GB2363537A

GB2363537A - Pixel array for a display device

Info

Publication number: GB2363537A
Application number: GB0014337A
Authority: GB
Inventors: Robert Bedford End
Original assignee: Motorola Inc
Current assignee: Motorola Solutions Inc
Priority date: 2000-06-13
Filing date: 2000-06-13
Publication date: 2001-12-19
Also published as: GB0014337D0

Abstract

A pixel array (20, 30, 41, 50) for a dot matrix character display having improved resolution is formed from a regular lattice of main pixels (21) bounding intermediate auxiliary pixels (22) of generally smaller dimension than the main pixels, such that any character can be formed by illuminating edgewise adjacent pixels only. The pixel array may include a regular lattice of main pixel boundaries having a first polygonal shape defining at mutually abutting edges thereof a respective auxiliary pixel boundary having a second polygonal shape of generally smaller dimension than the first polygonal shape. The main and auxiliary pixels are contained within each of the main and auxiliary pixel boundaries, respectively. Preferably, the pixel array has a pixel resolution compatible with existing display drivers so as to allow easy modification of existing display drivers by substitution of the character map therein. Tri-colour pixels may be employed to allow colour rendition of bit-mapped characters.

Description

2363537 Pixel array for a display device

Field Of The Invention

This invention relates to display devices. In particular, the invention concerns improvements to a pixel array for a display device.

Background Of The Invention

It has long been recognised that conventional dot matrix character display devices exhibit poor resolution when reproducing lines that are not either vertical or horizontal. In the prior art this deficiency has been addressed either by increasing the number of pixels in the display device or by using smoothing techniques to

10 improve rendition.

For example, US Patent No. 5,404,233 (Nagata et al.) and assigned to Kyocera Corporation discloses a method for smoothing images composed of a matrix of dots in a printer, such as a laser printer or an LED printer, and a bit map display unit such as a CRT display. The method includes dividing a pixel into a 15 plurality of sub-pixels along a vertical scanning line or a horizontal scanning line, and reversing a signal for a sub-pixel following a reversion signal to smooth the image as desired. The reversion signal may be provided by subjecting a specific pixel to a Boolean operation, conjunction or disjunction, with the adjacent pixels bordering the specific pixel.

20 Such an approach attempts to compensate for poor resolution by adjusting which pixels are illuminated. Thus, a pixel that is set to be illuminated by the display circuitry may, in fact, be extinguished in favour of one or more bordering pixels so as to improve the rendition of segments that are not vertical or horizontal.

Apart from such pixel-processing techniques, the prior art arrangements lack

25 suggestions for modifying the pixel arrangement of the display device. The conventional character dot-matrix display elements comprising either 7x5 or 13x9 addressable pixels have become standard. Indeed, so much so have the 7x5 and 13x9 pixel resolutions become the industry standard, that dot-matrix display drivers have been customised for this standard. This tends to militate against an arbitrary increase in pixel resolution since this would compromise the interchangeability of display devices, unless the driver circuitry too were replaced. Complete re-design 5 of existing driver circuitry is not desirable owing to economies of scale.

Moreover, increasing the pixel resolution whilst maintaining pixel size necessarily increases the display size and so is not always feasible. Many portable appliances, such as mobile telephones, pagers and so on, employ LCD displays that are used to display alphanumeric data and other symbols. In the case of such 10 appliances, there is a need to display characters at higher resolution without increasing the display size. The characters are stored in a character bit-map or ROM associated with driver circuitry for driving the pixel array. The driver circuitry must be capable of addressing each of the memory locations in the character bit-map and writing the bit value ("0" or " 1 ") to a corresponding pixel in 15 the pixel array so as to switch the respective pixel OFF or ON. Increasing the number of bits in the character bit-map requires a complete redesign of the driver circuitry owing to the greater number of addressable memory locations. Frequently, the driver circuitry and the character bit-map are designed by the same manufacturer as the appliance itself. In such case, there is some cost benefit in 20 maintaining the size of the character bit-map, even if the bit-map itself changes, since much of the driver circuitry design can then be left intact. This leads to the desirability of increasing the resolution of a character bit-map, whilst maintaining the number of pixels in the bit-map constant.

Figs. I and 2 show such a prior art display arrangement 10 having a 7x5

25 pixel resolution displaying a set of characters including C, N, V, R, S, a, d, 4, D, 4. All of these characters are either curved or contain line segments that are neither vertical nor horizontal and in all cases at least some adjacent pixels make contact at the respective comers of bordering pixels. For example, the letter "C" is formed of a vertical line segment I I adjoining at its upper and lower extremities respective horizontal line segments 12 and 13 comer to comer. The free ends of the letter are curved, but the only way to emulate this using a conventional 7x5 pixel matrix is to assign one more pixel 14 for each free end adjoining an end pixel 15 of the horizontal segments comer to comer. The resulting sharp change in gradient 5 between the adjacent line segments which abut each other at adjoining comers militates against a faithful reproduction of the character. Moreover, the poor reproduction is due to an inherent lack of resolution. This lack of resolution is not amenable to correction using smoothing techniques, since the pixel arrangement is optimised in advance, and there exist no other adjacent pixels available to "play 10 with". An arbitrary increase in the number of pixels in each display element would improve the pixel resolution, but this is not feasible for the reasons noted above.

There is therefore a need to provide a better approach for dot matrix pixel arrays, which improves pixel resolution whilst not requiring that existing display drivers be completely redesigned.

15 Summary Of The Invention

It is an object of the invention to provide an improved pixel arrangement for dot matrix pixel arrays, which improves pixel resolution whilst not requiring any increase in overall character size.

According to the invention there is provided a pixel array for a display 2o device, comprising a regular lattice of main pixels bounding intermediate auxiliary pixels of generally smaller dimension than the main pixels such that any character can be fornied by illuminating edgewise adjacent pixels only.

Preferably such an array is formed from a regular lattice of main pixel boundaries having a first polygonal shape defining at mutually abutting edges 25 thereof a respective auxiliary pixel boundary having a second polygonal shape of generally smaller dimension than the first polygonal shape. Respective main and auxiliary pixels are contained within each of the main and auxiliary pixel boundaries.

Preferably, the pixels are dimensioned to fill their respective boundaries completely, whereby adjacent pixels are also contiguous. However, as will be seen from the following detailed description, the advantages of the invention are still largely realised even if round pixels are disposed within the pixel boundaries.

5 According to one detailed arrangement of the invention as part of a display, there is provided a display device comprising: an array of abutting octagonal main pixels; an array of square auxiliary pixels, each square auxiliary pixel abutting four hexagonal main pixels; wherein each octagonal main pixel and each square auxiliary pixel are adapted to be addressable by display driver circuitry, thereby to display an image of one or more alphanumeric characters.

Brief Description Of The Drawings

In order to understand the invention and to see how it may be carried out in practice, a preferred embodiment will now be described, by way of nonlimiting example only, with reference to the accompanying drawings, in which:

Figs. 1 and 2 are pictorial representations of a prior art 5x7 pixel array for a dot matrix pixel character display device showing conventional formation of problematic characters; Fig. 3 is a pictorial representation showing a novel pixel arrangement according to the invention; Figs. 4 and 5 are pictorial representations of a 9x 13 pixel array according to the invention for a dot matrix pixel character display device showing the formation of the same characters depicted in Figs. I and 2, respectively; Figs. 6 and 7 are pictorial representations showing a comparison of a character formation using the 9x 13 pixel array according to the invention with a prior art 9x13 dot matrix pixel array; and

Fig. 8 is a pictorial representation showing the pixel arrangement according to the invention adapted for use with a colour display, Detailed Description Of Preferred Embodiments

Fig. 3 shows a pixel array 20 comprising a regular lattice of main octagonal pixel boundaries 21 which adjoin along mutually common edges such that four adjacent octagonal boundaries define an enclosed boundary 22. In the case where 5 the octagonal boundaries 21 are regular, the enclosed boundary 22 is square in shape. If the octagonal boundaries 21 were irregular, then the enclosed boundary would be rectangular. The octagonal boundaries 21 constitute a first polygonal shape that defines, at mutually abutting edges thereof, a respective auxiliary pixel boundary constituted by the enclosed boundary 22. The square shape of the 10 enclosed boundary 22 constitutes a second polygonal shape of generally smaller dimension than the first polygonal shape.

Within each of the pixel boundaries 21 and 22 there is disposed a respective pixel. These may fill the boundaries so that the pixel array 20 includes octagonal and square pixels. However, the invention also contemplates disposing in each of 15 the boundaries round pixels, preferably dimensioned to contact the respective boundaries. Thus, round pixels contained within regular octagonal and square boundaries can be maximally dimensioned to all eight edges of the octagon and all four sides of the square.

Figs. 4 and 5 are pictorial representations of a 9x 13 pixel array 30 for a dot 20 matrix pixel character display device employing the configuration described above with reference to Fig. 3 of the drawings. Figs. 4 and 5 show the formation of the same characters depicted in Figs. I and 2, respectively.

The improvement of the pixel array 30 shown in Fig. 4 over the prior art pixel array 10 shown in Fig. 1 is apparent by comparing the character "C". Thus, it

25 is noted that none of the pixels in the pixel array 30 adjoins an adjacent pixel comer to comer. The curved free ends of the "C" each have an end pixel 34 adjoining a respective end pixel 35 of the lower and upper horizontal segments 32 and 33 via an intermediate auxiliary pixel 36, thus avoiding the sharp comer to comer contact characteristic of Prior art pixel arrays. it Is to be noted that, whIlst the pixel array 32 shown in Fig. 4 requires more pixels than the pixel array 10 shown in Fig. 1, the overall character size remains unaltered. This is particularly important for portable appliances where display size is frequently at a premium.

5 The character resolution of the 9x 13 pixel array shown in Figs. 4 and 5 is clearly better than that of the 7x5 pixel arrays shown in Figs. I and 2. However, the character resolution of the 9x 13 pixel array according to the invention is also improved over that of conventional 9x 13 pixel arrays. This can be seen from Figs.

6 and 7. Figures 6 and 7 show pixel arrays 40 and 4 1. Pixel arrays 40 and 41 depict 10 character formation of the letter "R" using, respectively, a prior art 9x13 dot matrix pixel array and the 9x 13 pixel array according to the invention.

It is thus clear that character resolution of the pixel array 41 shown in Fig. 7 is improved over the conventional 13x9 pixel array 40 shown in Fig. 6, owing to the availability of the intermediate auxiliary pixels, even though the nominal pixel 15 resolution of the pixel array remains unaltered. Moreover, since the same number of bits in the character bit-map must be addressed by the driver circuitry, this means that much of the driver circuitry design can remain unchanged. This can provide a significant saving, particularly when the driver circuitry and the character bit-map are in any case customised by the manufacturer of an appliance having a 20 dot-matrix display.

Fig. 8 shows pictorially a pixel array 50 adapted for a colour dot-matrix display. Pixel array 50 comprises a lattice of regular octagonal main pixels having vertical blue, green and red stripes 51, 52 and 53, respectively. The octagonal pixels adjoin along mutually common edges, such that four adjacent octagonal 25 pixels define an enclosed square auxiliary pixel also having vertical blue, green and red stripes 54, 55 and 56, respectively. As explained above, the octagonal shape constitutes a main boundary having a first polygonal shape, defining at mutually abutting edges thereof a respective auxiliary pixel boundary. The auxiliary pixel boundary has a second polygonal shape of generally smaller dimension than the first polygonal shape. As further noted previously, the pixels need not fill the boundaries but can be constituted by round pixels having large and small diameters disposed within the respective main and auxiliary pixel boundaries. Such a pixel array allows for the colour display of characters at improved resolution, without requiring an increase in the size of a display device employing such a pixel array.

The pixel array according to the invention is characterised by a regular lattice of main pixels bounding intermediate auxiliary pixels of generally smaller dimension than the main pixels, such that any character can be formed by illuminating edgewise adjacent pixels only. This is distinct from hitherto-proposed 10 arrays, where some characters require the illumination of pixels that are mutually adjacent at their respective comers. Whilst a prefer-red embodiment has been described with regard to octagonal main pixels bounding square auxiliary. pixels, it will be understood that these shapes are by way of example only. The precise shapes of the pixels and the pixel boundaries are not critical factors in realising the 15 improvement offered by the invention.

The pixel array of the invention may be used to advantage in a display device. The display device comprises an array of abutting octagonal main pixels and an array of square auxiliary pixels, with each square auxiliary pixel abutting four hexagonal main pixels. In this device, each octagonal main pixel and each 20 square auxiliary pixel are adapted to be addressed by display driver circuitry, thereby to display an image of one or more alphanumeric characters. Such a display device shows enhanced readability of alphanumeric characters.

Claims

1. A pixel array (20, 3 0, 41, 50) for a display device, comprising: a regular lattice of main pixels (2 1) bounding intermediate auxiliary pixels (22) of 5 generally smaller dimension than the main pixels such that any character can be formed by illuminating edgewise adjacent pixels only.

2. The pixel array according to claim 1, comprising: a regular lattice of main pixel boundaries having a first polygonal shape defining at 10 mutually abutting edges thereof a respective auxiliary pixel boundary having a second polygonal shape of generally smaller dimension than the first polygonal shape; said main and auxiliary pixels being contained within each of said main and auxiliary pixel boundaries, respectively.

3. The pixel array according to claim 2, wherein the main pixels are of the first polygonal shape.

4. The pixel array according to claim 2 or 3, wherein the auxiliary pixels are of the 20 second polygonal shape.

5. The pixel array according to any of claims 2 to 4, wherein the first polygonal shape is octagonal and the second polygonal shape is rectangular.

25

6. The pixel array according to claim 5, wherein the octagonal first polygonal shape is regular and the second polygonal shape is square.

7. The pixel array according to any of the preceding claims, being modified for colour rendition.

S. The pixel array according to claim 7, wherein each of the main and auxiliary 5 pixels includes three stripes having respective primary colours.

9. The pixel array according to any of the preceding claims, implemented in a modified character bit-map having a number of addressable memory locations that is compatible with an existing character bit-map associated with available display 10 driver circuitry, so as to allow said modified character bit-map to be substituted for said existing character bit-map.

10. A pixel array substantially as herein described with reference to, or as illustrated by, any of figures 3, 4, 5, 7 or 8 of the drawings.

11. A display device comprising a pixel array in accordance with any previous claim.

12. A display device comprising:

20 an array of abutting octagonal main pixels; an array of square auxiliary pixels, each square auxiliary pixel abutting four hexagonal main pixels; wherein each octagonal main pixel and each square auxiliary pixel are adapted to be addressed by display driver circuitry, thereby to display an image of one or more 25 alphanumeric characters.