An integral 3DTV system needs high-density elemental images to increase the reconstructed 3D image's resolution,
viewing zone, and depth representability. The dual green pixel-offset method, which uses two green
channels of images, is a means of achieving ultra high-resolution imagery. We propose a precise and easy method
for detecting the pixel-offset distance when a lens array is mounted in front of the integral imaging display. In
this method, pattern luminance distributions based on sinusoidal waves are displayed on each panel of green
channels. The difference between phases (amount of phase variation) of these patterns is conserved when the
patterns are sampled and transformed to a lower frequency by aliasing with the lens array. This allows the
pixel-offset distance of the display panel to be measured in a state of magnification. The relation between the
contrast and the amount of phase variation of the pattern is contradicted in relation to the pattern frequency.
We derived a way to find the optimal spatial frequency of the pattern by regarding the product of the contrast
and amount of phase variation of the patterns as an indicator of accuracy. We also evaluated the pixel-offset
detection method in an experiment with the developed display system. The results demonstrate that the resolution
characteristics of the projected image were refined. We believe that this method can be used to improve
the resolution characteristics of the depth direction of integral imaging.
We propose a method for measuring the multidirectional modulation transfer function (MTF) of digital image
acquisition devices using a Siemens star. There are two leading methods for measuring the MTF: the slanted-edge
method and the modulated Siemens star method. The former measures the MTF in the horizontal or vertical spatial
frequency based on the line spread function (LSF) derived from the edge profile of a slanted knife-edge image. The
latter measures the multidirectional MTF using a pattern circumferentially modulated with continuous gray levels. Our
method measures the multidirectional MTF using the multidirectional knife-edges of a Siemens star, which is a simple
binary image consisting of radial spokes. The vertical edge of the Siemens star is slightly slanted so that the
multidirectional edge profiles are obtained in super-resolution. A portion image consisting of the knife-edge is selected
in each direction and rotated so that the knife-edge stands upright with a slight tilt. Along the edge slope detected by
fitting a cumulative distribution function to the pixel levels, the pixels are projected onto the horizontal axis, forming the
edge profile. The resulting multidirectional MTF computed from the edge profiles is in excellent agreement with that
measured by the modulated Siemens star method.
Achieving ultimate visual realness of natural images on a display requires high resolution, so that artifacts due to finite
image resolution are undetectable. An image resolution of 30 cycles/degree (cpd) or one pixel/arc-minute is often used as
the criterion for viewing conditions when assessing displayed image quality. It is reasoned that if the pixel size is smaller
than the separable angle of normal vision (20/20), the pixel structure is invisible and doesn't negatively affect image
quality. However, it is not clear whether 30 cpd resolution is adequate to prevent seeing artifacts, especially for observers
with better than 20/20 vision. We conducted experiments to find the threshold resolution of natural images and its
dependence on visual acuity. Three objects were used; each object was presented 60 times at 5 resolutions (19.5, 26, 39,
52, or 78 cpd) next to the same image at a resolution of 156 cpd. Forty-five observers with visual acuity of 20/20 or
better were asked to make a forced-choice distinction between the image pair in regard to resolution. Each observer
indicated which image of the pair appeared at a higher resolution. The results show that the mean resolution for 75%
correct responses for each of the visual acuity groups increased from more than 30 cpd as visual acuity increased and
reached a plateau at 40-50 cpd at -0.3 logMAR.
Image resolution is one of the important factors for visual realness. We performed subjective assessments to examine
the realness of images at six different resolutions, ranging from 19.5 cpd (cycles per degree) to 156 cpd. A paired-comparison
procedure was used to quantify the realness of six images versus each other or versus the real object. Three
objects were used. Both real objects and images were viewed through a synopter, which removed horizontal disparity
and presented the same image to both eyes. Sixty-five observers were asked to choose the viewed image which was
closer to the real object and appeared to be there naturally for each pair of stimuli selected from the group of six images
and the real object. It was undisclosed to the observers that real objects were included in the stimuli. The paired
comparison data were analyzed using the Bradley-Terry model. The results indicated that realness of an image increased
as the image resolution increased up to about 40-50 cpd, which corresponded to the discrimination threshold calculated
based on the observers' visual acuity, and reached a plateau above this threshold.
We propose a system to calculate the spatial distortion in 3-D images based on the shooting, display, and viewing conditions. It can be used to predict the extent of the perceived puppet-theater effect and the cardboard effect. The magnitude of the spatial distortion and the extent of the puppet-theater and cardboard effects are displayed using a space grid whose size can be estimated based on the objects' depths, calculated from the binocular parallax of the acquired stereoscopic images. This system can also be used to predict excessive binocular parallax and excessive parallax distribution. Several cases in which puppet-theater and cardboard effects are expected to be produced are presented. We also demonstrate how the proposed system might be used to predict ratings of naturalness and quality of depth.
We are investigating psychological aspects to obtain guidelines for the design of TVs aimed at future high-presence broadcasting. In this study, we performed subjective assessment tests to examine the psychological effects of different combinations of viewing conditions obtained by varying the viewing distance, screen size, and picture resolution (between 4000 and 1000 scan lines). The evaluation images were presented in the form of two-minute programs comprising a sequence of 10 still images, and the test subjects were asked to complete a questionnaire consisting of 20 items relating to psychological effects such as "presence", "adverse effects", and "preferability". It was found that the test subjects reported a higher feeling of presence for 1000-line images when viewed around a distance of 1.5H (less than the standard viewing distance of 3H, which is recommended as a viewing distance for subjective evaluation of image quality for HDTV), and reported a higher feeling of presence for 4000-line images than for 1000-line images. The adverse effects such as "difficulty of viewing" did not differ significantly with resolution, but were evaluated to be lower as the viewing distance increased and tended to saturate at viewing distances above 2H. The viewing conditions were evaluated as being more preferable as the screen size increased, showing that it is possible to broadcast comfortable high-presence pictures using high-resolution large-screen displays.