels composing an image sensor. This imaging element has the function of outputting an increase/decrease of light intensity over time as binary data by comparing the light received in a certain frame period with signal information of a previous frame stored in the frame memory for each pixel. When using this function, highly efficient detection of a blinking signal of a light source such as the above application becomes possible.
Patent Document 1: Japanese Patent Publication (A) No. 2001-292379 (page 5, FIG. 1)