We are researching a form of spatial imaging technology, called the integral method, as a way of creating a more natural and viewable 3D television that does not require special glasses. In FY 2013, we studied ways to improve the quality of 3D images and their reproduction.
■ Increasing 3D image quality
Generating high-quality 3D images using the integral method requires many more pixels than for ordinary 2D imaging, both for capture and display. We studied ways to make 3D images with more pixels by using multiple imaging devices. For capture, we used two sets of an image sensor and a lens array. This structure, however, suffers from a loss of information and a difference in luminance level between image sensors. To solve this problem, we interpolated the missing information and reduced the luminance level difference. Thus, we were able to use a large number of pixels, two image sensors worth, to make 3D images (1). For the display, we prototyped equipment consisting of four projectors (Figure 1). We found that we could expand the viewing zone (the areas in which the 3D image can be viewed) by a factor of 2.5 in the horizontal direction and 2.0 in the vertical direction, by using projective and affine transformations to correct the distortion in the images from each projector (2).
Part of this research was conducted under contract with the Ministry of Internal Affairs and Communications for its project titled, “R&D on spatial information acquisition system using multiple image sensors.”
Figure 1. Integral display equipment using four projectors
■ Reproduction quality of 3D images
We have been studying the quality of 3D images reproduced using the integral method since FY 2012. The integral method reproduces the light rays from an object and forms the equivalent 3D image in the air near the viewer. It is expected to have the advantage of not straining the viewers’ eyes, because the ocular accommodation of viewing such a 3D image is said to be at the same depth as when one observes the actual object.
In FY 2012, we measured the ocular accommodation response when viewing integral 3D images with both eyes in order to verify the relation between the accommodation position and the image’s depth. The results showed that the accommodation conforms to the depth of the 3D image. Meanwhile, the accommodation is directed to the point of regard by moving the right and left eyeballs. To eliminate this factor, we measured the accommodation response in viewing integral 3D images with a single eye in FY 2013. The results confirmed that the accommodation has a tendency to conform to the image’s depth position even with monocular vision (3).
To evaluate the reproduction quality of 3D images against the display parameters of the integral method, we conducted subjective evaluations on image quality versus the depth of the image by using the pixel pitch of an image displayed by a lens array as a parameter. The experiment provided us with enough data to derive the relation between the pixel pitch and the reproduction range of the depth. We plan to conduct evaluations with a wider range of parameters to further study the relationship between pixel pitch and the reproduction range of the depth.
We began a study on coding technologies for the integral method in FY 2013 and decided to participate in the standardization activities of the MPEG-FTV ad hoc group, which studies the integral method’s coding and other subjects.
(1) H. Hiura, T. Yamashita, J. Arai: “The Expansion of the Capturing Area for Integral Imaging using Two Imaging Units,” ITE Technical Report, Vol. 38, No. 11, pp. 27-30 (2014) (in Japanese)
(2) N. Okaichi, H. Hiura, M. Miura, J. Arai: “Integral 3D display with multi-projection system using distortion compensation,” ITE Annual Convention 2013, p.11-5 (2013) (in Japanese)
(3) H. Hiura，T. Mishina，J. Arai, Y. Iwadate: “Accommodation response measurements for integral 3D image,” Proc. SPIE, Vol. 9011, 9011-48 (2014)