DE19837307A1 - Pulse width modulated image display such as a plasma screen that is controlled using a number of sequential time intervals within the display period - Google Patents

Abstract

The display image period is subdivided into a number of sequential time intervals and the display elements are divided into two partial time slots. The brightness component is derived from an RGB signal via an activation sequence. The image display uses a motion sensor and is used as part of a means of modifying the activation sequence.

Description

The invention relates to a pulse width controlled image display device in particular a plasma display with control means for controlling a Screen with the specified in the preamble of claim 1 Characteristics. The invention further relates to a method for control a pulse width controlled image display device with those in the preamble of claim 10 specified features.

Such a method and device come for example in color plasma displays, which will be used in the future Color television tubes currently used in higher quality televisions will complement or replace. Is related to color picture tubes the user of high quality television sets since the late eighties accustomed to a flicker-free display due to the 100 Hz technology.

From the magazine Radio Fernsehen Elektronik RFE, Issue 2, 1997, pages 18- 20, a plasma display is known which consists of two glass plates with a matrix arranged electrodes, between which there is a noble gas mixture located. The image information is not displayed line by line in plasma displays shown as with cathode steel tubes, but full frame. Because through the Matrix addressing of a plasma display does not close the individual pixels can be switched on and off individually at any time, the Activation of the pixels for the entire display in one Activation pass.

Controlling a plasma display consists of several phases: one  Addressing or initializing, holding or activating and a deletion phase.

In the addressing or initialization phase, all cells of the Plasma displays preloaded, which in the subsequent holding or Activation phase should be activated. In the last step, the Deletion phase, the preloaded cells are unloaded again Image information is deleted.

The one available for displaying a television picture Time interval is broken down into part-time intervals of different duration, during which depending on the brightness value of the respective A predetermined activation sequence is selected. This corresponds to one or more flashes of the respective Pixel during the available for image display Time interval, each lighting up a predetermined period of time assigned.

Such known plasma displays are from Fujitsu for example as a 42 '' plasma display with the designation. . . on the market expelled.

The object of the invention is a device and a method for Control of a pulse width controlled image display device indicate which lead to improved image reproduction.

This object is achieved by a device with the features of Claim 1 and a method with the features of claim 10 solved. Advantageous embodiments of the invention are in the dependent Claims specified.  

The invention is based on the finding that it is slow when present moving or still images when displayed on a pulse width controlled display device for flickering, especially in the 50 Hz range, although for illustration of a frame in a time interval of 20 msec Part time interval frequency due to the use of part time intervals Is 400 Hz. The same applies to systems in the 60 Hz range. in the the invention is further described using a 50 Hz system.

Simulations have confirmed that such flickering, which this is particularly noticeable with slow moving images can be reduced that the order of the part-time intervals and / or the activation sequences of the part-time intervals in a certain way can be varied. Such a variation aims at flickering on minimize images to be displayed on the screen.

To achieve a flicker-free display, it has proven to be proven to be advantageous, the activation sequences of the part-time intervals in to be distributed substantially evenly over the part-time intervals.

Different grayscales are generated by a suitable one Selection of the activated part-time intervals.

When fast moving images are available, the order of the Part-time intervals and / or the activation sequences of the part-time intervals see above chosen that an image display free of motion artifacts is achieved becomes.

In practical applications, the number has proven to be advantageous of the activation sequences generated in the part-time intervals on 12 and set the number of part-time intervals to 8. The part-time intervals  are divided into two part-time groups.

In a preferred embodiment of the invention is for illustration a time interval of 20 msec is provided and the Partial interval frequency is therefore 400 Hz.

The corresponding tasks of the picture tube television sets The intended deflection control takes place with the pulse width controlled Image display device in such a way that the control means for driving of the screen have a timing device which and horizontal sync signals processed and the timing of the Pulse width modulator and a horizontal driver device of the Controls the plasma screen.

In the following, the invention is illustrated by the figures Exemplary embodiments described and explained in more detail.

Show it:

Fig. 1 is a block diagram of a television receiver with a pulse-width-controlled plasma display,

Fig. 2 is an illustration of a first partial pattern time interval,

Fig. 3 a due to the portion of time interval pattern of Fig. 2 diagram illustrating the 50-Hz flicker,

Fig. 4 is a diagram illustrating the brightness distribution during one frame period for a particular input signal level at which strong 50 Hz flicker occurs,

Fig. 5 is a partial optimized time interval pattern in which the 50 Hz flicker is reduced,

FIG. 6 shows a diagram belonging to the part-time interval pattern from FIG. 5 to illustrate the reduced 50 Hz flickering, FIG.

Fig. 7 is a diagram illustrating the motion detector-dependent mode switching with z. B. two operating states.

Fig. 1 shows a block diagram of a television receiver with a pulse width controlled plasma display. The television receiver 1 , 2 has a television signal processing part 1 and an image processing part 2 . The television signal processing part 1 has a first input 17 , to which the signals of an antenna device 19 are fed. The signals of the input 17 are forwarded to a high-frequency and intermediate-frequency processing unit 4 and an audio signal processing unit 3 . An FBAS signal is present at the output of the high-frequency and intermediate-frequency processing unit 4 and is fed to an analog / digital converter 5 . An external CVBS signal can be fed in via a second signal input 20 . The output signal of the analog / digital converter 5 is then passed to a so-called feature box 6 . The feature box 6 performs certain functions such as demodulation of the composite signal, still picture, zoom, format adaptation, image sharpness optimization, picture-in-picture, etc. The resulting digital components Y, U, V of an image signal 21 are forwarded to a digital matrix unit 8 of the image processing part 2 . The feature box 6 also serves to convert the interlaced signal into an interlaced signal and the necessary adaptation of the signals to the screen 14 by line interpolation. This is done using the synchronization signals 23 , 24 for vertical and horizontal synchronization.

The digital matrix unit 8 also has a connection 27 for supplying a VGA signal supplied via an external signal input 18 , which is converted into a digital signal by means of an analog / digital converter 25 . An RGB signal 22 is present at the output of the digital matrix unit 8 and is used to control the controllers ( 10 , 13 ). The controller ( 10 , 13 ) generates the control signals 26 for an address driver 11 . A memory 9 is coupled to the controller ( 10 , 13 ) for this signal generation. The controller ( 10 , 13 ) has a part-time interval weighting unit, which is used to weight the part-time intervals, ie to determine their sequence and duration.

The column driver device 11 controls the individual columns of the plasma screen 14 . The associated time control takes place with the help of the controller ( 10 , 13 ), which defines the start of the part-time intervals and the times for the addressing and activation phase. The part time interval line control device contained in the time control is used for this. The controller ( 10 , 13 ) is connected to a horizontal driver 12 . This horizontal driver 12 is active during the activation phases. Power is supplied using a power supply 7 .

While the mode of operation and the construction of the television signal processing part 1 essentially corresponds to that of a conventional television receiver with picture tube, the construction of the image processing part 2 is fundamentally different. The main reason for this is that the plasma display device 14 has a digital relationship between the input variable and the luminance. There are therefore only two states: switched on or switched off. In order nevertheless to be able to achieve a large range of different intermediate gray levels, a digital time-division multiplexing method is used for the image processing part 2 shown in FIG. 1. In this, the RGB signals 22 are broken down into several part-time intervals of different durations. This is done with the help of the controller ( 10 , 13 ) and other units such as a memory 9 . Due to the inertia of the human eye, individual image changes no longer appear on the plasma display device 14 , but rather a gray value that depends on the average activation time. If this duration is weighted in the part-time intervals, then many gray levels can be displayed with just a few part-time intervals. With a binary weighting (1, 2, 4, 8, ...), two grayscales can be displayed exponentially with the number of part-time intervals. In order to be able to display as many gray levels as possible, it is therefore desirable to use as many part-time intervals as possible, but this is not possible due to technological constraints. The controller ( 10 , 13 ) determines the sequence and activation of the individual part-time intervals by means of an assignment that depends on its input signal level. In the case of binary weighting, this assignment is such that the longest part-time interval is assigned to the digitally weighted bit, the second longest part-time interval to the second-highest weighted bit, and so on.

Simulations and subjective considerations have shown that, despite a part-time interval frequency of 400 Hz, flickering artifacts of 50 Hz, especially from medium luminance levels, can be disruptive. The conspicuousness of the 50 Hz flickering varies with the luminance to be displayed and depends on the luminance level of the activated part-time interval and on the sequence of the part-time intervals within the 20 msec frame period. For this reason, the controller ( 10 , 13 ) of the image display device 2 is controlled in such a way that the sequence of the part-time intervals and their activation sequence can be changed as a function of the movement content of the image signal. In one operating state, when there are rapid movements, the signals displayed on the screen are shown in the correct direction of movement, and in another operating state there is a flicker-free image display.

FIG. 2 shows a diagram of a part-time interval pattern, in which the displayed images are displayed with the correct movement. The letter L denotes the luminance input level of the RGB signal designated by reference number 22 in FIG. 1. The partial time interval groups TG1 and TG2 identify the time interval TG available for an image display. The part-time interval groups TG1 and TG2 are each divided into a number of successive part-time intervals t1 to t8. During the part-time intervals t1 to t8, the luminance signal L assigned to a respective pixel is generated by converting an analog brightness value into a predetermined number of activation times which are present during one or more of the part-time intervals t1 to t8. The number of activation times generated in the part-time intervals t1 to t8 is 12 in the exemplary embodiment shown in FIG. 2 and the number of part-time intervals t1 to t8 is 8, the part-time intervals t1 to t8 forming two part-time inter-groups TG1 and TG2, each of which has an identical activation duration exhibit.

The temporal length of each part-time group TG1, TG2 is 20 msec. The temporal length of each of the part-time intervals t1 to t8 of each part-time group is different, which is expressed in FIG. 2 by the "weighting factors" 12, 8, 4, 2 and 1 indicated at the bottom of the diagram.

If, for example, the luminance input level L assigned to a pixel of the plasma display 14 has the value 44, then this pixel lights up during the part-time intervals t1, t2, t3, t7 and t8 of the part-time group TG1 and during the part-time intervals t1, t2, t6, t7 and t8 of the second Part-time group TG2 and is dark during the part-time intervals t4, t5 and t6 of the first part-time group TG1 and during the part-time intervals t3, t4 and t5 of the second part-time group TG2.

FIG. 3 shows a diagram belonging to the part-time interval pattern of FIG. 2 to illustrate a 50 Hz flickering as a function of the brightness H and the input signal level L. The course of the characteristic curve F, which characterizes the 50 Hz flickering, shows in particular at input signal levels L. <30 an increased 50 Hz flickering. A maximum can be determined on the basis of this simulation result with an input signal amplitude of 44 as flicker value Fm.

FIG. 4 shows the course of the average brightness Hm for a special input signal amplitude level of 44 as a function of time t. The 50 Hz flicker disturbance can be clearly seen from the sinusoidal or cosine-shaped brightness curve Hv.

FIG. 5 shows a partial time interval pattern optimized with respect to the 50 Hz flickering. The reference symbols already introduced in connection with FIG. 2 are used here. In contrast to the pattern shown in FIG. 2, the part-time interval pattern shown in FIG. 5 has a changed order of the part-time intervals t1 to t8. Thus, in the exemplary embodiment shown in FIG. 5, the order of the weights 12, 4, 8, 1, 2, 12, 4, 8, while the order of the weights in the part-time interval pattern shown in FIG. 2 is 12 , 8 , 4 , 2 , 1 , 4 , 8 , 12 . The corresponding order of the part-time intervals in FIG. 5 is t1, t3, t2, t5, t4, t8, t6, t7, while the order of the part-time intervals in FIG. 2 is t1, t2, t3, t4, t5, t6, t7, t8 reads.

Fig. 6 shows the simulation result to that shown in t5 part time interval pattern. The reference symbols already introduced in connection with FIG. 3 are used here. The simulation shows that the partial time interval pattern shown in FIG. 5 leads to a significantly reduced 50 Hz flickering, in particular at higher input signal levels.

Since the aforementioned 50 Hz flickering only occurs with standing or slowly moving picture contents, the partial time interval pattern according to FIG. 5 is used according to the invention only with standing or slowly moving picture contents. In the case of rapidly moving image contents, however, the part-time interval pattern according to FIG. 2 is used, in which less movement artifacts occur.

To this end 6, the television receiver shown in Fig. 1 as part of the feature box on a motion detector 6 a, the output signals of the controller (10, 13) are supplied. In a first operating state, when there are still or slowly moving images, the sequence of the part-time intervals and / or the activation sequences in the part-time intervals is specified in such a way that the flickering of the images shown on the display 14 is minimized. Furthermore, in a second operating state when fast moving images are present, he specifies the sequence of the part-time intervals and / or the activation sequences in the part-time intervals in such a way that the movement artifacts in the images shown on the display 14 are minimized.

To implement these operating states, the controller ( 10 , 13 ) accesses data records assigned to the respective movement content, which are stored in different memory areas of the memory 9 .

This is illustrated in FIG. 7. In Fig. 7 it is shown that the memory has 9 as two different memory areas 9 a and 9 b. Data corresponding to the respective part-time interval pattern are stored in each of these memory areas. Depending on the motion content of the image, which is detected by the motion detector 6 a, one of the two memory areas is addressed in order to read out the data associated with the respective part-time interval pattern.

An advantageous development of the invention consists in providing, in addition to the two operating states already mentioned, further operating states, each of these further operating states corresponding to a specific movement content. In this case, the memory 9 has further memory areas which contain data records for these further operating states.

In an advantageous embodiment of the invention, the controller ( 10 , 13 ) is implemented by a pulse width modulator ( 10 ) and a timing control device ( 13 ).

Claims (11)

1. Pulse-width-controlled image display device ( 1 , 2 ), in particular a plasma display, with control means ( 10-13 ) for controlling a screen ( 14 ), the time interval available for image display having two part-time interval groups (TG1, TG2), each in several temporally successive part-time intervals (t1,..., t8) are divided, and wherein the brightness signal assigned to a pixel is generated by converting an RGB signal into a number of activation sequences which are present during one or more of the part-time intervals, characterized in that

• - The image display device has a motion detector ( 6 a),
• the image display device has means ( 9 , 10 ) for changing the order of the part-time intervals and / or means ( 9 , 10 ) for changing the activation sequences in the part-time intervals,
• - And the change in the order of the part-time intervals and / or the change in the activation sequences in the part-time intervals depending on the output signal of the motion detector ( 6 a).

2. Pulse width controlled image display device according to claim 1, characterized in that it can be operated in several operating states, in a first Operating status when there are still or slow moving images the order of the part-time intervals and / or the activation sequences in the part-time intervals are specified such that the flickering from  images displayed on the screen is minimized, and being in one second operating state when there are fast moving images Order of the part-time intervals and / or the activation sequences in the Part-time intervals are specified such that the movement artifacts in the images displayed on the screen are minimized. 3. Pulse width controlled image display device according to claim 2, characterized in that it has a memory ( 9 ) with a plurality of memory areas, each memory area being provided for storing data records which are associated with one of the operating states. 4. Pulse width controlled image display device according to one or more of the preceding claims, characterized in that the control means ( 10-13 ) have a controller ( 10 , 13 ) which is composed of a pulse width modulator ( 10 ) and a timing control device ( 13 ). 5. Pulse width controlled image display device according to one or more of the preceding claims, characterized in that it has a digital matrix ( 8 ) which is provided for processing a digital image signal ( 21 , 27 ) and as the output signal that the pulse width modulator ( 10 ) of the control means ( 10-13 ) supplied RGB signal. 6. Pulse-width-controlled image display device according to one or more of the preceding claims, characterized in that the control means ( 10-13 ) have a timing control device ( 13 ), which vertical and horizontal signals ( 23 , 24 ) are supplied and which on the output side with the pulse width modulator ( 10 ) and a horizontal driver ( 12 ) is connected. 7. Pulse width controlled image display device according to one of the claims 2 to 6, characterized in that In the first operating state, the sequence of the part-time intervals in the part-time interval groups is selected in such a way that the following relationship applies to the activation times of the part-time intervals:
t1: t2: t3: t4: t5: t6: t7: t8 = 12: 4: 8: 1: 2: 12: 4: 8. 8. Pulse-width-controlled image display device according to one of claims 2 to 7, characterized in that in the second operating state the sequence of the part-time intervals in the part-time interval groups is selected such that the following relationship applies to the activation times of the part-time intervals:
t1: t2: t3: t4: t5: t6: t7: t8 = 12: 8: 4: 2: 1: 4: 8: 12. 9. Pulse width controlled image display device according to one of the claims 2 to 8, characterized in that in the first operating state, the order of the part-time intervals it is specified that there is a substantially uniform distribution of the Activation sequences over the part-time intervals results.   10. Method for controlling a pulse width controlled Image display device in which the for an image display for Available time interval (TG) two part-time interval groups (TG1, TG2), each in several consecutive times Part-time intervals (t1,..., T8) are divided and at which one Brightness signal assigned to the pixel by converting an RGB Signal is generated in a number of activation sequences that during one or more of the part-time intervals are available, characterized in that the order of the part-time intervals and / or the activation sequences in the part-time intervals depending on the movement content of the image to be displayed is changed.