Approaches to control the moiré effect are discussed. To improve the image quality, especially in the autostereoscopic three-dimensional displays, the minimization of the moiré effect is considered, including the minimization by angle, by period, by distance, etc. Also, less known nontraditional but effective approaches, such as spectral trajectories, statistical treatment, convolution-based minimization, and the amplitude of the moiré patterns, are at issue. On the other hand, the maximum moiré can be useful in displays. A proposed “2.5-D” display represents a new type of displays, the displays based on the moiré effect as on the main physical principle. As of today, binary black-and-white images are displayed, but this is not a principal limit and color imaging is also possible. A positive usage of the moiré effect to show images instead of its removal may be considered as an approach in displaying.
The tutorial describes essential features of moiré patterns, as well as the circumstances, when the moiré patterns appear and how to estimate their characteristics (parameters) such as the orientation and period. The moiré effect is described in two domains, the image space (spatial domain) and in the spectral domain using the complex numbers. The tutorial covers the indicial equation method, the coplanar and noncoplanar sinusoidal gratings, the moiré effect in a spatial object (a cylinder), as well as explains the moiré wave vector, the moiré spectra, the spectral trajectories, and summarizes behavior of the visible patterns in moved/rotated gratings.
The moiré effect is an optical phenomenon which has a negative influence to the image quality; as such, this effect should be avoided or minimized in displays, especially in autostereoscoipic three-dimensional ones. The structure of the multiview autostereoscoipic displays typically includes two parallel layers with an integer ratio between the cell sizes. In order to provide the minimization of the moiré effect at finite distances, we developed a theory and computer simulation tool which simulates the behavior of the visible moiré waves in a range of parameters (the displacement of an observer, the distance to the screen and the like). Previously, we have made simulation for the sinusoidal waves; however this was not enough to simulate all real-life situations. Recently, the theory was improved and the non-sinusoidal gratings are currently included as well. Correspondingly, the simulation tool is essentially updated. In simulation, parameters of the resulting moiré waves are measured semi-automatically. The advanced theory accompanied by renewed simulation tool ensures the minimization and make it convenient. The tool run in two modes, overview and detailed, and can be controlled in an interactive manner. The computer simulation and physical experiment confirm the theory. The typical normalized RMS deviation is 3 - 5%.
The quality of visual image in an autostereoscopic 3D display was found for case of multiple observer regions. This was
made in the projective coordinates for which the forward and backward transformation matrices were found. It was
demonstrated that the quality is kept along the nodal lines in all regions as well as between them. The distinctive
locations were found together with the exact values of the quality function in these points. This allows estimating the
behavior of the quality function for bigger number of views and image cells as well as across the longer and wider area.
A two dimensional quality function which counts both the number of mixed view images and disparity between images
is derived based on the one dimension quality function which counts the number of mixed view images in multiview 3
dimensional imaging systems. This function predicts the quality of images with reasonable accuracy. This is proved
experimentally.
A two-dimensional light-emitting diode array is used to replace the viewing-zone-forming optics in-multiview full-parallax three-dimensional image display systems. Since the array is not working merely as the viewing-zone-forming optics but also as the backlight panel for the liquid-crystal display (LCD) panel, it allows constructing three-dimensional imaging systems having the same structure as the current LCD display. The designed system displays images with good depth sense.
A mobile phone (Hand Phone) is designed to display stereo images taken from a camera attached to it. Software of processing a stereo image pair to be displayed on the display panel of the phone is developed and a detachable viewing zone forming optics is installed for the stereoscopic image generation without moires. Since the phone is operating only in the palm of the phone's owner, special cares needed in photographing the image pair are described.
The methods of presenting multiview images, such as IP, the Multiview, Multiple Imaging and Focused light array are reviewed and their image forming principles were compared. These methods have their own ways of presenting multiview images but the images projected to viewer's eyes are mostly synthesized by the small part of each view image in the different view images presented to the viewers. This is a common property for all those methods.
In autostereoscopic display systems which are based on lenticular, barrier, and lens array plates, the quality of perceived images is different in different regions of the viewing zone. In these systems, a visual image is a composition of several view images which depends on the current observer position. A quantification of the visual quality is suggested basing on the inverse number of different view images involved in a composed visual image. This definition of the quality can only be applied directly to the monoscopic seeing. A new method to estimate the quality value for binocular seeing is therefore devised. It is based on the mapping of different regions of the viewing zone onto a uniform map. The map is scanned by virtual probes "equipped" with single/dual sensors expressing observer's eyes for mono/stereo seeing. The virtual readings of both type probes can be represented in a matrix form giving very similar values for both cases. We found a generalized analytical solution which estimates the image quality as a coordinate-dependent function for both, monoscopic and stereoscopic cases. The generalized solution does not depend on the individual interocular distance.
Moire patterns originated from overlapping display panel with the viewing zone forming optics are one of major factors of deteriorating the visual image quality of contact-type 3 dimensional imaging systems. An analysis showed that the visual effects of the patterns can be minimized at a specific overlapping angle between the panel and the plate. This angle is implemented by approximating each side of a pixel cell as a discrete line which is drawn along the boundaries of each pixel which lies along the side of the cell. The slope of the line is presented by as the ratio of pixel numbers in vertical and horizontal directions and equals to the tangential value of 1/2 of the angle. This method allows creating pixel cells with shapes of parallelograms and rhombs with a desired vertex angle for minimizing the moire pattern, especially in full-parallax imaging systems. The image generated reveals almost invisible moire pattern at the predefined viewing distance range.
Moiré fringes appearing in contact-type three-dimensional imaging systems cause serious image quality deterioration. The fringes are inevitable because the systems require overlapping a viewing-zone-forming optical plate on a display panel. An analysis shows that the visual effects of the fringes can be minimized by finding a proper overlapping angle between the panel and the plate. This angle imposes that pixel cell in full-parallax imaging systems should have the shape of either rhombus or parallelogram with a specific vertex angle. The pixel cell with the shape of the rhombus or parallelogram is implemented by approximating the boundaries of each pixel cell by staircase lines drawn along sides of the pixel. The slopes of the lines are determined by the ratio of the pixel numbers in the vertical and horizontal directions. This method allows creating pixel cells with a desired vertex angle for minimizing the moiré fringes, especially in full-parallax imaging systems.
Moire fringes appearing in multiview full-parallax 3 dimensional imaging systems can be minimized by proper selection of the vertex angle of pixel cells. Pixel cells with arbitrary vertex angles are built by crossing a pair of discrete line arrays with gradients ± α. The discrete lines are form by the sides of pixels along the straight lines approximating the discrete lines. The gradient of the lines is defined as the ratio between pixel numbers in vertical and horizontal directions. This method allows creating rhomb approximating pixel cells with a desired shape.
In autostereoscopic imaging systems using lenticular, parallax barrier and integral photography plates as the viewing zone forming optics, the quality of the perceived image is different for different part of the viewing zone because of different view image mixing. The image quality is quantified by the number of different view images viewed simultaneously along the viewing axis. The image quality decreases as the viewing distance increases.
Voxel is a basic picture element for composing 3D images. Since the generation of each voxel involves at least four pixels from four different view images for the case of full parallax 3D images, any voxel can be generated if the pixel pattern can be found. To find the pixel pattern, a set of voxels with known coordinated values are created by an optical geometry of the point light source array based 3D imaging system. This geometry provides that voxels aligned in planes parallel to the point light source array plane. The pixel pattern corresponding to each voxel is determined as the passage of seeing the point light sources related with the voxel, in the viewing zone. The resulting pixel patterns creates a good 3D image.
Characteristics and two building methods of diamond shaped pixel cell are introduced. It can provide wider horizontal direction size of viewing zone compared with its corresponding square or rectangular pixel cell and reduce the pseudoscopic effect. The two building methods are named as integer and non-integer depending on the number of different view pixels involved with the pixel cell. The full parallax images generated by these two methods shows that the integer method provides better image quality than the non-integer.
There are several ways of processing Images from multiview cameras for full parallax image generation. Among them, the most used one is laying the images as a rectangular shape pixel cell on the image display panel. However, it cannot maximize the stereoscopic effect and viewing zone size in horizontal direction with a given full parallax image set. A diamond shape pixel cells can maximize the stereoscopic effect and the viewing zone size in vertical direction. The sequence of making the diamond shape pixel cell includes two rotations of a multiview image with the rectangular pixel cell in opposite to each other with the same angle.
In designing an autostereoscopic imaging system, the parameters related with viewing zone are the main to be determined first for the system. The viewing zone is a spatial region where viewers can perceive stereoscopic image through the image displayed on the screen of the system. To define the viewing zone parameters such as width, distance from the image screen, depth range, and shape, an optical configuration composed of an image mask aligned on the top of a point light source array is used. This configuration shows that a lenticular or a parallax barrier plate is just doing the same role as the array and the obtainable image depth is related with the viewing zone parameters.
Adopting a pixel cell plate designed by use of geometrical optics, a full parallax imaging is realized. The pixel cell plate is consisted of 2-dimensional array of pixel cells which are made of the same number pixels in each image of a N X N multiview image array.
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