WO2013142990A1 - System and method for providing light efficient stereo projection - Google Patents

Abstract

Systems and methods are provided for projecting a stereo image. In one aspect, a method comprises obtaining a stereo pair comprising a left view and a right view; generating a triplet comprising a modified left view, a modified right view, and a common view, the common view comprising a common portion of the left view and the right view; and projecting the modified left view for viewing by a left eye, the modified right view for viewing by the right eye, and the common view for viewing by the left and right eyes at the same time.

Description

SYSTEM AND METHOD FOR PROVIDING LIGHT EFFICIENT STEREO PROJECTION

[0001] This application claims priority to U.S. Provisional Application Nos. 61/685,987 filed on March 29, 2012; and 61 /690,789 filed on July 5, 2012, the contents of both applications being incorporated herein by reference.

TECHNICAL FIELD

[0002] The following relates to systems and methods for providing light efficient stereo projection.

DESCRIPTION OF THE RELATED ART

[0003] Stereo displays are displays which are capable of showing two different views of the same scene, one for each eye, and each eye sees only its own view. Stereo displays should therefore address two requirements: (i) displaying two different views of the same scene; and (ii) directing each view to its designated eye. Stereo displays may differ from each other according to the way the particular stereo display addresses these requirements. For example, the two views can be displayed side-by-side (as in stereoscope), they can be overlapped one over the other (as in anaglyph and passive polarized stereo), they can be interlaced (as in auto- stereoscopic displays), or they can be temporally multiplexed by alternating them one after the other repeatedly (as in z-screen passive stereo and active stereo displays). Directing the views to the correct eyes can be done using separate field of view displays (as in stereoscope), color coding (as in anaglyph), polarization coding (as in passive polarized stereo), special optics (as in auto-stereoscopic displays) and time synchronization (as in active stereo displays).

[0004] The following introduces various existing stereo display techniques.

[0005] Dual Projection - This is the most straightforward methods for stereo projection. The display system is simply replicated having a dedicated display for each view. The views are directed to each eye using wavelength coding (i.e., a particular type of coding that uses one part of each red-green-blue (RGB) band for the left view and the other part of the RGB band for the right view), or polarization coding. The viewers are required to wear special passive eye glasses that transmit only the correct view for each eye. The greatest disadvantages of dual projection systems, are typically that they are double in size and cost, and require a relatively complex setup for physical placing, alignment and synchronization. [0006] Time Multiplexed Active Stereo Display - This method multiplexes the two views rapidly and repeatedly over time. The viewer wears synchronized shutter glasses that pass only the correct view to each eye. This method is commonly used in projectors as well as 3D stereo games. The disadvantages of time multiplexed active stereo displays include: (i) low brightness due to viewing temporal multiplexing and low efficiency of the shutter glasses, (ii) flicker due to time multiplexing, and (iii) relatively high cost of the shutter glasses, and the special equipment needed to synchronized them with the display.

[0007] Time Multiplexed Passive Stereo Display - This method also temporally multiplexes the two views. However, routing the views to the correct eye is not done by time

synchronization. Instead, the views are coded using an electronically alternating polarizing filter, or alternating wavelength group (two different sets of RGB) which is placed in front of the projector and is synchronized with the projector. The viewer wears passive polarized glasses or passive glasses with two different sets of RGB filters that pass only the correct view to each eye. The advantage of this method over the above-described method is that the glasses are relatively inexpensive. The disadvantages of time multiplexed passive stereo display systems include low brightness and flicker, and the need for the electronically alternating filter or a filter wheel when stereo projection is used while removing the alternating filter for non-stereo use (since it reduces the brightness even when not active).

[0008] Auto-Stereoscopic Displays - These displays use column interleaving to spatially multiplex two or more views together. Each view is directed to the correct eye using special optics, such as lenticuar lens arrays, barrier screens or light column arrays. The greatest advantage of auto-stereoscopic display is that they do not require special glasses. The disadvantages are: (i) reduced resolution due to spatial interleaving, (ii) reduce sharpness in lenticular array displays due to optical imperfections, (iii) significantly reduce light in barrier screen and light column array displays, and (iv) the appearance of dark bars in light column array displays.

[0009] Spatial Multiplexed Passive Stereo Display - In this method that appears in the literature, the left and right views are column interleaved. The columns are coded by different polarization and the user is required the wear special polarized glassed. The advantage of this method is the elimination of flicker as both views are displayed simultaneously. The disadvantages are reduced spatial resolution, and the need to wear special glasses.

[0010] When a stereo image should be viewed by more than one person, it is common to project the image onto a big screen as in presentations, slide shows and cinema. When projecting an image, the brightness of the projector being used plays an important role. Brighter projectors can produce larger images, they are clearer (i.e., have better contrast), and can be used in the presence of some ambient light. Light is therefore an important but limited resource in projector technology. However, the brightness of the light source itself (typically referred to as the "projector lamp"), is limited by the heat generated during operation. Excessive heat can significantly reduce the expected life span of the lamp. Since projector lamps are expensive components, it is highly desirable to utilize the available light with maximal efficiency.

[0011 ] The need to display two views and to apply polarization and/or wavelength coding to the view so they can be directed to the correct eye, creates a heavy burden upon stereo projectors. As a result, virtually all stereo projectors that use single lens to project stereo images utilize a relatively small portion of the available light.

[0012] The following provides stereo projection apparatus and methods that improve light efficiency, improve smoothness, improve power consumption efficiency, reduce energy costs by increasing efficiency over increasing brightness to address at least some of the above.

SUMMARY

[0013] In one aspect, there is provided a method of projecting a stereo image, the method comprising :obtaining a stereo pair comprising a left view and a right view; generating a triplet comprising a modified left view, a modified right view, and a common view, the common view comprising a common portion of the left view and the right view; and projecting the modified left view for viewing by a left eye, the modified right view for viewing by the right eye, and the common view for viewing by the left and right eyes at the same time.

[0014] There is also provided a computer readable storage medium comprising computer executable instructions for performing the above method. [0015] There is also provided a system comprising at least one projector, a light source for each projector, a processor, and memory, the memory comprising computer executable instructions for performing the above method.

[0016] There is also provided a polarizing wheel to be used in a stereo projector in addition to an existing wheel, the polarizing wheel comprising a clear segment where light is not polarized.

[0017] There is also provided a stereo projector comprising a lamp, a color wheel, and the above polarizing wheel.

[0018] There is also provided a method of operating a stereo projector, the method comprising: splitting light from a light source in the stereo projector into first and second orthogonally polarized channels using a polarizing beam splitter, coding the first and second channels at the same time, and merging the channels for projector through a common lens.

[0019] There is also provided a stereo projector comprising: a lens; a light source; first and second mirror wheel, the first mirror wheel for splitting light from the light source, the second mirror wheel for merging separate light channels to be projected by the lens; a first coding assembly for coding a first light channel and directing the first light channel to the second mirror wheel; and a second coding assembly for coding a second light channel and directing the second light channel to the second mirror wheel.

[0020] There is also provided a method of enhancing spatial resolution for a projector, the method comprising: shifting at least one pixel grid for a corresponding modulating component in the projector by half of a pixel with respect to a first pixel grid for a first modulating component.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021 ] Embodiments will now be described by way of example only with reference to the appended drawings wherein:

[0022] FIG. 1 (a) is a schematic diagram of a single digital light processing (DLP) projector; [0023] FIG. 1 (b) is a schematic diagram of a triple DLP projector; [0024] FIG. 2(a) is a schematic diagram of a single DLP active stereo projector;

[0025] FIG. 2(b) is a schematic diagram of a triple DLP active stereo projector;

[0026] FIG. 3(a) is a schematic diagram of a single DLP passive stereo projector;

[0027] FIG. 3(b) is a schematic diagram of a triple DLP passive stereo projector;

[0028] FIG. 4 provides a series of stereo views;

[0029] FIG. 5 provides a series of RGB channel histograms for a left image, a right image, a minimum image, a left delta, and a right delta;

[0030] FIG. 6(a is a schematic diagram of a single DLP active stereo projector;

[0031 ] FIG. 6(b is a schematic diagram of a triple DLP active stereo projector;

[0032] FIG. 7 illustrates a number of color wheels for a projector;

[0033] FIG. 8(a is a schematic diagram of a color wheel projector;

[0034] FIG. 8(b is a schematic diagram of a color and polarizing wheel projector;

[0035] FIG. 8(c is a schematic diagram of a two wheel projector;

[0036] FIG. 8(d is a schematic diagram of a two wheel projector with a clear window;

[0037] FIG. 9(a is a schematic diagram of a single DLP projector with a two segment polarizing wheel;

[0038] FIG. 9(b) is a schematic diagram of a triple DLP projector with a two segment polarizing wheel;

[0039] FIG. 10(a) is a schematic diagram of a single DLP projector with a two segment polarizing wheel;

[0040] FIG. 10(b) is a schematic diagram of a triple DLP projector with a two segment polarizing wheel; [0041] FIG. 1 1 (a) is a schematic diagram of a single DLP projector with a two segment polarizing wheel and a clear window;

[0042] FIG. 1 1 (b) is a schematic diagram of a triple DLP projector with a two segment polarizing wheel and a clear window;

[0043] FIG. 12(a) is a schematic diagram of a single DLP projector with a two segment polarizing wheel and a clear window;

[0044] FIG. 12(b) is a schematic diagram of a triple DLP projector with a two segment polarizing wheel and a clear window;

[0045] FIG. 13(a) is a schematic diagram of a single DLP projector with a three segment polarizing wheel;

[0046] FIG. 13(b) is a schematic diagram of a triple DLP projector with a three segment polarizing wheel;

[0047] FIG. 14(a) is a schematic diagram of a two DLP chip and single color wheel projector;

[0048] FIG. 14(b) is a schematic diagram of a two DLP chip and single color wheel projector with the two color channels rendered simultaneously;

[0049] FIG. 15(a) is a schematic diagram of a color wheel and polarizing beam splitter projector in a normal mode;

[0050] FIG. 15(b) is a schematic diagram of a color wheel and polarizing beam splitter projector in a stereo mode;

[0051 ] FIG. 16 is a schematic diagram of a dichrotic mirror wheel system;

[0052] FIG. 17(a) is a schematic diagram of a dichrotic color wheel and polarizing beam splitter in a normal mode;

[0053] FIG. 17(b) is a schematic diagram of a dichrotic color wheel and polarizing beam splitter in a stereo mode; [0054] FIG. 18(a) is a schematic diagram of a pixel grid for a pair of DLP chips;

[0055] FIG. 18(b) is a schematic diagram of a pixel grid for a quartet of DLP chips;

[0056] FIG. 19 provides a series of images illustrating a down-sampling and view integration process;

[0057] FIG. 20 provides a series of images illustrating a down-sampling and view integration process;

[0058] FIG. 21 illustrates a number of color wheels for a split spectrum;

[0059] FIG. 22(a) is a schematic diagram of a barrier screen in a stereo mode;

[0060] FIG. 22(b) is a schematic diagram of a barrier screen in a non-stereo mode;

[0061 ] FIG. 23 is a flow chart illustrating example computer executable operations that may be performed in projecting a stereo image;

[0062] FIG. 24 is a flow chart illustrating example computer executable operations that may be performed in projecting a stereo image; and

[0063] FIG. 25 is a block diagram illustrating an example of a configuration for a stereo projection system.

DETAILED DESCRIPTION

[0064] It will be appreciated that for simplicity and clarity of illustration, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the examples described herein. However, it will be understood by those of ordinary skill in the art that the examples described herein may be practiced without these specific details. In other instances, well-known methods, procedures and components have not been described in detail so as not to obscure the examples described herein. Also, the description is not to be considered as limiting the scope of the examples described herein. [0065] It will be appreciated that the examples and corresponding diagrams used herein are for illustrative purposes only. Different configurations and terminology can be used without departing from the principles expressed herein. For instance, components and modules can be added, deleted, modified, or arranged with differing connections without departing from these principles.

[0066] As discussed above, light is an important resource in projector technology. The brightness of the projector determines the achievable size and contrast of the projected image under a given set of viewing conditions or parameters (e.g., ambient illumination and screen properties such as reflectance, viewing angle, etc.). However, the brightness of the light source itself (e.g., the projector lamp) is typically limited by the heat generated by the light source. Excessive heat can significantly reduce the expected life span of the lamp. As projector lamps are expensive components it is highly desirable to utilize the available light with maximal efficiency. It has been recognized that most single lens projection methods used to project stereo images utilize 15% or less of the available light.

[0067] The following provides systems and methods to increase the light efficiency of a single lens stereo projector. Some of the proposed designs also provide improved refresh rates and enhanced resolution. These methods provide projectors with stereo capability which is enabled internally, which do not require external optics nor any calibration and adjustment in order to change between normal and stereo modes. Stereo enabled projectors are also suitable for home theater and other applications that require occasional stereo with little to no user intervention. Some of the presented methods are also applicable to auto-stereoscopic displays.

Minimum Delta Composition

[0068] It is widely accepted that the views for stereo (or any 3D multi-view system) should be completely separated. Any amount of cross-talk is considered harmful for stereo perception. It has been recognized that this notion is not entirely true since a stereo pair has much in common between the two views. As such, it has been found that ensuring that the common part of the two views separately reach each eye can be considered, at least in part, wasted effort. Instead, the inventor has realized that the common part can be intentionally directed to both eyes simultaneously. In this way the brightness of the image can be increased, flicker cased by the time multiplexing of views can be reduced. In configurations that spatially interlace the left and the right view, this method may increase the perceived resolution, for at least of part of the image, by displaying the common part in full resolution.

Separate Polarizing Wheel

[0069] It has also been recognized that a separate wheel can be added to both single DLP projectors and triple DLP projectors in order to polarize the light for left and right views in passive stereo projectors. A separate polarization wheel can have a clear segment where it does not polarize the light, with the following important uses: (i) when the projector is not used for stereo display, the clear segment can be fixed in the light path position all the time, hence it does not degrade the brightness of the projector in non-stereo mode; and (ii) when the projector is used in stereo mode, the clear segment is used to project the common part of the views to both eyes simultaneously, hence increasing the brightness of the projector and reducing the flicker.

Dual Path Split Merge

[0070] Light polarization by a polarizing filter, either a static polarizer or an electronically alternating polarizer, typically filters out more than 50% of the available light. The inventor has also recognized that the light can instead be split into two orthogonally polarized channels using a polarizing beam splitter, the two channels coded simultaneously, and the coded channel merged back and projected using the same lens. When not in stereo mode, the two chips can be used to double the refresh rate, and to improve resolution as described below. In other words, it has been found that the light in a projector can be split into two orthogonally polarized channels using double refraction (i.e. crystals which refract light with different polarizations), passed through film, and then the generated stereo image projected using two separate lenses to increase the efficiency of the projector.

Embedded Super Resolution

[0071 ] It has also been found that when using a dual path split merge technique in a non- stereo (or "normal") mode, it is possible to increase the spatial resolution of the system by shifting one of the image coding mechanism (e.g., a DLP chip), by half a pixel with respect to each other. It has been recognized that while the use of several projectors with a camera to resolve the homography between the different overlapping projectors has been used in order to enhance resolution, this technique is not very efficient, as the integration is done after the optical system, and suffers from calibration problems. In general, tiling provides better results when multiple projectors are used. In contrast from a technical point of view the "super resolution" may be embedded inside the projector before the lens at optimal half-pixel displacement. This provides better result and does not require either a camera or calibration. From a functional point of view, this is an additional benefit for the stereo optics when used in non-stereo mode.

Groupings of Configurations

[0072] The following examples are arranged in several groups to aid in illustration. It can be appreciated that the accompanying figures provide illustrative and/or simplified calculations of light efficiency for a corresponding configuration with detailed calculations provided in tables described below. The groups described are as follows:

[0073] Existing Configurations - This group describes the light efficiency of existing single lens projector technology for non-stereo, active stereo and passive stereo configurations. The group describes both single DLP and triple DLP configurations.

[0074] Active Stereo using Minimum and Delta Images - This group introduces the use of three temporally interleaved images for active stereo in both single DLP and triple DLP configurations. This approach is also applicable for active stereo of computer displays and cinema.

[0075] Two Segment Polarizing Wheel - This group introduces the use of polarizing wheel for passive stereo in both single DLP and triple DLP configurations.

[0076] Two Segment Polarizing Wheel with a Clear Window - This group describes a further improvement to the non-stereo mode of a two segment polarizing wheel configuration.

[0077] Three Segment Polarizing Wheel - This group introduces the use of a three segment polarizing wheel for passive stereo in both single DLP and triple DLP configurations. [0078] Color Wheel and Polarizing Beam Splitter - This group introduces the use of color wheel and a polarizing beam splitter for a double DLP configuration. This group also introduces a better refresh rate and an improved resolution for a non-stereo mode.

[0079] Dichrotic Color Wheel and Polarizing Beam Splitter - This group describes an improvement to the previous group using a quad-DLP configuration. This group also provides improved resolution for stereo and non-stereo modes.

Existing Configurations

[0080] FIG. 1 (a) describes the light efficiency of a single DLP projector 10. The single DLP projector 10 in FIG. 1 (a) includes a lamp 12 whose light is filtered by a four segment color wheel 14, which temporally multiplexes red, green, blue and white light. Assuming that these filters pas 1/3, 1/3, 1/3, 1 /1 of the incoming light respectively, the maximum efficiency of the wheel would be (3/4 x 1/3) + (1 /4 x 1 /1 ) = ½ or 50%. As shown in FIG. 1 (a), an additional 5% is typically lost by the need to blank the transition between colors, and finally 5% of the remaining light is lost due to the fill-factor and reflectance of a DLP chip 16 in the projector 10 to provide an output beam 18. In a non-stereo mode, the efficiency of a single DLP projector is therefore only 43% mostly due to the time multiplexing of the color channels.

[0081] A triple DLP projector 20 renders all color channels simultaneously and therefore can reach 90% efficiency as seen in FIG. 1 (b). The projector 20 shown in FIG. 1 (b) includes a lamp 12, a light splitter 24, and a dedicated DLP chip 26 for each channel. The projector 20 renders all three color channels simultaneously by splitting the light into three chromatic channels and modulating each channel by its dedicated DLP chip 26, which can significantly enhance the efficiency of the output beam 28 of such a triple DLP projector 20.

[0082] FIGS. 2(a) and 2(b) illustrate single and triple DLP active stereo projectors respectively, which temporally alternate the left and right views, which reduces their duty cycle to 50%, with an additional 5% being lost due to extra blanking needed to ensure good stereo separation. By synchronizing the alternating views with a pair of special shutter glasses 30, which use polarizing film and an LCD layer to create an electronic light valve, each eye sees only its designated view. As noted, due to the view multiplexing, the duty cycle of each view is reduced by half. Moreover, the shutter glasses 30 pass only 35% of the incoming light. As a result, the light efficiency of a single DLP active stereo projector 10 is only 7% as shown in FIG. 2(a). The light efficiency of triple DLP stereo projector 20 is better, and may increase to 15% as shown in FIG. 2(b).

[0083] Single lens passive stereo projectors, shown in FIGS. 3(a) and 3(b), temporally alternate the left and right views temporally, which reduces their duty cycle to 50%. Since passive stereo projectors are not synchronized with the passive glasses 34, they need to use light polarization for view separation using an electronically alternating polarizing screen 32 (also known as a "z screen"), which transfers only 35% of the light and requires longer blanking between views, which reduces light by an additional 10%. Passive polarized glasses 34 used in such a system transfer 84% of the correctly polarized light resulting in an overall efficiency of 5% for a single DLP projector 10 and 1 1 % for a triple DLP projector 20.

[0084] Although not shown, another existing configuration includes the Dolby wheel, which includes a special rotating wheel placed before or after the lens.

Active Stereo using Minimum and Delta Images

[0085] As discussed above, it is widely accepted that the views for stereo (or any 3D multi- view system) should be completely separated since any amount of cross-talk is considered harmful for stereo perception. The inventor has recognized that this however is not entirely true, since a stereo pair has much in common between the two views. In other words, ensuring that the common part of the view will separately reach each eye can be considered a wasted effort. Instead, it has been recognized that the common part can be intentionally directed to both eyes simultaneously. In this way, the brightness of the image can be increased, and the flicker cased by the time multiplexing of the views can be reduced.

[0086] FIGS. 4(a) and 4(b) show a stereo pair taken by a displaced camera. FIG. 4(c) shows an anyglyph image of the stereo pair in views (a) and (b). It can be seen that the disparity between the views in this case is quit considerable as shown by the anyglyph image.

[0087] Let L(x, y) and R(x, y) be the left and right views respectively. The minimum image M(x, y) may then be defined as M(x, y) = min(L(x, y),R(x, y)), for each color channel separately, and the left and right delta images DL and DR to be DL(x, y) = L(x, y) -M(x, y); and DR(x, y) = R(x, y) -M(x, y). [0088] The middle row, FIGS. 4(d), 4(e), and 4(f), show a left delta image, a minimum image and a right delta image for the same stereo pair shown in FIGS. 4(a) and 4(b). It can be seen that the minimum image looks more similar to the views than each of the delta images. If one directs the common part to both eyes one third of the time, and alternate between the right views during the remaining two thirds of the times, the exposure can be improved by a factor of 1 1 /3. For example, a projector with an illumination rating between 1000 to 2000 lumens, the improvement can be significant as it is equivalent to having a 2600 lumen projector instead of a 2000 lumen projector.

[0089] It has been recognized that with the above, the minimum image is displayed twice as long as the delta image and to overcome this, image histograms can be considered, as shown in FIG. 5.

[0090] FIG. 5 provides histograms for the example stereo image pair shown in FIG. 4, its minimum image, and its delta images. It can be seen that, at least for this example image, the delta images are relatively dark - only a low percent of the image pixels exceed an intensity level of 128. If it assumed that the values of the delta images do not exceed a predetermined value, for example 128, then the projected images can be adjusted to provide the desired improvement, 1 1/3 in the present example. Some examples are shown in Table 1 below. Table 1 shows the emitted light from a projector in 0-255 units, which can be normalized to reflect the emitted lights in lumens for any given projector. The top portion of Table 1 includes original values for the left and right views, the minimum and delta images that correspond to these values, and the light output of an ideal conventional stereo system (half left and half right time multiplexing). The bottom portion of Table 1 shows corrected values of the two views, the actual values which are emitted to left eye only, the right only, and to both eyes and the resulting output. It can be seen that the results show 1 1 /3 improvement in the output value over the conventional stereo. The last line shows a contrast on 129 which cannot be fully reconstruction, as this would require a left value of 258 which exceeds the maximum possible value of 255. Orig ^"rial Views Minimi ui and Delta Images Coi.vensioi.al Stereo

Left Right Delta-L Min Img Delta-R Left Right

255 255 0 255 0 127 , 5 127 , 5

255 128 123 123 0 127 , 5 64

128 128 0 123 0 64 64

128 0 123 0 0 64 0

0 0 0 0 0 0 0

129 0 129 0 0 64 , 5 0

1.33 Im proven .ei.t Projected Images Resulting Views

Left Right Left Both Right Left Right

170 170 255 255 255 170 170

170 S5.33 255 255 0 170 85

35.33 S5.33 123 123 12G 85 , 33 35 , 33

35.33 0 255 0 0 85 0

0 0 0 0 0 0 0

36 0 253 0 0 8(5 0

Table 1

[0091 ] By cutting the intensity level of the delta images at the predetermined value, one can guarantee that the intensity value of the delta image does not exceed the predetermined value. If half the error is added (caused by the cut-off) to the minimum images one can equally divide the error between the two views. If the remaining error is too large, the light efficiency can be reduced or the contrast of the original views can be reduced. There is, therefore, a tradeoff between brightness, contrast, and cross talk. FIGS. 4(g), 4(h), and 4(i) show the reconstructed views obtained using cut-off at 128, with no contrast reduction, and the corresponding error image (4(i)). The absolute value of the error between the reconstructed views and the original views, which is the same for both left and right views can be appreciated from FIG. 4 (i).

[0092] FIG. 6 illustrates the light efficiency of the method illustrated in FIGS. 4 and 5. AS can be seen in FIG. 6, the increased exposure time of the views for each eye due to the common (minimum) image increases the light efficiency of the projector 10, 20, and reduces the flicker as each view is blanked for only 1/3 of the time.

[0093] Table 2 below illustrates further detailed computations.

Table 2

[0094] Table 2 above provides detailed calculations of the light efficiency of all configurations that appear in the present disclosure. The configurations are divided into groups that match the groups as organized above. Highlighted boxes designate significant factor or significant changes, which are explained below. [0095] Lines 3,4: Shutter Glasses - The shutter glasses 30 used for active stereo are usually LCD based. These glasses utilize an LCD layer between a pair of polarizing film. When the LCD is activated it modifies the orientation of the polarized light that passes thought it, creating a light valve. The light efficiency of this set is rather low - only 35% of the incoming light pass though.

[0096] Lines: 5,6: View Multiplexing and z-screen - The z-screen 32 is a device that polarizes light and electronically changes its orientation. Its efficiency is low - only 35%. In addition it is also a slow device which requires extra blanking time between views, hence the efficiency of the view-multiplexing is reduced.

[0097] Line 9,10: View multiplexing - Due to the shared part each eye views its own view for about 2/3 of the time instead of only 1 /2 of the time.

[0098] Lines 13,14: Channel Separation and Polarization - For a single DLP projector 10, adding polarization to the color wheel doubles the number of segments from four to eight. This requires more blanking time between segments, which reduces the efficiency of the color wheel. For a triple DLP projector introducing a polarizing wheel adds blanking time for two segments.

[0099] Lines 13,14: View Multiplexing - The efficiency of a passive polarizer is slightly higher than that for a z-screen 32. Also, since it is a rotating wheel and the transition time was already counted for as channel separation, the view multiplexing time is set to 0.5.

[00100] Line 15: Polarization - The clear window eliminates the degradation due to polarization when the projector is used in regular mode.

[00101 ] Lines 20,21 : Channel Separation and Polarization - For a single DLP projector, adding three segments polarizing wheel triples the number of segments from four to twelve. This requires more blanking time between colors/polarization, which reduces the efficiency of the color wheel. For a triple DLP projector introducing a polarizing wheel adds blanking time for three segments. The light efficiency of the polarizing wheel increases due to the clear window.

[00102] Lines 20,21 : View Multiplexing - Due to the shared part each eye views it own view for about 0.6 of the time instead of only 0.5 of the time. [00103] Lines 20,21 : Passive Glasses - Part of the light that reaches the glasses 34 is not polarized, therefore the glasses 34 filter out larger portion of the light then they do for correctly polarized light.

[00104] Lines 23,24: Prism, View Multiplexing and Passive Glasses - Beam splitter efficiency is about 95%. There is no view multiplexing as both views are rendered together. The passive glasses receive both polarization and only pass 40% of the total light.

[00105] Lines 25,26: Wheel Efficiency and Channel Separation - The dichrotic color wheel passes most of the light view transmission and reflection paths, however it is a six segment wheel and requires more blanking time between views.

[00106] Further detail of these configurations is provided below in subsequent sections.

[00107] The same principle of splitting the two views into left only right only and shared view can be done using equations such as those described below. Three sets of equations are presented, representing different cases, but should not be considered exhaustive. The equation sets vary in their gain factor, relative weight of each channel and the way they handle errors. Some absorb the error by increasing the cross talk between the stereo channels at erroneous location, while other absorb the error by reducing the brightness gain in these location.

[00108] Set 1.1 - Equal weights [ 1/3, 1/3, 1/3], and gain = 2.

[00109] It can be appreciated that the actual gain depends on duty cycle of the projecting device and that errors absorbed by decreasing intensity at pixels with errors. This example uses a range of 0-255 brightness values.

Lo = original left channel pixel value

Ro = original right channel pixel value

Ld = left delta pixel value

Rd = right delta pixel value

Mo = min original left, right pixel value

Ln = new left channel only pixel value

Rn = new right channel only pixel value

Bn = new both (shared) channel pixel value Mo =min(Lo,Ro)

Ld = Lo-Mo

Rd = Ro-Mo

Bn =Mo-max(Mo-max(Ld,Rd),0)/2

Ln =min(Ld+Mo-Bn,127)

Rn =min(Rd+Mo-Bn,127)

[00110] Consequently:

Bn = Bn ^* 2

Ln = Ln ^* 2

Rn = Rn ^* 2

[00111 ] Set 1.2 - Equal weights [1/3, 1/3, 1/3], and gain = 2.

[00112] It can be appreciated that the actual gain depends on duty cycle of the projecting device and that errors absorbed by increasing cross talk at pixels with errors.

Lo = original left channel pixel value

Ro = original right channel pixel value

Ln = new left channel only pixel value

Rn = new right channel only pixel value

Bn = new both (shared) channel pixel value

[00113] Then:

Bn = max(Lo,Ro) 1 2

Ln = max(Lo-Bn,0)

Rn = max(Ro-Bn,0)

[00114] Consequently:

Bn = Bn ^* 2

Ln = Ln ^* 2

Rn = Rn ^* 2

[00115] Set 1.3 - [1/4, 1/2, 1/4] relative weight, and gain = 4 Lo = original left channel pixel value

Ro = original right channel pixel value

Ln = new left channel only pixel value

Rn = new right channel only pixel value

Bn = new both (shared) channel pixel value

Bn = max(Lo,Ro) / 4

Ln = max(Lo-2^*Bn,0)/2

Rn = max(Ro-2^*Bn,0) 12

[00116] Consequently:

Bn = Bn ^* 4

Ln = Ln ^* 4

Rn = Rn ^* 4

[00117] Equation sets that specifically handle error conditions (e.g., by forcing

predetermined, non-linear handling) are also possible. Similarly, equations that work in diffident color spaces, for example Brightness + Chroma may also be used to avoid color artifacts.

[00118] It should be noted that tradeoffs may occur. For example, a movie can have any contrast within each frame, but if the contrast of the same pixel between eyes exceeds an adaptive threshold (1/2 the max contrast for 1 /3 1/3 1/3 partition) then the contrast of the specific pixels (only) in a frame in one of the eyes (only) will be reduced accordingly to compensate. The frame at the second eye will not be affected. It is also possible to divide the error between eyes and reduce its magnetite in each eye - the preferred method depends on subjective perception test.

[00119] It can be appreciated that in examples throughout this disclosure using DLPs 16, other methods such as reflective LCD may also apply.

Two Segment polarizing Wheel

[00120] Color wheels used to multiplex color channels have recently found applications in single DLP projectors 10. Conventional color wheels have three or four segments for RGB and optionally white, as seen in FIG. 7(a). The same wheel can be used to polarize the light, however applying a linear polarizer to a wheel does not provide the view separation, since the orientation of the polarizer changes when the wheel turns. In order to obtain view separation, an orientation invariant polarization scheme such as: (i) Left and right circular polarization and (ii) Radial (polarization lines are radiuses) and concentric (polarization lines are concentric circles) polarization can be used.

[00121 ] Left and right circular polarization encodes the views by using left and right circular polarization and requires circular polarized lenses. Radial and concentric polarization when applied to a small segment of the wheel (i.e. the light path window) provides linear

perpendicular polarization, and requires linear polarized glasses. FIG. 7(b) shows an example of a color wheel which also polarizes the light into left and right views.

[00122] Since the synchronization is now done be the color wheel itself, which is slightly more efficient than the electronically alternating polarizing screen 32, and since the polarization efficiency of the a passive filter is slightly higher, the overall performance is also slightly increased to 7% instead of 5%.

[00123] Triple DLP projectors 20 do not utilize color wheels, Therefore a two segment polarizing wheel shown in FIG. 7(c) needs to be added. This improves the light efficiency of the projector from 1 1 % to 14% however, it reduces the efficiency of non-stereo projection from 90% to 36%.

[00124] FIGS. 8(a) through 8(d) illustrate example configurations for a color and polarizing wheel operation. In FIG. 8(a), a color wheel projector 40 is shown in which light from a lamp 12 at A is filtered by a color wheel 14 at B and modulated by a DLP chip 16 at C. The modulated light is then projected by a lens 42 at D.

[00125] In FIG. 8(b), a color and polarizing wheel projector 50 is shown in which light from the lamp 12 at A is filtered and polarized by a color wheel 52 at B rotating at a different speed, and modulated by the DLP chip 16 at C. The modulated light is then projected by the lens 42 at D.

[00126] In FIG. 8(c), a two wheel projector 60 is shown in which light from the lamp 12 at A is filtered by a color wheel 14 at B and polarized by a polarizing wheel 62 at C, modulated at D by the DLP chip 16, and projected at D by the lens 42. [00127] In FIG. 8(d), a two wheel projector with clear window 70 is shown in which light from the lamp 12 at A is filtered by the color wheel 14 at B, passes through a clear window of a polarizing wheel 72 at C, is modulated at D by the DLP chip 16, and is projected at E by the lens 42.

[00128] FIGS. 9 and 10 illustrate the light efficiency of two segment color wheel projectors, wherein detailed computations appear above in Table 2. In FIG. 9, it can be seen that the light efficiency of a two segment polarizing wheel 80 in non-stereo single DLP projector 10 is degraded as light is being polarized, even when stereo functionality is not being used. FIG. 10 illustrates that the light efficiency of a two segment polarizing wheel 82 in a stereo triple DLP projector 20 is further degraded by the viewer's polarized glasses 34, which transfer only 84% of the correctly polarized light passing therethrough.

Two Segments polarizing Wheel with a Clear Window

[00129] To overcome the efficiency problem in non-stereo mode, a separate polarizing wheel shown in FIG. 7(d) can be used for both single and triple DLP projectors 10, 20. When operating in stereo mode, this method is the same of the previous one. However when operating in non-stereo projection the wheel can be "parked" in a fixed location having the clear window facing the light path to avoid degrading the performance in a non-stereo mode.

[00130] FIGS. 1 1 and 12 illustrate the light efficiency of a two segment color wheel with a clear window, with detailed computations provided above in Table 2. It can be appreciated in FIGS. 1 1 that light efficiency improvements are achievable by parking the clear window facing the light path when in a regular/normal or "non-stereo" mode. As illustrated in FIG. 12, since the clear window is small, it has a negligible effect on the light efficiency, which is therefore similar to the configuration shown in FIG. 1 1 .

Three Segment Polarizing Wheel

[00131 ] The minimum and delta images used in the active stereo enhancement described above can also be used more efficiently since the shared image passes only one polarizer (i.e., the glasses 34). This can be implemented by having the clear window size for the polarizing wheel equal to 0.2 ^* 360 = 72^° and by having each of the polarized sections equal to 144^°.

Assuming for illustrative purposes that the polarization reduces light by 50%, it can be concluded that the efficiency improvement for an intensity cut-off of 128 is 1 .6 as seen in Table 3 below (emitted light only):

Original Views i nl mini and Delta Images Convensional Stereo

Left Right Delta-L Min Img Delta-R Left Right

255 255 0 255 0 63.75 63.75

255 128 128 128 0 63.75 25.6

128 128 0 128 0 25.fi 32

128 0 128 0 0 32 0

0 0 0 0 0 0 0

129 0 129 0 0 32.25 0

1.6 Improvement Projected Images Resulting Views

Left Right Left Both Right Left Right

102 102 255 255 255 102 102

102 40.96 255 255 0 102 51

40.96 51.2 128 128 128 51.2 51.2

51.2 0 255 0 0 51 0

0 0 0 0 0 0 0

51.6 0 258 0 0 51.6 0

Table 3

[00132] FIG. 13 illustrates the light efficiency of a three segment polarizing wheel in a stereo mode. The shared non-polarized segment increases the light efficiency due to both the better transmission factor and a longer exposure for each eye. The efficiency of the polarized glasses 34 is reduced since part of the light is non-polarized. Detailed computations are provided above in Table 2.

Color Wheel and Polarizing Beam Splitter

[00133] Single lens stereo projectors have a relatively low efficiency mainly due to: (i) time multiplexing of views, and either the low efficiency of the shutter glasses 30 used in active stereo or the z-screen 32 used in passive stereo systems. The proposed approach addresses both issues by splitting the light into two orthogonal polarization orientations, then

simultaneously encoding the two views using two DLP chips, and merging the two views to be projected by a single lens 42. This process is illustrated in FIG. 14(a). FIG. 14(b) shows an alternate configuration which codes two color channels simultaneously. This alternate configuration doubles the refresh rate in non-stereo mode as only half a turn of the color wheel is sufficient to render a frame using both DLP chips 16. In FIG. 14(a) a dual DLP chip and color wheel projector 1 10 is shown. The light from a lamp 12 at A is filtered by the color wheel 1 12 at B and split by the polarizing beam splitter 1 14 at C. Each polarized beam is modulated by a dedicated DLP chip 1 16 at D and merged by a second polarized beam splitter 1 18 at E and projected by the lens 42 at F. In FIG. 14(b), a similar configuration 122 is used, however, the light is split before the color wheel 1 12 such that two color channels can be rendered simultaneously. This doubles the refresh rate in a non-stereo mode. It may be noted that the light path length from the DLP chips 1 16 to the lens 42 is the same in both FIGS. 14(a) and 14(b).

[00134] FIG. 15 illustrates the light efficiency of a color wheel and polarizing beam splitter configurations in stereo (b) and non-stereo (a) modes. Detailed computations are provided above in Table 2. The polarizing beam splitter 1 10 splits the light into perpendicular polarization orientations and the two beams are modulated for both views simultaneously. A second polarizing beam splitter is used to merge the two views into a single beam which is projected. The result is increased light efficiency and flicker free stereo projection. In a non-stereo mode, a negligible amount of light is lost due to the additional optics. It may be noted that only 40% of the emitted light passes through the glasses 34 since the emitted light contains both polarization orientations. It can be seen that in the regular mode (a) 41 % efficiency is achieved and in stereo mode (b), 16% efficiency is achieved.

Dichrotic Color Wheel and Polarizing Beam Splitter

[00135] The dichrotic mirror color wheel shown in FIG. 7(e) can increase the light efficiency of the color wheel by reflecting the complementary color rather than absorbing it, as shown in FIG. 16. The color coding is done using six colors which provide more flexibility than the four colors used in conventional projectors (minimum of two color channels (complement colors) is larger or equal to the minimum of three color channels (white)). The system 150 shown in FIG. 16 is more complex than the configuration 1 10 shown in FIG. 14. The color wheels can be omitted by using dichrotic prisms, which it may be noted that such a configuration would require six DLP chips 16.

[00136] The dichrotic mirror wheel configuration 150 shown in FIG. 16 uses two dichrotic mirror wheels 152 and four DLP chips 158 to efficiently use the available light and improve resolution in both stereo and non-stereo modes. The light from a lamp 12 is split into two complementary colors at B using a first dichrotic mirror wheel 152. Each component is split by a respective polarizing beam splitter 156 at D and is modulated by a DLP chip 158 at E and merged by a second polarizing beam splitter 160 at F. The two color channels are merged by a second dichrotic mirror wheel 152 at G and projected by the lens 42 at H. It may be noted that the optical path length from the DLP chips 158 to the lens 42 is the same for all DLP chips 158 in this example and that the orientation of the reflection of a polarization beam splitter 156, 160 can be controlled by rotating the beam splitter 156, 160.

[00137] FIG. 17 illustrates the light efficiency of a dichrotic color wheel projector 150 in stereo (b) and non-stereo (a) modes. Detailed computations are provided above in Table 2. The dichrotic wheel shown in FIG. 7(e) can increase the light efficiency of the color wheel by reflecting the complementary color rather than absorbing it. The color coding is done using six colors which provides more flexibility that the four color versions used in conventional projectors.

Resolution Enhancement

[00138] It is recognized that by obtaining several images with different sampling grids, the resolution of the image can be enhanced by a computational process known as super- resolution. When an image is projected, no such computation takes place. However, averaging or integration can be done, which alone can significantly improve the projected image.

[00139] It is proposed to shift the DLP chips 16 used for stereo mode in a two DLP configuration by half a pixel horizontally and vertically as shown in FIG. 18(a). It may be noted that such a displacement (shifting) does not affect the stereo perception. FIG. 18(a) illustrates a pixel grid alignment 200 for a pair of DLP chips 16. The pixels in each grid 202 are shifted by half a pixel both horizontally and vertically. FIG. 18(b) illustrates a pixel grid alignment 210 for a quartet of DLP chips 16. In FIG. 18(b), the pixels of grid 212 are shifted by half a pixel horizontally (grid 214), vertically (grid 216) and both horizontally and vertically (grid 218). It may be noted that certain overlaps in FIG. 18(b) are equivalent to the shift in FIG. 18(a).

[00140] Although the total number of pixels is only twice the number of pixels in a single view, and no operation other then averaging takes place (hence double resolution cannot be obtained), still the sharpness and clarity of the image can be significantly enhanced as shown in FIG. 19. This figure simulates a scenario in which the projector is fed with an image with double (four times the number of pixels) its native resolution (shown in (a)) The projector down-samples the image (e.g., using bi-cubic interpolation as shown) and then projects the down-sampled image (shown in (b)). Using the proposed method, the image is down-sampled again - this time with half a pixel displacement (shown in (c)) and then the two different down-sampled images are projected together, hence integrated. The simulated result is shown in (d). This image, although not as good as the high-resolution input, is significantly better than the best down- sampled image that would otherwise be projected. The result is not only sharper and smoother, but has better resolution as clearly some of the text that was unreadable in the single DLP view become readable when the two views are integrated.

[00141 ] FIG. 20 illustrates another down-sampling and view integration example. View (a) is the original high resolution image and (b), (c), (d), and (e) are four bi-cubic down-sampled images with half pixel offsets horizontally and vertically and both horizontally and vertically as illustrated in FIG. 18(b). View (f) is the integrated image which is clearly smoother and shows more detail than any of the down-sampled images (b) - (e).

General Commentary

[00142] It can be appreciated that the color wheel of a single DLP projector 10 can have three four or, possibly more color channels.

[00143] Also, the method described above which uses minimum and delta images can also be applied to multi-view configurations, for example a lenticular can display the minimum image (the area which is in vergence) on top of the lenticular (using flat thin transparent plate) hence increasing the resolution of that part. It may be noted that this will work for complete or nearly complete vergence areas since the low resolution delta cannot compensate for the high resolution minimum image, a low pass filter can be applied to parts of the minimum image to correct this.

[00144] It can also be appreciated that the proposed minimum delta images can be used with multiple projectors for example, where one projects the minimum image and the second alternates between the corrected delta images; where three projectors are used, one for the minimum image and two for the corrected delta images; and where even more projectors are used, if more views need to be displayed.

[00145] Moreover, the term projector as herein used may refer to any projection device, including box contained projection based televisions. Similarly, the techniques and principles described herein should not be considered to be limited to DLP projectors and other light modulating components can be used, for example: light emitting devices such as phosphor and light valve devices such as LCDs, with care taken using LCDs since they polarize light themselves, and appreciating that light emitting devices act as color modulated light sources. The principles discussed herein also should not be considered limited to the specific optical configurations shown in the figures, such figures are for illustrative purposes only.

Split spectrum stereo devices

[00146] Split spectrum stereo devices such as the Dolby 3D stereo use close but different pairs of wavelength bands for red, green and blue channels for projection. Each of the passive filters in the glasses 34 allows only for one member of the pair through bringing each view to its intended eye. This method is similar to coding using polarization, but it does not require a silver screen. In principle, anywhere polarization appears in the above described configurations, it can also applies to split-spectrum by replacing the polarizing filter with its counterpart split- spectrum filter, e.g., the setup shown in FIG. 8(c) replacing the polarization with split spectrum. Likewise, changing the polarization to split spectrum in the configuration shown in FIG. 8(d) can be used for displaying the triplet stereo Left-only, Both, Right-only as described above.

[00147] It is also possible to combine the properties of both wheels into a single wheel, which is better appropriate for 3D only projectors as shown FIG. 21 . FIG. 21 shows a color wheel for split spectrum projection. The left wheel is a 3-color wheel, where 'L' designates left only filter, 'R' eight only filter, and 'B' wide band filter for both eyes simultaneously. Colors represent the respective band. The wheel at the middle has an additional white channel to utilize shared values in the color channels. White 'R' and 'L' are comb-like filters which each send RGB values to one eye only, whereas the white 'B' is simply a transparent window (all color channels and both eyes are shared). [00148] The right wheel only has white comb-like filters that splits the spectrum between the eyes and a transparent window. This wheel works in conjunction with a conventional color wheel. Because the color wheel moves significantly faster, it is not a required to synchronize the wheels. This configuration also allows lossless 2D projection by locking the wheel at the 'B' position, eliminating the need to insert the wheel into the light path for 3D and retract it for 2D. The wheels in FIG. 21 can also be used for a single wheel polarized light based 3D projection by using polarization filters instead of split spectrum filters.

[00149] The segments show [½, ½, ½] partition. Other partitions such as [¼, ½, ¼] are also possible. The order 'LBR' is set so the transition for each color channel will be from one eye to both to the other eye. A finer partition may enable smoother transition LBRBLBRBLBR order by splitting the 'B' part. The exact size of each partition is determined by radiometric and photometric considerations. For example shared region will also transfer more energy because it does not block part of the bandwidth (or part of polarization directions). Without limiting the general principle that split spectrum can be used everywhere polarization is mentioned in in the configurations described above, the following may be highlighted:

[00150] - Configuration shown in FIGS. 8(b) and 8(d), FIG. 1 1 , FIG. 12, and FIG. 13, for 2D and 3D projection.

[00151] - Configurations shown in FIG. 14, FIG. 15 that use multiple DLPs where the filtered light and its complement can both be used (by using dichroic filter reflects the 'filter-out' part of the light and does not absorb it and two DLPs).

Barrier Screen Displays

[00152] Barrier screen displays as shown in FIG. 22 are auto-stereoscopic displays capable of directing different views to different eyes without the need for special glasses. These screens use a special barrier 300 that blocks some of the rays thus allowing only the rays from the left view to be seen by the left eye and only rays from the right view to be seen by the right eyes. The views themselves are interlaced in columns 302 as seen in Figure 21 . The barrier 300 can be placed in front of the screen, or between the light source and the screen illuminating only the correct rays for each eye. Alternatively, the light source itself can be arranged as an array of light strips. [00153] The largest advantage of barrier screen displays over other auto-stereoscopic displays such as lenticular array displays, is their ability to switch between stereo and non- stereo mode, making them suitable as TV/computer displays with stereo capability.

[00154] Barrier screen displays suffer from several problems: (i) the barrier screen blocks approximately 2/3 of the light creating a very dim display, (ii) the horizontal resolution is reduced due to interlacing, and (iii) some displays exhibit wide dark vertical bars when in stereo mode.

[00155] It is suggested to use the minimum delta images in barrier screen displays. The display shows the left and right images part of the time and minimum image during the rest of the time. This can improve brightness as shown in Table 4 below. Also, since the minimum image can be displayed in full resolution, all areas that are in vergence can be displayed in full resolution. It is possible that some areas that are not in vergence can also benefit from enhanced resolution (this depends on human vision response to minimum-delta images with different resolutions).

[00156] The following table shows that the minimum delta image can provide approximately 150% improvement in brightness. In this table, the delta images were shown 3/4 of the time and the minimum image was shown during the remaining 1/4 of the time.

Original Views Minimi i and Delta Imaqes Coiivensional Stereo

Left Right Delta -L Min Img Delta-R Left Right

255 255 0 255 0 30.6 30.6

255 128 123 123 0 30.6 15.36

128 128 0 123 0 15.36 15.36

128 0 123 0 0 15.36 0

0 0 0 0 0 0 0

1 9 0 129 0 0 15.48 0

1.5 Improvement Projected Images Result! \g Views

Left Right Left Both Right Left Right

45.9 45.9 255 255 255 45.2625 45.2625

45.9 23.04 255 255 0 45.2625 22.3125

23.04 23.04 123 123 128

23.04 0 255 0 0 22.95 0

0 0 0 0 0 0 0

^3 0 253 0 0 n 0

Table 4 [00157] In FIG. 22(a), stereo mode, the barrier 300 allows light from the columns 302 belonging to the left view (blocks marked by 'L') to be seen by the left eye only, and light from the right view (blocks marked by 'R') to be seen by the left eye only. The barrier 300 blocks approximately 2/3 of the light at the dark areas. The remaining 1 /3 of the light that passes though the barrier slits loses approximately 65% due to light polarization used to create the barrier (as in shutter glasses). As shown in FIG. 22(b), when not in stereo mode, the barrier is turned off, turning into a transparent layer 304 (that still block 65% of the light). It may be noted that displays that use a light strip array instead of an LCD barrier screen 300 do not suffer from degraded brightness in non-stereo mode.

Color LED illumination

[00158] For high-power projection (cinema, home theater etc.) the use of a high power lamp in conjunction with color filters (either on a color wheel or on color splitting prism) is particularly advantageous. On the other hand, LEDs are very useful for small and battery operated projectors and can produce continuous illumination, or pulsed illumination for use with single DLP projectors.

[00159] In any of the configurations herein described, where light + color-wheel, or light + filter is used, it can be replaced with LEDs, resulting in better energy efficiency. In particular, a system can have LED with fixed polarization or fixed spectral wavelengths, or less efficient white LEDs with filters attached to them. The selected LEDs can be turned on only when the specific coding is needed. LEDs are far less costly than projector lamps 12 and can be quickly turned on and off. With the critical resource of small and portable projectors being energy (i.e., battery time), having multiple LEDs and using only part at a given time is a viable option.

Multiple projector setup

[00160] For polarized light or, for example, split spectrum based stereo configurations, it is possible to use a multiple projector system instead of a single projector system to use the proposed triplet methods for energy saving or to increase brightness.

[00161] Stereo projector + regular projector configuration - In this configuration a

conventional stereo projector is used to project the left only and right only parts in alternating manner, for example Z-Screen or Dolby 3D. The additional regular projector projects the shared part synchronously with the stereo projector. The light efficiency of the stereo projector with a color wheel is 12.5% or less (50% are lost by color filters, 50% are lost due to duty cycle, and another 50% are lost by the polarized/spectral filters. There is some additional loss caused by glasses even for the pass through band/polarization.

[00162] In contrast the regular projector efficiency is about 25% due to the color wheel loss and the (needless) absorbed by the 3D glasses (No loss caused by duty cycle or filter on the projector).

[00163] The configuration shown in Table 5 below illustrates how adding a 2 regular projector with half power of the main projector can increase the received brightness by a factor of x2 (an overall improvement of x4/3).

Polarizer /

4 segments Split

Light Color Wheel Spectrum Duty Cycle Glasses Overall

Main 100.00% 50.00% 50.00% 50.00% 100.00% 12.50%

Mono 50.00% 50.00% None 100.00% 50.00% 12.50%

Table 5

Dynamic Control for saving energy

[00164] The partitioning into shared and left/right parts depends on the differences between the two stereo views, and these are determined by the scene, the alignment between views (that controls the relative to screen depth) and pre-processing applied to the movie. These factors, in particular the scene itself, vary from time to time. For example, a view of a very far object, or a front-parallel planar object will have no significant 3D disparity and can be sent to both eyes with no exclusive left/right components.

[00165] Increasing the shared partition time to increase the apparent brightness only af the eligible frames is undesirable because it likely causes unwanted brightness fluctuations.

Instead, these variations can be used to save energy in systems that can have frame-to-frame dynamic control over the light output - such as LED based system. In these systems it is possible to increase the shared part duration while simultaneously reducing the light output power. This will keep the brightness constant while reducing the amount of energy used. [00166] The analyzing and processing can be done on the fly by the projector using few frames look ahead buffer, or it can be done off-line by providing the projector with the needed information to control the shared / exclusive partition lengths. It may be noted that when shutter based glasses are used, they need to be synchronized accordingly.

Environmental Benefits

[00167] As demonstrated above, the principles described herein may be used to improve the efficiency of 3D projection by an estimated average factor of 4/3 to 5/3 depending on the specific application. This translates into saving of 25% to 40% of the energy cost while obtaining the same brightness level. For high-power projector, this saving applies directly to electricity consumption, and can also apply to bulb lifetime reducing potentially toxic waste from bulbs or reducing costs of recycling. For low-power projectors such as battery operated Pico- projectors, this applies to battery's lifetime and reducing potentially toxic waste from batteries and reducing costs of recycling.

Adapting the Projection Methods for Relatively Low Frame Rate

[00168] The following notation will be used for illustrative purposes:

[00169] l_r : stereo imaging rate of a scene, e.g., I_r = 24 fps;

[00170] P_r : projection sequential rate, e.g., wherein P_r = 2l_r = 48 fps;

[00171] R_t, B_t : delta-left, delta-right, common channels at time t, where t refers to world (imaging) time; and

[00172] A_t, A_t+k .... A_t+n : projection sequence where A is in {L,R,C}, and subscripts refer to world time. The projection time of a certain frame refers to the location of the frame within the sequence.

[00173] The following principles address the following problem, namely to find a method to distribute the stereo frames into the projection sequence (e.g. at step 304 in FIG. 23 below) that: 1 ) maximizes the illumination efficiency of the illumination, 2) maximizes the smoothness of illumination (i.e. to reduce flicker), and 3) Maximizes the smoothness of motion (i.e. to reduce jumps). [00174] In the most general form of the problem, one would have control of the brightness of the illumination source, on the relative durations of the L,R, and B channels and information of the 3D and motion content of the scene. In that case, the problem can be formulated as an optimization problem that provides a solution between two extreme case: (i) scene has no 3D and "infinite" motion - "β_?β₂...β_η"; and (ii) the scene has no motion and "infinite" disparity: "LiRiL₂R₂...L_nR_n".

[00175] For illustrative purposes, consider a restricted form that is suited for constant illumination and partition of a coding wheel into [½,½,½] segments. The simplest case is to project the entire data sequentially: L₁R₁B₁L₂R₂B₂L₃R₃B₃ ... L_nR_nB_n. This is equivalent to the sequence Z_-?B_?/^:?_?Z-2B2/¾...from a different starting point. In this configuration each world stereo pair taken at time t requires 3 projection frames to display (compare to two with regular stereo).

[00176] Consequently, this 1 ) reduces the effected word frame rate by ¾ (24 to 16 fps); 2) increases the total light exposure time of each eye by x1 ½ (½ to ¾), which is also the estimated increase of illumination efficiency; and 3) max interval of blocking each eye is the same - 1 frame (no change in frame duration).

[00177] An alternative is to put B_x every second frame. Since the ratios are different, to satisfy all frames, a delay accumulates, for example: LiBiRiB₂L₂B₃R₂B₄L₃B₅R₃.... To address this, rather than embedding the projection sequence L₁R₁L₂R₂L₃R₃ the following projection sequence can be embedded: LiR₂L₃R₄ ... LnR_n+1.

[00178] The following may be noted:

[00179] 1 ) This sequence can be tested with a regular stereo projector for appearance.

[00180] 2) The sequence has double the frame rate - by dropping half of the frames for each eye (staggered).

[00181 ] 3) When the scene is static, it makes no difference to either motion or stereo perception. [00182] 4) When the scene is dynamic motion smoothness is actually improved, instead of having a real world time sequence 1 1 , 22, 33, 44... (pause move pause move), we have a more continuous flow 1 , 2, 3, 4 ...

[00183] 5) The possible drawback is in stereo perception for close, fast moving objects (which are correlated), (i) One of the earliest methods of stereo projection involved using a neutral density filter in front of one eye, the dimmer view is processes slower by the eye/brain and creates a stereo disparity for moving objects, (ii) Some 2D->3D movies have such delays which does not seem to affect the stereo perception.

[00184] After embedding, the resulting sequence will be: L₁B₁R₂B₂L₃B₃R₄B₄L₅B₅R₆B₆... (or generally according to the pattern: L_nB_nR_n+1B_n+1L_n+2B_n+2R_n+3B_n+3...) , in other words, wherein each B frame has an L frame of the same n value before and an R frame of the next n value after, and the B views are sequenced to occur on every second frame.

[00185] In this configuration each world stereo pair taken at time t requires 2 projection frames to display, but part of the delta (only) channel is lost every other frame. This should: 1 ) keep the same world frame rate (24 fps); 2) increase the total light exposure time of each eye by x1 ½ (½ to ¾), which is also the estimated increase of illumination efficiency; 3) max interval of blocking each eye is the same - 1 frame (no change in frame duration); 4) for static scene or scene with no disparity it is the same as regular stereo; and 5) for fast moving scene and large disparity there can be drawbacks as mentioned before.

[00186] The sequence may be even more condensed as: B₂R₃B₄ but may not be as advantageous for commercial applications.

[00187] Turning now to FIG. 23, a set of computer executable operations is shown for projecting a stereo image using the minimum delta composition technique described above and shown in, for example, FIG. 4. At 300 a stereo pair (L,R) is obtained and the triplet (Ln,Rn,Bn) is generated at 302. The triplet is then projected at 304, e.g., according to a projection timing or schedule as described above and, optionally, the stereo image may be displayed at 306, e.g., if the projector is part of a displaying device such as a 3D television.

[00188] FIG. 24 illustrates a set of computer executable operations that may be performed in projecting an image according to the dual-path split merge technique described above and shown in, for example, FIG. 16. At 400 light is received from a light source 12 and the light is split into two channels at 402. The first channel is coded at 404a and the second channel is coded at 404b. The channels are then multiplexed at 406 for projection.

[00189] FIG. 25 illustrates a block diagram of an example projector 10, 20 that includes a lens 42 and light source 12. As described above, various coding and modulation components 500 may be used in order to project the image. Also shown in FIG. 25 is a controller 502 which may be implemented using software, hardware, or both in order to program or otherwise configure the projector 10, 20 to operate according to any of the above-noted methods, in conjunction with the components of the projector 10, 20.

[00190] It will be appreciated that any module or component exemplified herein that executes instructions may include or otherwise have access to computer readable media such as storage media, computer storage media, or data storage devices (removable and/or non-removable) such as, for example, magnetic disks, optical disks, or tape. Computer storage media may include volatile and non-volatile, removable and non-removable media implemented in any method or technology for storage of information, such as computer readable instructions, data structures, program modules, or other data. Examples of computer storage media include RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can be accessed by an application, module, or both. Any such computer storage media may be part of the projector 10, 20, any component of or related thereto, etc., or accessible or connectable thereto. Any application or module herein described may be implemented using computer readable/executable instructions that may be stored or otherwise held by such computer readable media.

[00191] The steps or operations in the flow charts and diagrams described herein are just for example. There may be many variations to these steps or operations without departing from the principles discussed above. For instance, the steps may be performed in a differing order, or steps may be added, deleted, or modified. [00192] Although the above principles have been described with reference to certain specific examples, various modifications thereof will be apparent to those skilled in the art as outlined in the appended claims.

Claims

Claims:

1 . A method of projecting a stereo image, the method comprising:

obtaining a stereo pair comprising a left view and a right view;

generating a triplet comprising a modified left view, a modified right view, and a common view, the common view comprising a common portion of the left view and the right view; and projecting the modified left view for viewing by a left eye, the modified right view for viewing by the right eye, and the common view for viewing by the left and right eyes at the same time.

2. The method of claim 1 , wherein at least a portion of the common view is added to each of the modified left and right views.

3. The method of claim 1 , wherein the common view is computed as a minimum image M(x,y) = min(L(x,y), R(x,y)), L(x,y) being the left view and R(x,y) being the right view.

4. The method of claim 3, wherein the modified left view is computed as a left delta image D_L(x,y) = L(x,y) - M(x,y), and the modified right view is computed as a right delta image D_R(x,y) = R(x,y) - M(x,y).

5. The method of claim 1 , wherein the common view is projected in full resolution.

6. The method of claim 1 , wherein the modified left view, modified right view, and common view are projected using time-multiplexing encoding.

7. The method of claim 6, wherein the common view is projected to the left and right eyes 1/3 of the time, and the modified left view and modified right view are alternated during a remaining 2/3 of the time.

8. The method of claim 1 , wherein the modified left view, modified right view, and common view are projected using light polarization encoding to provide a first polarization for the modified left view, a second polarization for the modified right view, and no separate polarization for the common view.

9. The method of claim 8, wherein the polarization comprises linear or circular light polarization.

10. The method of claim 1 , wherein the modified left view, modified right view, and common view are projected using light wavelength encoding to provide a first set of wavelengths for the modified left view, a second set of wavelengths for the modified right view, and the first and second sets of wavelengths for the common view.

1 1 . The method of claim 1 , wherein the modified left view, modified right view, and common view are projected using time-multiplexing encoding and passive wavelength coded glasses.

12. The method of claim 1 , wherein the modified left view, modified right view, and common view are projected using time-multiplexing encoding and passive light polarization coded glasses.

13. The method of claim 1 , further comprising operating synchronized shutter glasses to open a left shutter and close a right shutter when the modified left view is projected, open the right shutter and close the left shutter when the modified right view is projected, and opening both the left shutter and right shutter when the common view is projected.

14. The method of claim 1 , further comprising providing an encoding wheel to be used in the projecting operation.

15. The method of claim 14, wherein the encoding wheel comprises separate polarization segments for each of the modified left view and the modified right view.

16. The method of claim 14, wherein the encoding wheel comprises separate wavelength segments for each of the modified left view, modified right view, and common view.

17. The method of claim 1 , further comprising operating an encoded light source.

18. The method of claim 17, wherein the encoded light source comprises an array of light sources having elements with different polarization properties for each of the modified left view, modified right view, and common view.

19. The method of claim 17, wherein the encoded light source comprises an array of light sources having elements with different wavelength properties for each of the modified left view, modified right view, and common view.

20. The method of claim 1 , further comprising operating a plurality of projectors to have at least one projector project the modified left view and modified right view, and at least one other projector project the common view.

21 . The method of claim 20, wherein two projectors are used, a first projector being a conventional stereo projector projecting the modified left view and modified right view using time-multiplexing, and a second projector being a lower power projector than the first projector operating continuously.

22. The method of claim 21 , further comprising performing one of operating active-shutter glasses and providing passive glasses for viewing from the first projector.

23. The method of claim 1 , wherein the common view is represented by Bn, the modified left view is represented by Ln, and the modified right view is represented by Rn, and Bn, Ln, and Rn are computed as follows:

Mo = min(Lo,Ro);

Ld=Lo-Mo;

Rd=Ro-Mo;

B = Mo - max(Mo-max(Ld,Rd), 0) / x;

L = min(Ld+Mo-B, y);

R = min(Rd+Mo-B, y);

Bn= B^*x; Ln=L^*x; and

Rn=R^*x;

wherein Lo is an original left channel pixel value, Ro is an original right pixel value, Ld is a left delta pixel value, Rd is a right delta pixel value, and Mo is a minimum original left and right pixel pair.

24. The method of claim 23, wherein at least one of the following applies:

equal weighting of 1 /3, 1/3, and 1/3, is used for the modified left view and modified right view, and common view;

a gain factor of x = 2 is used

y = 127; and

grey levels from 0-255 are used.

25. The method of claim 1 , wherein the common view is represented by Bn, the modified left view is represented by Ln, and the modified right view is represented by Rn, and Bn, Ln, and Rn are computed as follows:

B = max(Lo,Ro) / x;

L = max(Lo-B, 0);

R = max(Ro-B, 0);

Bn= B^*x;

Ln=L^*x; and

Rn=R^*x;

wherein Lo is an original left channel pixel value and Ro is an original right pixel value.

26. The method of claim 25, wherein at least one of the following applies:

equal weighting of 1 /3, 1/3, and 1/3, is used for the modified left view and modified right view, and common view;

a gain factor of x = 2 is used; and

grey levels from 0-255 are used.

27. The method of claim 1 , wherein the common view is represented by Bn, the modified left view is represented by Ln, and the modified right view is represented by Rn, and Bn, Ln, and Rn are computed as follows:

B = max(Lo,Ro) / 2x;

L = max(Lo-x^*B, 0) / x;

R = max(Ro-x^*B, 0) / x;

Bn= B^*2x;

Ln=L^*2x; and

Rn=R^*2x;

wherein Lo is an original left channel pixel value and Ro is an original right pixel value;

28. The method of claim 27, wherein at least one of the following applies:

unequal weighting is used for the modified left view and modified right view, and common view as ¼, ½, and ¼ respectively;

a gain factor of 2x = 4 is used; and

grey levels from 0-255 are used.

29. The method of claim 1 , wherein a projection sequence is utilized that embeds the common view for every second frame.

30. The method of claim 29, wherein the projection sequence embeds the modified left view and the modified right view using: LnRn+1 , where L is the modified left view, R is the modified right view, and n is a sequence number.

31 . The method of claim 31 , wherein the projection sequence is:

L_nB_nR_n+1B_n+1L_n+2B_n+2R_n+3B_n+3. . . , where B is the common view.

32. A computer readable storage medium comprising computer executable instructions for performing the method of any one of claims 1 to 31 .

33. A system comprising at least one projector, a light source for each projector, a processor, and memory, the memory comprising computer executable instructions for performing the method of any one of claims 1 to 31 .

34. The system of claim 33 when dependent on claim 13, further comprising at least one pair of synchronized shutter glasses.

35. The system of claim 33 when dependent on any one of claims 14 to 16, further comprising the encoding wheel.

36. The system of claim 33 when dependent on any one of claims 17 to 19, further comprising the encoded light source.

37. The system of claim 33 when dependent on any one of claims 20 to 22, further comprising the plurality of projectors.

38. A polarizing wheel to be used in a stereo projector in addition to an existing wheel, the polarizing wheel comprising a clear segment where light is not polarized.

39. A stereo projector comprising a lamp, a color wheel, and the polarizing wheel of claim 38.

40. The stereo projector of claim 39, configured to position the clear segment in a light path for a non-stereo configuration.

41 . The stereo projector of claim 39, configured to have the clear segment project a common portion of left and right views.

42. A method of operating a stereo projector, the method comprising:

splitting light from a light source in the stereo projector into first and second orthogonally polarized channels using a polarizing beam splitter, coding the first and second channels at the same time, and merging the channels for projector through a common lens.

43. A stereo projector comprising:

a lens;

a light source; first and second mirror wheel, the first mirror wheel for splitting light from the light source, the second mirror wheel for merging separate light channels to be projected by the lens;

a first coding assembly for coding a first light channel and directing the first light channel to the second mirror wheel; and

a second coding assembly for coding a second light channel and directing the second light channel to the second mirror wheel.

44. The stereo projector of claim 43, wherein the first and second coding assemblies each comprise a first polarizing beam splitter to split the respective light channel, a pair of modulating components to modulate each split component of the respective light channel, and a second polarizing beam splitter to merge the split components of the respective light channel.

45. A method of enhancing spatial resolution for a projector operating in a non-stereo mode, the projector configured to project in a stereo mode by projecting left, right, and common views, the method comprising:

shifting at least one pixel grid for a corresponding modulating component in the projector by half of a pixel with respect to a first pixel grid for a first modulating component.

46. The method of claim 45, wherein a second pixel grid is shifted horizontally by half a pixel relative to the first pixel grid, a third pixel grid is shifted vertically by half a pixel relative to the first pixel grid, and a fourth pixel grid is shifted both horizontally by half a pixel and vertically by half a pixel relative to the first pixel grid.