HK1112292B - High dynamic range display devices - Google Patents

Description

High dynamic range display device

This application is a divisional application of Chinese patent application No. 02805551.9, filed on February 27, 2002, and entitled “High Dynamic Range Display Device”.

Technical Field

The present invention relates to displays for displaying digital images.

Background Art

Dynamic range is the ratio of the intensity of the brightest part of a scene to the intensity of the darkest part of the scene. For example, a video projection system may project an image with a maximum dynamic range of 300:1.

The human visual system is capable of discerning features in scenes with an extremely high dynamic range. For example, a person can observe the shadows of an unlit garage during bright daylight hours and see details of objects within the shadows, even though the brightness of the adjacent sunlit areas is thousands of times greater than that of the shadowed portion of the scene. Creating a realistic reproduction of such scenes may require a display with a dynamic range exceeding 1000:1. The term "high dynamic range" refers to a dynamic range of 800:1 or greater.

Modern digital imaging systems are capable of capturing and recording digital representations of scenes that preserve the scene's dynamic range. Computer imaging systems are capable of synthesizing images with a high dynamic range. However, current display technology cannot reproduce images in a way that faithfully replicates that high dynamic range.

U.S. Patent No. 5,978,142 to Blackham et al. discloses a system for projecting an image onto a display screen. The system includes first and second light modulators, each of which modulates light from a light source. Each light modulator modulates light from the light source at the pixel level. The light modulated by the two light modulators is projected onto the display screen.

PCT Application No. PCT/US01/21367 to Gibbon et al. discloses a projection system including a premodulator that controls the amount of light incident on a deformable mirror display device. A separate premodulator can be used to dim a selected area (e.g., a quadrant).

There is a need for cost-effective displays capable of reproducing a wide range of light intensities in displayed images.

Summary of the Invention

The present invention provides a display for displaying an image and a method for displaying an image. One aspect of the present invention provides a display comprising: a light source; a first spatial light modulator for modulating light from the light source; a display screen comprising a second spatial light modulator; and an optical system configured to image the light modulated by the first spatial light modulator onto a first surface of the display screen.

Another aspect of the present invention is to provide a display comprising: a light source; a first spatial light modulator for modulating light from the light source, the first spatial light modulator comprising a controllable pixel array; and a second spatial light modulator for modulating light modulated by the first spatial light modulator, the second spatial light modulator comprising a controllable pixel array; wherein each pixel of one of the first and second spatial light modulators corresponds to multiple pixels of the other modulator of the first and second spatial light modulators.

Another aspect of the present invention is to provide a display device comprising: a first spatial modulation device for providing light spatially modulated at a first spatial resolution; a second spatial modulation device for further spatially modulating the light at a second spatial resolution different from the first spatial resolution; and a device for controlling the first and second spatial modulation devices to display an image defined by image data.

Another aspect of the present invention is to provide a method for displaying an image with a high dynamic range, comprising: generating light; spatially modulating the light according to image data in a first light modulation step; and imaging the spatially modulated light onto a display screen including a light modulator.

Further aspects of the invention and features of specific embodiments of the invention are described below.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, which illustrate non-limiting embodiments of the present invention,

FIG1 is a schematic diagram of a display according to an embodiment of the present invention;

FIG1A is a schematic diagram of a particular implementation of the display of FIG1 ;

2 is a schematic diagram of a display including four spatial light modulators according to an alternative embodiment of the present invention;

3 is a schematic diagram of a rear projection display according to another embodiment of the present invention;

4 is a schematic diagram of a front projection display according to yet another embodiment of the present invention;

5 is a diagram showing one possible relationship between pixels in a higher resolution spatial light modulator and pixels in a lower resolution spatial light modulator in a display according to the present invention;

FIG5A illustrates the effect of providing a light modulator having a lower resolution than another light modulator;

FIG6 is a schematic diagram of a front projection color display having an alternative projector configuration;

6A and 6B are partially enlarged cross-sectional views of the front projection display screen of the color display of FIG. 6 ;

FIG7 is a graph showing how light imaged from pixels of a lower resolution light modulator onto a higher resolution light modulator can overlap to produce a smooth variation in light intensity with respect to position; and

FIG. 7A shows how the variation of light intensity with respect to position of an image of a pixel of a light modulator can be represented as the convolution of a square curve and a spreading function.

DETAILED DESCRIPTION

In the following description, specific details are provided to provide a more thorough understanding of the present invention. However, the present invention can be practiced without these details. In other instances, well-known elements are not shown or described in detail to avoid unnecessarily obscuring the present invention. Accordingly, the description and drawings are to be regarded as illustrative rather than restrictive.

The present invention provides a display capable of reproducing images with a high dynamic range. The display according to the present invention comprises two light modulation stages. Light passes through the two stages successively to provide an image with an increased dynamic range.

FIG1 schematically illustrates a display 10 according to a simple embodiment of the present invention. The dimensions of the elements and the distances between them in FIG1 are not drawn to scale. Display 10 includes a light source 12. Light source 12 may, for example, include a projector lamp such as an incandescent lamp or an arc lamp, a laser, or another suitable light source. Light source 12 may include an optical system comprising one or more reflectors, lenses, or other optical elements that cooperate to direct light to the remainder of display 10.

In the illustrated embodiment, light from a light source 12 is directed toward a first light modulator 16. Light source 12 preferably provides substantially uniform illumination of first light modulator 16. Light modulator 16 comprises an array of individually addressable elements. Light modulator 16 may comprise, for example, an LCD (Liquid Crystal Display) or a DMD (Deformable Mirror Device), examples of transmissive and reflective light modulators, respectively. Display driver circuitry (not shown in FIG. 1 ) controls the elements of light modulator 16 based on data defining the image to be displayed.

The light modulated by the first light modulator 16 is imaged onto the rear-projection display screen 23 via a suitable optical system 17. Light from a small area of the first light modulator 16 is directed to a corresponding area on the rear-projection display screen 23 via the optical system 17. In the illustrated embodiment, the optical system 17 comprises a lens with a focal length f. Generally, the optical system 17, which images the light modulated by the first light modulator 16 onto the rear-projection display screen 23, may comprise one or more mirrors, lenses, or other optical elements. This optical system functions to image the light modulated by the first light modulator onto the second light modulator.

In the illustrated embodiment, the rear-projection display screen includes a second light modulator 20 and a collimator 18. The primary function of the collimator 18 is to direct light passing through the rear-projection display screen 23 preferentially toward the viewing area. The collimator 18 may include a Fresnel lens, a holographic lens, or another arrangement of one or more lenses and/or other optical elements that direct light toward the viewing area.

In the illustrated embodiment, collimator 18 directs light through the elements of second light modulator 20 in a direction generally perpendicular to display screen 23. Light incident from collimator 18 is further modulated as it passes through second light modulator 20. This light then passes to diffuser 22, which scatters the exiting light over a range of directions so that an observer on the opposite side of diffuser 22 from first light modulator 16 can see light emanating from the entire area of display screen 23. Generally, diffuser 22 can scatter light to different angles in both the horizontal and vertical planes. Diffuser 22 should be selected so that the light modulated by second light modulator 20 is scattered over a range of angles, such that the maximum scattering angle is at least equal to the angle subtended by display screen 23 when viewed from a desired viewing position.

The area of the rear-projection display screen 23 may be different from that of the first light modulator 16. For example, the area of the rear-projection display screen 23 may be larger than that of the first light modulator 16. In this case, the optical system 17 expands the light beam modulated by the first light modulator 16 to illuminate a larger corresponding area on the rear-projection display screen 23.

The second optical modulator 20 may be of the same or different type as the first optical modulator 16. In the case where both the first and second optical modulators 16 and 20 are of a type that polarizes light, the second optical modulator 20 should be oriented so that its plane of polarization matches the plane of polarization of the light incident thereon from the first optical modulator 16 as closely as practical.

The display 10 may be a color display. This may be achieved in different ways, including:

● One of the first light modulator 16 and the second light modulator 20 is a color light modulator;

• providing a plurality of different first light modulators 16 operating in parallel on different colors; and

● Provide a mechanism for quickly guiding different color filters into the light path before the second light modulator 20.

As an example of the first method described above, the second light modulator 20 may include an LCD panel having a plurality of pixels, each pixel including a plurality of colored sub-pixels. For example, each pixel may include three sub-pixels, one connected to a red filter, one connected to a green filter, and one connected to a blue filter. The filters may be integrated with the LCD panel.

1A , the light source 12, the first light modulator 16, and the optical system 17 may all be part of a digital video projector 37 for projecting an image defined by a signal 38A from a controller 39 onto the rear of the rear projection display screen 23. The elements of the second light modulator 20 are controlled by a signal 38B from the controller 39 to provide an image having a high dynamic range to the viewer.

As shown in FIG2 , a display 10A according to the present invention may include one or more additional light modulation stages 24. Each additional light modulation stage 24 includes a collimator 25, a light modulator 26, and an optical system 27. The optical system 27 focuses light from the light modulator 26 onto the next additional light modulation stage 24 or onto the collimator 18. In the device 10A of FIG2 , there are two additional light modulation stages 24. The device according to this embodiment of the present invention may have one or more additional light modulation stages 24.

The brightness at any point on the output diffuser 22 can be adjusted by controlling the amount of light passing through corresponding elements of the light modulators 16, 20, and 26. This control can be provided by a suitable control system (not shown in FIG. 2 ) connected to drive each light modulator 16, 20, and 26.

As described above, the light modulators 16, 20 and 26 can all be of the same type or can be two or more different types. Figure 3 shows a display 10B according to an alternative embodiment of the present invention, including a first light modulator 16A, which includes a deformable mirror device. The deformable mirror device is a "binary" device, meaning that each pixel can be "on" or "off". By quickly turning the pixels on and off, different apparent brightness levels can be produced. Such devices are described in, for example, U.S. Patent Nos. 4,441,791 and 4,954,789 and are commonly used in digital video projectors. The light source 12 and the first light modulator 16 (or 16A) can be, for example, the light source and modulator from a commercial digital video projector.

FIG4 shows a front projection display 10C according to the present invention. The display 10C includes a display screen 34. A projector 37 projects an image 38 onto the display screen 34. The projector 37 includes a suitable light source 12, a first light modulator 16, and an optical system 17, adapted to project the image defined by the first light modulator 16 onto the display screen 34. The projector 37 may include a commercially available display projector. The display screen 34 incorporates a second light modulator 36. The second light modulator 36 includes a plurality of addressable elements that can be individually controlled to affect the brightness of corresponding areas of the display screen 34.

Light modulator 36 can have any of a variety of configurations. For example, light modulator 36 can include an array of LCD elements positioned in front of a reflective backing, with each LCD element having a controllable transmittance. Light projected by projector 37 passes through each LCD element and is reflected back through that LCD element by the reflective backing. The brightness of any point on display screen 34 is determined by the intensity of light received by projector 37 at that point and the degree of absorption of the transmitted light by light modulator 36 (e.g., the LCD element at that point).

The light modulator 36 may also include an array of elements having variable retroreflective properties. The elements may be prismatic elements. Such elements are described, for example, in U.S. Patent No. 5,959,777 to Whitehead, entitled "Passive High-Efficiency Variable Reflectivity Image Display Device," and U.S. Patent No. 6,215,920 to Whitehead et al., entitled "Electrophoretic, High-Reflectivity, and Phase-Shift Control of Total Internal Reflection in a High-Efficiency Variable Reflectivity Image Display."

The light modulator 36 may also include an array of electrophoretic display elements, such as those described in U.S. Patent No. 6,172,798 to Albert et al., entitled "Electrophoretic Display of Shutter Mode Microcapsules"; U.S. Patent No. 6,120,839 to Comiskey et al., entitled "Electro-osmotic Display and Materials for Making Same"; U.S. Patent No. 6,120,588 to Jacobson, entitled "Ink and Display of Electrically Addressable Microcapsules"; U.S. Patent No. 6,323,989 to Jacobson et al., entitled "Electrophoretic Display Using Ultrafine Particles"; U.S. Patent No. 6,300,932 to Albert, entitled "Electrophoretic Display with Luminescent Particles and Materials for Making Same" or U.S. Patent No. 6,327,072 to Comiskey et al., entitled "Microcell Electrophoretic Display".

As shown in Figures 6A and 6B, the display screen 34 preferably includes a lens element 40 for preferentially directing light toward the viewer's eyes. In the illustrated embodiment, the lens element 40 comprises a Fresnel lens whose focal point coincides exactly with the apex of the light cone emitted from the projector 37. The lens element 40 may comprise another type of lens, such as a holographic lens. The lens element 40 incorporates scattering centers 45 that provide a desired degree of diffusion in the light reflected from the display screen 34. In the illustrated embodiment, the second light modulator 36 comprises a reflective LCD panel having a plurality of pixels 42, which is backed by a reflective layer 43 and mounted on a backing plate 47.

Where light modulator 36 comprises an array of elements with variable retroreflective properties, the elements themselves can be designed to direct the retroreflected light preferentially in the direction of a viewing area in front of display screen 34. Reflective layer 43 can be designed to scatter light to augment the effect of scattering centers 45 or to replace scattering centers 45.

As shown in FIG4 , a controller 39 provides data defining an image 38 to each of the first light modulator 16 and the second light modulator 36. The controller 39 may comprise, for example, a computer equipped with a suitable display adapter. The controller 39 may include image processing hardware to accelerate the image processing steps. The brightness of any point on the display screen 34 is determined by the combined effect of the pixels in the first light modulator 16 and the second light modulator 36 corresponding to that point. At some points, there is a minimum brightness; for these points, the corresponding pixels of the first and second light modulators are set to their "darkest" state. At some points, there is a maximum brightness; for these points, the corresponding pixels of the first and second light modulators are set to their "brightest" state. Other points have intermediate brightness values. The maximum brightness value may be, for example, approximately 10 ⁵ cd/m ^2. The minimum brightness value may be, for example, approximately 10 ^-2 cd/m ² .

The cost of an optical modulator and its associated control circuitry tends to increase with the number of addressable elements in the optical modulator. In some embodiments of the present invention, one of the optical modulators has a much higher spatial resolution than the other one or more optical modulators. When one or more optical modulators are lower resolution devices, the cost of a display according to such an embodiment of the present invention can be reduced. In a color display comprising two or more optical modulators, one of which is a color light modulator (a combination of multiple monochromatic light modulators can constitute a color light modulator, as shown in, for example, FIG6 ), and one of which is a higher resolution light modulator, the higher resolution light modulator can also be a color light modulator. In some embodiments, the higher resolution light modulator is imaged onto the lower resolution light modulator. In other embodiments, the lower resolution light modulator is imaged onto the higher resolution light modulator.

FIG5 shows one possible configuration of pixels in the display 10 shown in FIG1 . Nine pixels 42 of the second light modulator 20 correspond to each pixel 44 of the first light modulator 16. The number of pixels 42 of the second light modulator 20 that correspond to each pixel 44 of the first light modulator 16 can be varied according to design choice. The pixels 44 of the higher resolution light modulator of the first and second light modulators 16 and 20 (or 36) should be small enough to provide the required overall resolution. There is generally a trade-off between increased resolution and increased cost. In a typical display, the higher resolution light modulator will provide a pixel array having at least several hundred pixels in each direction, and more typically over 1000 pixels in each direction.

The size of the pixels 42 of the lower-resolution light modulator of the first and second light modulators determines the range over which the light modulator can reliably change from maximum intensity to minimum intensity. For example, FIG5A illustrates a situation in which one wishes to display an image of a small dot at maximum brightness against a larger background at minimum brightness. To achieve maximum brightness at point 47, the pixels of each of the first and second light modulators corresponding to point 47 should be set to their maximum brightness values. If the resolution of the pixels of one light modulator is lower than the pixels of the other light modulator, some pixels of the lower-resolution light modulator will straddle the boundary of point 47. This is the situation, for example, in FIG5A .

Outside point 47, there are two regions. In region 48, it is impossible to set the brightness to its minimum value because the lower-resolution light modulator in this region is set to its highest brightness value. In region 49, both light modulators can be set to their lowest brightness value. If, for example, each of the first and second light modulators has a brightness range of 1 to 100 units, then region 47 might have a brightness of 100 x 100 = 10,000 units, region 48 would have a brightness of 100 x 1 = 100 units, and region 49 would have a brightness of 1 x 1 = 1 unit.

The result of one light modulator having a lower resolution than the other is that each pixel of the lower-resolution light modulator corresponds to more than one pixel of the higher-resolution light modulator. It is impossible for a point corresponding to any one pixel of the lower-resolution light modulator and a different pixel of the higher-resolution light modulator to have a brightness value that reaches the dynamic range limit of the device. The maximum brightness difference between such points is determined by the dynamic range of the higher-resolution light modulator.

The inability of a display to achieve the full dynamic range of the display's brightness differences between closely spaced points is not usually a problem. The human eye has enough inherent scattering to be unable to perceive large brightness changes at very short distances in any case.

In a display according to the present invention that includes a lower-resolution spatial light modulator and a higher-resolution spatial light modulator, the controller 39 can determine a value for each pixel of the lower-resolution spatial light modulator and adjust the signal controlling the higher-resolution spatial light modulator to reduce artifacts caused by each pixel of the lower-resolution spatial light modulator being shared with multiple pixels of the higher-resolution spatial light modulator. This can be addressed in any of a number of ways.

For example, consider a scenario where each pixel of a lower-resolution spatial light modulator corresponds to multiple pixels of a higher-resolution spatial light modulator. Image data specifying a desired image is provided to a controller. This image data represents a desired brightness for an image region corresponding to each pixel of the higher-resolution spatial light modulator. The controller can set the pixels of the lower-resolution light modulator to provide an approximation of the desired image. This can be achieved, for example, by determining an average or weighted average of the desired brightness values for the image region corresponding to each pixel of the lower-resolution light modulator.

The controller can then set the pixels of the higher-resolution light modulator so that the composite image approximates the desired image. This can be achieved, for example, by dividing the desired brightness value by the known intensity of light incident on the corresponding pixel of the higher-resolution light modulator from the lower-resolution light modulator. The processing to generate the signal for driving the light modulator can be performed on the fly by the controller 39, can be performed earlier by the controller 39 or some other device and integrated into the image data, or some processing can be performed earlier and the controller 39 can perform the final processing to generate the control signal.

If the low-resolution pixels are too large, a viewer may be able to see halos around bright elements in the image. The low-resolution pixels are preferably small enough so that the appearance of bright blocks on a dark background or dark spots on a light background is not unacceptably degraded. It is currently contemplated that a range of about 8 to about 144, more preferably about 9 to 36, pixels on the higher-resolution light modulator is provided for each pixel of the lower-resolution light modulator.

The steps in which each pixel 42 and 44 can adjust the brightness of a point on the image do not have to be equal. The steps in which the pixels of a lower-resolution light modulator adjust the light intensity can be coarser than the pixels of a higher-resolution light modulator. For example, a lower-resolution light modulator may allow the light intensity to be adjusted in 8 steps over an intensity range of 1 to 512 units for each pixel, while a higher-resolution light modulator may allow the light intensity to be adjusted in 512 steps over a similar range for each pixel. Although pixels 42 and 44 are both shown as squares in FIG5 , this is not necessary. Pixels 42 and/or 44 may be other shapes, such as rectangular, triangular, hexagonal, circular, or elliptical.

The pixels of the lower-resolution light modulator preferably emit somewhat diffuse light so that the light intensity varies reasonably smoothly as it passes through the pixels of the lower-resolution light modulator. This is the case where the light from each pixel of the lower-resolution light modulator spreads into adjacent pixels, as shown in Figure 7. As shown in Figure 7A, the intensity profile of a pixel in the lower-resolution light modulator can generally be approximated by the convolution of a Gaussian spread function with a rectangular curve whose width _d1 is equal to the actual width of the pixel. The spread function preferably has a full width at half- _maximum in the range of 0.3× _d2 to 3×d2, where _d2 is the center-to-center spacing between pixels, to produce the desired smoothly varying light intensity. Typically, _d1 is approximately equal to _d2 .

In the embodiment of FIG. 5 , each pixel includes three sub-pixels 43R, 43G, and 43B (for clarity, FIG. 5 omits the sub-pixels of some pixels 42). Sub-pixels 43R, 43G, and 43B are independently addressable. They are respectively connected to red, green, and blue filters integrated into the second light modulator 20. Various configurations of LCD panels containing multiple color sub-pixels and suitable for use with the present invention are known in the art.

For front projection displays (e.g., display 10C of FIG. 4 ), it is typically most practical for first light modulator 16 to comprise a high-resolution light modulator that provides color information, and for light modulator 36 to comprise a monochromatic light modulator. Light modulator 36 preferably has addressable elements that are reasonably small so that the boundaries of its elements do not form a visually unclear pattern. For example, light modulator 36 can have the same number of addressable elements as projector 37 (although the size of each such element will typically be much larger than the corresponding element in light modulator 16 of projector 37).

Projector 37 can have any suitable construction. All that is required is that projector 37 is capable of projecting light that has been spatially modulated to provide an image to display screen 34. Figure 6 shows a display system 10D according to another alternative embodiment of the present invention. System 10D includes display screen 34 having an integrated light modulator 36 as described above with reference to Figure 4. System 10D includes projector 37A having a separate light modulator 16R, 16G and 16B for each color. The light modulated by each light modulator 16R, 16G and 16B is filtered by a corresponding one of three color filters 47R, 47G and 47B. The modulated light is projected onto display screen 34 through optical system 17. A single light source 12 can provide light to all three light modulators 16R, 16G and 16B, or a separate light source (not shown) can be provided.

Obviously, for a skilled person, in light of the above disclosure, many changes and modifications are possible in practicing the present invention without departing from its spirit or scope. For example:

The diffuser 22 and the collimator 18 can be combined with each other;

● The diffuser 22 and collimator 18 can be in reverse order;

● Multiple cooperating elements may be provided to perform light diffusion and/or collimation;

The order of the second light modulator 20, the collimator 18 and the diffuser 22 in the display screen 23 can be changed;

• The signal 38A driving the first optical modulator 16 may include the same data that drives the second optical modulator 20, or may include different data.

Therefore, the scope of the present invention should be construed as defined by the following claims.

Claims (26)

1. A display controller, which can be connected as follows: In the case where each pixel pair of a first means for providing light spatially modulated at a lower spatial resolution is applied to multiple pixels of a second means for further spatially modulating the light at a higher spatial resolution. Receive image data that specifies the required image; and Drive the first and second devices; The controller is configured as follows: The pixels of the first device are configured to provide an approximation of the desired image; and The pixels of the second device are adjusted to make the resulting image approximate the desired image. The controller is configured to control the pixels of the second device to modulate the light incident on the pixel based on the desired brightness value at the image position corresponding to the pixel position in the second device divided by the determined light intensity from the first device on the second device. 2. The controller according to claim 1, wherein for each pixel in the first device, the second device has more than one corresponding pixel, and wherein the controller is configured to: The contribution of a pixel in the first device to the brightness is set as an average or weighted average of multiple desired brightness values in an image region in the second device corresponding to that pixel in the first device. 3. The controller according to claim 1, wherein the controller is configured to: The brightness level of a pixel in the first device is selected from N discrete brightness levels; and The brightness level of a pixel in the second device is set to be selected from a number of M discrete brightness levels, where N is greater than M. 4. The controller according to claim 1, wherein the controller is configured to: The brightness level of a pixel in the first device is selected from N discrete brightness levels; and The brightness level of a pixel in the second device is set to be selected from a number of M discrete brightness levels, where N is less than M. 5. The controller according to claim 1, wherein the controller is configured to set the pixels of the second device based on the intensity curve of light from the pixels of the first device convolved with a spread function and a rectangular distribution, wherein the spread function has a full width at the half maximum in the range of 0.3×d ₂ to 3×d ₂ , where d ₂ is the center interval of the distribution of light modulated by adjacent pixels of the first device on the second device. 6. The controller according to claim 1, wherein the pixels in the second device have controllable transmissive properties, and wherein the controller is configured to control the pixels in the second device by adjusting the transmissive properties of the pixels in the second device. 7. The controller according to claim 1, wherein the first device comprises an array of color pixels, wherein the controller is configured to control the pixels in the first device by setting the color value of each pixel in the first device respectively. 8. The controller according to claim 7, wherein the controller is configured to control the pixels in the first device by setting a plurality of color values for each pixel in the first device. 9. The controller according to claim 1, wherein the controller is configured to set the pixels of the first device such that the first device emits diffuse and smoothly varying light, the first device comprising one of a transmissive light modulator, a reflective light modulator, and an electrophoretic display element array, wherein light from each pixel of the first device is extended to adjacent pixels, and the pixels of the second device are set by dividing a desired brightness value by a known intensity of light incident from the first device onto the corresponding pixel of the second device. 10. The controller of claim 1, wherein the controller is configured to estimate the approximate intensity of light from a pixel of a first device by convolving a spread function with a rectangular distribution, wherein the spread function has a full width at its half maximum in the range of 0.3× _d² to 3× _d² , where _d² is the center spacing of the distribution of light modulated by adjacent controllable elements of the first device on the second device. 11. The controller according to claim 9, wherein the pixel brightness adjustment step sizes of the first device and the second device are not equal. 12. The controller according to claim 11, wherein the pixels of the first device adjust the light intensity in larger steps than the pixels of the second device. 13. The controller according to claim 1, wherein the controller is configured to approximate the light intensity of a pixel from a first device by means of a Gaussian spread function having a full width at half maximum in the range of 0.3× _d² to 3× _d² , where _d² is the center interval of the distribution of light modulated by adjacent controllable elements of the first device on the second device; The Gaussian spread function is convolved with a rectangular curve whose width is equal to the actual width of a pixel. 14. A display comprising: Pixels of a first device for providing light spatially modulated at a lower spatial resolution are connected to emit controllable amounts of light to pixels of a second device for further spatially modulating the light at a higher resolution; pixels of the second device are connected to transmit controllable portions of the light. The controller is connected as follows: In the case where each pixel of the first device corresponds to multiple pixels of the second device. The controller controls the pixels in the first and second devices, the controller being configured to control the pixels in the first device to provide a desired image approximation as specified by the image data; The pixels in the second device are controlled to make the resulting image approximate the desired image. The controller is configured to control the pixels of the second device to modulate the light incident on the pixel based on the desired brightness value at the image position corresponding to the pixel position in the second device divided by the determined light intensity from the first device on the second device. 15. The display according to claim 14, wherein light from a pixel of the first device extends to adjacent pixels. 16. The display according to claim 14, wherein the number of pixels in the first device is less than the number of pixels in the second device. 17. The display according to claim 14, wherein light emitted by a pixel in the first device is approximated by convolving a Gaussian spread function with a rectangular curve having a width equal to the actual width of the pixel, the Gaussian spread function having a full width at its half maximum in the range of 0.3× _d² to 3× _d² , where _d² is the center-to-center spacing of the distribution of light modulated by adjacent controllable elements of the first device on the second device. 18. The display according to claim 14, wherein the controller is configured to: The brightness level of the light emitted by the pixels in the first device is selected from N discrete brightness levels; and The transmittance level of the pixel in the second device is controlled, and it is selected from a number of M discrete transmittance levels, where N is greater than M. 19. The display according to claim 14, wherein the controller is configured to: The brightness level of the light emitted by the pixels in the first device is selected from N discrete brightness levels; and The transmittance level of the pixel in the second device is controlled, and it is selected from a number of M discrete transmittance levels, where N is less than M. 20. The display according to claim 14, comprising: a diffuser located on one side of the second device, the diffuser facing away from the first device. 21. The display according to claim 14, comprising: an optical system located between the first device and the second device for imaging light emitted by a pixel in the first device to the second device. 22. A method of displaying an image on a display comprising pixels of a first means for providing light spatially modulated at a lower spatial resolution, wherein pixels of the first means emit light to pixels of a second means for further spatially modulating the light at a higher spatial resolution, the method comprising: In the case where each pixel of the first device corresponds to multiple pixels of the second device. The pixels of the first device are controlled to obtain a pattern of light that approximates the desired image specified by the image data on the second device; The pixels of the second device are controlled so that the resulting image closely approximates the desired image. The control of the pixel of the second device includes: controlling the pixel of the second device to modulate the light incident on the pixel based on the desired brightness value at the image position corresponding to the pixel position in the second device divided by the determined light intensity from the first device on the second device. 23. The method of claim 22, wherein light from a pixel of the first device extends to an adjacent pixel. 24. The method of claim 22, comprising: approximating the light intensity of a pixel from the first device by convolving a Gaussian spread function with a rectangular curve having a width equal to the actual width of the pixel; The Gaussian spread function has a full width at its half maximum in the range of 0.3× _d² to 3× _d² , where _d² is the center interval of the distribution of light modulated by adjacent controllable elements of the first device on the second device. 25. The method according to claim 22, comprising: Select the brightness level of a pixel in the first device from a number of N discrete brightness levels; and The transmittance level of the pixel in the second device is selected from a number of M discrete transmittance levels, where N is greater than M. 26. The method according to claim 22, comprising: Select the brightness level of a pixel in the first device from a number of N discrete brightness levels; and The transmittance level of the pixel in the second device is selected from a number of M discrete transmittance levels, where N is less than M.