Analglyphic representations of image and elevation data

Details Analglyphic representations of image and elevation data Analglyphic representations of image and elevation data

1999-07-06

2002-12-03

Saras, Steven (Department: 2675)

Computer graphics processing and selective visual display system

Computer graphics processing

Three-dimension

C345S008000

Reexamination Certificate

active

06489962

ABSTRACT:

BACKGROUND OF THE INVENTION
(1) Field of the Invention
This invention relates to the fields of digital image processing and more particularly to the creation and presentation of three-dimensional (3-D) images on a two dimensional viewing surface.
(2) Description of the Related Art
Since the invention of the stereoscope in the mid 1800s, there have been many successful attempts to make full use of human binocular vision's ability to combine two separate images, one each obtained by each eye viewing the same scene from slightly different angles, into one image which is perceived as having depth. The mechanics by which the human brain combines two flat images into one image producing the sensation of a three dimensional world is not fully understood. However, many techniques have been developed which deliver, by way of differing processes, slightly different two dimensional images to each eye so as to produce in the brain a perception indistinguishable from that obtained by actually viewing the three dimensional world. These techniques belong generally to two major classes, specifically the autostereoscopic imaging class which produces 3-D images viewable by the unaided eye, and the binocular stereoscopic imaging class which produces 3-D images requiring observers to wear spectacles or viewers. Techniques of the later class can be found in 3-D movies of the 1950s and in recent images returned from the surface of Mars.
Early stereoscopes commonly utilized a specialized device into which was inserted an image comprised of two nearly identical but separate images reproduced side-by-side. Each separate image was created by photographing a scene from one of two slightly different angles. When viewed through the stereoscope, each eye was constrained so as to see only one of the images and the perception of three dimensions was achieved. While this sort of stereoscope does allow for each separate image to be viewed in color and with minimal distortion of the original scene, it possesses the drawback of requiring apparatus to properly constrain each eye's field of vision and, by so doing, the ability of the viewer to move closer or further, up or down, right or left about the image is severely restricted. Anaglyphs, while generally restricting the creation of 3-D images to those comprised of varying shades of gray, provide the advantage of requiring less obtrusive apparatus for viewing, consist of only one image to be viewed as opposed to two images placed side by side, and allow the viewer to move freely about the image.
An anaglyph is defined as a composite picture printed in two colors that produces a three-dimensional image when viewed through spectacles having lenses of corresponding colors. The best results are obtained when the colors (or, more precisely, hues) used to produce the anaglyph represent orthogonal hues. That is to say, a change in the intensity of one of the hues present at any point on the image does not affect the intensity of the other hue. One typical choice of hues used to produce anaglyphs is that of red and cyan. When a red image is combined with a slightly different cyan image and viewed through glasses having one lens filtering out all but the cyan light and the other lens filtering out all but the red light, the perception of 3-D is accomplished. Because the filters allow only light of one particular wavelength to pass through, the anaglyph is effectively split into two images with each eye seeing a scene depicting the original scene as viewed from one of two slightly different angles.
Barring occlusion, each picture element (hereinafter “pixel”) is represented twice in the anaglyph, once in cyan and once in red. The horizontal distance separating the two pixels of differing hue, each of which represents the same pixel in the original image, determines the extent to which the pixel appears in front of or behind the image plane. The “image plane” is defined as the plane containing the paper or other medium upon which the anaglyph is displayed. A pixel which rests in three dimensions upon the image plane is unique in that both its red and cyan representations occur at the exact same spot on the anaglyph and, hence, appear to rest in three dimensions upon the image plane. The greater the distance separating the red and cyan representations of a pixel in an anaglyph, the greater the distance the pixel appears to rest in 3-D either above or below the image plane.
Historically, the most common method of producing both stereograms and anaglyphs has been photographic in nature. In such instances, the separate images used to comprise the stereogram or anaglyph are captured photographically. Early 3-D stereograms of cityscapes and anaglyphic movies were created by utilizing two cameras separated by a distance, aimed in the same direction, and operated simultaneously. More recently, satellite images have been used to form stereograms. For instance, stereograms have been assembled from images in the overlap region of two geostationary satellites. With the proliferation of computer technology, it is now possible to describe mathematically, in a computer, objects which need not exist in the natural world, generate realistic two dimensional views from slightly different angles, and combine the views to form stereograms and anaglyphs.
While creation of 3-D images on a computer allows for complete control over the components of the final image, computer-generated 3-D images require considerably more expertise and information to create than do their photographic forbears. One need simply open one's eyes or point two cameras in any direction to obtain two scenes from slightly different angles. It is not necessary for the perception of depth to acquire a detailed mathematical description of any one object's relative distance let alone the exact positioning in three dimensions of every single point, comprising every single surface, of every single object which is visible to the observer. In contrast, the creation of a computer generated stereogram or anaglyph does require such detailed information.
While photographic and computer generated anaglyphs differ in the manner by which they are created, the results obtained by either method are quite similar in many important respects. Most importantly, both methods seek to provide each of the viewer's eyes with a scene that is substantially similar to that which would be observed were the observer to look with unaided vision from a particular vantage point at his surroundings. Photographic anaglyphs produce the sensation of viewing a three dimensional landscape from the vantage point at which the cameras were situated. Computer generated anaglyphs, while able to choose any hypothetical vantage point from which to create the necessary images, must choose only one vantage point.
The restriction imposed by choosing one vantage point imposes both advantages and disadvantages. One primary advantage is that the perception of a three dimensional scene is virtually free of distortion. By mimicking that which the unaided eye would normally observe, the anaglyph produces a sensation quite similar to that produced by natural binocular vision. As discussed, early stereoscopes were comprised of apparatus which constrained the motion of the observer around the image. Early 3-D anaglyphic movies required all observers to be seated some distance from the screen and hence constrained all viewers to a viewing angle approximately perpendicular to the image plane. While producing a quite realistic three dimensional sensation, such applications of 3-D technology have remained interesting gimmicks with little wide spread application.
One primary reason for the limited application of anaglyph technology has been the general requirement that the 3-D image be viewed from a single point approximating the location from which the anaglyph was photographed or from which it was computed. The sensation of 3-D produced when viewing the real world is most pronounced when objects are viewed from a relatively small distance. When viewing far a

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