WO2009157915A1

WO2009157915A1 - Field-sequential color display systems and methods with reduced color break-up

Info

Publication number: WO2009157915A1
Application number: PCT/US2008/010561
Authority: WO
Inventors: Mark Flynn; Louis D. Silverstien
Original assignee: Aurora Systems, Inc.
Priority date: 2008-06-27
Filing date: 2008-09-10
Publication date: 2009-12-30

Abstract

Systems for and methods of reducing color breakup in field-sequential color display systems (10) are disclosed. The method includes reading Red, Green and Blue (R, G, B) input video signals (S'v) corresponding to Red, Green and Blue primary colors. The method also includes re-distributing a select portion of the primary color input signals to a composite output video signal (Sv) that includes composite-primary signal corresponding to composite-primary color (Y*) formed by the linear sum of the primary colors of the system. The method further includes reducing the output primary color signals by an amount equal to that re-distributed to the composite signal, so as to not change the overall color and intensity of the total output video signal as compared that of the input video signal.

Description

FIELD-SEQUENTIAL COLOR DISPLAY SYSTEMS AND METHODS WITH REDUCED COLOR BREAK-UP

CLAIM OF PRIORITY

[0001] This application claims the benefit of priority under 35 U.S.C. § 119(e) of U.S. Provisional Application Serial No. 61/133,326, filed on June 27, 2008.

FIELD OF THE INVENTION

[0002] The present invention relates generally to field-sequential color display systems, and in particular relates to such display systems that have reduced color break-up.

BACKGROUND ART

[0003] Any color display synthesizes a full-color image from a limited set of primary colors. Several approaches to color synthesis have been employed for electronic displays. The most successful of these conform to the principles of additive color mixture and include optical superposition, spatial synthesis and temporal synthesis. Fortunately, two characteristics of the human visual system (HVS) offer great flexibility in techniques for synthesizing color. Since the HVS is quite limited in both the spatial and temporal resolution of visual input, with integration taking place as these limits are exceeded, spatial or temporal patterns composed of three (or more) appropriately selected primary colors are sufficient for producing a full range of colors when the spatial or temporal frequencies of the patterns exceed the respective resolution limits.

[0004] Spatial color synthesis has by far been the most successful method and is the foundation of modern color display technology. The two most successful electronic color display devices available, the shadow-mask color cathode-ray tube (CRT) and the color liquid crystal display (LCD), conform to this principle.

[0005] Two important limitations of temporal color synthesis (also called field- sequential color) constrain the efficacy of field-sequential color displays. First, although the field-sequential approach produces effective additive color mixtures, residual luminance differences between the time-varying components can produce observable luminance flicker for temporal frequencies at or above those at which effective chromatic integration has taken place. A more difficult limitation results from relative movement between the displayed image and the viewer's retina, whether the motion arises from the image or from the viewer's head and eye movements. In either case, the time-varying color components are no longer imaged on the same retinal region and the observer experiences what has come to be known as "color break-up" or "the rainbow effect." Avoiding color break-up for RGB field- sequential displays in the presence of high- velocity eye movements such as saccades requires color field rates well in excess of those needed to eliminate flicker and can easily exceed 1000 Hz when the display luminance and contrast are high. The current "de facto" standard for sequential color field rates is in the range of 360-480 fields-per-second. These high field rates impose severe bandwidth requirements on field-sequential displays and make the temporal isolation of primary color image fields very difficult.

SUMMARY OF THE INVENTION

[0006] The present invention is directed to systems for and methods of reducing color breakup in field-sequential color display systems, and such systems and methods are disclosed.

[0007] An aspect of the invention includes a method of receiving input video signals corresponding to Red, Green and Blue primary colors. The method also includes re-distributing a select portion of the primary color input signals to a composite output video signal, where the color corresponding to the composite signal is a composite primary color formed by the linear sum of the primary colors of the system. The method further includes reducing the output primary color signals by an amount equal to that re-distributed to the composite signal, so as to not change the overall color of the total output signal. The use of dither in combination with the composite primary fields is optionally used to further minimize the required display system bandwidth.

[0008] Another aspect of the invention includes a method of reducing color breakup in a field sequential color system. The method comprises forming a composite-primary-color output video signal corresponding to a composite-primary color by redistributing portions of at least two of three primary-color input video signals corresponding to Red, Green and Blue input primary colors that define an associated total input intensity and a total input color. The method also includes forming a total output video signal having an associated total output color and a total output intensity and defined by the redistributed Red, Green and Blue input primary color video signals and the composite-primary color output video signal, wherein the total output color and intensity is substantially the same as the total input color and intensity, respectively.

[0009] Another aspect of the invention includes a Color & Field Management System (CFMS) that includes a Color Management System (CMS) and a Field Management System (FMS). The CMS is configured to receive input video signals for Red, Green and Blue primary colors and to re-distribute a select portion of the primary color input signals to a composite output video signal. The color corresponding to the composite signal is a composite primary color formed by the linear sum of the primary colors of the system. The CMS reduces the output primary color signals by an amount equal to that re-distributed to the composite signal, so as to not change the overall color of the total output signal. The FMS is configured to read the Red, Green, Blue and composite primary signals from the Color Management System (CMS) and to re-distribute them in time so as to produce sequential color fields for the native primary inputs Red, Green, and Blue, and composite sequences for the composite primary input.

[0010] Another aspect of the invention is a CMS operably coupled to a FMS, wherein the CMS system is configured for forming a composite-primary-color output video signal corresponding to a composite-primary color by redistributing portions of at least two of three primary-color input video signals corresponding to Red, Green and Blue input primary colors that define an associated total input intensity and a total input color. The CMS system is also configured for forming a total output video signal having an associated total output color and a total output intensity and defined by the redistributed Red, Green and Blue input primary color video signals and the composite-primary color output video signal, wherein the total output color and intensity is substantially the same as the total input color and intensity, respectively. The FMS is configured for receiving the redistributed Red, Green and Blue primary-color input video signals and composite-primary-color output video signal from the CMS means and forming therefrom a field-sequential output signal.

[0011] Another aspect of the invention is a method of forming a sequentially modulated light beam for use in forming a color display image having reduced color break-up. The method includes receiving first, second and third primary-color input video signals corresponding to first, second and third primary colors and that define an associated total input intensity and a total input color. The method also includes forming a composite-primary-color output video signal corresponding to a composite-primary color by redistributing portions of at least two of the first, second and third primary-color input video signals, thereby forming redistributed first, second and third primary-color video signals. The method also includes forming a total output video signal having an associated total output color and a total output intensity and defined by the redistributed first, second and third primary-color video signals and the composite-primary color output video signal, wherein the total output color and intensity is substantially the same as the total input color and intensity, respectively. The method additionally includes providing a modulation signal to a spatial light modulator (SLM) so as to modulate the SLM. The method further includes sequentially illuminating the modulated SLM based on the total output video signal so as to form the modulated light beam.

[0012] Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein, including the detailed description which follows, the claims, as well as the appended drawings.

[0013] It is to be understood that both the foregoing general description and the following detailed description present embodiments of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments of the invention, and together with the description serve to explain the principles and operations of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 shows various examples of system color gamuts as displayed in the CE 1976 color space;

[0015] FIG. 2 shows the basic architecture of a color display system that generates mixture colors by the rapid alternation of the primary colors of the system, a method of color synthesis known as Field-Sequential Color (FSC); [0016] FIG. 3 is a schematic diagram of the Color and Field Management System (CFMS) of FIG. 2;

[0017] FIG. 4 is a schematic diagram illustrating the operation of the Field Management System;

[0018] FIG. 5 is a schematic diagram of an example embodiment of a field- sequential spatial light modulator (FS-SLM) system as shown in FIG. 2;

[0019] FIG. 6 is a schematic diagram of an example SLM such as used in the FS- SLM System of FIG. 5;

[0020] FIG. 7 is similar to FIG. 2 and illustrates an alternate method of generating a field-sequential image;

[0021] FIG. 8 is similar to FIG. 3 and illustrates an example CFMS configured to modify the output video signals.

[0022] FIG. 9 illustrates how the R and G video signals are modified in the CFMS of FIG. 8;

[0023] FIG. 10 is a schematic diagram similar to FIG. 8 that illustrates an example embodiment of the CFMS that includes a dither system for performing dither; and

[0024] FIG. 11 is a schematic diagram of an example embodiment of a field- sequential color display system that uses the color and field management systems and methods of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0025] The present invention provides a novel method for implementing field- sequential color in an electronic display system while simultaneously minimizing display bandwidth requirements and mitigating perceived color break-up.

Terms and Definitions

[0026] In the description below, the primary color red is represented by R, the primary color green is represented by G and the primary color blue is represented by B. Primary colors that are inputted to a video processing system (such as in an input video signal) as described below are identified by a superscript "in" such as R^ιn, G^m and Bⁱⁿ, while colors outputted by the video processing system, such as in an output video signal sent to a spatial light modulator, (SLM) are identified by a superscript "out" such as R^out, G^out and B^out _. Note that R, G and B are used to refer to both actual colors generated by respective R, G and B light sources as well as to electronic color signals (i.e., video signals), and that one skilled in the art will recognize the difference in meaning based on the context of the discussion. Also note that letters without superscripts can refer to either the input and output colors or signals, where the meaning is clear from context.

[0027] The following terms and phrases are used herein:

[0028] Video frame or frame (F): A complete reconstructed image composed by an electronic imaging or video system which contains all of the spatial and color information of the image.

[0029] Frame period and frame rate: the period of time during which a complete image is reconstructed by an electronic imaging or video system. Typically this is l/60^th of a second, corresponding to a frame rate of 60 Hz.

[0030] Field-sequential color: a method of synthesizing a full spectrum of visible colors by rapidly alternating a sequence of primary-color fields or primary- color images at a rate beyond the temporal resolution of the human visual system (HVS).

[0031] Color Field or field (f): A segment of a frame during which one color is displayed in a field- sequential video system. In such a system, each frame is broken up into a number of fields. At a minimum, there must be one field for each primary color of the incoming image or video sequence, and these would typically be one each for Red, Green and one Blue.

- [0032] Field period and field rate: the periods of time into which a video frame is subdivided in a field-sequential color imaging system. The field rate is the frequency at which the fields are repeated per unit time. For a frame rate of 60 Hz, the minimum field rate for a three primary system would be 180 Hz, wherein the data for each color is presented one time in each frame.

[0033] "Color field sequence" or "sequence": is the ordering of color fields contained in a single frame, such as R-G-B.

[0034] "Color sequence cycle" or "cycle": The basic repeated pattern present in the color sequence. For example, a color sequence of R-G-B-R-G-B contains two R- G-B color cycles, each composed of three fields. [0035] "Native primary" or "Primary": An elemental color used to synthesize mixture colors in a colorimetric system. A primary color in a colorimetric imaging system is one of the colors in the system that define the extent of the color gamut. For example, the vertices of the various polygons shown in FIG. 1 are native primaries of the system.

[0036] "Composite primary": an elemental system color that is formed by simultaneously displaying two or more native primary colors of the system. Since it is composed of two or more native primaries, a composite color does not extend the gamut of the system.

[0037] Primary field: A field corresponding to a native primary. [0038] Composite field: A field corresponding to a composite primary.

[0039] Color break-up: Color break-up arises from the use of a field-sequential mode of operation to achieve temporal color synthesis and manifests itself as a spatial separation of mixture colors (e.g., white and yellow) into their color field components (e.g., RGB) during motion of the eyes and/or head.

[0040] Dither: Method of adjusting the intensities of neighboring pixels so that their combined intensities average out to the desired values. In essence, this technique trades spatial area (or spatial resolution) for intensity (or gray level) resolution. The above definition describes the dither method applied to the spatial domain. Similar methods can be applied in the temporal domain, leading to improved intensity resolution at the expense of temporal resolution of an imaging system.

[0041] FIG. 1 shows various examples of a system color gamut, displayed in the CIE 1976 color space. Typically, a color gamut is defined by three native primary colors, designated by the terms Red, Green and Blue, but may be defined by more than three primaries in multi-primary imaging systems. The three examples shown are for the NTSC and sRGB (Rec. 709) standard image formats and for a four- primary display system.

General color display system

[0042] FIG. 2 shows the basic architecture of a color display system that generates mixture colors by the rapid alternation of the primary colors of the system, a method of color synthesis known as Field-Sequential Color (FSC). There are three primary- color input video signals (i.e., "inputs" or "input video signals") R, G and B, corresponding to the primaries defined in the input video specification. For example, if the input video specification is Rec. 709 for HDTV, than the input video primaries are those defined in the aforementioned specification.

[0043] The color display system of FIG. 2 includes a Color and Field Management System (CFMS) operably connected to a field-sequential spatial light modulator (FS- SLM), which is operably connected to an imaging system.

[0044] The input video signals enter the CFMS, details of which are shown in FIG. 3. The CFMS is composed of two elements: a Color Management System (CMS) and a Field Management System (FMS).

[0045] The CMS is optional. In the case where it is absent, the RGB video signals are passed to the FMS unchanged. In the case where the CMS is present, it is configured to transform the RGB video signals from the input primaries as defined in the input video specification to those of the actual output video primaries, which are determined by the actual primaries produced by the system, as is known in the art and as described below.

[0046] In the case where the CMS is present, it is configured to receive input signals appropriate for input primaries RGB and to generate output signals appropriate for the actual display output primaries (RGB) corresponding to the physical properties of the illumination sources used in the display systems. For example, if the illumination system is composed of R, G and B light emitting diodes (LEDs), the display primaries R, G and B are the colors produced by the corresponding LEDs. This color-space conversion process is of particular importance when input colors RGB are significantly different from the display output primaries RGB available in system. The difference between the input colors and the display colors can result in substantial differences in the color gamuts (FIG. 1), which results in a display image that is not faithful to the input colors. This occurs, for example, when light sources are LEDs or lasers.

CMS color conversion

[0047] The color conversion in the CMS is accomplished using the following matrix equation: r

wherein the two vectors of R, G and B values are the input and output primary values, and the product of two matrixes are the mappings between the primaries and the tristimulus values, given below. The functions Ψ and its inverse Ψ^"1 are transformations which remove the nonlinearity from gamma-corrected color input signals prior to color conversion and subsequently reestablish the nonlinearity in the converted color output signals, respectively. These transformations are important because accurate color conversion can only be performed in a color space which is linear with luminance.

a out ^XR R^out G _a>n ^XR βin ^XG in ^XB

I y_R y_G y_B y_R y_G y_B

1 OUl, W _ cT /T rp min..WW __ a'" β^m γ^m cT < ±R_ βo _a"> IK β^m ΞΩ_ γ"> ^B_ y_R y_G y_B y_R y_G y_B

The scalars α, β and γ are chosen so as to set the appropriate white point of the output primaries, and are determined by solving the following linear set of equations. Note that there is one set of equations to be solved for both the input and output primaries.

[0048] The FMS reads the RGB video inputs, and generates the output signals required for field-sequential operation, as detailed in FIG. 4 for a sequence where each of the primaries R, G and B are displayed once per frame (referred to as an RGBxI sequence). FIG. 4 shows three video inputs entering the FMS, labeled R, G and B. Each of these is a time sequence of frames. As indicated in FIG. 4, the data for each of these signals can vary from frame to frame. As shown, in frame 1, R is "off', G is "on" and B is "on", whereas in frame 2 this has changed to "on", "on" and "off," respectively. [0049] There are two related types of output from the FMS, both of which are broken down into a number of fields. FIG. 4 shows three fields per frame, in a sequence of RGB. One output is a single video stream (a "modulator signal") provided to the SLM, which instructs each pixel to be in a specific state within each frame. The second output is a set of three illumination switching signals, one for each emitter within the illumination system. These signals are synchronized with the output video signal, so as to ensure that the SLM data and the illumination output color are properly aligned in time.

[0050] For example, as shown in FIG. 4, during each R field, the R emitter is on, and the others are off, etc. The synchronization of the SLM data (i.e., the modulator signal) and illumination signals shown in FIG. 4 are detailed in Table 1.

Table 1

Field-sequential spatial light modulator (FS SLM)

[0051] FIG. 5 is a schematic diagram similar to that of FIG. 2, but that includes more details of the FS SLM system. In the example embodiment of FIG. 5, the FS SLM system is broken down into two parts: the SLM itself and a Switchable Illumination System (SIS). The different illumination sources must be switchable in a FS display system, as the different fields in each frame have different colors.

[0052] An example SLM is shown in FIG. 6. The SLM has a number of pixels PX. SLM data (i.e., modulator signal) enters the SLM, and the various pixels PX are shown in different shades to indicate that each of the pixels can be in different optical states, depending on the input data for each pixel. It is noted here that for all of the references to video data (whether it be the R, G and B input data, or the FS SLM data) it is implicit that there is distinct data for each and every pixel PX. [0053] There are two general types of SLMs in use, which can generally be referred to as analog and digital, and each of these will accept a different type of video signal from the FMS.

[0054] The pixels PX of a digital SLM can only be in one of two electrical states, generally referred to as "OFF" (the optically darkest state) and "ON" (the optically brightest state). Since the pixels PX can only have two possible states, something must be done to allow this two-state SLM to generate a number of distinct optical states equal to at least the number of states in the input video stream. A typical number of input video states is 8 bits per color, or 2⁸ = 256 possible states. This can be done in a number of ways, but they all have in common a process whereby each input state can be mapped to, or expressed as, a series of bits, or ON or OFF states. This is what the "ON" & "OFF" refer to in Table 1.

[0055] In contrast, the pixels PX of an analog SLM are able to display a large number of different optical states, each one generally determined by a specific voltage applied across each pixel. Therefore, the video signal sent to the SLM from the FMS will specify one of a large number of possible states for each pixel. In this case, the "ON" and "OFF" states of Table 1 would be replaced by one of the possible optical states.

[0056] There are many different ways of driving a FS display, as described below. The acronym "RGB" is used as shorthand for "red-green-blue." FIG. 4 shows a sequence where the three primaries are cycled through once per frame. Thus, there is a single RGB cycle, which can be referred to as RGBxI. This implies that for a frame rate of 60 Hz, the field rate is 180 Hz. If the three primaries were cycled through twice per frame, the system would be said to be using an RGBx2 sequence, and the field rate would be 360 Hz.

Color Breakup

[0057] Perhaps the most complex and vexing problem for field-sequential color displays is color break-up during relative motion between the displayed image and the observers eyes. Although image motion can cause this phenomenon, the velocity of displayed image motion is typically orders of magnitude less than the highest velocity eye movements. Color break-up arises from the use of a field-sequential mode of operation to achieve temporal color synthesis and manifests itself as a spatial separation of mixture colors (e.g., white and yellow) into their color field components (e.g., RGB) during motion of the eyes and/or head. [0058] In order for temporal color synthesis to succeed without incident, the time- sequenced color image components must be imaged at the same position (or very close proximity) on the observer's retinas. When the eye moves with respect to the displayed image, the color components of the temporally synthesized color image are spatially displaced with respect to one another on the observer's retinas. The result is a spatial separation of colors during the eye movement. The size of the retinal displacement, and thus the magnitude of the perceived color break-up, are directly proportional to the velocity of the eye movement. The image may also appear to flash or jump during the eye movement, and many observers find this phenomenon very disturbing.

[0059] The precise nature of the visual phenomena underlying color break-up is not well understood and has not been thoroughly investigated, despite the fact that engineers and visual scientists have been attempting to use field-sequential color systems for many years. It is known, however, that the visual and perceptual sensitivities to color break-up are very complex and are strongly affected by eye movement velocity, field of view, image color, image luminance, image contrast, and visual masking arising from structure or patterns in the displayed image and the visual surround. Color break-up is most apparent during saccadic eye movements, which can produce rotational velocities of the eye up to 1000 degrees per second for large excursions of the point of regard within the visual field.

[0060] The general effects of a number of display parameters on the visibility of color break-up are well documented. Increasing the color field rate results in a direct, linear decrease in the retinal displacement of temporally adjacent color fields during relative motion between the displayed image and the retina. For most observers this produces a commensurate decrease in perceived color break-up. Decreasing image luminance and/or image contrast also tends to make color breakup less perceptible, although reductions in these two principal display parameters also reduce overall image quality. Decreasing the luminance and/or chromaticity differences between sequential primary color fields substantially reduces the visibility of color break-up, particularly between G and R color components since they provide most of the image luminance. Finally, visual masking by complex, textured or luminous solid backgrounds also tends to reduce the perceptibility of displaced color fields on the retina. Alternate FS image methods using composite primary Y* [0061] FIG. 7 shows an alternative method of generating a field-sequential color image, wherein the CFMS has been changed, as shown in FIG. 8, to modify the output video signals. Specifically, the R and G video signals have been modified as illustrated in FIG. 9. The method illustrated here is as follows.

[0062] We first define a composite primary Y* = R+G. That is, the color of Y* is set to the combination of the R and G native primaries.

[0063] For each frame, we put as much as possible of the input R and G signals into the Y* signal instead. For example, if we have 8 bit video signals, and for a given frame Rⁱⁿ=127 and Gⁱⁿ=240, then we would set Y*^out to 127, R^out to 0 and G^out to 240-127=113.

[0064] The benefit of performing this transformation on the input video signals can be seen by comparing FIG. 4 and FIG. 9. In Frame 2 of both FIGS. 4 and 9, the input signal has both R and G set to high. In FIG. 4, this results in a frame two sequence of R on and G on in two sequential fields, which as discussed above would be the worst case situation for color breakup, since these are both high brightness fields, but of very different colors. In contrast, in Frame 2 of FIG. 9, we instead generate a single Y* field with both R and G activated simultaneously, so there will be no color breakup at all.

[0065] Of course this is the ideal situation, and for the more general case of arbitrary R, G and B input video levels, there will still be some residual color breakup. However, by maximizing the amount of signal put into the Y* fields, the amount of residual color breakup is minimized.

[0066] There is a further important advantage to the invention, which is that it allows a substantial reduction in data rate provided to the SLM. In the prior art, where the primaries are unchanged, the only way to mitigate color breakup is to increase the field rate, which means increasing the amount of data provided to the SLM. This can become very expensive in terms of electronics and power, so that there are significant advantages to minimizing the data rate. Since the invention produces a reduction in color breakup for a fixed field rate, this allows for running a lower field rate while still achieving equivalent or better color breakup performance.

[0067] The above description of the aspect of the invention that utilizes a composite primary Y* is only one preferred embodiment of the present invention. It would be readily understood by those of ordinary skill in the art that other composite primaries could be defined from the R, G and B native primaries of a field-sequential color (FSC) display system and utilized in a similar manner to reduce color break-up and system bandwidth requirements or achieve other FSC performance objectives.

[0068] It would also be readily understood by those of ordinary skill in the art that the invention is not limited to any three specific primaries Red, Green and Blue. Any three primaries Cl, C2 and C3 can be used to define a color gamut, as shown in FIG. 1, and these can be used in the identical way as described above. Any combination of these primaries can be used to generate a composite primary. The above description used Red, Green and Blue by way of illustration. Thus, other example composite primaries include for example: White (W*) output composed of a select portion of Red, Green and Blue; Cyan (C*) output composed of a select portion of Green and Blue; and Magenta (M*) output composed of a select portion of Red and Blue signals.

[0069] Further, the invention is not limited to only three primaries. Again referring to FIG. 1, more than three primaries can be used to define a gamut, and at least one composite field can be generated by summing two or more of the primaries Cl, C2, C3, ... Cn.

Dither

[0070] In some cases, a display may not be able to generate all of the required (or desired) intensity and color levels for high-quality image reconstruction. For example, in an 8-bit digital intensity scale, there may be duplicates or gaps in some of the 256 levels produced by the display device. To overcome this limitation, the display electronics or image processing software may be configured to automatically adjust the intensities of neighboring pixels so that their combined intensities average out to the desired values. In essence, this technique trades spatial area (or spatial resolution) for intensity (or gray level) resolution. Methods to implement this technique are called spatial dithering, and it increases the perceived gray-scale resolution and number of addressable colors that can be displayed.

[0071] Similar methods can be applied in the temporal domain, leading to improved intensity resolution at the expense of temporal resolution of an imaging system. When applied in the temporal or time domain, the resulting averaging of intensity levels over time is designated as temporal dither. While we focus on spatial dither, the current invention can readily incorporate temporal dither or some combination of spatial and temporal dither, termed "spatio-temporal dither," to increase gray level resolution.

[0072] The averaging process in spatial dither may involve only adjacent pixels, or it can encompass larger groupings of nearby pixels to produce a finer intensity scale. The dithering algorithm may involve a fixed pixel pattern, which is often more noticeable because it tends to produce repeating pixel patterns on the screen, or a quasi-random pattern based on stochastic methods for assigning weights to patterns of pixels. This generates a seemingly random pattern and a finer intensity scale.

[0073] The use of dither in combination with the composite primary fields can be particularly advantageous. The use of the composite primary technique is motivated by the desire to minimize bandwidth and yet not suffer from unacceptable color breakup. This can be combined with dither so as to further minimize required bandwidth to the SLM.

[0074] FIG. 10 is a schematic diagram similar to that of FIG. 8, but that includes a dither system arranged between the CMS and the FMS to effectuate dithering to obtain the above-described advantages.

Field-sequential color display system

[0075] FIG. 11 illustrates an example embodiment of a field-sequential color display system 10 that uses the color and field management systems and methods discussed above in CFMS 20. Note that an example of the SIS of FIG. 5 includes light sources LR, LG and LB, the dichroic mirrors Ml and M2, the homogenizing unit HU, and the condenser lens CL as illustrated in FIG. 11. The primary-color input video signal is provided to CFMS 20 as S'v and the composite-primary-color output video signal (i.e., the modulation signal) is Sv-

[0076] System 10 of FIG. 11 includes an SIS having light sources LR, LG and LB arranged relative to an axis Al. In an example embodiment, collimating lenses CR, CG and CB are arranged in front of light sources LR, LG and LB, respectively. Light source LB emits light beam LB-B down axis Al in response to a "blue" illumination switching signal S_B from CFMS 20. Light sources LR and LG are activated by respective illumination "red" and "green" switching signals S_R and S_G have their respective light beams LB-R and LB-G folded by dichroic fold mirrors Ml and M2 arranged along axis Al so that all three light beams share a common optical path OP along axis Al.

[0077] System 10 includes a light homogenizer unit HU arranged along axis Al downstream of dichroic mirror M2 that is configured to homogenize light passing therethrough. A condenser lens CL arranged along axis Al and downstream of homogenizer unit HU receives homogenized light HL from the homogenizer unit and focuses the light onto SLM 30, which is modulated via modulator signal Sy. In an example embodiment, this is accomplished with the assistance of optical system 40, which in an example embodiment includes a polarizing beam splitter PBS. Polarizing beam splitter PBS serves to direct light 53 to SLM 30, which generates modulated light beam LM. Modulated light beam LM is polarized upon reflection from SLM 30 so that it passes through PBS and to a projection optical system PO of optical system 40. Light from projection optical system 40 is then displayed on a display screen DS to form color display image DI.

Other aspects and embodiments of the invention

[0078] There are many other aspects and embodiments of the invention in addition to those described above. For example, rather than have an SLM with a switchable illumination system as shown in FIG. 5, one could use an SLM in combination with a non-switchable illumination system, and a switchable filter, placed either before or after the SLM. In this case, the switching signals would be sent to the switchable filter instead of the illumination system. Alternatively, one could use a switchable emissive SLM. In this case, the SLM itself would be the source of the illumination, and both the SLM data signals and the illumination switching signals would go to the SLM.

[0079] As is clear from the description above, the present invention can be used in combination with a very broad class of SLMs. Examples include, but are not limited to, the following: LCOS SLM, DLP and other MEMS-type SLM, Direct View LCD panels, and Emissive SLMs such as FEDs and OLEDs.

[0080] It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention. Thus it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

Claims

What is claimed is:

1. A method of reducing color breakup in a field sequential color system, comprising. forming a composite-primary-color output video signal corresponding to a composite-primary color by redistributing portions of at least two of three primary-color input video signals corresponding to Red, Green and Blue input primary colors that define an associated total input intensity and a total input color; and forming a total output video signal having an associated total output color and a total output intensity and defined by the redistributed Red, Green and Blue input primary color video signals and the composite-primary color output video signal, wherein the total output color and intensity is substantially the same as the total input color and intensity.

2. The method of claim 1, wherein said redistributing includes reducing one or more of the Red, Green and Blue primary-color input video signals by an amount equal to that re-distributed to the composite-primary color output video signal.

3. The method of claim 2, wherein said redistributing includes reducing all three primary-color input video signals by an amount equal to that redistributed to the composite-primary color output video signal.

4. The method of claim 1, further comprising forming the composite-primary- color output video signal as select portions of the Red and Green primary color input video signals so that the corresponding composite-primary color is Yellow (Y*).

5. The method of claim 1, further comprising forming the composite-primary- color output video signal as select portions of the Red, Green and Blue primary color input video signals so that the corresponding composite- primary color is White (Y*).

6. The method of claim 1, further comprising forming the composite-primary- color output video signal as select portions of the Green and Blue primary color input video signals so that the corresponding composite-primary color is Cyan (C*).

7. The method of claim 1, further comprising forming the composite-primary- color output video signal as select portions of the Red and Blue and primary color input video signals so that the corresponding composite-primary color is Magenta (M*).

8. The method of claim 1, including defining the composite-primary color as being substantially the same as a native white point defined by the Red, Green and Blue primary colors.

9. The method of claim 1, wherein there are maximum portions of the at least two of three primary-color input video signals that can be distributed in forming the composite-primary-color output video signal, and wherein said redistributing is performed so as to distribute said maximum portions.

10. The method of claim 1, wherein Red, Green and Blue input primary colors have corresponding input intensities, and wherein said redistributing includes minimizing at least two of the Red, Green and Blue input intensities.

11. The method of claim 1 , further comprising: forming each of a plurality of full-color image frames from at least three or more individual color temporal fields, Cl, C2, C3, ... Cn; and forming at least one additional temporal field by simultaneously activating two or more of the individual color temporal fields Cl, C2, C3, ... Cn.

12. The method of claim 12, wherein said simultaneous activating of two or more individual color temporal fields comprises activating Red and Green color temporal fields.

13. The method of claim 1, further including: providing the total output video signal to a spatial light modulator (SLM); and sequentially activating the SLM with Red, Green and Blue light sources using respective Red, Green and Blue illumination switching signals based on the total output video signal.

14. A Color and Field Management System (CFMS) comprising: a) Color Management System (CMS) means for: i. forming a composite-primary-color output video signal corresponding to a composite-primary color by redistributing portions of at least two of three primary-color input video signals corresponding to Red, Green and Blue input primary colors that define an associated total input intensity and a total input color; and ii. forming a total output video signal having an associated total output color and a total output intensity and defined by the redistributed Red, Green and Blue primary color input video signals and the composite-primary color output video signal, wherein the total output color and intensity is substantially the same as the total input color and intensity; and b) Field Management System (FMS) means operably connected to the CMS means, for receiving the redistributed Red, Green and Blue primary-color input video signals and composite-primary-color output video signal from the CMS means and forming therefrom a field-sequential output signal.

15. The system of claim 14, wherein said redistributing is performed so as to distribute a maximum amount of the of at least two of three primary-color input video signals into the composite-primary-color output video signal.

16. The system of claim 14, wherein the composite-primary color is substantially the same as a native white point defined by the Red, Green and Blue input primary colors.

17. A field-sequential display system comprising: the CFMS of Claim 14; a field-sequential spatial light modulator system (FS-SLM) operably connected to the CFMS; and an imaging system operably coupled to the FS-SLM.

18. A method of forming a sequentially modulated light beam for use in forming a color display image having reduced color break-up, comprising: receiving first, .second and third primary-color input video signals corresponding to first, second and third primary colors and that define an associated total input intensity and a total input color; forming a composite-primary-color output video signal corresponding to a composite-primary color by redistributing portions of at least two of the first, second and third primary-color input video signals, thereby forming redistributed first, second and third primary-color video signals; forming a total output video signal having an associated total output color and a total output intensity and defined by the redistributed first, second and third primary- color video signals and the composite-primary color output video signal, wherein the total output color and intensity is substantially the same as the total input color and intensity, respectively; providing a modulation signal to a spatial light modulator (SLM) so as to modulate the SLM; and sequentially illuminating the modulated SLM based on the redistributed first, second and third primary-color output video signals and the composite-primary color output video signal so as to form the modulated light beam.

19. The method of claim 18, wherein the first, second and third input primary colors are Red, Green and Blue

20. The method of claim 19, wherein the composite-primary color is one selected from the group comprising: Yellow (Y*), White (W*), Cyan (C*), Magenta (M*)

21. The method of claim 18, further including receiving the modulated light beam with an optical system so as to create a color display.