WO2012074393A1

WO2012074393A1 - An electronic display with improved grey level partition

Info

Publication number: WO2012074393A1
Application number: PCT/NL2011/050816
Authority: WO
Inventors: Wieger Markvoort; Bart Peeters; Marcel Van Mil; Petrus Van Lieshout
Original assignee: Polymer Vision B.V.
Priority date: 2010-12-01
Filing date: 2011-11-29
Publication date: 2012-06-07
Also published as: CN103329189A; CN103329189B; EP2646998A1

Abstract

The invention relates to an electronic display comprising a plurality of pixels, each pixel being operable within a pre-defined intrinsic number of grey levels, the display being capable of displaying an image comprising a plurality of adjacent pixels, wherein said pixels are provided with different dimensions for generating an image having a further number of grey levels being higher than the intrinsic number of grey levels, wherein the pixels having different dimensions are arranged to enable regrouping of pixels, whereby in at least a portion of a pixel sequence two pixels having a smaller size are provided between the pixels having the largest size. The invention further relates to an electronic apparatus and a method of manufacturing an electronic display.

Description

Title: An electronic display with improved grey level partition

FIELD OF THE INVENTION

The invention relates to an electronic display providing grey level capability, wherein a grey scale is effectuated using area modulation.

The invention further relates to an electronic apparatus comprising an electronic display whose grey level scale is effectuated using area modulation.

The invention further relates to a method of manufacturing an electronic display whose grey level scale is effectuated using area modulation.

BACKGROUND OF THE INVENTION

An embodiment of the electronic display as is set forth in the opening paragraph is known from US 5, 254, 981. The known electronic display is operable using the electrophoretic principle wherein each pixel is being electrically energized for obtaining a desired grey level selectable from pre-defined intrinsic grey levels.

In the known display in order to achieve grey level modulation, the adjacent pixels may be addressed and energized in such a way, for example, by altering black and white pixels, that their cumulative appearance will be perceived by a human eye as a certain (intermediate) grey level. The number of thus obtained grey levels is a function of the display's resolution.

It is a disadvantage of the known display that by carrying out area modulation the overall resolution decreases by combination of individual pixels into envisaged grey areas.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an electronic display having an enhanced grey level scale without substantially hampering the display resolution.

To this end an electronic display according to the invention comprises a plurality of pixels, each pixel being operable to any of the grey levels within a pre-defined intrinsic number of grey levels, the display being capable of displaying an image comprising a plurality of adjacent pixels, wherein said pixels are provided with different dimensions for generating an image having a further number of grey levels being higher than the intrinsic number of grey levels, wherein the pixels having different dimensions are arranged to enable regrouping of pixels, whereby in at least a portion of a pixel sequence two pixels having a smaller size are provided between the pixels having the largest size.

In an embodiment of the electronic display it is operable using the electrophoretic principle. Generally, the display operable using the electrophoretic principle comprises a plurality of capsules provided with black particles or white particles or black and white particles which may drift inside the capsules in accordance with the applied voltage. In order to change image content on an electrophoretic display, the new image information is written for a certain amount of time (100ms - 800ms) using suitable electrodes connected to the capsules. As the refresh rate of the active-matrix is usually higher than these values, such difference results in addressing the same image content during a number of frames (5 to 40 frames at a frame rate of 50 Hz). Addressing of the electrophoretic display containing both black and white particles from black to white, for example, requires the pixel capacitors to be charged to a negative voltage during 200ms to 250ms. During this time the white particles drift towards the top (common) electrode, while the black particles drift towards the bottom (active-matrix backplane) electrode. Switching to black requires a positive voltage. At 0V on the pixels the electrophoretic capsules do not switch, i.e. the black and white particles do not move. Addressing the electrophoretic display for a short time with a certain voltage (for example, pulse width modulation) will result in a situation in which a mixture of white and black particles is visible. Because the particles are very small the human eye will integrate the ratio of black and white particles to a certain grey level. Grey levels generated in this way referred to as intrinsic grey levels of the electrophoretic display.

By suitable addressing, so-called intrinsic grey levels can be generated. The technical measure of the invention is based on the insight that due to the limited spatial resolution of the human eye, it is possible to generate grey levels using only a few (e.g. two) intrinsic grey levels and enhance the grey scale by combining the intrinsic grey level with a possibility to modulate an area ratio of the pixels available in the display.

For this purpose the pixels are provided with different dimensions for generating an image having a further number of grey levels being higher than the intrinsic number of grey levels, wherein the pixels having different dimensions are arranged to enable regrouping of pixels, whereby in at least a portion of a pixel sequence two pixels having a smaller size are provided between the pixels having the largest size. It will be appreciated that pixel area modulation is known per se and is discussed with reference to Figure 1. However, in the known pixel area modulation principle the resulting pixels have a substantially larger dimension than the original pixels which disadvantageous ly reduces the overall resolution of the display.

In accordance with the invention, however, the rearranged pixels do not substantially deviate from the original size of the largest pixel provided in the display's hardware. Accordingly, in the invention the pixel scale in the enhanced and the original resolution is not substantially different.

In an embodiment of the electronic display according to the invention, said regrouping is arranged to yield a sequence of regular pixels having the same size equal to the size of a largest pixel. Preferably, the regular pixels are square is shape. More preferably, in the electronic display according to the invention a sequence of the pixels in a pixel matrix is provided with the following rule:

WH 1/2WH1/2WHWH

W1/2H 1/2W1/2H 1/2W1/2H W1/2H

WH 1/2WH1/2WHWH,

wherein W is a width of a nominal pixel and H is a height of a nominal pixel. This pixel sequence may be extended in both directions using the same rule, i.e. by concatenating the same sequence again.

In order to enable regrouping under preservation of the original largest pixel size, the regrouping is carried out by combining smaller pixels having the same dimension. Accordingly, full width half height (W1/2H) pixels are regrouped with the adjacent full width half height (W1/2H) pixels, whereas half width half height (1/2W1/2H) pixels are regrouped with the adjacent 1/2W1/2H pixels. It will be appreciated that for full width half height two such pixels are combined for yielding a new pixel, whereas for the half width half height pixels four such pixels are combined for yielding a new pixel. It will be further appreciated that in the display according to the invention pixels forming the row and/or the column are mirrored in the sequence, see WH 1/2 WH 1/2 WH WH in a column and WH W1/2H W1/2H WH in a row. However, it will be appreciated that such mirroring may be applied to pixels having different absolute dimensions than mentioned in this embodiment. More details on this embodiment will be discussed with reference to Figure 2. In a further embodiment of the electronic display according to the invention, the said regrouping is arranged to yield a sequence of non-regular pixels having about the same size.

It is found to be possible to combine pixels which do not yield a regular (square or rectangular) shape, as the human eye will not be able to make such distinction on the microscopic scale. However, by allowing the largest pixel to be combined with the smaller pixels an extra freedom to design the size of the sub pixels is provided, as the sub- pixels are not limited to a half or quarter square area of the largest pixel. In such a case a geometric centre of the resulting non-regular pixels may be aligned along a broken line. Accordingly, even more enhanced grey level scale may be provided. In this case the regrouping may be arranged by combining the largest pixel with pixels of smaller sizes. This embodiment will be discussed in more detail with reference to Figure 3.

In a still further embodiment of the electronic display according to the invention the display is switchable between a high resolution mode having the intrinsic grey level scale and a further mode having enhanced grey level scale.

Such feature is found to be advantageous as high grey level scale and resolution may sometimes be competing. Accordingly, the thus switchable display allows to be operable in the mode having the highest resolution and the mode having the highest grey level scale. Preferably, in the electronic display according to the invention a display area is dividable into a first sub-area having the intrinsic grey level scale and a second sub- area having the enhanced grey level scale. In this mode it is possible to provide the highest resolution to specific image areas, like a picture with text around it. The picture may be shown with an enhanced number of grey levels while the text may be shown with a higher number of pixels per inch.

The invention further relates to an electronic display apparatus comprising a display according to any one of the preceding claims.

The inventions still further relates to a method of manufacturing a display comprising a plurality of pixels comprising the steps of:

arranging each pixel to be operable within a pre-defined intrinsic number of grey levels,

arranging the display to be capable of displaying an image comprising a plurality of adjacent pixels, providing said pixels with different dimensions for generating an image having a further number of grey levels being higher than the intrinsic number of grey levels,

arranging the pixels having different dimensions to enable regrouping of pixels, whereby in at least a portion of a pixel sequence two pixels having a smaller size are provided between the pixels having the largest size.

In a preferred embodiment of the method the said regrouping is arranged to yield a sequence of regular pixels having the same size equal to the size of a largest pixel. Preferably, a sequence of the pixels in a pixel matrix is provided with the following rule:

WH 1/2WH1/2WHWH

W1/2H 1/2W1/2H 1/2W1/2H W1/2H

WH 1/2WH1/2WHWH,

In an alternative embodiment, of the method according to the invention the said regrouping is arranged to yield a sequence of non-regular pixels having about the same size. For example, a geometric centre of the resulting non-regular pixels may be aligned along a broken line.

These and other aspects of the invention will be discussed in more detail with reference to Figures. It will be appreciated that Figures are presented for explanatory purposes only and may not be used for limiting the scope of the appended claims. In the Figures, for convenience purposes, like reference numerals refer to like elements.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 presents in a schematic way an embodiment of the pixel area modulation provided in the prior art.

Figure 2a presents in a schematic way an embodiment of the pixel area modulation provided according to a first aspect of the invention.

Figure 2b presents schematically a pixel regrouping for the embodiment of

Figure 2a. Figure 3 presents in a schematic way an embodiment of the pixel area modulation provided according to a second aspect of the invention.

Figure 4 presents schematically a further embodiment of the display according to the invention.

DETAILED DESCRIPTION

Figure 1 presents in a schematic way an embodiment of the pixel area modulation provided in the prior art. In the prior art arrangement 10 in a first row the pixels having a larger area la, 2a are interleaved with pixels having a smaller area lb, 2b. In a subsequent row, the smaller pixels lc and Id are interleaved.

When pixel area modulation is applied to the prior art display 10, the total pixel area is substantially increased, as the largest pixel la is supplemented with 0.5 width in both directions. Accordingly, the resolution is reduced correspondingly, which is disadvantageous.

The prior art display 10 is capable of generating bout 10 grey levels using two intrinsic grey levels of each pixel, when pixels la, lb, lc, Id are combined to form a first pixel and the pixels 2a, 2b, 2c and 2d are combined to form a second pixel. Should each pixel be arranged with three intrinsic grey levels, the total number of grey levels which is possible with the display 10 is about 20. It will be appreciated that this principle is not limited to electrophoretic displays and may be applied to any display effect principle.

Figure 2a presents in a schematic way an embodiment of the pixel area modulation provided according to a first aspect of the invention. The technical measure of the invention is based on the insight that by rearranging the layout of the pixels, in particular, their sequence, it is feasible to construct a pixel matrix 20, 25 which provides enhanced grey levels without substantial deterioration of image resolution.

Accordingly, in at least a portion of a pixel sequence two pixels having a smaller size 20b, 21a are provided between the pixels having the largest size 20a, 21b. This offers the possibility to regroup the sub pixels into smaller pixels, by regrouping 20a, 20b, 20c, 20d and 21a, 21b, 21c, 2 Id, or, alternatively, by regrouping pixels 20b, 21a, 20c, 20c', 20d, 21c, 20d', 21c'. Such regrouping results in a sequence of pixels whose dimensions are not enlarged with respect to the original size of the largest pixel 20a in the display. The corresponding array of grey levels achievable with such arrangement is shown in Figure 2b, see pixels 25a, 25b, 25c, 25d, 25e, 25f. By correspondingly energizing the large pixels 25a, 25c and the combined pixels 25d, 25b, 25e, 25f a desired enhancement of the grey levels may be achieved. The absolute size of the large pixel 25a may be 137x137 micrometers yielding 190 pixels per inch. In an alternative embodiment the size of the large pixel 25a may be 100 micrometers yielding 254 pixels per inch.

In the situation of Figure 2a, all subpixels need to be addressed separately. But in the situation of Figure 2b, subpixels that are driven to the same grey level (e.g. 20b and 21a or 20d, 20d', 21c and 21c') can be refreshed at the same time. Driver outputs can be connected together (physically or logically). This way, a more efficient drive scheme can be employed resulting in a lower line frequency and thereby lower power usage. Also, unwanted effects like crosstalk can be reduced.

It is found that with the display according to the invention the following grey levels (totlev) are achievable as a function of the intrinsic grey levels per pixel (intlev), see Table 1.

Table 1 Grey level rendering in the display according to the invention

Figure 3 presents in a schematic way an embodiment of the pixel area modulation provided according to a second aspect of the invention. In this embodiment the pixels 31 and 36 are the largest pixels, while the pixels 32, 35, 33, 34, 37, 38 are the smaller pixels. In the present embodiment the smaller pixels are not aligned, therefore, when the larger pixel s suitably combined with the neighbouring smaller pixels an irregular pixel shape may be obtained, see 31, 32, 33, 34. The next pixel in a row may be formed by combining pixels 35, 36, 37, 38. As a result, the pixel row may have at least one border which does not follow a straight line. The centre of gravities of the individual combined pixels follow a broken like L.

It is found that the layouts presented in Figures 2a, 2b and 3 are comparable in terms of pixel count and therefore may have a comparable manufacturing yield. However, such layouts may render different spatial and grey level resolutions. When using the layout of Figure 3, 190ppi with 2 grey levels or 127ppi with 10 grey levels can be obtained. When using equally sized sub pixels, as shown in Figure 2b, 254ppi with 2 grey levels or 127ppi with 5 grey levels can be obtained.

It will be appreciated that in a preferred embodiment the display may be switchable between a high resolution mode having the intrinsic grey level scale and a further mode having enhanced grey level scale. More preferably, in the electronic display a display area may be dividable into a first sub-area having the intrinsic grey level scale and a second sub-area having the enhanced grey level scale. The latter is particularly suitable for imaging different objects requiring different grey level rendering and/or resolution.

Figure 4 presents schematically a further embodiment of the display according to the invention. To mitigate the difference between pixels consisting of one single part (e.g. 20a in Figures 2a and 4) and composite pixels (such as e.g. 25b/d and 25e in Figure 2b), a pixel layout that compensates for the inter-pixel spacing may be employed. All pixels (e.g. 20a, and 20b/c in Figure 2a) shown in view 40a may be constructed from either 2 or 4 pixel areas the size of pixel 20d in Figure 2a, interconnected to the same pixel circuit, see subpixels 20a', 20a", 20a" 'and 20a" 'in view 40b. The total active area of the pixel is reduced somewhat by this measure. The inter-pixel spacing may be about 5-10μιη.

It will be appreciated that although specific embodiments of the electronic device according to the invention are discussed separately for clarity purposes,

interchangeability of compatible features discussed with reference to isolated figures is envisaged. While specific embodiments have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the invention as described in the foregoing without departing from the scope of the claims set out below.

Claims

An electronic display comprising:

a plurality of pixels, each pixel being operable within a pre-defined intrinsic number of grey levels, the electronic display being capable of displaying an image comprising a plurality of adjacent pixels, wherein said pixels are provided with different dimensions for generating an image having a further number of grey levels being higher than the intrinsic number of grey levels, wherein the pixels having different dimensions are arranged to enable regrouping of pixels, whereby in at least a portion of a pixel sequence two pixels having a smaller size are provided between the pixels having the largest size.

The electronic display according to claim 1 , wherein said regrouping is arranged to yield a sequence of regular pixels having the same size equal to the size of a largest pixel.

The electronic display according to claim 2, wherein the regular pixels are square in shape.

The electronic display according to any one of the preceding claims, wherein a sequence of the pixels in a pixel matrix is provided with the following rule:

WH 1/2WH1/2WHWH

W1/2H1/2W1/2H 1/2W1/2H W1/2H

WH 1/2WH1/2WHWH,

wherein W is a width of a nominal pixel and H is a height of a nominal pixel.

The electronic display according to claim 1 , wherein such regrouping is enabled by combining smaller pixels having the same dimension.

The electronic display according to claim 1 , wherein said regrouping is arranged to yield a sequence of non-regular pixels having about the same size. The electronic display according to claim 2, wherein said regrouping is arranged to yield a sequence of non-regular pixels having about the same size. The electronic display according to claim 6, wherein a geometric centre of the resulting non-regular pixels is aligned along a broken line.

The electronic display according to claim 6 wherein said regrouping is arranged by combining the largest pixel with pixels of smaller sizes.

The electronic display according to 7, wherein said regrouping is arranged by combining the largest pixel with pixels of smaller sizes.

The electronic display according to claim 1 , wherein the display is switchable between a high resolution mode having the intrinsic grey level scale and a further mode having enhanced grey level scale.

The electronic display according to claim 1 , wherein a display area is dividable into a first sub-area having the intrinsic grey level scale and a second sub-area having the enhanced grey level scale.

An electronic display according to any claim 1 , wherein pixels in a pixel row and/or pixel column are provided in a mirrored sequence.

An electronic display apparatus comprising a display according to any one of the preceding claims.

A method of manufacturing a display comprising a plurality of pixels comprising the steps of:

- arranging each pixel to be operable within a pre-defined intrinsic number of grey levels,

- arranging the display to be capable of displaying an image comprising a plurality of adjacent pixels,

- providing said pixels with different dimensions for generating an image having a further number of grey levels being higher than the intrinsic number of grey levels,

- arranging the pixels having different dimensions to enable regrouping of pixels, whereby in at least a portion of a pixel sequence two pixels having a smaller size are provided between the pixels having the largest size.

The method according to claim 15, wherein said regrouping is arranged to yield a sequence of regular pixels having the same size equal to the size of a largest pixel.

The method according to claim 16, wherein a sequence of the pixels in a pixel matrix is provided with the following rule: WH 1/2WH1/2WHWH

W1/2H1/2W1/2H 1/2W1/2H W1/2H

WH 1/2WH1/2WHWH

wherein W is a width of a nominal pixel and H is a height of a nominal pixel.

18. The method according to claim 15, wherein said regrouping is arranged to yield a sequence of non-regular pixels having about the same size. 19. The method according to claim 18, wherein a geometric centre of the resulting non-regular pixels is aligned along a broken line.

20. An electronic display comprising an array of a plurality of pixel units, wherein each of the pixel unit has a predefined dimension formed by selecting from a group of a first type of pixel element, a second type of pixel element and a third type of pixel element, the area of the first type of pixel element is larger than the area of the second type of pixel element; the area of the second type of pixel element is larger than the area of the third type of pixel element, and the dimension of the first type of pixel element is the predetermined dimension of the pixel unit.

21. The electronic display of Claim 20, wherein the area of the second type of pixel element is a half of the area of the first type of pixel element. 22. The electronic display of Claim 21, wherein the area of the third type of pixel element is a half of the area of the second type of pixel element.

23. An electronic display comprising an array of a plurality of pixel units, wherein each of the pixel unit has a predefined dimension formed by selecting from a group of a first type of pixel element and a second type of pixel element, the area of the first type of pixel element is larger than the area of the second type of pixel element, and the dimension of the first type of pixel element is the predetermined dimension of the pixel unit.