JP5743782B2 - Image display device - Google Patents

Description

  The present invention relates to an image display device that displays an image using a backlight composed of a plurality of divided light guide plates, and more particularly to a backlight that divides an image display area into a plurality of areas and corresponds to each area. The present invention relates to an image display device capable of individually controlling the brightness of the image.

  In general, in a non-light-emitting display device such as a liquid crystal display device using a liquid crystal panel as a display device, light is irradiated from the back side of the liquid crystal panel by a backlight in order to form an image on the liquid crystal panel. The backlight method in the liquid crystal display device is roughly classified into two types, a direct method and an edge light method. The direct method is a method in which fluorescent tubes and LEDs (Light Emitting Diodes) serving as light sources are arranged directly under a liquid crystal panel. In the edge light system, a fluorescent tube or LED serving as a light source is arranged at an end (edge portion) of a plate-shaped light guide plate made of an acrylic plate or the like, and a surface light source is used by using multiple reflections inside the light guide plate. It is what you do.

  In recent liquid crystal display devices, the image display area is divided into a plurality of areas (areas) for improving the contrast characteristics and saving power of the backlight power supply, and the feature amount (brightness level) of the image signal corresponding to each area is divided. ), A so-called area control (also called local dimming) technique for controlling the brightness of the backlight in the corresponding area is adopted. In area control, it is necessary to accurately control the brightness of each area in order to improve contrast. In this regard, in the liquid crystal display device described in Patent Document 1, the light guide plate is divided into a plurality of blocks, and a groove is formed on the lower surface of the light guide plate so that light from the block where the light source is lit does not leak into the adjacent block. It has a structure such as.

  On the other hand, the liquid crystal display device has an optical member such as a diffusion plate for uniformly irradiating the liquid crystal panel with the light emitted from the light source or the light guide plate. Therefore, as the liquid crystal panel becomes larger, the light guide plate and the diffusion plate itself also have a larger area. Increasing the size of these optical members leads to an increase in the size of equipment for manufacturing them, and there are problems such as an increase in manufacturing cost and a decrease in processing accuracy. In this regard, in the liquid crystal display device described in Patent Document 2, the light guide plate has a structure in which a plurality of divided light guide plates are combined, and the size of each divided structure plate is the same shape and is a common divisor constituting the size of the liquid crystal panel. . Thus, it is stated that the light guide plate is configured at low cost, and the image quality is high and uniform regardless of the screen size.

JP 2009-199926 A JP 2009-69712 A

  In the technique described in Patent Document 1, since the light emitted from the light source is totally reflected at the boundary surface between adjacent blocks, the contrast can be improved with little leakage to other blocks other than the lit block. . However, since the leakage to the adjacent block is eliminated, the luminance distribution in the lighting block, that is, the sharp luminance decrease at the boundary surface with the adjacent block occurs, which causes image quality deterioration.

  In the technique described in Patent Document 2, adjacent divided light guide plates are combined in a matrix by a holding member or an adhesive member to form an integrated structure, and the light guide plate constituting the backlight is configured at low cost. However, Patent Document 2 does not mention area control for dividing the image display area into a plurality of areas and controlling the luminance of the corresponding backlight for each area.

  Here, when area control is performed using a divided light guide plate (hereinafter referred to as “divided light guide plate”), a luminance step generated at an end portion (hereinafter referred to as “boundary portion”) of the adjacent divided light guide plate. Will be described.

  FIG. 15 is a diagram for explaining the occurrence of a luminance step, and is a diagram showing a light spread distribution in the light guide plate when a light source corresponding to one area in the divided light guide plate is turned on. The vertical axis is the normalized luminance value, and the horizontal axis is the area number. Here, only the light source for area 3 is turned on. A curve 300 is a case where the boundary portion of the divided light guide plate does not exist at the boundary between the areas, and a curve 301 is a case where the boundary portion of the divided light guide plate exists at the boundary between the area 3 and the area 4.

  Comparing the curve 300 and the curve 301, since the boundary portion exists between the area 3 and the area 4, the spread of light from the area 3 to the area 4 is prevented, and the luminance values of the boundary portion and the area ahead are determined. It is falling. As a result of such a sharp luminance step at the boundary, the luminance distribution in the area 3 is deteriorated, which causes image quality deterioration. This decrease in luminance is caused by the difference in refractive index between the divided light guide plate and the air layer due to a part of light incident at various angles from the edge of the divided light guide plate to the air layer (or from the air layer to the end of the divided light guide plate). It happens to be totally reflective. As a countermeasure, it is possible to reduce a decrease in luminance by forming a space between the divided light guide plates not by an air layer but by a holding member or an adhesive member having the same refractive index as the material constituting the divided light guide plate. However, such a structural change has problems such as an assembly accuracy problem and a cost increase, and is difficult to realize.

  In this way, when area control is performed using a backlight configured by dividing the light guide plate into a plurality of divided light guide plates, the luminance step generated at the boundary (end) of the divided light guide plate is not structurally changed. It is necessary to suppress it.

  The present invention has been made in view of the above problems, and in an image display device using a backlight composed of a plurality of divided light guide plates, it is preferable to suitably suppress a luminance step generated at a boundary portion of the divided light guide plates. Objective.

  The present invention includes a backlight having a light guide plate configured by combining a plurality of divided light guide plates in which a plurality of areas are arranged in a matrix, and a light source capable of individually controlling emission intensity corresponding to each area, In an image display device including a liquid crystal panel that displays an image by modulating light emitted from a backlight for each pixel, a light emission amount determination that determines a light emission amount of a corresponding light source according to an input image signal in each area And an image signal correction unit that corrects the amplitude of the image signal displayed on the liquid crystal panel in accordance with the determined light emission amount. Here, the light emission amount determination unit includes a boundary determination unit that determines whether or not the processing target area for determining the light emission amount has a boundary part that joins the divided light guide plate between the adjacent area and the boundary determination unit. It has a configuration including a boundary area processing unit that corrects the light emission amount of the processing target area determined to have the boundary portion so that the ratio R to the light emission amount in the adjacent area across the boundary portion becomes a certain ratio or more. .

  According to the present invention, it is possible to suppress a luminance step at the boundary portion of the divided light guide plate and obtain a display image without image quality deterioration in area control.

Schematic which shows an example of the backlight apparatus used for the image display apparatus of this invention. FIG. 3 is an exploded cross-sectional view of an image display device using a backlight device. 1 is a block configuration diagram of an image display apparatus according to a first embodiment. 2 is a detailed configuration diagram of a second dimming value determination unit 12 in Embodiment 1. FIG. The figure explaining operation | movement of the spatial filter part 22. FIG. The figure explaining operation | movement of the boundary area process part 23 (when a boundary part is not pinched | interposed). The figure explaining operation | movement of the boundary area process part 23 (when pinching a boundary part). The detailed block diagram of the 2nd light control value determination part 12 in Example 2. FIG. The figure explaining operation | movement of the boundary control space filter part 26 (when a boundary part is not pinched | interposed). The figure explaining operation | movement of the boundary control space filter part 26 (when pinching a boundary part). The figure which shows the luminance distribution of the area pair which does not separate a boundary part. The figure which shows the luminance distribution of the area pair which separated the boundary part. The figure explaining the definition of the brightness | luminance level difference (DELTA) L. The figure which shows the relationship between the brightness | luminance level difference (DELTA) L and the light control value ratio R. FIG. The figure explaining generation | occurrence | production of a brightness | luminance level | step difference.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic view showing an example of a backlight device used in the image display device of the present invention. The backlight device 100 is an edge light system, and the light guide plate is configured by arranging a plurality of (here, four) divided light guide plates 101a to 101d made of an acrylic material or the like. 18) rectangular display areas (hereinafter referred to as “areas”) 102 are arranged in a matrix. Each divided light guide plate 101 has an integral structure, and each area 102 included therein is composed of the same material continuously. A light source 103 is disposed at the lower end of each area 102, and the light emitted from the light source 103 travels toward the upper end of the area 102. That is, in the case of FIG. 1, the optical axis direction is a direction from the lower part of the screen toward the upper part of the screen. Hereinafter, the horizontal direction of the screen is the X direction and the vertical direction of the screen (however, the downward direction) is the Y direction. Also, area numbers 1 to 12 are assigned to indicate the X-direction position of each area.

  The four divided light guide plates 101a to 101d are coupled by a holding member or an adhesive member, and their boundaries are arranged with a gap of D1 in the X direction and D2 in the Y direction. The reason for providing the gap is that the split light guide plate 101 itself extends due to heat from the light source or the like, and absorbs the extension. In addition, it has an effect of suppressing warpage of the divided light guide plate 101 due to vibration or the like. The sizes of the gaps D1 and D2 are 0.5 to 1.0 mm, and D1 and D2 may be the same value or different values. The gaps D1 and D2 are filled with a holding member, an adhesive member, or an air layer. Hereinafter, the end portion of the divided light guide plate 101 that faces the gap is referred to as a “boundary portion”.

  As described above, since the divided light guide plate 101 is disposed with the gaps D1 and D2, each of the areas 102 arranged on the divided light guide plate 101 has the above-described gap between the adjacent area. Some have, ie, have the “boundary portion” described above. Hereinafter, such an area is referred to as a “boundary area”.

  FIG. 2 is an exploded cross-sectional view of an image display device using the backlight device 100 of FIG. In the backlight device 100, the light source 103 is mounted on the wiring board 104. The light source 103 uses one or a plurality of (for example, 3 to 5) light emitting diodes (LEDs) that emit white light, but three-color LEDs or lasers that emit red, blue, and green light. Other light emitting elements such as a diode may be used. The divided light guide plate 101 is attached to face the wiring board 104 on which the light source 103 is mounted. At that time, the divided light guide plate 101 is provided with a recess 105 for accommodating the light source 103, and each light source 103 is arranged to irradiate the corresponding area 102 of the divided light guide plate 101. The light emitted from the light source 103 is reflected in the divided light guide plate 101 and emitted as irradiation light in the left direction (Z direction) in the drawing.

  Three diffusion sheets 201 are arranged on the exit side of the divided light guide plate 101. Fine irregularities are formed on the surface of each diffusion sheet, and this diffuses light from the divided light guide plate 101. Here, the number of diffusion sheets 201 may be other than three. Moreover, you may use another optical sheets, such as a prism sheet which improves the front luminance of a screen as needed.

  A liquid crystal panel 202 is disposed on the emission side of the diffusion sheet 201, and the light diffused by the diffusion sheet 201 is configured to illuminate the entire display area of the liquid crystal panel 202. This display area is assumed to be substantially equal to the irradiation surface of the backlight device 100, that is, the size of the four divided light guide plates 101a to 101d.

  Hereinafter, an embodiment of an image display device including the above-described backlight device 100 will be described.

  FIG. 3 is a block diagram of the image display apparatus according to the first embodiment of the present invention. The image display device includes an image frame receiving unit 10, a first dimming value determining unit 11, a second dimming value determining unit 12, a time filter unit 13, a backlight control unit 14, and a backlight unit 15. The backlight luminance distribution calculation unit 16, the image signal correction unit 17, the liquid crystal control unit 18, and the liquid crystal panel 20 are configured. The first dimming value determination unit 11 and the second dimming value determination unit 12 are collectively referred to as a light emission amount determination unit 19. The backlight unit 15 corresponds to the backlight device 100 in FIGS. 1 and 2, and includes a light guide plate configured by arranging a plurality of divided light guide plates 101, and a light source 103 placed on the wiring substrate 104. The The liquid crystal panel 20 corresponds to the liquid crystal panel 202 in FIG.

  The overall operation of the image display apparatus will be described. The image frame signal received by the image frame receiving unit 10 is sent to the light emission amount determining unit 19 and the image signal correcting unit 17 for correcting the image signal.

  The first dimming value determination unit 11 of the light emission amount determination unit 19 decomposes the input image frame signal for each area 102 in the screen, and the luminance distribution in each area 102 based on the luminance information for each pixel (that is, A histogram indicating the number of pixels included in each of a plurality of luminance ranges is detected. Further, the relationship between the histogram detection result and the light emission amount of the light source corresponding to the area is stored in advance in a table format in a memory (not shown) such as a ROM. By referring to the table based on the histogram detection result, an initial light emission amount (hereinafter referred to as a first dimming value signal) of the light source 103 corresponding to each area 102 is determined and sent to the second dimming value determination unit 12. To do.

  Here, the luminance information for each pixel is a luminance value on the liquid crystal panel obtained from the maximum gradation value or gradation value in each pixel of the image frame signal. The histogram detection result refers to an arbitrary value from the top 5% of the luminance information value frequency to the maximum value (maximum luminance information value) by detecting the frequency of the luminance information value in the area. That is, the maximum gradation information that is substantially the maximum gradation (luminance) in each area is detected.

  Further, in the table showing the relationship between the histogram detection result and the light emission amount of the corresponding light source, the light emission amount of the corresponding light source (first dimming value signal) in the area where the maximum gradation (luminance) is small based on the area control. ) Is set smaller. Several types of tables may be prepared in advance, and may be switched and used depending on the video mode set by the user, video genre information of the input video, ambient illuminance, ambient temperature, presence / absence of a person, viewing position of a person, and the like.

  Next, the second dimming value determination unit 12 of the light emission amount determination unit 19 corrects the light emission amount of the light source 103 corresponding to each area 102 so as to make it difficult to visually recognize the luminance step between the divided light guide plates 101. The processing in the second dimming value determination unit 12 includes spatial filter processing and boundary area processing. In the spatial filtering process, a spatial filtering process is performed on the first dimming value signal in order to compensate for the influence of the spread of light between the areas constituting the backlight. In the boundary area processing, the dimming value signal for the boundary area (area having the boundary portion) is corrected so that the light sources corresponding to the area pairs separating the boundary portions are turned on at a certain ratio or more. In this way, the second dimming value signal is generated in which the luminance step generated at the boundary portion of the divided light guide plate 101 is suppressed. Details of the spatial filter processing and the boundary area processing will be described later.

  The time filter unit 13 performs filtering in the time direction on the second dimming value signal determined by the second dimming value determination unit 12 so as to suppress a steep luminance variation. This processing is performed by, for example, the second dimming value signal obtained at the timing of the frame of the current image signal and the timing of the previous frame, or the second dimming value signal obtained at the timing of the previous frame and the previous frame. Is a process for obtaining a weighted average of. The second dimming value signal that has been subjected to the filtering process in the time direction is sent to the backlight control unit 14 and the backlight luminance distribution calculation unit 16 as the light emission amount of the light source corresponding to the area.

  The backlight control unit 14 receives the light emission amount determined by the time filter unit 13 and controls lighting of the light source 103 in the backlight unit 15. The signal for driving the light source 103 is a PWM (Pulse Width Modulation) signal or an amplitude modulation signal. In the case of a PWM signal, the PWM frequency is constant, and driving is performed by changing the ratio (duty ratio) between the ON period and the OFF period according to the light emission intensity. Further, it is desirable that the PWM frequency is equal to or higher than the frame frequency of the image display device.

  The backlight luminance distribution calculation unit 16 receives the light emission amount determined by the time filter unit 13, calculates the luminance distribution immediately below the liquid crystal panel 20, and sends an appropriate gain amount to the image signal correction unit 17. The image signal correction unit 17 performs image correction based on the obtained gain amount. For example, if the light emission amount of the light source is reduced to ½ of the maximum luminance, the amplitude of the image signal is doubled, and the image correction is performed so as to cancel the luminance reduction of the image due to the reduction of the light emission luminance. The corrected image signal is sent to the liquid crystal control unit 18 to drive the liquid crystal panel 20. The liquid crystal panel 20 modulates the light emitted from the backlight unit 15 for each pixel to form and display an image.

Next, the operation of the second dimming value determination unit 12 will be described in detail.
FIG. 4 is a detailed configuration diagram of the second dimming value determination unit 12. The first dimming value receiving unit 21 inputs (receives) the first dimming value signal determined by the first dimming value determination unit 11 and sends it to the storage area unit 24. The storage area unit 24 is composed of a RAM or the like and stores the first dimming value signal. The first dimming value reception unit 21 sends a reception completion signal to the spatial filter unit 22 when the input of the first dimming value signal is completed. The spatial filter unit 22 reads the first dimming value signal from the storage area unit 24, performs spatial filtering, and generates a second dimming value signal. The boundary area processing unit 23 performs boundary area processing on the dimming value belonging to the boundary area in the second dimming value signal. At that time, the boundary determination unit 25 determines whether or not the processing target area is a boundary area. Hereinafter, spatial filter processing and boundary area processing will be described.

  FIG. 5 is a diagram for explaining the operation of the spatial filter unit 22. (A) shows the area to be referred to in the spatial filter processing and its first dimming value signal, and (b) shows the spatial filter coefficient α used for the calculation. In this example, the central area of the screen position (x, y) to be processed and the eight surrounding areas are shown, and BL indicates the first dimming value signal of the light source in each area. For the position (x, y), for example, the area at the upper left end of the screen is the origin (x = 0, y = 0).

The spatial filter unit 22 performs spatial filtering on the first dimming value signal held in the storage region unit 24 in order to compensate for the effect of the spread of light between the areas constituting the backlight. Apply. That is, the dimming value BLo (x, y after passing through the spatial filter section is obtained by performing the calculation of the formula (1) using the spatial filter coefficient α (m, n) on the distribution of BL (x, y). ) Is calculated.
BLo (x, y) = Max {α (m, n) × BL (x + m, y + n)} (1)
However, m = −1 to +1, n = −1 to +1

  This calculation means that each dimming value in the central area and the surrounding area is multiplied by the filter coefficient α, and the maximum value among them is adopted. That is, the dimming values multiplied by the coefficient α are compared, and if there is a surrounding area value larger than the central area value, the central area value is replaced with a larger surrounding area value.

  FIG. 5B shows an example of the spatial filter coefficient α (m, n). α (m, n) is stored in the storage area unit 24 in advance. Here, the value of the coefficient α (m, n) indicates the degree of contribution (weighting) from each area to be referred to. The value α (0, 0) of the center area to be processed is set to the maximum value 1.2 and the surrounding area The value of is reduced. Specifically, the coefficient α of the surrounding area is desirably 0.4 or less.

  For example, when the light control value BL (x, y) = 0 in the central area and the light control value BL (x + 1, y) = 100 in the surrounding area, the light control value BLo (x, y after passing through the spatial filter) ) Is replaced by α (1,0) × BL (x + 1, y) = 0.3 × 100 = 30. In this way, by controlling the spread of light between adjacent areas, the spatial change in the light emission amount of the light source corresponding to each area can be moderated. By performing the above processing on all areas, the BLo of the entire screen is calculated and a second dimming value signal is generated.

  In this example, the surrounding eight areas adjacent to the central area to be processed are set as the reference range. However, the area adjacent to the outside may be added to the reference range to make a total of 24 areas.

  6 and 7 are diagrams illustrating the operation of the boundary area processing unit 23. FIG. FIG. 6 shows a case where the processing target area does not correspond to the boundary area (a boundary portion is not sandwiched), and FIG. 7 illustrates a case where the processing target area corresponds to the boundary area (a boundary portion is sandwiched). In both cases, (a) shows an area to be referred to in the processing and its second dimming value signal, and (b) shows a boundary area coefficient β used for calculation.

  The boundary determination unit 25 determines whether the target area corresponds to the boundary area, determines a boundary area coefficient β (m, n), and outputs the boundary area coefficient β (m, n) to the boundary area processing unit 23. When the boundary area is satisfied, the boundary area coefficient β (m, n) is determined by determining which area and the boundary part have the boundary area. For this determination, the storage area 24 stores the positional relationship between the divided light guide plate 101 and the area 102.

The boundary area processing unit 23 calculates the expression (2) for the second dimming value signal BLo (x, y) generated by the spatial filter unit 22 using the boundary area coefficient β (m, n). By doing so, the second dimming value signal BLd (x, y) after the boundary area processing is calculated.
BLd (x, y) = Max {β (m, n) × BLo (x + m, y + n)} (2)
However, m = −1 to +1, n = −1 to +1

  In FIG. 6A, since the central area of the screen position (x, y) to be processed does not have a boundary with the surrounding area, as shown in FIG. 6B, the coefficient β ( 0,0) = 1, and coefficient β (m, n) = 0 for all surrounding areas. As a result of the calculation of the expression (2), BLd (x, y) = BLo (x, y) is obtained, and the second dimming value signal BLo (x, y), which is the output of the spatial filter unit 22, is output as it is. The

  On the other hand, in FIG. 7A, the central area of the screen position (x, y) to be processed is the boundary (gap D1) between the area of the screen position (x + 1, y) adjacent in the X direction. )have. In this case, as in (b), a value other than 0, for example, 0.7 is set as the coefficient β (1, 0) of the area (x + 1, y) adjacent to the boundary portion. As a result of the calculation of the expression (2), as BLd (x, y), a larger value of BLo (x, y) or 0.7 × BLo (x + 1, y) is output. For example, when BLo (x, y) = 30 and BLo (x + 1, y) = 100, the value of BLd (x, y) is replaced with 0.7 × 100 = 70.

  As described above, the process of correcting the dimming value BLo (x, y) is performed only when the processing target area is a boundary area. Also in this correction, the dimming value of the target area is raised by the value of the adjacent area having a high dimming value. In the above example, the ratio of the dimming value before processing is 30: 100, but the ratio of the dimming value after processing is 70: 100. As a result, the difference in dimming value between the pair of areas separating the boundary portion is reduced, and the dimming value ratio R increases from 0.3 to 0.7, and the light is turned on at a rate determined by the coefficient β. The dimming value ratio R is expressed as a fraction with the larger dimming value as the denominator, and is in the range of 0 to 1.

  When the target area is a boundary area, the position of the boundary portion exists in various directions. For example, if there is a boundary (gap D2) between areas (x, y + 1) adjacent in the Y direction, β (x, y + 1) = 0.7. Further, when there are boundary portions in both the X direction and the Y direction, β (x + 1, y) = β (x, y + 1) = β (x + 1, y + 1) = 0.7 may be set. If a luminance step is strongly visible only in a certain direction, for example, the X direction due to the directivity of the light source, a value (0.7) is set only for β (x + 1, y) in the certain direction. Also good.

  In addition, the boundary area processing according to the present embodiment can be always applied regardless of the type of video. However, when the visibility of the luminance level changes depending on the type of video, the boundary area coefficient β is changed depending on the type of video. A configuration may be adopted in which the value is switched or the boundary area processing function is turned ON / OFF.

  As described above, the light sources corresponding to the pair of areas separating the boundary portions are turned on when the dimming value ratio R is equal to or larger than the boundary area coefficient β, and the luminance steps generated at the boundary portions of the divided light guide plates cancel each other. As a result, it is possible to suppress the luminance step. In the above example, 0.7 is set as the value of the boundary area coefficient β, but it is set by appropriately selecting from a range of 0.5 to 1.0 according to the structure of the light guide plate (that is, the ease of occurrence of a luminance step). To do. This is because if the coefficient β is smaller than 0.5, the effect of canceling the luminance step generated at the boundary portion of the divided light guide plate is reduced. When the coefficient β approaches 1.0, the dimming value of each area is the same. This is because it does not make sense for area control.

Next, the effect of suppressing the luminance step according to the present embodiment will be specifically described.
1. Select an area pair that does not separate the boundary from the area 102 of the backlight device in FIG. 1 and an area pair that separates the boundary, and light the light sources corresponding to the selected areas by changing their dimming value ratio R. The brightness distribution was compared.

  FIG. 11 is a diagram showing the luminance distribution of an area pair that does not separate the boundary portion. As such an area pair, for example, areas of area numbers 3 and 4 in FIG. 1 are taken up. (A) is dimming value ratio R = 0.3, (b) is dimming value ratio R = 1.0, and the light source of each area is turned on. In any case, since the luminance distribution when the single area is lit changes smoothly, the total luminance distribution when the areas 3 and 4 are lit simultaneously is the luminance even at the boundary position between them. There are no steps and the transition is smooth.

  FIG. 12 is a diagram showing the luminance distribution of an area pair separated by a boundary portion. As such an area pair, for example, areas of area numbers 6 and 7 in FIG. 1 are taken up. (A) is dimming value ratio R = 0.3, (b) is dimming value ratio R = 1.0, and the light source of each area is turned on.

  In the areas (boundary areas) 6 and 7 having the boundary portion, the spread of light is blocked at the boundary portion, so that the luminance decreases sharply. This is because part of the light incident on the gap (air layer) from the end of the light guide plate is totally reflected due to the difference in refractive index between the light guide plate and the air layer. As a result, when only a single area is lit, the luminance level difference at the boundary portion is visually recognized. On the other hand, the total luminance distribution when the areas 6 and 7 are turned on simultaneously has the effect of reducing the luminance step at the boundary position between the two. The effect depends on the ratio R of the dimming values of both areas. (A) is a case where R = 0.3, and a step is still visible at the boundary. (B) is the case of R = 1.0, the step at the boundary is eliminated, and the distribution is smooth.

Here, the dimming value ratio R necessary for eliminating the luminance step is analyzed.
FIG. 13 is a diagram for explaining the definition of the luminance step ΔL used for the analysis. In an area adjacent to the boundary, the boundary position is S0, and the positions that enter the respective areas from S0 by a certain distance are measurement positions S1 and S2. The luminances at the positions S1 and S2 are L1 and L2. At this time, the normalized luminance change rate at the boundary portion is expressed by equation (3), which is defined as a luminance step ΔL.
ΔL = | L1-L2 | / {Max (L1, L2) × | S1-S2 |} (3)

  FIG. 14 is a diagram showing the relationship between the luminance step ΔL and the dimming value ratio R. FIG. 14 shows the luminance step characteristic ΔL1 when the boundary portion is separated and the luminance step characteristic ΔL0 when the boundary portion is not separated for comparison, and the dimming value ratio R is changed in the range of 0 to 1. ing. Note that the interval between the measurement positions is set to | S1−S2 | = 5 mm.

  From FIG. 14, in any dimming value ratio R, the luminance step ΔL1 when the boundary is separated is larger than the luminance step ΔL0 when the boundary is not separated, and the luminance step as the dimming value ratio R approaches 1 is obtained. ΔL1 and ΔL0 become smaller. Here, the luminance step ΔL0 when the boundary is not separated has a maximum value of 0.015 when R = 0, and this is the allowable value of the luminance step. According to this criterion, the dimming value ratio R may be about 0.5 or more in order to set the luminance step ΔL1 when the boundary portion is separated within the allowable value 0.015. That is, the original area control is performed while suppressing the luminance step by turning on the dimming value ratio R of the pair of areas separating the boundary portions at a constant ratio within the range of 0.5 to 1.0. Is possible.

  As described above, according to the present embodiment, in the backlight device configured by arranging a plurality of divided light guide plates, the light sources corresponding to the area pairs separating the boundary portions by the boundary area processing are turned on at the dimming value ratio within the predetermined range. By controlling to do so, it is possible to suppress the luminance step generated at the boundary portion of the divided light guide plate.

  FIG. 8 is a detailed configuration diagram of the second dimming value determination unit 12 of the image display apparatus according to the second embodiment of the present invention. In the second embodiment, a boundary control spatial filter unit 26 for simultaneously performing spatial filter processing and boundary area processing in the second dimming value determination unit 12 is provided, and the spatial filter unit 22 and boundary area in the first embodiment (FIG. 5) are provided. The functions of the processing unit 23 are integrated. Other configurations are the same as those of the first embodiment (FIGS. 4 and 5). Hereinafter, the process in which the spatial filter process and the boundary area process are integrated is referred to as “boundary control spatial filter process”.

  The second dimming value determination unit 12 stores the first dimming value signal determined by the first dimming value determination unit 11 in the storage area unit 24. The storage area unit 24 stores the boundary spatial filter coefficient γ used for the boundary control spatial filter processing, and the boundary determination unit 25 determines whether the processing target area is a boundary area. The boundary control space filter unit 26 reads the first dimming value signal from the storage area unit 24, performs boundary control space filter processing, and generates a second dimming value signal. At that time, the boundary determination unit 25 switches and outputs the boundary spatial filter coefficient γ used in the boundary control spatial filter processing according to whether or not the processing target area is the boundary area.

  9 and 10 are diagrams for explaining the operation of the boundary control space filter unit 26. FIG. 9 shows a case where the processing target area does not correspond to the boundary area (a boundary portion is not sandwiched), and FIG. 10 illustrates a case where the processing target area corresponds to the boundary area (a boundary portion is sandwiched). In either case, (a) shows an area to be referred to in the process and its first dimming value signal, and (b) shows a boundary spatial filter coefficient γ used for calculation. This example also shows the center area of the screen position (x, y) to be processed and the surrounding eight areas.

  The boundary determination unit 25 determines whether or not the target area corresponds to the boundary area, determines a boundary spatial filter coefficient γ (m, n), and outputs it to the boundary control spatial filter unit 26. When the boundary area falls under the boundary area, the boundary space filter coefficient γ (m, n) is determined by determining which of the surrounding areas the boundary portion exists.

The boundary control spatial filter unit 26 uses the boundary spatial filter coefficient γ (m, n) for the first dimming value signal BL (x, y) held in the storage area unit 24 to obtain the equation (4). By calculating the above, the second dimming value signal BLd (x, y) after the boundary control space filter processing is calculated.
BLd (x, y) = Max {γ (m, n) × BL (x + m, y + n)} (4)
However, m = −1 to +1, n = −1 to +1

  In FIG. 9A, since the central area of the screen position (x, y) to be processed does not have a boundary portion with the surrounding area, the boundary space filter coefficient γ shown in FIG. The same value as the spatial filter coefficient α shown in FIG. Thus, by performing the calculation of equation (4), the function of only the spatial filter processing that compensates for the influence of the spread of light between the respective areas constituting the backlight is realized.

  On the other hand, in FIG. 10A, the central area (x, y) to be processed has a boundary (gap D1) between the area (x + 1, y) adjacent in the X direction. Yes. In this case, the same value as the spatial filter coefficient α shown in FIG. 5B is once set as the boundary spatial filter coefficient γ shown in (b), and then the adjacent area (x + 1, y across the boundary part). ) (Γ) (1,0) is set by replacing the boundary area coefficient β (= 0.7) of the corresponding area (x + 1, y) in FIG. Thus, the function of the spatial filter processing described above is realized by performing the calculation of the expression (4), the difference between the dimming values of the area pairs separating the boundary portions is reduced, and the dimming value ratio R is equal to or higher than a predetermined ratio. Boundary area processing function to be lit at the same time.

  For example, consider a case where the first dimming value signal is BL (x, y) = 30 in the central area to be processed, BL (x + 1, y) = 80 in the adjacent area, and 0 in the other areas. At this time, if the processing target area is not a boundary area as shown in FIG. 9A, γ (0,0) × BL (x, y) = 1.2 × 30 = 36 and γ (1,0) × From the comparison of BL (x + 1, y) = 0.3 × 80 = 24, BLd (x, y) = 36. On the other hand, when the processing target area is a boundary area as shown in FIG. 10A, γ (0,0) × BL (x, y) = 36 and γ (1,0) × BL (x + 1, y) From a comparison of 0.7 = 80 = 56, BLd (x, y) = 56. As a result, the dimming value ratio R with the adjacent area across the boundary increases from 30/80 = 0.37 to 56/80 = 0.7.

  When the target area is a boundary area, the position of the boundary portion exists in various directions. For example, if there is a boundary (gap D2) between areas (x, y + 1) adjacent in the Y direction, γ (x, y + 1) = 0.7. Further, when there are boundary portions in both the X direction and the Y direction, γ (x + 1, y) = γ (x, y + 1) = γ (x + 1, y + 1) = 0.7 may be set.

  Here, the boundary space area coefficient γ set for the areas adjacent to each other across the boundary is appropriately selected from the range of 0.5 to 1.0 according to the structure of the light guide plate, similarly to the boundary area coefficient β. To set. This is because when the coefficient γ is smaller than 0.5, the effect of canceling the luminance step generated at the boundary portion of the divided light guide plate is reduced, and when the coefficient γ approaches 1.0, the dimming value of each area is the same. This is because it does not make sense for area control. The effect of suppressing the luminance level difference in this embodiment is the same as that in the first embodiment.

  In the present embodiment, the spatial filter processing that moderates the change in the backlight luminance distribution and the boundary area processing that suppresses the luminance step generated at the boundary portion of the divided light guide plate are performed at the same time, thereby reducing the calculation processing time. is there.

  The present invention can be suitably applied to a liquid crystal display device such as a liquid crystal television or a portable display that employs so-called area control in which the backlight is divided into a plurality of display areas and the light source luminance is individually controlled.

10: Image frame receiver,
11 ... 1st light control value determination part,
12 ... Second dimming value determination unit,
13 Time filter part,
14 ... Backlight control unit,
15 ... Backlight part,
16 ... Backlight luminance distribution calculation unit,
17: Image signal correction unit,
18 ... Liquid crystal control unit,
19 ... the light emission amount determining unit,
20 ... Liquid crystal panel,
21 ... 1st dimming value receiving part,
22 ... Spatial filter section,
23 ... Boundary area processing unit,
24 ... storage area part,
25 ... boundary determination unit,
26: Boundary control space filter unit,
100 ... Backlight device,
101 (101a-101d) ... split light guide plate,
102 ... area,
103 ... light source,
104 ... wiring board,
201 ... diffusion sheet 202 ... liquid crystal panel,
D1, D2 ... boundary gap,
ΔL: Luminance level difference.

Claims (5)

A backlight having a light guide plate configured by combining a plurality of divided light guide plates in which a plurality of areas are arranged in a matrix, and a light source capable of individually controlling the emission intensity corresponding to each area, and from the backlight In an image display device including a liquid crystal panel that modulates irradiated light for each pixel and displays an image,
A plurality of the divided light guide plates are arranged in each of a first direction and a second direction orthogonal to the first direction,
A light emission amount determining unit that determines a light emission amount of a corresponding light source according to an input image signal in each area;
An image signal correction unit that corrects the amplitude of the image signal displayed on the liquid crystal panel according to the determined light emission amount,
The light emission amount determining unit
A boundary determination unit that determines whether or not a processing target area for determining the amount of light emission has a boundary part that couples the divided light guide plate between adjacent areas;
A boundary area processing unit that corrects the light emission amount of the processing target area determined to have a boundary portion by the boundary determination unit so that the ratio R to the light emission amount in the adjacent area across the boundary portion is a certain ratio or more. I have a,
The boundary area processing unit has a light emission amount ratio R1 between a processing target area determined to have a boundary part and a first adjacent area adjacent to the processing target area in the first direction across the boundary part. And a light emission amount ratio R2 between the processing target area and a second adjacent area adjacent to the processing target area in the second direction across the boundary portion. . The image display device according to claim 1,
The light emission amount determining unit includes a first dimming value determining unit and a second dimming value determining unit,
The first dimming value determination unit detects luminance information for each area from the input image signal, and determines a first dimming value signal that is an initial light emission amount of a light source corresponding to the area based on the luminance information. And
The second dimming value determination unit includes a spatial filter unit that corrects the first dimming value signal determined by the first dimming value determination unit in the spatial direction to compensate for the spread of light between the areas. And a second dimming value signal which is a light emission amount of the light source is determined by processing the signal from the spatial filter unit by the boundary determination unit and the boundary area processing unit. The image display device according to claim 2,
The second dimming value determination unit includes a boundary control spatial filter unit that integrates the functions of the spatial filter unit and the boundary area processing unit, and the first dimming value determination unit determines the first dimming value determination unit The process of correcting the light control value signal in the spatial direction and the process of correcting the light emission amount of the processing target area so that the ratio R between the light emission amount in the adjacent area with the boundary portion is a certain ratio or more are executed simultaneously. An image display device characterized by that. A backlight having a light guide plate configured by combining a plurality of divided light guide plates in which a plurality of areas are arranged in a matrix, and a light source capable of individually controlling the emission intensity corresponding to each area, and from the backlight In an image display device including a liquid crystal panel that modulates irradiated light for each pixel and displays an image,
A plurality of the divided light guide plates are arranged in each of a first direction and a second direction orthogonal to the first direction,
A light emission amount determining unit that determines the light emission amount of the corresponding light source according to the input image signal in each area,
The light emission amount determining unit corrects the ratio R of the light emission amounts to be within a certain range with respect to the adjacent area pairs across the boundary portion connecting the divided light guide plates ,
The light emission amount determining unit includes a ratio R1 of the light emission amount of the first area pair adjacent to the first direction across the boundary portion, and a second adjacent to the second direction across the boundary portion. An image display device characterized in that the ratio R2 of the light emission amount of the area pair is different . The image display device according to any one of claims 1 to 4,
The light emission amount determining unit corrects the light emission amount ratio R to be in a range of 0.5 to 1.0.

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