JP5611500B2 - Image display device and control method thereof - Google Patents

Description

  The present invention relates to an image display apparatus and a control method thereof, and more specifically, it is possible to suppress overall brightness of a screen that is too bright such that it exceeds a threshold value, and to reproduce a brightness change above a threshold value in a subsequent frame. Provide a technique that becomes.

Conventionally, in order to suppress the luminance of the screen, it has been control to uniformly suppress the luminance of the entire panel. For example, as a first conventional technique, a technique (refer to Patent Document 1) is proposed that corresponds to the entire range of luminance that can be specified in a range where the luminance is lower than the threshold value, and saturates the luminance to be specified in the range exceeding the threshold value. Has been. As a second conventional technique, a technique (see Patent Document 2) is proposed in which the brightness of a displayed image is controlled to be equal to or lower than a predetermined brightness for a predetermined period immediately after power-on.
JP 2005-55800 JP JP 2005-79748 A

  In the conventional technique, since the brightness of the screen is uniformly suppressed, it is not possible to display all the brightness information included in the original video information, and there is a problem that the reproducibility of the image is deteriorated. For example, in the first prior art, the luminance change cannot be reproduced on the actual screen in a range equal to or greater than the threshold value, and thus the user cannot recognize the luminance change in a bright scene. In the second prior art, the screen brightness may suddenly change after a certain period of time, and the screen may become unsightly. In addition, since the control works only at the start-up, and the control works regardless of the display screen, the brightness is suppressed even on a screen that does not need to suppress the brightness, and as a result, a dark screen is displayed. It becomes difficult for the user to see.

In order to solve the above-described problems, an image display device according to a first invention is a calculation means for calculating a total luminance of display means composed of a plurality of self-luminous elements and preceding image data to be displayed on the display means. And the image display device by converting the preceding image data so that the total luminance becomes the predetermined threshold when the total luminance of the preceding image data calculated by the calculating unit exceeds a predetermined threshold. And when the total luminance of the subsequent image data following the preceding image data changes beyond the predetermined threshold, the total luminance of the converted image data does not exceed the predetermined threshold before the conversion. Means for converting the subsequent image data and displaying it on the image display device so as to reproduce and change the luminance change of the image data .

As described above, the solving means of the present invention has been described as an apparatus. However, the present invention can be realized as a method, program, and storage medium storing the program, which are substantially equivalent thereto, and falls within the scope of the present invention. It should be understood that these are also included.
As an example, a control method for an image display device according to the second invention that implements the present invention as a method is a control method for an image display device composed of a plurality of self-luminous elements (using an arithmetic means). When the total luminance of the preceding image data to be displayed on the image display device exceeds a predetermined threshold, the preceding image data is converted so that the total luminance becomes the predetermined threshold, and the image display is performed. A step of displaying on the apparatus, and when the total luminance of the subsequent image data following the preceding image data transitions beyond the predetermined threshold, the total luminance of the converted image data does not exceed the predetermined threshold before the conversion. Converting the subsequent image data and displaying it on the image display device so as to reproduce and change the luminance change of the image data .

  According to the present invention, since a screen that is too bright is not displayed, wasteful battery consumption and a low current can be peaked when designing a power supply circuit for the display panel, and a system that has a limited power supply, such as a portable terminal. Therefore, it is possible to efficiently use electric power and further to extend the continuous use time. Also, because it is not suppressed on all screens, it has good luminance reproducibility, and on a screen with a low total luminance value, all the luminance information included in the image information can be displayed, and a frame with a high total luminance value that cannot be displayed as it is on this panel In this case, when the total luminance value exceeds the threshold, it is possible to suppress the luminance as a whole, and to reproduce the luminance change at the threshold value or more in the subsequent frame. Furthermore, peak current can be reduced by reducing the brightness on a screen with a high total brightness value, so that fluctuations in the supply voltage due to large currents can be suppressed. An effect of extending the screen life of the element can also be obtained.

  In the image display device according to the present invention, before displaying on the screen, the luminance of one frame is integrated and the current consumption is estimated. A threshold is set to limit the total luminance displayed in one frame so that the total current consumption of the display panel does not exceed the specified value. If the total luminance exceeds the threshold, the luminance is limited. When the total luminance value does not exceed the threshold value, it is displayed with the luminance as it is. After the limit is applied, the brightness of the screen that is actually displayed for a predetermined period is changed to reduce the overall brightness, and the brightness is controlled so that the threshold value is not exceeded even when the frame with the maximum brightness is displayed. To do. After the specified period of time has passed and the brightness of the screen to be actually displayed is increased from before the specified period of time, the threshold for starting control is lowered and the brightness is reduced only when a frame with a brightness higher than the threshold is displayed. It is characterized by that. The above control is gradually performed to return to the initial state, that is, the original luminance so that the user does not know.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Description will be made by applying the present invention to a portable communication terminal device (portable electronic device) which is a typical application of an image display device using a self-luminous element. FIG. 1 shows a system configuration diagram of a mobile communication terminal device to which the present invention is applied. As shown in the figure, the mobile communication terminal device 100 includes a signal processing unit 101, a CPU 107, a memory 108, an operation unit 109, and a display panel 110 using self-luminous elements such as EL elements. The signal processing unit 101 is a block that processes an image signal to be displayed, and includes a frame buffer 102, a luminance integrating unit 103, a luminance conversion graph storage unit 104, a luminance converting unit 105, and a panel driving unit 106.

  Various functions in the signal processing unit 101 will be described in detail. The frame buffer 102 temporarily stores one frame of screen data in the signal processing unit. The luminance integrating unit 103 calculates the total luminance by integrating the luminance of the screen data of one frame in the frame buffer. The luminance conversion graph storage unit 104 is a luminance conversion graph storage unit (memory), and stores a plurality of conversion graphs in advance. The luminance conversion unit 105 converts the luminance total value of one frame based on the luminance conversion graph. The panel drive unit 106 drives the data actually displayed on the display panel by sending it to the display panel. The CPU 107 controls the entire terminal and performs various calculations and processes. The memory 108 is storage means for storing various data. The operation unit 109 is an operation unit in which a user operates a terminal to perform selection / input. The display panel 110 is a display panel composed of self-luminous elements. Although not shown here, there are a power supply block, an audio block, a speaker unit, a radio unit, and the like.

  FIG. 2 is a flowchart illustrating an example of a luminance adjustment sequence performed by the signal processing unit illustrated in FIG. At this time, a plurality of luminance conversion graphs (tables) shown in FIG. 4 are used, which will be described in detail later. As shown in FIG. 2, in step S201, the total luminance value of the frame is calculated in the frame buffer from the image information before luminance conversion to be displayed. Next, in step S202, it is determined whether or not the total value is equal to or greater than threshold value 1. If the total value is less than threshold value 1 (less than 85 in this case), the process proceeds to step S203 and an image is displayed with the luminance included in the video information as it is. Then, the process returns to step S201. If the total value is greater than or equal to the threshold value 1 (85 or more in this case), the process proceeds to step S204, and the total value of the luminance of one frame becomes 85 so that the total luminance value of one frame is the same as the threshold value A. So that it is dropped as a whole.

  In step S205, control is performed such that the luminance conversion graph 2 is applied and displayed from the next frame, but if the next frame does not come into the frame buffer, the current frame is displayed as it is at the current luminance. In steps S206 and S207, the luminance conversion graph 2 is applied and displayed until a predetermined period elapses. When a certain period of time elapses in step S207, the brightness conversion graph 3 is applied and controlled from the next frame in S208, but if the next frame does not come to the frame buffer, the current frame is used as it is at the current brightness. indicate. In step S209, the total luminance value of the frame is calculated in the frame buffer from the image information before luminance conversion to be displayed next. If the threshold value in the luminance conversion graph 3 is 3 or more (95 or more in this case) in step S210, the process proceeds to S218, the luminance conversion graph 3 is applied, and the total luminance is displayed with the threshold value A saturated. Returning to S205, control is performed so that the luminance conversion graph 2 is applied and displayed.

  In step S210, when it is less than the threshold 3 in the luminance conversion graph 3 (in this case, less than 95), the process proceeds to S211 and an image is displayed based on the luminance conversion graph 3. In step S212, the luminance conversion graph 3 is continuously applied until a certain period elapses. When a certain period of time elapses in step S212, the luminance conversion graph 4 is applied from the next frame in step S213. If the next frame does not come into the frame buffer, the current frame is displayed as it is at the current luminance. In step S214, the total luminance value of the frame is calculated in the frame buffer from the image information before luminance conversion to be displayed next. If the threshold value in the luminance conversion graph 4 is 4 or more (90 or more in this case) in step S215, the luminance conversion graph 4 is applied in S219 and the luminance is saturated with the threshold A and displayed. Control is performed so that the luminance conversion graph 2 is applied and displayed. If it is less than the threshold value 4 (less than 90 in this case) in the luminance conversion graph 4 in step S215, an image is displayed based on the luminance conversion graph 4 in 216. The luminance conversion graph 4 is continuously applied until a predetermined period has elapsed in step S217. When a certain period of time elapses in step S217, the display returns to the brightness conversion graph 1, returns to the display with the original brightness, and ends a series of brightness conversion processing flows, and again waits for a frame exceeding the threshold value.

  The predetermined period referred to here is preferably about 10 seconds. When the predetermined period is as short as 1 second, for example, when the user is browsing the screen, the luminance change changes in units of 1 second, which makes it unsightly. When the predetermined period is extended to 1 minute, it takes a very long time to return to the original luminance conversion, and a screen darker than the original luminance is displayed for a long time, which makes it difficult to see the screen.

  In this way, when the total luminance value is low, the entire image is reproduced as it is, and the restriction is applied only within the range exceeding the limit of the display panel, so that the user can watch without any problem in the normal state, and the luminance conversion is performed after the restriction is applied. By changing the value and gradually returning it to the original state, it is possible to prevent the user from feeling uncomfortable. In addition, it is possible to reproduce a luminance change where the luminance total value is high. In this sequence, when there is luminance display information that is equal to or greater than the threshold value, control is always made to change to the luminance conversion graph 2 in step S205, but from the luminance conversion graph 4 to the luminance conversion graph 3 depending on the level of the luminance information. You may make it transfer. An example is shown in FIG.

  FIG. 3 is a flowchart showing a modification of the luminance adjustment sequence of FIG. As shown in the figure, in processing step S301, the total luminance value of the frame is calculated in the frame buffer from the image information before luminance conversion to be displayed. In step S302, the luminance conversion graph 1 is applied to display the image in the frame buffer. In step S303, it is determined whether or not the result calculated in S301 is greater than or equal to threshold 3, and if it is greater than or equal to threshold 3, the process proceeds to S304, and if it is less than threshold 3 in S303, the process proceeds to S310. In step S310, if the result calculated in S301 is greater than or equal to the threshold value 4, the process proceeds to S311, and if less than the threshold value 4, the process proceeds to S318. In step S318, if the result calculated in S301 is greater than or equal to the threshold 1, the process proceeds to S319, and if less than the threshold 1, the process returns to S301.

  If the timer is activated in step S304, the timer is reset, the luminance conversion graph 2 is applied from the next frame, and the control is changed so as to suppress the luminance as a whole. In step S305, when the next frame to be displayed reaches the frame buffer, the sum of luminance information values in one frame is calculated. In step S306, the luminance conversion graph 2 is applied to display the image in the frame buffer. In step S307, it is determined whether or not the result calculated in S305 is greater than or equal to threshold value 3. If the threshold value is 3 or more, the process returns to S304. If it is less than the threshold 3, the process proceeds to S308, where a timer is started, and it is determined in S309 whether or not a predetermined period has elapsed (whether the timer has expired). If the predetermined period has not elapsed in step S309, the process returns to S305 and the same sequence is repeated. If the predetermined period has elapsed in step S309, the process proceeds to S311.

  In step S311, if the timer is started, it is reset, and the luminance conversion graph 3 is applied from the next frame, and the control is changed so as to suppress the luminance as a whole. In step S312, when the next frame to be displayed reaches the frame buffer, the sum of luminance information values in one frame is calculated. In step S313, the luminance conversion graph 3 is applied to display the image in the frame buffer. In step S314, it is determined whether or not the result calculated in S312 is equal to or greater than threshold 3, and if it is greater than or equal to threshold 3, the process returns to S304. If it is less than the threshold 3, the process proceeds to S315. In S315, it is determined whether or not the threshold value is 4 or more. If the threshold value is 4 or more, the process returns to S311. If it is less than the threshold value 4, the process proceeds to S316 and the timer is started. In S317, it is determined whether a predetermined period has elapsed (whether the timer has expired). If the predetermined period has not elapsed, the process returns to S312 and the same sequence is repeated. If the predetermined period has elapsed in S317, the process proceeds to S319.

  In step S319, if the timer is activated, the timer is reset, and the luminance conversion graph 4 is applied from the next frame, and the control is changed so as to suppress the luminance as a whole. When the next frame to be displayed in S320 arrives in the frame buffer in S320, the sum of luminance information values in one frame is calculated. In S321, the luminance conversion graph 4 is applied to display the image in the frame buffer. In step S322, it is determined whether or not the result calculated in S320 is greater than or equal to threshold 3, and if it is greater than or equal to threshold 3, the process returns to S304. If it is less than the threshold 3, the process proceeds to S323. In S323, it is determined whether or not the threshold value is 4 or more. If the threshold value is 4 or more, the process returns to S311. If the threshold is less than 4, proceed to 324. In S324, it is determined whether or not the threshold value is 1 or more. If the threshold value is 1 or more, the process returns to S319. If it is less than the threshold value 1, the process proceeds to S325 to start the timer. In S326, it is determined whether or not a predetermined period has elapsed (whether or not the timer has expired). If the predetermined period has not elapsed, the process returns to S320 and the same sequence is repeated. If the predetermined period has elapsed, the process returns to S301 and returns to the initial state.

  FIG. 4 is a luminance conversion graph used in the present invention. FIG. 4A shows a luminance conversion graph 1 by default and shows a luminance conversion line L1. The horizontal axis represents the total luminance value of one frame of luminance information indicated from the video signal. Here, the maximum luminance is 100. The vertical axis represents the total value of one frame of luminance actually displayed on the display panel. Here, the maximum luminance is 100. Here, when the total luminance indicated by the video signal in one frame is less than a predetermined value (in the range of level 0, the luminance is 0 to 85), the original luminance indicated by the video signal is actually displayed and the total value is displayed. Is equal to or greater than a predetermined value (in the range of levels 1 to 3 and the luminance is in the range of 85 to 100), the luminance is controlled so that the luminance to be actually displayed is saturated to the displayable maximum value (85 in this example).

  FIG. 4B is a luminance conversion graph 2 when the restriction is applied, and shows a luminance conversion line L2. Here, the display is controlled so as to reduce the overall luminance. For example, when the total of luminance information included in one frame is 90, when this luminance conversion graph 2 is used, the entire screen is darkened so that the total is 76.5 when displayed on the screen.

  FIG. 4C is a luminance conversion graph 3 when the restriction is applied, and shows a luminance conversion line L3. Again, the threshold value for controlling the luminance level is changed. In the range of level 0 to 2, display control is performed so as to suppress the luminance as a whole than in actuality, and in the level 3 range, control is performed to saturate to this displayable maximum value.

  FIG. 4D is a luminance conversion graph 4 when the restriction is applied, and shows a luminance conversion line L4. The threshold value for controlling the luminance level is changed compared to the case of FIG. In the range of level 0 to 1, display control is performed so as to suppress the luminance as a whole compared to the actual level, and in the range of level 1 to 2, control is performed so as to saturate the displayable maximum value.

  The threshold value of the total luminance included in the video information for luminance saturation in FIG. 4A is the threshold value 1, the threshold value of the total luminance included in the video information for luminance saturation in FIG. The threshold value of the total luminance included in the video information for luminance saturation in (d) is called threshold value 4, and the limit value that can be displayed on the display panel (OLED) is called threshold value A.

  Furthermore, the luminance level less than threshold 1 in FIG. 4A is level 0, the luminance level less than threshold 4 in threshold 1 or more (d) in FIG. 4A is level 1, and FIG. The luminance level of threshold 4 or higher (c) and lower than threshold 3 is called level 2, and the luminance level of threshold 3 or higher and the luminance total maximum value in FIG.

Luminance information included in image information of one frame, Y signal of each pixel is integrated if in YUV format, RGB → YUV conversion formula if in RGB format
Y = 0.299 * R + 0.587 * G + 0.114 * B
Further, the luminance signal Y is obtained and integrated. For example, if this is 89, if the current luminance conversion graph 1 is applied, the threshold value 1 to be controlled is 85 or more, so it is sufficient to apply 85/89 to the luminance signal so that the total luminance is 85. The luminance signal of each pixel is displayed by multiplying it by 85/89. When the luminance conversion graph 2 is applied, 85/100 is displayed over the luminance signal of each pixel, and the total luminance value is 75.7.

  FIG. 5 is a schematic diagram showing an example of a screen display that is actually subjected to luminance conversion by the prior art. FIG. 5A shows an original screen display based on video information, and FIG. 5B shows a screen display after conversion according to the prior art. In FIG. 5, if the total luminance value of the original luminance screen A1 is 60, the threshold value 1 is less than 85, so that the converted screen C1 is displayed with the same luminance as shown in FIG. 5B. To do. The number in the lower right of the screen is not on the actual screen, but for the sake of convenience, the total luminance of the screen is displayed for the sake of understanding of the invention. Since the total luminance is 85 or more in the screen A2-A5 having the original luminance, the luminance is uniformly suppressed to 85 in the luminance conversion according to the conventional technique, and the total luminance becomes constant as in the screen C2-C5. The right side of FIG. 5 schematically shows a locus line V1 of the total luminance converted by the prior art. As described above, in the conventional technique, the luminance is saturated at the threshold value, and the luminance change above the threshold value cannot be reproduced. In the figure, the frame transition of C1, C2, and C2 is described as the next frame, but these frames are assumed to be I frames that are standard frames such as MPEG, and between these frames, There are multiple P and B frames.

  FIG. 6 is a schematic diagram showing an example of a screen display that is actually subjected to luminance conversion according to the present invention. FIG. 6A shows an original screen display based on video information (exactly the same as FIG. 5A), and FIG. 6B shows a screen display after conversion according to the present invention. As shown in FIG. 6A, it is assumed that the original luminance of the screen based on the video information exceeds the threshold value 85 of 85 and the total luminance value is 89. Originally, it should be displayed like the screen A2, but it cannot be displayed as it is because the luminance exceeds the threshold value of 85 and the power consumption is too large. Therefore, the brightness of the entire screen is controlled based on the brightness conversion graph 1, and the screen is darker than the actual screen B2 after the conversion according to the present invention, and in this case, the brightness total value is 85. Then, if the total luminance value 92 of the subsequent image data exceeds the threshold value 85 based on the luminance conversion graph 1, the luminance conversion graph 2 is applied to the luminance conversion until the next frame is displayed. As a result, the luminance can be gradually lowered until the next frame.

  The luminance conversion graph 2 is applied for a certain period of time, and the luminance (total luminance value 92) screen as the original luminance screen A3 does not become 85 based on the luminance conversion graph 1 but the luminance total as the screen B3. Even if the value becomes 75.7, the value is converted based on the luminance conversion graph 2 of the previous image, so that the luminance change (becomes bright) can be expressed at the display stage of the screen B3. After a certain period of time, change to apply the luminance conversion graph 3, and even if it is the same luminance screen (luminance total value 93) as in screen A4, the screen so that the total luminance value is 83.2 as in screen B4 To display.

  Furthermore, after a certain period of time, the luminance conversion graph 3 is changed to apply, and even if it is a luminance screen (luminance total value 94) such as the original luminance screen A5, the total luminance value is 84.1 as in screen B5. To be displayed on the screen. Further, after a certain period of time, the original state is restored, and the luminance information included in the original frame is reproduced as it is within the range where the luminance conversion graph 1 is applied and the threshold value is not exceeded. The locus line V2 of the total luminance converted by the present invention is schematically shown. As shown in the figure, according to the present invention, it is possible to reproduce a subtle change in luminance above a threshold that has not been possible in the past.

  Here, the luminance conversion graph is returned to the original state in three stages, but it is better to further increase the stages. In addition, the arrow which connects each figure in FIG. 4 shows the process in which it returns to original luminance in steps in this way. If only the luminance conversion graph 1 and the luminance conversion graph 2 are changed without stepping, the screens B3 and B2 are repeated in FIG. 6 when a screen with similar luminance is displayed for a while. A change in brightness suddenly occurs, and the change becomes intense when it becomes darker or brighter, making it unsightly for the user. Therefore, by returning to the original state while applying the luminance conversion graph in two or more steps, the change in brightness becomes slow and hardly recognized by the user, and the luminance can be adjusted while realizing the reproduction of the luminance change. become able to.

  Further, even in the case of an image in a range exceeding the threshold, it is possible to display the luminance change by changing the luminance conversion graph in a stepwise manner in a timely manner. That is, by having a plurality of luminance conversion graphs and changing the graph stepwise after a certain amount of time, it is possible to prevent the user from knowing the change.

FIG. 7 is a schematic diagram showing a case where B and P frames (intermediate image data) between I frames which are reference frames are converted. As shown in the figure, when the luminance of the preceding I frame exceeds the threshold value, the subsequent I frame also exceeds the threshold value, and the conversion graph 2 having a different conversion rate is used in the subsequent I frame, this adjacent I frame is used. B ₁ , B ₂ between frames. . . B _x frame, P frame, etc. can also be converted into total luminance using conversion graph 2. This makes it possible to reproduce the change in the total luminance even for intermediate image data that may be uniformly restricted by exceeding the threshold.

  Although the present invention has been described based on the drawings and examples, it should be noted that those skilled in the art can easily make various modifications and corrections based on the present disclosure. Therefore, it should be noted that these variations and modifications are included in the scope of the present invention. In addition, the functions included in each member, each means, each step, etc. can be rearranged so as not to be logically contradictory, and a plurality of means, steps, etc. can be combined into one or divided. Is possible. In this embodiment, the use of a reference frame (I picture) such as MPEG as an object (preceding image data and subsequent image data) for calculating the total luminance and comparing it with a threshold value has been described. It is not limited to this. The reference frame (I picture) can be decoded without referring to other frames, is also used as a reference source when decoding other frames, and is put in the frame buffer relatively early. It is only used because it is convenient as a target. For example, when the device has a high decoding capability of image data and a large number of frames are stored in the frame buffer in advance, the total luminance of image data other than the reference frame may be used as a target to be compared with a threshold value. Note that the invention can be realized.

1 is a system configuration diagram of a mobile communication terminal device to which the present invention is applied. It is a flowchart which shows an example of the brightness | luminance adjustment sequence performed with the signal processing part shown in FIG. 6 is a flowchart showing a modification of the brightness adjustment sequence in FIG. 2. It is a brightness | luminance conversion graph used by this invention. It is a schematic diagram which shows an example of the screen display actually luminance-converted by the prior art. It is a schematic diagram which shows an example of the screen display actually luminance-converted by this invention. It is a schematic diagram which shows the case where B and P frames (intermediate image data) between I frames which are reference frames are converted.

Explanation of symbols

100 Mobile communication terminal
101 Signal processor
102 frame buffer
103 Luminance accumulator
104 Brightness conversion graph storage
105 Brightness converter
106 Panel drive unit
108 memory
109 Control panel
110 Display panel
A1-A5 Original brightness screen
B1-B5 Screen after conversion according to the present invention
C1-C5 Screen after conversion by conventional technology
L1-L4 luminance conversion line
V1-V2 locus line

Claims (2)

An image display device,
Display means comprising a plurality of self-luminous elements;
Computing means for computing the total luminance of the preceding image data to be displayed on the display means;
When the total luminance of the preceding image data calculated by the calculating means exceeds a predetermined threshold, the preceding image data is converted and displayed on the image display device so that the total luminance becomes the predetermined threshold. Means,
When the total luminance of the subsequent image data following the preceding image data changes beyond the predetermined threshold, the luminance change of the image data before conversion is performed without the total luminance of the converted image data exceeding the predetermined threshold. Means for converting the subsequent image data and displaying it on the image display device so as to reproduce and transition ;
An image display device comprising: A control method for an image display device comprising a plurality of self-luminous elements,
When the total luminance of the preceding image data to be displayed on the image display device exceeds a predetermined threshold value, the preceding image data is converted and displayed on the image display device so that the total luminance becomes the predetermined threshold value. Step to do,
When the total luminance of the subsequent image data following the preceding image data changes beyond the predetermined threshold, the luminance change of the image data before conversion is performed without the total luminance of the converted image data exceeding the predetermined threshold. Converting the subsequent image data and displaying it on the image display device so as to reproduce and transition ;
A control method for an image display device.

Images