1.  Field
Example embodiments relate to two dimensional (2D)/three dimensional (3D) switchable integral imaging systems capable of displaying 3D images and/or 2D images. 
2.  Description of the Related Art
Recently, stereoscopic image display apparatuses may have been used in various fields such as medical imaging, games, advertisements, education, military applications, etc.  Methods of displaying stereoscopic images such as holographic methods, stereoscopic methods, integral imaging methods, and so forth may be being researched. 
In holographic methods, when a light beam is illuminated onto a hologram, the observer who is in front of the hologram at a predetermined distance from the hologram may see a virtual three dimensional (3D) image.  In holographic methods, by seeing a hologram manufactured using a coherent light source such as a laser, a virtual stereoscopic image, that may look the same as an actual object, may be seen without using special glasses.  Thus, holographic methods may be regarded as ideal in that a good 3D effect may be obtained and/or a 3D image may be seen without fatigue.  However, holographic methods may use a coherent light source and/or may have difficulty in realizing a large object located at a long distance.  Also, due to the large amount of data involved, it may be difficult to transmit and/or reproduce images in real-time using holographic methods.  Thus, practical applications of holographic methods may be limited. 
In stereoscopic methods, two separate two dimensional (2D) images may be respectively shown to the eyes of a person in order to obtain a 3D effect.  In stereoscopic methods, two plane images may be used and, thus, a 3D image having high resolution and/or a large depth may be displayed.  Stereoscopic methods may be classified into glasses-type methods, in which polarization and/or a shutter may be used in order to see the images separated for each eye, and non-glasses-type methods, in which images may be separated directly on a display unit in order to create a viewing zone.  Examples of the non-glasses-type display methods may include parallel-barrier-type display methods and/or lenticular-type display methods. 
In stereoscopic methods, systems may be constructed using a flat panel display and/or relatively simple optical components.  Thus, slim 3D displays may be realized.  However, since left and right images may be formed on one screen, the resolution of the images may be reduced by a half or more, and/or visual fatigue may be generated due to a difference in parallax between the two images shown to the eyes of a person and the focusing capability of the person.  Thus, it may be difficult to see a 2D image due to the structure of the system using stereoscopic methods. 
In integral imaging methods, image information that is transmitted from an object using a lens array may be stored as an integral image that includes a number of unit images, and/or the integral image may be reconstructed using a lens array to reproduce the whole information of the object.  Integral imaging methods may have been suggested by Lippmann in 1908.  However, integral imaging methods may not have been observed much in the past due to limitations in imaging devices and/or display devices, but may have been researched more recently with the development of high resolution imaging devices and/or high resolution displays.  Integral imaging devices may not require glasses and/or other elements in order to observe a stereo image, and/or may provide continuous horizontal and/or vertical parallax not only at a viewpoint (that may or may not be predetermined), but within a viewing angle (that may or may not be predetermined).  Thus, an image may be continuously realized without visual fatigue.  Thus, integral imaging methods may be being researched more in recent times. 
However, since a lens array having a fixed focal point may be used in integral imaging methods, image information obtained from an object may be distorted according to positions and may be recorded in that manner, so integral imaging methods may only be used to display 3D images.