JP4492126B2 - Level control method, display panel drive circuit and display device - Google Patents

Description

  The present invention relates to a drive circuit for driving a display panel such as a PDP panel, a display device using the drive circuit, and a level control method used for the drive circuit.

  Specifically, by suppressing slight fluctuations in the input level due to quantization noise and the like, a stable output can be obtained, and when this is applied to a display panel, the display image based on the minute fluctuations in the input level is reduced. It is designed to dispel the sense of incongruity.

  As a display monitor for displaying images, a flat display monitor has been frequently used. When a PDP (Plasma Display Panel) panel is used as a display monitor, the drive circuit (PDP drive circuit) often has an APC (Automatic Power Control) function.

  The APC function is used for current limitation to prevent a current exceeding a predetermined value from flowing through the PDP panel. By limiting the current to the PDP panel, the brightness (contrast) of the PDP panel is limited. The power consumption of the PDP panel is suppressed by limiting the current.

  In order to prevent a current exceeding a predetermined value from flowing, the PDP drive circuit limits the power consumption of the PDP panel. FIG. 8 shows a driving circuit for a display panel as an example.

  In FIG. 8, an input video signal, for example, digitized R, G, and B primary color signals are supplied to and input to an average luminance level calculating means (average luminance level calculating means) 12 for calculating the average luminance level of the input signal. An average luminance level APL (Average Picture Level) per frame (or per field) of the video signal is calculated. The average luminance level of the PDP panel is substantially proportional to the display rate of the video signal. The display rate of the video signal is the ratio of the integrated value of the luminance level of all pixels when displaying an image based on the actual video signal to the integrated value of the luminance level of all pixels when displaying an all-white video signal. Desired.

  When the display rate corresponding to APL exceeds a predetermined value, for example, 25%, the light emission luminance of the PDP panel is limited. Therefore, as shown in FIG. 8, a limiting means 14 for outputting the emission luminance limiting amount of the PDP panel by APL as data is provided at the subsequent stage of the average luminance level calculating means 12. This limiting means 14 is normally configured as a LUT (Look Up Table) that stores the correspondence between the APL and the luminance limit amount. The limiting means 14, the response control means 16 for controlling the response of the temporal change in the brightness limit amount, and the display brightness level control means 18 for controlling the brightness level of the PDP panel by the brightness limit amount for which the response is controlled. For example, as shown in FIG. 9, when the display rate is 25% or more, the light emission luminance is limited by the APL level so that the light emission luminance of the PDP panel is lowered.

  The relationship between the display rate and the light emission luminance as shown in FIG. 9 is disclosed in Patent Document 1. The display rate to be limited may be 25% as described above, or may be set to a value (40%) as disclosed in Patent Document 1.

  After being supplied to the display luminance level control means 18 via the response control means 16 described above, and specifically converted into a light emission maintenance frequency corresponding to the APL level, a drive unit (illustrated) of the PDP panel (PDP display panel). Not supplied). If the light emission maintenance frequency is high, the light emission luminance of the PDP panel increases, and if the light emission maintenance frequency is low, the light emission luminance of the PDP panel decreases accordingly.

  Thus, by providing the driving circuit 10 of the PDP panel with the APC function, the power consumption of the PDP panel can be limited to an appropriate value. The limitation on the power consumption of the PDP panel leads to a longer life of the PDP panel itself.

JP-A-8-223507

  By the way, when the APL limiting means 14 having a look-up characteristic as shown in FIG. 9 is used, a change in display rate, that is, a change in average luminance level, appears as a change in direct emission luminance. As a result, if the average luminance level fluctuates finely, the light emission luminance also changes accordingly.

  The input video signal may contain noise, and the averaged luminance level itself may slightly increase or decrease due to quantization noise or the like generated when the input video signal is digitized. Therefore, even for still images and moving images with little change, if the average luminance level changes slightly, it will be easy to see how the luminance changes, especially when the gray level is darker than the bright tone, and the luminance changes visually. It becomes like this. As a result, the change in the image is uncomfortable.

  In order to eliminate this defect, response control means 16 such as a low-pass filter is provided after the APL limiting means 14 as shown in FIG. 8, but in this case, an image slightly delayed from the original image change is displayed. Therefore, the display response is different from that of the original input video, and the change of the image is accompanied with a sense of incongruity.

  Therefore, the present invention solves such a conventional problem, and in particular, even when the average latitude level changes slightly, it is devised not to follow this level change, thereby eliminating the sense of incongruity of the image change. A level control method and a display panel drive circuit are proposed.

In order to solve the above-described problem, a level control method according to the present invention described in claim 1 is a level control method for suppressing minute fluctuations in an average luminance level of an input video signal, and the level control method described above. Setting the average luminance level of the video signal of the frame or field at the time of starting as a first reference level, comparing the average luminance level of the input video signal with the reference level of the immediately preceding frame or field , The average luminance level of the video signal is higher than the reference level in the immediately preceding frame or field, or the quantization step width when the average luminance level of the video signal is quantized with n bits (n is an integer) from the reference level. when minus the reference value is set based on the quantization level corresponding to less than min, the video signal Outputting an average luminance level as the output level, the steps of the average luminance level of the video signal as a new reference level and the average luminance level of the video signal only reference value low against the reference levels in the previous frame or field It has the steps of an average luminance level of the video signal and the output level, if the immediately preceding frame or the average luminance level of a field of the video signal is further previous frame or only the reference value than the average luminance level of the video signal field low When the average luminance level of the current video signal is higher than the average luminance level of the video signal of the previous frame or field by the reference value, the average luminance level of the current video signal is lowered by the reference value. by the level and output level, the average luminance level of the video signal fine And step of suppressing variation, and having the steps of: outputting a correction signal for correcting the luminance level of the display panel in response to the output level.

According to a third aspect of the present invention, there is provided a display panel driving circuit comprising: a calculating means for calculating an average luminance level of an input video signal; and an average luminance level of a first frame or field video signal as an initial reference level. The current average luminance level calculated by the calculating means is supplied, the average luminance level of the input video signal is compared with the reference level of the immediately preceding frame or field, and the average luminance level of the video signal is A reference value that is higher than the reference level or set based on a quantization level corresponding to a quantization step width when the average luminance level of the video signal is quantized with n bits (n is an integer) from the reference level. When it is less than the subtracted amount, the average luminance level of the video signal is output as an output level and the average luminance level of the video signal is newly set. When the average luminance level of the video signal is lower than the reference level in the previous frame or field by a reference value, the average luminance level of the video signal is set as the output level, and the video signal in the previous frame or field Is lower than the average luminance level of the video signal in the previous frame or field by the reference value, the average luminance level of the current video signal is the average luminance of the video signal in the immediately preceding frame or field. When the level is higher than the reference level, the output level is set to a level that is lower than the average brightness level of the current video signal by the reference value, so that the current average brightness level is slightly smaller than the previous average brightness level. Control to output the average brightness level with suppressed fluctuations Level control means, brightness level correction means for supplying a correction signal for correcting the brightness level of the display panel in accordance with the average brightness level, the brightness level correction means for supplying the correction brightness signal to the correction brightness signal; And display luminance level control means for controlling the display luminance level on the display panel.

Furthermore, the display device according to the present invention described in claim 8 includes a display panel for displaying video, calculation means for calculating an average luminance level of the input video signal, and an average luminance level of the video signal of the first frame or field. Is the first reference level, the current average luminance level calculated by the calculation means is supplied, the average luminance level of the input video signal is compared with the reference level of the immediately preceding frame or field, and the average of the video signal is Set based on the quantization level corresponding to the quantization step width when the luminance level is higher than the previous reference level or the average luminance level of the video signal is quantized with n bits (n is an integer) from the reference level When it is less than the subtracted reference value, the average luminance level of the video signal is output as the output level and the video signal When the average luminance level is a new reference level and the average luminance level of the video signal is lower than the reference level in the previous frame or field by a reference value, the average luminance level of the video signal is set as the output level, and the previous frame Alternatively, when the average luminance level of the video signal in the field is lower than the average luminance level of the video signal in the previous frame or field by the reference value, the average luminance level of the current video signal is in the previous frame or field. When the reference value is higher than the average luminance level of the video signal, the current level relative to the previous average luminance level is set to the output level by setting the level lower by the reference value than the average luminance level of the current video signal . Outputs an average brightness level that suppresses minor fluctuations in the average brightness level. Level control means for performing control, and brightness level correction means for supplying a signal for correcting the brightness level of the display panel in correspondence with the average brightness level, which is supplied with an average brightness level in which the minute fluctuation is suppressed. And display luminance level control means for controlling the display luminance level on the display panel based on the signal for correcting the luminance level.

  In the present invention, even when the average luminance level changes slightly, the output level is suppressed so as not to follow the level change. The phenomenon in which the average luminance level slightly fluctuates is a kind of oscillation state. Therefore, when it is considered that an oscillation state has occurred, the level control means functions as an oscillation prevention means. By providing the oscillation prevention function, an average luminance level that does not follow subtle level changes can be obtained.

  That is, when the current average luminance level is the average luminance level calculated from the input video signal in the current frame or field, the previous average luminance level is in the frame or field immediately before the current frame or field. The average luminance level calculated from the input video signal is used. At that time, in the level control means of the average luminance level, when the current average luminance level is within a predetermined value range with respect to the previous average luminance level, the previous average luminance level is changed to the average luminance level in which slight fluctuation is suppressed. When the current average luminance level is out of a predetermined value range with respect to the previous average luminance level, the current average luminance level is output as an average luminance level in which slight fluctuations are suppressed.

  As a result, even when noise is superimposed on the average luminance level, the image can be displayed without being affected by the noise even when the average luminance level repeats slight fluctuations, and the sense of incongruity associated with image changes is eliminated. it can. The level control can be realized by computer control, that is, by executing a level control processing program stored in a control unit including a CPU, in other words, by software processing.

  As the means for suppressing the average luminance level, in addition to the oscillation preventing means, a hysteresis circuit having a hysteresis characteristic capable of absorbing a slight vertical fluctuation can be used.

  In the present invention, when the average luminance level slightly fluctuates (small fluctuation) by performing level control (level suppression) processing that does not follow the level change even when the average luminance level slightly changes. However, an average luminance level that does not follow this subtle level change can be obtained.

  As a result, even when noise is superimposed on the average luminance level, an image can be displayed without being affected by the noise, and an uncomfortable feeling associated with luminance change (image change) can be eliminated.

  Next, preferred embodiments of a level control method, a display panel drive circuit and a display device according to the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a case where the present invention is applied to a display device of a PDP panel having a display panel drive circuit. As shown in FIG. 1, a display device 100 for a PDP panel includes a PDP panel 30 that is a flat display panel and a drive circuit 10 for the PDP panel 30.

  The driving circuit 10 of the PDP panel 30 is supplied with calculation means 22 for calculating the average luminance level of the input video signal, and outputs the new average luminance level that is supplied with the calculated average luminance level and in which slight fluctuations are suppressed. As a parameter indicating a level (a luminance limit amount) for limiting the display luminance of the panel displayed in correspondence with the average luminance level, and the level luminance control unit 24 for controlling the average luminance level to which slight fluctuations are suppressed. The brightness level correction means 26 for outputting and the display brightness level control means 28 for controlling the display brightness level on the PDP panel 30 based on the parameter indicating the brightness limit amount.

  In this embodiment in which the PDP panel 30 is used as a display panel, the display luminance level control means 28 changes the frequency of the light emission sustain pulse supplied to the PDP panel 30 based on the parameter indicating the luminance limit amount. The light emission luminance level in the pixel is controlled.

  In this embodiment, the level control processing by the level control means 24, including the level calculation processing of the average luminance level calculation means 22, is also realized by executing a processing program stored in a control unit comprising a CPU. Can do. FIG. 2 is a processing block diagram by a computer illustrated with a focus on processing functions showing an example.

  FIG. 2 shows a case where a personal computer is used, such as a control unit 31 composed of a CPU, a flash memory storing various processing programs for realizing the above-described processing including level control for suppressing minute level fluctuations, and the like. Memory means (ROM) 32 and working memory means (RAM) 34 are connected to bus 36. An interface 38 for an input video signal (digital primary color signal), a PDP panel 30, and the like are further connected to the control unit 31 via the bus 36.

  Further connected to the bus 36 is a processing unit 200 for realizing the same processing functions as in FIG. This processing unit 200 is a functional representation of the processing executed by the processing program described above, and includes an average luminance level calculation unit 220 that functions as a calculation means for calculating the average luminance level of the input video signal, and an average luminance. An average luminance level control unit 240 functioning as a level control unit, an average luminance level correction unit 260 functioning as an average luminance level correction unit, and a display luminance level control unit 280 functioning as a display luminance level control unit Become.

  Here, the average luminance level calculation unit 220 calculates the average luminance level of the input video signal, and the average luminance level control unit 240 is supplied with the calculated average luminance level, and a new one in which the slight fluctuation is suppressed. A control function for the input average luminance level is provided so that a large average luminance level is output. Further, the average luminance level correction unit 260 is supplied with an average luminance level in which slight fluctuations are suppressed, and a parameter indicating an amount (luminance limit amount) for limiting the display luminance of the panel displayed corresponding to the average luminance level. The display brightness level control unit 280 functions to control the display brightness level on the PDP panel 30 based on a parameter indicating the brightness limit amount.

  In this embodiment in which the PDP panel 30 is used as a display panel, the display luminance level control unit 280 changes the frequency of the light emission sustain pulse supplied to the PDP panel 30 based on the parameter indicating the luminance limit amount. The light emission luminance level in the pixel is controlled.

Subsequently, for convenience of explanation, the present invention will be described in more detail with reference to FIG.
In this example, which is an input video signal, digital primary color signals R, G, B are supplied to the average luminance level calculation means 22. It is assumed that this input video signal is quantized by n bits (n is an integer). The luminance level of the input video signal is averaged for each field or frame. An averaged luminance level (input level) or a signal having this average luminance level is defined as an average luminance level APL.

  The average luminance level APL is supplied to the subsequent level control means 24. The level control means 24 has a very small digitized average luminance level (input video signal) due to quantization noise generated when the input video signal is quantized or external noise mixed in the input video signal. This is a processing means for obtaining an output video signal (new average luminance level APLad) in which the minute fluctuation is suppressed by suppressing the minute fluctuation when it is fluctuating. By performing the suppression process with respect to the minute fluctuation, the luminance change due to the minute fluctuation is suppressed, so that the uncomfortable feeling of the image change can be eliminated.

  The average luminance level APLad in which the slight fluctuation is suppressed is further supplied to the luminance level correcting means 26. The brightness level correction means 26 and the display brightness level control means 28 are provided for correcting (adjusting) the light emission brightness level of the PDP panel 30. For example, the brightness level correction means 26 and the display brightness level control means 28 are averaged so as to have the characteristics shown by the curve La in FIG. The characteristic of the light emission luminance level with respect to the luminance level is adjusted.

  In this example, as shown in the figure, when the average luminance level APL becomes about 25%, correction of the luminance level is started, and the PDP panel 30 is driven at the corrected luminance level, so that the light emission luminance as shown by the curve La is obtained. Controlled to be level. This luminance level correction characteristic is an example. The input / output characteristics of the curve La in FIG. 9 can be changed like the linear input / output characteristics, and the characteristic curve can be selected in accordance with the light emission luminance characteristics of the display panel to be used.

  The brightness level correction means 26 is for outputting a correction signal for lowering the display brightness level on the PDP panel 30 as the average brightness level is suppressed, and in this example, a look-up table ( LUT) is used. That is, when the average luminance level APL is input, the input / output relationship is tabulated so as to output a parameter indicating the luminance limiting amount corresponding to the average luminance level APL, that is, the amount limiting the light emission luminance of the PDP panel 30. ing.

  The luminance limit amount corresponding to the average luminance level APLad is directly supplied to the display luminance level control means 28 without going through correction means such as a low-pass filter. In this display luminance level control means 28, the light emission sustain frequency of the light emission sustain pulse of the PDP panel 30 is controlled by the luminance limit amount corresponding to the average luminance level APLad inputted here. By controlling the emission frequency, the emission luminance can be appropriately controlled. The display luminance level control means 28 is often incorporated in the PDP panel 30.

  In the level control unit 24 shown in FIG. 1, when the average luminance level of the input video signal slightly moves up and down as described above, the level fluctuation is appropriately suppressed. This level control process can be realized by hardware as shown in FIG. 1, but as shown in FIG. 2, the control unit 31 for realizing the process by the computer, specifically, the function of the processing unit 200. This can also be realized by executing a corresponding processing program.

For convenience of explanation, an example of level control processing by software will be described with reference to FIG. FIG. 3 is a diagram for easy understanding of the level fluctuation of the average luminance level. In the section a, the input level (average luminance level) APL gradually increases, in the section b, the input level gradually decreases, and the section c becomes a constant level. The input level is illustrated. Sections d to f show a minute fluctuation section of the input level generated due to quantization noise or the like. An example in which the input level gradually decreases again as in the section g after passing through the minute fluctuation section.

(Sections a and b)
The input level APL is latched as a reference level (latch level) APLla (APLlatch). When the input level APL is more than the reference value than the reference level APLla, the input level APL is replaced with the reference level APLla. At the same time, the input level APL is output as the current average luminance level APLad (APLadjusted).

  That is, when the current average luminance level is the average luminance level calculated from the input video signal in the current frame or field (hereinafter, an example of a frame), the immediately preceding average luminance level is one before the current frame. The average luminance level is calculated from the input video signal in the frame. Therefore, the input level APL described above becomes the current average luminance level.

  In this section (a, b), when the current average luminance level is outside the range of a predetermined value with respect to the previous average luminance level, the current average luminance level is output as an average luminance level in which slight fluctuations are suppressed. It is a section to do.

  Here, the reference value can be a quantization level corresponding to the quantization step width when the input video signal is digitized. In the example shown below, the unit quantization level (1 quantization step width) is set as a reference value, but the value is arbitrary and is selected as m times the quantization step width (m is an integer). You can also For example, a 2-quantization level corresponding to a 2-quantization step width can be set as a reference value. When the unit quantization level is used as a reference value, “outside the predetermined value range” means a level fluctuation of (± 2) or more.

Section a is an example when the input level fluctuates twice or more than the reference value, exceeding the reference value with respect to the reference level, and section b is twice the reference value below the reference value with respect to the reference level. This is an example when the input level has changed as described above. In this case, the state flag F (Flag) indicating the slight change state with respect to the input level APL is reset (Flag = 0).

(Section c)
This section c is when the input level (average luminance level) APL is the same as the reference level APLla. In this case, the input level APL is used as the reference level APLla, and the input level APL itself is the output level. (Average luminance level) Output as APAd. The state flag F holds the reset state (Flag = 0).

(Section d)
This section d is a case where the input level APL is lower than the immediately preceding input level by a reference value. That is, it is a level fluctuation state at the time of entering a minute fluctuation. The quantization step used as the reference value is illustrated as +1 (higher) or -1 (lower) as described above.

  When the input level APL is lowered by the reference value (−1), the input level APL is APL = APLla−1. Therefore, this input level (the previous average luminance level) itself is the output level (the current average luminance level). ) Although output as APLad, the reference level APLla is controlled to maintain the previous reference level. Therefore, as shown in the figure, the reference level APLla is higher by +1 (reference value) than the output level APLad.

When the input level APL decreases by the reference value, a state flag F indicating a slight fluctuation state is set (Flag = 1) as will be described later.

(Sections e and f)
The sections e and f show a case where the input level APL is higher or lower than the previous input level by a reference value. That is, the intervals e and f indicate intervals (oscillation intervals) in which the input level repeats slight fluctuations. This slight variation is caused by noise superimposed on the input video signal as described above, or quantization noise when quantizing.

(Section e)
The interval e is when the input level APL is higher by +1 (reference value) than the previous input level. In this case, a value (APL-1) obtained by subtracting the reference value from the input level APL is used as the output level APLad. At the same time, the reference level APLla holds the previous reference level APLla. The state flag F also holds the immediately previous state (set) (Flag = 1).

  By performing such processing, the output level APLad retains the previous output level even though the input level APL has changed by the reference value. As a result, the output level APLad maintains a constant level as shown by the broken line, and even when the input level slightly fluctuates and oscillates, it can be output as a stable average luminance level APLad. it can.

That is, the section e corresponds to a section in which the previous average luminance level is output as an average luminance level in which slight fluctuations are suppressed when the current average luminance level is within a predetermined value range with respect to the previous average luminance level.

(Section f)
In this section f, the input level APL is lower than the previous input level by a reference value. In this case, the processing is the same as that in the section d, and the output level APLad is output as the input level APL itself. However, since the reference level APLla holds the previous value, it does not change when the input level APL is a fluctuation within the reference value, and the state flag F also holds the previous state (set state) (Flag). = 1).

  This section f also corresponds to a section in which the previous average brightness level is output as an average brightness level in which slight fluctuations are suppressed when the current average brightness level is within a predetermined value range with respect to the previous average brightness level.

When the input level slightly fluctuates as in the sections e and f, the value immediately after the minute fluctuation is held, and the oscillation state is not transmitted to the output side as it is.

(Section g)
This section shows a case where the input level APL fluctuates more than the reference value, for example, a case where the input level APL is lowered by 2 quantization levels. In this case, since the processing operation is the same as that in the section b, the lowered input level APL itself is used as the output level APLad, and the lowered input level APL is used as the reference level APLla. In this case, the state flag F indicating a slight fluctuation is reset (Flag = 0). Similarly, when the input level APL becomes higher than the reference value, the same processing as that in the section a is performed.

  The level control means 24 performs the above processing. An example of processing by the processing program for this level control is shown in FIG.

  In FIG. 4, first, initialization is performed in step 41. The initialization process is a process in which the reference level APLla is set to zero and the output level APLad is set to the maximum value (MAX).

  Next, an input level APL input standby state is entered (step 42). When the input is confirmed, a level comparison process between the input level APL and the reference level APLla is performed (step 43).

This level comparison process is a level comparison process as shown in the following case.
(Case 1)
The input level APL is APL> APLla or APL <APLla-1.
(Case 2)
The input level APL is APL = APLla.
(Case 3)
The input level APL is APL = APLla-1.

  The level is judged for these three cases. In the case of (Case 1), the processing of the section a and the section b in the figure, where the section a is a case of APL> APLla and the section b is a case of APL <APLla−1. As shown in step 44, a process of replacing the input level APL with a new reference level APLla and using the input level APL as the output level APLad is performed. Further, the state flag F indicating a slight fluctuation is reset (Flag = 0).

  As described above, in (Case 1), when the current average luminance level is outside the range of the predetermined value with respect to the previous average luminance level, the current average luminance level is output as an average luminance level in which slight fluctuations are suppressed. It becomes.

  When it is determined in step 43 that the input level APL is the same value as the previous reference level APLla (case 2), the state of the flag F is determined (step 45).

  When the flag F is in the reset state, that is, when Flag = 0, it can be determined that the input level APL has not fluctuated slightly. In this case, the process proceeds to step 46 and the input level APL itself is referred to. The level APLla is updated, and the input level APL is used as the output level APLad. This process corresponds to section c.

  On the other hand, when it is determined that the state flag F is in the set state, that is, the input level APL up to the last minute fluctuates and the level fluctuates in the increasing direction (Flag = 1), the slight fluctuation is caused. In order to suppress this, a value obtained by subtracting a minute fluctuation (unit quantization step width which is a reference value in this example) from the input level APL is set as the output level APLad (step 48).

  However, in this step 48, only the output level APLad is updated, and processing is performed in which the reference level APLla and the status flag F hold the previous values. Such processing corresponds to the section f.

  Next, in step 43, when it is determined that the input level APL is lower than the immediately preceding reference level APLla by a reference value (case 3), the processing using the input level APL as the output level APLad and slight variations are shown. Processing for setting the status flag F (Flag = 1) is performed (step 49).

  Therefore, (Case 3) corresponds to a case where the previous average luminance level is output as an average luminance level in which slight fluctuations are suppressed when the current average luminance level is within a predetermined value range with respect to the previous average luminance level. .

When a slight fluctuation occurs, the output level APLad in which the fluctuation is suppressed is supplied to the luminance level correction means 26 at the subsequent stage shown in FIG.
The brightness level correction means 26 is a processing means for limiting the light emission brightness of the PDP panel 30 when the APL level becomes a predetermined level or more. In this example, the average brightness level APL is 25% or so. When the average luminance level is APL as described above, the average luminance level is corrected (controlled) so that an average luminance level APL that ultimately limits the emission luminance of the PDP panel 30 is output. Examples of characteristics for limiting the light emission luminance are shown in FIG.

  In the example of FIG. 5 and subsequent figures, a case where the light emission luminance is selected so as to have a characteristic that draws a quadratic curve (for example, a hyperbola) is shown. 5 to 7, the horizontal axis represents the average luminance level APL, and the vertical axis represents the parameter (%) indicating the luminance limit amount for the PDP panel 30 when the corrected average luminance level is added.

  Since the luminance limit amount is increased, the light emission luminance of the PDP panel 30 is reduced as the luminance limit amount is increased, and the screen is darkened. In this example, the emission luminance is limited as indicated by the curve Lb with APL = 25% as a boundary. The curve Lb is the same as the curve La shown in FIG. 9 except that its vertical axis is different.

  FIG. 5 shows the case (case 1) described above, and the numerical value “1” shown in the figure indicates the unit quantization level (= reference value). In the section a, the light emission luminance is controlled to be more limited, and in the section b, the light emission luminance is controlled to be higher.

  FIG. 6 shows the case of (Case 2), which shows a case where the input level APL is constant (= reference level APLla), and an image is displayed with a specific light emission luminance.

  FIG. 7 shows the case (Case 3), where the input level APL slightly fluctuates up and down, and the output level APLad is maintained at the input level APL that is lowered by the quantization level. The reference level APLla at that time is higher than the input level APL by one quantization step.

  For the average luminance level APLad to which such a luminance limiting characteristic is given, the display luminance level control means 28 in the subsequent stage selects a light emission maintenance frequency corresponding to the average luminance level APL, and based on this light emission maintenance frequency, the PDP panel 30 Driven. As a result, the light emission luminance of the PDP panel 30 is limited as shown in FIGS.

  In the embodiment described above, the unit quantization step is exemplified as the reference value. For example, when the input video signal is quantized and encoded with 8 bits, an input level of 1/256 is a unit quantization step. The reference value is not limited to this unit quantization step, and m times the quantization step can be set as the reference value. If the reference value is increased, the level fluctuation range can be suppressed accordingly, and there is an advantage that a stable image can be displayed.

  In the embodiment, when the increase in the input level APL with respect to the previous level is smaller than the reference value, the previous level is output as the output level (average luminance level) APlad, and the input level APL decreases from the previous level. The input level APL is output as the output level APlad. Conversely, when the decrease in the input level APL with respect to the immediately preceding level is smaller than the reference value, the immediately preceding level is output as the output level APlad and input from the immediately preceding level. When the level APL increases, the input level APL may be output as the output level APlad.

  In other words, the present invention can be widely realized by controlling the input fluctuation when the input level is within a predetermined value range with respect to the previous level.

  The characteristic curve Lb in the luminance level correction means 26 is not limited to a quadratic curve as shown, but may be a polygonal line approximation.

  In the above-described embodiments, the PDP panel is used as the display panel. However, the present invention in which the display brightness is controlled based on the average brightness level in which minute fluctuations are suppressed is a display panel such as a liquid crystal display element (LCD) or an organic EL panel. It can be widely applied to. The liquid crystal display element may be applied to one that controls the brightness of the backlight in place of the light emission luminance of each pixel of the PDP panel according to the average luminance level of the input signal.

  The present invention relates to a driving method, a driving circuit, and a display device for driving a display panel such as a PDP panel, a liquid crystal display element (LCD), or an organic EL panel that needs to limit light emission luminance as the luminance level increases. The present invention is applicable, and is particularly suitable for a PDP panel having an APC function that limits power supplied to the display panel and suppresses power consumption.

FIG. 4 is a system diagram of a main part showing an embodiment when the present invention is applied to a display device having a display panel drive circuit. It is a figure which shows the structural example of the display apparatus containing a control part. It is a figure which shows the level fluctuation | variation of the input level for showing the example of a level control process. It is a flowchart which shows the example of level control. It is a characteristic view which shows the relationship between an input level and a brightness | luminance limitation amount (the 1). It is a characteristic view which shows the relationship between an input level and a brightness | luminance limitation amount (the 2). It is a characteristic view which shows the relationship between an input level and a brightness | luminance limitation amount (the 3). It is a systematic diagram which shows the drive circuit of the conventional display panel. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Drive circuit, 12 ... Luminance level calculation means, 14 ... Luminance level correction means, 18 ... Display luminance level control means, 20 ... Level control means, 30 ... PDP panel, 31 ... Control unit (CPU)

Claims (8)

A level control method for suppressing minute fluctuations in the average luminance level of an input video signal ,
A step of setting an average luminance level of a video signal of a frame or a field at the time when the level control method is started as an initial reference level;
Comparing the average luminance level of the input video signal with the reference level in the previous frame or field ;
The average luminance level of the video signal is higher than the reference level in the immediately preceding frame or field, or the quantization step width when the average luminance level of the video signal is quantized with n bits (n is an integer) from the reference level. when minus the reference value is set based on the quantization level corresponding to less than minute, and outputs the average luminance level of the video signal as an output level, an average luminance level of the video signal as a new reference level Steps,
When the average luminance level of the video signal only reference value low against the reference levels in the previous frame or field, the steps of the average luminance level of the video signal and the output level,
If the previous frame or the average luminance level of a field of the video signal is further previous frame or only the reference value than the average luminance level of the video signal of the field low, the average luminance level of the current video signal is the previous frame or field Is higher than the average luminance level of the video signal by the reference value, the level that is lower than the average luminance level of the current video signal by the reference value is set as the output level . A step of suppressing minute fluctuations;
Outputting a correction signal for correcting the luminance level of the display panel corresponding to the output level;
A level control method characterized by comprising: 2. The level control method according to claim 1, wherein the average luminance level is calculated based on a video signal in units of frames or fields. Calculating means for calculating an average luminance level of the input video signal;
The average luminance level of the video signal of the first frame or field is set as the first reference level, the current average luminance level calculated by the calculating means is supplied, and the average luminance level of the input video signal is set to the previous frame or field. Quantization when the average luminance level of the video signal is higher than the previous reference level or the average luminance level of the video signal is quantized with n bits (n is an integer) from the reference level. When the value is less than the reference value set based on the quantization level corresponding to the step width, the average luminance level of the video signal is output as the output level and the average luminance level of the video signal is newly referred to Level, and the average luminance level of the video signal is the standard value for the reference level in the previous frame or field When it is low, the average luminance level of the video signal is set as the output level, and the average luminance level of the video signal in the immediately preceding frame or field is further lower than the average luminance level of the video signal in the immediately previous frame or field by the reference value. If the average luminance level of the current video signal is higher than the average luminance level of the video signal in the previous frame or field by the reference value, the average luminance level of the current video signal is lowered by the reference value. levels by an output level, and level control means for controlling to output the average luminance level small variations in the current average brightness level to the average luminance level immediately before is suppressed,
Brightness level correction means for supplying a correction signal for supplying a correction signal for correcting the brightness level of the display panel in correspondence with the average brightness level;
And a display luminance level control means for controlling a display luminance level on the display panel based on the correction signal. The current average brightness level is
The average luminance level calculated from the input video signal in the current frame or field, and the previous average luminance level is calculated from the input video signal in the frame or field immediately before the current frame or field. a drive circuit for a display panel according to claim 3, wherein the Ru average luminance level der <br/> was. The brightness level correction means outputs the correction signal for controlling the display brightness level control means so as to lower the display brightness level on the display panel as the average brightness level with the slight fluctuations suppressed is increased. The display panel drive circuit according to claim 3 . The display panel is a plasma display panel,
4. The display panel drive circuit according to claim 3, wherein the display luminance level control means controls a light emission sustaining frequency of the plasma display panel according to the supplied correction signal. 4. The display panel drive circuit according to claim 3, wherein the calculation of the average luminance level by the calculating means and the level control processing in the level control means are software processing using a control unit comprising a CPU. A display panel for displaying images,
Calculating means for calculating an average luminance level of the input video signal;
The average luminance level of the video signal of the first frame or field is set as the first reference level, the current average luminance level calculated by the calculating means is supplied, and the average luminance level of the input video signal is set to the previous frame or field. Quantization when the average luminance level of the video signal is higher than the previous reference level or the average luminance level of the video signal is quantized with n bits (n is an integer) from the reference level. When the value is less than the reference value set based on the quantization level corresponding to the step width, the average luminance level of the video signal is output as the output level and the average luminance level of the video signal is newly referred to Level, and the average luminance level of the video signal is the standard value for the reference level in the previous frame or field When it is low, the average luminance level of the video signal is set as the output level, and the average luminance level of the video signal in the immediately preceding frame or field is further lower than the average luminance level of the video signal in the immediately previous frame or field by the reference value. If the average luminance level of the current video signal is higher than the average luminance level of the video signal in the previous frame or field by the reference value, the average luminance level of the current video signal is lowered by the reference value. levels by an output level, and level control means for controlling to output the average luminance level small variations in the current average brightness level to the average luminance level immediately before is suppressed,
Brightness level correction means for supplying a signal for correcting the brightness level of the display panel corresponding to the average brightness level, wherein an average brightness level in which the minute fluctuation is suppressed is supplied;
A display luminance level control means for controlling a display luminance level on the display panel based on a signal for correcting the luminance level.

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