WO1988007249A1

WO1988007249A1 - Display with pseudo-colour pixels

Info

Publication number: WO1988007249A1
Application number: PCT/AU1988/000083
Authority: WO
Inventors: Antony Paul Van De Ven
Original assignee: Colour Cells Pty. Ltd.
Priority date: 1987-03-20
Filing date: 1988-03-21
Publication date: 1988-09-22

Abstract

A travelling display sign for displaying multi-coloured images in which pixels thereof are produced from a matrix (1) of light sources of three colours (R, G and B) the light sources of two of the colours being provided by individual LEDs arranged in the first two columns of a repeated group of three columns of the matrix with the light sources of the third colour constituting the third column and all being illuminated by a single illuminating element.

Description

DISPLAY WITH PSEUDO-COLOUR PIXELS TECHNICAL FIELD This Invention relates to multi-coloured signs or displays.

BACKGROUND ART Such displays are often constructed of a multiplicity of light control devices arranged In a matrix of horizontal rows and vertical columns. Each light control device, or pixel, may consist of either a single lamp or a cluster of lamps of the same or of different colours. On such displays multi-colours are generally displayed using Additive Colour Mixing. This 1s the process by which the human eye can perceive a broad spectrum of colours from a smaller number of coloured sources by adding the colours together and perceiving an Intermediate or different colour.

There are several arrangements of lamps that allow Additive Colour Mixing to occur and they are:

1. Spacial arrangements, where the light control devices each comprise lamps of different colours clustered into a single pixel, so that from a distance a blending of colours is perceived. Such blending 1s dependent on the Illumination state of the Individual lamps and the combinations thereof. The most common application of this arrangement 1s 1n colour television receivers. Variations of this arrangement Include the use of a diffusing material mounted 1n front of the pixels to Improve the Additive Colour Mixing effect when the display is viewed close up.

2. Beta superimposed arrangements, where travelling or moving Images are displayed on a matrix of pixels of differing colours and are perceived 1n a multiplicity of colours with a resolution not less than the number of Individual light sources.

Such displays are constructed using a large variety of light sources Including Incandescent lamps, electron activated phosphors, light emitting diodes, neon tubes and liquid crystals etc. While it is within the scope of the Invention to apply all these means, for Illustrative purposes the following description will be confined to displays using predominantly light emitting diodes (LEDs).

Normally each pixel or part thereof is controlled Independently. Such control 1s often implemented by control logic such as a micro-computer. While such individual control of pixels' or parts thereof, is the most versatile arrangement each individually controlled pixel requires associated control circuits and 1t 1s known that such a multiplicity of individual pixels in a given area is generally much more expensive to manufacture than a single light source of the same given area. Certain colours of pixels are also more expensive to manufacture e.g. light sources in the blue/purple area of the spectrum due to the greater luminence required to achieve eye response comparable to that achieved from sources of red and green light. This is a particular problem when displays are made using LEDs. Therefore while displays using the red - yellow - green spectrum are known, the inclusion of blue or purple light sources makes the sign too expensive to be commercially viable. It is therefore a disadvantage with such red - yellow - green displays that many potential users of these displays for advertising cannot do so because the colour range does not allow accurate colour representation of their products and services.

DISCLOSURE OF INVENTION It is the object of this invention to provide a means of generating different colour sources in such displays at a reasonable cost. While it is within the scope of the invention to use this method to generate any colour or hue of the spectrum, for illustrative purposes the following description will refer to blue and/or purple light. An important advantage, of course, is that practically all colours of the spectrum can then be displayed. Generally the invention is attained by the use of individual light sources of red and green, usually LEDs, each being independently controlled, and light sources of blue and/or purple controlled in areas hereinafter sometimes termed "General Blue Illumination areas".

In accordance with the invention there is provided a multi-coloured display comprising a display panel for providing a plurality of imaging pixels, each of said pixels being composed of one or more primary light sources arranged in a matrix of rows and columns, control means for individually controlling illumination of said primary light source to create partly a predetermined image, secondary light sources associated with at least some of said pixels and being arranged in one or more groups, at least some of said secondary light sources being illuminated as a group by a lighting element, and electrical energising means for said lighting element controlled by said control means for effecting illumination thereof.

BRIEF DESCRIPTION OF DRAWINGS The invention will be described in more detail with reference to the accompanying drawings, in which: Fig. 1 is a CIE colour chart with solid black dots showing major colour selections;

Fig. 2a is a fragmentary front elevation of a display panel of the invention showing one possible arrangement of pixels; Fig. 2b is a similar arrangement but using general areas of illumination in clustered pixels;

Fig. 2c is a plan view of a display substrate and pixel showing phosphor pixels deposited on substrate and illuminated by UV light;

Fig. 2d is a plan view of another form providing re-illumination using small longitudinal light sources corresponding to the vertical columns of a matrix;

Fig. 3 is a simplified schematic block diagram of a display matrix with drive;

Fig. 4 shows a more specific arrangement thereof; Fig. 5 is a simplified block diagram of a control board for the matrix; and,

Fig. 6 is a more detailed block diagram thereof.

BEST MODE OF CARRYING OUT THE INVENTION With reference to Fig. 2, four different forms of a display matrix are shown which comprises a substrate 3 provided with light sources of three colours which may be red, green and blue (or purple). The blue or purple coloured light sources B may be produced by depositing fluorescent paint 2 as shown in Fig. 2c onto selected positions on the display matrix substrate 3 and illuminating such devices as a group by reflection from the application of a single source of ultraviolet (UV) light 4. A preferred arrangement is depicted in Fig. 2a, 2b, 2d where holes 5 are provided at selected positions on the substrate 3 with transparent light guides 6 inserted and re-illuminated using a radiant device such as a fluorescent lamp(s) 7. The red and green light sources R and G, respectively, being individually controllable, provide visual information to the viewer relating to the shape, size, position and red and green colour content of the images being displayed, while the blue provides overall colour content information within the area being illuminated. The general illumination of the blue sources B allows different ranges of colour to be displayed within the illuminated area⁽s⁾. The size of the areas of General Blue Illumination are always greater in size than one pixel and can cover the entire display.

On displays that are used as travelling signs the areas of General Blue Illumination are ideally arranged in columns. In such an arrangement (Fig. 2a) the blue pixels B within a designated vertical column are controlled collectively and each column individually controlled. Columns are chosen as the desired shape for the General Blue Illumination areas because images on such travelling signs mostly move across the screen in a horizontal direction and control of such areas allow the leading and trailing edges"of the image, or portions thereof, to be clearly delineated.

If, for example, the blue columns are disabled then the image can be displayed in combinations of colours from the red to yellow to green portion of the spectrum A of Fig. 1. However when blue is enabled the image can be displayed in the green to blue red through white portion of the spectrum B of Fig. 1. Such colour alternatives for the preferred arrangement are listed below: a) Without General Blue Illumination -

Red, reddish Orange, Orange, Amber, Yellow, greenish Yellow, lime, yellowish Green, and Green, b) With General Blue Illumination -

Blue, Purple, red Purple, purplish Red, purplish Pink, Pink, orangish Pink, White, Green, blueish Green.

Such arrangement allows a total of 32 colours and hues. Therefore, the invention allows the display of a much greater colour range on the screen without the substantial increase in cost required for individually controlled blue/purple pixels. The preferred arrangement consists of a display substrate 3 normally of a fibreglass material on which is mounted alternating columns of red and green light emitting diodes (LED) and areas of General Blue Illumination.

Such LED's, as shown in Fig. 3, are connected in rows to current source drivers 8 and in columns connected to current sink drivers 9 in a matrix configuration. Rows of LED's are addressed and refreshed in cyclic manner. Information relating to the luminance state of each individual LED in a selected row is clocked serially into shift registers 10. The selected row is then enabled by applying current to the row of LED's through the selected current source driver 8. Current sink drivers 9 connected to the serial to parallel shift registers 10 then sink current through the selected LED's in that row. This process is repeated for each row on a time sharing basis. Each row is enabled for approximately 2 milliseconds. When the total time to refresh all the rows is less than 20 milliseconds the viewer perceives a complete image. The columns of General Blue Illumination include small fluorescent tubes 11 such as a mercury vapour discharge type which may have a generally blue colour. They are placed between the pairs of red and green LED columns. Associated with each tube 11, or area, is a mask 12, which may act as a blue filter, so that the blue pixels B are of similar shape and appearance to the red and green LED's. Alternatively, transparencies or masks of a different colour may be used. The tubes are connected between a high voltage source and current sink drivers 9 to the shift registers 10.

Another feature of the invention is that whereas with the red and green individually controllable pixels, a change in the column data from row to row will determine the shape of the displayed image, changes in the data relating to the areas of General Blue Illumination result in pulse width modulation of the blue illumination state allowing the number of colour hues and tones available on the display to be increased.

A specific arrangment of a display matrix is shown in Fig. 4. The display consists of light sources arranged in a matrix of 192 columns and 16 rows. The columns are arranged in an alternating format of a column of red LEDS R then a column of green LEDS G and then a column of blue light masks (not shown). The red and green LEDS are connected between the row driver (not shown) and column sink drivers 9A through current limiting resisters 13.

The blue light masks are optically linked to respective blue fluorescent tubes 11A with one tube per column. Each tube is powered by a high voltage inverter 14 which is enabled or disabled by a column sink driver 9A. The column sink drivers 9A are connected to a parallel to serial shift register 10A which places on its output the data clocked into it from the serial data in line. Control apparatus is provided for determining images to be displayed and is shown generally in Fig. 5. The image to be displayed is stored in a memory such as a Random Access Memory (RAM) 15 or Read Only Memory (ROM) 16. Such images are controlled, changed and displayed by control logic such as a micro-computer 17. The transfer of the graphic information from the computer memory 15, 16 by the processor 17 to the display is via a multiplexer 18 which is used to select the required column data for the row being refreshed. Timing control logic 19 synchronises all transfers and provides clocks to shift column enable data into the shift registers 10, 10A (Figs. 3 and 4⁾. The communication interface 20 and input device 21 allow the entry by an operator, or other source, of the graphic information to be displayed.

With reference to Fig. 6, the construction and operation of the control logic will be made clearer. The CPU 17 is typically a Z80 micro-processor. It is reset on power on and using the crystal 22 for clocking, it reads the first of its instruction programmed into the ROM 16. The ROM 16 is typically of 32k-bytes and contains various software routines to handle the functions of the display, it also contains the character generator and various graphic characters. The RAM 15 is used to store the ascii code of the message being displayed and also contains workspace areas for the micro-processor 17. The micro-processor 17 addresses the other chips in the circuit using chip select lines generated by the address bus and memory or control lines through the address decoder 23. Text and graphic information is input into the system through the UART (Universal assyncronous receiver/transmitter) 24 which converts the applied industry standard RS232 format into byte format and supplies it to the processor on request. The processor stores this data in the RAM 15. The major functions of these components discussed above are

1. the input and storage of external commands and information

2. the generation of basic timing for the system

3. the generation and supply of the dot matrix data to the CRC (display controller) 25. In order to display a graphic on the display, two steps are required:

(A) firstly the ascii information stored in the RAM 15 must be converted to dot matrix information and such dot matrix information is then transferred to an empty portion of the display RAM 15. This information contains all the data concerning the graphic including shape, colour and brightness. In order to transfer the data to the RAM 15 the processor 17 waits until the CRC 25 interrupts. An interrupt indicates that the CRC 25 requires more information and the processor stops whatever it is doing and provides the required data immediately. (B) secondly the CRC 25 accesses this data by switching data multiplexers 26a-26d between itself and the screen RAM 15. This data is then clocked out to the display via multiplexer 27 one row at a time. Each row is updated consecutively starting at the bottom and working toward the top until all the rows have been refreshed. By ensuring that the complete refresh of all the rows takes place within 16-20ms the viewer will perceive a solid image on the screen.

The particular row being refreshed is controlled by the CRC 25 which puts a count onto latch 28 to apply power to a selected row via demultiplexers 29 and 30 and row drivers 31 and 32. The count is also placed on multiplexer 33 which connects the correct row information to the shiftregisters 10, 10A on the display panel. The graphic data is stored in the screen RAM 16 in three buffers, each of which contains the colour information for a primary colour, that is; buffer 1 contains the red data, buffer 2 contains the green data and buffer 3 contains the blue data.

It has been found when using a time sharing method of updating the display certain optical effects occur. Because individual red and green LEDS in a particular column are turned on one at a time consecutively, that is the LED in the bottom row first, followed by the second row, etc, and since the image being displayed is generally moving, the perceived shape of the blue dots elongates. This is because all of the blue dots in a particular column are controlled collectively and because of the imposed switching on of adjacent red and green pixels, the separate switches on the red and green LEDS are perceived as small incremental steps in the position of the blue pixels. Due to the rapid switching the steps integrated into a perceived image of a bar of light even though the light guide may have a circular section.

Another consideration is that the life of a fluorescent tube is primarily dependent on the number of times the tube is turned on and the amount of current passed though the tube. In order to maximize brightness, minimize current, minimize the number of switch on times and generate a circular pixel shape, the light guide shape is optimal when it is formed by two arcs of the final radius connected at the ends with a width of .694 times the final diameter, in this case 3.47mm for a 5mm circular pixel. When this shape is used and- the tube is fired over the period of four consecutive rows the maximum brightness for the desired shape with minimum switching is achieved.

The position of a specific blue pixel relative to the blue pixel above and below it in the same column is offset to allow for the illusion of leading edge slope which occurs when a travelling image is displayed on a multiplexed display. Since the blue pixels are not mulitplexed it is necessary to physically position the pixels so that the blue pixels align with the perceived slope of the red and green pixels. Whereas a preferred embodiment has been described in the foregoing passages it should be understood that other forms, modifications and refinements are feasible within the scope of this invention.

Claims

DISPLAY WITH PSEUDO-COLOUR PIXELS CLAIMS

1. A multi-coloured display comprising a display panel for providing a plurality of imaging pixels, each of said pixels being composed of one or more primary light sources arranged in a matrix of rows and columns, control means for individually controlling illumination of said primary light source to create partly a predetermined image, secondary light sources associated with at least some of said pixels and being arranged in one or more groups, at least some of said secondary light sources being illuminated as a group by a lighting element, and electrical energising means for said lighting element controlled by said control means for effecting illumination thereof.

2. A display according to claim 1, for displaying images appearing to travel along the length of the display, and wherein said primary light sources are LEDS, and said lighting element is a single element.

3. A display according to claim 1 or 2, wherein said primary light sources are arranged in two colours and the secondary light sources are a third colour different therefrom.

4. A display according to claim 3, wherein said two colours are red and green, and said third colour is blue.

5. A display according to claim 3, wherein said columns of said matrix are arranged in repeated groups of three columns along said display panel with the first two columns of each groups composed of alternating red and green light sources and the third column of each group composed of a line of areas all illuminated by a single fluorescent tube.

6. A display according to claim 5, wherein said matrix is mounted upon a substrate and said areas are a line of apertures in the substrate with said tube positioned behind the substrate and with a colour mask between said aperatures and said tube. A multi-coloured display substantially as hereinbefore described with reference to the accompanying drawings.