JP2007225729A - Display device and its control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a display device capable of improving a display grade and its control method. <P>SOLUTION: The display device is equipped with a display element for displaying an image based on image data inputted by using irradiation light from an illumination section 6 including a plurality of light emitting elements. The illumination section 6 is constituted of the two or more light emitting element groups which can be respectively and independently controlled. A memory section 4A stores light emission history including at least either of the past light emission gradation and the light emission time are memorized for each light emitting element group. A correction section 3 computes the light emission gradation of the light emitting element based on the luminance included in the image data and the light emission history of every light emission group. A light emission controller 5 controls the illumination section 6 based on the computed light emission gradation. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to lighting control of an illuminating device used as a light source of a display element that does not emit light, such as a liquid crystal display, and particularly relates to an illuminating device including a plurality of light sources suitable for large display applications and a display device using the same.

  The liquid crystal display is a so-called non-light-emitting display in which the display pixels themselves do not emit light. However, because of the low drive voltage, low power consumption, and ease of multi-gradation display, the application has been expanded to large displays. Yes.

  Non-light-emitting displays include reflective displays that use reflected light from outside light such as sunlight and room light, transmissive displays that use backlight light, and transflective displays that use both external light and backlight. There is a display.

  An illumination device such as a backlight includes a plurality of light emitting elements and emits light continuously and continuously. By adjusting the brightness to the luminance gradation of the image data signal and partially reducing the emission gradation, A technique for improving energy saving and display quality has been devised.

  The display device described in Patent Document 1 includes a gradation correction unit that corrects the gradation of an image signal converted according to the illumination brightness based on the brightness information of the surrounding illumination area, and has a large brightness within the screen. High-quality display is possible even for images with a tilt.

Japanese Patent No. 3523170

  A light emitting element used in a lighting device has a characteristic called temporal change or deterioration with time, in which the light emission efficiency changes according to the light emission luminance and the light emission time, and the light emission amount changes even if the same input is continuously given. . Uniform light emission does not matter as long as the light emission efficiency does not become extremely low, since the luminance of the entire screen only changes uniformly even if a change with time occurs.

  However, in the case of a display with a large display screen size, the display screen is divided into a plurality of areas and each control is performed independently. A difference occurs in the luminous efficiency of each region, which causes luminance unevenness and degrades display quality.

  Such deterioration in display quality is not so noticeable when displaying natural images such as photographic images where the color tone changes continuously. This is particularly noticeable when displaying a non-natural image including a large amount of a solid portion (solid portion).

  The objective of this invention is providing the display apparatus which can improve display quality, and its control method.

The present invention includes a lighting unit including a plurality of light emitting elements, each of which is configured to be independently controllable as two or more light emitting element groups, and input light using irradiation light from the lighting unit. A display device control method comprising a display unit for displaying an image based on image data,
For each light emitting element group, a light emission history including at least one of a past light emission gradation and a light emission time is stored,
In the display device control method, the light emission gradation of the light emitting element is calculated based on the luminance included in the image data and the light emission history for each light emitting element group.

In addition, the present invention includes a plurality of light emitting elements, an illumination unit configured to be independently controllable as two or more light emitting element groups, and light input from the illumination unit. And a display unit that displays an image based on the image data,
A storage unit that stores a light emission history including at least one of a past light emission gradation and a light emission time for each light emitting element group;
A calculation unit that calculates the light emission gradation of the light emitting element based on the luminance included in the image data and the light emission history for each of the light emitting element groups;
And a control unit that controls the illumination unit based on the calculated light emission gradation.

  According to the present invention, the calculation unit calculates a luminance change with time based on the light emission history, and the light emission gradation of the light emitting element based on the calculated change with time and the luminance included in the image data. Is calculated.

  According to the present invention, the calculation unit is configured such that a light emission gradation is increased for a light emitting element group having a temporal change amount smaller than a predetermined value than an average value of the temporal change amounts of all the light emitting element groups. The light emission gradation is calculated.

  According to the present invention, an illumination unit that includes a plurality of light emitting elements and is configured to be independently controllable as two or more light emitting element groups, and input light by using irradiation light from the illumination unit. It is a control method of a display apparatus provided with the display part which displays the image based on the performed image data.

  For each light emitting element group, a light emission history including at least one of the past light emission gradation and light emission time is stored, and when calculating the light emission gradation of the light emitting element, the luminance included in the image data, Calculation is performed based on the light emission history for each light emitting element group.

  Thereby, the occurrence of luminance unevenness due to the difference in the light emission history can be suppressed, so that the display quality can be improved.

  Further, according to the present invention, using an illumination unit including a plurality of light emitting elements, each of which is configured to be independently controllable as two or more light emitting element groups, and irradiation light from the illumination unit, And a display unit that displays an image based on input image data.

  The storage unit stores a light emission history including at least one of a past light emission gradation and a light emission time for each of the light emitting element groups, and the calculation unit calculates the luminance included in the image data, and the light emitting element group. When the light emission gradation of the light emitting element is calculated based on the light emission history, the control unit controls the illumination unit based on the calculated light emission gradation.

  Thereby, the occurrence of luminance unevenness due to the difference in the light emission history can be suppressed, so that the display quality can be improved.

  According to the invention, the calculation unit calculates a change in luminance with time based on the light emission history, and emits light from the light emitting element based on the calculated change with time and the luminance included in the image data. Tone is calculated. Thereby, the display quality can be easily improved.

  According to the invention, the calculation unit has a higher light emission gradation for a light emitting element group having a change over time that is a predetermined value or more smaller than an average value of the change over time of all the light emitting element groups. Thus, the light emission gradation is calculated.

  The fact that the change over time is smaller than the average value of the whole means that the past light emission time is short, so the difference in change over time between the light emitting element groups can be reduced by emitting light with a high light emission gradation. Display quality can be further improved. Thereby, the display quality can be improved more easily.

FIG. 1 is a block diagram showing a configuration of a display device 1 according to an embodiment of the present invention.
The display device 1 is connected to an information processing device such as a personal computer, a recording device such as a video deck, an antenna cable for television broadcasting, and the like, and displays an image based on the captured image data.

  The display device 1 includes a control unit 2, a correction unit 3, a storage unit 4, a light emitting element control unit 5, an illumination unit 6, a display element control unit 7, a display unit 8, and a data capturing unit 9.

  The image data is captured by the data capturing unit 9, the display method is converted by the control unit 2, and output to the correction unit 3. The control unit 2 is realized by a CPU (Central Processing Unit) or the like, and controls the entire display device 1.

  The correction unit 3 corrects the light emission gradation of the illumination unit 6 and the display gradation of the display unit 8 based on the light emission history of the illumination unit 6 as described later. The storage unit 4 temporarily stores image data, stores the light emission history of the illumination unit 6, and stores various programs necessary for operating the display device 1.

  The light emitting element control unit 5 controls the light emitting elements of the illumination unit 6 according to the light emission gradation instructed from the correction unit 3. The display element control unit 7 controls the display unit 8 according to the display gradation instructed from the correction unit 3.

FIG. 2 is a block diagram illustrating a configuration of the correction unit 3.
The correcting unit 3 includes an image area dividing unit 10, a light emission gradation calculating unit 11, and a display gradation correcting unit 12.

  The image area dividing unit 10 divides the input image data into small areas composed of pixel groups for each frame. The small area is a pixel group that is displayed by irradiating light from an independently controllable light-emitting element group that is configured to be independently controllable as two or more light-emitting element groups. .

  The image area dividing unit 10 is more preferably realized by signal processing hardware such as a DSP (Digital Signal Processor) in terms of processing speed, but may be realized by the CPU constituting the control unit 2 using software. Good.

  The light emission gradation calculation unit 11 calculates the light emission gradation of the light emitting element for each small region based on the input image data.

  The storage unit 4 stores the calculation result for the current frame and the sum of the calculation results for all the frames so far for each small region as the light emission history.

  Further, the light emission gradation calculation unit 11 calculates the temporal change amount of the issuance gradation for each small area based on the light emission history, and compares it with a predetermined allowable value. When the amount of change with time exceeds the allowable value, the power value applied to each light emitting element is output to the light emitting element control unit 5 so as to correct the light emission gradation of the small area.

  The calculated light emission gradation is also given to the display gradation correction unit 12 so that the sum of the brightness in all the small areas after the correction becomes equal to the sum of the brightness of the input image data. The display gradation is corrected. The display gradation correction unit 12 outputs a power value applied to each display element to the display element control unit 7 so as to correct the display gradation.

  The small regions may all have the same shape and size, or may have different shapes and different sizes.

Moreover, the light emitting element which comprises the illumination part 6 is LED (Light Emitting Diode), CCFL (
Cold Cathode Fluorescent Lighting (EL) and EL (Electro Luminescence) can be used.

  In addition, the light emitting element control unit 5 and the display element control unit 7 may be incorporated in the functional units of the illumination unit 6 and the display unit 8.

FIG. 3 is a flowchart showing display control processing of the display device 1.
The following display control process is a flowchart for one frame, and needs to be performed every time the frame changes.

  First, in step S1, the image data input to the image area dividing unit 10 is divided into a plurality of small areas.

  Next, in step S2, the light emission gradation calculating unit 11 calculates the light emission gradation of the light emitting element corresponding to the small area from the image data corresponding to each small area and the image data corresponding to the adjacent small area. At this time, by determining the light emission gradation according to the maximum luminance of the image data, the energy saving effect by the light control is maximized.

In step S3, the luminance variation with time in each small region is calculated based on the light emission history, and it is determined whether or not the luminance is larger than a predetermined allowable value.
α = (ΔI−ΔI _AVE ) −I _TH
ΔI = F ₁ (∫F _{2 It t} · dt)
ΔI: Amount of luminance change with time
ΔI _AVE : Average change in luminance over time
I _TH : Tolerance for luminance change difference
F ₁ , F ₂ : The light emission efficiency of the device is determined from the past light emission gradation and light emission time.
Characteristic functions of light-emitting elements that express aging characteristics
I _t: past of the light-emitting brightness
t: time

  In the above calculation formula, when α is positive, the amount of change with time in luminance exceeds an allowable value, so the process proceeds to step S4, and the light emission gradation of the small area is corrected. The light emitting element control unit 5 is instructed to adjust the power supplied to the light emitting elements belonging to the small area.

Note that the luminance change difference allowable value I _TH is a value derived from a luminance difference that can be discriminated by human vision, and is a constant value that does not change according to time or history. The characteristic function F ₁ is a function representing the influence of the defect of the semiconductor crystal of the light emitting element on the light emission amount, and the characteristic function F ₂ is the energy not irradiated as light among the energy given to the light emitting element. This is a function representing the contribution of damage to the semiconductor crystal. These allowable values and characteristic functions are stored in the storage unit 4 in advance.

  In many cases, the change over time changes in the direction in which the light emission efficiency of the light emitting element decreases and the amount of light emission decreases, so if the change over time becomes significant, an instruction to supply more power is given. Therefore, the light emission gradation that is higher than the gradation based on the image data is output to the light emitting element control unit 5.

In step S5, an average value of luminance change with time is obtained for each small area.
In step S6, the amount of change with time and the average value are tabulated for each small region, and it is determined whether or not there is variation in change over time based on the distribution state.

  For example, the average value of all the areas is calculated, and if there is a small area having an average value lower than a certain value with respect to the average value, the gradation of the small area is increased in step S7. By so doing, the temporal change of the small area is promoted, and the temporal change is made uniform.

  If the difference in change over time between the divided small areas is too large, even if correction is performed in step S4, the luminance unevenness between the small areas will be conspicuous. It becomes easy.

  Similarly, if there is a small area having an average value higher than a certain value with respect to the average value of all areas, the gradation of the area other than the small area is made higher, and the change with time is made uniform.

  The light emission gradation of each small area after correction and the light emission history of the light emission gradation before correction are stored in the storage unit 4.

  When a non-volatile storage medium such as a hard disk drive or flash memory is used for the storage unit 4, these generally have a low writing speed, and when processing a high-speed moving image, a light emission gradation is written for each frame. Since it is difficult, it is desirable to temporarily accumulate light emission gradations of a plurality of frames in a high-speed memory and store the light emission history again.

In step S8, the display gradation is corrected based on the light emission gradation of each small area.
In the non-self-luminous display device as in the present embodiment, the gradation of the pixel of the image data, that is, the gradation of the light output from the display unit 8 is the emission gradation of the illumination unit and the display gradation of the display unit. Is proportional to Therefore, when the light emission gradation is increased by the correction, the display gradation needs to be lowered, and when the light emission gradation is lowered by the correction, the display gradation needs to be increased.

  When the amount of decrease in the light emission gradation is large, it is desirable to perform γ correction in consideration of human visual characteristics when correcting the display gradation.

  In step S9, the light emitting element control unit 5 and the display element control unit 7 drive the illumination unit 6 and the display unit 8, respectively, according to the light emission gradation and display gradation calculated so far.

  At this time, in the control of the light emitting element, the light emission luminance of the light emitting element may be changed, or the amount of light detected by duty control represented by PFM (Pulse Frequency Modulation) or PWM (Pulse Width Modulation) may be changed. .

It is a block diagram which shows the structure of the display apparatus 1 which is one Embodiment of this invention. 3 is a block diagram illustrating a configuration of a correction unit 3. FIG. 4 is a flowchart showing display control processing of the display device 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Display apparatus 2 Control part 3 Correction | amendment part 4 Memory | storage part 5 Light emitting element control part 6 Illumination part 7 Display element control part 8 Display part 9 Data acquisition part 10 Image area division | segmentation part 11 Light emission gradation calculation part 12 Display gradation correction | amendment part

Claims (4)

An illumination unit that includes a plurality of light-emitting elements and is configured to be independently controllable as two or more light-emitting element groups, and based on input image data using irradiation light from the illumination unit A display device control method comprising a display unit for displaying an image,
For each light emitting element group, a light emission history including at least one of a past light emission gradation and a light emission time is stored,
A method for controlling a display device, comprising: calculating a light emission gradation of the light emitting element based on a luminance included in the image data and the light emission history for each light emitting element group. An illumination unit that includes a plurality of light-emitting elements and is configured to be independently controllable as two or more light-emitting element groups, and based on input image data using irradiation light from the illumination unit A display device including a display unit for displaying an image,
A storage unit that stores a light emission history including at least one of a past light emission gradation and a light emission time for each light emitting element group;
A calculation unit that calculates the light emission gradation of the light emitting element based on the luminance included in the image data and the light emission history for each of the light emitting element groups;
And a control unit that controls the illumination unit based on the calculated light emission gradation.   The calculation unit calculates a luminance change with time based on the light emission history, and calculates a light emission gradation of the light emitting element based on the calculated change with time and the luminance included in the image data. The display device according to claim 2, characterized in that:   The calculation unit calculates a light emission gradation so that a light emission gradation is higher for a light emitting element group having a change over time that is a predetermined value or more smaller than an average value of the change over time of all the light emitting element groups. The display device according to claim 3, wherein:

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