GB2229847A - Colour image discharge display - Google Patents

Abstract

An image display apparatus has a single generator (12) for generating an electric signal corresponding to an image to be displayed. This electric signal is converted into a predetermined color image signal by an image processor (28). This color image signal is sent over to a display controller (40) in a display section (32) and is subjected to pulse width modulation control by the display controller (40). The color image signal controlled by this controller (40) is displayed on a display panel (42) having a plurality of discharge paths two-dimensionally arranged. Each discharge path displays one of a plurality of predetermined colors. The display controller (40) permits those discharge paths of the same color of the display panel (42) to be connected to the same ballast, and performs lighting control through time-division of a lighting time of these discharge paths of the same color. <IMAGE>

Description

"IMAGE DISPLAY APPARATUS FOR CONTROLLING LIGHTING OF A PLURALITY OF DISCHARGE PATHS IN TIME DIVISIONAL MANNER" The present invention generally relates to an image display apparatus which has a plurality of discharge paths arranged in matrix form and performs illumination control of the discharge paths to thereby display an image, and, more particularly, to an image display apparatus which controls time-divisional lighting of the discharge paths.

Conventionally, large image display apparatuses or large color image display apparatuses such as large displays called color display panels have been used at stadiums, such as baseball fields or race tracks.

Such a large color image display apparatus has many discharge lamps arranged in matrix form on its display surface, and each discharge lamp has a color filter provided at the front, which permits only one of three colors, red (R), green (G) and blue (B), to pass through. Passing each filter, the R, G or B light provides a display of one of the primary colors (R, G and B). Each discharge lamp is driven by PWM (Pulse Width Modulation) for its illumination and lighting control to thereby provide a display of the desired color image.

There is another image display apparatus known which uses a discharge tube of a tricolor single tube type to cope with a smaller display surface. As its name clearly implies, this discharge tube has three discharge lamps for three colors incorporated into a single tube. In using this type of discharge tube in the aforementioned large color image display apparatus, in order to reduce the size of electric circuits, the ballasts such as inductances provided for the respective discharge lamps are shared by the discharge lamps (for three colors) of one discharge tube and the individual discharge lamps are subjected to a time-divisional lighting control. In this case, the discharge lamp G which most includes luminance data included in one image signal, are separated into two lamps, G1 and G2, to improve the resolution.This measure is taken because of the necessity to increase the luminance (which will be described later) as large color image display apparatuses are generally used outdoors, of easier arrangement of the discharge tube, or of the number of scanning lines appearing to increase.

In a case where four discharge lamps R, G1, G2 and B are connected to the same ballast, discharge currents (lamp currents) of the individual discharge lamps all become the same and display luminance vary color by color. In order to provide the white balance, therefore, it is still necessary to control the lighting time (pulse width) for each color or adjust the transmittivity of each filter for the associated color.

This lighting time control requires different gradation/lighting time conversion ROMs for the respective colors. In addition, there may be an adverse influence on reddening which causes high display luminance with the same current or, in some case, the resolution of brightness due to the lighting time being too short. Further, adjusting the transmittivity of a color filter reduces general brightness or efficiency, thus adversely influencing the saturation, hue and so forth.

There is another type of a large color image display apparatus which, as different from the one with the above-described structure, employs a single tube multicolor or single tube monohromatic display element (e.g., mercury discharge lamp) at each point on this display face. The "single tube multicolor display element" is designed to display different colors simultaneously or individually for a plurality of discharge paths in one lamp. This display element alone can serve as a plurality of display elements, whereas the single tube monochromatic display element displays one color with one lamp.

As a lighting device for such a display element, for example, a single tube multicolor lamp has an anode R for forming a discharge path for displaying red, green display discharge lamps G1 and G2, blue display discharge lamp B, a common cathode and an activating auxiliary electrode. A switching transistor for supplying a current to the discharge path for each color display is connected for each color. These transistors each have their base supplied with a pulse lightingcontrol signal from a controller. Based on this control signal, the transistors are turned on or off to supply a current to the discharge lamps for the individual colors, thus switching its dots (pixels) on or off.

This type of lighting apparatus needs adjusting brightness of the dots for each color. That is, even if a current with the same value is rendered to flow through a blue dot and a green dot for the same period of time, the luminance is low for blue and high for green. If similar control is executed for each color, therefore, luminance balance cannot be attained for individual colors so that the brightness of dots for each color needs to be preadjusted.

To adjust the brightness of each dot, conventionally, the section to supply a current to a dot for luminance adjustment is controlled or the ballast resistance is changed for each dot to alter the value of the current through pulse width control. For instance, if one discharge path (lamp) is to initiate in white lighting, when lighting power is supplied from a power source, dots for the individual colors are switched on in the order of, for example, from B to G1 to R to G2. By repeating the lighting of the individual dots at such a timing in time divisional manner, the discharge path is lit white. In view of the aforementioned low/high relation of luminance, the pulse width of the lighting control signal for B is set long and that for G is set short. As R generally falls within the intermediate range, its pulse width is shorter than that of B and longer than that of G.

According to the type which controls the lighting time of each dot by altering each pulse width under the pulse width control, it is always necessary to perform this control dot by dot when white lighting is initiated, thus complicating the control system. Particularly, in executing gradation control, the pulse width of the lighting control signal is segmented into, for example, 64 sections, and a pulse having the same pulse width as the width of the desired one of the 64 segments is given as a control signal, thus ensuring expression of 64 different gradations. Since the pulse width at the time of providing white lighting differs color by color, the segmented pulse widths also vary for each color. The control system therefore becomes further complicated. Provided that the pulse width for given dots consisting G1 and G2 are a half that for blue, making such a narrow pulse width even narrower to be 1/256 (8 bits) causes the pulse width for one gradation to be too narrow to activate or turn on the lamp.

Further, there is a system in which a ballast resistance is provided for each dot or each color so that luminance can be controlled by altering the value of the ballast resistance and thus changing the value of a current flowing through each dot. This system however requires different ballast resistances with different values for the individual dots, which increases the cost. In a particular case where a transformer, not a resistance, is used as a ballast, many different types of transformers are necessary, which also increases the cost.

Accordingly, it is a primary object of this invention to provide an image display apparatus which permits one ballast to be shared by a plurality of discharge paths for time divisional lighting of the individual discharge lamps to reduce the number of required ballasts and can adjust color balance such as white balance without adjusting the lighting time and filter transmittivity.

It is another object of this invention to provide an image display apparatus which adjusts the brightness for each display element not by pulse width control and eliminates the need to provide a ballast for each element.

According to one aspect of the present invention, there is provided an image display apparatus comprising: signal generating means for generating an electric signal corresponding to an image to be displayed; image processing means for converting the electric signal generated by the signal generating means into a predetermined color image signal; display control means for executing pulse width modulation control to display the color image signal processed by the image processing means; and display means for displaying the color image signal controlled by the display control means, the display means having a plurality of discharge paths twodimensionally arranged each for displaying one of a plurality of predetermined colors, the display means having ballast means connected to the discharge paths, wherein the display control means permits a plurality of discharge paths of the same color of the display means to be coupled to the same ballast means to thereby timedivide a lighting time of the plurality of discharge paths for lighting control.

According to another aspect of the present invention, there is provided an image display apparatus comprising: signal generating means for generating an electric signal corresponding to an image to be displayed; image processing means for converting the electric signal generated by the signal generating means into a predetermined color image signal; display control means for executing pulse width modulation control to display the color image signal processed by the image processing means; and display means for displaying the color image signal controlled by the display control means, the display means having a plurality of discharge paths two-dimensionally arranged each for displaying one of a plurality of predetermined colors, the display means having power supply means connected to the discharge paths, wherein the display control means permits a plurality of discharge paths of the same color of the display means to be coupled to the same power supply means to thereby time-divide a lighting time of the plurality of discharge paths for lighting control.

According to still another aspect of the present invention, there is provided a light circuit for an image display apparatus, comprising: control means for executing pulse width modulation control of an image signal corresponding to an image to be displayed; a plurality of discharging means for displaying the image signal controlled by the control means and each displaying one of a plurality of predetermined colors; and a plurality of ballast means for supplying power to those of the plurality of discharging means which supply a current with the same current value, wherein the control means permits a plurality of discharge electrodes of the same color of the discharging means to be coupled to same ballast means to thereby time-divide a lighting time of the plurality of discharge electrodes of the same color for lighting control.

Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrates presently preferred embodiments of the invention and, together with the general description given above and the detailed description of the preferred embodiments given below, serve to explain the principles of the invention.

This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: Fig. 1 is a block diagram schematically illustrating an image display apparatus according to the first embodiment of this invention; Fig. 2 is a circuit diagram illustrating a controller and a lighting circuit of the image display apparatus shown in Fig. 1; Figs. 3A through 3D are timing charts for explaining the controller shown in Fig. 2; Figs. 4A through 4G are timing charts for explaining the lighting circuit shown in Fig. 2; Figs. 5A through 5D are exemplary diagrams illustrating the lighting order of the lighting circuit shown in Fig. 2; Fig. 6 is a circuit diagram of a lighting circuit for an image display apparatus according to the second embodiment of this invention;; Figs. 7A through 7D are timing charts illustrating lighting timings in the lighting circuit shown in Fig. 6 at a time white is lit; Fig. 8 is a circuit diagram of a lighting circuit for an image display apparatus according to the third embodiment of this invention; Figs. 9A through 9C illustrate arbitrary lighting timings in the lighting circuit shown in Fig. 8, and are a timing chart for a power control transistor, a timing chart for a lighting control transistor and a timing chart for a lighting dot corresponding to a lamp, respectively; Fig. 10 is a circuit diagram of a lighting circuit for an image display apparatus according to the fourth embodiment of this invention; Fig. 11 is a circuit diagram of a lighting circuit for an image display apparatus according to the fifth embodiment of this invention; ; Fig. 12 is a circuit diagram of a lighting circuit for an image display apparatus according to the sixth embodiment of this invention; and Figs. 13A through 13C illustrate lighting timings in the lighting circuit shown in Fig. 12 at a time white is lit, and are a timing chart for a power control transistor, a timing chart for a lighting control transistor and a timing chart for a lighting dot corresponding to a lamp, respectively.

Preferred embodiments of this invention will now be described referring to the accompanying drawings.

Fig. 1 schematically illustrates an image display apparatus according to the first embodiment of this invention. A signal generator 12 for generating a video signal (for NTSC) and a digital signal (for a computer) is coupled with an image processor 14 for converting these electric signals into optical signals. This image processor 14 has a color decoder 16 for separating a video signal into three color signals, R (red), G (green) and B (blue), an A/D converter 18 for performing A/D conversion of the separated R, G and B signals, and an approximation processor 20 for executing a process for thinning scanning lines, a process for adding scanning lines, etc., for example.The image processor 14 further includes a memory 22 for storing character data or the like by a digital signal from the signal generator 12, a mixer 24 for mixing the output of the memory 22 with the output of the approximation processor 20, a CPU (Central Processing Unit) 26 for controlling the memory 22 upon reception of the output of the mixer 24, and an optical link 28 for converting an mixed electric signal from the mixer 24 into an optical signal.

The image processor 14 outputs the optical signal converted by the optical link 28 to a display section 32 through an optical cable 30. In the display section 32, the optical signal sent over the optical cable 30 is converted into an electric signal by an optical link 34.

This electric signal is sent via a receiver 36 and a transmitter 38 to a plurality of display controllers 40.

Each display controller 40, whose detailed description will be given later, executes time divisional lighting control of individual display elements of a display panel 42 comprising many discharge tubes (display elements). Through this control, the desired image having gradation or the like controlled is displayed.

Fig. 2 illustrates the display controller 40 serving as a controller of the image display apparatus and the display panel 42 serving as a lighting circuit.

Each signal based on the video signal sent from the transmitter 38 is stored into a dynamic memory 44.

Stored in this memory 44 is image data of R, G and B, i.e., data of display luminance of each discharge path on the display face (although G here is the luminance resulting from combining two discharge paths G1 and G2, if there is a single discharge path, it is a single luminance). The memory 44 sequentially outputs display luminance data corresponding to each discharge tube in accordance with the output signal of a counter 46.

The counter 46 receives at its input CK a periodic signal from an oscillator 48 and outputs a signal through an inverter 50 to a flip-flop 52 from its carry (CA) output. The Q output of the flip-flop 52 is sent to the counter 46, and the Q output is sent together with the output of the oscillator 48 to an OR circuit 54. The counter 46, inverter 50 and flip-flop 52 constitute a reset circuit.

The counter 46 sends its output representing the lighting order of a discharge path (which will be described later) to a data selector 56 constituting a time-divisional memory 54. The data selector 56 has output terminals corresponding in number to the discharge paths. For instance, provided that there are four discharge tubes as will be described later, the data selector 56 has 16 output terminals. The outputs from these output terminals 1 to 16 are input to NAND circuits 581, 582, 583 and 584.More specifically, the NAND circuit 581 receives the outputs "1," "4," "14" and "15" of the data selector 56, the NAND circuit 582 the outputs "2," "7," "12" and "13," the NAND circuit 583 the outputs "3," "6," "9" and "16," and the NAND circuit 584 the outputs "5," "8," "10" and "11." The outputs of these NAND circuits are supplied to input terminals 1 to 4 of a data selector 60.

A counter 62 receives a vertical sync signal (60 Hz) VD/ and a quadruple vertical sync signal (240 Hz) 4VD/ having a frequency four times that of the former sync signal. The vertical sync signal 4VD/ is supplied through output terminals QA and QB of the counter 62 to input terminals A and B of the data selector 60. Both vertical sync signals VD/ and 4VD/ are input through an AND circuit 64 to a PR terminal of the flip-flop 52.

A data selector 66 receives a signal from the data selector 60 as well as data (8 bits) from the aforementioned memory 44 at its terminal A and reference data (8 bits) at its terminal B. 8-bit gradation data of the data selector 66 is input to a PWM (Pulse Width Modulation) controller 68 which performs PWM control to determine the lighting duty ratio. The PWM controller 68 also receives the output of the aforementioned OR gate 54 as a data strobe signal DSTB/, This controller 68 generates a switch ON signal having a pulse width corresponding to the data from the data selector 66 and sends it to those switching elements which render the currents of the associated discharge paths, such as SW1 to So16.

Reference numeral 70 is a tricolor single tube type discharge tube having a common electrode, as disclosed in, for example, Unexamined Published Japanese Patent Application No. 63-198023. Generally, there are 100 to 250 discharge tubes vertically and 150 to 400 discharge tube horizontally arranged on the display face of the display panel 42 of the image display apparatus, though only four discharge tubes are illustrated here. The four discharge tubes 70 have four types of discharge paths, B (701, 703, 705, 707), G1 (702, 704, 706, 708), G2 (709, 7011, 7013, 7015) and R (7010, 7012, 7014, 7016), inside, as shown in Figs. 5A-5D referred to later.Those of 16 discharge paths which are of the same color are coupled together through respective switching elements SW1-SW16, and are coupled to one ends of inductances (choke coils) 72 (B), 74 (G1), 76 (G2) and 78 (R) as corresponding ballasts. The ballasts 72, 74, 76 and 78 each have their other end coupled to a high frequency generator (not shown).

The operation of thus constituted image display apparatus will now be described referring to the timing charts of Figs. 3A through 3D and 4A through 4G and the exemplary diagrams of the lighting order of the discharge paths shown in Figs. 5A through 5D.

A vertical sync signal VD/ of a period of 16.7 ms as shown in Fig. 3A and a quadruple vertical sync signal 4VD/ (Fig. 3B) whose period (4 ms) is about 1/4 of the period of the former sync signal VD/ are input to the counter 62 and AND circuit 64. Upon reception of these signals VD/ and 4VD/, the data shown in Fig. 3C (the data being indicated by the oblique lines) is written in the succeeding PWM circuit by the data strobe signal DSTB/ shown in Fig. 3D. The data added to the signal DSTB/ is determined in accordance with the number of discharge paths (i.e., display elements). In the case of this embodiment, data corresponding to 16 discharge paths is used, due to the use of discharge paths 701-7016. The time between the rising and falling of the signal DSTB/ is a time in which PWM driving is done.

Data divided into 16 segments by the counter 46 and data selector 56 are output to the data selector 66 through the data selector 60 from the NAND circuits 581, 582, 583 and 584 according to the lighting order of the discharge tube 70. The data selector 66 selects data on the terminal A side when input data is "L." When the counter 46 counts up to "15" from "0,!! the reset circuit having this counter 46 outputs CA to reset the counter to "0." When the input data is "H," however, data on the terminal B side is selected (data on the terminal B side being "L" to be data off).

In this manner, the PWM controller 68 switches the switching elements SW1 to SW16 to light the individual discharge paths 701-7016 in accordance with the lighting order of the discharge tubes 70.

Referring to Figs. 4A through 4G and 5A through 5D, assume that the vertical sync signal VD/ has fallen as shown in Fig. 4E. Then, the individual discharge paths 701-7016 shown in Figs. 4A-4D are sequentially rendered in lighting enable state, by writing the data in the PWM circuit on the basis of the data strobe signal DSTB/ (Figs. 4F and 4G), as mentioned above.

In this case, Fig. 4A illustrates the discharge tubes 701, 703, 705 and 707 of B, Fig. 4B the discharge tubes 702, 704, 706 and 708 of G1, Fig. 4C the discharge tubes 709, 7011 7013 and 7015 of G2, and Fig. 4D the discharge tubes 7010, 7012, 7014 and 7016 of R.

At time tl, the PWM controller 68 sets only the switching elements SW1, SW4, SW14 and SW15 on and the other off so as to turn on the discharge tubes corresponding to the input of the NAND circuit 581, i.e., the discharge tubes 701, 704, 7014 and 7015, as shown in Fig. 5A. In this case, it is assumed that shaded portions in Figs. 5A through 5D are light. Then, at time t2, only the switching elements SW2, SW7, Swl2 and SW13 are likewise set on in association with the input of the NAND circuit 582, and the discharge tubes 702, 707, 7012 and 7013 are lit as shown in Fig. 5B.

Similarly, at time t3, only the switching elements SW3, SW6, SWg and SW16 are likewise set on in association with the input of the NAND circuit 583, and the discharge tubes 703, 706, 709 and 7016 are lit as shown in Fig. 5C. At time t4, only the switching elements SW5, SW8, SW10 and Swll are likewise set on in association with the input of the NAND circuit 584, and the discharge tubes 705, 708, 7010 and 7011 are lit as shown in Fig. 5D.

Referring to Figs. 4A through 4G, times tl and t2, t2 and t3, t3 and t4, and t4 and t5 are timings (time of the maximum illumination) at of 4-ms width which provides the time divisional lighting enable state of each discharge path at an "H" level. The PWM controller 68 controls the "H" level width with the illustrated state as the maximum width, thereby controlling the display luminance of each discharge path. The time division should not necessarily be done at equal intervals.

Further, although the foregoing description of this embodiment has been given with the switching elements for time divisional lighting also serving as the switching elements for the PWM control, this embodiment is not restricted to this particular type.

For instance, the switching elements may be provided separately.

Although a medium size image display apparatus employing a tricolor single tube type discharge tube has been explained in the foregoing description, the image display apparatus is not restricted to this particular type. For instance, this invention can also apply to a large image display apparatus using a single discharge lamp for each color as well as an image display apparatus employing two color lamps or four or more color lamps.

As described above, according to this invention, since one ballast is shared by a plurality of discharge paths, the number of required ballasts which are relatively large components can be reduced, thus permitting electric circuits to be more compact. In addition, since the same ballast is shared by those discharge paths which display the same color and the discharge paths are lit at equal intervals in time divisional manner, the discharge paths coupled to that ballast can be lit at the same luminance. This can eliminate the need for lighting time control or relative luminance adjustment between the discharge paths. Further, conducting the time divisional lighting at equal intervals requires a less number of components such as a flip-flop circuit.

Furthermore, the luminance for each color or the lamp current for each color can be easily set by setting the specifications of a ballast or setting the inductance if it is an L ballast. Color balance such as white balance can be adjusted by setting the ballast specifications. In other words, color ballast can be provided without the lighting control or controlling the transmittivity of a color filter.

The second embodiment of this invention will be described below referring to Figs. 6 and 7A through 7D.

Referring to Fig. 6, VB, VG1, VR and VG2 are power supplies for supplying power to single tube multicolor lamps LP1 to LP4 of display discharge paths, which are constituted by B, G1, R and G2. The lamps LP1 to LP4 each have an anode B for forming a discharge path for displaying blue, anodes G1 and G2 for green display and an anode R for red display as well as common cathodes El to E4. AE1 to AE4 are starting auxiliary electrodes, V2 is an excess heating power supply for the cathodes El to E4, and F is a high-frequency power supply used for ionization electrodes (i.e., third electrodes) TrB is a switching transistor for supplying a current to the anode B, and TrG1, TrR and TrG2 are likewise switching transistors for supplying a current to the anodes G1, R and G2, respectively.These transistors each have their base supplied with a pulse lighting control signal from a controller 80, and their activation is controlled based on this control signal.

Controlling the activation of the transistors supplies a current to the discharge paths of the individual colors to turn on or off the associated discharge tubes.

Rs, RGl, RR and RG2 are ballast resistances which have the same value.

The operation of the second embodiment will be described below referring to Figs. 7A through 7D, which illustrate the timing at which the lamp LP1 in Fig. 6 is lit white.

The power supplies VB, VGl, VR and VG2 supplies predetermined power through ballast resistances Rg, RG1, RR and RG2 to the switching transistors TrB, TrG1, TrR and TrG2. The controller 80 outputs a control signal to the bases of these transistors TrB, TrG1, TrR and TrG2 at a predetermined timing according to which the transistors are turned on or off. In accordance with the ON/OFF timing of the transistors TrB, TrG1, TrR and TrG2, power is supplied to the individual discharge paths of the lamps LP1-LP4. For instance, at the lighting timings as given in Figs. 7A-7D, B becomes lighting enable state first, then G1, R and G2 become lighting enable state in the named order.In the above, the lighting enable state of lamp LP1 was described, but the time during which B of lamps LP2, LP3 and LP4 is kept in the lighting enable state is different from the time during which B of lamp LP1. is kept in the lighting enable state. This is also true in the case of G1, R, G2.

According to the second embodiment, power is supplied from a common power supply to the discharge paths associated with the same lamp current, i.e., the discharge paths for each color. Accordingly, controlling the voltages of these power supplies can adjust the luminance for each color. Since the source voltages can be controlled for each color, a single type of ballast resistances may be used. This can eliminate the need for various types of ballasts or ballast transformers.

Nor is it necessary to adjust the pulse width for luminance control.

The third embodiment of this invention will be described below referring to Figs. 8 and 9A through 9C.

The same reference numerals as used for the components shown in Fig. 6 are also used to denote the identical-or corresponding elements in the second embodiment, thus omitting their description.

Referring to Fig. 8, the power supplies VB, VG1, VR and VG2 are connected wih power source control transistors TrlB, TriGi, TrlR and TrlG2 as illustrated.

These transistors have their bases coupled to a controller 82, so that their activation is controlled by the controller 82. Ballast resistances R1 and R2 are coupled at one end to the transistors TrlB, TrlG1, TrlR and TrlG2 through reverse-current preventing diodes DB, DG1 DR and DG2. The other ends of the ballast resistances R1 and R2 are coupled through lighting control switching transistors Tr2B, Tr2Gl, Tr2R and Tr2G2 to single tube multicolor lamps LP1 and LP2 of display discharge paths, respectively.The transistors Tr2B, Tr2G1, Tr2R and Tr2G2 serve to control power supply to the individual discharge paths of the lamps LP1 and LP2 to lit dots corresponding to the individual discharge paths for the desired period of time. Although the case of using two lamps has been described above, this embodiment is not restricted to this type; for example, the same arrangement can also apply to a case involving four lamps in use.

The operation of the third embodiment will be described below referring to Figs. 9A through 9C, which illustrate the lighting timings for those dots which correspond to the power supply control transistors TrlB, TrlG1, TrlR and TrlG2, the lighting control switching transistors Tr2B, Tr2G1, Tr2R and Tr2G2, and the lamp LP1.

As shown in Fig. 9A, the transistors TrlB, TrlG1, TrlR and TrlG2 repeatedly switched on in sequential manner with a pulse width common to the individual discharge paths. In order to turn on the individual dots at gradation based on an instruction from the controller 82, the switching transistors Tr2B, Tr2G1, Tr2R and Tr2G2 are turned on at a pulse width according to the gradation (see Fig. 9B). When the transistors Tr2B, Tr2Gl, Tr2R and Tr2G2 are turned on for lighting the dots, those dots which are associated with the individual discharge paths are lit in accordance with the ON activation of the transistors Trip, TriGi, TrlR and TrlG2, as shown in Fig. 9C.Therefore, the time for the lighting enable state of the dots of the discharge paths can be determined.

Fig. 10 illustrates the fourth embodiment of this invention. In the fourth embodiment, AC power supplies VFB, VFG1 VFR and VFG2 of different frequencies are inserted in the power supplies VB, VG1 VR and VG2 of the circuit of the third embodiment shown in Fig. 8. As the other portions are the same as those of the third embodiment, a description of the structural elements of those portions and the operation will be omitted.

Referring to Fig. 10, the selection of arbitrary frequencies for the power supplies VFB, VFGl, VFR and VFG2 determines the levels of the currents of the lamps LP1 and LP2. Therefore, altering the frequencies of the power supplies can facilitate luminance adjustment for each color.

According to the second to fourth embodiments, a triode type having a activating auxiliary electrode is used as a lamp. The fifth and sixth embodiments, which will be described below, are modifications of the second and third embodiments in which the lamp is replaced with a fine discharge type. The same reference numerals as used to denote components of the above-described embodiments will also be used to specify the identical or corresponding elements in the fifth and sixth embodiments, thus omitting their otherwise redundant description.

Fig. 11 illustrates the fifth embodiment of this invention, which corresponds to the second embodiment shown in Fig. 6. Although the diagram illustrates two lamps connected in the fifth embodiment, four or more lamps may be connected as in the circuit shown in Fig. 6. Referring to Fig. 11, Vsa is a power supply for fine discharging, and R01 and R02 are fine discharge limiting resistances. D01 and D02 are reverse-current preventing diodes.

With the above arrangement, this invention can apply to a lamp which has only two electrodes (anode and cathode), but no activating auxiliary electrode.

Fig. 12 illustrates the sixth embodiment of this invention, which corresponds to the circuit of the third embodiment shown in Fig. 8. Although the diagram illustrates two lamps connected in the sixth embodiment, this embodiment is not restricted to this type. Referring to this diagram, RB1, RB2, RB3, RB4, ... are main discharge limiting resistances, which become RB1 = RB2 = RB3 = RB4 by varying the source voltages. If the currents for G1 and G2 are equal to each other, the power supply VG2 can be omitted.

The operational timing of the lighting circuit for thus constituted image display apparatus will now be described referring to Figs. 13A through 13C. Fig. 13A illustrates the timing chart for the power supply control transistors TrlB, TrlG1, TrlR and TrlG2,; according to this timing chart, transistors are activated in the order from Tr1B to TrlG1 to TrlR to TrlG2.

In response to the activation of the transistors, the transistors Tr2B, Tr2G1, Tr2R and Tr2G2 for lighting the lamp LP1 are sequentially turned on as shown in Fig. 13B. The transistors Tr2B, Tr2G1, Tr2R and Tr2G2 for lighting the lamp LP2 are likewise turned on sequentially. In other words, those dots corresponding to the individual discharge paths of each lamp are lit in accordance with the ON activation of the transistors TrlB, TrlG1, TrlR and TrlG2. Accordingly, the time for the lighting enable state for the dots of the discharge paths is determined.

Although the description of the second to sixth embodiments has been given with reference to the case where a single tube multicolor discharge lamp is turned on, these embodiments are not restricted to this particular type, but can apply to a single tube monochromatic lamp. Further, this invention can apply to a display element having tricolor (RGB) dot structure which does not require separation of G (green) into two components, or a display element constituted by a combination of two or more colors.

Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, and representative apparatuses shown and described. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

Claims (20)

Claims:

1. An image display apparatus comprising: signal generating means for generating an electric signal corresponding to an image to be displayed; image processing means for converting said electric signal generated by said signal generating means into a predetermined color image signal; display control means for executing pulse width modulation control to display said color image signal processed by said image processing means; and display means for displaying said color image signal controlled by said display control means, said display means having a plurality of discharge paths two-dimensionally arranged each for displaying one of a plurality of predetermined colors, said display means having ballast means connected to the discharge paths, wherein said display control means permits a plurality of discharge paths of the same color of said display means to be coupled to the same ballast means to thereby time-divide a lighting time of said plurality of discharge paths for lighting control.

2. An apparatus according to claim 1, wherein said plurality of discharge paths constitute a discharge element having a plurality of discharge paths of different colors, and said display control means performs such a control as to permit discharging of only one discharge path in said discharge element having said plurality of discharge paths within a specific time.

3. An apparatus according to claim 1, wherein said display control means includes switch means for switching an on/off state of desired discharge paths to be lit in accordance with a predetermined lighting enable state signal.

4. An apparatus according to claim 1, wherein said display control means includes power supplies for individual colors, and switch circuit means for controlling on/off switching of said discharge paths of different colors in accordance with values of voltages of said power supplies.

5. An apparatus according to claim 1, wherein said display control means controls a lighting enable state of said discharge paths of different colors for a same period of time.

6. An image display apparatus comprising: signal generating means for generating an electric signal corresponding to an image to be displayed; image processing means for converting said electric signal generated by said signal generating means into a predetermined color image signal; display control means for executing pulse width modulation control to display said color image signal processed by said image processing means; and display means for displaying said color image signal controlled by said display control means, said display means having a plurality of discharge paths two-dimensionally arranged each for displaying one of a plurality of predetermined colors, said display means having power supply means connected to the discharge paths, wherein said display control means permits a plurality of discharge paths of the same color of said display means to be coupled to the same power supply means to thereby time-divide a lighting time of said plurality of discharge paths for lighting control.

7. An apparatus according to claim 6, wherein said plurality of discharge paths constitute a discharge element having a plurality of discharge paths of different colors, and said display control means performs such a control as to permit discharging of only one discharge path in said discharge element having said plurality of discharge paths within a specific time.

8. An apparatus according to claim 6, wherein said display control means includes power supply means for individual colors, and switch circuit means for controlling on/off switching of said discharge paths of different colors in accordance with values of voltages of said power supply means.

9. An apparatus according to claim 6, wherein said display control means controls a lighting enable state of said discharge paths of different colors for a same period of time.

10. An apparatus according to claim 8, wherein frequencies of said power supply means for individual colors can be variably set.

11. An apparatus according to claim 6, wherein said display control means has a plurality of discharge lamps each for display one of a plurality of predetermined colors, said power supply means supply power to those of said plurality of discharge lamps which provide a current with the same value, and a plurality of discharge electrodes of the same color of said discharge lamps are connected to the same power supply means of said display control means to thereby control time divisional lighting of a lighting time of said plurality of discharge electrodes of the same color.

12. An apparatus according to claim 11, wherein said plurality of discharge lamps have a plurality of discharge electrodes of different colors, and said display control means performs such a control as to permit discharging of only one discharge electrode in said plurality of discharge electrodes within a specific time.

13. An apparatus according to claim 11, wherein said display control means includes power supply means for individual colors, switch circuit means for controlling on/off switching of said discharge lamps of different colors in accordance with values of voltages of said power supply means, and a controller for controlling on/off activation of said switch circuit means.

14. An apparatus according to claim 13, wherein said display control means controls a lighting enable state of said discharge lamps of different colors for a same period of time.

15. An apparatus according to claim 13, wherein frequencies of said power supply means for individual colors can be variably set.

16. A light circuit for an image display apparatus, comprising: control means for executing pulse width modulation control of an image signal corresponding to an image to be displayed; a plurality of discharging means for displaying said image signal controlled by said control means and each displaying one of a plurality of predetermined colors; and a plurality of ballast means for supplying power to those of said plurality of discharging means which supply a current with the same current value, wherein said control means permits a plurality of discharge electrodes of the same color of said discharging means to be coupled to same ballast means to thereby time-divide a lighting time of said plurality of discharge electrodes of the same color for lighting control.

17. An apparatus according to claim 16, wherein said plurality of discharging means have a plurality of discharge electrodes of different colors, and said display control means performs such a control as to permit discharging of only one discharge electrode in said plurality of discharge electrodes within a specific time.

18. An apparatus according to claim 16, wherein said display control means includes power supply for individual colors, switch circuit means for controlling on/off switching of said discharging means of different colors in accordance with values of voltages of said power supply.

19. An apparatus according to claim 16, wherein said display control means controls a lighting enable state of said discharging means of different colors for a same period of time.

20. An image display apparatus for controlling lighting of a plurality of discharge paths in time divisional manner, substantially as hereinbefore described with reference to the accompanying drawings.