# Patent

## Title
Anti-piracy image display methods and systems

## Abstract

Image display methods and systems are provided wherein only portions of a still image of a motion picture, generated for display during an image time interval, are displayed during respective sub-intervals of the image time interval. A still image is thereby separated into portions and displayed separately during corresponding sub-intervals. Preferably, no single portion of the image includes all of the content of the entire image. However, the sum of all of the portions preferably includes all of the content of the image, and all of the portions are displayed within the image time interval. Although an image displayed in this manner can be correctly perceived by a viewer, recording of such an image may capture fewer than all of the portions of the image to thereby degrade the quality of recorded copies of the image and thus the motion picture.

## Background
RELATED APPLICATION
This application claims the benefit of prior U.S. Provisional Application No. 60/552,732 filed Mar. 15, 2004.


FIELD OF THE INVENTION
This invention relates generally to image display and, in particular, to anti-piracy image display methods and systems.
BACKGROUND
Movie producers are continually becoming more concerned about movie piracy. In the past year, for example, more than 50 major movies were illegally copied and publicly released even before they came out in theaters, according to the Motion Picture Association of America (M.P.A.A.). The film industry lost a reported US$3.5 billion last year, and estimated losses may rise to US$5.4 billion this year. Illegally copied movies filmed during projection, with video cameras or camcorders and similar devices, are a significant contributing factor to revenue loss. While it may not be possible to completely eliminate theft by copying, it can be advantageous to modify image display and projection techniques so that pirated copies are of such low quality that they are of little or no commercial value.
It is known to provide a distinct symbol or watermark on an original still image as a means of image or copy identification, so as to enable authentication of a copy. As examples, U.S. Pat. No. 5,875,249 (Mintzer et al.), U.S. Pat. No. 6,031,914 (Tewfik et al.), U.S. Pat. No. 5,912,972 (Barton), and U.S. Pat. No. 5,949,885 (Leighton) disclose methods of applying a perceptually invisible watermark to image data as verification of authorship or ownership or as evidence that an image has not been altered. However, while such methods identify and validate image data, they provide no direct means of protection against copying an image, such as using a conventional scanner and color printer.
In contrast, U.S. Pat. No. 5,530,759 (Braudaway et al.) discloses providing a visible, color correct watermark that is generated by altering brightness characteristics but not chromaticity of specific pixels in an image. This approach could be objectionable if used for a motion picture, since the continuing display of a watermark on film could annoy an audience and adversely affect the viewing experience.
The above examples for still-frame images illustrate a key problem: an invisible watermark identifies but does not adversely affect the quality of an illegal copy, while a visible watermark can be distracting and annoying. With video and motion picture images, there can be yet other problems with conventional image watermarking. For example, U.S. Pat. No. 5,960,081 (Vynne et al.) discloses applying a hidden watermark to MPEG data using motion vector data. But this method identifies and authenticates the original compressed data stream and would not provide identification for a motion picture that was copied using a camcorder.
Other patents, such as U.S. Pat. No. 5,809,139 (Girod et al.), U.S. Pat. No. 6,069,914 (Cox), and U.S. Pat. No. 6,037,984 (Isnardi et al.) disclose adding an imperceptible watermark directly to the discrete cosine transform (DCT) coefficients of a MPEG-compressed video signal. If such watermarked images are subsequently recompressed using a lossy compression method (such as by a camcorder, for example) or are modified by some other image processing operation, the watermark may no longer be detectable.
These particular invisible watermarking schemes add a watermark directly to the compressed bit stream of an image or image sequence. Alternatively, there are other watermarking schemes that add the watermark to the image data itself, rather than to the compressed data representation. An example of such a scheme is given in U.S. Pat. No. 6,044,156 (Honsinger et al.), which discloses a spread spectrum technique using a random phase carrier.
However, regardless of the specific method that is used to embed a watermark, there is always a concern that a watermarking method might not be robust, that is, able to withstand various “attacks” that can remove or alter the watermark. Some attacks may be deliberately aimed at the underlying structure of a given watermarking scheme and require detailed knowledge of watermarking techniques applied, although most attack methods are less sophisticated, performing common modifications to the image such as using lossy compression, introducing lowpass filtering, or cropping the image, for example. Such modifications can be made when a video camera is used to capture a displayed motion picture. These methods present a constant threat that a watermark may be removed during the recording process.
The watermarking schemes noted above are directed to copy identification, ownership, or authentication. However, even if a watermarking approach is robust, provides copy control management, and succeeds in identifying the source of a motion picture, an invisible watermark may not be a sufficient deterrent for illegal copying.
As an alternative to watermarking, some copy deterrent schemes used in arts other than video or movie display operate by modifying a signal or inserting a different signal to degrade the quality of any illegal copies. The modified or inserted signal does not affect playback of a legally obtained manufactured copy, but adversely impacts the quality of an illegally produced copy. As one example, U.S. Pat. No. 5,883,959 (Kori) discloses deliberate modification of a burst signal to foil copying of a video. Similarly, U.S. Pat. No. 6,041,158 (Sato) and U.S. Pat. No. 5,663,927 (Ryan) disclose modification of expected video signals in order to degrade the quality of an illegal copy. As yet another example of this principle, U.S. Pat. No. 4,644,422 (Bedini) discloses adding a degrading signal to discourage copying of audio recordings. An audio signal having a frequency at and above the high threshold frequency range for human hearing is selectively inserted into a recording. The inserted signal is not detectable to the listener. However, any unauthorized attempt to copy the recording onto tape obtains a degraded copy, since the inserted audio signal interacts adversely with the bias oscillator frequency of a tape recording head.
The above-mentioned copy protection schemes deliberately inject a signal in order to degrade the quality of a copy. While such methods may be effective for copy protection of data from a tape or optical storage medium, these methods do not discourage copying of a motion picture image using a video camera.
As a variation of the general method where a signal is inserted that does not impact viewability but degrades copy quality, U.S. Pat. No. 6,018,374 (Wrobleski) discloses the use of a second projector in video and motion picture presentation. This second projector is used to project an infrared (IR) message onto the display screen, where the infrared message can contain, for example, a date/time stamp, theater identifying text, or other information. The infrared message is not visible to the human eye. However, because a video camera has broader spectral sensitivity that includes the IR range, the message will be clearly visible in any video camera copy made from the display screen. The same technique can be used to distort a recorded image with an “overlaid” infrared image. While the method disclosed in U.S. Pat. No. 6,018,374 can be effective for frustrating casual camcorder recording, the method has some drawbacks. A more sophisticated video camera operator could minimize the effect of a projected infrared watermark using a filter designed to block infrared light. Video cameras are normally provided with some amount of IR filtering to compensate for silicon sensitivity to IR.
Motion picture display and video recording standards have well-known frame-to-frame refresh rates. In standard motion picture projection, for example, each film frame is typically displayed for a time duration of 1/24th of a second. Respective refresh rates for interlaced NTSC and PAL video recording standards are 1/60th of a second and 1/50th of a second. Video camera capabilities such as variable shutter speeds allow close synchronization of a video camera with film projection, making it easier for illegal copies to be filmed within a theater. Attempts to degrade the quality of such a copy include that disclosed in U.S. Pat. No. 5,680,454 (Mead) and U.S. Pat. No. 6,529,600 (Epstein), which disclose use of a pseudo-random variation in frame rate, causing successive motion picture frames to be displayed at slightly different rates than nominal. Using this method, for example, frame display periods would randomly change between 1/23rd and 1/25th of a second for a nominal 1/24th second display period. Timing shifts within this range would be imperceptible to the human viewer, but significantly degrade the quality of any copy filmed using a video camera. The randomization proposed therein would prevent resynchronization of a video camera to a changed display frequency. While these methods may degrade the image quality of a copy made by video camera, they also have limitations. As noted in the disclosure of U.S. Pat. No. 5,680,454, the range of frame rate variability is constrained, since the overall frame rate must track reasonably closely with accompanying audio. Furthermore, a video camera can easily be modified to so that its frame rate tracks with the motion picture.
U.S. Pat. No. 5,959,717 (Chaum) also discloses a method and apparatus for copy prevention of a displayed motion picture work. The apparatus of U.S. Pat. No. 5,959,717 includes a film projector along with a separate video projector. The video projector can be used, for example, to display an identifying or cautionary message or an obscuring pattern that is imperceptible to human viewers but can be recorded using a video camera. Alternately, the video camera may even display part of the motion picture content itself. By controlling the timing of the video projector relative to film projector timing, a message or pattern can be made that will be recorded when using a video camera, but will be imperceptible to a viewing audience. This method, however, requires distribution of a motion picture in multiple parts, which greatly complicates film replication and distribution. Separate projectors are also required for the film-based and video-based image components, adding cost and complexity to the system and to its operation. Image quality, particularly for large-screen environments, may not be optimal for video projection, and alignment of both projectors to each other and to the display surface must be precisely maintained.
U.S. Published Patent Application No. 2002/0168069 describes an apparatus and method for displaying a copy-deterrent pattern within a digital motion picture in order to discourage recording of the motion picture using a video camera or other sampling recording device. The copy-deterrent pattern comprises a plurality of pixels within each frame of the digital motion picture, and the displayed pixel intensities are modulated at a temporal frequency using modulation characteristics deliberately selected to be imperceptible to human observers while simultaneously producing objectionable aliasing in any copy made using a video camera. There are drawbacks in this approach. During recording using a video camera the camera shutter can be set to open long enough to average out the modulation. For example, in the example shown in FIG. 12 of the reference, the frame rate is 24 frames per second, and the modulation is at 96 Hz. If the camera shutter speed is set at 1/48 sec, then there will be no or minimal alias effect. Furthermore, if sampling rate is fast enough (e.g. 96 Hz) then all the information will be recorded in the pirate copy and the modulation in pixel intensities can be removed by digital signal processing.
U.S. published Application No. 2004/0033060 describes a method of modulation of a video signal with an impairment signal to increase the video signal masked threshold. With this arrangement, an impairment signal is applied to a version of the movie having a higher frame rate than normal. The impairment signal is designed to produce an apparent motion across the frame when applied at a high frame rate and less rapid apparent motion when viewed at a lower frame rate. When a person views the high frame rate movie, the brain is capable of summing rapid frames such that the impairment is not visible. When a lower frame rate video camera records such a signal, it will not capture all of the images, but rather only particular ones and as such the summing of successive images to produce the proper result will not be achieved. However, with recent improvements in CCD technology, the exposure period possible with video recorders is much longer. Where previously a 60 frame per second camera would have an exposure time that was much less than 1/60th of a second, new technologies allow exposures approaching the full 1/60th of a second duration. In such a case, the video camera would be able to perform an integration to sum successive rapid frames such that the slower frames are substantially correct.
Conventional methods such as those described above could be adapted to provide some measure of copy deterrence and watermarking for digital motion pictures. However, none of the methods noted above is wholly satisfactory, for the reasons stated.
SUMMARY OF THE INVENTION
According to one broad aspect, the invention provides a method comprising: for each of a plurality of still images of a motion picture, rendering a respective sequence of sub-frames such that each sub-frame comprises a respective portion of the still image with the sequence of sub-frames substantially summing to the still image, an overall sequence of sub-frames comprising the respective sequences of sub-frames ordered according to an order of the plurality of still images; wherein for at least some pairs of consecutive still images, there is a variation in a manner in which the respective portions are generated.
In some embodiments, each pair of consecutive still images comprises in sequence a first still image for which a first sequence of sub-frames is rendered, and a second still image for which a second sequence of sub-frames is rendered; the variation is such that a gap left in the first still image due to omission of one or more sub-frames of the first sequence of sub-frames is not filled by a corresponding one or more sub-frames of the second sequence of sub-frames.
In some embodiments, the at least one pair of consecutive still images comprises every pair of consecutive still images.
In some embodiments, the method further comprises: defining a set of portion shapes for use in rendering the sub-frames for all still images, such that for each portion shape of the set and each still image, one of the respective portions of the still image has the portion shape; wherein the variation in the manner in which the respective portions are generated comprises rendering the sequences of sub-frames to have a variation in an order of the set of portion shapes among the pairs of consecutive still images.
In some embodiments, rendering comprises displaying.
In some embodiments, the method further comprises displaying the sub-frames such that there is some variation in a time of display of the sequence of sub-frames between different still images.
In some embodiments, rendering the sub-frames comprises displaying the sub-frames with differing durations.
In some embodiments, rendering comprises recording.
In some embodiments, the plurality of sub-frames of the still image comprises n sub-frames, wherein n is a positive integer greater than 1, and wherein each sub-frame is displayed for sub-intervals that is approximately a fraction 1/nth of an image time interval.
In some embodiments, the method further comprises generating each still image in a motion picture projector for projection onto a screen; wherein rendering comprises filtering the generated still image to allow the plurality of portions of the generated still image to pass to the screen during respective sub-intervals.
In some embodiments, filtering comprises: providing a sequence of apertured filters each comprising at least one aperture; and moving the apertured filters to position the at least one aperture to allow one of the plurality of portions of the still image to pass to the screen during each of the sub-intervals.
In some embodiments, providing the apertured filter component comprises providing the apertured filter component in the motion picture projector.
In some embodiments, providing the apertured filter component comprises providing the apertured filter component at a location between the motion picture projector and the screen.
In some embodiments, the method further comprises: projecting each still image onto a mirror; wherein rendering comprises reflecting the plurality of portions of the still image from the mirror to a screen during respective sub-intervals.
In some embodiments, rendering comprises illuminating a mirror in a digital motion picture projector.
In some embodiments, displaying comprises: providing an LCD (liquid crystal display) covering at least a portion of the mirror; and controlling the liquid crystal display to position liquid crystals of the LCD to allow the portions of the generated still image to pass through the LCD during respective sub-intervals.
In some embodiments, rendering comprises filtering each still image to display the plurality of portions of the still image during the respective sub-intervals.
According to another broad aspect, the invention provides a method comprising: for each of a plurality of still images of a motion picture, rendering a respective sequence of sub-frames such that each sub-frame comprises a respective portion of the still image with the sequence of sub-frames substantially summing to the still image, an overall sequence of sub-frames comprising the respective sequences of sub-frames ordered according to an order of the plurality of still images; wherein there is no relationship between the sequences of sub-frames.
According to another broad aspect, the invention provides a method comprising: for each of a plurality of still images of a motion picture, rendering a respective sequence of sub-frames such that each sub-frame comprises a respective portion of the still image with the sequence of sub-frames substantially summing to the still image, an overall sequence of sub-frames comprising the respective sequences of sub-frames ordered according to an order of the plurality of still images; wherein there is randomness or pseudo-randomness in the sequences of sub-frames.
According to another broad aspect, the invention provides a system comprising: an image generator configured to generate a plurality of still images of a motion picture for display during respective image time intervals; and a display controller configured, for each of a plurality of still images of a motion picture, display a respective sequence of sub-frames such that each sub-frame comprises a respective portion of the still image with the sequence of sub-frames substantially summing to the still image, an overall sequence of sub-frames comprising the respective sequences of sub-frames ordered according to an order of the plurality of still images; wherein for at least some pairs of consecutive still images, there is a variation in a manner in which the respective portions are generated.
In some embodiments, the still image comprises a frame of the motion picture.
In some embodiments, the plurality of sub-frames of each generated still image comprises n sub-frames, and wherein each of the sub-frames is displayed for approximately a fraction 1/nth of the image time interval.
In some embodiments, the plurality of sub-frames of each generated still image comprises n sub-frames, and there is some variation in the length of time the sub-frames are displayed.
In some embodiments, the image generator comprises a motion picture projector.
In some embodiments, the display controller comprises: a filter configured to filter each generated still image responsive to the display controller to pass the plurality of portions of the generated still image to the screen as respective sub-frames.
In some embodiments, the system further comprises: a mirror, wherein the motion picture projector is configured to project each generated still image onto the mirror.
In some embodiments, the system further comprises: an LCD (liquid crystal display) covering at least a portion of the mirror, wherein the display controller is further configured to control the LCD to position liquid crystals of the LCD to allow the portions of each generated still image to pass through the LCD as respective sub-frames.
In some embodiments, the mirror comprises a plurality of mirrors, and wherein the display controller is further configured to control an angle of each of the plurality of mirrors to reflect the portions of each generated still image to a screen as respective sub-frames.
According to another broad aspect, the invention provides an accessory for a moving picture projector configured to generate still images of a moving picture and to maintain the generated still images for an image time interval, the accessory comprising: an input for receiving the generated still images; and an image separator configured to separate each of the received generated still images into a plurality of portions, and to display the plurality of portions during respective sub-intervals of the image time interval; wherein for at least some pairs of consecutive still images, there is a variation in a manner in which the respective portions are generated.
In another embodiment, the manner in which the sub-frames is generated can be changed in real time locally and/or remotely.
Other aspects and features of embodiments of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention.



BRIEF DESCRIPTION OF THE DRAWINGS
Examples of embodiments of the invention will now be described in greater detail with reference to the accompanying diagrams, in which:
FIG. 1 is a representation of a set of sub-frames;
FIG. 2 shows the effect of using the set of sub-frames of FIG. 1;
FIG. 3 shows the effect of recording the pattern of FIG. 2 with a frame synchronization offset by one frame;
FIG. 4 is an example of sub-frame sequencing provided by an embodiment of the invention;
FIG. 5 is a flow diagram illustrating a method according to an embodiment of the invention;
FIG. 6 is a block diagram of a system according to an embodiment of the invention;
FIG. 7 is an embodiment of an apertured filter component; and
FIG. 8 is a block diagram of a system according to an embodiment of the invention; and
FIG. 9 is a block diagram of a digital projector in which embodiments of the invention may be implemented.



DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Embodiments of the invention generally relate to methods and systems for displaying portions of a still image instead of a complete still image, such as a set of sub-frames instead of a standard frame in a motion picture. Each sub-frame does not have all the information of the frame, but the set of sub-frames preferably contains the same information as the frame. To an audience viewing a motion picture displayed in this manner, there is no visible difference, but for a video capture device such as video camera, there will be information missing if not all the sub-frames are captured.
If a still image is divided into a collection of small colored dots, then the human brain is able to effectively reassemble the dots into a meaningful image. Similarly, if a moving scene is divided into a sequence of still images which are shown in rapid succession, then the brain reassembles the still images into a single moving scene.
Movies work because of persistence of vision. The human eye generally retains an image for about 1/20th of a second after seeing it. Such persistence of vision creates the illusion of motion from still images. This phenomenon, however, is not exhibited to the same extent in recording devices such as a video camera. For example, when a video camera records a moving scene from a TV or computer monitor, there tends to be pronounced flicker and often a black rolling bar in the recorded image instead of the stable image that eyes see.
This flicker is caused by two characteristics, namely a difference in the scanning frequency between the TV or monitor and the camera, and a difference between the way in which phosphor dots are perceived by the human eye and the camera's image sensor. In a standard CRT display, a single electron beam scans horizontal lines of pixels across the screen, lighting up each pixel when the beam hits it. The pixels are made of individual phosphor dots that glow when the beam hits them. In human eyes, the dots glow for about 1/30th of a second, so we see a steady image. For a video camera, however, the dots do not appear to glow nearly as long. The camera is much less persistent than the eye.
With monitor refreshing every 1/60th of a second and a camera taking a frame every 1/60th of a second, for example, the video camera's lower persistence results in low quality recording. The black bar that is observed when the recorded video is played back is essentially a collection of pixels that had faded by the time the camera tried to image them. The bar rolls because the camera and monitor are not exactly synchronized, even though the frame rates may be nominally the same.
In projecting a movie from film for instance, each frame is exposed for a short time and then advanced to the next frame. Normally, the film is advanced at the rate of 24 frames per second.
If a regular repeating pattern of sub-frames is used, it is possible that a video capture device with a long enough exposure time will be able to capture all of the sub-frames. For example, referring to FIG. 1, suppose each original image frame 10 is sub-divided into five sub-frames 12,14,16,18,20 according to a repeating pattern with each sub-frame having portions of the original image blocked out as shown. The sum of the five images 12,14,16,18,20 adds up to the original frame 10.
Now referring to FIG. 2, when a sequence of sub-frames generally indicated at 22 is displayed, with sets 24,26,28,30 of five sub-frames shown for each of four different frames, sub-frames 24 are perceived as the original image 32, sub-frames 26 are perceived as image 34, sub-frames 28 are perceived as image 36 and sub-frames 30 are perceived as original image 38. That is to say the fact that the sub-frames 22 are played at a rapid pace allows the brain to add consecutive sub-frames sub-consciously to produce the original images. Thus, the fact that the images have been transformed into the sub-frames with blocked out portions as shown in FIG. 1 does not result in a perceptable degradation in the picture quality.
Disadvantageously, with the sub-frame format of FIG. 1, if a video capture device is successfully synchronized with the first sub-frame of each frame, and has an exposure time long enough to capture all five frames of each image, then no picture degradation will result in the recorded video. Furthermore, in the event the video camera is capable of synchronizing not to the first sub-frame of each original image, but to one of the other sub-frames, for example each second sub-frame, there still would not be significant degradation. This is shown in FIG. 3 where the exposure intervals are indicated at 50,52,54. Now it can be seen that during exposure interval 50, the second, third, fourth and fifth sub-frames of original image 24 and the first sub-frame of image 26 are summed and recorded. During exposure interval 52, the second, third, fourth and fifth sub-frames of original image 26 and the first sub-frame of image 28 are summed and recorded, and during exposure interval 54, the second, third, fourth and fifth sub-frames of original image 28 and the first sub-frame of original image 30 are summed and recorded. The resulting sum is indicated at 56,58,60 for the three exposure periods. For each exposure period, four of the sub-frames are accurately recorded, but the fifth sub-frame is from the following image. However, because consecutively images generally do not differ by that much, the fact that a portion of the image is taken from a following image in a repeating manner will not significantly degrade the perception of the movie. In particular, it can be seen that the resulting recorded image for the first frame 24 contains three blocks 68,70,72 (corresponding to the blocks of the first sub-frame 12 of FIG. 1) for the succeeding frame 26 with a remainder of the image taken from the current image 24. So long as the two images are not significantly different, this will not create a significant perceptable degradation in the image quality. Thus, the entire effort of degrading the image does not achieve the desired result of deterring video piracy.
Referring now to FIG. 4, in an effort to deal with this, an element of variation is introduced into the sub-frame sequencing. This will be described with the specific example of FIG. 4 with more general concepts introduced later. In this case, there are again four sets of five sub-frames 80,82,84,86. Each of these sub-frames contains a respective portion of an original image. For the purpose of this example, it is assumed that the sub-frames are produced using the sub-frame patterns shown in FIG. 1. However, in this case, the sequence of sub-frames for each frame is not repeating. Rather, there is a variation in the order of the sub-frames between adjacent images. For the first image 80, the sequence of sub-frames is 1, 2, 3, 4, 5. For the next image 82, the sequence is 2, 5, 3, 1, 4. For the next image 84, the sequence is 5, 1, 4, 3, 2. Finally, for the next image 86, the sequence is 1, 4, 5, 2, 3. The effect of this upon a video recording of such a sequence of sub-frames can be seen at 90. In this case, it is assumed that the video recording device is capable of synchronizing on the second sub-frame of each frame. This means that during the first exposure interval 92, sub-frames 2,3,4,5 of the first image 80 and sub-frame 2 of the second image 82 are summed to produce image 94. It can be seen that such a sum has gaps in the image indicated at 96,98,100 due to the fact that the sum does not include sub-frame 1 from either the current image 80 or from a following image 82. Furthermore, there is also degradation in the areas indicated at 102,104,106 where the contribution of the second sub-frame of each of two successive frames 80,82 has been summed resulting in distortion. It can be seen that the randomness introduced in the sub-frame order results in the degradation in each frame with the degradation being different in successive frames.
In some embodiments, the fast response of advanced LCDs (liquid crystal displays) and DLPs (digital light processors) is exploited to display a number of sub-frames instead of a standard frame in a motion picture within a standard frame period of 1/24th of a second, which may be referred to more generally as an image time interval.
FIG. 5 is a flow diagram illustrating a method according to an embodiment of the invention. At 10, one of a number of still images of a motion picture is processed for display during an image time interval, illustratively the frame duration described above to produce sub-frames with variation in the manner in which still images are divided into sub-frames. Examples of this variation include, but are not limited to: a) variation in the number of sub-frames per image interval; b) variation in the impairment pattern applied to successive sub-frames (specific example given in FIG. 4); c) variation in the duration of the sub-frames per image interval. Portions of the generated still image are then displayed at 12 during respective sub-intervals of the image time interval. Thus, in each sub-interval, only a portion of the generated still image is displayed. As indicated at 14, these operations are repeated for each still image in the motion picture.
Generally, an image is separated into n portions, and each of the sub-intervals is preferably approximately a fraction 1/nth of the image time interval, where n is a positive integer greater than one. However, it should be appreciated that the portions need not be of equal size, and that the sub-intervals may also be of different lengths.
In another embodiment, the sub-frames of a given image interval on average are displayed during a period equal to the image interval, but with a small variation in the period used for successive images. This type of variation will not be perceptable to a user, but will further degrade the ability of a video capture device to synchronize to a frame or sub-frame rate.
In one embodiment, a sequence of impairment masks is applied to each image to produce a set of sub-frames for each interval with the order of the resulting sub-frames being randomized between successive image intervals.
The order does not need to be truly random. Rather, there needs to be some variation between at least some, and preferably all, consecutive image intervals to achieve the desired effect.
In one embodiment, the still image is generated in a projector for projection onto a screen. The operation at 12 in such embodiments may include filtering the generated still image to allow the portions of the generated still image to pass to the screen one at a time during the sub-intervals. This filtering may be accomplished, for example, by providing an apertured filter component and moving the apertured filter component to position apertures such that only a portion of the generated still image is allowed to pass to the screen during each of the sub-intervals. Such a filter component may be provided either within the projector or as an external component, such as in an accessory for the projector, and is preferably but not necessarily synchronized with the projector, such as once per image time interval. For a film projector, for example, movement of a filter component is preferably synchronized with the frame rate. Illustrative examples of a filter component are described in further detail below.
According to other embodiments of the invention, a projector projects generated still images onto a mirror, which may be internal or external to the projector. Portions of the still images are then reflected from the mirror to a screen during respective sub-intervals of an image time interval. Control of the portions that are reflected to the screen during any sub-interval may be provided by an LCD covering at least a portion of the mirror. Liquid crystals of the LCD are then positioned to allow the portions of the still image to pass through the LCD during the respective sub-intervals. In another embodiment, the mirror includes multiple mirrors with controllable angles, in a DMD (digital micromirror device) for instance. Each mirror is positioned at a particular angle during each sub-interval to reflect a portion of the generated still image to the screen.
Each image time interval preferably has substantially the same duration. Similarly, each sub-interval of an image time interval also preferably has substantially the same duration, which is less than the image time interval. However, it should be appreciated that the invention is in no way limited thereto. Embodiments of the invention may be used in conjunction with variable frame rate projectors, with synchronization at the beginning of each image time interval or frame for example, and may display portions of an image for different amounts of time.
FIG. 6 is a block diagram of a system according to an embodiment of the invention. The system includes an image generator 16 operatively coupled to a display controller 18 via a connection 17. Of course, a motion picture display or projection system may include further elements than those explicitly shown in FIG. 6.
The image generator 16 generates still images of a motion picture for display during respective image time intervals. In a preferred embodiment, the image generator 16 is a motion picture projector such as a film projector which illuminates motion picture film or a digital projector. One example of a digital projector is described in further detail below with reference to FIG. 7.
Although shown and referred to as a connection, the connection 17 should be understood to include a physical connection, an optical connection with or without an actual physical carrier connected between the image generator 16 and the display controller 18, or possibly combinations thereof or a logical connection. For example, a physical connection may be provided to enable synchronization between the image generator 16 and the display controller 18, whereas still images generated by the image generator 16 are provided to the display controller 18 through an optical “line-of-sight” path.
The display controller 18 displays portions of each still image generated by the image generator 16 during respective sub-intervals of the image time interval in which the still image is generated. Thus, the display controller 18 effectively separates generated still images into portions for display in corresponding sub-intervals. The display controller 18 may be implemented in a projector which also incorporates the image generator 16, or as an external accessory for such a projector.
In one embodiment, the display controller 18 includes a filter for filtering each generated still image. Portions of each generated still image are thus passed, to a projection screen for example, during respective sub-intervals. Such a filter may include an apertured filter component, an illustrative example of which is shown in FIG. 7. Apertured filter component 70 includes apertures 72,74,76 that define one portion or sub-frame. The portion consists of three square areas 72,74,76. Further filters would be defined for the other sub-frames. The filters are applied in sequence to the still image. The filters might for example be implemented with a transparent liquid crystal display. Alternatively, motion between a series of different physically distinct filters may be used. Those skilled in the art will appreciate that different numbers, shapes, and sizes of apertures and filter components than those specifically shown may be used for display control in accordance with the techniques disclosed herein. The size of the aperture or apertures determines the number of portions into which an image is separated.
Other forms of filter components will be apparent to those skilled in the art to which this application pertains. It should thus be appreciated that the invention is in no way limited to the filter component 70.
Where physically distinct components are provided, the display controller 18 moves the filter components during each image time interval to position any apertures to pass or transmit portions of a generated still image during respective sub-intervals. As will be apparent, the filter components may be moved through control of a motor, linkage, or other device (not shown) for moving the filter component.
According to further embodiments of the invention, the image generator 16 projects an image onto a mirror, which reflects the image onto a screen. In one embodiment, an LCD covers at least a portion of the mirror, and the display controller 18 controls the LCD to position liquid crystals of the LCD so as to allow portions of the image to pass through the LCD to the screen during respective sub-intervals an image time interval. It should also be appreciated that an LCD may be used in a similar manner on its own as a filter component as discussed above.
The mirror includes multiple mirrors in another embodiment of the invention, and the display controller 18 controls an angle of each mirror to reflect portions of the image to the screen during the respective sub-intervals.
FIG. 8 is a block diagram of a system incorporating an embodiment of the invention. In the system of FIG. 8, a DMD or mirror/LCD combination 82 is provided externally to a projector 80, and reflects portions of images generated by the projector 80 onto the screen 84. This type of system is particularly adapted to projectors which do not incorporate a mirror, such as film projectors, for example.
As will be apparent from FIG. 8, an image separator, which includes a mirror in the example system of FIG. 8 but may instead include a filter component or other type of separator, may be provided externally to a projector. However, digital projectors incorporate such mirrors. FIG. 9 is a block diagram of a digital projector in which embodiments of the invention may be implemented.
There are currently two major digital cinema projector technologies: micromirror projectors and LCD projectors. Micromirror projectors form images with an array of microscopic mirrors. In this type of system as shown in FIG. 9, a high-power lamp 100 shines light through a prism 102. The prism 102 splits the light into the component colors red, green and blue. Each color beam hits a different DMD 104, which is a semiconductor chip that is covered in hinged mirrors, often more than a million hinged mirrors. Based on information encoded in a video signal, the DMD turns over the tiny mirrors to reflect the colored light. Collectively, the tiny dots of reflected light form a monochromatic image.
In actuality, most of the individual mirrors are flipped from “on” (reflecting light) to “off” (not reflecting light, or reflecting light to a location outside an area of a projection screen) and back again thousands of times per second. A mirror that is flipped on a greater proportion of the time will reflect more light and so will form a brighter pixel than a mirror that is not flipped on for as long. This is how the DMD creates a gradation between light and dark. The mirrors that are flipping rapidly from on to off create varying shades of gray (or varying shades of red, green and blue, in this case). Each micromirror chip reflects the monochromatic image back to the prism, which recombines the colors. The red, green and blue rejoin to form a full color image, which is projected onto a screen.
LCD projectors reflect high-intensity light off of a stationary mirror covered with an LCD. Based on a digital video signal, the projector directs some of the liquid crystals to let reflected light through and others to block it. In this way, the LCD modifies the high-intensity light beam to create an image.
Since signal information is already encoded in digital format for digital projectors, and each micromirror (in micromirror technology) or pixel (in LCD technology) is independently addressable, embodiments of the invention can be easily incorporated into digital projectors.
According to a further embodiment of the invention, portions of a still image or frame of a motion picture, the still image or frame having an associated image or frame rate, are generated. The portions of the still image or frame are then displayed during respective sub-image or frame time intervals at a sub-image or sub-frame rate which is greater than the image or frame rate. Where there are n portions (n a positive integer greater than one), the sub-image or sub-frame rate is preferably n times the image or frame rate.
Such an embodiment of the invention may be implemented, for example, by recording the portions of the image or frame on a recording medium and then operating a projector at the sub-image or sub-frame rate instead of the image or frame rate. The recording medium may be motion picture film or a digital recording medium such as a DVD (digital video disk) for instance.
In another embodiment, the manner in which the sub-frames is generated can be changed in real time locally and/or remotely.
What has been described is merely illustrative of the application of the principles of the invention. Other arrangements and methods can be implemented by those skilled in the art without departing from the spirit and scope of the present invention.
For example, although described primarily in the context of separating an entire image into separately displayed portions, the techniques described herein may alternatively be applied to only a particular section of an image, with other sections of the image being displayed during an entire image time interval. In this case, illumination strengths are preferably controlled to avoid any perceptible differences in intensity between the sections of the image.
In the embodiments described, the sub-frames are generated by first generating the still image and then applying a sequence of impairments to generate these sub-frames. More generally, any method of rendering the sub-frames may be employed. For example, the film may be produced to have a higher frame rate in which these sub-frames are present. It may be that the entire image is never actually generated, but rather the sequence of sub-frames alone is generated. The rendered images may in some embodiments be projected or otherwise displayed. Alternatively, the rendered images may be recorded for later display. This recording can take place in any suitable recording medium.
Preferably, the variation in the manner in which the portions of the still image are generated is selected such that a gap left in a first still image due to the omission of a first sub-frame of the sequence of sub-frames for that still image is not filled by a first sub-frame of the next still image. Preferably, this variation is present for multiple pairs of consecutive images and in some embodiments for all pairs of consecutive images.
In some embodiments, the portion shapes used for rendering the sub-frames of each still image are the same. In such an embodiment, the variation in the manner in which the respective portions are generated is achieved by rendering the sequences of sub-frames to have a variation in the order of the set of portion shapes among the pairs of consecutive still images. For example, if five different portion shapes are used such as was the case in the example of FIG. 4, the desired effect can be achieved by employing a different order among the portion shapes for the sub-frames of consecutive images.
In another embodiment, there is no relationship between the sub-frames, this not being the case for the “picket fence” approach taught in above-referenced Application No. 2004/0033060.
In another embodiment, there is randomness or pseudo-randomness in the sequences of sub-frames.
In addition, enhanced control of image separation and illumination intensity may be provided to implement variable separation schemes, wherein a number of image portions and sub-intervals are varied during projection of a motion picture.

## Claims

1. A method comprising:
using a computer or a motion picture playback apparatus to perform steps of:
for each of a plurality of still images of a motion picture, rendering a respective sequence of sub-frames such that each sub-frame comprises a respective portion of the still image with the sequence of sub-frames summing to the still image, an overall sequence of sub-frames comprising the respective sequences of sub-frames ordered according to an order of the plurality of still images;
wherein:
each pair of consecutive still images of the plurality of still images of the motion picture comprises in sequence a first still image for which a first sequence of sub-frames is rendered, and a second still image for which a second sequence of sub-frames is rendered; and
for at least some pairs of consecutive still images of the plurality of still images of the motion picture, there is a variation between the pair of consecutive still images as to a manner in which the respective portions are generated such that a gap left in the first still image due to omission of one or more sub-frames of the first sequence of sub-frames is not filled by a corresponding one or more sub-frames of the second sequence of sub-frames.

2. The method of claim 1 wherein the at least some pairs of consecutive still images comprises every pair of consecutive still images of the motion picture.

3. The method of claim 1 further comprising:
defining a set of portion shapes for use in rendering the sub-frames for all still images, such that for each portion shape of the set and each still image, one of the respective portions of the still image has the portion shape;
wherein the variation in the manner in which the respective portions are generated comprises rendering the sequences of sub-frames to have a variation in an order of the set of portion shapes among the pairs of consecutive still images.

4. The method of claim 1 wherein rendering comprises displaying.

5. The method of claim 4 further comprising displaying the sub-frames such that there is some variation in a time of display of the sequence of sub-frames between different still images.

6. The method of claim 4, wherein the plurality of sub-frames of the still image comprises n sub-frames, wherein n is a positive integer greater than 1, and wherein each sub-frame is displayed for sub-intervals that is approximately a fraction 1/nth of an image time interval.

7. The method of claim 1 wherein: rendering the sub-frames comprises displaying the sub-frames with differing durations.

8. The method of claim 1 wherein rendering comprises recording.

9. The method of claim 1, further comprising generating each still image in a motion picture projector for projection onto a screen;
wherein rendering comprises filtering the generated still image to allow the plurality of portions of the generated still image to pass to the screen during respective sub-intervals.

10. The method of claim 9, wherein filtering comprises:
providing a sequence of apertured filters each comprising at least one aperture; and
moving the apertured filters to position the at least one aperture to allow one of the plurality of portions of the still image to pass to the screen during each of the sub-intervals.

11. The method of claim 10, wherein providing the apertured filter component comprises providing the apertured filter component in the motion picture projector.

12. The method of claim 10, wherein providing the apertured filter component comprises providing the apertured filter component at a location between the motion picture projector and the screen.

13. The method of claim 1, further comprising:
projecting each still image onto a mirror;
wherein rendering comprises reflecting the plurality of portions of the still image from the mirror to a screen during respective sub-intervals.

14. The method of claim 1, wherein rendering comprises illuminating a mirror in a digital motion picture projector.

15. The method of claim 14, wherein displaying comprises:
providing an LCD (liquid crystal display) covering at least a portion of the mirror; and
controlling the LCD (liquid crystal display) to position liquid crystals of the LCD to allow the portions of the generated still image to pass through the LCD during respective sub-intervals.

16. The method of claim 1, wherein rendering comprises filtering each still image to display the plurality of portions of the still image during the respective sub-intervals.

17. A system comprising:
an image generator configured to generate a plurality of still images of a motion picture for display during respective image time intervals; and
a display controller configured, for each of a plurality of still images of a motion picture, to display a respective sequence of sub-frames such that each sub-frame comprises a respective portion of the still image with the sequence of sub-frames summing to the still image, an overall sequence of sub-frames comprising the respective sequences of sub-frames ordered according to an order of the plurality of still images;
wherein:
each pair of consecutive still images of the plurality of still images of the motion picture comprises in sequence a first still image for which a first sequence of sub-frames is rendered, and a second still image for which a second sequence of sub-frames is rendered; and
for at least some pairs of consecutive still images of the plurality of still images of the motion picture, there is a variation between the pair of consecutive still images as to a manner in which the respective portions are generated such that a gap left in the first still image due to omission of one or more sub-frames of the first sequence of sub-frames is not filled by a corresponding one or more sub-frames of the second sequence of sub-frames.

18. The system of claim 17, wherein each still image comprises a frame of the motion picture.

19. The system of claim 17, wherein the plurality of sub-frames of each generated still image comprises n sub-frames, wherein n is a positive integer greater than 1, and wherein each of the sub-frames is displayed for approximately a fraction 1/nth of the image time interval.

20. The system of claim 17, wherein the plurality of sub-frames of each generated still image comprises n sub-frames, wherein n is a positive integer greater than 1, and there is some variation in the length of time the sub-frames are displayed.

21. The system of claim 17, wherein the image generator comprises a motion picture projector.

22. The system of claim 21, wherein the display controller comprises:
a filter configured to filter each generated still image responsive to the display controller to pass the plurality of portions of the generated still image to the screen as respective sub-frames.

23. The system of claim 17, further comprising:
a mirror,
wherein the image generator is configured to project each generated still image onto the mirror.

24. The system of claim 23, further comprising:
an LCD (liquid crystal display) covering at least a portion of the mirror,
wherein the display controller is further configured to control the LCD (liquid crystal display) to position liquid crystals of the LCD (liquid crystal display) to allow the portions of each generated still image to pass through the LCD (liquid crystal display) as respective sub-frames.

25. The system of claim 23, wherein the mirror comprises a plurality of mirrors, and wherein the display controller is further configured to control an angle of each of the plurality of mirrors to reflect the portions of each generated still image to a screen as respective sub-frames.

26. An apparatus for a moving picture projector configured to generate still images of a moving picture and to maintain the generated still images for an image time interval, the apparatus comprising:
an input for receiving the generated still images; and
an image separator configured to separate each of the received generated still images into a plurality of portions, and to display the plurality of portions during respective sub-intervals of the image time interval, each plurality of portions summing to the respective received generated still image;
wherein:
each pair of consecutive still images of the moving picture comprises in sequence a first still image for which a first sequence of portions of the first still image is displayed during respective sub-intervals of the image time interval and a second still image for which a second sequence of portions of the second still image is displayed during respective sub-intervals of the image time interval; and
for at least some pairs of consecutive still images of the plurality of still images of the moving picture, there is a variation between the pair of consecutive still images as to a manner in which the respective portions are generated such that a gap left in the first still image due to omission of one or more portions of the first sequence of portions is not filled by a corresponding one or more portions of the second sequence of portions.