WO2004064408A1

WO2004064408A1 - Device and method of scanning an image in a projection system

Info

Publication number: WO2004064408A1
Application number: PCT/IB2003/006288
Authority: WO
Inventors: Adrianus J. S. M. De Vaan; Ronald M. A. M. Breukers
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2003-01-16
Filing date: 2003-12-10
Publication date: 2004-07-29
Also published as: AU2003288663A1

Abstract

The present invention relates to the field of projection-type image display devices allowing scanning of an image and a scanning method. The device comprises a light source (1) for emitting a white light luminous flux in one direction. Modulating means (2) comprise light valves for modulating lights contained in luminous fluxes and thus produce an image comprising pixels. Projection-optical means (3) are provided for projecting said image on a screen. The image display device further comprises scanning means (4) arranged to scan said image in such a way that each modulated pixel illuminates a multitude of positions within a unit cell having a predetermined area size.

Description

Device and method, of scanning an image in a projection system

FIELD OF THE INVENTION

The present invention relates to the field of projection-type image display devices, and particularly to a projection-type image display device allowing scanning of an image as well as a scanning method.

BACKGROUND OF THE INVENTION

The use of projection type image display devices is increasing, because such display devices have become very popular for presentations at meetings, conferences, home entertainment, etc. One reason for this is the increasing affordability. Moreover, such display devices have a higher quality of the image and a more compact construction. The requirement for a higher resolution and a better contrast in the displayed image is, however, getting more stringent. The current projection type image display devices have gaps in between the pixels, i.e. they do not have a 100% fill-factor. These gaps are needed for the electronics supplying each pixel and can be seen as a black frame around each pixel when taking a closer look at the displayed image. Manufacturing displays with a better fill-factor is very difficult and expensive.

One prior-art approach is disclosed in US 5.032.924, which suggests a projection type video image display device comprising means for scanning the image at a non-linear rate and means for modulating the basic illumination and intensity of pixels as a function of scanning speed. According to this prior-art approach, a light source is coupled to provide a beam through a shutter assembly, which in turn is coupled to a horizontal scanning mirror and, thence, to a vertical scanning mirror, the output scan of which is directed to impinge upon a screen. The horizontal scanning mirror is arranged to scan bi-directionally, left and right, with a scan characteristic which is preferably sinusoidal. The vertical scanning mirror scans at a relatively slow rate of speed.

However, this prior-art approach requires two scanning mirrors, one of which operates with high speed scanning. Also, the modulating means according to the prior art need to modulate with pixel speed instead of frame speed. OBJECT AND SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide an improved projection type image display device allowing scanning of an image.

This object is achieved by providing an optical sub-system in the imaging parts to scan the pixels of the display over the image plane such that each pixel illuminates a multitude of positions within a unit cell having a predetermined area size.

Another object of the invention is to provide an improved method of scanning an image in a projection type image display.

This object is achieved by a method of providing an optical sub-system in the imaging parts to scan the pixels of the display over the image plane such that each pixel illuminates a multitude of positions within a unit cell having a predetermined area size.

Still other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, wherein like reference characters denote similar elements throughout the several views:

Fig. 1 discloses a schematic view of a projection type image display device according to a general embodiment of the invention; Fig. 2 discloses a pixel layout of a display panel;

Fig. 3 discloses a pixel layout of a display panel showing a circular unit cell; Fig. 4 discloses the pixel layout according to Figure 3 showing a plurality of circular unit cells;

Fig. 5 discloses a schematic view of a projection type image display device according to a first embodiment of the invention;

Fig. 6 discloses a schematic view of a driving unit according to a preferred embodiment of the present invention;

Fig. 7 discloses a schematic view of a projection type image display device according to a second embodiment of the invention; Fig. 8 discloses a schematic view of a projection type image display device according to a third embodiment of the present invention;

Fig. 9 discloses an achromatic circular polarizing beam splitter according to the third embodiment of the invention according to Figure 8; Fig. 10 discloses a schematic view of a projection type image display device according to a fourth embodiment of the present invention;

Fig. 11 discloses color filtering means comprising dichroic filters for filtering white light into red light, green light and blue light;

Fig. 12 discloses a schematic view of a projection type image display device showing an angular color splitting system comprising dichroic mirrors for splitting white light into red light, green light and blue light;

Fig. 13 discloses how pixels are moved over a rectangular unit cell;

Fig. 14 discloses a driving unit according to another embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Fig. 1 is a conceptual diagram showing a basic constitution of a projection type image display device according to a general embodiment of the present invention. The projection type image display device mainly comprises a light source 1, such as e.g. a halogen lamp, a metal halide lamp, an ultrahigh pressure mercury-vapor lamp, or a similar lamp, from which a white light luminous flux is emitted. Furthermore, the projection type image display device comprises a display panel 2 comprising light valves for optically modulating the luminous flux and thus producing an image comprising pixels. The display panel may be of either a transmissive or a reflective type, such as a Liquid Crystal Display (LCD) or a Liquid crystal on Silicon display (LCoS). Also, the projection type image display device comprises scanning means which, in a preferred embodiment, is a scanning mirror 4 for scanning the pixels of the display 2. A projection lens 3 is provided for magnifying and projecting the scanned modulated luminous flux on a projection screen (not shown).

One method of generating colors in a display, is to apply absorption-type mosaic color filters. Fig. 2 shows the pixel layout of such a display panel. In a white display, all wavelengths of the light pass through and, therefore, all wavelengths can be manipulated to create the desired color. To get full color, each individual pixel 5 is divided into three sub- pixels 5R, 5G, 5B, red, green and blue (RGB). That is to say, for each full color pixel 5, three distinct pixels 5R, 5G, 5B are employed. These sub-pixels 5R, 5G, 5B are created by applying the color filters which only allow certain wavelengths of the light to pass through them while absorbing the rest.

The scanning mirror 4 is arranged to scan the individual color pixels 5R, 5G, 5B within a unit cell 6, shown in Fig. 3, having a predetermined shape and area size. In such a way, each color pixel 5R, 5G, 5B illuminates time-sequential multiple positions on the projected image. Using a sufficiently fast switching display with respect to the required time for displacement of one pixel, where the switching time is shorter than the time for displacement, the displayed image has full modulation depth at each pixel position in the projected image, provided that the display is scanned properly. The reflective LCoS panels allows a faster switching time than the transmissive LCD panels and such higher refresh rates of the system to reduce visible display artifacts. In the preferred embodiment, shown in Figs. 3 and 4, each color pixel 5R, 5G, 5B is moved circularly across the image plane. In order to obtain this circular motion, the mirror 4 is rotated at a constant speed. Thus, a homogeneous image is obtained and the required switching time of the used display effect remains reasonable. If the used display is an LCD, the used effect may be a very thin Twisted Nematic (TN) layer or a Ferro-Electric LCD effect.

Fig. 5 illustrates a first embodiment of the present invention, where the scanning mirror 4 is a circular-shaped mirror that rotates on a shaft 7 driven by a driving unit 8, such as an electric motor. The shaft 7 is almost but not quite perpendicular to the scanning mirror 4 in order to move each color pixel 5R, 5G, 5B across the image plane, as can be seen in Fig. 6. The display panel 2 is of a transmissive type, such as an LCD panel.

The process until an image, such as a video image or data graphics, is magnified and projected on the projection screen in the first embodiment, shown in Fig. 5, is described below. A white light luminous flux emitted from the light source 1 passes through the absorption type color filter (not shown) and the display panel 2 comprising light valves, modulating the white light luminous flux into the three principal colors, red, green and blue, represented as pixels 5R, 5G, 5B.

The modulated color light from each pixel is reflected on the scanning mirror 4, which is rotated by the driving unit 8 and the shaft 7, and projected on a projection screen (not shown) through a projection lens 3 which is a projection-optical means.

Three examples of possible pixel refresh rates are described below. Example 1 : If the scan frequency is taken to be 50 Hz, the pixel may be refreshed at fixed time intervals, such that after 20 mS its first position is repeated. E.g. at a 50 Hz refresh rate, a 50*12=600 Hz pixel refresh rate results in a three times higher number of resolvable pixels in the projected image, supposing that the display switches faster than 20/12 mS. However,, the refresh rate of the display panel seems to be higher because each original pixel position is now refreshed at 50*4=200 Hz. Example 2: If the scan frequency is taken to be 50 Hz, the pixel may be refreshed at fixed time intervals, such that after 20 mS its first position is repeated. E.g. at a 50 Hz refresh rate, a 50*8=400 Hz pixel refresh rate results in a two times higher number of resolvable pixels in the projected image, supposing that the display switches faster than 20/8 mS. However, the refresh rate of the display panel seems to be higher because each original pixel position is now refreshed at 50*4=200 Hz.

Example 3: If acceptable, the scan frequency is taken to be 25 Hz and the pixel may be refreshed at fixed time intervals, such that after 40 mS its first position is repeated. E.g. at a 25 Hz refresh rate, a 25*16=400 Hz pixel refresh rate results in a four times higher number of resolvable pixels in the projected image, supposing that the display switches faster than 40/16 mS. However, the refresh rate of the display panel seems to be higher because each original pixel position is now refreshed at 25*4=100 Hz.

The size of the scanned unit cells may be taken to be such that the scanned pixel does not intersect with any of the original pixel positions, which means that a maximum of locations is addressed with a minimum of pixels in the display panel. This requires different scan frequencies than in the examples above. However, the increment in resolution becomes the number of pixel addressings during one scan cycle. Also, the size of the scanned unit cells is optimized for maximum resolution and best fit with respect to a homogeneous screen illumination. Furthermore, the intensity of the pixel may be corrected during the scan to improve homogeneity of the image. Fig. 7 illustrates a second embodiment of the present invention, where the scanning mirror 4 is the circular-shaped mirror that rotates on the shaft 7 driven by the driving unit 8. The display panel 2 is of a reflective type, such as an LCoS panel. A polarizing beam splitter (PBS) 9 is arranged to transmit incident light in a first polarization state and to reflect incident light in a second polarization state. The process until an image, such as a video image or data graphics, is magnified and projected on the projection screen in the second embodiment, shown in Fig. 7, is described below. A white light luminous flux emitted from the light source 1 reaches the polarizing beam splitter (PBS) 9 arranged to transmit incident light in a first polarization state and to reflect incident light in a second polarization state.

The reflected light in the second polarization state is deviated towards the display panel 2, passes through the absorption type color filter (not shown) and is reflected on the display panel 2 comprising reflective light valves, whereby the white light luminous flux is modulated into the three principal colors, red, green and blue, represented as pixels 5R, 5G, 5B.

The modulated color light now in the first polarization state from each pixel is reflected, via the PBS 9 transmitting the modulated color light, on the scanning mirror 4, which is rotated by the driving unit 8 and the shaft 7, and projected on the projection screen (not shown) through the projection lens 3, which is a projection-optical means.

Fig. 8 illustrates a third embodiment of the present invention, where the scanning means is an achromatic PBS 10 instead of a normal scanning mirror. The achromatic PBS rotates on the shaft 7 driven by the driving unit 8 in the same manner as the scanning mirror of the first and the second embodiment of the present invention. The display panel 2 is of the reflective type, such as an LCoS panel. The achromatic PBS 10 scans each pixel in the image plane and simultaneously acts as a PBS in front of the reflective display panel 2 to illuminate the display panel 2 and to analyze the reflected modulated light from the reflective display panel 2. An extra quarter-wave film 11 is positioned in between the scanning achromatic PBS 10 and the reflective type display panel 2, because the reflective display panel 2 requires linearly polarized light. In case the contrast from the light beam that is incident in the projection lens 3 has an insufficient contrast ratio due to the performance of the achromatic PBS 10, an additional clean-up polarizer 12, blocking any light having an undesired polarization direction, is required between the achromatic PBS 10 and the projection lens 3. The clean-up polarizer 12 is, for example, made of a stack of a quarter- wave film and a polarizer film of the linear absorption type.

The achromatic PBS 10 may be obtained by laminating a wired grid type of PBS plate 13 in between two achromatic quarter-wave plates 14a, 14b, shown in Fig. 9, such that the wired grid plate 13 operates for circularly polarized light. A wired grid plate 13 can be obtained from Moxtek Corporation USA. The projection image display device according to the third embodiment of the invention minimizes the back focal length of the projection lens 3 and thus decreases the cost of the projection lens 3, as the optical path of the light is folded. The process until an image, such as a video image or data graphics, is magnified and projected on the projection screen in the third embodiment, shown in Fig. 8, is described below.

A white light luminous flux emitted from the light source 1 passes through the achromatic PBS 10, through the extra quarter- wave film 11 in order to get linearly polarized light and through the absorption-type color filter (not shown) and is reflected on the display panel 2 comprising light valves of the reflective type. The white light luminous flux is modulated into the three principal colors, red, green and blue, represented as pixels 5R, 5G, 5B. The modulated color light from each pixel is reflected on the achromatic PBS

10, which is rotated by the driving unit 8 and the shaft 7, and projected on the projection screen (not shown), via the clean-up polarizer 12, through the projection lens 3, which is a projection-optical means.

Fig. 10 illustrates a fourth embodiment of the present invention, where the scanning mirror 4 is the circular-shaped mirror that rotates on the shaft 7 driven by the driving unit 8. The display panel 2 is of a reflective type, such as an LCoS panel and the PBS 9 is arranged to transmit incident light in a first polarization state and to reflect incident light in a second polarization state. The projection image display device of the fourth embodiment further comprises a photon recycler 15 and a light focusing lens 16. The photon recycler 15 is arranged to recycle the light that is bounced back from the reflective display panel 2 to the illumination system, showing dark pixels on the screen, and thus increasing the brightness in the white area of the projected image. This embodiment of the invention is excellent for extreme miniaturized LCoS panels, where the active pixel area has become of the same order as the gaps in between the pixels. For this reason, this embodiment is perfect with required solutions for visible pixel gaps and/or reduced efficiency due to geometrical aperture at extreme miniaturization.

The process until an image, such as a video image or data graphics, is magnified and projected on the projection screen in the fourth embodiment, shown in Fig. 10, is described below. A white light luminous flux emitted from the light source 1 passes through the photon recycler 15 and the lens 16 and reaches the polarizing beam splitter 9 arranged to transmit incident light in a first polarization state and to reflect incident light in a second polarization state. The reflected light in the second polarization state is deviated towards the display panel 2, passes through the absorption type color filter (not shown) and is reflected on the display panel 2 comprising reflective light valves, whereby the white light luminous flux is modulated into the three principal colors, red, green and blue, represented as pixels 5R, 5G, 5B.

The modulated color light now in the first polarization state from each pixel is reflected, via the PBS 9 transmitting the modulated color light, on the scanning mirror 4, which is rotated by the driving unit 8 and the shaft 7, and projected on the projection screen (not shown) through the projection lens 3, which is a projection-optical means. As mentioned above, one method of generating colors is by applying a mosaic color filter which allows certain wavelengths to pass through them while absorbing the rest and thus creating the desired colors. In another embodiment, when the display panel is of the reflective type such as an LCoS panel, internal dichroic mirror-based color filter patterns are used. Such a color filter is shown in Fig. 11. In the dichroic mirror-based color filter, the white light luminous flux passes through a top glass plate 17 in a first polarization state and hits the dichroic filter pattern 18. The R-field is arranged to allow red light to pass through while reflecting green and blue light, the G-field is arranged to allow green light to pass through while reflecting red and blue light and the B-field is arranged to allow blue light to pass through while reflecting red and green light. The filtered color lights of red light, green light and blue light pass through a liquid crystal layer 21 and reflect on reflective pixel electrodes 19 and are thus modulated to a second polarization state. The reflective pixel electrodes 19 are arranged on a semiconductor body 20 containing an active matrix drive.

All the light that does not leave the system via the projection lens 3 is bounced from the display panel 2 via the PBS 9 back into the photon recycler 15. The photon recycler 15 consists, for instance, of a rectangular glass pipe having a mirror on the entrance surface (lamp side). The light from the light source 1 enters the glass pipe 15 via a hole in the mirror on its entrance surface. Most of the light that bounced back from the display panel 2 into the photon recycler will hit the mirror on its entrance surface (lamp side) and as such will be bounced back via this mirror on the entrance surface to the display 2. Fig. 12 illustrates still another embodiment for generating colors, in which an angular color splitting system is used. The angular color splitting system comprises a set of three mirrors 22, two of which are dichroic mirrors, the first dichroic mirror reflecting red light and allowing green and blue light to pass, the second dichroic mirror reflecting green light and allowing blue light to pass and the third mirror reflecting the blue light. The display panel 2, comprising transmissive light valves, is provided with microlenses arranged to focus the light in the corresponding pixels.

Fig. 13 illustrates how the pixel 5 is moved over the unit cell 23 according to another embodiment of the present invention, where the unit cell 23 is rectangular. The scanning mirror 24 is moved around its center position 25 using transducers, one of which is horizontal 26 and one of which is vertical 27, at two edges on the mirror, which is shown in Fig. 14. The transducers 26, 27 may be based on electro-magnetic coils (loudspeaker) or may use piezo-electric elements. The transducers 26, 27 are more or less arranged to make the scanning mirror 24 vibrate, such that each pixel 5 is moved over the rectangular unit cell 23. The person skilled in the art will realize that the pixels do not necessarily need to move over a circular or rectangular unit cell. Other geometries for unit cells are also possible, such as a quadratic unit cell.

A method of scanning an image of a projection image display device will be described hereinafter, wherein the display device comprises a light source for emitting a white light luminous flux in one direction, modulating means comprising light valves for modulating lights contained in luminous fluxes and thus producing an image comprising pixels, and projection-optical means for projecting said image on a screen, according to any one of the above described embodiments, and the method comprises the step of: providing scanning means for scanning said image such that each modulated pixel illuminates a multitude of positions within a unit cell having a predetermined area size.

In a further embodiment, the method further comprises the step of providing color filtering means for filtering the white light from said light source into three color lights of red light, green light and blue light, such that each pixel of the image represents either one of the colors red, green or blue. In a further embodiment, the method comprises the step of providing moving means for rotating or vibrating said scanning means around its center causing each modulated pixel to illuminate a multitude of positions within the circular or rectangular unit cell. In a still further embodiment, the method further comprises the step of providing a polarizing beam splitter arranged to transmit incident light in a first polarization state and to reflect incident light in a second polarization state.

In an additional further embodiment, the method comprises the steps of providing color splitting means for splitting the white light from said light source into three color lights of red light, green light and blue light, such that each pixel of the image represents either one of the colors red, green or blue, which color splitting means comprise three dichroic mirrors having characteristics for selectively passing and selectively reflecting red light, green light or blue light.

In yet further embodiments, the method comprises the steps of providing modulating means comprising transmissive or reflective light valves. In still further embodiments, the method comprises the steps of providing scanning means comprising a scanning mirror or an achromatic circularly polarizing beam splitter arranged to act as a polarizing beam splitter in front of reflective light valve-based modulating means and thus arranged to illuminate the modulating means as well as to analyze the reflective light from the modulating means. The achromatic circularly polarizing beam splitter comprises a Moxtek type of polarizing beam splitter which is sandwiched between two achromatic quarter-wave plates.

In yet additional further embodiments, the method further comprises the steps of providing photon recycling means for recycling light which is bounced back from the modulating means to the illumination path. As illustrated above, a projection image display device and a method of scanning an image of a projection image display device has been described, where the resolution of the display panel is taken to be much lower than before because each pixel is imaged at multiple screen positions. The approach according to the present invention is advantageous in comparison with the previously discussed prior-art approach, which requires two scanning mirrors, one of which operates with high speed scanning. Also, the modulating means according to the prior art need to modulate with pixel speed instead of frame speed. The present invention eliminates these restrictions of such a prior-art approach by providing scanning means which scan the image in such a way that each pixel illuminates time- sequential multiple positions on the projected image. Thus, while fundamental novel features of the invention as applied to a preferred embodiment thereof have been shown, described and pointed out, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.

Claims

CLAIMS:

1. A projection-type image display device comprising a light source (1) for emitting a white light luminous flux in one direction, modulating means (2) comprising light valves for modulating lights contained in luminous fluxes and thus producing an image comprising pixels (5, 5R, 5G, 5B), and projection-optical means (3) for projecting said image on a screen, wherein the image display device further comprises scanning means (4, 10, 24) arranged to scan said image such that each modulated pixel (5, 5R, 5G, 5B) illuminates a multitude of positions within a unit cell (6, 23) having a predetermined area size.

2. The projection-type image display device of claim 1 , further comprising color filtering means (18) for filtering the white light from said light source (1) into three color lights of red light, green light and blue light, such that each pixel (5R, 5G, 5B) of the image represents either one of the colors red, green or blue.

3. The projection-type image display device of claim 1, further comprising moving means (8, 26, 27) for moving said scanning means (4, 10, 24) around its center causing each modulated pixel to illuminate a multitude of positions within the unit cell (6, 23).

4 The projection-type image display device of claim 3, wherein said moving means (8) is arranged to rotate the scanning means (4, 10) and thus moves each pixel over a circular unit cell (6).

5. The projection-type image display device of claim 3, wherein said moving means (26, 27) is arranged to vibrate the scanning means (24) and thus moves each pixel over a rectangular unit cell (23).

6. The projection-type image display device of claim 1, further comprising a polarizing beam splitter (9) arranged to transmit incident light in a first polarization state and to reflect incident light in a second polarization state.

7. The projection-type image display device of claim 1, further comprising color splitting means (22) for splitting the white light from said light source into three color lights of red light, green light and blue light, such that each pixel (5R, 5G, 5B) of the image represents either one of the colors red, green or blue.

8. The projection-type image display device of claim 7, wherein the color splitting means comprises two dichroic mirrors (22) having characteristics for selectively passing and selectively reflecting either of red light, green light or blue light.

9. The projection-type image display device of claim 1 , wherein the modulating means comprises transmissive light valves.

10. The projection-type video image display device of claim 1 , wherein the modulating means comprises reflective light valves.

11. The projection-type image display device of claim 1 , wherein the scanning means comprises a scanning mirror (4, 24).

12. The projection-type image display device of claim 1 , wherein the scanning means comprises an achromatic circular polarizing beam splitter (10) arranged to act as a polarizing beam splitter in front of reflective light valve-based modulating means and thus arranged to illuminate the modulating means as well as to analyze the reflective light from the modulating means.

13. The projection-type image display device of claim 12, wherein the achromatic circular polarizing beam splitter (10) comprises a wired grid type of polarizing beam splitter (13) which is sandwiched between two achromatic quarter- wave plates (14a, 14b).

14. The projection-type image display device of claim 1, further comprising photon recycling means (15) for recycling light which is bounced back from the modulating means to the illumination path.

15. A method of scanning an image of a proj ection-type image display device comprising: a light source for emitting a white light luminous flux in one direction, modulating means comprising light valves for modulating lights contained in luminous fluxes and thus producing an image comprising pixels, and projection-optical means for projecting said image on a screen, wherein said method comprises the step of: providing scanning means for scanning said image such that each modulated pixel illuminates a multitude of positions within a unit cell having a predetermined area size.

16. The method of claim 15, further comprising the step of providing color filtering means for filtering the white light from said light source into three color lights of red light, green light and blue light, such that each pixel of the image represents either one of the colors red, green or blue.

17. The method of claim 15, further comprising the step of providing moving means for moving said scanning means around its center, causing each modulated pixel to illuminate a multitude of positions within the unit cell.

18. The method of claim 17, further comprising the steps of providing moving means arranged to rotate the scanning means and thus moving each pixel over a circular unit cell.

19. The method of claim 17, further comprising the steps of providing moving means arranged to vibrate the scanning means and thus moving each pixel over a rectangular unit cell.

20. The method of claim 15, further comprising the steps of providing a polarizing beam splitter arranged to transmit incident light in a first polarization state and to reflect incident light in a second polarization state.

21. The method of claim 15, further comprising the steps of providing color splitting means for splitting the white light from said light source into three color lights of red light, green light and blue light, such that each pixel of the image represents either one of the colors red, green or blue.

22. The method of claim 21, further comprising the steps of providing color splitting means comprising two dichroic mirrors having characteristics for selectively passing and selectively reflecting either of red light, green light or blue light.

23. The method of claim 15, further comprising the steps of providing modulating means comprising transmissive light valves.

24. The method of claim 15, further comprising the steps of providing modulating means comprising reflective light valves.

25. The method of claim 15, further comprising the steps of providing scanning means comprising a scanning mirror.

26. The method of claim 15, further comprising the steps of providing scanning means comprising an achromatic circularly polarizing beam splitter arranged to act as a polarizing beam splitter in front of reflective light valve-based modulating means and thus arranged to illuminate the modulating means as well as to analyze the reflective light from the modulating means.

27. The method of claim 26, further comprising the steps of providing an achromatic circularly polarizing beam splitter comprising a wired grid type of polarizing beam splitter which is sandwiched between two achromatic quarter- wave plates.

28. The method of claim 15, further comprising the steps of providing photon recycling means for recycling light which is bounced back from the modulating means to the illumination path.