WO2009007901A2

WO2009007901A2 - Image projection method

Info

Publication number: WO2009007901A2
Application number: PCT/IB2008/052717
Authority: WO
Inventors: Carsten Deppe; Holger Moench
Original assignee: Philips Intellectual Property & Standards Gmbh; Koninklijke Philips Electronics N. V.
Priority date: 2007-07-10
Filing date: 2008-07-07
Publication date: 2009-01-15
Also published as: WO2009007901A3

Abstract

The invention describes an image projection method, which method comprises the steps of displaying a micro-image in a liquid crystal display element (1, 1'), which liquid crystal display element (1, 1') comprises rows (R1, R2,..., Rj,..., Rm) of pixels (P1, P2,..., Pi,..., Pn) arranged in a two-dimensional array for displaying the micro-image, generating laser light (BR, BG, BB, LR, LG, LB) by means of a laser light source (2RGB, 2R, 2G, 2B), scanning the laser light (BR, BG, BB, LR, LG, LB) to traverse the micro-image on the liquid crystal display element (1, 1') in a line- wise manner to generate an image and projecting the image onto a screen (3). The invention further describes a projection system (10, 10', 10') comprising a liquid crystal display element (1, 1'), which liquid crystal display element (1, 1') comprises rows (R1, R2,..., Rj,..., Rm) of pixels (P1, P2,..., Pi,..., Pn) arranged in a two-dimensional array for displaying a micro-image, a laser light source (2RGB, 2R, 2G, 2B) for generating laser light (BR, BG, BB, LR, LG, LB), a scanning unit (4RGB, 4R, 4G, 4B) for scanning the laser light (BR, BG, BB, LR, LG, LB) to traverse the micro -image on the liquid crystal display element (1, 1') in a line- wise manner to generate an image and a projection optic unit (8) for projecting the image onto a screen (3).

Description

IMAGE PROJECTION METHOD

FIELD OF THE INVENTION

The invention describes an image projection method, and a projection system.

BACKGROUND OF THE INVENTION

In recent years, developments in various technological fields are making flat screen displays more economical to manufacture and therefore more affordable for the consumer. While such displays are suitable for presentation and business solutions, they are also of particular interest for use in a domestic environment.

Images were first displayed on a screen using CRT (cathode ray tube) technology, in which an array of fluorescent picture elements on the front of an evacuated glass tube is caused to emit light by a electron beam aimed at the display in a controlled manner. Even though a CRT display can offer a high resolution, this type of display is rapidly becoming outdated, since the trend is towards bigger and flatter displays, and a CRT required for a large display area is proportionately large, deep, and heavy.

As one alternative to the cathode-ray tube, flat-panel displays using plasma display panels (PDPs) have been developed. Using this technology, two panels of glass enclose an array of isolated cells containing a gas, which is electrically converted into a plasma which in turn excites phosphors so that light is emitted. However, PDPs are expensive, and the display can suffer from a decline in image quality over time. Another disadvantage of a PDP is its relatively high energy consumption.

Another type of flat screen display is the TFT LCD (Thin Film Transistor Liquid Crystal Display), which is commonly used for computer monitors, replacing the older bulky CRT -type monitors. Projection displays offer an alternative to flat-screen displays such as plasma and TFT displays, in which the image is directly generated on the display surface. In a projection display, a video signal is processed to create an image in a small display panel, and this image is magnified and projected onto a projection display, or screen. A screen can be a backdrop in the case of a front-projection system - the projector or 'beamer' is in front of the screen and is usually positioned behind the viewer, for example suspended from the ceiling, in order to project the image onto the front of the screen; or a transparent / opal screen in the case of a rear-projection system, in which all components are contained in a single device, and the image is projected onto the screen from behind. State of the art projection displays utilise a high-intensity discharge (HID) lamp or ultra-high pressure (UHP) lamp to produce the required bright beam of white light. The white light is then either split into the light primaries, for example red, blue and green, or passed through a colour wheel with appropriate colour filters, and the primaries are then directed at the two-dimensional display panel to generate a sequence of 'sub-images' in the primary colours, which are perceived as combined images by the viewer. The display panel can be, for example, an array of micro-mirrors as in DLP^® (Digital Light Processing^®) or an LCD or LCoS (Liquid Crystal on Silicon) array. A single panel can be used for generating the red, blue and green sub-images, or three panels can be used, one for each primary. The display panel can also be referred to as a 'micro-display', since an image is first rendered on this very small element before being projected onto a screen or backdrop for viewing by a user.

In a single panel system, the light primaries are directed in quick succession at the display panel to create red, blue and green sub-images which are projected onto the display and perceived as a combined image by the viewer. In a three- panel system, each primary is directed at a separate panel so the sub-images are created simultaneously. This type of system is more efficient and free from potential artefacts, but obviously more expensive.

A liquid crystal display can comprise a transmissive LCD, through which the light passes before being projected onto the screen, or a reflective liquid crystal display, such as a 'liquid crystal on silicon' (LCoS) display. In either case, the liquid crystal display comprises microscopic liquid crystal cells or picture elements arranged in a regular two- dimensional array or matrix. Basically, by applying a voltage to a cell, the liquid crystal molecules are caused to twist or untwist, so that the polarization of the incident light is rotated or not depending on the level of the applied voltage and, depending on the resulting rotation plane, the light is blocked by or passed through a following polarization filter. The functionality of an LCD display will be known to a person skilled in the art, and need not be explained in further detail here.

The size of the liquid crystal matrix array ultimately determines the pixel resolution of the final image. For example, the liquid crystal display can be realised as a 1920 by 1080 array of pixels as required for a high-definition television (HDTV) picture, or an array of any other suitable size. Naturally, as will be known to a person skilled in the art, a large array can also be used to render images with different resolution, for example a 1920 by 1080 array can be used to render PAL (Phase Alternating Line) images with 720 by 576 pixels, by addressing and scanning only the pixels that are required. The state of the art projection systems that use UHP lamps have the disadvantage of requiring a very complex optics system for obtaining the primaries from the white light source. Another drawback shared by these systems is that the lamp may fail if not driven according to certain criteria. In time, such a lamp can be subject to blackening or recrystallization of the quartz bulb and burn back of the electrodes, so that the projected image does not provide the desired quality. Replacement lamps can be prohibitively expensive.

Alternative solutions have been proposed which implement electroluminescent LEDs (light-emitting diodes) instead of a white UHP lamp. However, UHP lamps and LEDs both exhibit a fairly large etendue, which is a limiting factor for the lighting efficiency in the type of projector systems described above. This is because the beam of light being directed at the display unavoidably illuminates the pixels in a relatively wide band in addition to the pixels actually being targeted, and these other pixels cannot be addressed with the image information for the following image until the beam of light has completely passed on. This problem is exacerbated by the fact that the liquid crystals of the display need a certain minimum length of time to twist or untwist, referred to in the following as the 'recovery time'. The scrolling frequency of the successive bands of light is ultimately limited by the recovery time of the display. In fact, the frequency that can be reached with such systems is so low that colour breakup can be observed on the screen. The etendue of the light source could be compensated for by manipulating the band of light to make it narrower, but only with an ensuing loss of brightness. To compensate for the loss in brightness in this approach, the display must be illuminated while simultaneously being addressed, which is undesirable from the point of view of image quality.

It is therefore an object of the invention to provide a method of image projection avoiding the disadvantages mentioned above.

SUMMARY OF THE INVENTION

To this end, the present invention describes an image projection method, which method comprises the steps of displaying a micro-image in a liquid crystal display element, which liquid crystal display element comprises rows of pixels arranged in a two- dimensional array for displaying the micro-image, generating laser light by means of a laser light source, and scanning the laser light to traverse the micro-image on the liquid crystal display element in a line-wise manner to generate an image. The image is subsequently projected onto a screen. The method according to the invention can be used with various different types of laser light source. However, the described method is particularly suitable for use in conjunction with semiconductor lasers diodes, e.g. vertical cavity surface emitting lasers (VCSELS) owing to their advantageously compact and economical realisation. In the following, therefore, but without restricting the invention in any way, the laser light source is assumed to be a semiconductor laser diode emitting coherent light. Such laser light sources are relatively economical to manufacture, have a long lifetime, and are not subject to the problems mentioned above, as is the case with state of the art UHP lamps, making their use particularly attractive from the consumer's point of view.

A further advantage of using a laser light source is that the etendue of the light is negligible, since a laser light source essentially provides a point source of coherent light. Therefore, the pixels of the display panel can be illuminated very precisely, i.e. it is possible to illuminate a pixel in a narrow band of the display, without also illuminating the pixels in too many other rows above or below, which is the case in display panels in projection systems using UHP lamps or the usual type of electroluminescent light-emitting diodes (LEDs). Since the pixels can be illuminated more precisely, the liquid crystals in the display have more time to recover and to be set up for the next image in the sequence of images. In a particularly advantageous realisation of the invention, with precisely calibrated components, pixels in a single row of the display can be illuminated, so that the light does not impinge on any pixels above or below this row. Therefore, immediately after being illuminated, the pixels can be addressed with the information for the next image. Here, the term 'image' can also mean 'sub-image' in the context of sub-images of different light primary colours, as explained in the introduction. Evidently, the method according to the invention can be used for full-colour applications as well as monochrome applications, depending on the choice of laser light source. An appropriate projection system comprises a liquid crystal display element, which liquid crystal display element comprises rows of pixels arranged in a two- dimensional array for displaying a micro -image, a laser light source for generating laser light, a scanning unit for scanning the laser light to traverse the micro-image on the liquid crystal display element in a line-wise manner to generate an image, and a projection optic unit for projecting the image onto a screen. The projection system also comprises a video processing unit for processing a video signal, such as a television signal from a satellite receiver, or a video signal from a DVD (digital versatile disc) recorder. The video signal is processed, as will be known to a person skilled in the art, to generate control signals for the display panel, the laser light source, and the scanning unit in order to generate a sequence of micro -images in the display panel that in turn are rendered on the screen for viewing by the user.

The scanning unit can comprise a number of mirrors and rotating prisms to scan, or direct, the laser light at the liquid crystal display panel in a controlled manner.

The dependent claims and the subsequent description disclose particularly advantageous embodiments and features of the invention. As mentioned above, state of the art image rendering systems usually generate separate red, blue and green sub-images in rapid succession, and these are perceived as a single colour image by the eye. In a system using a UHP lamp, which is a white light source, the white light must either be passed through red, blue and green colour filters using a colour wheel, or be split into red, blue and green light by means of appropriate dichroic filters. In the projection system according to the invention, however, the laser light source can simply comprise an array of semiconductor lasers of different colours such as red, blue and green. These can be individually controlled to be switched on or off in rapid succession, and the intensity of each laser can also be individually controlled.

In a projection system according to the invention, the scanning unit can be realised such that a beam of laser light traverses the pixels in a row of the liquid crystal display element to successively illuminate the pixels in that row. In other words, the laser light can travel back and forth in a zig-zag manner across the rows of the panel, for example starting in one corner and moving back and forth, and impinging on the panel as a point of light. However, scanning the panel with a point of light in this manner is relatively complicated, since the motion of the point of light requires horizontal and vertical scanning, so that the scanning unit is necessarily complex.

Therefore, in a particularly preferred embodiment of the invention, the scanning unit is realised such that a line or band of laser light traverses the pixel rows of the panel, taking in an entire row at a time, and moving from the top of the display to the bottom. In this way, the line or band of laser light is simultaneously incident on all of the pixels in a pixel row. Since the electrodes of the display are grouped for technical reasons in rows and columns, so that addressing must be carried out in a line-wise manner, the technique of row- wise traversal with a band of light is particularly suited to the LCD type of micro-display.

To convert the narrow beam of light issued from the laser light source into the required line or band of light, the projection system according to the invention comprises a beam shaping optic, for example a cylindrical lens, for shaping the output of the laser light source. When scanned by the scanning unit to traverse the liquid crystal display element, the band of laser light simultaneously illuminates all of the pixels in a row of the liquid crystal display panel. Shaping the laser light into a band in this way has the additional advantage of making the laser light safer from the point of view of the user, since the intensity of the laser light is lessened. In a further preferred embodiment of the invention, beams or bands of laser light of different primary light colours simultaneously traverse the micro -image on the liquid crystal display element in a spatially separate fashion. For example, three bands of laser light - red, blue and green - can traverse the micro-image in the panel in such a manner that the bands are staggered or separated by regular distances, while all three bands traverse the display line-wise from top to bottom. When a band reaches the bottom of the display, it is scanned to recommence at the top of the display. In one frame or cycle, a sub-image is generated for each of the light primaries. This method of display illumination is also known as 'scrolling colour', and will be explained graphically in the description of the Figures.

The image information for a pixel row is written or addressed to that row, and, after a certain interval of time, or temporal delay, the liquid crystals have twisted or untwisted appropriately and are ready to be illuminated again by the light source for the next image in the image sequence. This temporal delay is determined by the type of liquid crystal display used, and may be sufficiently brief so that it may be possible for more than one beam or band of laser light to traverse the micro-image at the same time, albeit in a staggered manner. The laser light source and the scanning unit are preferably controlled or synchronised so that the timing of the display illumination takes into account the temporal delay of the liquid crystal display element. The image information for a pixel of a following image is preferably applied or addressed to that pixel directly after illuminating that pixel by the laser light. Here, the term 'directly' is taken to mean after a brief interval of time (given by the temporal delay mentioned above). Evidently, the interval of time can be so short that the image information for the following sub-image is addressed or written to a pixel essentially immediately after the pixel has been illuminated by the laser light. On the other hand, a certain interval of time can elapse before the image information is applied to the pixel. For example, when a beam of laser light is traversing the pixels of a row, the beam must have illuminated the last pixel in the row before the image information can be addressed to the (entire) row. Alternatively, when a band of laser light has illuminated the entire row, the image information can be applied more or less directly to that row once the beam of laser light has moved on downwards. However, since the beam or band of laser light might in fact illuminate neighbouring pixels in the rows above and below the rows actually being scanned, it can be favourable to wait for a certain, preferably brief, length of time to elapse before applying the new image information. In other words, the line of the display can be addressed with new information as soon as the band of light has passed on, and allowing for a certain tolerance.

Therefore, the delay between two scans of a row preferably comprises exactly the recovery time for that display type, or the recovery time with the addition of a slight tolerance. For example, in a preferred version of the invention, two consecutive scans of a row can be temporally offset by a delay comprising at least 0.5ms, more preferably at least 4ms. In the case of a projection system in which the display is simultaneously illuminated with more than one beam or band of light, for example with three light primaries, the physical distance between the beams or bands of light is preferably chosen accordingly.

Including such a temporal delay in a projection system according to the invention - in which the display is illuminated in a row- wise fashion and not all at once - makes possible the use of a relatively cheap but 'slow' display in which the liquid crystals have a recovery time of up to 5.56 ms. The method according to the invention therefore allows the realisation of an economical projection system with high image quality.

As already indicated above, a known problem with state of the art projection systems is that of dimming. For instance, in a projection system using a UHP lamp and in which the entire display panel is illuminated at once, the level of dimming is determined by the brightest pixel in that image. For example in a DLP^® system, the amount of light reflected from the individual micro-mirrors of the display is regulated by using some of the pixel information to toggle the mirrors during a frame. Therefore, in high-contrast scenes, such as dark scenes with only some bright elements, the light source cannot be dimmed and some of the dynamic range of the display is wasted, and the overall contrast of the rendered image can be quite unsatisfactory. In such state of the art systems, the full dynamic range of the display cannot be used.

The image projection method according to the invention advantageously permits dimming to be carried out in a line-wise manner. In a particularly preferred embodiment of the invention, therefore, a maximum brightness level for the pixels in a row of a micro-image is determined, and the intensity of the laser light is adjusted according to this maximum brightness level. At the same time, the transparency of the pixels in that row of the liquid crystal display element is adjusted according to the maximum brightness level in this row. In other words, the brightest pixel of a row is addressed to be completely transparent, and the transparency levels of the remaining pixels are adjusted accordingly, while the intensity of the laser light is adjusted to suit the maximum brightness of that row. In this way, it is possible to perform adaptive dimming, in a row- wise fashion, making use of the full dynamic range of the display. In this way, a much improved contrast is obtained in comparison to the state of the art projection methods.

A projection system according to the invention therefore also comprises a brightness adjustment unit for adjusting the intensity of the laser light according to a maximum brightness level and for adjusting the transparency of the pixels in a row of the liquid crystal display element according to the maximum brightness level. The laser light could be scanned vertically or horizontally with respect to the micro-image in the display panel. However, the laser light is particularly preferably scanned to traverse the micro-image in a horizontal manner with respect to the microimage, for example commencing at the top edge of the micro-image and working downwards to the bottom edge, or vice-versa, from bottom edge to top edge. This has the advantage of offering a further improvement in contrast for images comprising distinct upper and lower regions such as sky and landscape, since the rows can be illuminated in a more even or homogenous manner.

The projection system according to the invention can also comprise a colour gamut adjustment unit, in which the colour gamut can be adjusted for each row in an image by appropriate control of the laser light source, according to information obtained from the video signal. Colour gamut adjustment could preferably be carried out in conjunction with the row- wise dimming of the laser light source. The principle of a global colour gamut adjustment is described in the publication "Field-Sequential-Colour Display with Adaptive Gamut" by JohanBergquist and Carl Wennstamin SID 06 DIGEST, page 1594. Other objects and features of the present invention will become apparent from the following detailed descriptions considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for the purposes of illustration and not as a definition of the limits of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. Ia shows a simplified schematic representation of a state of the art transmissive LCD display panel; Fig. lbshows a simplified schematic representation of a state of the art reflective LCoS display panel;

Fig. 2 shows a projection system according to a first embodiment of the invention;

Fig. 3 shows a projection system according to a second embodiment of the invention;

Fig. 4 shows a projection system according to a third embodiment of the invention.

In the drawings, like numbers refer to like objects throughout. Objects in the diagrams are not necessarily drawn to scale.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The schematic illustration of the state of the art transmissive LCD display panel 1 shown in Fig. 1 is only intended to give an indication of the pixel array. Basically, such a panel 1 comprises several layers - a glass layer, a liquid crystal layer, and, on each side of the liquid crystal layer, two layers of transparent electrodes. The actual construction of such an LCD panel will be known to a person skilled in the art, and need not be described in detail here. The electrodes are realised to give an m x n array of liquid crystal picture elements. In this example, the pixel array comprises m rows Ri, R2, ..., R_J, ..., R_m, each of which comprises n pixels Pi, P₂, ..., Pi, ..., P_n. The amount of light let through by a pixel Pi, P₂, ... , Pi, ... , P_n depends on the voltage applied to the electrodes for that pixel. In the example shown, the pixels Pi, P₂, ..., P_n in row R, are all 'off except for one pixel P₁, which is addressed to let some or all of the light through. A beam of light B directed at this pixel P₁ will pass through, at least to some extent, depending on the level of the voltages applied to the electrodes controlling this pixel P₁. Light that is let through by a pixel emerges on the other side of the panel as a ray of light B' where it can be projected by a magnifying optic onto a screen (not shown in the diagram).

Fig. Ib shows another type of LCD panel, namely a reflective LCoS panel. The same notation as in the previous example is used for the pixel array, again comprising m rows Ri, R₂, ..., R_J, ..., R_m, each of which comprises n pixels Pi, P₂, ..., P₁, ..., P_n. Here, the liquid crystal layer is backed by a layer of reflective metal electrodes. So, instead of emerging on the other side of the panel, a beam of light B that is passed by a pixel, in this case the pixel P₁, is reflected back off the panel. Again, the amount of light reflected will depend on the voltages applied to the electrodes controlling this pixel P₁. Light directed at the other pixels Pi, P₂, ..., P_n in this row R_j will be absorbed since they are turned 'off. Again, light that is passed by a pixel is partially or completely reflected as a ray or beam of light B' which can be projected by a magnifying optic onto a screen (not shown in the diagram). Fig. 2 shows a schematic representation of a projection system 10 according to a first embodiment of the invention. Here, a laser light source 2_RGB, which is an array of red, blue and green semiconductor lasers, is controlled to provide a light output L, which is successively red, blue, or green. An LCD panel 1 is addressed with information to control the pixels of the pixel array according to video information from a video processing unit (not shown in the diagram) to cause a micro-image to be set up in the display panel 1. For example, for a red sub-image, the pixels that are not required for the red sub-image are turned 'off, and the remaining pixels are made more or less transmissive, depending on the amount of red light to be let through each pixel.

In this rather simple example, the laser light source 2_RGB is currently generating red laser light L which passes through a lens 7_B to give a red laser light beam B_R. This is scanned with a scanning unit 4 so that a point of laser light travels back and forth in a zig-zag manner across the LCD panel 1, in which the micro-image has been set up. According to the micro-image rendered in the LCD panel 1, the red laser light beam B_R is blocked by or passes to some extent through the pixels of the LCD panel 1. The passed red laser light beam B_R' is projected by magnifying optics 8 onto a screen 3. The magnifying optics 8 is shown as a simple lens, but it will be understood that this comprises complex components that cannot be shown here in any great detail, but that will be known to a person skilled in the art.

After the beam has passed each pixel, these can be set up for the green sub-image. Once the red sub-image has been created completely, the laser light source 2_RGB switches to produce green light, and a green sub-image is created in the same way. The process is repeated for a blue sub-image. These sub-images are generated quickly enough for a user to perceive them as a combined image on the screen 3.

In this diagram and in the following Figs. 3 and 4, the LCD panel 1 is shown, for easier illustration, as a transmissive LCD panel 1. In each of the embodiments, however, a reflective LCoS panel could be used in lieu of the transmissive panel 1 and with a different arrangement or realisation of the magnifying optics 8. In each case, once the laser light has passed on to a following row in the micro-image, the pixels of the row that have just been illuminated can now be addressed with the image information for the next image. In this way, the liquid crystals of the pixels in the display panel have as much time as possible to be set up before being illuminated for the next image. The embodiments shown represent both rear-projection and front-projection systems, and the choice of system realised will govern the selection of magnifying optics 8 and screen 3.

Fig. 3 shows a further embodiment of a projection system 10' according to the invention. Again, laser light source 2_RGB successively provides red, blue and green laser light output L. In this embodiment, a shaping lens 7_L shapes the light output L from the laser light source 2_RGB to give a band or line of laser light. In the diagram, a band of red laser light L_R is being scanned by the scanning unit 4 so that an entire horizontal band of the panel 1, covering at least one entire row of pixels, is illuminated by the line of laser light L_R, as indicated by the wide band superimposed on the LCD panel 1. According to the row of the micro-image currently set up in the panel 1, light is either blocked or passed to some extent through the pixels in the row being illuminated by the line of laser light L_R.

In this embodiment, a dimming control unit 9 is shown, which analyses a video signal to determine the amount of dimming to be carried out in each row of the micro- image (the video signal input has not been included in the diagram, since it is evident that such a signal is required for setting up the display panel in a projection system). Since the scanning is performed so that horizontal rows of the LCD panel 1 are illuminated by the line of laser light L_R, and since images are often such that an upper area in the image is bright (e.g. sky) while a lower area is dark, the full dynamic range of the panel 1 in the projection system 10' according to the invention can be utilised by performing the necessary dimming in a row-wise manner. To this end, the dimming control unit 9 determines the brightest point in a row of the micro-image, and controls the transmissiveness of the pixels in that row accordingly. At the same time, the intensity of the laser light source 2_RGB can be increased or decreased as appropriate. This type of horizontal dimming offers a great advantage over systems such as the vertical one- dimensional GLV, which is generally scanned to create vertical columns of a sub-image. The dimming control unit 9 could also be realised or configured to carry out a colour gamut correction to coincide with the row- wise dimming of the display 1.

The passed line of laser light L_R' (now modulated in intensity by dimmed pixels) is projected onto the screen 3 by the magnifying optics 9. The scanning unit 4 causes the line of laser light L_R to traverse the panel 1 from top to bottom, as indicated by the arrow superimposed on the panel 1, so that the passed laser light L_R' is projected by the magnifying optics 8 to traverse the screen 3, thus yielding a red sub-image. Again, the process is repeated with green and blue laser light to give green and blue sub-images. Each time the band of laser light moves on to a following row, the previously illuminated row is immediately addressed with image information for the next sub-image. The red, green and blue images projected onto the screen are perceived as a combined image by the user.

In Fig. 4, another type of realisation is shown for a projection system 10" according to the invention, in which separate laser light sources 2_R, 2_G, 2_B are used to generate red, green and blue laser light. The laser light sources 2_R, 2_G, 2_B are simultaneously active, so that red, blue and green sub-images can be rendered simultaneously. At the price of more components, therefore, a considerably faster image rendering can be achieved. In this embodiment, the light output by the laser light sources 2_R, 2_G, 2_B is shaped by shaping lenses 7, in this case to provide lines of laser light L_R, L_G, L_B. The scanning unit 4 scans these lines of laser light L_R, L_G, L_B so that they traverse the LCD panel 1 in a staggered fashion, also referred to as 'scrolling colour'.

For example, after a row of the LCD panel 1 has been illuminated by the line of red laser light L_R, the relevant green sub-image information is written to that row. The row is then illuminated by the green line of laser light L_G as this traverses the panel 1 from top to bottom. Subsequently, the information for the blue sub-image row is written to this row, which is then illuminated by the blue line of laser light L_B. This type of display illumination can be visualised as three lines of red, green and blue light, separated by constant time intervals and descending across the panel as indicated by the arrow superimposed on the panel 1. The time interval is chosen according to the recovery time required by the liquid crystal display panel used. When one line of laser light reaches the bottom, it commences again at the top of the panel 1. Since all three lasers are simultaneously used to illuminate a row of the display, the intensity of each laser can be lower than if only one laser were in use. Such an embodiment, the magnifying optics 8 are realised to be able to simultaneously project three bands of light onto the screen 3. For the sake of simplicity, the dimming control unit shown in Fig. 3 is not included here, but evidently this projection system 10" would preferably be equipped with such a dimming control unit.

Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention.

Claims

CLAIMS:

1. An image projection method, which method comprises the steps of displaying a micro-image in a liquid crystal display element (1), which liquid crystal display element (1) comprises rows (Ri, R2, ..., R_j, ..., R_m) of pixels (Pi, P₂, ..., Pi, ..., P_n) arranged in a two-dimensional array for displaying the micro -image; generating laser light (B_R, B_G, B_B, L_R, L_G, L_B) by means of a laser light source (2_RGB, 2_R, 2_G, 2_B); scanning the laser light (B_R, B_G, B_B, L_R, L_G, L_B) to traverse the microimage on the liquid crystal display element (1) in a line-wise manner to generate an image; projecting the image onto a screen (3).

2. An image projection method according to claim 1 , wherein a beam of laser light (B_R, B_G, B_B) traverses the pixels (Pi, P₂, ..., P₁, ..., P_n) in a row (Ri, R₂, ..., R₁, ..., R_m) of the liquid crystal display element (1) to successively illuminate the pixels (Pi, P₂, ..., P₁, ..., P_n) in that row (R₁, R₂, ..., R₃, ..., R_n).

3. An image projection method according to claim 1, wherein a line of laser light (L_R, L_G, L_B) traverses pixel rows (Ri, R₂, ..., R,, ..., R_m) of the liquid crystal display element (1, 1') such that the line of laser light (L_R, L_G, L_B) simultaneously illuminates the pixels (Pi, P₂, ... , P₁, ... , P_n) in a pixel row (R_h R₂, ... , R,, ... , R_n).

4. An image projection method according to any of the preceding claims, wherein beams or lines of laser light (B_R, B_G, B_B, L_R, L_G, L_B) of different primary light colours simultaneously and separately traverse the micro-image on the liquid crystal display element (1, 1').

5. An image projection method according to any of the preceding claims, wherein the laser light (B_R, B_G, B_B, L_R, L_G, L_B) is scanned to traverse the micro -image in a horizontal manner.

6. An image projection method according to any of the preceding claims, wherein two consecutive beams or lines of laser light (B_R, B_G, B_B, L_R, L_G, L_B), for generating two consecutive images, traverse the micro-image on the liquid crystal display element (1, 1') such that the consecutive beams or lines of laser light (B_R, B_G, B_B, L_R, L_G, L_B) are offset by a temporal delay, which temporal delay is at least 0.5ms, preferably at least 4ms.

7. An image projection method according to any of the preceding claims, wherein image information for a pixel (P₁) of a following image is applied to that pixel (P₁) directly after illuminating that pixel (P₁) by the laser light (B_R, B_G, B_B, L_R, L_G, L_B).

8. An image projection method according to any of the preceding claims, comprising the steps of determining a maximum brightness level for the pixels (Pi, P2, ... , P₁, ... , P_n) in a row (Ri, R₂, ..., R,, ..., R_m) of a micro-image; - adjusting the intensity of the laser light (B_R, B_G, B_B, L_R, L_G, L_B) according to the maximum brightness level; and adjusting the transparency of the pixels (Pi, P₂, ..., P₁, ..., P_n) in that row (Ri, R₂, ..., R_J, ..., Rm) of the liquid crystal display element (1, 1') according to the maximum brightness level in that row (Ri, R₂, ... , R_J? ... , R_n).

9. A projection system (10, 10', 10") comprising a liquid crystal display element (1, 1'), which liquid crystal display element (1, 1') comprises rows (Ri, R₂, ..., R,, ..., R_n) of pixels (Pi, P₂, ..., P₁, ..., P_n) arranged in a two-dimensional array for displaying a micro-image; a laser light source (2_RGB, 2_R, 2_G, 2_B) for generating laser light (B_R, B_G,

a scanning unit (4 _RGB, 4_R, 4_G, 4_B) for scanning the laser light (B_R, B_G, B_B, L_R, L_G, L_B) to traverse the micro-image on the liquid crystal display element (1, 1') in a line-wise manner to generate an image; and a projection optic unit (8) for projecting the image onto a screen (3).

10. A projection system (10, 10', 10") according to claim 9, comprising a beam shaping optic (7_L) for shaping the output (L) of the laser light source (2_RGB, 2_R, 2_G, 2_B) to give a line of laser light (L_R, L_G, L_B), which line of laser light (L_R, L_G, L_B),when scanned by the scanning unit (4 _RGB, 4_R, 4_G, 4_B) to traverse the liquid crystal display element (1, 1'), illuminates all of the pixels (Pi, P2, ..., Pi, ..., P_n) in a row (Ri, R2, ..., R_J, ..., R_m) of the liquid crystal display element (1, 1').

11. A projection system (10, 10', 10") according to claim 9 or claim 10, comprising a brightness adjustment unit (9) for adjusting the intensity of the laser light (B_R, B_G, B_B, L_R, L_G, L_B) according to a maximum brightness level and for adjusting the transparency of the pixels (Pi, P2, ..., Pi, ..., P_n) in a row (Ri, R2, ..., R,, ..., R_m) of the liquid crystal display element (1, 1') according to the maximum brightness level.