False contour correction apparatus and method in an image display system

Abstract: A false contour correction apparatus and method in an image display system, by which a false contour at a place where conversion of the unit bits of data is severe on a display device driven in a digital system is corrected, is provided. According to the present invention as described above, received image data is displayed by reversely-symmetrically arranging the bits of two digital driving display means, so that fatal false contour during digital driving can be removed.

Description: The present invention relates an image display apparatus comprising a light source, means for receiving image data and a first digitally controlled light modulator for modulating light from said source in a first path and whose state is controlled sequentially by the states of the bits of received image data, the duration of the modulator's response to each control bit being dependent on its significance. Existing types of display devices driven in a digital system include a plasma display panel (PDP), a liquid crystal display (LCD) panel, a ferroelectric liquid crystal (FLC) panel, and the like. FLC panels have a structure in which ferroelectric liquid crystal is sandwiched between an optical planar mirror formed on a silicon substrate and glass, and have a wide viewing angle and a fast response speed compared to other panels. In a display device driven in a digital system, distortion of picture due to an optical illusion, which is referred to as a false contour, usually occurs at a place where conversion of the unit bits of data is severe. In a display apparatus driven in a digital system, a false contour having serial bit conversion is generated on a changing picture, for example, at the gentle boundary where a data value is changed from 63 to 64 and from 127 to 128. That is, even when a data value is change just by one, for example, from 127 to 128, if a picture changes, data of 225 or 0 is perceived at the boundary according to the direction of the movement of the picture, resulting in a fatal degradation in the quality of image. I have found that an image can be degraded to an undesirable level due to the false contour phenomenon, Efforts have been made to reduce false contouring and improve image display systems. Exemplars of recent efforts in the art include US-A-6072555, US-A-5963190, US-A-6088012, US-A-6052112, US-A-5109282, US-A-6100939, US-A-6018329, US-A-4574636, US-A-6134025, US-A-5706063, JP-A-116980, JP-A-8168039, JP-A-0990402, JP-A-10123477, JP-A-1023445, JP-A-08294138 and JP-A-10148885. While these recent efforts provide advantages, I note that they fail to adequately provide a false contour correction apparatus and method in an image display system. An image display apparatus according to the present invention is characterised by a second digitally controlled light modulator for modulating light from said source in a second path and whose state is controlled sequentially by the states of the bits of received image data, the duration of the modulator's response to each control bit being dependent on its significance, combining means for combining said paths downstream of the modulators and the modulators operating in dependence on said image data from most significant bit to least significant bit and from least significant bit to most significant bit respectively. Preferably, the light source is configured to cyclically produce light of different colours. More preferably, the light source comprises a light unit for emitting the white light, a colour switching unit arranged to receive the white light from said light unit and to receive colour switch signals, and being responsive to the colour switching signals to selectively and cyclically pass light having different colours, and a first lens for collimating the light received from said light unit and outputting collimated light to said colour switching unit. Yet more preferably, the means for receiving image data comprises a control unit which also receives synchronization signals, outputs said colour switch signals in accordance with said synchronization signals and outputs control data corresponding to said received image data to said modulators. Still more preferably, said synchronization signals are horizontal and vertical synchronization signals. Even more preferably, said colour switching unit outputs each one of said plurality of colours seriatim at intervals of 1/3 of a period in accordance with said colour switch signals. Yet more preferably, said plurality of colours output from said colour switching unit are red, green and blue. Still more preferably, said colour switching unit outputs a first colour while blocking all other colours. Even more, preferably said colour switching unit comprises a liquid crystal display shutter or a colour wheel. Preferably, a first polarising beam splitter for splitting the light from the light source into two beams and directing them along the first and second paths is included. Preferably, said modulators comprise respectively LCD panels. Preferably, the combining means comprises a second polarising beam splitter. Alternatively, the combining means may comprise the first polarizing beam splitter. Preferably, a screen onto which the output of the combining means is directed is included. Preferably, said means for receiving image data comprises a control unit for controlling the offset, contrast and brightness of the displayed image. More preferably, said control unit performs gamma correction for the received image data. Preferably, each path includes a mirror for directing light from the first polarizing beam splitter to the respective modulator. Preferably, the control signals provided to the modulators are different. An embodiment of the present invention will now be described, by way of example, with reference to the accompany drawings, in which: FIG. 1 is a block diagram illustrating the structure of a display device using a ferroelectric liquid crystal (FLC) panel; FIG. 2 is a detailed configuration view of the optical engine of FIG. 1; FIG. 3 is a block diagram illustrating the structure of a false contour correction apparatus in an image display system, in accordance with the principles of the present invention; FIG. 4 shows the arrangement sequence of the bits of data on an LCD panel in a false contour correction method in an image display system, in accordance with the principles of the present invention; FIG. 5 is a detailed configuration of a first embodiment of the optical engine of FIG. 3, in accordance with the principles of the present invention; FIG. 6 is a detailed configuration of a second embodiment of the optical engine of FIG. 3, in accordance with the principles of the present invention; and FIG. 7 shows a displayed bit specification of LCD data to explain false contour correction, in accordance with the principles of the present invention. While the present invention will be described more fully hereinafter with reference to the accompanying drawings, in which a preferred embodiment of the present invention is shown, it is to be understood at the outset of the description which follows that persons of skill in the appropriate arts may modify the invention here described while still achieving the favorable results of this invention. Accordingly, the description which follows is to be understood as being a broad, teaching disclosure directed to persons of skill in the appropriate arts, and not as limiting upon the present invention. As shown in FIG. 1, a display device using an FLC display panel is made up of a signal processing unit 101, a timing control unit 102, an optical engine 103 and a screen 104. As shown in FIG. 2, the optical engine 103 is made up of an optical source 201, a collimating lens 202, a color switching means 203, a polarized beam splitter 204, an FLC panel 205, and a projection lens 206. The signal processing unit 101 receives R, G, and B (red, green, and blue) signals, controls the offset, contrast and brightness of the received signals, performs signal processing such as gamma correction, and then generates R/G/B data to be displayed on the FLC panel on a field-by-field basis in synchronization with a vertical synchronization signal and also generates a clock and panel control signal for controlling an FLC panel. The timing control unit 102 receives a vertical synchronization signal and a horizontal synchronization signal, and generates a color switching control signal for controlling the color switching means 203. The operation of displaying R/G/B data output from the signal processing unit 101 on the screen 104 will now be described with reference to FIG. 2. The optical source 201 is made up of a lamp for producing light, and a reflective mirror for reflecting light emitted from the lamp to guide the light, and radiates light. The collimating lens 202 focuses light radiated from the optical source 201 into parallel light or focusing light. The color switching means 203 is an LCD shutter or a color wheel type, and receives white light from the collimating lens 202 and sequentially switches and outputs three colors R, G and B at intervals of a 1/3 vertical period during one vertical period according to a color switching control signal received from the timing control unit 102. That is, during the first 1/3 vertical period, only the wavelength of the color R among the received light is transmitted, while the remaining wavelengths are blocked. Then, the wavelength of each of the colors G and B is switched and transmitted during a 1/3 vertical period. The polarized beam splitter 204 reflects an S wave among light received from the color switching means 203 and guides the reflected S wave to the FLC panel 205, and transmits a P wave. The FLC panel 205 reflects incident light to the polarized beam splitter 204 in accordance with the R/G/B data values applied by the signal processing unit 101 to the data lines of each cell formed as a matrix, under the control of a clock and panel control signal, thereby displaying the image of each pixel. Then, the polarized beam splitter 204 transmits a P wave among light reflected by the FLC panel 205 and guides the P wave to the projection lens 206, and reflects an S wave. The projection lens 206 magnifies the light received from the polarized beam splitter 204 and projects the magnified light toward the screen 207. As shown in FIG. 3, a false contour correction apparatus in an image display system according to the present invention includes a controller 301, an optical engine 302 and a screen 303. In the controller 301, a signal processing unit receives R, G and B signals, controls the offset, the contrast and the brightness, performs signal processing such as gamma correction, and then outputs R/G/B data for driving two liquid crystal display (LCD) panels, in accordance with a vertical synchronization signal. Also, the signal processing unit generates control signals for driving LCD panels. A timing control unit in the controller 301 generates a color switching control signal for controlling the R, G, B color switching of a color switching means included in the optical engine 302, in accordance with a synchronization signal. As described above, the R, G and B data output from the controller 301 is applied to the LCD panels of the optical engine 302, and the LCD panel transmits or reflects incident light R, G and B corresponding to the values of the R, G and B data to display images. The operation of the optical engine 302 will now be described with reference to FIG. 5. As shown in FIG. 5, the optical engine 302 includes an optical source 501, a collimating lens 502, a color switching means 503, first and second polarized beam splitters 504 and 505, first and second LCD panels 506 and 507, first and second reflective mirrors 508 and 509 and a projection lens 510. The optical source 501 is made up of a lamp for producing light, and a reflective mirror for reflecting light emitted from the lamp to guide the light, and radiates light. The collimating lens 502 focuses light irradiated from the optical source 501 into parallel light or focusing light. The color switching means 503 is an LCD shutter or a color wheel type, and receives white light from the collimating lense 502 and sequentially switches and outputs three colors R, G and B at intervals of 1/3 of a vertical period during one vertical period in accordance with a color switching control signal received from the controller 301. That is, during the first 1/3 vertical period, only the wavelength of R color among the received light is transmitted, while the remaining wavelengths are blocked. Then, the wavelengths of the colors G and B are sequentially switched and transmitted during the remaining two 1/3 vertical periods. The first polarized beam splitter 504 transmits, for example, a P wave among light received from the color switching means 503, and reflects an S wave to change the travel direction of the S wave by 90 degrees. The first reflective mirror 508 reflects incident light transmitted by the first polarized beam splitter 504 and guides the reflected light to the first LCD panel 506 (LCD #1), and the second reflective mirror 509 reflects incident light reflected by the first polarized beam splitter 504 and guides the reflected light to the second LCD panel 507 (LCD #2). The first LCD panel 506 is installed on the path of light reflected by the first reflective mirror 508, and transmits incident light corresponding to the data values of R, G and B applied by the controller 301 to the data lines of each cell formed as a matrix, according to a clock and panel control signal. That is, the first LCD panel 506 displays the R/G/B data received from the controller 301 each in a sequence starting from the most significant bit to the least significant bit, as shown in LCD #1 of FIG. 4. The second LCD panel 507 is installed on the path of light reflected by the second reflective mirror 509, and transmits incident light corresponding to the data values of R, G and B applied to the data lines of each cell formed as a matrix, according to a clock and panel control signal, as in the first LCD panel 506. As shown in LCD #2 of FIG. 4, the second LCD panel 507 displays the Ro, Go and Bo data from the controller 301 each in a sequence starting from the least significant bit to the most significant bit, opposite to the LCD #1. That is, a false contour is removed by the bit arrangements made by the first and second LCD panels 506 and 507 in the opposite orders. Hereinafter, the removal of false contour by the bit arrangements made by the first and second LCD panels 506 and 507 according to the present invention will be described by referring to only red data among the data R, G and B, for convenience of explanation. If data is set to be composed of 5 bits, the first LCD panel 506 displays data in the order from MSB b4 to LSB b0, and the second LCD panel 507 displays data in the order from LSB b0 to MSB b4 which is opposite to the first LCD panel 506. Consequently, when a data value of 15 is converted into a data value of 16, data is shown brightly with a data value of 31 in the first LCD (LCD #1) panel 506, and data becomes dark with a data value of 0 in the second LCD (LCD #2) panel 507, as shown in FIG. 7. Thus, a data value of 15.5, which is the average of the data values of the first and second LCD panels 506 and 507, is perceived by eyes, so that false contour is removed. The second polarized beam splitter 505 transmits P wave light among light received from the first and second LCD panels 506 and 507, and reflects S wave light so that the travel direction of the S wave light from the first LCD panel 506 is consistent with that of the P wave light from the second LCD panel 507. The projection lens 510 magnifies and projects the light received from the polarized beam splitter 505 toward the screen 511. The operation of a second embodiment of the optical engine 302 will now be described with reference to FIG. 6. The first embodiment of the optical engine 302 use transmissive LCD panels, but the second embodiment uses reflective ferroelectric liquid crystal (FLC) panels. A transmissive LCD panel displays an image by transmitting incident light corresponding to a data value input to the data line of the transmissive LCD panel, and a reflective FLC panel displays an image by reflecting incident light corresponding to a data value input to the data line of the reflective FLC panel. The second embodiment of the optical engine 302 includes an optical source 601, a collimating lense 602, a color switching unit 603, a polarized beam splitter 604, first and second FLC panels 605 and 606 and a projection lens 607. The optical source 601 is made up of a lamp for producing light and a reflective mirror for reflecting light emitted from the lamp to guide the light, and radiates light. The collimating lens 602 focuses light irradiated from the optical source 601 into a parallel beam or focusing beam. The color switching unit 603 is an LCD shutter or a color wheel type, and receives white color light from the collimating lense 602 and sequentially switches and outputs three colors R, G and B during one vertical period under the control of a color switching control signal received from the controller 301. That is, during a first 1/3 vertical period, only the wavelength of the color R among the received light is transmitted, while the remaining wavelengths are blocked. Then, the wavelengths of the colors G and B are sequentially switched and transmitted during the remaining two 1/3 vertical periods. The polarized beam splitter 604 transmits, for example, P wave light among light received from the color switching unit 603 and guides the P wave light toward the second FLC panel 606, and reflects an S wave light to change the direction of travel of light by 90 degrees and guides the reflected S wave light toward the first FLC panel 605. The first and second FLC panels 605 and 606 reflect the incident light beams corresponding to the R/G/B data values applied by the controller 301 to the data lines of each cell formed as a matrix, under the control of the clock and panel control signal, thereby displaying the image of each pixel. The first and second FLC panels 605 and 606 arrange bits in the opposite orders to remove a false contour, as shown in FIG. 4. Then, the polarized beam splitter 604 transmits P wave light among light reflected by the first FLC panel 605, and reflects S wave light among light reflected by the second FLC panel 606 so that the travel path of the S wave light is consistent with that of the P wave light. The projection lens 607 magnifies the light received from the polarized beam splitter 604 and projects it toward the screen 608. Please refer now to Figure 4. The Figure 4 shows a timing diagram of a three color sequence (R then G then B) according to a method of compensating for false contour, in accordance with the principles of the present invention. Figure 4 shows red (R) data in detail, which is followed by symbols G and B representing green data and blue data. In Figure 4, the red data can have a minimum brightness level of 0 and a maximum brightness level of 31, because five bits are used for indicating the brightness level. The five bits are b4, b3, b2, b1, and b0. The minimum brightness level 0 exists when each one of the five bits is equal to zero, which is 00000. The maximum brightness level 31 exists when each one of the five bits is equal to one, which is 11111. The most significant bit is b4. The least significant bit is b0. As shown in Figure 4 for liquid crystal display panel #1 (LCD #1), the data bits are ordered so that the least significant bit b0 is output first, and the most significant bit b4 is output last. As shown in Figure 4 for liquid crystal display panel #2 (LCD #2), the bits are ordered so that the most significant bit b4 is output first, and the least significant bit b0 is output last. The data bits are output from LCD#1 and from LCD#2 substantially simultaneously, and the two data streams are output to a screen substantially simultaneously, and the two data streams are viewed by a user substantially simultaneously. In this manner, a false contour phenomenon is reduced or removed. Please refer now to Figure 7. The Figure 7 shows a correction of false contour, in accordance with the principles of the present invention. In Figure 7, five bits are used for indicating a brightness level. The five bits are b4, b3, b2, b1, and b0. The most significant bit is b4. The least significant bit is b0. In Figure 7, a transition from brightness level 15 to brightness level 16 is illustrated, in accordance with the principles of the present invention. A brightness level of a pixel could transition from level 15 to level 16 at a certain moment while a movie was being shown on a high definition television (HDTV), for example. Brightness level 15 is depicted in Frame 1 on Figure 7. Brightness level 16 is depicted in Frame 2 on Figure 7. Frame 1 is earlier in time than Frame 2. Frame 2 corresponds to a brightness level of a particular pixel after that particular pixel had a brightness level corresponding to Frame 1, for example. In Figure 7, a ferroelectric liquid crystal display panel #1 (FLC #1) and a ferroelectric liquid crystal display panel #1 (FLC #1) are shown to be outputting data corresponding to brightness levels. The FLC #1 of Figure 7 is shown to be outputting data corresponding to a brightness level of 15 in Frame 1. The FLC #1 in Frame 1 is outputting five data bits b4=0, b3=1, b2=1, b1=1, and b0=1. The brightness level 15 corresponds to bit values 01111. After Frame 1, the Frame 2 is depicted. In Frame 2, the FLC #1 is shown to be outputting data corresponding to a brightness level of 16. In Frame 2 the FLC #1 is outputting five data bits b4=1, b3=0, b2=0, b1=0, and b0=0. The brightness level 16 corresponds to bit values 10000. The FLC #2 of Figure 7 is shown to be outputting data corresponding to a brightness level in an order where the bits are reversed from the order of FLC #1. The FLC #2 is shown to be outputting data corresponding to a brightness level of 15 in Frame 1, with the bits in reverse order. In Frame 1 the FLC #2 is outputting five data bits b4=0, b3=1, b2=1, b1=1, and b0=1. The brightness level 15 corresponds to bit values 01111. In Frame 1 for FLC #2, the bits are output in reverse order so that they are depicted as 11110. After Frame 1, the Frame 2 is depicted. In Frame 2, the FLC #2 is shown to be outputting data corresponding to a brightness level of 16 with the bits in reverse order. In Frame 2 the FLC #2 is outputting five data bits b4=1, b3=0, b2=0, b1=0, and b0=0. The brightness level 16 corresponds to bit values 10000. In Frame 2 for FLC #2, the bits are output in reverse order so that they are depicted as 00001. In a device which does not utilize the apparatus and method of the present invention, there will be a problem when a brightness level changes from brightness level 15 to brightness level 16. The problem is known as false contour. Even though the change from level 15 to level 16 is a small change, an image will have a degraded quality on a device which does not utilize the apparatus and method of the present invention. In a device which does not utilize the apparatus and method of the present invention, when a brightness level changes from level 15 (which corresponds to 01111) to level 16 (which corresponds to 10000), false contour will occur at the picture having a change from 15 brightness to 16 brightness, and the brightness level is changed to brightness level 31 or 0 at the interface between frames or fields. As a false contour, a white line or black picture appears on the screen. However, in the present invention as shown in Figures 3-7, the false contour can be controlled regardless of the order of bit because FLC #1 and FLC #2 are arranged to output data in reverse order. Figure 4 shows the horizontal line as a time domain. Figure 7 shows the brightness level of R signal and indicates an example of 15 brightness and 16 brightness levels at which a bit reversion occurs between the first R (Frame 1) and the second R (Frame 2). In Figure 7, the hatched or shaded areas correspond to bits having a value of 1 (one). In Figure 7, the unshaded areas correspond to bits having a value of 0 (zero). In a device which does not utilize the apparatus and method of the present invention, the brightness level can be changed to 31 at an interface between frames even though there is only one level between brightness level 15 and brightness level 16. That is the false contour phenomenon. However, in the present invention as shown in Figures 3-7, when two panels are disposed to be in reverse order, the contour portion becomes 31 and 0 (zero). Therefore, an average brightness level of contour becomes (31+0)/2=15.5, and the contour is compensated smoothly. In the specification, a digital display panel has been described by being limited to a transmissive LCD panel or reflective FLC panel, for convenience of explanation. However, it is apparent that the present invention can be applied to other types of digital display panels. The above-described optical engines have been simplified for convenience of explanation. However, it is apparent to one of ordinary skill in the optical engine designing techniques that the optical engines can further include a glass polarizer, various shutters, cubes, and the like in order to improve the quality of image such as contrast, and that the location of collimating lenses can be changed. According to the present invention as described above, received image data is displayed by reversely symmetrically arranging the bits of two digital driving display means, so that fatal false contour during digital driving can be removed.

Claims: An image display apparatus comprising a light source (501, 502, 503), means for receiving image data (301) and a first digitally controlled light modulator (506) for modulating light from said source in a first path and whose state is controlled sequentially by the states of the bits of received image data, the duration of the modulator's response to each control bit being dependent on its significance, characterised by a second digitally controlled light modulator (507) for modulating light from said source in a second path and whose state is controlled sequentially by the states of the bits of received image data, the duration of the modulator's response to each control bit being dependent on its significance, combining means (505) for combining said paths downstream of the modulators and the modulators operating in dependence on said image data from most significant bit to least significant bit and from least significant bit to most significant bit respectively. An apparatus according to claim 1, wherein the light source (501, 502, 503) is configured to cyclically produce light of different colours. An apparatus according to claim 2, wherein the light source comprises: a light unit (501) for emitting the white light; a colour switching unit (503) arranged to receive the white light from said light unit (501) and to receive colour switch signals, and being responsive to the colour switching signals to selectively and cyclically pass light having different colours; and a first lens (502) for collimating the light received from said light unit (501) and outputting collimated light to said colour switching unit (503). An apparatus according to claim 3, wherein the means for receiving image data comprises a control unit (301) which also receives synchronization signals, outputs said colour switch signals in accordance with said synchronization signals and outputs control data corresponding to said received image data to said modulators. An apparatus according to claim 4, wherein said synchronization signals are horizontal and vertical synchronization signals. An apparatus according to claim 3, 4 or 5, wherein said colour switching unit (503) outputs each one of said plurality of colours seriatim at intervals of 1/3 of a period in accordance with said colour switch signals. An apparatus according to claim 6, wherein said plurality of colours output from said colour switching unit (503) are red, green and blue. An apparatus according to any one of claims 3 to 7, wherein said colour switching unit (503) outputs a first colour while blocking all other colours. An apparatus according to any one of claims 3 to 8, wherein said colour switching unit (503) comprises a liquid crystal display shutter or a colour wheel. An apparatus according to any preceding claim, comprising a first polarising beam splitter (504) for splitting the light from the light source (501, 502, 503) into two beams and directing them along the first and second paths. An apparatus according to any preceding claim, wherein said modulators (506, 507) comprise respectively LCD panels. An apparatus according to any preceding claim, wherein the combining means comprises a second polarising beam splitter (505). An apparatus according to any preceding claim, including a screen (511) onto which the output of the combining means is directed. An apparatus according to any preceding claim, wherein said means for receiving image data comprises a control unit (301) for controlling the offset, contrast and brightness of the displayed image. An apparatus according to claim 14, wherein said control unit (301) performs gamma correction for the received image data. An apparatus according to claim 10, wherein each path includes a mirror (508, 509) for directing light from the first polarizing beam splitter (504) to the respective modulator (506, 507). An apparatus according to any preceding claim, wherein the control signals provided to the modulators (506, 507) are different. An apparatus according to claim 10, wherein the combining means comprises said first polarizing beam splitter (604).

Inventors: KIM YOUNG-SUN, KIM, YOUNG-SUN
Applicants: SAMSUNG ELECTRONICS CO LTD, SAMSUNG ELECTRONICS CO., LTD.
Application year: 2000
Main classification: H04N5
IPC codes: G09G3, H04N5, H04N9