System for distributing auto-stereoscopic images

A system for distributing auto-stereoscopic images, a parallax blocking mask and methods for producing a parallax blocking mask. A parallax blocking mask is provided as an “add-on” for an existing image display device having a flat panel type display screen. The mask is tailored to the needs of the existing device and delivered to a remote user of the display device. The user mounts the mask to the display device so that the mask overlies the display screen. 3D content in the form of composite stereoscopic images derived from one or more stereoscopic image pairs, and application software, are downloaded to the display device over the Internet, and the application software interleaves the composite stereoscopic images for display on the display screen while the mask is in place. Use of a parallax blocking mask having variable edge transitions, a duty cycle less than fifty percent, or both, is disclosed.

TECHNICAL FIELD

The embodiments of the present invention disclosed herein relate generally to the field of distributing auto-stereoscope images to remote viewers, and more particularly to distributing such images as digital video over the Internet.

BACKGROUND

3D image data are stereoscopic (or binocular), comprising pairs of stereoscopic images, each pair representing the same scene viewed from slightly different vantage points, to stimulate viewing the scene through two eyes. Each image of a stereoscopic pair of images therefore corresponds to a different one of the two eyes, and 3D image display technologies must ensure that each eye receives only the image corresponding to that eye with the other image being blocked or filtered out.

Three-dimensional (“3D”) images, like two-dimensional (“2D”) images, are viewed with an intended orientation relative to the viewer's eyes, in which from the user's perspective there is a “top” of the image, a “bottom” of the image, and “left” and “right” sides of the image. If the image is digital, it is defined by pixels arranged in a matrix that define rows running from left to right, and columns running from top to bottom (the columns run vertically, and the rows run horizontally, as the image is normally viewed).

Even if the image is not in digital form or has not been digitized, e.g., where it exists only on film, it can be specified as being defined by a finite number of pixels of a given size, where the image resolution is proportional to the number of pixels, and inversely proportional to the size of the pixels.

Most commonly, the two stereoscopic images are merged into a composite stereoscopic image in which the two stereoscopic images are distinctly coded, such as by color or light polarization, and interleaved with one another. Thus if each stereoscopic image has a resolution of X, the composite stereoscopic image will likewise have a resolution of X. Thus the pair of stereoscopic images taken together will have a resolution (or number of pixels) that is twice that of the resulting composite stereoscopic image; or looked at in reverse, the composite stereoscopic image will have only have the resolution of the pair of stereoscopic images taken together.

A pair of stereoscopic images corresponds to a single video frame, so they must be transmitted, for display in real-time, within the video frame rate, typically 1/60 second.

In the active shutter technology, the two stereoscopic images are transmitted sequentially; but again, for display in real-time, both must be transmitted within the video frame rate.

In general then, 2× pixels will need to be transmitted within the time defined by the video frame rate to enjoy full resolution of a 3D image, whereas only X pixels would have been required to enjoy the same resolution if the image were displayed in 2D. Since transmission bandwidth is normally a limiting factor in the transmission of video data, it is more practical, if the video is to be streamed or viewed in real-time, to transmit the composite stereoscopic image instead of the pair of stereoscopic images and sacrifice resolution.

A number of different 3D display technologies are currently in use. These technologies are typically used for displaying 3D video, but they can be used to display 3D still images as well.

Typically, the two stereoscopic images of a pair of stereoscopic images are distinctly coded such as by color or by light polarization, and the viewer must wear special glasses with distinctly different lenses for each eye, each lens having a filter suitable for passing only the image intended for that eye.

A different approach is known as “active shutter” display technology, which also requires special glasses. Here the two stereoscopic images are streamed in sequence, and the lenses of the glasses are independently controlled to either pass or block light from the display screen in appropriate synchronization.

Viewers generally prefer not to be required to wear special glasses to view 3D content, and to address this preference, there are a number of auto-stereoscopic display technologies that eliminate this requirement. These can be broadly categorized as being either “volumetric” technologies, such as holography, and “flat panel” technologies that display 3D from an essentially flat (from the viewer's perspective) display screen.

The flat panel auto-stereoscopic display technologies utilize two basic methods for distinguishing the two stereoscopic images of a stereoscopic image pair, namely, lenticular, and parallax blocking.

In the lenticular display technology, the panel is provided with a series of columnar lenses overlaying the columns of the display screen. Each lens preferentially directs the light emitted or reflected from the column (or columns) in particular directions within a limited range, so that the image defined by the column (or columns) is visible only if the eye is (or eyes are) within that range.

In the parallax blocking technology, the panel is provided with a mask defining a series of alternating and periodically spaced-apart stripes of opaque material, between which are defined corresponding light transmissive stripes. The stripes are aligned with the columns and overlay the display screen, but they are spaced some distance away, in front of the display screen, to generate parallax between the stripes of the mask and the columns of the display. Then, depending on the location of the viewer's eye, the parallax may be such as to either allow or prevent the viewer from being able to see one or more of the columns under the mask.

The lenticular technology is most often used for inexpensively displaying still images in 3D, or multiple 2D images (where different images are seen from respective different directions). In common usage, a molded lenticular screen is adhered on top of an image on a greeting card, or on packaging for consumer items, for example.

The parallax blocking technology is currently the technology of choice for displaying 3D video. It has been incorporated into 3D video cameras and televisions typically by use of patterned liquid crystal material, built-on to the display screen, which is turned on to define the opaque stripes when it is desired to view data in 3D, and turned off to allow the display to be used for viewing 2D images. This has cost and convenience drawbacks, which the present invention is directed to solving.

SUMMARY

Systems for distributing auto-stereoscopic images are disclosed herein. Among other things, the system provides for a method for providing a parallax blocking mask for attachment to the display device having a flat panel display screen and a particular configuration so as to enable auto-stereoscopic viewing with the display device. This method includes the steps of creating the mask at a first location, and sending the mask to a second location remote from the first location by common carrier, so that, when the mask is attached to the display device so as to overlie the display screen, an auto-stereoscopic image is produced by the mask.

The following additional features may be provided within the method for providing a parallax blocking mask, either separately or in combination: (1) providing the mask with alternating and periodically spaced-apart stripes of substantially opaque material and arranging the stripes to define a spatial duty cycle that is either substantially less than 50%, or more preferably within the range 20-40%, or most preferably, essentially ⅓, or as close to ⅓ as possible; and (2) where the display device displays an array of pixels and the pixels define columns, arranging the stripes so that they are periodically repeated at intervals equal to two of the columns.

The following feature may also be provided within the method for providing a parallax blocking mask, either alone or in combination with either or both of the features (1) and (2): (3) forming one or more composite stereoscopic images from a respective one or more stereoscopic image pairs, selecting, from within the image display device, data from each composite image obtained from just one of the associated stereoscopic image pairs, and displaying the data on the display screen with the mask mounted to the image display device.

The feature (3), in any combination within the method for providing a parallax blocking mask in which it is provided, may be combined with another feature (4) of storing the one or more composite images in the image display device.

The system also provides for a method for distributing 3D image content derived from one or more stereoscopic image pairs. This method includes forming respective compressed composite stereoscopic images from the one or more stereoscopic image pairs, storing the one or more compressed composite stereoscopic images on an Internet web server, downloading the one or more compressed composite stereoscopic images from the Internet web server to a remote image display device having a display screen, interleaving the one or more compressed composite stereoscopic images within the remote image display device, and displaying the interleaved one or more compressed composite stereoscopic images on the display screen.

The following additional features may be provided within the method for distributing 3D image content, either separately or in combination: (1) anamorphically compressing the one or more stereoscopic images; and (2) creating a parallax blocking mask having alternating and periodically space-apart stripes of substantially opaque material, each stripe having an equal width, wherein the display device defines an array of pixels arranged in columns, each column having an equal width, the step of creating including defining the width of the stripes based on the width of the columns, and sending the created mask to a remote location so that, when the mask is attached to the display device so as to overlie the display screen, an auto-stereoscopic image is produced by the mask.

The following feature may also be provided within the method for distributing 3D image content, either alone or in combination with either or both of the features (1) and (2): (3) providing a software application for performing said step of interleaving that is specially adapted for use in the remote image display device; and downloading the software application from the Internet web service to the remote image display device.

The feature (3), in any combination within the method for distributing 3D image content in which it is provided, may be combined with another feature (4) of producing multiple compressed composite stereoscopic images, wherein said step of downloading includes transmitting each compressed composite stereoscopic image over the Internet at a standard television frame rate.

The system also provides for a parallax blocking mask for an auto-stereoscopic image display device having a flat panel display screen, the blocking mask comprising alternating and periodically spaced-apart stripes of substantially opaque material defining a spatial duty cycle that is substantially less than 50%, or more preferably within the range 20-40%, or most preferably, essentially ⅓, or as close to ⅓ as possible.

The following additional features may be provided in the parallax blocking mask either separately or in combination: (1) the blocking stripes are permanently opaque; and (2) where the display device defines an array of pixels arranged in columns, the blocking stripes are periodically repeated at intervals equal to two of the columns.

The system also provides for an auto-stereoscopic display system, including a flat panel display, a parallax blocking mask attached to the flat panel display, the mask comprising a plurality of parallax blocking stripes defining a spatial duty cycle that is less than 50%, or more preferably within the ranged 20-40%, or most preferably, essentially ⅓, or as close to ⅓ as possible, and a signal processor disposed within the display system adapted to receive one or more pairs of stereoscopic images, interleave the images horizontally, and display the interleaved images so that when the blocking stripes of the mask are aligned with respective columns of pixels in the display, an auto-stereoscopic image is produced by the mask.

Preferably within the auto-stereoscopic display system, the spatial duty cycle of the blocking stripes is essentially one-third substantially opaque to two-thirds substantially transmissive.

The system also provides for a method for providing 3D television content over a communications channel. This method includes the steps of providing a server adapted to receive 3D image content and distribute that content over the communications channel to a selected subscriber as pairs of stereoscopic images, providing to the selected subscriber a parallax blocking mask adapted to overlay a flat panel display so as to produce auto-stereoscopic images in response to a display of interleaved pairs of stereoscopic images, and providing to the subscriber application software suitable for use by the display to receive the pairs of stereoscopic images and produce and display interleaved pairs of stereoscopic images.

The method for providing 3D television content over a communications channel may include providing a token to the subscriber for identifying the subscriber to the server to request receipt of 3D image content from the server, and providing administrative software within the server to receive a token sent over the communications channel, verify that the token qualifies the subscriber to receive 3D image content and, if so, send selected 3D image content to the subscriber.

It is to be understood that this summary is provided as a means for generally determining what follows in the drawings and detailed description, and is not intended to limit the scope of the invention. The foregoing and other objects, features, and advantages of the invention will be readily understood upon consideration of the following detailed description taken in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Content Provider and Service Provider

FIG. 1shows a preferred system10for distributing auto-stereoscopic images, or “content”, according to the present invention. The system includes a “content provider”12and a “service provider”16. The content provider is a source of stereoscopic image pairs, referred to as “3D content”14, which may be obtained in any known manner and provided in any known form.

The stereoscopic image pairs are typically a part of a video production, in which case there will be many of the stereoscopic image pairs associated together for sequential viewing, but they may represent stand-alone still images as well.

The 3D content14is provided by the content provider12to the service provider16, preferably according to the terms of a pre-arranged agreement between the content provider and the service provider. The 3D content is typically in digital form, but this is not essential. The 3D content may be downloaded to the service provider over the Internet, but it could also be mailed in the form of hard media such as film or digital video disc (DVD). The format of the 3D content and the manner of its transmission or conveyance to the service provider14is not an important aspect of the invention.

With additional reference toFIG. 2, the service provide14includes a “content processing” module18that receives the 3D content14and, if not it is not in digital form already, digitizes it to produce digital stereoscopic image pairs A and B. It should be understood that each image of the pair represents the same scene at the same time seen from a different vantage point, where the vantage points of the two images A and B are within a limited distance from one another, typically 2.5″ corresponding to the average separation of a viewer's eyes. Two camera lenses are utilized to view respectively the images A and B, with the fields of view of the two lenses overlapping. The result is illustrated graphically inFIG. 3, showing an overlapping area26in which the same objects are visible in both images A and B.

The content processing module18preferably further includes software for combining the stereoscopic image pairs A and B to form a corresponding composite stereoscopic image20.FIG. 2illustrates this result, in which the composite stereoscopic image20includes two halves A/and B/, which are each horizontally, but not vertically (reference the axes “V” (vertical) and “H” (horizontal)), “compressed” versions of the images A and B, respectively. This is referred herein as an “anamorphic” compression, by which whole columns of pixels are eliminated from the A and B images, as will next be explained.

FIG. 4shows the pixelated form of the pair of stereoscopic images A and B ofFIG. 2. Image A is either actually or conceptually represented by pixels PA(m, n)where “m” is an integer ranging from 1 to “M”, and “n” is an integer ranging from 1 to “N”, and where M is the total number of rows and N is the total number of columns of the image A. Likewise, image B is either actually or conceptually represented by pixels PB(m, n). A few of these pixels are shown, it being understood that both images have M×N total pixels, arranged in M rows and N columns.FIG. 4represents 3D content as it is received from the content provider10.

FIG. 5corresponds toFIG. 4, showing particularly the columns N in the images A and B, namely (from left to right) A1, A2. . . AN; and B1, B2, . . . BN. So there are 2N total columns. It is desired to be able to transmit the 2N columns at the standard video frame rate, i.e., the frame rate at which, normally, only N columns are transmitted, corresponding to a single 2D image of resolution M×N.

Thus it is desired to eliminate half the data, and the anamorphic data reduction is preferably accomplished by eliminating alternating pairs of corresponding columns, e.g., eliminating columns A2, A4, A6etc. in the image A, to form the anamorphically compressed image of A/ofFIG. 2, and eliminating corresponding columns B2, B4, B6, etc. in the image B, to form the anamorphically compressed image B/. However, other strategies for eliminating columns could be used without departing from the principles of the invention.

Turning toFIG. 6, the anamorphically compressed images A/and B/are concatenated to form an anamorphic composite stereoscopic image20that is ready for transmission. The width of the anamorphic composite stereoscopic image is W=N, since the width of each stereoscopic image of the original stereoscopic image pairs has been reduced in width from N to N/2 by the elimination of one-half of the original columns. Thus the anamorphic composite stereoscopic has a resolution M×N, the same as a single one of the stereoscopic images of a stereoscopic image pair.

Such compression is desired for video images so that the data contained in the images are reduced sufficiently to allow 3D content to be transmitted from the service provider over the Internet, to a subscriber28, within the available bandwidth at the standard video frame rate. However, such processing may be omitted if the available bandwidth is large enough that it does not impose a limitation. Moreover, where image compression is desired, other compression strategies could be used, either lossy or lossless. Also, the video frame rate is not generally a limitation for still images, but still images are preferably anamorphically compressed in the same way as video data for consistency.

The anamorphic composite stereoscopic images20are stored by the service provider16in a “content storage” memory24, which is shown in residing within a “web server”22, but which need only be accessible by the web server22. Alternatively, if it is not necessary to form compressed or composite images, the stereoscopic image pairs may themselves be stored in the memory24. For purposes of discussion, it will be assumed that anamorphic composite stereoscopic images will be formed and stored in the memory24.

Service Provider and Subscriber

The service provider16also interacts with a subscriber28, preferably according to the terms of a pre-arranged agreement between the service provider and the subscriber. Particularly, the service provider provides the following services to the subscriber: (1) downloading, over the Internet, the anamorphic composite stereoscopic images to a “subscriber device”30, which is typically a smart phone but which could be any camera, phone, computer or television having a flat panel display screen32: (2) downloading or otherwise providing “image processing software”26to the subscriber device (3); and (3) providing an “optical mask”36to the subscriber.

The service (1) may be provided in any known commercial form, such as subscription TV, video on demand, and pay per view, and the images may be stored in a memory (not shown) of the subscriber's device for either controlled or uncontrolled periods of time.

Under the service (2), the image processing software is preferably downloaded over the Internet to the subscriber device30as a result of the subscriber communicating a “token”17to the web server22, the token having been issued to the subscriber by the service provider16.

However, the image processing software could also be provided as a physical object, such as a CD-ROM or flash drive, and delivered to the subscriber by the common carrier38(FIG. 1); and under either or both the services (2) and (3) a physical object may be delivered o any specified remote location by common carrier38. The remote location could be anywhere the subscriber28specifies as a mailing address, or it could be a retail store at which the subscriber28may purchase or pick the object(s) up.

In connection with the service (2), the service provider16includes an account memory19for storing subscriber account information and a memory21for storing the issued tokens. The service provider16also includes a token verification software module23for comparing a token, received from the subscriber over the Internet, with the memory21to verify that the token is valid, and with the memory19for verifying that the subscriber's account is current.

In connection with the service (3),FIG. 1shows the common carrier delivering the optical mask36, either directly to the subscriber28or to a retail store40to which the subscriber28has access. It should be understood that the common carrier could deliver a hardcopy of the image processing software26to the same remote location.

Where the remote location at which a physical object is made available to the subscriber28under either service (2) and (3) is a retail store, preferably it is the same retail store that sells the subscriber devices.

Image Processing

The image processing software26that is made resident in the subscriber device30, either by downloading or streaming it from the Internet or by other means, is an application that forms an interleaved composite stereoscopic image34from an anamorphic composite image20, and fits the interleaved composite stereoscopic image34to the display screen32.

FIG. 7shows the resulting interleaved anamorphic composite image34, obtained by interleaving the columns A1, A3, A5, etc., of the left hand half A/of the anamorphic composite image20ofFIG. 6, with the corresponding columns B1, B3, B5, etc., of the right hand half B/, on the assumption that the even numbered columns in both images have been eliminated in the anamorphic compression discussed above.

Preferably this interleaving is performed at the subscriber device30by the image processing software26, but it could be instead be performed at the content processing module18at the service provider16.

The interleaved composite stereoscopic images34are to be mapped to the display screen32of the subscriber device30.

FIG. 8represents the display screen32of the subscriber device30. It has “P” rows, and “Q” columns “C”, of pixels, namely C1, C2, . . . CQ, defining a pixel space of size P×Q. Generally, P will be less than M (FIGS. 4 and 5); and Q will be less than N, so that there are more data in the interleaved composite stereoscopic image34, in both the vertical and horizontal directions (seeFIG. 4—axes “V” and “H”), than are needed to “fill” the pixel space P×Q. In that case, each column of the display screen32will be mapped to one column of the interleaved composite stereoscopic image34, leaving behind columns at the left and/or right of the interleaved composite stereoscopic image, and leaving behind rows at the top and/or bottom of the interleaved composite stereoscopic image, as needed.

Referring back toFIG. 3, it should be noted that only the overlapping region of the images A and B provide 3D stereoscopic data. So the interleaved composite stereoscopic images34should be centered on the matrix P×Q, and the columns representing the extreme edges of the interleaved composite stereo images34would not be displayed. These unwanted columns may be discarded in the anamorphically compressed composite image20with the image processing software18at the service provider16, and they may alternatively be discarded by the image processing software26at the subscriber device.

If there are not enough rows or columns in the interleaved composite stereoscopic image34to fill the pixel space P×Q, which could happen if either P>M or Q>N, the image processing software may insert a letterbox matte, or use any number of standard techniques to expand the images to fit the screen. However again, only the columns representing the overlapping region of the original images A and B should be displayed.

Optical Mask

FIG. 9shows, enlarged, a representative three of the columns C of the display screen32as shown inFIG. 9, namely, Columns C1, C2, and C3. Registered to these three columns are a representative two optical mask elements “OM” namely OM1and OM2, of a parallax blocking optical mask36. The optical mask elements OM are periodically spaced opaque stripes. Corresponding light transmissive stripes are defined between the opaque optical mask elements OM.

The optical mask elements OM have equal widths W1, whereas the spacing W2is the width of two adjacent pixel columns C. The spacing W2is obtained by dividing the width of the display screen32by the number of columns Q and multiplying by two.

The spacing W2between the optical mask elements OM is therefore determined by the column width (i.e., it is twice the column width) of the particular display screen32; and the width W1also bears a relationship to the spacing W2. As noted previously, in the prior art the opaque portions and the transmissive portions of a mask typically have the same width that is, the width of a single column of pixels on the display screen, and the mask is built in to the display screen.

The present inventor has recognized however, that the mask could be provided as an overlay tailor for the display screen32, and such an optical mask together with image processing software also tailored to the subscriber device30can be provided for user installation on any subscriber device.

Thus there is no need for the image processing software26to have the flexibility to handle all the anticipated display screen variations such as was discussed above.

Instead, the service provider16can provide a specific version of image processing software that will work with the particular subscriber device.

Also as noted previously, the built-in prior art asks employ liquid crystals for the optical mask elements so that they can be turned on, for viewing 3D content, and off, for viewing ordinary 2D content. This requires additional manufacturing and operating expense as well as user involvement. However, the inventor herein has discovered that using an appropriate ratio of opaque stripe width to light transmissive stripe width, either 3D or 2D images may be viewed without alternating the mask.

Prior art stripes have typically been provided in a 1:1 width ratio, i.e., equal widths of opaque stripes alternating with light transmissive stripes, each width being the width of one column of display pixels. Then, 50% of the light from the display screen is blocked. So it is important to turn the mask off when it is desired to view 2D content.

But the present inventors have discovered that a 1:2 width ratio, with the opaque stripes having a width W1that is ½ the width of the light transmissive stripes, and more particularly where the width W1of the opaque stripes is ⅓ the width W2of two adjacent columns of display pixels, provides two outstanding advantages; first, it provides for significantly wider angle viewing, and second it reduces the light blockage so that it is feasible to leave a permanently striped mask on the display screen when viewing 2D content. The insight leading to this discovery was to recognized an advantage in “seeing around” the stripes, which is counterintuitive because the purpose of parallax blocking is essentially to prevent that.

Since the optical mask according to the invention is overlaid on an existing screen rather than being built into it, it is applied over a (typically) glass layer having thickness, and there are variations in the thickness of the glass with different devices. These variations may call for some adjustment of the 1:2 ratio.

It is convenient to recognize that the ratio of opaque stripe width to light transmissive stripe width in the case of a 1:2 width ratio is ⅓:⅔, and to define a spatial “duty cycle” or the opaque stripes of W1/W2, in this case ⅓ or 33%. Using this terminology, the spatial duty cycle is preferably less than 50%; more preferably within the range 20%-40%; and most preferably as close to ⅓ as possible.

Returning briefly toFIG. 1, the optical mask36is provided by the service provider16to the subscriber28. Since the optical mask is a physical object, it is delivered by a common carrier, such as the US postal service or a private carrier, to the subscriber, or it may be delivered by the same type of carrier to a retail store for purchase or pick-up by the subscriber. The subscriber manually attaches the mask to the subscriber device30so that it overlies the display screen32. The mask may be attached to the subscriber device in a number of different ways that will be apparent to persons of ordinary mechanical skill. Particularly if the display device30is a smart phone, the mask may be integrated with the standard screen protector and thereby be applied by snap fit to the outer contour of the phone, although other fastening means may be used.

It is important to minimize rotational misalignment between the optical mask36and the display screen32, to eliminate the creation of Moire patterns, and this consideration calls for maintaining a close vertical alignment between these two components, but it has been found to be unimportant to maintain horizontal alignment, i.e., the mask elements OM inFIG. 10may be shifted arbitrarily to the right or to the left without noticeably affecting their function.

An optical mask has been created by using a clear acetate sheet, of the sort used on overhead projectors, with a stripe pattern defining a 33% spatial duty cycle repeating over a width equal to two pixel columns being printed thereon by use of a standard Hewlett Packard LASERJET®. The mask was then used to overlay a liquid crystal device (LCD) display screen with outstanding results. In particular, the mask was found to provide for extreme wide angle viewing of 3D content.

Subscriber Generated Content

Also according to the invention, the subscriber28may upload 3D content captured at the subscriber device30to the service provider16, and view the 3D content as it is being captured on the display screen32.

Returning toFIG. 1, if as is typical the subscriber30has a camera40, a standard stereoscopic lens attachment42is preferably provided to the subscriber28for the subscriber to install over the existing camera lens. Since the subscriber device already has a camera lens, the principle function of the lens attachment is to capture two stereoscopic images and couple them side-by-side to the entrance pupil of the camera lens.

The lens attachment42, like the optical mask26, may be either delivered to the subscriber28by common carrier, or made available for purchase at a retail store, preferably the same retail store that sells the subscriber devices. More preferably where the distribution channel is a retail store, the optical mask and the lens attachment are preferably bundled together, along with information defining a “token” or password for the user to use to request from the service provider16that the image processing software26be downloaded over the Internet to the subscriber device from the web server22.

As an alternative, the software could also be provided as a physical object, such as a CD-ROM or flash drive, and bundled with the mask and lens attachment for distribution in a single package.

The stereoscopic lens attachment42may be used to cause the camera to acquire 3D stereoscopic images like the images A and B ofFIG. 2. Such images can be uploaded to the service provider16, over the Internet, in the same manner that like images have been downloaded to the service provider16from the content provider12, routed to the content processing module18. In such case, the images are processed to form anamorphically compressed composite stereoscopic images as described above, for downloading to the other subscribers.

The content could also, of course, be downloaded to the same subscriber who originally captured the images; however, the invention also provides for this subscriber to view the 3D content as it is being captured.

As noted above, the image processing software26is made resident in subscriber device30, wherein it performs the functions of forming an interleaved composite stereoscopic image34from the anamorphic composite stereoscopic image20received from the service provider, and fitting the interleaved composite stereoscopic image34to the display screen32.

For allowing the subscriber to view 3D content captured at the subscriber device30, the image processing software26may provide, as an optional processing step, the same anamorphic composite stereoscopic image formation function that is ordinarily performed in the content processing module18. The anamorphic stereoscopic lens would perform the anamorphic compression optically, eliminating the need for anamorphic compression to be accomplished in software.

Displaying 3D Content as 2D Content

According to the invention, 3D content may be displayed in 2D even with the optical mask36being present. The image processing software26may be adapted for this purpose to refrain from forming the interleaved composite stereoscopic image, and instead displaying just one half of the (preferably anamorphically compressed) composite stereoscopic image20as received from the service provider16.

It has also been found that while the use of a parallax blocking mask having a duty cycle significantly less than fifty percent increases viewing angle and enables a single mask to be used for both 3D and 2D viewing, a further advantage can be achieved by using a blocking mask where the edges of the opaque stripes make a gray scale transition, particularly if the transition is dithered, and more particularly, stochastically dithered. This reduces the visibility, or contrast, of Moire patterns that are produced by optical interaction between different spatial frequency content of the mask and the display itself, especially when the mask is misaligned with the display. It also reduces the effects of color fringing in the case of a color display.

Turning toFIG. 10, which is a view from the top of a monochromatic display50, a conventional mask52with nominally sharp edges is placed in front of the display50, separated from the display by distance D in the axial dimension54. The viewer is located in front of the mask with the viewer's left and right pupils located at positions PLand PRin the lateral (horizontal) dimension56, respectively. It can be seen that, to achieve a three-dimensional effect, C1of the image is blocked by conventional opaque mask stripe COM2from being seen by the viewer's right eye at PR, and C2of the image is blocked by opaque mask stripe COM2from being seen by the viewer's left eye at PL. Thus, every odd numbered column of pixels, but none of the even numbered columns of pixels, can be seen by the viewer's left eye. Similarly, every even numbered column of pixels, but none of the odd numbered columns of pixels, can be seen by the viewer's right eye, and vice-versa. Where the odd numbered pixels display the left image of a stereoscopic pair of images and the even numbered pixels display the right image of the stereoscopic pair, the viewer at that position can perceive a three-dimensional image.

With this conventional mask properly aligned in the horizontal dimension with the display pixel columns, and the viewer located at the optimum axial and lateral location, the viewer should ordinarily see a three dimensional image without any interference effects. However, if the mask52is misaligned in the lateral, or the viewer is not at the optimum axial distance, the viewer will see some amount of a Moire interference pattern due to the different spatial frequency content of the mask compared to the display arising from the fact that the period of the mask is different than a multiple of the pixel period. The Moire interference fringes appear when the mask is not precisely manufactured and has a slightly different periodicity than the optimal design. The fringes increase in visibility with misalignment of the mask. They also appear and increase in visibility as the viewer moves away from the optimum viewing position.

FIG. 11is similar toFIG. 10, but in this case each pixel has a red light source LSR, such as a red-filtered liquid crystal retarder or a red light emitting diode, a green light source LSG, and a blue light source LSB, so that the display can produce colored images. The mask ensures that the colored light sources at each pixel can only be seen by one eye when the viewer is in the optimum viewing position.

FIG. 12Ais the same asFIG. 11, except that it shows that the intensity code for each color is 255. (This code has no intrinsic meaning; it is only used to illustrate relative intensities.) These intensities are the relative intensities of each color as perceived by the viewer, without regard to color mixing.

However, inFIG. 12B, the mask has been moved slightly to the left in the lateral dimension. A consequence of this change is that a portion of the red light from pixel P1, 1is blocked, which changes the intensity of red light from that pixel as seen by the viewer, thereby altering the perceived color, as illustrated by the color mixing chart ofFIG. 13. In addition, this shift in mask position enables a portion of the blue light from other pixels to be seen by the viewer with both eyes, which produces undesirable color fringing.

Similarly, inFIG. 12C, the mask has been moved slightly to the the right. In this case a portion of the blue light from pixel P1, 1is blocked, which changes the intensity of blue light from that pixel as seen by the viewer, thereby altering the perceived color, as illustrated by the color mixing chart ofFIG. 13. In addition, this shift in mask position enables a portion of the red light from other pixels_to be seen by the viewer from both, which also produces undesirable color fringing.

The front view58and lateral density profile60of a conventional mask with sharp edges62are illustrated inFIG. 14A. These sharp edges yield high contrast fringing effects discussed above. It can be shown that the spatial frequency content, visibility and color (in the case of a color display), depend on the duty cycle of the mask and the slope of the opaque stripe edges. In particular, the color, or tint, of the Moire pattern depends on the positions and slope of the edges. Changing the position of the edges will change the central color of the pattern; the slope will affect the distribution of colors within the fringes.

By adjusting these parameters, for example as shown inFIGS. 14B and 14C, these fringe characteristics can be controlled to some extent, but not completely.FIG. 14Bshows a front view64and lateral density pattern66with a sloped density change68, which produces a grey scale transition from opaque to transparent, and vice-versa.FIG. 14Cshows a front view70and lateral density pattern72with a more gradually sloped density change74, which produces a grey scale transition from transparent to opaque. Generally, the more gradual is the change in density, the lower the visibility of fringes produced by misalignment will be.

One preferred method of printing that can be adapted to for the purpose of producing a parallax blocking mask of the type disclosed herein is halftone printing, commonly used in the publishing industry to produce images for presentation to a viewer. Other methods that can be used are, for example, the xerographic transfer process, inkjet printing and the silver halide film process. In all of these printing methods, greyscale perception is achieved by the size, distribution and quantity of printed particles. A salient distinction here is that the methods are used to produce a blocking mask, rather than an image for presentation to a viewer.

A front view of the density of a heuristically determined grey scale parallax blocking mask that was found to considerably reduce the production and visibility of Moire fringes in general and color fringing in the face of mask misalignment is shown inFIG. 15.

It has been discovered that, by printing the mask on a transparent medium using a binary printing method such that the perceived density of the printed pattern depends on the size, position and quanta of material deposited on the medium, the Moire patterns and color fringing can be significantly reduced. Specifically, by two-dimensional redistribution of such quanta of material so as to introduce spatial noise (dithering) while reducing their number or average randomized spacing so as to produce a gradual change from opaque to transparent at the edges of the stripes, the visibility of Moire fringes and color fringing in the face of mask misalignment, change in view position from the optimal position, or both, can be greatly reduced. This can be thought of as a mask with noisy transitions.

Moreover, it has been discovered that fringing can be greatly reduced by using a mask that has been stochastically dithered. One known dithering method that is particularly effective is “diffusion dithering.” An example of a parallax blocking mask produced by that method is shown in.FIG. 16. More specifically, the greyscale pattern ofFIG. 15was transformed to the mask pattern ofFIG. 16using a stochastic transformation algorithm known as the diffusion dither transform. A parallax blocking mask having this diffusion dithered greyscale pattern printed by binary printing process was found to greatly reduce the Moire and color fringing, sensitivity of the 3D image to mask misalignment, and sensitivity to user position.

It is to be understood that a mask having a duty cycle of less than fifty percent, as described herein, may be combined with the features of a mask having gradual edge transitions as also described herein to achieve optimal performance in a parallax blocking three dimensional display system as described herein.