NL2015183B1

NL2015183B1 - Display device and text display method that make use of a font defining variable ray direction dependent distributions.

Info

Publication number: NL2015183B1
Application number: NL2015183A
Authority: NL
Inventors: Goedknegt Lennard; Fabrizio Vona Raffaele; Mendes Richard; Zagwijn Jan
Original assignee: Rabbit-Eyes B V
Priority date: 2015-07-16
Filing date: 2015-07-16
Publication date: 2017-02-02
Also published as: WO2017010886A1

Abstract

A display device is provided for displaying text to users that need a reading aid. The device has a display screen that provides for control of distributions of transmitted light intensity as a function of ray direction at each of a plurality of locations of pixels or groups of pixels on the display screen. A processor retrieves font data under control of successive characters in received text data, the font data defining character fields for a set of characters in the font, each character field with a pattern of ray direction dependent light intensity distributions as a function of position in the character field. The patterns are configured to sharpen character outlines in the projection of light from the display screen on a retina, under conditions wherein the reading aid is not used. The processor controls patterns of ray direction dependent light intensity distributions oflight transmitted from successive character locations on the display screen dependent on the retrieved font data for the successive characters.

Description

Title: Display device and text display method that make use of a font defining variable ray direction dependent distributions

Field of the invention

The invention relates to a text display method for assisting persons that normally need reading aids, such as reading glasses, to read text. The invention relates to a device that makes use of such a method, and to a method of computing a font for use in such a method.

Background

Eye problems can make it impossible to focus objects on the retina. Thus for example, it may be impossible to focus an image from the display of a mobile phone on the retina. Conventionally, such eye problems are addressed by use of viewing aids such as reading glasses, i.e. lenses placed closely (e.g. less than five centimeter) in front of the eye or on the eyeball, usually with positive diopter values. In the prior art, it has been proposed to address such problems by special display techniques that are designed to provide for increased sharpness on the retina. For example, in an article titled “Eyeglasses-free Display: Towards Correcting Visual Aberrations with Computational Light Field Displays”, published in the ACM Transactions on Graphics 33(4) (2014), Huang et al disclose an image display method to assist the formation of sharpened retinal images of objects at distances outside a person’s accommodation range. Huang’s method uses a device that controls the dependence of a transmitted pattern of fight intensity dependent on a combination of the position from which the fight is transmitted and the direction in which the fight is transmitted. This differs from conventional display devices in which the transmitted pattern of fight intensity depends substantially in the same predetermined way on the direction at every position where fight is transmitted. Devices that control combined dependence on position and angle have long been known for 3D imaging, where they are used to differentiate the images transmitted light fields for different eyes.

Huang et al use the controlled position+direction dependent light intensity to control the intensity distribution of light in the pupil of an individual eye independently for different locations on the display device from which the light is transmitted. Huang teaches that it is possible to obtain a sharper reconstruction of an image on the retina, by selecting controlled position-direction dependent fight intensity distribution on the display device. Given the image that should ideally be obtained on the retina, and values of the optical parameters that represent the limited focusing effect of the eye, Huang et al compute a position-direction dependent fight intensity distribution that maximizes the sharpness of the image on the retina. The display device uses this computed distribution to transmit the fight pattern.

Huang et al define the computation of the position-direction dependent fight intensity distribution as an optimization problem, i.e. a search for a distribution that minimizes deviations between the desired image and a predicted intensity on the retina. This is a complex computation that cannot be performed simply by adding local pixel contributions. Interactions between pixels at different locations also have to be taken into account. This may be handled by repeatedly recomputing the fight distribution in successive iterations, each accounting for non-local effects of the fight distribution from the previous iteration. Such a computation results in a significant computational burden. Huang et al. illustrate the success of this technique for a number of exemplary images, including an image of an optometrist’s chart with characters of different sizes.

Unfortunately, the complexity of such a computation effectively limits the usefulness of the method to non-real time compiled images. Real time implementation is difficult, and may require so much hardware that consumer applications to for example real time display of messages received on a mobile communication device are not practical.

Among others, it is an object to provide for real time text display to persons that normally need eyeware like reading glasses to read text. A display device is provided for displaying text to users that need a reading - a display screen that provides for control of distributions of transmitted light intensity as a function of ray direction at each of a plurality of locations of pixels or groups of pixels on the display screen; - a processor configured to retrieve font data under control of successive characters in received text data, the font data defining character fields for a set of characters in the font, each character field with a pattern of ray direction dependent light intensity distributions as a function of position in the character field, the patterns being configured to sharpen character outlines in the projection of light from the display screen on a retina, under conditions wherein the reading aid is not used; the processor being configured to control patterns of ray direction dependent light intensity distributions of light transmitted from successive character locations on the display screen dependent on the retrieved font data for the successive characters.

By using a predetermined font that defines ray direction dependent distributions as a function of position on the screen, a display content that the user can better read without the reading glass can be generated without significant computational burden, for example in real-time. The pattern of ray direction dependent intensity distributions is selected to sharpen the character outline on the retina. It deviates from the sharp outline pattern of the character that would be used for conventional imaging when the ray direction dependent intensity distribution is independent of position. The font sharpens the projected outlines on the retina and preferably maximizes the sharpness along reference outlines for the characters for a specific optical correction that corresponds to a reading aid needed by a user.

In an embodiment, the predetermined font data defines alterative patterns for at least one of the characters in the font, dependent on a context of said at least one of the characters, the processor being configured to select one of the alternative patterns when an instance of the at least one of the characters occurs in the successive characters, dependent on a further character that occurs adjacent to said instance in the successive characters, and to control the pattern of ray direction dependent light intensity distributions using the selected one of the alternative patterns.

In this way characters from the context are used to control context sensitive selection of the patterns in order to provide for sharpened and preferably maximally sharpened outlines at positions near a neighboring character. Use of the context in terms of only immediately neighboring characters suffices as a correction. In an embodiment, this only left and/or right context is used. In a further embodiment, the context above and below the character may also be used. However, the above-below context usually has less disturbing effect, which makes it possible to simplify the correction by using only left/right context.

In an embodiment, a distance indication is used to select the font.

In this embodiment, the processor being configured to select the patterns of ray direction dependent fight intensity distributions for the characters from predetermined font data for respective viewing distances, dependent on an indicated distance to a viewer. In a further embodiment, the distance may be measured by the distance sensor. By using distance dependent font selection an optimal effect can be achieved by selecting adapted font according to the viewing distance, to compensate for dependence of the effect of ray direction dependent intensity distribution on distance.

The display screen may be a device that generates the fight itself on or behind the screen surface to transmit the fight from the screen surface, or a device that merely modulates external light in order to transmit it from the screen surface. In an embodiment the display screen comprises a controllable light modulator configured to modulate light intensities transmitted by respective pixels on the display screen and optical refraction elements on the controllable light modulator configured to refract hght transmitted from adjacent pixels into mutually different predetermined ray direction dependent intensity distributions. By controlling the overall intensities of pixels as a function of position with different predetermined ray direction dependent intensity distribution, the ray direction dependent intensity distribution of groups of pixels can be controlled.

Brief description of the drawing

These and other objects and advantageous aspects will become apparent from a description of exemplary embodiments with reference to the following figures:

Figure 1 shows a display device

Figures 2a-c show display screens

Figure 2d shows an example of intensity distribution along a line

Figure 3 shows a character field

Figure 4 illustrates an intensity distribution in a character field

Detailed description of exemplary embodiments

For the generation of the light pattern a font based display device may be used that is conventional except for the use of a display panel that provides for control over combined position and direction dependence of transmitted light (and more generally any device that comprises a light modulator that provides for such control), and the use of at least one special font. Examples of conventional font based display devices are mobile phones, tablets, PCs, e-readers, car dashboard etc. The special font defines a set of characters designed for a specific optical correction, which correspond to a reading aid that the user would need for reading conventional text.

Figure 1 shows a font based display device, comprising a receiver 10, a processor 12, a memory 14 wherein font data is stored and a display screen 16. The font data defines display patterns for a predetermined set of characters. Processor 12 is coupled to receiver 10, memory 14 and display screen 16. In operation, receiver 10 receives text information, such as an SMS message, a web page, an electronic document or a text file. From the text information a sequence of successive characters can be derived (e.g. because text information contains successive character codes or successive characters can be obtained by decompression). Processor 12 extracts identifications of characters from the text information, and uses the identifications to retrieve font data corresponding to the identified characters from memory 14. Memory 14 may be any type of storage device, such as a semi-conductor memory (e.g. a non-volatile memory), a disk memory etc. Processor 12 uses the retrieved font data to control display screen 16. A font defines image generation parameters for each of a set of characters. In an embodiment, the set of characters includes at least the letters a-z in capitalized and non capitalized versions, and the digits 0-9. In a conventional font, each character is an image defined by an outline (or outlines) that defines a sharp border between virtually “inked” and not inked image locations in a pattern of fight intensities that represents the character. Thus, a conventional font defines the pattern of fight intensity only as a function of position. In the present display device, the font may be considered to define a pattern of distributions of transmitted fight intensity as a function of ray direction relative to the display device independently for different positions, or groups of positions on the display device for each character. The dependence on the ray direction may be stronger than the dependence on position, for example at positions near the outline of the character in the pattern.

Processor 12 preferably uses a font that is particular to an optical correction. As used herein, an optical correction is a correction that could be made by a reading glass to form a focused image of conventional characters on the retina of the eye of a human user that normally needs such a reading glass to do so. The font is designed to provide a sharpened character image on the retina of such a user when such a reading glass is not used, wherein the provided character image on the retina represents the outline of the character.

In an embodiment, a memory 14 contains a collection of fonts, each for a different optical correction. In this embodiment, processor 12 is configured to select a font to be used based on an indication based on a predetermined optical correction. Alternatively, a collection of fonts may be stored elsewhere and processor 12 may download a dedicated font for a predetermined optical correction into memory 14 prior to use. In yet another embodiment, processor 12 may be configured to compute the characters of such a dedicated font for the predetermined optical correction. As will be explained, this may be done by executing a search algorithm that searches for a character field that minimizes a measure of difference between a nominal character and the predicted intensity distribution obtainable by projecting the pattern on the retina of a user in need of the optical correction. The required optical correction may be defined for example by a diopter value of a reading glass that would be needed and optionally by an intended viewing distance and viewing angle if no predetermined standard distance and angle is used.

The display device may be configured to input a selection of the predetermined optical correction for a particular user from a user interface. The input of parameters like diopter number astigmatism corrections may be used. An diopter may be an effective diopter that accounts for the adaptive power of the eye, by using a remaining required diopter correction when the eye lens is adapted to reading as much as possible in view of the lens power. Optionally, lens power may be used as an additional parameter. Because lens power is related to age, age may be used as an optional parameter instead of lens power. Diopter of "myopia" or "hyperopia", concerns the refraction capability of eyeball. However, the cause of myopia and hyperopia is different. Myopia is mainly caused by the deformation of eyeball, often in young people. Hyperopia, which often occurs in the elderly, may be caused both by hardening of the eyeball muscle and hardening/thickening of the lens. The power of the lens, which is a parameter that depends on age, may be considered in addition to the diopter. For calculating the focus distance, the effective diopter equals the diopter of the relaxed eye (e.g. a relaxed eye diopter) plus the lens power (e.g. 2D-8D, based on age) plus the hyperopia diopter. For instance, when the diopter is 5.75, and the assumed power of the lens is 2, the effective diopter needed for glasses is in fact 3.75.

In an alternative embodiment, the display device may be configured to select the predetermined optical correction interactively. Processor 12 may be configured to execute an interactive selection process by causing display of characters from successive fonts for different optical correction, inputting feedback responses from user, and selecting the successive fonts based on the feedback responses until a feedback response indicates that the font to be used has been displayed.

In an embodiment the light that is transmitted with ray direction dependent intensity distribution is colored fight, fight with different colors being transmitted from different locations. In another embodiment, the fight that is transmitted with ray direction dependent intensity distribution may be white fight.

Sharpening

Although a specific theory behind the effect of sharpening is not needed to enable use of the display device, the following may be noted about the theory to illustrate the properties of the font. A human eye that needs a reading glass cannot focus the surface of the display device on the retina when the display device is held at a reading distance (e.g.at 0.4 or in a range of 0.2 to 0.6 m). Instead the display surface would be in focus only on a virtual focal surface, which lies further from the eye than the retina when the user needs reading glass with positive diopter number (a convex lens).

This means that fight intensity on a point on the retina is the sum of fight intensities of rays from different points on the surface of the display device. There is a strict correlation between the ray directions and the locations of these different points. This can be seen by virtually considering the point on the retina as a pin-hole and tracing the rays from this pin-hole to their in-focus target positions on the virtual focal surface, which correspond to positions on the display device from which the rays emerge. The required ray directions for the different points correspond to the direction from the pin-hole to the in-focus position.

If all pixels on the display device would transmit rays only in the same single direction, the pixels would be projected onto the retina in the same spatial relation as they occur on the display screen. But in reality, a pixel on the display device does not transmit fight in a single ray direction but in a range of ray directions, or more generally with a distribution of fight intensity as a function of ray direction. This has the effect of distributing pixel intensity with different offsets over the retina, thus widening the projection of the pixel on the retina and making its boundary less sharp. The projection of different pixels will overlap on the retina.

The ray direction dependent intensity distribution of fight produced by the display screen will be referred to as a fight field. For a conventional font, the ray direction dependent intensity distribution in the fight field is the same for all pixels, and the shape of the distribution of projected light on the retina is the same for each pixel. As a result, with the conventional font, light transmitted from pixels on either side of the outline of a character wih be projected distributed over overlapping retinal locations near the character outline, which gives rise to reduced sharpness of the character outline on the retina.

The present device uses a font wherein the light field has a different ray direction dependent distribution of light intensity for different pixels or groups of pixels. This results in different intensity distributions of the projected light from the pixel or group of pixels. The present font uses patterns of ray direction dependent distribution wherein the ray direction dependent distribution varies as a function of the location of pixels or pixel groups in the pattern. The pattern enhances sharpness of the character outline by selectively adapting the ray direction dependent intensities distributions of pixels or groups of pixels dependent on their position in the pattern.

The pattern on the display device need not exhibit a sharp localized outline, but it is intended to make a user perceive such a sharp outline. For the sake of definition a virtual character outline on the display device may be defined as a virtual back-projection of the sharpened outline on the retina from the retina to the display device, that would be obtained using only predetermined ray directions for the back-projection, e.g. only ray directions perpendicular to the display surface of the display device.

In the patterns for the characters of the font, the ray direction dependent intensity distribution from pixels or groups of pixels dependent on the location of the pixels or groups of pixels relative to the virtual character outline on the display device. As the locations on the brighter side of the virtual character outline becomes closer to the virtual character outline, the ray direction dependent intensity distribution contains decreasingly less intensity in ray directions with a direction component towards the virtual character outline and increasingly more intensity in ray directions with a direction component away from the virtual character outline. Similarly, locations near the virtual character outline on the darker side may have more ray direction dependent intensity in ray directions with a direction component towards the virtual character outline than in other ray directions. Such redistributions of intensity as a function of ray direction sharpen the outline. By means of optimization a pattern of ray direction dependent distributions for different pixels or pixel groups in the character field can be selected that optimizes a sharpening criterion.

As used herein, “sharpened” means that the intensity transition in the across the character outline (e.g. between 10% and 90% of the range between the maximum and minimum intensity) occurs over a smaller distance on the retina. This need not be the case everywhere along the character outline, preferably it is made to occur over at least 50% or 80% of the length of the character outline and more preferably along the entire outline. It is preferred that the font sharpens all characters in the font, but at least a majority of the characters in the font is sharpened. The font provides such sharpening by making the ray direction dependent intensity distribution for pixels or groups of pixels for the characters dependent on the location of the pixel or group of pixels in the character field displayed on the display device, relative to the location of the virtual character outline.

Although the sharpening effect has been described in terms of the human retina of the sake of explanation, it should be appreciated that it is an optical effect that can be defined independent of the optical system (including the user’s eye) that is actually used to project the light. The retina is merely an example of a surface on which light from the display screen can be projected and that lies displaced from a virtual focal surface. A virtual focal surface is a surface where the optical system puts the display screen in focus. In the context of reading glasses the position of the virtual focal surface depends on the distance to the display device, but for definition purposes the display device may be assumed to be at a typical reading distance of say 0.4 meter from the eye, or another distance in a reading range of 0.2-0.6 meter. The surface on which light from the display screen is projected usually lies at a distance in front of this virtual focal surface.

The sharpening effect of the font can be generated and evaluated by projecting the light on any surface at a corresponding distance to the virtual focal surface, optionally also dependent on other optical correction parameters, but independent of which optical system (including the user’s eye or not) is used to perform the projection. The distance between the surface on which the light is projected and the virtual surface are in one to one relation with the parameters of a lens that would need to be added to the optical system as a reading glass to focus the display screen on the surface on which the light is projected.

When the font is used, reading glasses are not needed. Instead characters are used that each have a pattern of ray direction dependent intensity distributions, wherein the distributions depend on the location of the pixels or groups of pixels in the pattern on the display device from which the ray direction dependent intensity distributions are transmitted. The font controls ray direction dependent intensity distributions that are designed to sharpen the character outlines on the surface on which the light is projected, and preferably to maximize the sharpness.

Compared to use of the same ray direction dependent intensity distributions for all positions in the character on the display screen, the font modifies at least the ray direction dependent intensity distributions of pixels or group of pixels that are located on or adjacent the virtual character outhne on the display surface. To such pixels or groups of pixels the font assigns differently distributed ray direction dependent intensity distributions. Redistributions are used that reduce intensity in ray directions with a direction component in the direction of the darker side of the virtual character outline.

Exemplary display screens

Fig. 2a,b show an example of a display screen, wherein the ray direction dependent distribution of light intensity in the light field is created with a display device that contains a pin-hole array. Fig. 2a shows a partial side view of the device in cross-section. The display device comprises a display matrix 200 and a mask layer 202 at a fixed position relative to display matrix 200. The display device may comprise spacers (not shown) to fix mask layer 202 at a fixed relative position. Display matrix 200 comprises a two dimensional array of pixels, whose intensities are individually controllable. The display matrix may comprise a backlight source, and an LCD matrix or another spatial light modulator, or it may comprise an array of light sources such as LEDs. Mask layer 202 is mounted above display matrix 200, in parallel with the surface of display matrix 200 at a distance L from the surface.

Figure 2b shows a top view of part of mask layer 202. Mask layer 202 comprises a two dimensional array of pin-holes 204. The number of pinholes 204 is smaller than the number of pixels of display matrix 200. One pin-hole may be provided for every block of NxM pixels of display matrix 200 (e.g. N=M=5). When a periodic array of pixels is used in display matrix 200, pin-holes 204 similarly form a periodic array, with periods in the x and y directions that are N and M times lower than those of the pixels of display matrix 200.

For practical purposes, it may be assumed that each pin-hole 204 transmits light to the viewer’s eye at most from a corresponding block of NxM pixels display matrix 200 (one block 206 of pixels of display matrix 200 indicated by dashed fines). The direction of maximal light transmission (schematically indicated by dashed fines for one block in figure 2a) is different for different pixels of display matrix 200 in the block 206, in correspondence with the relative locations of the pixels in display matrix 200 with respect to the pin-hole 204 in mask layer 202. The distance is not shown to scale. The distance L between mask layer 202 and display matrix 200 may be selected so that the angle between the direction of a central pixel location in the block 206 of display matrix 200 and the direction of peripheral pixel locations in that block is about five degrees for example.

Fig. 2d shows an example of intensity values of transmitted fight along a fine of pixels of display matrix 200 for displaying an isolated letter “I”, i.e. a vertical bar, with 5x5 blocks. In figure Y sub-pixel positioning is assumed. The long direction of the letter T is perpendicular to the fine of pixels. The position of the pixels in display matrix 200 is plotted horizontally along the x-axis and intensity is plotted vertically. The range of values of positions of the pixels extends from 0-50, i.e. over the length of ten blocks. The pin-holes are located over positions nx5 (n=0, 1, ...).

As result, fight transmitted from display matrix 200 at pixels positions 10 and 15 emerges from mask layer 202 with a peak direction perpendicular to the surface of mask layer 202. Light transmitted from display matrix 200 at pixels position 1 emerges with a peak direction left of the perpendicular direction. The fact that there are two such positions corresponds to the fact that sub-pixel positioning is used, which distributes fight over adjacent positions. Light transmitted from display matrix 200 at pixels positions 14, 29, 33, 38, 47 emerges with peak directions increasingly further right of the perpendicular direction.

Once this fight reaches the eye of a user in need of reading glasses, this has the effect of concentrating intensity from all these pixel positions on a narrow region of the retina. The eye is only able to form a focused image of the display device in a virtual plane within the eye in front of the retina. In this virtual plane, the pixels from different positions on display matrix 200 are imaged at different positions. But because of the difference between the peak directions of the fight emerging from mask layer 202 due to the different pixel positions on display matrix 200, the fight at different positions in the virtual plane has different peak directions. Due to the fact that the peak directions from mask layer 202 are increasingly directed more to the right for increasing x-positions, the light converges beyond the virtual plane, which results in a sharpened image on the retina.

The distance between the virtual plane and the retina depends on the required eye correction, and accordingly the optimal distribution of intensity depends on this eye correction. In figure Y corrections for a diopter of six are shown by way of example. For an optimal result with an eye that needs a weaker correction the light intensity distribution may be provided over a narrower range of pixel positions on display matrix 200, with a larger range of peak directions of light emerging from mask layer 202. For an optimal result with an eye that needs a stronger correction the light intensity distribution may be provided over a wider range of pixel positions on display matrix 200, with a smaller range of peak directions of light emerging from mask layer 202.

Although figure 2d illustrates specific values for a character “Γ and use of a mask in the display device, it illustrates the more general principle that the ray direction dependent distribution of fight intensity is made position dependent. In this particular embodiment, each pin-hole 204 produces its own ray direction dependent distribution of fight intensity as defined by the position dependent intensity on display matrix 200 in the block of pixels from which observable fight its transmitted through the pinhole.

The figure illustrates the more general principle that the angle of maximum or minimum character intensity in the ray direction dependent distribution of fight intensity shifts dependent on the position relative to the character outline from which the ray direction dependent distribution of fight intensity is transmitted. The angular directions of the maximum or minimum intensity contribution for the same character from different display positions at least partly converge towards the same position on the retina. The angle at which the character related distribution rises and/or falls in correspondence with cross-section of the stem of the character similarly shifts dependent on the position relative to the character outline from which the ray direction dependent distribution of light intensity is transmitted.

Figure 2c shows another embodiment of the display screen in cross section. In this embodiment, the display screen comprises a backlight source 20, a spatial light modulator 22 located in front of backlight source 20, and an array of lenses 24 in front of spatial light modulator 22. Backlight source 20 may comprise an array of LEDs for example. Spatial light modulator 22 defines an array of pixels and provides for control of the individual pixels. Spatial fight modulator 22 may comprise an LCD array for example. Processor 12 controls spatial fight modulator 22 dependent on the retrieved font data corresponding to the identified characters. The lenses in array of lenses 24 define the distribution of intensity over ray directions of transmission of fight passed at different pixel locations in spatial fight modulator 22. Lenses 24 that define different ray directions are provided interleaved with one another as a function of position on the device. Thus, the intensity distributions of fight as a function of ray direction of different ones of the interleaved pixels are different.

Although an embodiment with a display screen is disclosed, wherein spatial fight modulator 22 is combined with backlight source 20, it should be appreciated that a spatial fight modulator 22 without a backlight source may suffice. For example, a device with a back reflector behind spatial fight modulator 22 may be used, or a transparent device, that relies on background fight as a fight source. Similarly, instead of a spatial fight modulator 22 that modulates transmission of back fighting, a spatial fight modulator 22 that modulates reflection of incident fight may be used. As another example, spatial fight modulator 22 may be a device that generates the modulated fight directly, e.g. by means of an array of LEDs.

Although the cross-section shows curved lens shapes in one direction, it should be appreciated that the curvature in two dimensions may be used, i.e. also in the direction perpendicular to the plane of the drawing.

In an embodiment, array of lenses 24 is organized as an array of 2d blocks, a lens or lenses being provided for each block to direct light from pixels in the block to respective intensity distributions from a set of different intensity distributions of light as a function of ray direction with which display screen 16 is configured to transmit fight. The font data defines character fields for respective characters. When blocks of pixels are used, each character field corresponds to a rectangle of pixels locations on the screen that contains a plurality of such blocks and optionally also fractions of blocks. Different characters may have character fields of different size.

In an embodiment the pixels with different colors may be used, e.g. red, green and blue pixels. For this purpose, the device may comprise color filters or colored fight sources. In another embodiment, substantially white pixels may be used.

Figure 3 shows an example of the organization of a character field 30. In this example, the character field is organized into blocks 32 (only one labeled by way of example) of locations for a plurality of different fight directions and the character field contains a plurality of such blocks. It is not necessary that the interleaving of pixels with different ray direction dependence is on a block by block basis. But in each case a character field contains pluralities of pixels of each available ray direction dependent fight intensity distributions.

In this embodiment, the character field for an identified character is a rectangular array of values that define relative fight intensities to be transmitted by display screen 16 as a representation of the identified character. Different locations in the array of values correspond to different locations on the display screen 16, and hence also to different ray direction dependent fight distributions defined by the lenses.

In the embodiment of figure 2 the display device provides for control fight of overall intensity of pixels that produce different predetermined intensity distributions of fight as a function of ray direction. Pixels that produce different predetermined distributions are provided interlaced with one another on the display screen, e.g. in rectangular blocks, each block containing pixels for the same set of predetermined distributions of fight as a function of ray direction.

The embodiment of figure 2 can be said to provide for control of the ray direction intensity distribution of fight from a pattern of groups of pixels as a function of ray direction, by means of relative adjustment of the overall intensities of the pixels in such a group that produced different ray direction intensity distributions. Accordingly, the pattern used for the groups of pixels can be used to sharpen character outlines as described in the context of figure 1.

Alternatively, the effect can be explained for this type of display screen in terms of a pattern of overall intensities of pixels that produce different predetermined ray direction dependent distributions, each of which the overall pixel intensities can be controlled. Projection of such a pixel results in an intensity distribution as a function of position on the retina that depends on the predetermined ray direction dependent intensity distribution of the pixel. Pixels with different predetermined ray direction dependent intensity distribution result in different projected position dependent intensity distributions on the retina.

The font sharpens the character outlines by assigning the pattern of overall pixel intensities to pixels in the character field according to the way in which the ray direction dependent intensity distribution extends to ray directions with components perpendicular to the virtual character boundary. In the pattern, the dependence of the overall intensity on the ray direction dependent distribution can outweigh dependence on distance to the character outline. Pixels of which more of the projected intensity distribution extends to the darker side of the character outline have relatively less assigned overall intensity than pixels of which less of the projected intensity distribution extends to the darker side. This is so even if the latter pixels he at the same distance to the darker side of the character outline as the former or closer to it. (A first pixel is closer to the darker side of the character outline than a second pixel when, if both would have the same predetermined ray direction dependent distribution, more of the projected intensity distribution from the first pixel would extend to the darker side than from the second pixel).

The font sets the pattern of modulation of the pixels dependent on their location relative to a virtual character outline in the character field on the display surface and the ray direction dependent intensity distribution of the pixel that is modulated, given the expected projected intensity distribution of the projection of the pixel on the retina as determined by its position in the character field and its predetermined ray direction dependent intensity distribution.

In patterns of the font, the fight intensities of pixel locations on the brighter side of the outline are lower for pixels with ray direction dependent intensity distributions that lead to more intensity in ray directions with a component across the outline than for ray directions that lead to less intensity in such ray directions. Similarly, the fight intensities of pixels on the darker side of the outline may be selectively higher for pixels with distributions that have more ray directions with a component toward the character boundary than away from the character boundary.

As a result, in characters of the font, the pattern of overall intensity of pixels near the character outline is usually more strongly correlated with the average ray direction in the ray direction dependent distribution of the pixels than on the pixels distance to the character outline. When the pixels are arranged in blocks, and the average ray direction changes monotonously along the axis directions of the block, this has the effect that for blocks on or near the character outline the dependence of the overall intensities on position of the pixels in the block exhibits the shape of the outline rather than its position relative to the block.

Figure 4 illustrates an intensity distribution as a function of position on the display device in a character field for the character “a”. It will be remembered that different pixel positions correspond to different hght intensity distributions as a function of ray direction. As may be noted, the intensity distribution as a function of position on the display device does not provide a binary “inked”/”not-inked” pattern on the display device. Rather the intensities of pixels near the character outline vary dependent on the intensity distributions of the pixels as a function of ray direction. The illustrated character field is designed to produce a hght distribution on the retina that approximates such a conventional text character pattern, but this does not mean that it forms such a conventional outline pattern on the display device.

Fonts

In an embodiment, the font data in memory 14 defines character fields for each character in a predetermined set of characters. Optionally, the font data in memory 14 may comprise character fields for each of those characters at a plurality of point sizes. The content of these character fields is computed before the text information is received that will be displayed using the character fields. For each character in the predetermined set of characters this computation is performed as a function of conventional (e.g. outline) input character pattern for that character and the optical correction, or other optical parameters that are specific for a user and optionally dependent on use parameters such as the eye-device distance for which the font will be used. The same optical parameters are used in the computation for each character and for all point sizes, if a plurality of point sizes is used.

The computation may be performed by a computer that need not be part of the display device. The computer may execute an optimization algorithm that is configured to perform a search for a set of values in the character field that minimizes a measure of difference between the input character outline pattern and a predicted pattern on the retina according to the user’s optical parameters. For example, a sum of squared intensity differences may be used. In the measure of difference, different weights may optionally be used to emphasize differences between the intensity patterns along the character’s outline.

Although the definition of the font has been described for a single eye, it should be appreciated that alternatively, the font may be designed to provide for correction for a pair of eyes, each with its own set of optical parameters. In this embodiment, use may be made of predictions of the retinal intensity distributions in the two eyes, when they are located a given distance apart and the search may be used to minimize a combined measure of the difference between the input character outline pattern and predicted patterns on two retinas.

Context sensitive character patterns

Due to optical interaction effects between individual characters at different locations in the text, the actual light patterns on the retina may differ from the patterns predicted for isolated characters of the font. This can affect sharpness. In an embodiment, this effect is reduced by context sensitive selection of characters fields. The character field for a character is selected dependent on another character that immediately precedes or follows the character in the text to the left or the right in the displayed text respectively, or dependent on a combination of the immediately preceding and following characters.

For text characters it is possible to account for non-local effects by a context dependent substitution of an alternative of an individual character, because context effect on the adaptation of the font data need not extend further than the immediate neighbors. The adaptation to a character on the left of a central character need not affect adaptations to the character on the right and vice versa, when the effect on retinal imaging extends only over a limited distance. For this reason only the immediately left and/or right neighbors need be taken in account as context.

In an embodiment, context sensitive retrieval of alternative font data is used. In this embodiment, a plurality of alternative character fields is stored in memory 14 for at least part of the characters in the predetermined character set. Processor 12 is programmed to select between different alternatives for a same character dependent on another character that immediately precedes or follows the character in the text to the left or the right in the displayed text respectively, or dependent on a combination of the immediately preceding and following character. Processor 12 uses the retrieved character field to control display screen 16.

Methods for providing context sensitive retrieval of alternative font data are known per se for fonts that represent handwritten text. In that case context sensitive retrieval is used to account for the fact that handwriting cannot be partitioned into boxes that each contain only a single character. Thus, context sensitive retrieval accounts for extensions of handwritten characters that extend into the box of the next character. In the present case, context sensitive retrieval is used to compensate for optical interaction of fight from inside the boxes of different characters.

The content of the alternative character fields may be computed before the text information is received that will be displayed using the character fields. This computation may be performed for each character in combination with all possible context characters, as a function of the outlines of the character and the character(s) in its possible contexts, dependent on the optical correction for which the font is computed. This computation may be performed by a computer that need not be part of the display device.

The computer may execute an optimization algorithm that is configured to perform a search for a set of values in the character field that minimizes the measure of difference between, on one hand, the input pattern of the character outline and the outline of its context character(s) and, on the other hand, their predicted pattern on the retina. For each character, such searches may be performed for combinations with all different possible neighboring characters.

In practice, the different alternatives usually only differ significantly from each other, if at all, in one or two rows of blocks at the left and right edge of the character field. This makes it possible to compose the alternatives for a character field from a context independent central block with context dependent alternatives left and right columns on either side. This may be used to simplify the computation of the character fields, by computing the left column alternatives for all different neighbor characters on the left without using a character on the right (or without changing the context on the right). Mutatis mutandis the right column alternatives for all different neighbor characters on the right can be calculated. Processor 12 may be configured to compose the alternative character field for a character at run time by selecting the left and right columns dependent on the characters to the left and right respectively and by combining the selected left and right columns with the context independent central part. This may also be used to derive underlined character versions from non-underlined versions.

In an embodiment, the font contains similar alternative character fields for combinations of a character in contexts with different subscripts and/or superscripts.

Dependence on viewing distance and direction

In the preceding embodiments it has been assumed that the user will use the display device at a predetermined distance from the eyes in a predetermined general direction from the eyes, e.g. substantially in front of the user’s head. A font optimized for this predetermined distance and direction is used.

In a further embodiment, the display device may comprise a plurality of stored fonts for respective different distances. In this embodiment, processor 12 may be configured to input an indication of the distance from the display device to the user’s eyes or face from the distance sensor and to control selection of the font dependent on the input distance. In this way readability of the text can be improved without performing new font computation.

In a further embodiment the display device comprises a distance sensor for providing the indication of the distance. Distance sensors are known per se. For example, a camera in the display device may be used. In an embodiment, the distance sensor may comprise a computer program, executed by processor 12, to measure a distance between the user’s eyes in an image from the camera. This distance between the user’s eyes may be used as an indication of the distance to the eyes. However any kind of distance measurement may be used.

In this further embodiment or another embodiment, a similar sensor based compensation for dependence on the direction from the display device to the user’s eyes may be provided for, using a direction sensor and a plurality of fonts for different directions.

Claims

A display device for displaying text to users in need of a reading aid, said device comprising - a display screen providing control of distributions of emitted light intensity as a function of beam direction on each of a plurality of locations of pixels or groups of pixels on the display screen; - a processor configured to retrieve font data under control of successive characters in received text data, wherein the font data defines character fields for a set of characters in the font, each character field having a pattern of beam direction-dependent light intensity distributions as a function of position in the character field, wherein the patterns are configured to sharpen character outlines in the projection of light from the display screen to a retina, under conditions in which the reading aid is not used, wherein the processor is configured to have beam direction dependent light intensity distributions patterns of light emitted from successive character locations on control the display screen depending on the retrieved font data for the consecutive characters.

A display device according to claim 1, wherein the predetermined font data defines alternative patterns for at least one of the characters in the font, depending on a context of said one of the characters, wherein the processor is configured to print one of the alternative patterns select when there is a copy of the at least one of the characters in the successive characters, depending on a further character occurring next to said instance in the successive characters, and to control the pattern of beam direction dependent light intensity distributions using the selected one of the alternative patterns.

A display device as claimed in claim 2, wherein the processor is configured to select one of the alternative patterns depending on a pair of further characters occurring in the successive characters to the left and right of said instance.

A display device according to any preceding claim, wherein the processor is configured to receive a distance indication and to select the patterns of beam direction-dependent light intensity distributions for the characters from predetermined font data for respective viewing distances, depending on the distance indication.

A display device according to claim 4, provided with a distance sensor configured to apply said distance indication to the processor based on a distance to the viewer measured by the distance sensor.

A display device according to any one of the preceding claims, provided with a memory in which the predetermined font data for the system of characters is stored, in which the processor is configured to perform said retrieval of font data from said memory.

A display device according to any preceding claim, wherein the display screen is provided with a controllable light modulator configured to modulate light intensities emitted by respective pixels on the display screen, and with optical refraction elements on the controllable modulator configured to transmit light through adjacent pixels is transmitted to break into mutually different predetermined beam direction dependent intensity distributions.

A display device according to claim 7, wherein the patterns in the character character fields of the font define pixel control signals for the controllable light modulator, which control signals for at least a part of the characters in the font provide for transmission of more light intensity of pixels for which the predetermined beam direction-dependent intensity distributions project more light onto a brighter side of the character's circumference than from pixels for which the predetermined beam direction-dependent intensity distribution projects less light onto a brighter side of the character's circumference from corresponding distances to the perimeter.

A display device according to claim 7 or 8, wherein the optical refraction elements in elements or groups are organized for respective blocks of pixels, each element or group providing refraction of the same system of a plurality of predetermined beam direction dependent intensity distributions.

A display device according to claim 9, wherein the patterns in the character fields for the characters of the font define pixel control signals for the controllable light modulator, which control signals for at least a part of the characters in the font provide for relative light intensities of the pixels in the font. block that is close to the circumference of the character depending on the extent to which the predetermined beam direction dependent intensity distributions result in projection of light on the bright side of the circumference.

A display device according to any one of the preceding claims, wherein the pattern for each of a plurality of the characters provides light intensity distributions that distribute more of the light intensity to light directions affecting the retina on a brighter side of the character outline and less on beam directions affecting the retina on a darker side of the character circumference, compared to beam direction dependent adhesion intensities.

A display device according to any preceding claim, wherein predetermined font data is specific to an optical correction for an individual user.

A display device according to claim 12, wherein the patterns of at least a portion of the characters of the font are patterns that each optimize a degree of difference between a perimeter of a reference character and an intensity distribution available with the pattern on the retina of a user who needs the optical correction.

14. A machine-readable medium provided with font data defining a font of characters, wherein the font data defines character fields for characters, each character field having a pattern of beam direction dependent intensity intensity distributions as a function of position defining the character field for controlling pattern transmission according to the pattern from a display screen, wherein the beam direction dependent intensity gains.

A machine-readable medium according to claim 14, wherein the patterns are configured to sharpen character outlines in the projection of the handle of the display screen obtained on the retina of eyes in need of a predetermined correction, under circumstances in which a separate reading aid is not used, wherein the patterns of at least a part of the characters of the font are patterns that each realize a minimization of a measure of difference between a perimeter of a reference character and an intensity distribution that is available with the pattern on the retina of a person who needs the optical correction when broadcast according to the pattern from a display screen.

A method of calculating font data for controlling display of light from a display screen that provides control of light intensity distributions as a function of beam direction at each of a plurality of locations of pixels or groups of pixels on the display screen, which method includes calculating font data defining character fields for individual characters, each character field defining a pattern of beam direction dependent light intensity distributions as a function of position of light pattern distributions in the character field for controlling light transmission according to the pattern from a display screen, and assigning beam direction dependent intensity intensity distributions that contain decreasingly less intensity in jet directions with a directional component in the direction of a virtual character outline and increasingly more intensity in jet directions with a directional component away from the virtual character outline, to the locations at d he clear side of the virtual character outline is closer to the virtual character outline.

A method according to claim 16, comprising calculating alternative patterns for at least one of the characters in the font, depending on a context of said at least one of the characters, for contexts in which respective different characters occur to the left and / or right of said at least one of the characters.

A method according to claim 16 or 17, comprising performing a search algorithm that searches for patterns that minimize a degree of difference between a reference circumference of a character and an intensity distribution obtainable with the pattern on a retina of a person who has a designated optical correction needs, as characterized by a diopter value and / or lens power, when transmitted according to the pattern from a display screen.

A computer program product comprising a program of instructions for a programmable computer which, when executed by the computer, cause the computer to perform a method of any of claims 16-18.

A method of displaying text to users who need reading glasses for a predetermined optical correction, the method comprising - receiving text data defining successive characters for display; - retrieving predetermined font data under control of the consecutive characters, wherein the font data defines character fields for the characters, wherein each character field contains a pattern of beam direction-dependent light intensity distributions as a function of position in the character field, the patterns being configured to project character outlines in projection of sharpened from the display screen obtained on the retina of eyes in need of optical correction, under conditions where the reading glasses are not used; - controlling patterns of beam direction dependent intensity intensity distributions of light emitted from for successive character fields on a display that provides control of distributions of intensity intensity as a function of beam direction on each of a plurality of locations of pixels or groups of pixels on the display screen, depending on the retrieved font data for the consecutive characters.