WO2005060265A1

WO2005060265A1 - System for improving colour purity for a wide colour gamut scrolling colour projection system

Info

Publication number: WO2005060265A1
Application number: PCT/IB2004/052608
Authority: WO
Inventors: Adrianus J. S. M. De Vaan
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2003-12-15
Filing date: 2004-11-30
Publication date: 2005-06-30

Abstract

The present invention relates to a system (100) for projecting scrolling colour bars on a display panel (110). The system (100) comprises a light source unit (102) communicating light towards light separating means (104), which comprises coloured light means (122, 124, 126) generating from the light a red, a green and a blue coloured light, respectively, to be communicated to a first, a second and a third slit (132, 134, 136). The slits (132, 134, 136) generate from the red, green and blue coloured light a red, green and blue coloured bar (304, 308, 312), which is communicated on to the display panel (110) adapted to modulate the red, green and blue colour bars (304, 308, 312) to an image. The system further comprises a blocking stripe in at least one of the slits (132, 134, 136) generating a dark zone between each of the colour bars (304, 308, 312) communicated to the display panel (110).

Description

System for improving colour purity for a wide colour gamut scrolling colour projection system

FIELD OF INVENTION This invention relates to system for improving colour purity for a wide colour gamut scrolling colour projection system. In particular, this invention relates to a colour projection system using three rotating prisms.

BACKGROUND OF INVENTION A scrolling colour projector, such as described in "Single Panel Reflective LCD Projectors", by J.A. Shimizu, in Projection Displays V, Proceedings SPIE, Vol. 3634, pp 197-206, (1999), produces full colour images from a single light modulator by illuminating a liquid crystal panel with multiple stripes of coloured light (red, green, blue) that continuously scroll, from top to bottom, over the liquid crystal panel. American patent no. US 6,540,362 discloses a scrolling colour projection system having an increased number of red, green and blue scrolling colour stripes achieved by a lenticular lens array and a second lens array for collimating the plurality of stripes. The collimated stripes are scrolled over the liquid crystal panel by using rotating prisms. Further, American patent application no. US 2002/0191154 discloses a single panel colour liquid crystal display (LCD) projector, shown in figure 1. The LCD projector system 100 utilising a scrolling colour system wherein un-polarized light split into constituent red, green and blue coloured light beams, and which LCD projection system 100 comprises a light source 102, colour separating means 104, a substantially non-absorptive polarizing element 106, a polarizing beam splitter 108, a light valve or modulator 110, and a projection lens 112. The light valve or modulator 110 is adapted to receive incident light and to impress a desired image upon the incident light, which image is then projected by the projection lens 112. The colour separating means 104 comprises dichroic colour filters 114, 116, 118 and 120, prisms 122, 124 and 126, and the reflecting mirrors 128 and 130. The colour separating means 104 generate scrolling and coloured light beams by rotating the prisms 122, 124 and 126. The phase and rotation of the prisms 122, 124 and 126 are important, because each stripe of coloured light must be projected and scrolled on the light valve or modulator 110 at specific times in relation to video information (electrical scan) that is also provided to the light valve or modulator 110. That is, the red, green and blue stripes of light must be present on a line of the display concurrently with the presentation of the corresponding video information. The American patent no. US 6,540,362, the American patent application no.

US 2002/0191154 and the article entitled "Single Panel Reflective LCD Projectors", which are hereby incorporated in present specification by reference, describe scrolling colour projection systems utilising red, green and blue colour stripes. It is a problem of these types of prior art scrolling colour projection systems is that the light valve or modulator 110 or the light crystal panel requires a switching time between different states associated with colours scanned across the pixels. Hence further improvements are required in order to reduce colour cross talk generated by these switching times.

SUMMARY OF THE INVENTION A particular object of the present invention is to provide a system for obtaining a high colour fidelity with a prism based scrolling colour system. A particular advantage of the present invention is the provision of a significant reduction in colour cross talk. The above object and advantage together with numerous other objects, advantages and features, which will become evident from below detailed description, are obtained according to a first aspect of the present invention having characterizing features as described in the characterizing part of claim 1. Further embodiments are obtained according to the first aspect of the present invention as described in dependent claims 2 - 9.

BRIEF DESCRIPTION OF THE DRAWING The above, as well as additional objects, features and advantages of the present invention, will be better understood through the following illustrative and non- limiting detailed description of preferred embodiments of the present invention, with reference to the appended drawing, wherein: figure 1, shows a block diagram of a prior art projection system, and figure 2, shows an illumination window according to a first embodiment of the present invention, figure 3, shows an illumination window according to a second embodiment of the present invention, figure 4, shows a graph of colour space in a projection system, figure 5, shows the illumination window according to the second embodiment of the present invention utilising a series of filters, and figure 6, shows an illumination window according to a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS In the following description of the various embodiments, reference is made to the accompanying drawing which form a part hereof, and in which are shown by way of illustration various embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural and functional modifications may be made without departing from the scope of the present invention. Figure 1, shows, as described above, a projection system 100, which may be a scrolling colour liquid crystal on silicon (LCoS) projection system, and shows the rotating prisms 122, 124, 126 for generating a scrolling colour effect on an illumination window. By positioning slits 132, 134 and 136 before each rotating prisms 122, 124 and 126 sharp colour bars are obtained on the display panel. Each slit 132, 134 and 136 is illuminated by its corresponding colour red, green or blue and is imaged on a display panel through the prisms 122, 124 and 126. A display panel in this context should be construed as a light valve means or light modulating means such as a transmissive liquid crystal display, a reflective liquid crystal on silicon or a reflective micro-electrical-mechanical (MEM) based display such as a DMD panel. Figure 2, shows an illumination window 200 projected on to a display panel, which illumination window 200 has red 202, green 204 and blue 206 scrolling colour bars. The widths 208, 210, and 212 of the respective slits 214, 216, and 216 matches the width of the colour bars 202, 204, and 206, so that the colour bars 202, 204, and 206 do not overlap each other on the display panel. Further, the widths 208, 210, and 212 are selected so as to generate exactly three colour bars 202, 204, and 206 on the display panel. Coloured images are generated by writing each line in the display panel with new colour information, as soon as a new colour starts to appear on the corresponding row in the display panel. Figure 3, shows an illumination window 300 projected on to a display panel, which illumination window 300 has six scrolling colour bars, namely a purple 302, a red 304, a yellow 306, a green 308, a cyan 310, and a blue 312 colour bar. The six colour bars are generated by extending the widths 208, 210, and 212, shown in figure 3 as extended widths 314, 316, 318a and 318b. Hence the slits 320, 322, and 324 (where slit 324 is shown as two separate parts 324a and 324b), so that the Red, Green and Blue colour bars 304, 308 and 312 partly overlap each other. The overlaps generate mixed colours namely purple 302, yellow 306 and cyan 310. Each pixel of the display panel is driven sequentially relative to time so that the total amount of light per colour balances the colour as required by each pixel. Since each red, green and blue colour bars 304, 308 and 312 cover a larger area of the display panel the throughput of the light path is increased and a greater amount of light from the projector light source is collected and guided through the projection system thereby achieving a higher brightness. Alternatively, one of the slits 320, 322 and/or 324 allows a wider wavelength range to be channelled through to associated prisms 122, 124, and/or 126. Thus if the green slit 322 in front of the green prism is projected on to the display panel as a colour bar that slightly overlaps with the red 304 and blue 312 colour bars the overlapping areas become cyan 310 and yellow 306 colour bars. Further, the green slit 322 may be configured so that the centre colour bar 308 resulting from the slit 322 is green, the top colour bar 306 in overlap with the red coloured bar 304 resulting from the slit 322 is yellow, and the lower colour bar 310 in overlap with the blue coloured bar 312 resulting from the slit 322 is cyan. Figure 4, shows a graph of colour space designated in entirety by reference numeral 400 in a projection system. The first set of colours (primaries red 402, green 404 and blue 406) defines a complete span 408 of colour space of the projection system. The second set of colours (primaries cyan 410, yellow 412 and purple 414) comprises primaries which generate high brightness values. The second set of colours are generated by combining the first set of colours, that is cyan = green + blue; yellow = red + green; and purple = blue + red. In prior art projection systems the full spectrum of the light source is generally not effectively utilised. Especially the spectral parts around the 500 nm (490 to 510 run) and around the 600 nm (590 to 610 nm) is filtered away since these parts de-saturate the primary red, green and blue colours. However, since the projection systems according to the present invention generates mixed colour bars 302, 306, and 310(purple, yellow, and cyan), the wavelength ranges around 500 nm and around 600 nm may now be utilised in the cyan and yellow colour bars 306, 310. Hence in the preferred embodiment the full 480 to 590 nm wavelength range is channelled through the green prism, the green colour de-saturates resulting in a green colour point with a low "y" value in the "χ"-"y" colour space 400. By adding filters, shown in figure 5 as reference numerals 502, 504, and 506, before the green prism a compensation of the low "y" value is achieved. Thus a 490 to 580 nm wavelength range filtering is added for the Green colour bar 308, pushing the "y"-value of the green primary 404 back to its desired value. A 480 to 10 nm wavelength range filtering is added for the yellow colour bar 306 and a 560 to 590 nm wavelength range filtering is added for the cyan colour bar 310. The brightness of the yellow and cyan colour bars 306 and 310 is increased, while their colour points, shown in figure 4 as reference numerals 410', 412', 414', are pushed outside the old colour space 400 as defined by the red 402, green 404 and blue 406 primary colours. Figure 6, shows an illumination window 600 according to the preferred embodiment of the present invention for projecting on to a display panel. The illumination window 602 comprises six scrolling colour bars, namely, as described with reference to figures 3 through 5, a purple 302, a red 304, a yellow 306, a green 308, a cyan 310, and a blue 312 colour bar. The colour bars 302 through 312 are generated by communicating light though slits 320, 322 and 324 on to rotating prism 122, 124 and 126. This particular embodiment of the present invention prevents for colour errors caused by the switching times of a display panel. Each pixel of the display panel has a first switching time for changing from darker to lighter and a second switching time for changing from lighter to darker. This error prevention is achieved by adding dark zones 602 between each colour bar 302 through 312. The dark zones 602 may be achieved by controlling the display panel to write black lines between each colour bar 302 through 312, or, even more advantageously, by adding dark bars between the colour bars 302 through 312. The dark bars are projected together with the colour bars 302 through 312 on to the display panel. The dark bars may be generated by separately combining the red, green and blue colour bars (304, 308, 312) or, as in the preferred embodiment of the present invention by providing each of the slits 132, 134, and 136 with light blocking stripes. The blocking stripes introduce dark bars between the colour bars 302 through 312 thereby allowing the liquid crystal material in the display panel to switch between states. The dark zones 602 establish a resetting effect of the display panel allowing each pixel of the display panel to switch between individual colour states. According to an alternative embodiment of the present invention the projection system utilises a three scrolling colour bar operation, in which the blocking stripes on each of the of the slits 132, 134, and 136 introduce dark bars between the colour bars 202, 204 and 206.

Claims

CLAIMS:

1. A system for projecting scrolling colour bars on a display panel (110), and comprising a light source unit (102) communicating light towards light separating means (104) comprising coloured light means (122, 124, 126) for generating from said light a red, a green and a blue coloured light, respectively, communicated to a first, a second and a third slit (132, 134, 136) for generating from said red, green and blue coloured light red, green and blue coloured bars (304, 308, 312) communicated on to said display ρanel(l 10) adapted to modulate said red, green and blue colour bars (304, 308, 312) to an image, characterized in further comprising a blocking stripe in at least one of the slits (132, 134, 136) for generating a dark zone between each of said colour bars (304, 308, 312) communicated to said display panel (110).

2. A system according to claim 1, wherein said slits (132, 134, 136) comprising a width (314, 316, 318) adapted to communicate said red, green and blue colour bars (304, 308, 312) partly overlapping one another on to said light valve (110) thereby further generating a purple, a yellow and a cyan colour bar (302, 306, 310) and wherein said at least one blocking stripe further generating a dark zone between said purple, yellow and cyan colour bars (302, 306, 10), and said red, green and blue colour bars (304, 308, 312).

3. A system according to any of claims 1 to 2, wherein said colour separating means (104) further comprises dichroic colour filters (114, 116, 118, 120), and reflecting mirrors (128, 130).

4. A system according to any of claims 1 to 3, wherein said coloured light means comprises a first, second and third rotating element such as a prism (122, 124, 126), a wheel, a drum, a polygon mirror, a vibrating element or any combination thereof, which first, second and third rotating element is positioned in light path from light source unit (102) to display panel (110) after said first, second and third slit (132, 134, 136) and is adapted to generate said red, green and blue colour bars (304, 308, 312).

5. A system according to claim 4, wherein said rotating element comprising a micro electro-mechanical element.

6. A system according to any of claims 1 to 5, wherein said display panel (110) comprising a LCD based light modulating element.

7. A system according to any of claims 4 to 6 further comprising a controller for controlling phase and rotation of said rotating elements (122, 124 and 126) so as to project and scroll on said colour bars (302, 304, 306, 308, 310, 312) on to said display panel 110 at specific times in relation to video information.

8. A system according to any of claims 1 to 7 further comprising filter means (402, 404, 406) for filtering of said red, green or blue colour bar (304, 308, 312).

9. A system according to any of claims 1 to 8, wherein each of said first, second and third slits (132, 134, 136) comprise a blocking stripe for generating a dark zone between each of said colour bars (304, 308, 312) communicated to said display panel (110).