Abstract:
A method of displaying balanced chromatic images for a liquid crystal display (LCD) device with a transmissive display mode and a reflective display mode. The LCD device generates an output image in the transmissive mode with a first white output signal Wo, whereby the brightness increases of red, green and blue, the saturations of which are not decreased from an input image. The LCD device generates an output image in the reflective mode with a second white output signal Wo′, whereby the brightness increases of red, green and blue, the hues of which are not decreased from an input image, but the saturations of which decrease. The first white output signal Wo in the transmissive mode is different from the second white output signal Wo′ in the reflective mode.

Description:
CROSS REFERENCE TO RELATED APPILCATIONS  
       [0001]     This application is a Continuation-In-Part of pending U.S. patent application Ser. No. 11/023,219, filed on Dec. 27, 2004 and entitled “transflective liquid crystal display device with balanced chromaticity”, the teachings of which are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to methods of image processing of liquid crystal display (LCD) devices, and more particularly to methods of displaying balanced chromatic images for LCD devices.  
         [0004]     2. Description of the Related Art  
         [0005]     Liquid crystal display (LCD) devices are widely used as displays in electronic devices such as portable computers, PDAs and cell phones. Liquid crystal display devices are classified into two types. One is transmissive type, and the other is reflective type. The former utilizes a backlight as the light source and the latter utilizes ambient light. It is difficult to reduce power consumption in transmissive LCDs due to the power requirements of the backlight. Reflective LCDs have the advantage of lower power consumption under bright ambient light, but are hindered by environments with less ambient light.  
         [0006]     In order to overcome the drawbacks of these two types of LCDs, a transflective LCD is disclosed. Transflective LCDs are capable of displaying images in both transmissive and reflective modes. Under bright ambient light, the backlight can be turned off to reduce power consumption to lower than that of a transmissive LCD. Additionally, when less ambient light is available, the backlight can be turned on, thus offering improved image quality over that of reflective LCDs.  
         [0007]      FIG. 1  is an exploded perspective view illustrating a typical transflective LCD device. The transflective LCD device includes an upper substrate  10  and a lower substrate  20  with a liquid crystal layer  50  interposed therebetween. The upper substrate  10  is a color filter substrate and the lower substrate  20  is an array substrate. In the upper substrate  10 , on a surface opposing the lower substrate  20 , a black matrix  12  and a color filter layer  14  including a plurality of red (R), green (G) and blue (B) color filters is formed. That is, the black matrix  12  surrounds each color filter, in the shape of an array matrix. Further on the upper substrate  10 , a common electrode  16  is formed to cover the color filter layer  14  and the black matrix  12 .  
         [0008]     In the lower substrate  20 , on a surface opposing the upper substrate  10 , a TFT “T” serving as a switching device is formed in the shape of an array matrix corresponding to the color filter layer  14 . In addition, a plurality of crossing gate and data lines  26  and  28  are positioned such that each TFT is located near each cross point of the gate and data lines  26  and  28 . Further on the lower substrate  20 , a plurality of pixel regions (P) is defined by the gate and data lines  26  and  28 . Each pixel region P has a pixel electrode  22  comprising a transparent portion  22   a  and an opaque portion  22   b . The transparent portion  22   a  comprises a transparent conductive material, such as ITO (indium tin oxide) or IZO (indium zinc oxide), and the opaque portion  22   b  comprises a metal having high reflectivity, such as Al (aluminum).  
         [0009]      FIG. 2  is a sectional view of a conventional transflective LCD device, which helps to illustrate the operation of such a device. As shown in  FIG. 2 , the conventional transflective LCD device includes a lower substrate  200 , an upper substrate  260  and a liquid crystal layer  230  interposed therebetween. The upper substrate  260  has a common electrode  240  and a color filter  250  formed thereon. The color filter  250  includes red (R), green (G) and blue (B) regions. The lower substrate  200  has an insulating layer  210  and a pixel electrode  220  formed thereon, wherein the pixel electrode  220  has an opaque portion  222  and a transparent portion  224 . The opaque portion  222  of the pixel electrode  220  can be an aluminum layer, and the transparent portion  224  of the pixel electrode  220  can be an ITO (indium tin oxide) layer. The opaque portion  222  reflects ambient light  270 , while the transparent portion  224  transmits light  280  from a backlight device  290  disposed at the exterior side of the lower substrate  200 . The liquid crystal layer  230  is interposed between the lower and upper substrates  200  and  260 . Therefore, the transflective LCD device is capable of display in both reflective and transmissive modes.  
         [0010]     Referring to  FIG. 2 , the backlight  280  penetrates the transmissive portion  224  and passes through the color filter  250  once, and the ambient light  270  is reflected by the reflective portion  222  and passes through the color filter  250  twice. This leads to different chromaticity in the reflective and transmissive regions, decreasing display quality.  
         [0011]     U.S. Pat. No. 5,233,385 discloses a method for increasing the brightness of a scene in a color projection. This method uses a white light to raise the brightness in both temporal and spatial filtering systems.  
         [0012]     U.S. Pat. No. 5,929,843 discloses a method and apparatus for processing image data comprising the steps of extracting white component data from input R, G, B data, suppressing the white component data in accordance with a non-linear characteristic, generating R, G, B, W display data and driving a liquid crystal display panel having R, G, B, W filters in accordance with R, G, B, W data in order to display a full color image.  
         [0013]     U.S. Publication No. 2004/0046725 discloses a four color liquid crystal display including R, G, B and W pixels, for improving optical efficiency.  
         [0014]     Moreover, U.S. Publication No. 2003/0128872, the entirety of which is hereby incorporated by reference, discloses a method for generating a white signal component and for controlling the brightness of an image of a transmissive LCD.  
         [0015]     None of the above cited references are directed to LCD devices with balanced chromatic image in the transmissive and the reflective displaying modes.  
       BRIEF SUMMARY OF INVENTION  
       [0016]     The invention is directed to a novel method for displaying balanced chromatic images for an LCD and an LCD structure configured to reduce the difference in chromaticity between the transmissive mode and the reflective mode by providing a substantively white light. In one aspect of the present invention, a novel structure is disclosed wherein the pixel area comprises a white sub-pixel area providing a white light in the reflective mode, compared to the transmissive mode. In another aspect of the present invention, a method for normalizing chromaticity between transmissive and reflective modes of a transflective LCD device is disclosed. The structure and method of the present invention comprises the provision of a white sub-pixel area that supports a white light to increase brightness in the reflective mode, compared to the transmissive mode.  
         [0017]     The invention provides a method of displaying balanced chromatic images for a liquid crystal display (LCD) device with a transmissive mode and a reflective mode. The method comprises displaying images on the LCD device in the transmissive mode with a first white output signal, and displaying images on the LCD device in the reflective mode with a second white output signal, wherein the first white output signal is different from the second white output signal.  
         [0018]     The invention also provides a method of displaying balanced chromatic image for a liquid crystal display (LCD) device with a transmissive mode and a reflective mode. The method comprises displaying the LCD device in the transmissive mode without a white input signal, and displaying the LCD device in the reflective mode with a white output signal, wherein the white output signal equals a×Ri+b×Gi+c×Bi, where 0&lt;a&lt;1, 0&lt;b&lt;1, or 0&lt;c&lt;1 respectively.  
         [0019]     The invention further provides an LCD device having a plurality of main pixel areas, wherein each main pixel area comprises three primary sub-pixels and a white sub-pixel. Each sub-pixel comprises a transmissive portion and a reflective portion and corresponds to a color filter. The color filter comprises three primary color regions and a white region, wherein the primary sub-pixels correspond to the primary color regions and the white sub-pixel corresponds to the white region. The white region may have no color layer or have a transparent resist layer. When the transflective LCD device is operated in a transmissive mode, the white sub-pixel is driven to not emit light. Conversely, when the transflective LCD device is operated in a reflective mode, the white sub-pixel area is driven to emit light. That is, the white sub-pixel only provides the white light in the reflective mode, thereby normalizing chromaticity between transmissive and reflective modes.  
         [0020]     The invention further provides an LCD device comprising a plurality of main pixel areas, wherein each main pixel area comprises three primary sub-pixels and a white sub-pixel and a color filter corresponding to the sub-pixels. Each primary sub-pixel comprises a transmissive portion and a reflective portion and the white sub-pixel is a reflective pixel. The color filter comprises three primary color regions and a white region, wherein the primary sub-pixels correspond to the primary color regions and the white sub-pixel corresponds to the white region. The white region may have no color layer or have a transparent resist layer. When the transflective LCD device is operated in a transmissive mode, there is no light transmitted through the white sub-pixel. Conversely, when the transflective LCD device is operated in a reflective mode, the white sub-pixel reflects ambient light to display white light, thereby normalizing chromaticity between transmissive and reflective modes.  
         [0021]     The invention further provides a liquid crystal display (LCD) device with three primary color sub-pixels and a white sub-pixel. A first substrate and a second substrate are disposed opposite to each other with a liquid crystal layer interposed therebetween. A transparent electrode is disposed on the first substrate at each of the three primary color sub-pixels. An electrode with a reflective portion is disposed on the first substrate at the white sub-pixel. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0022]     The invention can be more fully understood by reading the subsequent detailed description in conjunction with the examples and references made to the accompanying drawings, wherein:  
         [0023]      FIG. 1  is an exploded perspective view illustrating a typical transflective LCD device;  
         [0024]      FIG. 2  is a sectional view illustrating operation of a conventional transflective LCD device;  
         [0025]      FIG. 3  illustrates a part of a transflective LCD device according to the present invention, showing a main pixel area consisting of three primary color sub-pixel areas and a white sub-pixel area;  
         [0026]      FIG. 4  is a sectional view of a transflective LCD device according to a first embodiment of the invention, illustrating the operation thereof in a transmissive mode;  
         [0027]      FIG. 5  is a sectional view of a transflective LCD device according to a second embodiment of the present invention, illustrating the operation thereof in a transmissive mode;  
         [0028]      FIG. 6  is a sectional view of a transflective LCD device according to a third embodiment of the invention, illustrating the operation thereof in a transmissive mode;  
         [0029]      FIG. 7  is a sectional view of a transflective LCD device according to a fourth embodiment of the invention, illustrating the operation thereof in a transmissive mode;  
         [0030]      FIG. 8  is a sectional view of a transflective LCD device according to a fifth embodiment of the invention, illustrating the operation thereof in a transmissive mode;  
         [0031]      FIG. 9A  is a block diagram illustrating a method of displaying balanced chromatic image for a liquid crystal display (LCD) device in a transmissive display mode;  
         [0032]      FIG. 9B  is a block diagram illustrating a method of displaying balanced chromatic image for a liquid crystal display (LCD) device in a reflective display mode;  
         [0033]      FIG. 10  is a CIE chromaticity diagram showing color gamut in reflective mode and in transmissive mode according to the present invention;  
         [0034]      FIG. 11  is a schematic diagram of an LCD module comprising an embodiment of an LCD device; and  
         [0035]      FIG. 12  is a schematic diagram of an electronic device, incorporating an LCD module comprising an embodiment of the LCD device. 
     
    
     DETAILED DESCRIPTION OF INVENTION  
       [0036]     The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims.  
         [0037]      FIG. 3  illustrates a portion of a transflective LCD device  300  according to one embodiment of the present invention. The transflective LCD device  300  comprises a plurality of main pixel areas  310 , wherein each main pixel area  310  consists of at least one color sub-pixel area (three primary color sub-pixel areas  3101 ,  3102  and  3103  are represented hereinafter) and a white sub-pixel area  3104 . In  FIG. 3 , numeral “ 3101 ” represents a red (R) sub-pixel area, numeral “ 3102 ” represents a green (G) sub-pixel area and numeral “ 3103 ” represents a blue (B) sub-pixel area. The arrangement of the sub-pixel areas  3101 ,  3102 ,  3103  and  3104  is a chessboard type shown in  FIG. 3 , but is not intended to limit the present invention. That is, the arrangement of the sub-pixel areas  3101 ,  3102 ,  3103  and  3104  can be a stripe type, a mosaic type, a delta type or others.  
       First Embodiment  
       [0038]      FIG. 4  is a sectional view schematically showing one main pixel area  310  of the transflective LCD device  300  according to the first embodiment of the present invention. The main pixel area  310  comprises red, green and blue sub-pixel areas  3101 ,  3102  and  3103  and a white sub-pixel area  3104 . For simplicity, the three primary color sub-pixel areas  3101 ,  3102 , and  3103  and a white sub-pixel area  3104  are respectively shown in  FIG. 4 .  
         [0039]     A first substrate  400 , serving as a lower substrate, can be a glass substrate including an array of pixel driving elements (not shown), such as an array of thin film transistors (TFTs). A backlight device  401  is disposed at the outer side (i.e. the backside) of the first substrate  400 . Three sub-pixel electrodes  410  and a sub-pixel electrode  415  are formed on the first substrate  400 , wherein each sub-pixel electrode  410  is located in each primary color sub-pixel area  3101 / 3102 / 3103  and the sub-pixel electrode  415  is located in the white sub-pixel area  3104 . Note that a representative sub-pixel electrode  410  is shown in  FIG. 4 . Each sub-pixel electrode  410  comprises a first transmissive portion  4101  and a first reflective portion  4102 . The sub-pixel electrode  415  comprises a second transmissive portion  4151  and a second reflective portion  4152 . The first and second transmissive portions  4101  and  4151  can be a transparent conductive material such as ITO (indium tin oxide) or IZO (indium zinc oxide). The first and second reflective portions  4102  and  4152  can be opaque and reflective materials such as aluminum, aluminum alloy or silver.  
         [0040]     A second substrate  490 , such as glass, opposite the first substrate  400  is provided. The second substrate  490  serves as an upper substrate. A color filter  480  is formed on the inner side of the second substrate  490 . The color filter  480  comprises three primary color regions R, G and B and a white region W. The white region W may have no color layer or have a transparent resist layer. Note that a representative primary color region R/G/B is shown in  FIG. 4 . Each sub-pixel electrode  410  corresponds to each primary color region RIG/B. The sub-pixel electrode  415  corresponds to the white region W.  
         [0041]     A common electrode  470  is then formed on an inner side of the second substrate  490 . The common electrode  470  may be an ITO or IZO layer. In  FIG. 4 , liquid crystal molecules fill a space between the first substrate  400  and the second substrate  490  to form a liquid crystal layer  465 . The liquid crystal orientation of the liquid crystal layer  465  is controlled by electric field generating electrodes such as sub-pixel electrodes  410  and  415  and the common electrode  470 .  
         [0042]     When operating in transmissive mode, a backlight  402  from the backlight device  401  passes through the primary color regions R, G and B once. According to this embodiment, the liquid crystal orientation above the sub-pixel electrode  415  is controlled to transmit backlight at different levels of brightness. In one aspect of this embodiment, when the white sub-pixel area  3104  is driven to not transmit light (i.e. the white sub-pixel area  3104  is dark), the color gamut is preserved in the transmissive mode. In another aspect of this embodiment, when the white sub-pixel area  3104  is allowed to transmit light, the color gamut will change with the different brightness levels.  
         [0043]     When operating in reflective mode, a reflective light  403  from an exterior light source (not shown) passes through the primary color regions R, G and B twice, causing display color in the reflective mode to be darker than that in the transmissive mode. At this time, according to the present invention, the liquid crystal orientation above the sub-pixel electrode  415  is controlled to cause the reflective light  403  to penetrate the liquid crystal layer  465  above the second reflective portion  4152  (i.e. the sub-pixel electrode  415 ). That is, when the white sub-pixel area  3104  is driven to transmit white light to raise display brightness and dilute the color purity in the reflective mode, the color gamut is thereby varied with different brightness levels.  
         [0044]     Thus, the overall chromaticity and color gamut for the two modes may be controlled to a desired value, which may be substantially the same or different chromaticity.  
       Second Embodiment  
       [0045]      FIG. 5  is a sectional view schematically showing one main pixel area of the transflective LCD device according to the second embodiment which is modified from the first embodiment. Elements in  FIG. 5  repeated from  FIG. 4  use the same numerals. The second embodiment differs from the first embodiment in the sub-pixel electrode  515 . The sub-pixel electrode  515  merely comprises a reflective portion  5152 . The reflective portion  5152  can be opaque and reflective materials such as aluminum, aluminum alloy or silver. That is, the sub-pixel electrode  515  is a reflective layer.  
         [0046]     An operational example of this embodiment is illustrated hereinafter.  
         [0047]     When operating in transmissive mode, a backlight  402  emitted from the backlight device  401  passes through the primary color regions R, G and B once. Note that the sub-pixel electrode  515  blocks backlight  402  from the backlight device  401  because the sub-pixel electrode  515  is opaque. That is, the white sub-pixel area  3104  does not transmit light (i.e. the white sub-pixel area  3104  is dark) in the transmissive mode.  
         [0048]     When operating in reflective mode, a reflective light  403  from an exterior light source (not shown) passes through the primary color regions R, G and B twice, causing display color in the reflective mode to be darker than that in the transmissive mode. At this time, according to the invention, the white sub-pixel area  3104  displays a white light to raise brightness by reflection of the sub-pixel electrode  515 ; furthermore, the white sub pixel area can be driven to display different brightness levels to change the color gamut in the reflective mode.  
       Third Embodiment  
       [0049]      FIG. 6  is a sectional view schematically showing one main pixel area of the transmissive LCD device according to the third embodiment of the present invention. The main pixel area comprises red, green and blue sub-pixel areas  3101 ,  3102  and  3103  and a white sub-pixel area  3104 . For simplicity, the three primary color sub-pixel areas  3101 ,  3102 , and  3103  and a white sub-pixel area  3104  are respectively shown in  FIG. 6 .  
         [0050]     A first substrate  400 , serving as a lower substrate, can be a glass substrate including an array of pixel driving elements (not shown), such as an array of thin film transistors (TFTs). A backlight device  401  is disposed at the outer side (i.e. the backside) of the first substrate  400 . Three sub-pixel electrodes  510  and a sub-pixel electrode  520  are formed on the first substrate  400 , wherein each sub-pixel electrode  510  is located in each primary color sub-pixel area  3101 / 3102 / 3103  and the sub-pixel electrode  520  is located in the white sub-pixel area  3104 . Note that a representative sub-pixel electrode  510  is shown in  FIG. 6 . Each sub-pixel electrode  510  and the sub-pixel electrode  520  can be transparent conductive material such as ITO (indium tin oxide) or IZO (indium zinc oxide).  
         [0051]     A second substrate  490 , such as glass, opposite the first substrate  400  is provided. The second substrate  490  serves as an upper substrate. A color filter  480  is formed on the inner side of the second substrate  490 . The color filter  480  comprises three primary color regions R, G and B and a white region W. The white region W may have no color layer or have a transparent resist layer. Note that a representative primary color region R/G/B is shown in  FIG. 6 . Each sub-pixel electrode  510  corresponds to each primary color region R/G/B. The sub-pixel electrode  520  corresponds to the white region W.  
         [0052]     A common electrode  470  is then formed on an inner side of the second substrate  490 . The common electrode  470  may be an ITO or IZO layer. In  FIG. 6 , liquid crystal molecules fill a space between the first substrate  400  and the second substrate  490  to form a liquid crystal layer  465 . The liquid crystal orientation of the liquid crystal layer  465  is controlled by electric field generating electrodes such as sub-pixel electrodes  510  and  520  and the common electrode  470 . A semi-transmissive layer  405  is disposed between the first substrate  400  and a backlight device  401  (as shown in  FIG. 6 ) or disposed between the sub-pixel electrodes  510  and  520  and the first substrate  400 , but the arrangement is not limited to this. The semi-transmissive layer  405  is capable of transmitting backlight and reflecting ambient light, thus, the transmissive LCD can be operated in both transmissive and reflective modes.  
         [0053]     When operating in transmissive mode, a backlight  402  from the backlight device  401  passes through the primary color regions R, G and B once. According to this embodiment, the liquid crystal orientation above the sub-pixel electrode  520  is controlled to transmit backlight at different brightness light levels. In one aspect of this embodiment, when the white sub-pixel area  3104  is driven to not transmit light (i.e. the white sub-pixel area  3104  is dark), thus, the color gamut is preserved in the transmissive mode. In another aspect of this embodiment, when the white sub-pixel area  3104  is allowed to transmit light, thus the color gamut will change with the different brightness levels.  
         [0054]     When operating in reflective mode, a reflective light  403  from an exterior light source (not shown) passes through the primary color regions R, G and B twice and is reflected by the semi-transmissive layer  405 , causing display color in the reflective mode to be darker than that in the transmissive mode. At this time, according to the present invention, the liquid crystal orientation above the sub-pixel electrode  520  is controlled to cause the reflective light  403  to penetrate the liquid crystal layer  465 . That is, when the white sub-pixel area  3104  is driven to transmit white light to raise display brightness and dilute the color purity in the reflective mode, the color gamut is thereby varied with different brightness levels.  
         [0055]     Thus, the overall chromaticity and color gamut for the two modes may be controlled to a desired value, which may be substantially the same chromaticity or different chromaticity.  
       Fourth Embodiment  
       [0056]      FIG. 7  is a sectional view schematically showing one main pixel area of the transmissive LCD device according to the fourth embodiment which is modified from the third embodiment. Elements in  FIG. 7  repeated from  FIG. 6  use the same numerals. The fourth embodiment differs from the third embodiment in the sub-pixel electrode  525 . The sub-pixel electrode  525  can be opaque and reflective materials such as aluminum, aluminum alloy or silver. That is, the sub-pixel electrode  525  is a reflective layer. In another aspect, the sub-pixel electrode  525  may comprise a reflective portion and a transmissive portion (not shown).  
         [0057]     An operational example of this embodiment is illustrated hereinafter.  
         [0058]     When operating in transmissive mode, a backlight  402  from the backlight device  401  passes through the primary color regions R, G and B once. Note that the sub-pixel electrode  525  blocks backlight  402  emitted from the backlight device  401  because the sub-pixel electrode  515  is opaque. That is, the white sub-pixel area  3104  does not transmit light (i.e. the white sub-pixel area  3104  is dark) in the transmissive mode. Thus, the color gamut can keep the same value for the transmissive mode.  
         [0059]     When operating in reflective mode, a reflective light  403  from an exterior light source (not shown) passes through the primary color regions R, G and B twice and is reflected by the semi-transmissive layer  405 , causing display color in the reflective mode to be darker than that in transmissive mode. At this time, according to the invention, the white sub-pixel area  3104  displays a white light to raise brightness by reflection of the sub-pixel electrode  515 ; furthermore, the white sub pixel area can be driven to display different brightness levels to change the color gamut in reflective mode.  
       Fifth Embodiment  
       [0060]      FIG. 8  is a sectional view schematically showing one main pixel area of the transmissive LCD device according to the third embodiment of the present invention. The main pixel area comprises red, green and blue sub-pixel areas  3101 ,  3102  and  3103  and a white sub-pixel area  3104 . For simplicity, the three primary color sub-pixel areas  3101 ,  3102 , and  3103  and a white sub-pixel area  3104  are respectively shown in  FIG. 8 .  
         [0061]     A first substrate  400 , serving as a lower substrate, can be a glass substrate including an array of pixel driving elements (not shown), such as an array of thin film transistors (TFTs). A backlight device  401  is disposed at the outer side (i.e. the backside) of the first substrate  400 . Three sub-pixel electrodes  510  and a sub-pixel electrode  520  are formed on the first substrate  400 , wherein each sub-pixel electrode  510  is located in each primary color sub-pixel area  3101 / 3102 / 3103  and the sub-pixel electrode  520  is located in the white sub-pixel area  3104 . Note that a representative sub-pixel electrode  510  is shown in  FIG. 6 . Each sub-pixel electrode  510  and the sub-pixel electrode  520  can be transparent conductive material such as ITO (indium tin oxide) or IZO (indium zinc oxide).  
         [0062]     A second substrate  490 , such as glass, opposite the first substrate  400  is provided. The second substrate  490  serves as an upper substrate. A color filter  480  is formed on the inner side of the second substrate  490 . The color filter  480  comprises three primary color regions R, G and B and a white region W. The white region W may have no color layer or have a transparent resist layer. Note that a representative primary color region R/G/B is shown in  FIG. 8 . Each sub-pixel electrode  510  corresponds to each color region R/G/B. The sub-pixel electrode  520  corresponds to the white region W.  
         [0063]     A common electrode  470  is then formed on an inner side of the second substrate  490 . The common electrode  470  may be an ITO or IZO layer. In  FIG. 5 , liquid crystal molecules fill a space between the first substrate  400  and the second substrate  490  to form a liquid crystal layer  465 . The liquid crystal orientation of the liquid crystal layer  465  is controlled by electric field generating electrodes such as sub-pixel electrodes  510  and  520  and the common electrode  470 . A diffusive layer  407  can be an optical component in the backlight device  401  or independent from the backlight device  401 . The backlight device  401  further comprises a reflective film (not shown). The diffusive layer  407  can be disposed between the first substrate  400  and the reflective film of the backlight device  401 . The reflective film of the backlight device  401  can reflect the ambient and the diffusive layer  407  can provide a scattering reflection light. Also, the diffusive layer  407  may be disposed between a lower polarizer (not shown) and a PCF (or DBEF, not shown). When the ambient light penetrates the lower polarizer and then passes through the diffusive layer  407 , the diffusive layer  407  will depolarized the linear polarized light. Non-depolarized light will keep passing through the PCF and the depolarized light will be reflected. Therefore, no matter where the diffusive layer  407  is disposed, the transmissive LCD can be operated both in transmissive mode and in reflective mode.  
         [0064]     When operating in transmissive mode, a backlight  402  from the backlight device  401  passes through the primary color regions R, G and B once. According to this embodiment, the liquid crystal orientation above the sub-pixel electrode  520  is controlled to transmit backlight at different brightness light levels. In one aspect of this embodiment, when the white sub-pixel area  3104  is driven to not transmit light (i.e. the white sub-pixel area  3104  is dark), thus, the color gamut is preserved in the transmissive mode. And in another aspect of this embodiment, when the white sub-pixel area  3104  is allowed to transmit light, so the color gamut will change with the different brightness levels.  
         [0065]     When operating in reflective mode, a reflective light  403  from an exterior light source (not shown) passes through the primary color regions R, G and B twice and is reflected by the reflective film of the backlight device  401  or is reflected by the PCF, causing display color in the reflective mode to be darker than that in the transmissive mode. At this time, according to the present invention, the liquid crystal orientation above the sub-pixel electrode  520  is controlled to cause the reflective light  403  to penetrate the liquid crystal layer  465 . That is, when the white sub-pixel area  3104  is driven to transmit white light to raise display brightness and dilute the color purity in the reflective mode, thereby the color gamut varies with different brightness level.  
         [0066]     Thus, the overall chromaticity and color gamut for the two modes may be controlled to a desired value, which may be substantially the same chromaticity or different chromaticity.  
         [0067]     The invention improves the chromaticity of the conventional LCD devices by introducing a white sub-pixel to provide white light in the transmissive and reflective modes. The white sub-pixel comprises a reflective portion reflecting the white light when in the reflective mode. Thus, the chromaticity of the reflective mode approaches that of transmissive mode, improving display quality.  
         [0000]     Normalizing Chromaticity and Adjusting Color Gamut  
         [0068]     According to the invention, the white sub-pixel is driven to pass white light to dilute color purity so that the LCD device can display brighter images with faithful color purity in the reflective mode. Because the LCD device in the transmissive mode has less reflection in the white sub-pixel area, to obtain better display performance, the white sub-pixel is suggested to be driven by at least 1% of maximum reflection ratio of white sub-pixel.  
         [0069]      FIG. 9A  is a block diagram illustrating a method of displaying balanced chromatic image for a liquid crystal display (LCD) device in a transmissive display mode. Signals of Ri, Gi and Bi  910  are input to a signal converter  920  converting the signals of Ri, Gi and Bi  910  to output signals of Ro, Go, Bo, Wo to the LCD device  950 . The RGB to RGBW conversion algorithm  930  for transmissive mode is designed to keep the same chromaticity in four-color RGBW displays as that in primary three color RGB displays, formula as below: 
   Ri:Gi:Bi =( Ro+Wo ):( Go+Wo ):( Bo+Wo )  
         [0070]     Ri, Gi, and Bi denote color inputs of red, green and blue respectively. Ro, Go, Bo, and Wo denote color outputs of red, green, blue, and white respectively. Ro, Go, Bo, and Wo can be given as: 
 
 Ro=M×Ri−Wo  
 
 Go=M×Gi−Wo  
 
 Bo=M×Bi−Wo  
 
 Wo=f ( Ri,Gi,Bi ) 
 
         [0071]     M is a predetermined constant and f(Ri, Gi, Bi) can be regarded as a function to show white color component extracted from color inputs of Ri, Gi, and Bi. Note that the f(Ri, Gi, Bi) is dependent from conditions of viewing angles, brightness, or applying electrical fields.  
         [0072]      FIG. 9B  is a block diagram illustrating a method of displaying balanced chromatic image for a liquid crystal display (LCD) device in a reflective display mode. Signals of Ri, Gi and Bi  910  are input to a signal converter  920  converting the signals of Ri, Gi and Bi  910  to output signals of Ro, Go, Bo, Wo′ to the LCD device  950 .  
         [0073]     For reflective mode, the algorithm I and II  930  and  940  converted from RGB to RGBW are represented as follows: 
 
 Ro=M×Ri−Wo  
 
 Go=M×Gi−Wo  
 
 Bo=M×Bi−Wo  
 
 Wo′=Wo+a×Ri+b×Gi+c×Bi,  
 
         [0074]     where 0&lt;a&lt;1, 0&lt;b&lt;1, or 0&lt;c&lt;1 respectively.  FIG. 10  is a CIE chromaticity diagram showing color gamut in a reflective mode and in a transmissive mode according to the present invention. If a=b=c=0 (i.e. Wo′=Wo), then the same algorithm converted from RGB to RGBW is achieved for transmissive mode and reflective mode. The color gamut in transmissive mode is quite greater than that in reflective mode. The chromaticity variations between transmissive mode and reflective mode are so significant that different white input signals are separately introduced to balance the color gamut and chromaticity in transmissive mode and reflective mode. To balance the chromaticity of an LCD display, the white sub-pixel brightness is modulated so as to dilute the color purity in the reflective mode. Therefore, the chromaticity of transmissive mode approaches that of reflective mode. When a=b=c=0.05 (i.e. Wo′≠Wo), a color gamut in the reflective mode approaches a color gamut in the transmissive mode. To achieve the desired color gamut, it is not limited that a=b=c.  
         [0075]      FIG. 11  is a schematic diagram of an LCD module  3  comprising an embodiment of an LCD device  1 . The LCD device  1  is coupled to a controller  2 , forming an LCD module  3  as shown in  FIG. 11 . The controller  3  comprises source and a gate driving circuits (not shown) to control the LCD device  1  to render image in accordance with an input. The controller  3  may comprise a converter converting input signals of Ri, Gi and Bi to output signals of Ro, Go, Bo, Wo and Wo′ to the LCD device  1 .  
         [0076]      FIG. 12  is a schematic diagram of an electronic device  5 , incorporating an LCD module  3  comprising an embodiment of the LCD device  1 . An input device  4  is coupled to the controller  2  of the LCD module  3 . Input device  4  includes a processor or the like to input data to the controller  2  to render an image. The electronic device  5  may be a portable device such as a PDA, notebook computer, tablet computer, cellular phone, or a desktop computer, for example.  
         [0077]     While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.