Patent Publication Number: US-9423607-B1

Title: Configuration of electrowetting elements in an array

Description:
BACKGROUND 
     In known electrowetting display devices the color gamut for images displayed by the device may be controlled by designing pixel color filters with appropriate hue and saturation parameters for example. However, such images can have a limited luminance and spatial resolution. 
     It is desirable to improve at least one of luminance and spatial resolution of display effects provided by an electrowetting display device. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  shows a cross section of an example electrowetting element; 
         FIG. 2  is a plan view showing an example electrowetting pixel with an example fluid configuration; 
         FIGS. 3 and 4  are plan views of example electrowetting display unit arrays; 
         FIGS. 5, 6, 7, and 8  are plan views showing different examples of electrowetting elements with white filters; 
         FIG. 9  is a plan view of an example electrowetting element array; 
         FIG. 10  is a plan view of an example array of electrowetting elements with an offset with respect to a display horizon; 
         FIG. 11  is a plan view of an example electrowetting element array; 
         FIG. 12  is a plan view of an example electrowetting element array offset with respect to a display horizon; 
         FIGS. 13, 14, 15, 16, 17, and 18  are plan views showing different examples of electrowetting elements with three display areas; 
         FIGS. 19, 20, 21, and 22  are plan views of example electrowetting element arrays; 
         FIGS. 23, 24, 25, 26, 27, 28, 29, and 30  are plan views showing example electrowetting elements with various configurations of fluids; 
         FIG. 31  is a flow diagram showing examples of a method of control; and 
         FIG. 32  schematically shows an example electrowetting display apparatus. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a diagrammatic cross-section of part of an example electrowetting device. In this example the device is an electrowetting display device  1  including a plurality of electrowetting elements, which are also referred to as electrowetting display elements  2 , and may otherwise be referred to as picture elements or electrowetting elements or cells, one of which is shown in the Figure. In examples described herein, a pixel may comprise one or more than one electrowetting element. Typically, a pixel may be considered a spatial unit for displaying an image, for example each pixel provides a display effect which together with the display effect of each other pixel generates an image for a viewer. A pixel may typically be formed for example of a plurality of sub-pixels. A sub-pixel is, for example, a component of a pixel for contributing to the display effect of a pixel. For example, a sub-pixel may correspond with one hue for contributing to a display effect of the pixel. For example, a pixel may comprise a red (R) subpixel, a (G) green subpixel and a blue subpixel (B) which respectively are configured to for example output red light, green light and blue light. By adjusting the amount of red, green and blue light contributed by each subpixel for a given display effect of the pixel, a color of the display effect of the pixel may be controlled. A pixel comprising an R, G and B subpixel may be considered a full color pixel or an RGB pixel. It is to be understood that in some examples a single electrowetting element may comprise more than one subpixel, whereas in other examples each electrowetting element may be a subpixel. A subpixel often, but not necessarily, in examples corresponds with a color or hue for display, to contribute to a display effect. Therefore, a subpixel may comprise or be associated with a color filter of the appropriate hue. For example, a color filter may overlap or substantially overlap an underlying surface which the first fluid is configurable to cover or uncover. For example, the underlying surface covered or overlapped by a color filter may be considered to be a display area or a subpixel area. Therefore, in examples below, a subpixel area may be referred to with for example an overlapping color filter. It is to be appreciated that each subpixel area is for example part of a different subpixel. For example, a first subpixel may comprise a first subpixel area and a second subpixel may comprise a second subpixel area. In examples to be described, the electrowetting elements may include a variety of different subpixel configurations. Example electrowetting elements described herein include a variety of plan-view configurations with for example walls delimiting a lateral extent of each electrowetting element, which may further be included in a variety of matrix configurations, examples of which are provided. 
       FIG. 1  depicts a cross section of part of an example electrowetting element  2 .  FIG. 2  depicts an example electrowetting pixel  100  in plan view, including a first display element  2   a  and a second display element  2   b . First and second display elements  2   a  and  2   b  are each an example of a display element  2 , and may each incorporate all of the features of the other display elements.  FIG. 1  represents an example cross section A-A of the first display element  2   a.    
     As may be seen in  FIG. 1 , the lateral dimension of the display element  2  is indicated by two dashed lines  3 ,  4 . The display elements comprise a first support plate  5  and a second support plate  6 . The support plates may be separate parts of each display element  2 , or the support plates may be shared in common by the plurality of display elements. The support plates may include a glass or polymer substrate  7   a ,  7   b  and may be rigid or flexible. The support plates in some examples include further layers and/or structures other than those illustrated, for example circuitry for controlling the display elements. Such features are not depicted for clarity. 
     The display device has a viewing side  8  on which an image or display formed by the display device can be viewed and a rear side  9 . In  FIG. 1  a surface of the first support plate  5 , which surface is in this example a surface of the substrate  7   a , defines the rear side  9 ; a surface of the second support plate  6 , which surface is in this example a surface of the substrate  7   b , defines the viewing side  8 ; alternatively, in other examples, a surface of the first support plate may define the viewing side. The display device may be of the reflective, transmissive or transflective type. The display device may be an active matrix driven display device. The plurality of display elements may be monochrome. For a color display device the display elements may be divided in groups, each group having a different color; alternatively, an individual display element may be able to provide more than one color display effect. 
     Display element  2  includes a first subpixel area  103   a  and second subpixel area  103   b  of the surface of the support plate, as indicated by arrows. A subpixel area is an area over which a subpixel display effect may be provided, for example an area which may overlap an electrode and which is contactable by a fluid to a greater or lesser extent in dependence on an applied voltage. Typically, an area is a two-dimensional area or surface for example. For example, pixel  100  of  FIG. 2  includes four subpixel areas. The first electrowetting element  2   a  includes first subpixel area  103   a  and second subpixel area  103   b , and the second electrowetting element  2   b  includes third subpixel area  103   c  and fourth subpixel area  103   d . While the example display elements  2 ,  2   a , and  2   b  each include two respective subpixel areas, this is not intended to be limiting. In further examples, some of which are provided below, there may be one subpixel area, three subpixel areas, or more than three subpixel areas in a single display element. 
       FIG. 1  depicts a first color filter F 1 , which substantially overlaps the first subpixel area  103   a , and a second color filter F 2 , which substantially overlaps a second subpixel area  103   b . By substantially overlapping it is typically the case that a majority of, for example nearly all, for example 90% or greater, or all of the surface area, in a plane parallel the subpixel area, of each filter is overlapping at least a portion of the surface areas of a respective subpixel area  103   a  or  103   b  in a plan view. For example, 90% or greater of first color filter F 1  and second color filter F 2  may be overlapping first subpixel area  103   a  and second subpixel area  103   b , respectively. This is not intended to be limiting, however, as other configurations of color filters are contemplated. In examples, a filter and a subpixel area may completely overlap or a filter may be formed to cover a very small area compared to the subpixel area. 
     A color filter is typically one or more layers of a material which are configured to filter light incident on the filter. Indeed, it may be a combination of layers show in cross-section of an electrowetting element which together filter out light of one or many wavelengths and provide an output color effect. For example, the colour filter removes or filters out a portion of light entering the color filter. The light that is filtered out is for example of one or a band of many wavelengths and/or colors of light. So, a color filter generally has a degree of transparency to permit light not removed by the color filter to be transmitted through the color filter. The filtering property of a color filter depends for example on a material the color filter is formed of or comprises. 
     The first color filter F 1  and the second color filter F 2  may be used separately to create a first color effect and a second color effect respectively for first and second subpixels. A color effect may include a hue and luminance. A hue, or a color or shade, is dependent on a dominant wavelength of light independent of intensity or lightness. For example, hues may include red, green, blue, yellow, magenta, cyan, and any other color. For example, color filters may be used to generate primary colors, or the color effect corresponding to a single subpixel area. For example, color filter F 1  or F 2  may each be used to provide one of a red, green, or blue hue respectively. Alternatively, color filters F 1  and F 2  may be used to generate a secondary color, or a color effect corresponding with a combination of at least two subpixel areas that each correspond with a different color effect. For example, color filters F 1  and F 2  may be used to provide a combined display element  2  color effect, for example if color filter F 1  provides a first color effect of a green hue and filter F 2  provides a second color effect of a blue hue, the combined display element color effect provided may be a cyan hue. In further examples, first color filter F 1  and second color filter F 2  may be used within a pixel  100  to contribute to provide a pixel  100  color effect. In further examples, however, a color filter in a first electrowetting element may be combined with a color filter in an adjacent electrowetting element to create a combined two electrowetting element color effect, as will be further described below. 
     Subpixel areas within display elements or pixels may further correspond with color effects through luminance. Luminance is typically a photometric measure of the luminous intensity per unit area of light travelling in a given direction for example. Luminance quantifies the amount of light that passes through, is emitted from or is reflected from a particular area, and falls within a given solid angle. Luminance is measured in candelas per square meters. When used within an electrowetting display element or a display unit, first color filter F 1  and second color filter F 2  may further be used to provide a plurality of display element or pixel luminance values. In an example, a display element with a display effect of a purple hue may have a relatively high or a relatively low luminance, as determined by a configuration of a first fluid and a second fluid in contact with at least part of a display area, as will be described below. 
     In examples, a subpixel area may correspond with a white filter. A white filter may be considered a color filter. White light comprises a greater or wider band of wavelengths than other color hues. Therefore a white filter, which may be formed of one or many layers, permits more incident light of more wavelengths to be transmitted through the white filter than for other hue filters. An output of a white filter is white or substantially white within acceptable variations, for example. In examples, a white filter may include light passing through a subpixel area through viewing side  8  of a display element or a pixel that is substantially the same as the light entering the display element or display unit. For example, a reflective or transreflective element may receive incident “white” light that includes a broad continuum of wavelengths or a spectrum of red, green, and blue. A subpixel area together with a white filter may transmit reflected light with little absorption or change or with more light than a non-white color filter from the incident light. In further examples, a white filter may be that the light passing through a subpixel area and through viewing side  8  includes a broad continuum of visible light, or that the relative difference between the wavelengths emitted do not provide a distinctive hue detectable to the human eye. In other words, the light emitted may be on a greyscale between white and black, as perceived by the human eye. 
     A white filter is in examples at least one layer of the electrowetting element through which light passes without being filtered or which is less filtered than for a non-white color effect. For example, for an entire path of a light ray incident on the viewing or rear side of the electrowetting element, and passing through and being emitted from the electrowetting element, such a light ray may have incurred no more filtering than inherent or background absorption of structural components of the electrowetting element such as a layer in between color filter layers of the electrowetting element. Therefore, whilst in some examples a color filter for effectuating a color effect may be a single color filter layer, in other examples a color filter may include more than one different part of the electrowetting element through which a light ray passes and which effectuate some color or white. Such a white filter may for example be a transparent filter which transmits light with minimal or background light absorption, for example by transmitting substantially all light in the visible spectrum, for example transmission of 90%, 95% or greater of incident light. The white filter may transmit three times greater, or more, light than the color filter for effectuating a color effect. Hence, depending on the backlight wavelength composition, or a wavelength composition of incident light which is reflected within the electrowetting element, the filter may be considered to effectuate a white effect. White may in some cases be considered a color, however, from a filtering point of view, white is light which for example has been minimally filtered or has incurred background absorption rather than filtering by a color filter to filter out a predetermined wavelength or wavelength band. The extent of such filtering depends on the specific construction and choice of materials (and their light absorption properties) of the subpixel. 
     In examples where subpixel areas correspond with color effects, the color filters F 1  and F 2  may be non-switchable color filters; in other words, the color filters may have a fixed shape and therefore a spatial configuration of the non-switchable color filters is not changeable, for example is not switchable. Thus, the non-switchable color filters may be non-fluid color filters. This may be contrasted with for example the first fluid described below, which may include a dye or pigment therefore to act as a color filter which is switchable between different first fluid configurations. As explained below, the color filters further contribute to a display effect provided by the electrowetting element, in addition to a configuration of the first and second fluids. In the example of  FIG. 1  there is a filter layer, in other words a layer including color filters F 1  and F 2 , and in this example is lying on a surface of the second support plate  7   b , which surface is a surface of the second support plate nearest to the space described below. It is to be appreciated in further examples that the filter layer may be located in a different position in the electrowetting element, for example on a surface of the second support plate furthest away from the space or as part of the first support plate, provided the filter layer is located such that light passing through the element to provide a display effect passes through the color filter layer. Alternatively, in other examples, the filter layer may be located in the first support plate; where the display element operates in a reflective manner, the filter layer is located between a reflector (such as a reflective electrode) and the surface adjoined by at least one of the first or second fluids. While the example of  FIG. 1  includes two filters for two display areas, this is not intended to be limiting. Those of skill in the art will readily understand that display element  2  may include a single filter, or any number of filters greater than two. 
     A color filter, for example a color filter layer in examples has at least one part formed of a material functionable as the color filter. The at least one part comprises the first or second color filters F 1  and F 2 . The color filters absorb at least one wavelength of light, for example in the visible spectrum, thus filtering the light passing through the color filters. The color filters may be formed of materials having a color filtering property. 
     The white filter may, for example, be formed of a suitable material or may be an opening, in other words an aperture or a hole or a space, for example in a color filter layer, through which light may pass. Examples of a material for forming the color filter include a resist material such as the JSR OPTMER™ CR series. These are pigment dispersed photo-resists. Where the white filter is formed of a material, an example material for forming the second region is selected from the JSR OPTMER SS series. These are heat-curable materials which can be used as protective overcoatings. They are mainly composed of acrylic polymers. The skilled person would readily understand how to form such a layer. 
     The term substantially used here is for example a degree of tolerance in the amount of light transmitted. A transmissive region may not therefore transmit all light but may transmit enough light such that a performance of the electrowetting element is not impeded. For example, 90%, 95% or greater of light may be transmitted by a white filter. The white filter may for example transmit three times greater, or more, light than a color filter. The white filter may for example be formed of a suitable material or may be an opening, in other words an aperture or a hole or a space, in the color filter layer, through which light may pass. Examples of a material for forming the color filter include a resist material such as the JSR OPTMER™ CR series. These are pigment dispersed photo-resists. Where the white filter is formed of a material, an example material for forming the white filter is selected from the JSR OPTMER SS series. These are heat-curable materials which can be used as protective overcoatings for a color filter region, but which can also be used to form the white filter. They are mainly composed of acrylic polymers. The skilled person would readily understand how to form such a color filter layer with patterned first and second regions. 
     The color effect or white filter corresponding to a subpixel area is not only dependent on the qualities of the respective color filter overlapping the subpixel area; the color effect is also dependent on the arrangement of a first and a second fluid in an electrowetting element. For example,  FIG. 1  depicts a space  10 , which may otherwise be considered to be a chamber, of each subpixel between the support plates and which is filled with two fluids, which in this example are liquids. In the example of  FIG. 1 , the space  10  is filled with a first fluid  11  and a second fluid  12  which, in the absence of an applied voltage, each form a layer. 
     The second fluid is for example electrically conductive or polar and may be water or a salt solution such as a solution of potassium chloride in water. The second fluid may be transparent, but may instead be colored, white, absorbing or reflecting. Electrically conductive typically is a second fluid capable of conducting electricity for example; for example an electrical current may flow through the second fluid due to the flow of ions through the second fluid. Polar typically is in examples that the second fluid comprises at least one compound (for example a liquid vehicle) having a molecule with a net dipole; i.e. that across the molecular structure the molecule has an overall dipole moment, due to an electron distribution, with at least one part of the molecule having a negative electrical charge and at least one different part of the molecule having a positive electrical charge. Such dipole moments include permanent dipoles. The polarity is caused for example by the presence of one or more atom to atom bonds in the molecule, with for example one of the atoms being a heteroatom such as oxygen or nitrogen. For example, such a polar atom to atom bond is a bond between an oxygen (O) atom and a hydrogen (H) atom, i.e. an —O—H bond. 
     The first fluid is for example electrically non-conductive and may for instance be an alkane like decane or hexadecane or may be an oil such as silicone oil. 
     The second fluid is immiscible with the first fluid. Therefore, the first fluid and the second fluid do not substantially mix with each other and in some examples do not mix with each other to any degree. The substantial immiscibility of the first and second fluids is due to the properties of the first and second fluids, for example their chemical compositions; the first and second fluids tend to remain separated from each other, therefore tending not to mix together to form a homogeneous mixture of the first and second fluids. Due to this immiscibility, the first and second fluids at least partially meet, for example contact, each other at an interface labelled  55  in  FIG. 1  for when no voltage is applied and labelled  57  for when a voltage is applied, which interface defines a boundary between the volume of the first fluid and the volume of the second fluid; this interface or boundary may be referred to as a meniscus. With the first and second fluids substantially not mixing with each other, it is envisaged in some examples that there may be some degree of mixing of the first and second fluids, but that this is considered negligible in that the majority of the volume of first fluid is not mixed with the majority of the volume of the second fluid. 
     The first fluid absorbs at least a part of the optical spectrum. The first fluid may be transmissive for a part of the optical spectrum, forming a color filter. For this purpose the first fluid may be colored by addition of pigment particles or a dye. Alternatively, the first fluid may be black, for example absorbing for substantially all parts of the optical spectrum, or reflecting. A reflective first fluid may reflect the entire visible spectrum, making the layer appear white, or part of it, making it have a color. In examples to be described below, the first fluid is black and therefore absorbs substantially all parts of the optical spectrum, for example in the visible light spectrum. Substantially absorbs includes for example a degree of variation; therefore the first fluid may not absorb all wavelengths, but the majority of wavelengths within a given spectrum such as the visible spectrum, so as to perform the function of the first fluid in the element. The first fluid is therefore configured to absorb substantially all light incident on the first fluid. For example the first fluid may absorb 90% or more of light in the visible spectrum and incident on the first fluid. 
     The support plate of each display element includes one or more electrodes. For example, display element  2  includes a first electrode  17   a  and a second electrode  17   b . Each respective electrode overlaps the surface of the support plate corresponding to the display area. In  FIG. 1 , it may be seen that first subpixel area  103   a  overlaps and therefore corresponds with an electrode  17   a  and second subpixel area  103   b  overlaps and therefore corresponds with a second electrode  17   b . This is not intended to be limiting, however. In examples, a display element may include any number of electrodes associated with any number of subpixel areas, examples of which are further provided herein. In the example display element  2 , each electrode  17   a  and  17   b  substantially overlaps a respective subpixel area  103   a  and  103   b . By substantially overlapping, it is typically that nearly all of the surface area of each electrode is overlapping at least a portion of a surface area of a respective subpixel area  103   a  or  103   b  in a plan view. For example, 90% of first electrode  17   a  and second electrode  17   b  may be overlapping first subpixel area  103   a  and second subpixel area  103   b , respectively. This is not intended to be limiting, however, as other configurations of electrodes are contemplated. In examples, an electrode and a subpixel area may completely overlap or an electrode may be formed to cover a very small area compared to the subpixel area. 
     The first and second electrodes  17   a  and  17   b  are separated from the fluids by the insulating layer  13 . Electrodes of neighbouring display elements are separated by a non-conducting layer. In the example of display element  2 , a small gap between electrodes  17   a  and  17   b  may be filled with non-conducting material to avoid a short between the first and second electrodes  17   a  and  17   b . For a display element having a reflective operation, rather than transmissive, the electrode in some examples is reflective. 
     In examples, the insulating layer  13  of display element  2  may be transparent or reflective. The insulating layer  13  may extend between walls of a display element. To avoid short circuits between the second fluid  12  and any electrodes arranged under the insulating layer, layers of the insulating layer may extend uninterrupted over a plurality of display elements  2 , as shown in  FIG. 1 . The insulating layer has a surface  14  facing the space  10  of the display element  2 . In examples the surface  14  may be hydrophobic. The thickness of the insulating layer may be less than 2 micrometers and may be less than 1 micrometer. 
     The insulating layer may be a hydrophobic layer; alternatively, it may include a hydrophobic layer  15  and a barrier layer  16  with predetermined dielectric properties, the hydrophobic layer  15  facing the space  10 , as shown in the Figure. The hydrophobic layer is schematically illustrated in  FIG. 1  and may be formed of Teflon®AF1600. The bather layer  16  may have a thickness, taken in a direction perpendicular the plane of the substrate, between 50 nanometers and 500 nanometers and may be made of an inorganic material like silicon oxide or silicon. 
     The hydrophobic character of the surface  14  causes the first fluid  11  to adhere preferentially to the insulating layer  13 , since the first fluid has a higher wettability with respect to the surface of the insulating layer  13  than the second fluid  12 . Wettability relates to the relative affinity of a fluid for the surface of a solid. Wettability may be measured by the contact angle between the fluid and the surface of the solid. The contact angle is determined by the difference in surface tension between the fluid and the solid at the fluid-solid boundary. For example, a high difference in surface tension can indicate hydrophobic properties. 
     In some examples, further layers may be arranged between the insulating layer  13  and the electrodes  17   a  and  17   b . The electrodes  17   a  and  17   b  may be of any desired shape or form. The electrodes  17   a  and  17   b  of a display element are supplied with voltage signals by signal lines  18   a  and  18   b , schematically indicated in the Figure. A second signal line  19  is connected to an additional electrode that is in contact with the conductive second fluid  12 . The additional electrode may be common to all elements, when they are fluidly interconnected by and share the second fluid, uninterrupted by walls. The display element  2  may be controlled by one or more voltages V applied between the signal lines  18   a ,  18   b , and  19 . The electrodes  17   a  and  17   b  may be coupled to an electrowetting display apparatus. In an electrowetting display apparatus having the display elements or display units arranged in a matrix format, the electrodes may be coupled to a matrix of control lines on the substrate  7   a.    
     A display effect provided by the display element may depend on the size of the first and second subpixel areas  103   a  and  103   b  and the extent the first fluid adjoins the surface, in dependence on the magnitude of the applied voltages V described above. The magnitude of the applied voltages V therefore may determine the configuration of the first and second fluids within the electrowetting element and may be used to control the fluid configuration. When switching the electrowetting element from one fluid configuration to a different fluid configuration, the size of the area where the second fluid adjoins the first and second display areas  103   a  and  103   b  may increase or decrease, with the area that first fluid adjoins first and second display areas  103   a  and  103   b  decreasing or increasing, respectively. 
     In the example of  FIG. 1 , the dimension of the display element  2 , indicated by the dashed lines  3  and  4 , corresponds with the centre of the walls  20 . A display region  23  is a space between the inner side of the walls  20 , indicated by the dashed lines  21  and  22  in  FIG. 1 . In the example of display element  2 , display region  23  includes the first and second subpixel areas  103   a  and  103   b , however in further examples display region  23  may include a single subpixel area or any number of subpixel areas. In examples described herein, with a display region of an electrowetting element comprising a number of subpixel areas, it is to be understood that in many examples the display region comprises only the areas described as part of that display region, which areas may for example be subpixel areas or white filters. For example, the sum of the area of each individual display area equals the area of the display region bounded for example by the walls. 
     In examples to be described, electrowetting display element  2  may include a variety of configurations of walls configured to confine or retain first fluid  11 . As will be discussed below, in examples a display region may have a variety of shapes defined for example by walls, including square, rectangular, triangular, or hexagonal, in addition to others. When the display elements are arranged into an array or matrix layout, different display element shapes formed by walls may provide for different arrangements of display elements in the arrays or matrices. In such examples it is envisaged that the plan view shape of the display element defined by the wall, in combination with a combination of one or more color filters or subpixel areas or white filter, may be used to control properties such as hue, luminance, and saturation of a display element. In examples, the walls may extend from the first to the second support plate, or the walls may extend only partly from the first support plate to the second support plate as shown in  FIG. 1 . 
     Although the walls are shown as structures protruding from the insulating layer  13 , in examples the walls may instead be formed by a surface layer of the support plate that acts as a boundary to retain fluid  11  by repelling the first fluid. For example, walls  20  may be formed of a surface layer with substantially different wettability than a portion of either first or second subpixel areas  103   a  and  103   b . For example, the walls may include a hydrophilic or less hydrophobic layer. In further examples, walls  20  may include any combination of materials, including materials that extend away from the first support plate and surface layers with a substantially different wettability than a portion of the display region  23 . 
     In the display element  2  depicted in  FIG. 1 , a first fluid  11  is configurable to adjoin at least a first part of at least one of the first subpixel area  103   a  or the second subpixel area  103   b , in dependence on at least a first voltage applied using at least one of the first electrode  17   a  or the second electrode  17   b . In other words, for example, by applying voltages to electrodes  17   a  and  17   b , it is possible to change the coverage of the first fluid over subpixel area  103   a  and/or subpixel area  103   b.    
     For example,  FIG. 2  provides a plan view of display unit  100  including the first display element  2   a  and the second display element  2   b . The second display element  2   b  is similar to the first display element  2   a , and includes a third subpixel area  103   c , a third filter, a third electrode, a fourth subpixel area, a fourth filter, a fourth electrode, and a third and fourth fluid which are similar respectively to the first subpixel area, the first filter, the first electrode and the second subpixel area, the second filter, the second electrode, and the first and second fluids, respectively. The first electrowetting display element  2   a  is adjacent to second display element  2   b , with the first and third subpixel areas  103   a  and  103   c  adjacent and the second and fourth subpixel areas  103   b  and  103   d  adjacent. 
     In examples, pixel  100  may include a wall positioned between the first surface region and the second surface region. In further examples, the display unit  100  may include a first wall positioned around the first surface region and a second wall positioned around the second surface region. In examples a first wall on the surface of the support plate is positioned between the first subpixel area and the third subpixel area, and positioned between the second subpixel area and the fourth subpixel area. In further examples a second wall on the surface of the support plate is positioned between the fifth subpixel area and the seventh subpixel area, and positioned between the sixth subpixel area and the eighth subpixel area. 
     A first fluid  111   a  may be configured to adjoin at least a first part of at least one of the first or second subpixel areas  103   a  or  103   b , in dependence on at least a first voltage applied using at least one of a first electrode or a second electrode. A third fluid  111   b  may also be configured to adjoin at least a second part of at least one of the third or fourth subpixel areas  103   c  or  103   d , in dependence on at least a second voltage applied using at least one of a third electrode or a fourth electrode. The electrowetting display element  2   a  further includes a second fluid immiscible with the first and electrowetting display element  2   b  further includes a fourth fluid immiscible with the third fluid. In further examples, the second and fourth fluids may be part of a common reservoir, however, as described above. 
       FIG. 2  depicts the first fluid  111   a  configured to cover an outer half of subpixel area  103   a  and third fluid  111   b  configured to cover a center portion of second display element  2   b  that includes a portion of each of the third subpixel area  103   c  and the fourth subpixel area  103   d . The example provided is not intended to be limiting, however. In examples, first and third fluids  111   a  and  111   b  may be configured to cover all or part of first, second, third, and fourth subpixel areas  103   a ,  103   b ,  103   c , and  103   d . When a subpixel area is exposed, for example at least partly uncovered by the first fluid, it is possible to reflect or transmit incident light through a respective subpixel area and filter to provide a color or white filter. The first, second, and third color effects are different for example. 
     The relative color effects and white filters provided by different of the first, second, third, and fourth electrowetting elements may determine a combined pixel hue and luminance. The respective contributions to pixel color or white filters provided by color filters corresponding with the first, second, third, and fourth subpixel areas may be determined by the amount of coverage due to the first or third fluid over each respective subpixel area and the respective luminance provided by the respective first, second, third, or fourth filter. For example, a filter providing a red hue color effect tends to emit less radiant flux than a filter providing a green hue color effect. The green filter may be said to be brighter than the red filter. Similarly, the white filter, which may remove almost or substantially no light for example, may be brighter than a green hue filter. Therefore, exposing one subpixel area by a predetermined amount may provide a different contribution to the total luminance and hue, which is related to the relative luminance of each subpixel area, than exposing a second subpixel area to the predetermined amount. 
     For example, if the first subpixel area corresponds with a first color effect and a second subpixel area corresponds with a second effect that is a red hue and a blue hue respectively, the first display element  2   a  will be capable of providing a display element color effect that includes the primary hues red and blue, the secondary hue purple, or no color effect at all. In the example, if the third subpixel area corresponds with a third color effect and a fourth subpixel area provides a fourth effect are a green hue and a white filter, respectively, the second display element  2   b  will be capable of providing a display element color effect that includes the primary color green with a plurality of luminance values. When the first display element and the second display element in the example configuration are used in combination as a pixel, it is possible to provide further color effects that include yellow and cyan. 
     In examples, the first and third fluids may be used to effectuate a pixel color effect comprising a plurality of combined electrowetting element luminance values for a predetermined pixel hue. In known devices, providing bright, saturated yellow hues, which are typically created using a combination of red and green, has presented challenges because it has been difficult to completely expose the red and green display areas to provide those color effects. In the example provided where the first display element  2   a  includes red and blue filters and the second display element  2   b  includes green and white filters, however, it is possible to move the first fluid  111   a  and the third fluid  111   b  completely off the subpixel areas corresponding to red, green color effects onto the subpixel areas corresponding to the blue and the white filter. 
     Therefore, in examples, the first fluid is configurable to adjoin substantially one of the first subpixel area or the second subpixel area without adjoining the second subpixel area or the first subpixel area, respectively. In further or alternative examples, the third fluid is configurable to adjoin substantially one of the third subpixel area or the fourth subpixel area without adjoining the fourth subpixel area or the third subpixel area, respectively. 
     In examples, the electrowetting pixel may provide a combined pixel luminance of the plurality of combined electrowetting element luminance that is greater than a maximum of a first subpixel luminance, a second subpixel luminance, and a third subpixel luminance. For example to improve luminance of yellow, it is further possible to expose the subpixel areas corresponding to the red hue and the green hue filter, and at least a portion of the subpixel area corresponding to the white filter. In this way, it may be possible to provide a plurality of electrowetting element luminance for a predetermined pixel hue. 
     In examples at least one of the first color filter or the second color filter may extend to a first edge of the first electrowetting element coincident for example with a lateral extent of the electrowetting element, and at least one of the third color filter or the fourth color filter may extend to a first edge of the second electrowetting element. This may provide the capability of controlling the saturation level of a color effect hue using the subpixel area that corresponds with the white filter, which is different from known devices. 
     In examples, an array of electrowetting pixels  100  may be provided.  FIG. 3  depicts example array  110 . Array  110  includes a first pixel  100   a , and a second pixel  100   b , both of which are similar to pixel  100  and incorporate similar features, however pixel  100   b  will be referred to using different reference numerals as explained herein but corresponding descriptions should be taken to apply where appropriate. The second pixel  100   b  includes a third display element  2   c  positioned adjacent to a fourth display element  2   d . The second display element  2   c  includes a fifth subpixel area  103   e  adjacent to a sixth subpixel area  103   f , and the fourth display element  2   d  includes a seventh subpixel area  103   g  and an eighth subpixel area  103   h  adjacent to the seventh subpixel area  103   g  and the sixth subpixel area  103   f . Each of the fifth, sixth, seventh, and eighth subpixel areas corresponds with a respective and substantially overlapping color filter F 5 , F 6 , F 7 , and F 8  and electrode (not pictured) and may correspond with a respective color or white filter. Third display element  2   c  further includes a fifth and sixth fluid which for example are similar to the first and second fluids respectively described earlier. 
     In the example of  FIG. 3 , the first electrowetting pixel is in a first array column  104   a  and the second electrowetting pixel is in a second array column  104   b  adjacent to the first array column  104   a . The fourth subpixel area  103   d  is adjacent to the seventh subpixel area  103   g . Array  110  may provide an aligned, ordered display upon which images may be depicted, including the color effect combinations of hue and luminance described above with regards to display unit  100 . 
     A further example is provided in  FIG. 4 , array  120 . Array  120  is similar to array  110 , except that the fourth subpixel area  103   d  of the first pixel  100   a  is adjacent to the fifth subpixel area  103   e  of second pixel  100   b.    
     In examples of array  110  and array  120 , the first color effect of the first color filter may be substantially the same hue as the fifth color effect of the fifth color filter, the second color effect of the second color filter may be substantially the same hue as the sixth color effect of the sixth color filter, and the third color effect of the third color filter may be substantially the same hue as the seventh color effect of the seventh color filter. By substantially the same color effect, it is for example where the color effect is the same hue or luminance per subpixel area within acceptable tolerances. This may provide for a regular ordering of subpixel areas including similar display effects in the array. In further examples, the first, second, and third color effects may be a red hue, a green hue, and a blue hue respectively. 
     In yet further examples the first, second, third color filters are respectively a green hue filter, a blue hue filter and a red hue filter. The fourth subpixel area corresponds with a white filter. 
     In examples the following rules may be applied for arranging the color filters including the white filter: a red hue filter and green hue filter should be each in a different display element, and the white filter is positioned adjacent to the green hue filter. 
     In order to provide improved luminance, further examples include white filters. For example,  FIG. 5  depicts electrowetting display element  200 . Display element  200  is similar to display element  2 , and includes similar features to display element  2 . Display element further includes for example the feature that first color filter F 1  extends to a first edge of the electrowetting element  200 , or edge  201   a , and second color filter F 2  extends for example to a second edge of the electrowetting element  200 , or edge  201   b . This is not intended to be limiting, however, as first and second color filters F 1  and F 2  may extend to contact the other edges of electrowetting element  200  as well. Display element  200  further includes first white filter I 1 , positioned between first and second color filters F 1  and F 2 . The first white filter I 1  corresponds with a white filter. Because first and second filters F 1  and F 2  extend to the edge of the electrowetting element  200  and the white filter is included inside the cell between filters F 1  and F 2 , where the first fluid may easily provide coverage, it may be possible to provide improved combined display unit color effects. In particular, it may be possible to provide greater luminance regulation without sacrificing the ability to control color effects for hue. 
     In examples, the first color filter is for a substantially different hue than the second color effect. This may provide the ability to generate primary and secondary color hues. 
     In examples, the first white filter may be substantially equal to 50% of a total area of the combined first filter area and the second filter area. Substantially 50% may for example be that the first white filter may cover 40-60% of the combined first and second filter areas. This may provide for adequate luminance in a display element. 
     In examples, display element  200  may include further subpixel areas. For example, display element  210  is depicted in  FIG. 6 . Display element  210  is similar to display element  200 , except that display element  210  further includes a third subpixel area  103   c  of the surface, a third electrode, and a third color filter F 3 . The third electrode may substantially overlap the third display area, and the third color filter F 3  substantially overlaps the third subpixel area. The third color filter F 3  is configured to effectuate a third color effect, and may extend to a third edge of the electrowetting element  201   c . The second subpixel area  103   b  is positioned between the first subpixel area  103   a  and the third subpixel area  103   c . The first fluid is further configured to adjoin the third subpixel area  103   c  in dependence on the at least a first voltage applied using at least one of the first electrode, the second electrode, or the third electrode. 
     In examples, the first color effect, the second color effect, and the third color effect may be a red hue, a green hue, and a blue hue respectively. This may allow for display element  210  to provide a full color gamut. 
     In examples, a second white filter  12  may be positioned between the second filter F 2  and the third filter F 3 . The second white filter  12  is configured to effectuate the white filter, similar to the first white filter I 1 . The example of display element  210  including first and second white filters I 1  and  12  may allow for further control of luminance in a three color display element. 
     In further examples, the combined first white filter and the second white filter I 1  and  12  may be equal to substantially 50% in size, within for example acceptable tolerances, of a combined first filter, second filter and third filter area  103   a ,  103   b , and  103   c . This may further provide for the ability to provide cells with the potential to generate a wide range of luminance over the full color gamut. 
     In examples, the first white filter of display element  200  or  210 , or the second white filter of display element  210  may be V-shaped. As may be seen in  FIG. 7 , display element  220  is similar to display element  210 , except that it includes first and second intermediate areas I 1  and  12  that include V-shapes, or chevron shapes. By shaping the first and intermediate regions to include a tail region  221  shifted longitudinally with respect to a point region  222 , it is possible to vary the rate at which the white filters are included in the display element color effects as the first, second, and third electrodes vary the position of a first fluid across display element  220 . In other examples, the first white filter substantially overlaps an area of the surface of the support plate which is one of: V-shaped, circular, triangular, rectangular or having a three pointed star shape. 
     In further examples, three subpixel areas may surround a white filter. For example  FIG. 8  depicts display element  230 . Display element  230  includes a first subpixel area  103   a , a second subpixel area  103   b , and a third subpixel area  103   c . Each subpixel area corresponds with a respective color filter and a respective electrode substantially overlapping the respective display area and configured to effectuate a respective color effect. A first white filter I 1  is positioned between the first color filter, the second color filter, and the third color filter, and is configured to effectuate a white effect. The first white filter I 1  is positioned such that any axis  231  pointing outward from a substantially, for example within acceptable measuring tolerances, central point  232  of the first white filter I 1 , and substantially, for example within acceptable geometric variations, in a plane of at least one of the first subpixel area, the second subpixel area or the third subpixel area, intersects at least one of the first subpixel area, the second subpixel area, or the third subpixel area. A first fluid for example similar to the first fluid described previously is configurable to adjoin at least a first part of at least one of the first subpixel area, the second subpixel area, or the third subpixel area in dependence on at least a first voltage applied using at least one of the first electrode, the second electrode, or the third electrode. Display element  230  further includes a second fluid similar to that described previously and immiscible with the first fluid. Display element offers the features of providing an efficient operation; it is easy to move the first fluid to cover at least part of the first, second, and third subpixel areas to obtain any combination of first, second, or third color effects. In the example where the first, second, and third color effects are a red hue, a green hue, and a blue hue respectively, any primary or secondary color effect on the color gamut may be available. Moreover, the white filter I 1  allows for the simple incorporation of white filters to control the luminance of a hue. 
     In examples, display element  230  may include a wall. For example, display element  230  may include a substantially, for example within acceptable geometric variations, triangle-shaped wall surrounding a combined area of the first subpixel area, the second subpixel area and the third subpixel area. For example,  FIG. 13  depicts display element  400 . In further examples, display element  230  may include a substantially, for example within acceptable geometric variations, hexagonal-shaped wall surrounding a combined area of the first subpixel area, the second subpixel area, and the third subpixel area. For example,  FIG. 17  depicts display element  440 . In examples, the first white filter may comprise at least one tapered area, for example tapering outwards, positioned between at least two of: the first filter, the second color filter, or the third color filter. Therefore, with the first white filter substantially overlapping an area of the surface, the overlapped area comprises the at least one tapered sub-area positioned between at least two of the first, second and third subpixel areas. For example,  FIG. 18  depicts display element  450 . The beneficial features of triangular and hexagonal walls and white filters with tapered areas are discussed below in the discussion relating to the example figures. 
     In examples, display element  230  may include at least one additional subpixel area of the surface. The display element  230  may include at least one additional color filter substantially overlapping the at least one additional subpixel area and configured to effectuate at least one additional color effect, the at least one additional color filter extending for example to at least one edge of the electrowetting element, wherein any axis  231  pointing outward from the substantially central point  232  of the first white filter, and substantially in a plane of at least one of the first subpixel area, the second subpixel area or the third subpixel area, intersects at least one of the first subpixel area, the second subpixel area, the third subpixel area, or the at least one additional subpixel area. 
     In further examples of display elements  200 ,  210 ,  220 , or  230  the first fluid may be further configurable to adjoin a part of the first white filter, in dependence on the at least a first voltage applied using at least one of the first electrode or the second electrode. This may provide further configurability of luminance for the display element color effect. In display applications, fine special resolution is desirable to provide sharp vertical and horizontal lines. Arrays of electrowetting display elements or pixels may sometimes provide for limited array resolutions, however. This may be seen in the example array  300  depicted in  FIG. 9 . Array  300  is similar to array  110  in that it includes features relating to a first display unit  100   a , including a first display element  102   a  and the second display element  102   b.    
     In examples, array  300  may further include a second pixel  100   b  including a third display element  102   c  and a fourth display element  102   d . In examples, the fifth color filter is for the same hue as the first color filter F 1 , the sixth color filter is for the same hue as the second color filter F 2 , the seventh color filter is for the same hue as the third color filter F 3 , and the eighth color filter is for the same hue as the fourth color filter F 4 . This may provide the feature that the adjacent pairs of display elements of array  300  include similar patterns of similar color effects, as is depicted in  FIG. 9  by the markings F 1 , F 2 , F 3 , and F 4 . 
     The luminance resolution of an array includes horizontal and vertical components. The horizontal luminance or vertical luminance is determined by the spacing of the one or more similar high luminance display areas within the array. In examples including display elements or pixels with three subpixel areas corresponding to the color effects red, green, and blue, the brightest color effect is typically green because green filters generally absorb less light than blue and red filters. In examples like array  300  that incorporate display elements or pixels with four subpixel areas corresponding to the color effects red, green, and blue, and white, however, the brightest color effects typically may be provided by a combination of green color and white filters. In order to form the highest resolution horizontal and vertical white lines in a display, it may be desirable to provide an array with equal horizontal and vertical resolutions, because a display may be limited to the lowest resolution of the two and may match with the square pixel pitch standards. 
     For example, if first subpixel area  103   a  corresponds to a first color effect including a green hue, and second subpixel area  103   b  corresponds to a second white filter green and white will align in the horizontal directions to create a horizontal resolution  302  that is equal to the spacing between the first and second subpixel areas, as indicated by a double-headed arrow. In the vertical direction, however, the spacing between subpixel areas corresponding to green color effects and white filters is for example the distance between first and second subpixel areas  103   a  and  103   b  and fifth and sixth subpixel areas  103   e  and  103   f , however. Vertical resolution  301  is indicated by a double-headed arrow that spans the distance of two pixels. Therefore, the vertical and horizontal luminance resolutions for array  300  are each approximately 2:1, and the overall luminance resolution of array  300  may be limited to two display areas. 
     The electrowetting pixel array  310  of  FIG. 10  may improve the luminance resolution of a display apparatus. Array  310  is similar to array  300 , including the first electrowetting pixel  100   a  including the first and second display elements  102   a  and  102   b . First display element  102   a  and second display element  102   b  are positioned in a first array column  311   a . First array column  311   a  has a first array column axis  312 , or a central axis along which first array column axis  312  is oriented. A first column axis angle offset  314  is defined by the offset between the first array column axis  312  and a predetermined display horizon  313 . The predetermined display horizon  313  is the horizon that images are aligned to when displayed on array  310 . In examples, predetermined display horizon  313  may be oriented to align with a dimension or an edge of a display apparatus. In further examples, the predetermined display horizon  313  may be selectable by a user of a display apparatus. In the example of array  310 , the first column axis angle offset  314  is substantially 45° from a predetermined display horizon. By substantially 45°, i.e. substantially 45 degrees, the first column axis angle offset may be 35° to 55° with respect to the predetermined display horizon, or in other examples 40° to 50° or 45° within acceptable measuring variations. 
     In examples the first and third subpixels are located on a first column axis having the column axis angle offset of substantially 45° from the predetermined display horizon. In further examples the second subpixel and the fourth subpixel are located on a second column axis having the column axis angle offset of substantially 45° from the predetermined display horizon. 
     In examples where first and fourth subpixel areas correspond to green color effects and white filters, respectively, the green and white filters may be considered to be positioned on a diagonal from each other, and the orientation of array  310  provides an improvement in luminance resolution. In  FIG. 10 , it may be seen that with the first column axis angle offset  314 , the first and fourth subpixel areas of a first and second pixel  100   a  and  100   b  may be aligned both horizontally and vertically in the array  310  so that vertical luminance resolution  310  and horizontal luminance resolution  302  are substantially equal, for example within acceptable measuring variations. In such examples the second subpixel area may correspond with a blue hue filter and the third subpixel area may correspond with a red hue filter. 
     Examples may be used with the red color filter and the green color filter being in different electrowetting elements of a pixel and the white filter positioned diagonally from the green filter in the pixel. Therefore, in examples, at least one of the first color filter or the second color filter is a red hue filter, and at least one of the third color filter or the fourth color filter is a green hue filter. In other examples, at least one of the first color filter or the second color filter is a blue color filter, and at least one of the third color filter or the fourth color filter is a white filter. 
     In further examples, array  310  may include a second array column  311   b . The second array column  311   b  may include a third pixel  100   c  and a fourth pixel  100   d , which are similar to the first and second pixels  110   a  and  100   b  described above. The second array column  311   b  may include a second column axis angle offset  314  that is substantially 45° from a predetermined display horizon. 
     In examples, the support plate in plan view is substantially rectangular or substantially square, for example rectangular or square within acceptable tolerances. At least one side of such a substantially rectangular or substantially square is substantially parallel the predetermined display horizon. In these examples of further examples a seal may be positioned on the support plate, surrounding the array of electrowetting elements, and sealing the support plate to the second support plate. In plan view the seal may be substantially rectangular or substantially square, with at least one side of the substantially rectangular or substantially square seal being substantially parallel the predetermined display horizon. 
     In further examples, a wall layer (which for example forms the walls described elsewhere herein) on part of the surface of the support plate has a grid shaped pattern and at least one grid axis of the grid shaped pattern is offset by substantially 45° from at least one side of the support plate. 
     In other examples, the first subpixel area and the fourth subpixel area are each substantially square. In a plane of the first subpixel area and the fourth subpixel area, a first corner and an opposing second corner of the first subpixel area and a first corner of the fourth subpixel area and an opposing second corner of the fourth subpixel area are located substantially on a linear axis. 
     In yet further examples the second subpixel area and the third subpixel area are each substantially square. In a plane of the second subpixel area and the third subpixel area, a first corner and an opposing second corner of the second subpixel area and a first corner and an opposing second corner of the third subpixel area are located substantially on a linear axis. 
     Arrays including triple display elements can present similar luminance resolution asymmetries as those identified with regards to array  310 . Electrowetting display element array  320  provides an example of an array composed of display elements including three color filters. Array  320  is like array  300 , but the first display element  102   a  further includes a fifth subpixel area  103   e  adjacent to the second subpixel area  103   b , and the second display element  102   b  includes a sixth subpixel area  103   f  adjacent to the fourth subpixel area  103   d . The fifth subpixel area  103   e  corresponds to a respective fifth color filter and a fifth electrode, and the sixth subpixel area  103   f  includes a sixth color filter and a sixth electrode. The first fluid is further configurable to adjoin at least part of the fifth subpixel area in dependence on the at least the first voltage applied using the third electrode, and the third fluid is further configurable to adjoin at least part of the sixth subpixel area in dependence on the at least the second voltage applied using the sixth electrode. 
     In the example of array  320 , the first color effect of the first color filter is substantially the same as the third color effect of the third color filter, the second color effect of the second color filter is substantially the same as the fourth color effect of the fourth color filter, and the fifth color effect of the fifth color filter is substantially the same as the sixth color effect of the sixth color filter, as is indicated by the labels F 1 , F 2 , and F 3 . For example, the first color effect, the second color effect, and the third color effect may be a red hue, a green hue, and a blue hue respectively. 
     As may be seen in  FIG. 11 , if the second subpixel area  103   b  and fourth subpixel area  103   d  correspond to the green hue, the color effect with the highest luminance, the horizontal resolution  302  is twice the vertical resolution  301 . Different horizontal and vertical luminance resolutions are undesirable because generally, the total luminance resolution of the array will be limited to the lower resolution. 
     In examples, array  320  may incorporate further features. Array  330  is similar to array  320 , including first display element  102   a  and second display element  102   b . Array  330  further includes a first array column  311   a  in which the first display element  102   a  and second display element  102   b  are positioned. Like array  310 , array  330  includes a first array column axis angle offset  314  that is substantially 45° from the predetermined display horizon. 
     In examples of array  330 , the third subpixel area  103   c  may be adjacent to the second subpixel area  103   b  and the fifth subpixel area  103   e . As may be seen in  FIG. 12 , this may produce a shift between the first and second display elements  102   a  and  102   b  within the array. In such an orientation, if the second subpixel area  103   b  and fourth subpixel area  103   d  correspond to a green hue, the color effect with the highest luminance, the horizontal resolution  302  is equal to the vertical resolution  301 . The array  330  therefore includes substantially equal, within acceptable variations, horizontal and vertical luminance resolution, which may be ideal for generating display effects with crisp or sharp or accurate horizontal and vertical lines. 
     In examples, arrays  310  and  330  may have display elements with a first white filter corresponding to a region positioned between the first color filter and the second color filter and able to effectuate a first white effect. In further examples, array  330  may include a second white filter corresponding to a region positioned between the second filter and the third filter and able effectuate a second white effect. 
     In further examples, array  330  may include a second array column  311   b . The second array column  311   b  may include a third pixel  100   c  and a fourth pixel  100   d , which are similar to the first and second pixels  110   a  and  100   b  described above with respect to array  330 . The second array column  311   b  may include a second column axis angle offset  314  that is substantially 45° from a predetermined display horizon. 
     Further examples of display elements including three display subpixels are provided, and will be described in relation to  FIGS. 13, 14, 15, and 17 .  FIG. 13  depicts display element  400 . Display element  400  is similar to display element  2 , however it further includes a different number and arrangement of display areas. Display element  400  includes a support plate having a surface with a first subpixel area  103   a , a second subpixel area  103   b , and a third subpixel area  103   c . The second subpixel area  103   b  is adjacent, for example adjoining or in contact with the first subpixel area  103   a , and the third subpixel area  103   c  is adjacent to the first subpixel area  103   a  and the second subpixel area  103   b . Like display element  2 , each of the first, second, and third subpixel areas  103   a ,  103   b , and  103   c  corresponds to a respective filter configured to effectuate a first color effect and an electrode. The first, second, and third electrodes are operable to move the first fluid quickly between the first, second, and third subpixel areas of the display element  400 , providing for efficient operation. 
     In examples, the first color filter F 1 , the second color filter F 2 , and the third color filter F 3  are positioned respectively so that an edge of each of the first, second, and third color filters subtends a substantially equal angle from a substantially central point  402  positioned between the first color filter F 1 , the second color filter F 2 , and the third color filter F 3 . In examples, substantially central point  402  may be positioned at a central point within display element  400 , for example substantially equidistant from first, second, and third wall portions  401   a ,  401   b , and  401   c . In further examples, substantially central point  402  may be positioned at a meeting point between the first, second, and third color filters F 1 , F 2 , and F 3 . In the example of display element  400 , if the first, second, and third color filters F 1 , F 2 , F 3  each substantially overlap and cover the same surface area as their respective subpixel areas, an edge of the first filter F 1  subtends an angle  402   a , an edge of the second filter F 2  subtends an angle  402   b , and an edge of the third filter F 3  subtends an angle  402   c  with respect to the substantially central point  402 . As may be seen in  FIG. 13 , each of angles  402   a ,  402   b , and  402   c  are substantially equal, or between 50° and 70°. This may provide an approximately equal distribution of filters between which the first fluid may easily travel to provide combined display element color effects in a compact design. 
     In examples, display element  400  may have a first color effect for the first filter, a second color effect for the second filter, and a third color effect for the third filter which are a red hue, a green hue, and a blue hue respectively. This may allow display element  400  to generate a wide range of color effects, including any primary or secondary hue. 
     Display element  400  further comprises a wall  20  surrounding the first subpixel area, the second subpixel area, and the third subpixel area. The wall incorporates a first wall portion  401   a  adjacent, to the first subpixel area  103   a  and the second subpixel area  103   b , a second wall portion  401   b  adjacent to the second subpixel area  103   b  and the third subpixel area  103   c , and a third-wall portion  401   c  adjacent to the third subpixel area  103   c  and the first subpixel area  103   a . In the example of display element  400 , each of the first wall portion  401   a , the second wall portion  401   b , and the third wall portion  401   c  are substantially straight within acceptable geometric tolerances and the wall is operable to retain or confine the first fluid within the electrowetting element. The wall may prevent the first fluid from moving too far from the subpixel areas covered by the filters. In the example of display element  400  provided in  FIG. 13 , it may be seen that the first, second, and third wall portions  401   a ,  401   b ,  401   c  meet together at three apexes to form a triangular shape. This is not intended to be limiting, however, as further wall configurations are contemplated, as discussed below. The display element wall  20  may further allow display element  400  to be placed into array orientations that provide further benefits, as further discussed below. 
     In examples, display element  400  may further comprise a first initiation area  411   a , a second initiation area  411   b , and a third initiation area  411   c  , as shown in  FIG. 14 . The first initiation area  411   a  is adjacent to the first wall portion and the third wall portion, the second initiation area  411   b  is adjacent to the first wall portion and the second wall portion, and the third initiation area  411   c  is adjacent to the second wall portion and the third wall portion. Each initiator  411   a ,  411   b , and  411   c  is for example an initiator of fluid motion comprising an area of the surface of the support plate with a wettability that is substantially different from a subpixel area wettability of at least one of the first subpixel area, the second subpixel area, or the third subpixel area. For example the initiation area may be more wettable to the second fluid than to the first fluid, and may for example be a hydrophilic area, to create a line along which fluid motion initiates due to a change in thickness of the first fluid close to the initiation area due to an aversion of the first fluid to wet the initiation area. In examples, the first, second, and third initiation areas may prevent the first fluid from traveling into an apex between wall portions of a wall, which it may be inefficient to move the first fluid out of later. Alternatively, the initiation areas may keep the first fluid substantially centrally located in the display element  400 , allowing for efficient operation of display element  400 . 
     In examples, initiation areas may be used to provide further color effects. For example, at least one of the first initiation area, the second initiation area, or the third initiation area may be configured to effectuate a white effect, and for example may each or at least one be a white filter. This may help to brighten a display image. In further examples, at least one of the first initiation area, the second initiation area, or the third initiation area may be configured to effectuate a substantially black effect, and may for example be a black filter. Substantially black may comprise a minimum of luminance. To the human eye, black is dark, the absence of luminance, and may include no distinguishing color hues. 
     Display element  400  may include one or more protrusions. A protrusion is for example a section of wall that may prevent or reduce movement, reorientation, or segmentation of the first fluid on the subpixel areas adjacent to the protrusion. For example, display element  410  includes a first protrusion  421   a  of the wall adjoining the first wall portion  401   a , at least a portion of the first protrusion  421   a  positioned between the first subpixel area  103   a  and the second display area  103   b ; a second protrusion  421   b  of the wall adjoining the second wall portion  401   b , at least a portion of the second protrusion  421   b  positioned between the second subpixel area  103   b  and the third subpixel area  103   c ; and a third protrusion  421   c  of the wall adjoining the third wall portion, at least a portion of the third protrusion  421   c  positioned between the third subpixel area  103   c  and the first subpixel area  103   a.    
     In examples, display element  400  may further include a first white filter. For example  FIG. 15  depicts display element  420 , which is similar to display element  400  and includes all of the same features which are the same, but further includes white filter I 1 . White filter I 1 , surrounded by dotted lines, is positioned between the first filter F 1 , the second filter F 2 , and the third filter F 3 , the white filter I 1  configured to effectuate a white effect. A white filter may allow display element  420  to control luminance. While the example of  420  includes a white filter I 1  shaped as a triangle between the first, second, and third filters those of skill in the art will understand that in further examples other configurations are possible, as will be described below. 
     In examples, at least a first portion of at least one of the first subpixel area  103   a , the second subpixel area  103   b , or the third subpixel area  103   c  are further configurable to effectuate a pixel color effect comprising a plurality of combined display unit luminance values for a predetermined pixel hue. In further examples, at least one combined pixel luminance of the plurality of combined display unit luminance is greater than a maximum of a first subpixel area luminance, a second subpixel area luminance, and a third subpixel area luminance. 
       FIG. 16  provides an example of a display element with a first further wall portion. Display element  430  is similar to display element  400 , and further comprises first further wall portion  431   a  connecting the first wall portion  401   a  to the third wall portion  401   c , wherein the first further wall portion  431   a  is substantially straight. An angle between an inner side of the first wall portion and an inner side of the first further wall portion, and an angle between an inner side of the third wall portion and the inner side of the first further wall portion may be substantially the same and are each an acute angle.  FIG. 16  depicts the first further wall portion  431   a  removing a relatively small portion of the apex formed by first and third wall portions  401   a  and  401   c , however this is not intended to be limiting. As will be further shown, other proportions are possible. Display element  430  also includes first and second initiation areas  411   b  and  411   c . In examples, any combination of further wall portions and initiation areas are possible. It is also possible to combine a further wall portion and an initiation area at the same apex between any two of first, second, and third wall portions  401   a ,  401   b , and  401   c.    
     For example, display element  440  depicted in  FIG. 17  includes a second further wall portion and a third further wall portion to form a substantially hexagonal shape. The second further wall portion  431   b  connects the first wall portion  401   a  to the second wall portion  401   b . The third further wall portion  431   c  connects the second wall portion  401   b  to the third wall portion  401   c . In the example of display element  440 , the second and third further wall portions are substantially straight. In the example display element  440  further comprises first, second, and third initiation areas  411   a ,  411   b , and  411   c . This is not intended to be limiting, however, as example display element  440  may have fewer initiation areas or no initiation areas. 
     Display element  440  may further include a first white filter between the first, second, and third subpixel areas which first white filter provides a white effect. For example,  FIG. 18  depicts hexagonal-shaped display element  450 . Display element  450  includes white filter I 1 , which is shaped to include three tapered areas, first tapered area  451   a , second tapered area  451   b , and third tapered area  451   c . The tapered areas  451   a ,  451   b , and  451   c  of display element  450  may provide further modulation of combined display element luminance. 
     Display elements  400  and  410  may be incorporated into an array to provide further benefits and features. For example,  FIG. 19  depicts an array of electrowetting display elements  500 . Array  500  includes a first electrowetting element  501   a  and a second electrowetting element  501   b , which may include all or any of the features described for display elements  400  and  410 . 
     Array  500  includes a support plate having a first surface region and a second surface region. The first electrowetting element  501   a  includes all or any of the features described regarding the display elements  400 ,  410 , and  420 . The second electrowetting element  501   b , positioned adjacent to the first electrowetting element  501   a , includes the same features as first display element  501   a , but is referenced and oriented as follows. The second display element  501   b  includes a fourth subpixel area, a fifth subpixel area adjacent to the fourth subpixel area, a sixth subpixel area adjacent to the fourth subpixel area and the fifth subpixel area, all of the fourth, fifth, and sixth subpixel areas being part of the second display region of the surface. The fourth, fifth, and sixth subpixel areas correspond with respective filters and electrodes. A third fluid, immiscible with a fourth fluid, is configurable to adjoin at least a second part of at least one of the fourth subpixel area, the fifth subpixel area, or the sixth subpixel area, in dependence on at least a second voltage applied using at least one of the fourth electrode, the fifth electrode, or the sixth electrode. The display element further includes a second wall surrounding the fourth display area, the fifth display area, and the sixth display area. The second wall includes a fourth wall portion adjacent to the fourth subpixel area and the fifth display area, a fifth wall portion adjacent to the fifth subpixel area and the sixth subpixel area, and a sixth wall portion adjacent to the sixth subpixel area and the fourth subpixel area. Each of the fourth wall portion, the fifth wall portion, and the sixth wall portion are substantially straight and the second wall is operable to retain the third fluid within the second electrowetting element, and the first wall portion adjacent to the fifth wall portion. 
     As it may be seen in  FIG. 19 , array  500  may provide an orderly layout of display elements, wherein each wall portion of each display element substantially overlaps with a wall portion of an adjacent display element. 
     In examples, the first color effect may be substantially the same as the fourth color effect; the second color effect may be substantially the same as the fifth color effect; and the third color effect may be substantially the same as the sixth color effect. In  FIG. 19 , this is represented by the placements of the first, second, and third filters F 1 , F 2 , and F 3 . 
     In examples, it may be desirable to provide a substantially equal horizontal and vertical luminance resolution. In display elements with subpixel areas corresponding with red, green, and blue color effects, the subpixel areas corresponding with red and green have the most luminance, and may therefore be used to create bright horizontal and vertical lines. Therefore, in examples the first color effect may be a green hue, the second color effect may be a blue hue, and the third color effect may be a red hue. As depicted in  FIG. 19 , this may provide a substantially equal vertical luminance resolution  301  and a horizontal luminance resolution  302 . It may also be used for the brightest color effects to be aligned with the horizontal and vertical axes. 
     Display element  430  may also be incorporated into an array.  FIG. 20  depicts array  510 . Array  510  comprises at least a first display element  501   a  and a second display element  501   b , both of which include a first further wall portion  431   a . The first display element is positioned so that the first further wall portion is level with the second wall portion  401   b  of the second display element  501   b . Additional display elements are positioned along the row with their respective first further wall portions  431   a  facing alternating directions. 
     Display element  420  may be incorporated into an array to provide further benefits and features. For example,  FIG. 21  depicts an array of electrowetting display elements  520 . Array  520  includes a first electrowetting element  501   a  and a second electrowetting element  501   b , which may include all of the features described for display element  420 . Array  520  is similar to array  500 , except that it includes first white filter I 1  between the first, second, and third filters, and a second white filter I 1  between the fourth, fifth, and sixth filters (labelled F 1 , F 2 , and F 3 ) as depicted in  FIG. 21 . In arrays with subpixel areas including white filters, the subpixel area corresponding with the green hue color effect may be the color effect with the most luminance. Therefore, in examples, the first color effect may be a blue hue, the second color effect may be a green hue, and the third color effect may be a red hue. This may provide a substantially equal horizontal luminance resolution  302  and vertical luminance resolution  301 , as may be seen in  FIG. 21 . 
     Display elements  440  and  450  may also be incorporated into an array.  FIG. 22  depicts array of display elements  540 . Array  540  includes a support plate having a first surface region and a second surface region. The first electrowetting element  501   a  includes the features described regarding the display elements  440 . The second electrowetting element  501   b , positioned adjacent to the first electrowetting element  501   a , includes the same features as first display element  501   a , but is referenced and oriented as follows. The second display element  501   b  includes a fourth subpixel area, a fifth subpixel area adjacent to the fourth subpixel area, a sixth subpixel area adjacent to the fourth subpixel area and the fifth subpixel area, all of the fourth, fifth, and sixth subpixel areas being part of the second display region of the surface. The fourth, fifth, and sixth subpixel areas include respective filters and electrodes. A third fluid, immiscible with a fourth fluid, is configurable to adjoin at least a second part of at least one of the fourth subpixel area, the fifth subpixel area, or the sixth subpixel area, in dependence on at least a second voltage applied using at least one of the fourth electrode, the fifth electrode, or the sixth electrode. The second display element further includes a second wall surrounding the fourth subpixel area, the fifth subpixel area, and the sixth subpixel area. The second wall includes a fourth wall portion adjacent to the fourth subpixel area and the fifth display area, a fifth wall portion adjacent to the fifth subpixel area and the sixth subpixel area, and a sixth wall portion adjacent to the sixth subpixel area and the fourth subpixel area. The second wall further contains a fourth further wall portion connecting the fourth wall portion to the fifth wall portion, a fifth further wall portion connecting the fourth wall portion to the fifth wall portion, and a sixth further wall portion connecting the fifth wall portion to the sixth wall portion. Each of the fourth wall portion, the fifth wall portion, the sixth wall portion, the fourth further wall portion, the fifth further wall portion, the sixth further wall portion are substantially straight and the second wall is operable to retain the third fluid within the second electrowetting element, and the first wall portion adjacent to the fifth wall portion. 
     In examples of array  540 , the first color effect may be substantially the same as the fourth color effect, the second color effect is substantially the same as the fifth color effect, and the third color effect is substantially the same as the sixth color effect. This may provide a maximum horizontal and vertical luminance resolution. 
     In further examples, array  540  may include a first white filter positioned between the first filter, the second filter, and the third filter, and a second white filter positioned between the fourth filter, the fifth filter, and the sixth filter, the first and second white filters providing a white effect. 
     Numerous examples of an electrowetting element and of arrays of such electrowetting elements are described above. 
     Examples of a method of controlling an array of electrowetting elements will now be described, with respect also to  FIG. 31 . It is to be appreciated that such examples may be applied to any of the arrays of electrowetting elements described above. However, for the sake of explanation, the array of  FIG. 10  will be referred to in the following example now to be described. Features described previously in relation to  FIG. 10  should be taken to apply here also, with common features having corresponding descriptions taken to apply here also. 
     As explained earlier, the extent of a subpixel area in an electrowetting element that is adjoined by a first fluid, for example an oil or alkane, is controllable in dependence on a voltage applied between the electrode substantially overlapping the subpixel area in question and the electrode in contact with the second fluid. 
     In known systems, a pixel may have a fixed combination of sub-pixels. In other words, for displaying different display effects, for example of a particular hue and luminance, the same sub-pixels are used each time for that pixel. Thus, the construction of a pixel is fixed. 
     It has now been found that with for example electrowetting elements in accordance with examples described herein, and arrays of such electrowetting elements also described herein, new methods of controlling the configuration of the fluids in each electrowetting element may be used to give improved display effects compared with known systems. 
     Referring now to  FIG. 23  there is shown an array of electrowetting elements in accordance with that described previously using  FIG. 10 . In  FIG. 23 , the first fluid in each electrowetting element is configured, using at least one applied voltage of appropriate magnitude, to adjoin a certain extent of the subpixel area. 
     The extent of each subpixel area of each electrowetting element is dependent on the display effect to be displayed, which is controlled for example as now explained. 
     Using for example a control system described below, which for example includes the at least one processor and the at least one memory, with appropriate computer program instructions, first pixel data may be received. The first pixel data represents a first display effect for a display unit, for example a pixel, of an array of display elements. The first pixel data may therefore in some examples be standard input data for example according to the sRGB format which is well known by the skilled person. Such input data may not be device specific, in that the data for example indicates for a given point in space a hue and a luminance value for displaying. Such data may therefore be input to other non-electrowetting type display devices. 
     Then, for example, the control system may select which of a plurality of subpixel areas of the electrowetting elements of the array to use for displaying a given display effect represented by the received first pixel data. Looking at the array of electrowetting elements shown for example by  FIG. 23 , there is a plurality of subpixel areas, for example each subpixel area indicated in this example with R, G, B or W, corresponding respectively to a red, green, blue or white hue attributed with that subpixel area, for example due to the association with a color filter for filtering light of the appropriate wavelength(s) to effectuate a particular color effect as explained previously. 
     The plurality of subpixel areas comprises a first subpixel area of a first electrowetting element of the array which substantially overlaps a first electrowetting element first filter configured to effectuate a first color effect. The plurality of subpixel areas also comprises a first subpixel area of a second electrowetting element of the array which substantially overlaps a second electrowetting element first filter configured to effectuate the first color effect. Therefore, the first subpixel area of the first and second electrowetting elements correspond with for example the same hue, despite being in different electrowetting elements. In examples, such first subpixel areas of two different electrowetting elements are located in two electrowetting elements which are adjacent to each other. Adjacent in some examples is where there is no further electrowetting element between the two electrowetting elements in question. In other examples, the two electrowetting elements may be separated from each other by at least one further electrowetting element. 
     An example is given with reference to  FIG. 23 , for explanation purposes. In  FIG. 23 , there is a first set of subpixel areas corresponding with an R, G, B and W hue respectively; each of those subpixel areas is labelled in  FIG. 23  with the appropriate R, G, B or W label with the suffix “1”. Similarly, a second set of subpixel areas corresponding with an R, G, B or W hue is labelled with the appropriate R, G, B or W label with the suffix “2”. The subpixel areas G 1  and G 2  may each be taken as a first subpixel area of a different electrowetting element which substantially overlap a first filter of the first or second electrowetting element, respectively, for effectuating a color effect of for example the same hue. For completeness, third and fourth sets of subpixel areas are similarly labelled using respectively the suffixes “3” and “4”. 
     Depending on the display effect to be displayed, a group of the subpixel areas of the plurality of subpixel areas is selected for displaying the display effect in question. The group of subpixel areas comprises at least one of: the first subpixel area of the first electrowetting element, or the first subpixel area of the second electrowetting element. Therefore, in some examples, for the first pixel data for a first display unit (for example a pixel), one or both of the first subpixel area of each of the first and second electrowetting elements may be selected. 
     Typically a group of subpixel areas which is selected is for example a sub-set of subpixel areas selected from a set of subpixel areas which together are the plurality of subpixel areas. Each subpixel area of the group of subpixel areas may not necessarily be adjacent each other; nor may the first subpixel area of the first electrowetting element be adjacent to the first subpixel area of the second electrowetting element. 
     Referring now to  FIGS. 23 and 24 , selecting of one of the first subpixel areas of the first and second electrowetting elements, in dependence on the display effect to be displayed, is illustrated. 
       FIG. 23  illustrates a configuration of first fluids in several electrowetting elements. The subpixel areas are labelled with the appropriate R, G, B or W label, with the suffix “1” or “2” where appropriate. The extent of each subpixel areas adjoined, for example covered, by the first fluid depends on the display effect and is controlled by the voltage applied in each electrowetting element using the electrodes. The extent of first fluid coverage of each subpixel area is indicated in  FIGS. 23 and 24  using diagonally hatched shading. Therefore an extent of each subpixel area which is not covered, for example uncovered, by first fluid is shown as an extent of a subpixel area which does not have diagonally hatched shading over it. 
     In  FIG. 23  a first display effect is illustrated. In this example the first display effect represents a display effect feature which is longitudinal in shape along a longitudinal axis L 1 , with the characteristic being an orientation of the longitudinal axis, which in this example is a horizontal axis as shown. To display this display effect the first fluid of each electrowetting element of the array of electrowetting elements is configured to uncover at least part of the following subpixel areas: G 1 , B 1 , R 1 , W 1 , B 2 , R 3 , G 4 , R 4 , B 4  and W 4 . Therefore, at least part of the following subpixel areas may therefore be adjoined, for example covered, by the first fluid: R 1 , G 2 , R 4 , W 2 , R 2 , B 4 , W 3 , B 1 , G 3  and R 3 . Further details of examples of such linear features will be described below. 
     In contrast to  FIG. 23 ,  FIG. 23  illustrates a different first display effect which is also a linear feature but with a longitudinal axis L 2  substantially perpendicular to the longitudinal axis L 1 . Therefore as illustrated the second longitudinal axis L 2  is a vertical axis. As can be seen, different extents of subpixel areas are covered by the first fluid and different extents of subpixel areas are uncovered by the first fluid, to display the different first display effect. 
     For example, for the linear display effect feature with axis L 1 , subpixel area G 1  is uncovered, for example not adjoined by the first fluid, whereas for the different linear display effect feature with axis L 2 , subpixel area G 1  is covered by the first fluid. Instead, for the linear display effect feature with axis L 1 , subpixel area G 2  is covered, and subpixel area G 2  is uncovered by the first fluid. In this way, a different subpixel area corresponding to a particular color effect, for example a hue, in this case a green hue, is selected in dependence on the first display effect to be displayed, for example an orientation of the longitudinal axis. Hence, depending on the first display effect, either the first subpixel area of the first electrowetting element may be selected for the group of subpixel areas, or the first subpixel area of the second electrowetting element may be selected for the group of subpixel areas. 
     The example given here with respect to subpixel areas G 1  and G 2  is one example of a selection between two different subpixel areas for displaying a certain display effect. For a certain display effect, in examples of the method, further subpixel areas may be selected in preference over a different subpixel area. 
     Once the group of subpixel areas has been selected, the control system may then output control data for switching the first fluid of each electrowetting element appropriately to obtain the extent of coverage and/or non-coverage of each subpixel area required to display the display effect. The outputting control data comprises for example selectively outputting: control data based on a first orientation of the longitudinal axis, using the first subpixel of the first electrowetting element; or control data based on a second orientation of the longitudinal axis, using the first subpixel of the second electrowetting element. Therefore the output control data is for displaying the first display effect using the first group of subpixel areas. The outputted control data may for example be signals corresponding to voltage levels for each electrode overlapping a subpixel area of the group of subpixel areas selected for displaying the display effect, so that a voltage of appropriate magnitude is applied to each subpixel area for obtaining the desired first fluid coverage of each subpixel area. 
     As explained above, depending on the display effect to be displayed, one or a different subpixel area may be selected as the group of subpixel areas. However, in relation to other subpixel areas in the array, the same subpixel area may be used for at least two different display effects. In other words the different display effects may have in common the same subpixel area. An example of this is illustrated using  FIGS. 23 and 24  where the subpixel area B 1  is at least partly uncovered of any first fluid for both the display effect of  FIG. 23  and for the display effect of  FIG. 24 . Thus, in examples, with the first display effect representing a linear display effect feature, which is longitudinal along a longitudinal axis, with a first orientation (for example corresponding with axis L 1 ) the group of subpixel areas selected comprises the first subpixel area of the first electrowetting element, and with the first display effect representing a linear display effect feature instead with a second orientation (for example corresponding with axis L 2 ) the group of subpixel areas selected also comprises the first subpixel areas of the first electrowetting element. It is to be appreciated that the same subpixel area of other electrowetting elements may also be used for different display effects; for example the subpixel area W 1  may be uncovered by first fluid for both the linear display effect of the first orientation (see  FIG. 23  for example) and for the linear display effect of the second orientation (see  FIG. 24  for example). Thus, for example, irrespective of an orientation of a linear display effect feature, the group of subpixel areas of the array may comprise a second subpixel area (different from the first subpixel areas referred to in earlier paragraphs in relation to  FIGS. 23 and 24 ) of an electrowetting element of the array, which second subpixel area substantially overlaps a second filter configured to effectuate a second color effect. 
     It is to be appreciated that, compared with a known system with a pixel having certain sub-pixels regardless of the display effect to be displayed, the method of controlling display of a display effect using examples of an array of electrowetting elements described herein may not be considered to use certain sub-pixels (which correspond with respective subpixel areas) for any display effect. Instead, by selecting certain subpixel areas to use in dependence on a display effect, for example based on a characteristic of the first display effect, the sub-pixels of a pixel (which may otherwise be referred to as a display unit) may be considered dynamically chosen in dependence on the display effect. Therefore, without any fixed construction of a pixel in the array, the sub-pixels and therefore a display unit may be considered flexible or virtual, as it can be changed based on the selection for the display effect in question. As will now be explained, this can offer benefits for improving the quality of a display effect, including for example any of: a brightness resolution of a linear display effect (for example horizontally and/or vertically, but also diagonally), a definition of a display effect for example a smoothness of an edge of a display effect, for example of text characters. 
     As the display effect is used to select which subpixel areas may be selected as the group of subpixel areas, and in dependence on the particular construction of electrowetting elements in the array, it is possible to display a first display effect with a minimum dimension which is less than a length of a respective display region of at least one electrowetting element of the array of electrowetting elements. These electrowetting elements may comprise at least two adjacent subpixel areas. In this way, the definition of a display effect feature is not limited to the resolution of a display unit, which is related to the size of the display region for an electrowetting element. Instead, different subpixel areas of different, for example adjacent, electrowetting elements may be selected for a given display effect, meaning that a display effect feature may have a minimum dimension less than the maximum dimension (such as a length) of the display region. Indeed, the minimum dimension of a display effect feature may not even be limited to the maximum dimension (for example a length) of a subpixel area, as with the ability to control the extent of each subpixel area covered or uncovered by the first fluid, a relatively light or relatively dark display effect feature (explained further below) may have a minimum dimension less than the maximum dimension (for example a length) and in some examples also a minimum dimension (for example a width), of the subpixel area, as it is the position of the edge of the meniscus of the first fluid in contact with the surface of the subpixel area which for example determines the extent of the subpixel area covered by the first fluid and therefore the definition of a display effect feature. 
     This greater definition allows display effects to be more precisely displayed and is for example therefore useful for presenting text content, for example individual text characters, precisely and with smooth edges whether curved or linear. Improved display of text is useful for e-readers for example, such that a user of an e-reader device with electrowetting elements of examples described herein is presented with higher quality images of text, which improve the user experience and for example reduce fatigue to a user when viewing text. 
     It is to be appreciated that a display effect to be presented may be formed of a combination of at least one extent of a subpixel area which is covered by a first fluid, and at least one extent of a subpixel area which is uncovered by a first fluid. Therefore, it is the edges between covered and uncovered parts of the subpixel areas and therefore a resulting contrast in the display effect which aid formation of a display effect. With this in mind, a display effect feature, for example a component of a display effect, which component may for example be a linear display effect feature such as a stripe, may correspond with a relatively light display effect feature or a relatively dark display effect feature. In such examples a shape of the first display effect may be a characteristic of the first display effect and the selecting the group of subpixels may be based on the shape. Depending on whether the input display effect data indicates a relatively dark or light display effect feature, will influence whether the group of subpixel areas is selected for being at least partly uncovered by the first fluid or at least partly covered by the first fluid. Therefore, the outputted control data may be indicative of a respective fluid coverage extent (of the first fluid) for each subpixel area of the group selected on the basis of the display effect. Further, or in other examples, the outputted control data may be indicative of a respective fluid non-coverage extent (of the first fluid) for each subpixel area of the group selected on the basis of the display effect. 
     Typically, the phrase relatively dark display effect feature is for example a display effect feature which is dark relative to an uncovered part of a subpixel area. Therefore, a relatively dark display effect feature may in examples correspond with a display effect feature created by and corresponding with at least part of a subpixel area covered by the first fluid. Therefore, in examples, a relatively dark display effect feature may not be a dark color such as black, or another color with a low luminance, but may for example be a color which is darker than an uncovered part of a subpixel area. 
     Similarly, typically, the phrase relatively light display effect feature is for example a display effect feature which is light relative to a covered part of a subpixel area. Therefore, a relatively light display effect feature may in examples correspond with a display effect feature created by and corresponding with at least part of a subpixel area uncovered by the first fluid. Therefore, in examples, a relatively light display effect feature may not be a light color such as white, or another color with a high luminance, but may for example be a color which is lighter than a covered part of a subpixel area. 
     In some examples, the relatively dark display effect feature and the group of subpixel areas selected comprises at least two adjacent subpixel areas, with the output control data comprising control data indicative of a fluid coverage extent of each of the at least two adjacent subpixel areas. For example, the fluid coverage extent for each of the at least two adjacent subpixel areas is substantially equal to (for example within acceptable coverage tolerances) a respective extent of each of the at least two adjacent subpixel areas. In this way, with the subpixel areas being adjacent each other, a dark display feature may be created which spans multiple subpixel areas. In other words, the first fluid covering the subpixel area of multiple adjacent subpixel areas together form a cluster of covered subpixel areas which form a relatively dark display effect feature. Thus, subpixels may be selected which together form the shape of the relatively dark or relatively light display effect feature. 
     Such a feature may for example be a relatively dark stripe where for example the first fluid of each electrowetting element is a relatively dark colored first fluid. A stripe is for example a band or other linear feature having an approximately uniform thickness along a longitudinal axis. 
     Such a stripe display effect feature may be useful in displaying text using the array. For example, text characters require stripes of other linear features to form the text characters. Further, if a curved edge is desired for a relatively dark display effect feature, the edge of the first fluid of at least one electrowetting element may be controlled to form a non-linear edge of a suitable shape to display the feature required. The ability to control the first fluid edge for each electrowetting element gives considerable granularity of control for displaying a display effect feature, and hence a greater definition for displaying display effects. 
     A similar explanation applies to a relatively light display effect feature, with the group subpixel areas selected comprising at least two adjacent subpixel areas for being uncovered by the first fluid in respective electrowetting elements, to form a cluster of multiple uncovered part extents and/or entire uncovered extents of subpixel areas adjacent to each other to form a relatively light display effect feature. 
     Such a display effect may be a stripe display effect feature and may for example be seen in  FIG. 23 , with the linear display effect along axis L 1  being considered a stripe. Note that although this stripe does not have straight sides parallel along the length of the stripe to the axis L 1 , this feature may still be considered to be a stripe on the basis that it is a stripe within the limits of the positioning of the first fluid edges for each electrowetting element, in dependence on the particular construction of the electrowetting elements and their positioning relative to each other in the array. Indeed, for a viewer of the array, any irregularities in a straight side of a stripe, parallel to the longitudinal axis L 1 , will at an appropriate distance of viewing the array merge to appear as a straighter sided stripe. A similar description applies to the stripe shown in  FIG. 24  with a different axis L 2 . Such a relatively light feature such as a stripe may be useful for displaying text to a viewer, for example to provide clear and bright stripes or bands between lines of text, to give for example suitable contrast to more clearly display the text to the viewer. Also, relatively light areas between parts of text characters or between text characters themselves are also required to display text, and therefore also their shape and brightness contribute to the quality of the displayed text. 
     As will be appreciated, the color effects corresponding to different subpixel areas of an array of electrowetting elements may be chosen in dependence on the particular array of electrowetting elements to be manufactured. Further, depending on the color gamut for display effects to be displayed, the choice of color effects and therefore color filter hues may be selected accordingly. 
     In the examples of  FIGS. 23 and 24 , the stripe display effects illustrated correspond with subpixel areas corresponding with green and white display effects, which as explained earlier, due to the adjacency of these subpixel areas along a longitudinal axis, give a brighter stripe than using other combinations of color effects. Hence, a vertical and/or horizontal brightness resolution may be improved compared with known systems by using the control method described in examples here with the appropriate electrowetting element construction and array layout of those electrowetting elements. 
     In some examples, such as that of  FIGS. 25 and 26 , an array of electrowetting elements comprises a first electrowetting element with a first subpixel area substantially overlapping a first filter configured to effectuate a first color effect, a second subpixel area substantially overlapping a second filter configured to effectuate a second color effect, and a third color filter substantially overlapping a third filter configured to effectuate a third color effect. The array further comprises a second electrowetting element also with a first subpixel area substantially overlapping a first filter configured to effectuate the first color effect, a second subpixel area substantially overlapping a second filter configured to effectuate the second color effect, and a third color filter substantially overlapping a third filter configured to effectuate the third color effect. In some examples the first, second and third color effects is a different one of a red hue, a green hue or a blue hue, Therefore, an electrowetting element has red, green and blue (RGB) color effect capabilities, for forming for example full color display effects. The electrowetting element may further include a subpixel area corresponding for example with a white (W) display effect. Therefore in some examples an electrowetting element may be considered to be an RGBW electrowetting element. 
     Further examples of how the first fluid of different electrowetting elements may be controlled to display different display effects by selecting the subpixel areas of a group of subpixel areas will now be illustrated using  FIGS. 23 to 30 . In many of these examples, a relatively light and/or relatively dark display effect such as a stripe is shown. It is however to be appreciated that other display effects, for example non-linear, are envisaged using the arrays of electrowetting elements described herein. Indeed, the method of selecting the group of subpixel areas may be based on at least one of: a shape of a display effect (such as the first display effect represented by the first pixel data), a linearity of the display effect, a minimum dimension of the display effect, a maximum dimension of the display effect or a color of the display effect (for example the characteristic of the first display effect is a predetermined color and the selecting the group of subpixels selects subpixels which together substantially form the predetermined color; the color may be white and in which case an approximately equal number of at least one red hue subpixel, at least one green hue subpixel and at least one blue hue subpixel may be selected). In such examples, the method may comprise analysing the first pixel data to determine the at least one characteristic of the first display effect; analysing the first pixel data to determine at least one characteristic of the first display effect; and spatially mapping the first display effect on to the plurality of subpixels of the array of electrowetting elements. The selecting the group of subpixels of the array of electrowetting elements may comprise selecting subpixels of the array of electrowetting elements spatially mapped to the first display effect. 
     With the increased definition available for displaying a display effect as explained above, the selecting of the group of subpixel areas may therefore be based on mapping a color effect at each point of location for input display effect data with a location of each subpixel area of the electrowetting elements, rather than in known systems mapping such a color effect with the location of each pixel of an array of display elements. Hence, a more granular approach may be applied for more precisely and with more definition displaying a display effect. Further, for a given color of a display effect, several subpixel areas corresponding with the same color effect may be selected from, which are generally around the point of location required for that display effect, in order to select the subpixel area which will offer the same color effect and an appropriate position in the array for more precisely displaying the display effect. 
     Referring to  FIGS. 25 and 26 , an array of electrowetting elements is illustrated similar to that described above with reference to  FIG. 12 . Such electrowetting elements are each rectangular in this example and include three subpixel areas corresponding with R, G and B color effects respectively, with a white filter between adjacent of the subpixel areas corresponding with the R, G and B display effects, as described previously with reference to  FIG. 12 . A linear display effect is shown in each of  FIGS. 25 and 26 , corresponding with those having axes labelled L 1  and L 2  described earlier; a corresponding description should be taken to apply here also. 
     Referring to  FIG. 27  and  FIG. 28 , an array of electrowetting elements is illustrated similar to that described above with reference to  FIG. 21 . Such electrowetting elements are each triangular in this example. A linear display effect is shown in each of  FIGS. 27 and 28 , corresponding with those having axes labelled L 1  and L 2  described earlier; a corresponding description should be taken to apply here also. 
     Referring to  FIG. 29  and  FIG. 30 , an array of electrowetting elements is illustrated similar to that described above with reference to  FIG. 22 . Such electrowetting elements are each hexagonal in this example. A linear display effect is shown in each of  FIGS. 29 and 30 , corresponding with those having axes labelled L 1  and L 2  described earlier; a corresponding description should be taken to apply here also. 
     It is to be appreciated that  FIGS. 23 to 30  are examples of other array implementations which may be used for the control method described herein. Other arrays described herein may also be used, as the skilled person will appreciate. 
     The above examples are to be understood as illustrative examples. Further examples are envisaged. 
       FIG. 32  shows schematically a system diagram of an example system, for example apparatus  64 , comprising an electrowetting display element, electrowetting display unit, array of electrowetting display elements, or array of electrowetting display units such as any of the examples described above. The apparatus is for example a portable, for example mobile, device such as an electronic reader device such as a so-called “e-reader”, a tablet computing device, a laptop computing device, a mobile telecommunications device, a watch or a satellite navigation device; the apparatus may alternatively be a display screen for installation in any machine or device requiring a display screen, for example a consumer appliance. 
     The system diagram illustrates an example of a basic hardware architecture of the apparatus  64 . The apparatus includes at least one processor  66  connected to and therefore in data communication with for example: a display device control subsystem  68 , a communications subsystem  70 , a user input subsystem  72 , a power subsystem  74  and system storage  76 . The display device control subsystem is connected to and is therefore in data communication with the display device. The at least one processor  66  is for example a general purpose processor, a microprocessor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, a discrete gate or transistor logic, discrete hardware components, or any suitable combination thereof designed to perform the functions described herein. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. The processor may be coupled, via one or more buses, to read information from or write information to one or more memories, for example those of the system storage  76 . The at least one processor may additionally, or in the alternative, contain memory, such as processor registers. 
     The display device control subsystem  68  for example includes electrowetting display element driver components, for use in applying a voltage to any of the electrowetting display elements, to address different such display elements. In examples the electrowetting display elements are configured according to an active matrix configuration and the display device control subsystem is configured to control switching elements such as thin film transistors (TFTs) of the display device via circuitry to control the electrowetting display elements. The circuitry may include signal and control lines such as those described above. 
     The communications subsystem  70  for example is configured for the apparatus to communicate with for example a computing device via a data network, for example a computer network such as the Internet, a local area network, a wide area network, a telecommunications network, a wired network, a wireless network, or some other type of network. The communications subsystem  70  may further for example comprise an input/output (I/O) interface, such as a universal serial bus (USB) connection, a Bluetooth or infrared connection, or a data network interface for connecting the apparatus to a data network such as any of those described above. Content data as described later may be transferred to the apparatus via the communications subsystem. 
     The user input subsystem  72  may include for example an input device for receiving input from a user of the apparatus. Example input devices include, but are not limited to, a keyboard, a rollerball, buttons, keys, switches, a pointing device, a mouse, a joystick, a remote control, an infrared detector, a voice recognition system, a bar code reader, a scanner, a video camera (possibly coupled with video processing software to, e.g., detect hand gestures or facial gestures), a motion detector, a microphone (possibly coupled to audio processing software to, e.g., detect voice commands), or other device capable of transmitting information from a user to the device. The input device may also take the form of a touch-screen associated with the display device, in which case a user responds to prompts on the display device by touch. The user may enter textual information through the input device such as the keyboard or the touch-screen. 
     The apparatus may also include a user output subsystem (not illustrated) including for example an output device for providing output to a user of the apparatus. Examples include, but are not limited to, a printing device, an audio output device including for example one or more speakers, headphones, earphones, alarms, or haptic output devices. The output device may be a connector port for connecting to one of the other output devices described, such as earphones. 
     The power subsystem  74  for example includes power circuitry  80  for use in transferring and controlling power consumed by the apparatus. The power may be provided by a mains electricity supply or from a battery  78 , via the power circuitry. The power circuitry may further be used for charging the battery from a mains electricity supply. 
     The system storage  76  includes at least one memory, for example at least one of volatile memory  82  and non-volatile memory  84  and may comprise a non-transitory computer readable storage medium. The volatile memory may for example be a Random Access Memory (RAM). The non-volatile (NV) memory may for example be a solid state drive (SSD) such as Flash memory, or Read Only Memory (ROM). Further storage technologies may be used, for example magnetic, optical or tape media, compact disc (CD), digital versatile disc (DVD), Blu-ray or other data storage media. The volatile and/or non-volatile memory may be removable or non-removable. 
     Any of the memories may store data for controlling the apparatus, for example components or subsystems of the apparatus. Such data may for example be in the form of computer readable and/or executable instructions, for example computer program instructions. Therefore, the at least one memory and the computer program instructions may be configured to, with the at least one processor, control a display effect provided by the electrowetting display device. 
     In the example of  FIG. 32 , the volatile memory  82  stores for example display device data  86  which is indicative of display effects to be provided by the display device. The processor  66  may transmit data, based on the display device data, to the display device control subsystem  68  which in turn outputs signals to the display device for applying voltages to the display elements, for providing display effects from the display device. The non-volatile memory  84  stores for example program data  88  and/or content data  90 . The program data is for example data representing computer executable instructions, for example in the form of computer software, for the apparatus to run applications or program modules for the apparatus or components or subsystems of the apparatus to perform certain functions or tasks, and/or for controlling components or subsystems of the apparatus. For example, application or program module data includes any of routines, programs, objects, components, data structures or similar. The content data is for example data representing content for example for a user; such content may represent any form of media, for example text, at least one image or a part thereof, at least one video or a part thereof, at least one sound or music or a part thereof. Data representing an image or a part thereof is for example representative of a display effect to be provided by at least one electrowetting element of the electrowetting display device. The content data may include data representing a library of content, for example a library of any of books, periodicals, newspapers, movies, videos, music, or podcasts, each of which may be represented by a collection of data which represents for example one book or one movie. Such a collection of data may include content data of one type, but may instead include a mixture of content data of different types, for example a movie may be represented by data including at least image data and sound data. 
     It is to be understood that any feature described in relation to any one example may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the examples, or any combination of any other of the examples. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the accompanying claims.