We compare two different modes of interaction with a large stereoscopic display, where the physical pointing device is
in a volume distinct from the display volume. In absolute mode, the physical pointer's position exactly maps to the
virtual pointer's position in the display volume, analogous to a 2D graphics table and 2D screen. In relative mode, the
connection between the physical pointer's motion and the motion of the virtual pointer in the display volume is analogous
to that obtained with a 2D mouse and 2D screen. Both statistical analysis and participants' feedback indicated a strong
preference for absolute mode over relative mode. This is in contrast to 2D displays where relative mode (mouse) is far
more prevalent than absolute mode (tablet). We also compared head-tracking against no head-tracking. There was no
statistically-significant advantage to using head-tracking, however almost all participants strongly favoured head-tracking.
We integrate stylized rendering with an efficient multiresolution
image representation, enabling a user to control how
compression affects the aesthetic appearance of an image. We
adopt a point-based rendering approach to progressive image transmission
and compression. We use a novel, adaptive farthest point
sampling algorithm to represent the image at progressive levels of
detail, balancing global coverage with local precision. A progressively
generated discrete Voronoi diagram forms the common foundation
for our sampling and rendering framework. This framework
allows us to extend traditional photorealistic methods of image reconstruction
by scattered data interpolation to encompass nonphotorealistic
rendering. It supports a wide variety of artistic rendering
styles based on geometric subdivision or parametric procedural textures.
Genetic programming enables the user to create original rendering
styles through interactive evolution by aesthetic selection.
We compare our results with conventional compression, and we
discuss the implications of using nonphotorealistic representations
for highly compressed imagery.
We apply two recent non-linear, image-processing algorithms to colour image compression. The two algorithms are
colorization and joint bilateral filtering. Neither algorithm was designed for image compression. Our investigations
were to ascertain whether their mechanisms could be used to improve the image compression rate for the same level of
visual quality. Both show interesting behaviour, with the second showing a visible improvement in visual quality, over
JPEG, at the same compression rate. In both cases, we store luminance as a standard, lossily compressed, greyscale
image and store colour at a very low sampling rate. Each of the non-linear algorithms then uses the information from the
luminance channel to determine how to propagate the colour information appropriately to reconstruct a full colour
image.
A head-tracked display could be made from a two-view autostereoscopic display where head-tracking allows the display to swap the two views when the eyes move from viewing zone to viewing zone. Variations in human interpupillary distance mean that this basic two-view version will not work well for the significant minority of the population who have interpupillary distance significantly different from the average. Woodgate et al. proposed, in 1997, that a three-view system would work well. Analysis of an ideal version of their proposal shows that it does work well for the vast majority of the population. However, most multi-view, multi-lobe autostereoscopic displays have drawbacks which mean that, in practice, such a system would be unacceptable because of the inter-view dark zones generated by the inter-pixel dark zones on the underlying display technology. Variations of such displays have been developed which remove the inter-view dark zones by allowing adjacent views to overlap with one another: the views appear to smoothly blend from one to the next at the expense of a little blurring. Such displays need at least five viewing zones to accommodate the majority of the adult population with head-tracking and at least six viewing zones to accommodate everyone.
By integrating stylized rendering with an efficient multiresolution image representation, we enable the user to control how compression affects the aesthetic appearance of an image. Adopting a point-based rendering approach to progressive image transmission and compression, we represent an image by a sequence of color values. To best approximate the image at progressive levels of detail, a novel, adaptive farthest point sampling algorithm balances global coverage with local precision. Without storing any spatial information apart from the aspect ratio, the spatial position of each color value is inferred from the preceding members of the sampling sequence. Keeping track of the spatial influence of each sample on the rendition, a progressively generated discrete Voronoi diagram forms the common foundation for our sampling and rendering framework. This framework allows us to extend traditional photorealistic methods of image reconstruction by scattered data interpolation to encompass non-photorealistic rendering. It supports a wide variety of artistic rendering styles based on geometric subdivision or parametric procedural textures. Genetic programming enables the user to create original rendering styles through interactive evolution by aesthetic selection. Comparing our results with JPEG, we conclude with a brief overview of the implications of using non-photorealistic representations for highly compressed imagery.
Histogram warping is a novel histogram specification technique for use in color image processing. As a general purpose tool for color correction, our technique constructs a global color mapping function in order to transform the colors of a source image to match a target color distribution to any desired degree of accuracy. To reduce the risk of color distortion, the transformation takes place in an image dependent color space, featuring perceptually uniform color axes with statistically independent chromatic components. Eliminating the coherence between the color axes enables the transformation to operate independently on each color axis. Deforming the source color distribution to reproduce the dominant color features of the target distribution, the histogram warping process is controlled by designating the color shifts and contrast adjustments for a set of key colors. Assisted by mode detection, matching quantiles establish the correspondence between the color distributions. Interpolation by monotonic splines serves to extend the mapping over the entire dynamic range without introducing artificial discontinuities into the resulting color density. We show how our method can be applied to color histogram equalization as well as color transfer from an example image or a color palette.
Mean interpupillary distance (IPD) is an important and oft-quoted measure in stereoscopic work. However, there is startlingly little agreement on what it should be. Mean IPD has been quoted in the stereoscopic literature as being anything from 58 mm to 70 mm. It is known to vary with respect to age, gender and race. Furthermore, the stereoscopic industry requires information on not just mean IPD, but also its variance and its extrema, because our products need to be able to cope with all possible users, including those with the smallest and largest IPDs. This paper brings together those statistics on IPD which are available. The key results are that mean adult IPD is around 63 mm, the vast majority of adults have IPDs in the range 50-75 mm, the wider range of 45-80 mm is likely to include (almost) all adults, and the minimum IPD for children (down to five years old) is around 40 mm.
The viewing zone of a multi-view autostereoscopic display can be shown to be completely determined by four parameters: the width of the screen, the optimal distance of the viewer from the screen, the width over which an image can be seen across the whole screen at this optimal distance (the eye box width), and the number of views. A multi-view display's viewing zone can thus be completely described without reference to the internal implementation of the device. These results can be used to determine what can be seen from any position in front of the display. This paper presents a summary of the equations derived in an earlier paper. These equations allow us to analyze an autostereoscopic display, as specified by the above parameters. We build on this work by using the derived equations to analyze the configurations of the extant models of the Cambridge autostereoscopic display: 10' 8- and 16-view, 25' 28-view, 50' 15-view displays and an experimental 25' 7-view display.
Multi-view auto-stereoscopic images and image sequences require large amounts of space for storage and large bandwidth for transmission. High bandwidth can be tolerated for certain applications where the image source and display are close together but, for long distance or broadcast, compression of information is essential. We report on the results of our two- year investigation into multi-view image compression. We present results based on four techniques: differential pulse code modulation (DPCM), disparity estimation, three- dimensional discrete cosine transform (3D-DCT), and principal component analysis (PCA). Our work on DPCM investigated the best predictors to use for predicting a given pixel. Our results show that, for a given pixel, it is generally the nearby pixels within a view that provide better prediction than the corresponding pixel values in adjacent views. This led to investigations into disparity estimation. We use both correlation and least-square error measures to estimate disparity. Both perform equally well. Combining this with DPCM led to a novel method of encoding, which improved the compression ratios by a significant factor. The 3D-DCT has been shown to be a useful compression tool, with compression schemes based on ideas from the two-dimensional JPEG standard proving effective. An alternative to 3D-DCT is PCA. This has proved to be less effective than the other compression methods investigated.
This paper describes Litton's time-multiplexed 3-D display technology, which allows groups of viewers to see full stereo with kineopsis (lookaround capability) without using any eye or head gear. We detail the construction of our latest 50'- screen prototype, which is brighter and has higher resolution than our 25'-prototype presented previously. The time- multiplexed concept allows the sequential projection of narrow strips of images into the viewer space and provides realistic movement parallax in a horizontal plane with full autostereoscopic images. The time-multiplexed nature allows full-screen resolution for each view and shared components for the optical trains. Our latest prototype, configured for entertainment applications, replaces our previous color sequential system with separate red, green, and blue CRTs for a brighter image [up to 120 foot-Lamberts (fL)] with much better color saturation. A new optical layout uses dichroics and beamsplitters to avoid the need for coatings with sharp cut-off frequencies, and a concave-mirror screen provides better image sharpness. We can also provide up to fifteen views in each eyebox without tube-abutment seams. Improved electronic performance provides capability of 30 frames-per- seconds interlaced at 640 by 480 pixel resolution. Special picture-shape correction circuitry has been added for a rectangular image-frame, despite a light path skewed out-of- plane.
We describe the development and construction of a large screen version of the Cambridge time-multiplexed autostereo display. The new device uses a 50 inch diagonal spherical mirror in place of the 10 inch Fresnel lens of the original Cambridge color display. A fivefold increase in image luminance has been achieved by the replacement of sequential color on a single CRT with separate red, green, and blue CRTs. Fifteen views are displayed at 640 X 480 (VGA) resolution with about 250 cd/m2 luminance and 30 Hz interlaced refresh rate. A 22 mm interview separation provides three views between a typical viewer's eyes, giving a smooth stereoscopic effect over a 330 mm wide eye box. Two identical optical systems have been built, allowing simultaneous use of the device by two viewers. The two system are off-axis with respect to the main mirror, requiring geometric compensation on the CRTs in addition to the normal color convergence. The prototype produces two independent full color, large 3D images which can be viewed under normal lighting conditions.
Image compression for multi-view autostereoscopic displays is one of the major governing factors for the development and acceptance of 3D technology. For example: the multi-view autostereo display developed at Cambridge uses between six and twenty-eight distinct views of the scene, each view being a complete image of the scene taken from a particular view point. Therefore it is of prime importance to use compression methods that would exploit the redundancy present in the view- point direction to allow for 3D image communication since the images require a very high bandwidth for transmission and a large amount of space for storage. In this paper an initial investigation on how the third dimension can be utilized is presented. Entropy measures for multi-view images are derived. It is shown that exploiting the similarities between views can give lower entropy, indicating higher compression rates. The parallel axes geometry of the cameras used for the autostereo display produces only horizontal shifts between stereo images, therefore investigation in using hierarchical row decomposition along with correlation and mean squared error measures for estimating disparity shifts and reducing search spaces respectively are presented.
An imaging system has been demonstrated which captures a 3D scene with six parallax images using only one stationary CCD. The parallax effect is achieved either by imaging through a pinhole which is translated in front of the CCD or by imaging through a solid-state ferroelectric shutter which simulates a translatable pinhole. A single set of six compatible images is referred to as a single autostereoscopic image; the images so captured are presented on an autostereoscopic display. An autostereoscopic display system provides the perception of depth by presenting several images on the display over a range of viewing angles. When viewed at the correct distance from the display, a different image is perceived by each eye. With suitable images, this results in the illusion of depth without using stereoscopic eyewear. Improvements in the imaging/display rate and miniaturization of the camera assembly will produce a system compatible with use in laparoscopic surgery.
When rendering or capturing stereoscopic images, two arrangements of the cameras are possible: radial (`toed-in') and parallel. In the radial case all of the cameras' axes pass through a common point; in the parallel case these axes are parallel to one another. The radial configuration causes distortions in the viewed stereoscopic image, manifest as vertical misalignments between parts of the images seen by the viewer's two eyes. The parallel case does not suffer from this distortion, and is thus considered to be the more correct method of capturing stereoscopic imagery. The radial case is, however, simpler to implement than the parallel: standard cameras or renderers can be used with no modification. In the parallel case special lens arrangements or modified rendering software is required. If a pinhole camera is assumed it should be readily apparent that the same light rays pass through the pinhole in the same directions whether the camera is aligned radially to or parallel to the other cameras. The difference lies in how these light rays are sampled to produce an image. In the case of a non-pinhole (real) camera, objects in focus should behave as for the pinhole case, while objects out of focus may behave slightly differently. The geometry of both radial and parallel cases is described and it is shown how a geometrical transform of an image produced in one case can be used to generate the image which would have been produced in the other case. This geometric transform is achieved by a resampling operation and various resampling algorithms are discussed. The resampling process can result in a degradation in the quality of the image. An indication of the type and severity of this degradation is given.
KEYWORDS: Cameras, Video, Multiplexers, Imaging systems, 3D displays, 3D video streaming, Multiplexing, 3D image processing, Clocks, Autostereoscopic displays
A camera system has been developed to provide live 3D video input for a time-multiplexed autostereoscopic display. The system is capable of taking video input from up to sixteen sources and multiplexing these into a single video output stream with a pixel rate an order of magnitude faster than the individual input streams. Both monochrome and color versions of the system have been built. Testing of the system with eight cameras and a Cambridge autostereo display has produced excellent live autostereoscopic video. The basic operation of the camera system is to digitize multiple input video streams, one for each view direction, and to multiplex these into a single autostereoscopic video stream. A simple circuit boards (the camera board) can digitize, process and buffer the video input from a single video source. Several of these are connected together via a backplane to another circuit board (the multiplexer board) which contains all the circuitry necessary for generating the output video and synchronization signals and for controlling the rest of the system. Alignment and synchronization were two major challenges in the design of the system. Pixel-level control of camera alignment is provided by an image processing chip on each camera board, while synchronization is provided by a number of carefully designed control mechanisms.
A practical color autostereoscopic display has been developed at Cambridge, and has been in operation since 1994. It provides six view directions at half VGA resolution (640 X 240 pixels) of 24-bit color at a luminance of 100 cd/m2. Each individual view direction is refreshed at standard television rates, so the display is capable of full motion animation or live 3D video. Versions with both 10 and 25 inch screen diagonal have been built. This paper describes the principles of the display, its development from an earlier monochrome version, the results of this development work, and ideas for future research. The original monochrome display, developed at Cambridge, has been in use since late 1991. It provides eight views at full VGA resolution or sixteen views at half VGA resolution. A series of views of a scene are displayed sequentially and an optical directional modulator, constructed from a liquid crystal shutting element, is synchronized with the image repetition rate to direct each image to a different zone in front of the display. The viewer's eyes thus see two different images and the head can be moved from side to side to look around objects, giving an autostereoscopic display with correct movement parallax. The use of a CRT makes for a flexible system where resolution and number of views can be easily varied. Development of the color display from the monochrome version was achieved by a color sequential system using a liquid crystal color shutter. As each view direction had to be displayed three times for the three primary colors, the maximum number of view directions was decreased to six. Full color (24-bit) images have been displayed on these six view autostereoscopic displays from a number of sources: computer generated images, digitized photographs, and live color video from a multiplexed camera also designed at Cambridge.
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