JP2012068655A - Image display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image display device preventing occurrence of unnatural luminance fluctuation.SOLUTION: An image display device comprises multiple light sources which illuminates in a first individually controllable emission intensity, a liquid crystal panel which modulates and displays illumination light from the multiple light sources, a first calculation part which calculates a second emission intensity assigned to each of subregions, based on picture signals of the subregions into which a display area is spatially divided and which are smaller than illumination areas into which the display area is virtually divided corresponding to spatial arrangement of the multiple light sources and bigger than a pixel, a second calculation part which calculates in combination the multiple second emission intensities assigned to the multiple subregions, based on positional relationship between the illumination area and the multiple subregions including at least more than one subregion that is not spatially overlapping with the illumination area, and calculates a first emission intensity assigned to each of the multiple light sources, and a control part which makes each of the multiple light sources illuminate in accordance with the first emission intensity.

Description

  The present invention relates to emission intensity control of a backlight that illuminates a liquid crystal panel.

  LCD (Liquid Crystal Display) modulates illumination light from a backlight with a liquid crystal panel and displays a desired image. There may be a plurality of light sources included in the backlight. Further, the light emission intensity of each light source included in the backlight may not be uniform and may be individually controlled. By individually controlling the light emission intensity of each light source, effects such as an expansion of the display dynamic range and a reduction in power consumption can be expected.

  For example, the transmissive display device described in Patent Document 1 controls the backlight luminance corresponding to each of a plurality of regions obtained by dividing the display screen of the liquid crystal panel. Specifically, the transmissive display device described in Patent Document 1 determines the backlight luminance corresponding to the area based on the maximum value of the video signal in each area.

JP 2008-122713 A

  The transmissive display device described in Patent Literature 1 determines a representative value from a video signal included in each of the regions (light emitting regions) in which the backlight luminance can be individually controlled, and determines the backlight luminance based on the representative value. ing. Such backlight brightness control may cause the observer to perceive unnatural brightness fluctuations.

  For example, when displaying an image of a fireworks display, an image in which a bright (high luminance) object (hereinafter referred to as a bright spot) gradually moves in a dark (low luminance) background is displayed. According to the control of the backlight brightness of the above-described prior art, a high backlight brightness is given to the light emitting area including the bright spot, and a low backlight brightness is given to the light emitting area not including the bright spot. Then, every time the bright spot crosses the boundary of the light emitting region with the movement, the reverse of the brightness of the backlight occurs. That is, the backlight luminance of the light emitting region into which the bright spot flows in increases rapidly, and the backlight luminance of the light emitting region from which the bright spot flows out decreases sharply. Such a backlight luminance variation can be perceived by an observer, which may cause a sense of incongruity.

  Accordingly, an object of the present invention is to provide a video display device that suppresses the occurrence of unnatural luminance fluctuations.

  A video display device according to an aspect of the present invention includes a plurality of light sources that are lit at first emission intensity that can be individually controlled, and a liquid crystal panel that modulates illumination light from the plurality of light sources and displays an image in a display region And a small area obtained by dividing the display area spatially finer than the illumination area obtained by virtually dividing the display area corresponding to the spatial arrangement of the plurality of light sources and coarser than the pixels. A first calculator that calculates a second emission intensity assigned to each of the small areas based on the video signal; the illumination area; and the one or more small areas that do not overlap at least partially spatially with the illumination area. Based on the positional relationship between the plurality of small regions including the region, the plurality of second light emission intensities assigned to the plurality of small regions are calculated in combination and assigned to each of the plurality of light sources. Said first Comprising a second calculation unit for calculating the emission intensity, and a control unit for lighting each of the plurality of light sources in accordance with the first emission intensity.

  According to the present invention, it is possible to provide a video display device that suppresses the occurrence of unnatural luminance fluctuations.

1 is a block diagram showing a liquid crystal display device according to a first embodiment. The figure which shows an example of the aspect of the backlight of FIG. The figure which shows an example of the aspect of the backlight of FIG. The figure which shows an example of the aspect of the backlight of FIG. The figure which shows an example of the aspect of the backlight of FIG. The figure which shows the emitted light intensity determination part of FIG. The figure for demonstrating the small area | region and illumination area which become the process target of the light emission intensity determination part of FIG. FIG. 4 is a diagram illustrating an example of a small region light emission intensity calculation unit in FIG. 3. FIG. 4 is a diagram illustrating an example of a small region light emission intensity calculation unit in FIG. 3. FIG. 4 is a diagram illustrating an example of a small region light emission intensity calculation unit in FIG. 3. The figure for demonstrating the assignment aspect of the weighting coefficient by the light source emitted light intensity calculation part of FIG. The graph figure which shows the spatial distribution of the weighting coefficient allocated by the light source emitted light intensity calculation part of FIG. The figure for supplementarily explaining the effect of the processing by the luminescence intensity determination part of FIG. The figure which shows the luminance distribution of each input image and each lighting pattern in each locus | trajectory cross section of the launch fireworks of FIG. 10A. The figure which shows the signal correction | amendment part of FIG. The graph which shows the spatial distribution of the brightness | luminance in the illumination area illuminated with the light source contained in the backlight of FIG. The figure which shows the liquid crystal panel and liquid crystal control part of FIG.

Embodiments of the present invention will be described below with reference to the drawings.
(First embodiment)
As shown in FIG. 1, the video display apparatus according to the first embodiment of the present invention includes a signal correction unit 10, a liquid crystal control unit 20, a liquid crystal panel 30, a backlight control unit 40, a backlight 50, and a light emission intensity determination unit. 100.

  The backlight 50 illuminates the liquid crystal panel 30 according to control from the backlight control unit 40. The backlight 50 includes a plurality of light sources 51 whose emission intensity can be individually controlled. The backlight 50 may be implemented with any existing or future configuration. For example, as shown in FIGS. 2A and 2B, the backlight 50 may be configured by distributing a plurality of point-like light sources 51 that directly illuminate the back surface of the liquid crystal panel 30. Alternatively, as illustrated in FIG. 2C, the backlight 50 may be configured by arranging plate-like light sources 51 that directly illuminate the back surface of the liquid crystal panel 30 in parallel. The arrangement method of the light source 51 as shown in FIGS. 2A to 2C is called a direct type. On the other hand, as shown in FIG. 2D, the light source 51 may be arranged in a so-called edge light type. In the edge light type, the light source 51 is arranged on the side surface, not the back surface of the liquid crystal panel 30, and illumination light from the light source 51 is guided to the back surface of the liquid crystal panel 30 by a light guide plate or a reflector (not shown in FIG. 2D). It is burned.

  Each of the plurality of light sources 51 may be composed of a single light emitting element, or may be composed of a group of light emitting elements arranged in close proximity to each other. Moreover, as a light emitting element which comprises the light source 51, LED, a cold cathode tube, a hot cathode tube, etc. are applicable, However, It is not limited to these. In particular, an LED is suitable as a light-emitting element because it has a wide range of maximum luminance and minimum luminance that can emit light and can easily realize a wide dynamic range. Each of the light sources 51 is individually controlled in light emission intensity (light emission luminance) and light emission timing by the backlight control unit 40.

  The backlight control unit 40 lights each light source 51 at a predetermined light emission timing according to the light emission intensity of each light source 51 determined by the light emission intensity determination unit 100.

  The light emission intensity determination unit 100 determines the light emission intensity of each light source 51 based on the input video signal, and inputs the light emission intensity to the signal correction unit 10 and the backlight control unit 40. Specifically, the light emission intensity determination unit 100 determines the light emission intensity of each light source 51 by performing a two-step light emission intensity calculation process. The emission intensity determination unit 100 includes a small area emission intensity calculation unit 110 and a light source emission intensity calculation unit 120 for performing the above-described two-stage emission intensity calculation processing.

  The small area emission intensity calculation unit 110 calculates the emission intensity assigned to each small area based on the input video signal. Here, the small area refers to an area obtained by spatially dividing the display area of the liquid crystal panel 30. On the other hand, the term illumination area is used in this specification as a term for a small area. The illumination area refers to an area where each light source 51 illuminates the liquid crystal panel 30. Here, “illuminate” means about “exclusively illuminate”. That is, a part of a certain illumination area may be illuminated by illumination light from the light source 51 corresponding to another illumination area. In other words, the illumination area is an area obtained by virtually dividing the display area of the liquid crystal panel 30 in accordance with the spatial arrangement of the light sources 51. The small area is an area obtained by dividing the display area of the liquid crystal panel 30 more finely than the illumination area.

  For example, in FIG. 4, an illumination area 401 corresponding to each light source 51 (displayed with a black circle at the center) is a display area of the liquid crystal panel 30 according to the spatial arrangement of each light source 51 (displayed with a solid line). This is a region virtually divided by. A small area 403 (for example, displayed as a hatched area) is an area obtained by dividing the display area of the liquid crystal panel 30 more finely than the illumination area 401 by a small area boundary 404 (displayed by a broken line).

  The small area emission intensity calculation unit 110 calculates the emission intensity of the small area based on the video signal of the calculation area corresponding to the small area. Here, the calculation area may be the same area as the small area, may be an area that includes a part of the small area but does not include other parts, or an area that includes the entire small area and other peripheral areas. It may be. Further, the calculation area determination method may be different among a plurality of small areas. In other words, the calculation area is an arbitrary area for calculating the emission intensity of the small area.

Hereinafter, an example of the small region emission intensity calculation unit 110 will be described with reference to FIG. 5 includes a maximum value calculation unit 111 and a gamma conversion unit 112.
The maximum value calculation unit 111 calculates the maximum value of the video signal in the calculation area corresponding to each small area. That is, the maximum value calculation unit 111 calculates the maximum video signal value in the calculation area. The maximum value calculation unit 111 inputs the maximum video signal value to the gamma conversion unit 112.

The gamma conversion unit 112 performs gamma conversion on the maximum video signal value from the maximum value calculation unit 111. Specifically, the gamma conversion unit 112 performs gamma conversion for converting the video signal value into relative luminance. For example, if the range of the video signal value is 0 or more and 255 or less (8-bit value), the gamma conversion unit 112 performs gamma conversion according to the following equation (1).

In Equation (1), α and γ represent constants, S represents a video signal value (in this example, the maximum video signal value from the maximum value calculation unit 111), and L represents relative luminance. Normally, α = 0.0 and γ = 2.2 are set, but α and γ are not limited to these values. In addition, the hardware configuration of the gamma conversion unit 112 may be a mode in which a mathematical expression (1) is actually calculated by combining multipliers, or the relative luminance L corresponding to the video signal value S can be searched. A mode using a simple lookup table (LUT) may be used. The gamma conversion unit 112 inputs the relative luminance L to the light source emission intensity calculation unit 120 as the emission intensity assigned to the small area.

According to the small area light emission intensity calculation unit 110 in FIG. 5, the light emission intensity assigned to each small area is calculated based on the maximum video signal value in the calculation area corresponding to each small area.
By the way, the small area light emission intensity calculation unit 110 may have an arbitrary configuration capable of calculating the light emission intensity assigned to each small area. For example, the small region emission intensity calculation unit 110 may be replaced with the small region emission intensity calculation unit 210 illustrated in FIG. 6 and the small region emission intensity calculation unit 310 illustrated in FIG.

6 includes an RGB maximum value calculation unit 211, a gamma conversion unit 212, an average value calculation unit 213, and a multiplication unit 214.
The RGB maximum value calculation unit 211 has a maximum RGB signal value (R (red) signal value, G (green) signal value, and B (blue) signal value) (hereinafter simply referred to as RGB maximum) for each pixel of the input video signal. (Referred to as value). That is, the maximum value calculation unit 111 calculates the RGB maximum value of each pixel constituting the calculation area. The maximum value calculation unit 111 inputs the RGB maximum value of each pixel constituting the calculation area to the gamma conversion unit 212.

  The gamma conversion unit 212 performs gamma conversion on each RGB maximum value from the RGB maximum value calculation unit 211. Specifically, the gamma conversion unit 212 performs gamma conversion for converting each RGB maximum value into relative luminance. For example, the gamma conversion unit 212 performs the same or similar gamma conversion as the gamma conversion unit 112 described above. The gamma conversion unit 212 inputs each RGB maximum value converted into relative luminance (hereinafter simply referred to as maximum RGB luminance) to the average value calculation unit 213.

  The average value calculation unit 213 calculates the average value of each maximum RGB luminance from the gamma conversion unit 212 (hereinafter simply referred to as average relative luminance). For example, the average value calculation unit 213 calculates the average relative luminance by dividing the sum of the maximum RGB luminances by the number of pixels constituting the calculation area. The average value calculation unit 213 inputs the average relative luminance to the multiplication unit 214.

  The multiplier 214 multiplies the average relative luminance by a predetermined constant to calculate the light emission intensity assigned to the small area. Note that the hardware configuration of the multiplication unit 214 may be a mode in which constant multiplication is actually performed by a multiplier or the like, or a mode in which an LUT capable of searching for the emission intensity corresponding to the average relative luminance is used. Good. The multiplication unit 214 inputs the light emission intensity assigned to the small area to the light source light emission intensity calculation unit 120.

  According to the small area light emission intensity calculation unit 210 in FIG. 6, the light emission intensity assigned to each small area is calculated based on the average value of the maximum RGB luminance of each pixel in the calculation area corresponding to each small area.

  7 includes a maximum value / minimum value calculation unit 311, a first gamma conversion unit 312, a center value calculation unit 313, a multiplication unit 314, and a second gamma conversion unit 315.

  The maximum value / minimum value calculation unit 311 calculates the maximum value and the minimum value of the video signal in the calculation area corresponding to each small area. That is, the maximum value / minimum value calculation unit 311 calculates the maximum video signal value and the minimum video signal value in the calculation area, respectively. The maximum value / minimum value calculation unit 311 inputs the maximum video signal value and the minimum video signal value in the calculation region to the first gamma conversion unit 312.

  The first gamma conversion unit 312 performs gamma conversion on the maximum video signal value and the minimum video signal value from the maximum value / minimum value calculation unit 311, respectively. Specifically, the first gamma conversion unit 312 performs gamma conversion for converting the video signal value into relative brightness. For example, the first gamma conversion unit 312 performs gamma conversion according to Equation (1) after setting α = 0.0 and γ = 2.2 / 3.0. The first gamma conversion unit 312 has a relative brightness (hereinafter simply referred to as maximum brightness) that is a conversion result of the maximum video signal value and a relative brightness (hereinafter simply referred to as minimum brightness) that is the conversion result of the maximum video signal value. Is input to the center value calculation unit 313.

  The center value calculation unit 313 calculates the center value between the maximum brightness and the minimum brightness from the first gamma conversion unit 312. This central value corresponds to the central value of the brightness in the calculation area. For example, the center value calculation unit 313 calculates the average value of the maximum brightness and the minimum brightness as the center value. The center value calculation unit 313 inputs the center value to the multiplication unit 314.

  The multiplier 314 multiplies the center value from the center value calculator 313 by a predetermined constant. The multiplication unit 314 inputs the multiplication result (hereinafter simply referred to as the brightness modulation rate) to the second gamma conversion unit 315.

The second gamma conversion unit 315 performs gamma conversion on the brightness modulation rate from the multiplication unit 314. Specifically, the second gamma conversion unit 315 performs gamma conversion for converting the lightness modulation rate into relative luminance. For example, the second gamma conversion unit 315 performs gamma conversion according to the following formula (2).

In Equation (2), α and γ represent constants, L represents relative luminance, and L * represents a lightness modulation rate. Normally, α = 0.0 and γ = 3.0 are set, but α and γ are not limited to these values. Further, the hardware configuration of the second gamma conversion unit 315 may be a mode in which the calculation of Formula (2) is actually performed by combining a multiplier or the like, or the relative luminance corresponding to the lightness modulation rate L *. An aspect using an LUT that can search for L may be used. The second gamma conversion unit 315 inputs the relative luminance L to the light source emission intensity calculation unit 120 as the emission intensity assigned to the small area.

  According to the small area light emission intensity calculation unit 310 in FIG. 7, the light emission intensity assigned to each small area is calculated based on the central value between the maximum value and the minimum value of the brightness in the calculation area corresponding to each small area. Is done.

  The light source emission intensity calculation unit 120 calculates a combination of a plurality of emission intensities assigned to the plurality of small areas based on the positional relationship between each illumination area and a plurality of small areas in the vicinity thereof, The light emission intensity assigned to the light source 51 is calculated. The light source emission intensity calculation unit 120 inputs the emission intensity assigned to each light source 51 to the signal correction unit 10 and the backlight control unit 40.

  For example, the light source emission intensity calculation unit 120 weights the emission intensities of the plurality of small areas based on the positional relationship (for example, the distance from the center of the illumination area) between each illumination area and the plurality of small areas in the vicinity thereof. The light emission intensity of each light source 51 may be calculated by assigning a coefficient and calculating a weighted average. FIG. 8 shows an example of a weighting factor assignment mode. The light source emission intensity calculation unit 120 assigns a weighting factor to the emission intensity of the light source 51 corresponding to the illumination area of the center 501, and assigns a weighting factor to each of the emission intensity of the small areas included in the range 502 near the center 501. Calculate as In FIG. 8, the small area indicates an area 503 divided by a broken line. Here, the weighting coefficient may be different between the small regions included in the range 502. For example, as shown in FIG. 9, a distribution of weighting factors that is gradually decreased as the distance from the center of the illumination area increases. Further, if the distribution of the weighting factors is made symmetric with respect to the center of the illumination region, the multiplication of the weighting factors can be made common with respect to a plurality of small regions, so that the calculation cost of the weighted average described later can be reduced. A low-pass filter coefficient having a low-pass frequency characteristic such as a Gaussian filter is also suitable as the weighting coefficient. If the low-pass filter coefficient is used as a weighting coefficient, the light emission intensity of the light source 51 can be changed more smoothly. Therefore, a rapid luminance fluctuation that is likely to occur when a bright spot moves between adjacent illumination areas. Can be relaxed.

The light source emission intensity calculation unit 120 calculates a weighted average as the emission intensity of each light source 51 according to, for example, the following mathematical formula (3).

In Equation (3), Lc (x, y) represents the light emission intensity of the light source 51 corresponding to the coordinates (x, y), and w (Δx, Δy) is the distribution value of the weighting coefficient in the relative coordinates (Δx, Δy). L _F (x + Δx, y + Δy) represents the light emission intensity of a small area corresponding to the coordinates (x + Δx, y + Δy), and rx and ry are weight coefficient assignment tables (in this example, a rectangular range). Specified, but not limited to).

  Further, the light source emission intensity calculation unit 120 may calculate the emission intensity of each light source 51 by another method. For example, the light source emission intensity calculation unit 120 uses the weighting coefficient as a spatial filter coefficient and performs spatial filter processing on the emission intensity of each small region. Then, the light source emission intensity calculation unit 120 performs interpolation processing (for example, linear interpolation processing) based on the positional relationship between the emission intensity of each small region that has undergone spatial filtering and the illumination region, and emits light from each light source 51. Calculate the intensity. According to the calculation method based on such interpolation processing, a calculation result similar to the calculation method based on the weighted average described above can be obtained only by assigning a constant weight coefficient to the light emission intensity of each small region. For example, when the calculation method based on the weighted average described above is applied, the weighting factor assigned to the light emission intensity of a certain small region may be different for each of a plurality of illumination regions. When applied, a common weighting factor for a plurality of illumination areas can be assigned to the emission intensity of each small area.

The signal correction unit 10 corrects the light transmittance (luminance) of each pixel in the input video signal based on the light emission intensity of each light source 51 from the light emission intensity determination unit 100. Specifically, the signal correction unit 10 corrects the light transmittance of the video signal in units of pixels constituting the display area of the liquid crystal panel 30. The signal correction unit 10 inputs a video signal reflecting the correction for the light transmittance (hereinafter simply referred to as a corrected video signal) to the liquid crystal control unit 20.
Hereinafter, an example of the signal correction unit 10 will be described with reference to FIG. The signal correction unit 10 in FIG. 11 includes a luminance distribution calculation unit 11, a gamma conversion unit 12, a division unit 13, and a gamma correction unit 14.

  The luminance distribution calculation unit 11 calculates a predicted value of the luminance distribution in the display area of the liquid crystal panel 30 based on the emission intensity of each light source 51 from the emission intensity determination unit 100. That is, the luminance distribution calculation unit 11 calculates the luminance distribution generated in the display area of the liquid crystal panel 30 when each light source 51 is turned on according to the emission intensity determined by the emission intensity determination unit 100. The luminance distribution calculation unit 11 inputs the calculated luminance distribution to the division unit 13. Hereinafter, an example of a method for calculating the luminance distribution will be described.

The light emission distribution of each light source 51 is determined by the actual hardware configuration. The intensity distribution of the illumination light incident on the back surface of the liquid crystal panel 30 when each light source 51 is turned on is based on the light emission distribution of each light source 51. Hereinafter, the intensity distribution of the illumination light may be referred to as backlight luminance or luminance of the light source 51. In FIG. 12, an example of the luminance distribution of the single light source 51 is shown. This luminance distribution is symmetric with respect to the center of the illumination area corresponding to the light source 51, and decreases as the distance from the center of the illumination area increases. The backlight luminance based on the illumination light from a single light source is expressed as, for example, the following formula (4).

In Equation (4), L _{SET, n} is the nth light source (n is an arbitrary integer, and is a convenient number for uniquely identifying the light source 51 (in the following description, from 1 to the total number N of light sources). L _{P, n} (x _n ′, y _n ′) is relative to the center of the illumination area corresponding to the nth light source. The luminance distribution value at the coordinates (x _n ', y _n ') is represented, and L _BL (x _n ', y _n ') is illumination light from the nth light source at the relative coordinates (x _n ', y _n '). Represents the backlight brightness based on. Note that the luminance distribution value in the relative coordinates may be calculated by substituting the relative coordinates (or distance) into an arbitrary function that approximates the luminance distribution of the light source 51, or the luminance corresponding to the relative coordinates (or distance). The distribution value may be derived by using a searchable LUT.

Actually, since the illumination light from the plurality of light sources 51 may overlap, the backlight luminance L _BL (x, y) at the coordinates (x, y) in the display area of the liquid crystal panel 30 is It is represented by the following formula (5).

In Equation (5), coordinates (x _{0, n} , y _{0, n} ) represent coordinates on the display area of the liquid crystal panel 30 at the center position of the illumination area corresponding to the nth light source. In Equation (5), all light sources 51 are subject to backlight luminance calculation, but some of the calculation subjects may be thinned in consideration of the luminance distribution of the light sources 51. For example, the light source 51 corresponding to the illumination region that is far away from the coordinates (x, y) may be excluded from the calculation target of the backlight luminance at the coordinates (x, y).

The gamma conversion unit 12 performs gamma conversion on the input video signal (RGB format). Specifically, the gamma conversion unit 12 performs gamma conversion for converting each of the R signal value, the G signal value, and the B signal value included in the video signal into light transmittance. For example, if the range of the video signal value is 0 or more and 255 or less (8-bit value), the gamma conversion unit 12 performs gamma conversion according to the following equation (6).

In Equation (6), α ₃ and γ ₃ represent constants, S _R , S _G and S _B represent R signal value, G signal value and B signal value included in the video signal, respectively, T _R , T _G and T _B represents respectively the light transmittance of each color (RGB). Normally, α ₃ = 0.0 and γ ₃ = 2.2 are set, but α ₃ and γ ₃ are not limited to these values. The gamma conversion unit 12 inputs the light transmittance of each pixel to the division unit 13.

  The division unit 13 divides the light transmittance of each pixel in the display area of the liquid crystal panel 30 by the luminance distribution value in the pixel. The division unit 13 inputs light transmittance (hereinafter simply referred to as corrected light transmittance) as a division result to the gamma correction unit 14. Note that the division unit 13 may use an LUT that can search for the corresponding corrected light transmittance from the light transmittance and the luminance distribution value.

The gamma correction unit 14 performs gamma correction on the corrected light transmittance from the division unit 13. Specifically, the gamma correction unit 14 performs gamma correction for converting the light transmittance into a video signal value (RGB format) again. For example, if the range of the video signal value is 0 or more and 255 or less (8-bit value), the gamma correction unit 14 performs gamma correction according to the following equation (7).

In Equation (7), α ₄ and γ ₄ represent constants, T _R ′, T _G ′, and T _B ′ represent corrected light transmittances of the respective colors (RGB), S _R ′, S _G ′, and S _B 'represents an R signal value, a G signal value, and a B signal value, respectively. The gamma correction unit 14 inputs S _R ′, S _G ′, and S _B ′ to the liquid crystal control unit 20 as corrected video signals. Normally, in order to display a faithful image to the image signal input, a minimum light transmittance of the liquid crystal panel 30 as alpha _4, but the gamma value of the liquid crystal panel 30 are respectively set as the gamma _4, alpha _4, and γ ₄ is not limited to these values. Further, the gamma correction performed by the gamma correction unit 14 may not be a conversion method based on Equation (7), but may be replaced with an existing or future conversion method. For example, the gamma correction unit 14 may perform reverse conversion corresponding to the gamma conversion table of the liquid crystal panel 30 as gamma correction. Further, the hardware configuration of the gamma correction unit 14 may be an aspect that realizes gamma correction through an operation by a multiplier or the like, or an aspect that realizes gamma correction using an appropriate LUT. Good.

  The liquid crystal control unit 20 controls the liquid crystal panel 30 according to the corrected video signal from the signal correction unit 10. Specifically, the liquid crystal control unit 20 controls the light transmittance of the liquid crystal panel 30 in units of pixels in order to display a video corresponding to the corrected video signal in the display area of the liquid crystal panel 30.

  The liquid crystal panel 30 includes a display area composed of a plurality of pixels, and displays an image in the display area. Specifically, the liquid crystal panel 30 displays a desired image by modulating the illumination light from the backlight 50 with the light transmittance controlled by the liquid crystal control unit 20.

Hereinafter, an example of the liquid crystal control unit 20 and the liquid crystal panel 30 will be described with reference to FIG.
In the example of FIG. 13, the liquid crystal panel 30 is a so-called active matrix type. The liquid crystal panel 30 includes an array substrate 31. On the array substrate 31, a plurality of signal lines 38 arranged in the vertical direction and a plurality of scanning lines 39 arranged in the horizontal direction so as to intersect these are arranged via an insulating film (not shown). Yes. A pixel 32 is formed in each of the intersecting regions of the signal line 38 and the scanning line 39. The pixel 32 includes a switch element 33 composed of a thin film transistor (TFT), a pixel electrode 34, a liquid crystal layer 35, a counter electrode 36, and an auxiliary capacitor 37. Note that the counter electrode 36 is a common electrode in all the pixels 32.

  The switch element 33 is a switch element for image writing controlled by the liquid crystal control unit 20. The gate terminal of the switch element 33 is connected to any one of the plurality of scanning lines 39, and the source terminal of the switch element 33 is connected to any one of the plurality of signal lines 38. Note that to which scanning line 39 and signal line 38 the gate terminal and the source terminal of the switch element 33 are connected is determined by the coordinates (vertical position and horizontal position) of the pixel 32 including the switch element 33. The drain terminal of the switch element 33 is connected in parallel to the pixel electrode 34 in the pixel 32 including the switch element 33 and one end of the auxiliary capacitor 37. Note that the other end of each auxiliary capacitor 37 is grounded.

  Each pixel electrode 34 is formed on the array substrate 31. On the other hand, each counter electrode 36 is electrically opposed to the pixel electrode 34 and is formed on a counter substrate (not shown) different from the array substrate 31. A predetermined counter voltage is applied to each counter electrode 36 from a counter voltage generation circuit (not shown). A liquid crystal layer 35 is held between the pixel electrode 34 and the counter electrode 36 and is sealed with a sealant (not shown) provided around the array substrate 31 and the counter substrate. The liquid crystal material used as the liquid crystal layer 35 may be any liquid crystal material, but for example, ferroelectric liquid crystal, OCB (Optically Compensated Bend) mode liquid crystal, and the like are suitable.

  In the example of FIG. 13, the liquid crystal control unit 20 includes a signal line driving circuit 21 to which one end of each signal line 38 is connected and a scanning line driving circuit 22 to which one end of each scanning line 39 is connected. The signal line drive circuit 21 controls the voltage applied to the source terminal of each switch element 33 via each signal line 38. Further, the scanning line driving circuit 22 controls the voltage applied to the gate terminal of each switch element 33 via each scanning line 39.

  The signal line drive circuit 21 includes, for example, an analog switch, a shift register, a sample hold circuit, and a video bus. A horizontal start signal and a horizontal clock signal are input as control signals from a display ratio control unit (not shown) to the signal line drive circuit 21 and a video signal (a corrected video signal in the video display device according to the present embodiment). Is entered.

  The scanning line driving circuit 22 includes, for example, a shift register, a level shifter, and a buffer circuit. The scanning line driving circuit 22 receives a vertical start signal and a vertical clock signal as control signals from the display ratio control unit. The scanning line driving circuit 22 outputs a row selection signal to each scanning line 39 based on the control signal.

  As described above, the video display device according to the present embodiment is based on the light emission intensity assigned to the small areas divided more finely than the illumination area corresponding to each light source, with the light emission intensity of the plurality of light sources included in the backlight. Has been decided. Therefore, according to the video display device according to the present embodiment, the light emission intensity of each light source can be changed stepwise by reflecting the fluctuation of the video signal in units of small areas smaller than the illumination area. Occurrence of unnatural luminance fluctuations in the area can be suppressed.

  Hereinafter, the effect of the light emission intensity determination process of each light source 51 by the video display apparatus according to the present embodiment will be supplementarily described with reference to FIGS. 10A and 10B. FIG. 10A shows the light source of each light source when the light emission intensity of each light source is determined by three methods based on the input video signal of 5 frames (frames # 24, # 32, # 40, # 48, # 56). The state of the lighting pattern is shown conceptually. In FIG. 10A, the input image is an image of a firework that moves in a generally vertical direction. FIG. 10B shows the input image of FIG. 10A and the luminance distribution of each lighting pattern in the cross section of the above-mentioned fireworks.

  In the lighting pattern 1, the light emission intensity of each light source is based on a video signal included in an area (corresponding to the illumination area described above) obtained by virtually dividing the display area of the liquid crystal panel corresponding to the spatial arrangement of the light sources. It has been decided. As is apparent from FIGS. 10A and 10B, the lighting pattern 1 does not sufficiently follow the movement of the fireworks. Specifically, the luminance distributions of the trajectory cross sections in frames # 24 and # 32 coincide with each other regardless of the position of the fireworks, and the same applies to frames # 48 and # 56. In addition, a sudden luminance fluctuation occurs between the frames # 32 and # 40 and between the frames # 40 and # 48. Therefore, when the input video is displayed by the lighting pattern 1, an unnatural (discontinuous) luminance variation is perceived by the observer.

  In the lighting pattern 2, the light emission intensity of each light source is determined by applying a low-pass spatial filter process to the light emission intensity of each light source obtained by the same method as that of the lighting pattern 1. As is clear from FIGS. 10A and 10B, the lighting pattern 2 has a reduced spatial distribution (unevenness) in the luminance distribution in each frame compared to the lighting pattern 1. That is, according to the lighting pattern 2, it can be said that a situation in which a single illumination area in each frame exhibits a very high luminance compared to the surrounding illumination area is less likely to occur than in the lighting pattern 1. However, the fundamental problem in the lighting pattern 1 that the lighting pattern 2 cannot sufficiently follow the movement of the fireworks is not solved (see frames # 24 and # 32 and frames # 48 and # 56, respectively).

  In the lighting pattern 3, the light emission intensity of each light source is determined based on the light emission intensity determination process in the video display device according to the present embodiment. As is clear from FIGS. 10A and 10B, it can be said that the lighting pattern 3 follows the movement of the fireworks, compared to the lighting patterns 1 and 2. In the lighting pattern 3, the luminance of each illumination area changes smoothly (stepwise) from frame # 24 to # 56. For example, in the lighting patterns 1 and 2, the lighting pattern of the frame # 32 is the same as the lighting pattern of the frame # 24, but in the lighting pattern 3, the lighting pattern of the frame # 32 is intermediate between the frames # 24 and # 40. It will be something. In lighting patterns 1 and 2, the lighting pattern of frame # 48 is the same as the lighting pattern of frame # 56, but in lighting pattern 3, the lighting pattern of frame # 48 is intermediate between frames # 40 and # 56. It will be something. In other words, according to the lighting pattern 3, the luminance of each illumination area varies smoothly following the movement of the fireworks, so that it is difficult to give the viewer a sense of discomfort associated with the luminance variation.

  In addition, the video display apparatus according to the present embodiment determines the light emission intensity of each light source by performing a two-step light emission intensity calculation process. However, it is possible to omit the first-step emission intensity calculation process. That is, without using the concept of a small region and a corresponding calculation region, based on the positional relationship between the illumination region and the plurality of pixels, for example, the video signal values of the plurality of pixels are calculated using a weighting factor. By calculating in combination, the emission intensity of each light source can be calculated. However, such a modification is not so preferable from the viewpoint of calculation cost. The light emission intensity calculation process at the second stage has a higher calculation cost than the light emission intensity calculation process at the first stage, and the calculation cost further increases as the calculation target increases. In view of this, it can be said that the first-stage emission intensity calculation process plays a role of compressing the calculation target of the second-stage emission intensity calculation process from the pixel unit to the small area unit. That is, by performing the first-stage emission intensity calculation process, it is possible to reduce the calculation cost required to determine the emission intensity of each light source.

(Second Embodiment)
In the video display device according to the first embodiment described above, the emission colors (spectral characteristics) of the plurality of light sources 51 included in the backlight 50 are not mentioned. If the light emission color of each light source 51 is single (for example, pseudo white), the first embodiment can be applied as it is. On the other hand, if the light emission color of each light source 51 is plural (for example, RGB (red, blue, green)), it is desirable to apply the first embodiment by partially correcting as follows.

  It is desirable that the light emission intensity determination unit 100 determines the light emission intensity for each light emission color of each light source 51. For example, if the video signal is in RGB format and the light emission color of each light source 51 is RGB, the light emission intensity determination unit 100 determines the light emission intensity of the red light source based on the R signal value of the video signal, and sets the G signal value. Based on this, the emission intensity of the green light source is determined, and the emission intensity of the blue light source is determined based on the B signal value. In this way, if the constituent color of the video signal matches the emission color of each light source 51, the emission intensity determination unit 100 determines the emission intensity for each emission color of each light source 51 based on the signal value of each color of the video signal. Can be determined. On the other hand, if the component color of the video signal and the emission color of each light source 51 do not match, the emission intensity determining unit 100 converts the color represented by the video signal into a combination of a plurality of emission colors of each light source 51, and What is necessary is just to determine the emitted light intensity for every luminescent color of the light source 51. FIG.

  As described above, the video display device according to the present embodiment is based on the light emission intensity assigned to the small areas divided more finely than the illumination area corresponding to each light source, with the light emission intensity of the plurality of light sources included in the backlight. And determined for each emission color. Therefore, according to the video display device according to the present embodiment, it is possible to suppress the occurrence of unnatural luminance fluctuations in each illumination region even when a light source having a plurality of emission colors is used.

  Note that the present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the components without departing from the scope of the invention in the implementation stage. Various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the above embodiments. Further, for example, a configuration in which some components are deleted from all the components shown in each embodiment is also conceivable. Furthermore, you may combine suitably the component described in different embodiment.

DESCRIPTION OF SYMBOLS 10 ... Signal correction part 11 ... Luminance distribution calculation part 12 ... Gamma conversion part 13 ... Dividing part 14 ... Gamma correction part 20 ... Liquid crystal control part 21 ... Signal line drive circuit DESCRIPTION OF SYMBOLS 22 ... Scanning line drive circuit 30 ... Liquid crystal panel 31 ... Array substrate 32 ... Pixel 33 ... Switch element 34 ... Pixel electrode 35 ... Liquid crystal layer 36 ... Counter electrode 37 ... Auxiliary capacity 38 ... Signal line 39 ... Scanning line 40 ... Backlight control unit 50 ... Backlight 51 ... Light source 100 ... Light emission intensity determination unit 110 ... Small region Emission intensity calculation unit 111... Maximum value calculation unit 112... Gamma conversion unit 120... Light source emission intensity calculation unit 210... Small area emission intensity calculation unit 211. -Gamma conversion unit 213- Average value calculator 214... Multiplier 310... Small region emission intensity calculator 311... Maximum value / minimum value calculator 312... First gamma converter 313. ... Multiplier 315 ... Second gamma converter

Claims (6)

A plurality of light sources that are lit at a first emission intensity that can be individually controlled;
A liquid crystal panel that modulates illumination light from the plurality of light sources and displays an image in a display area;
A video signal of a small area obtained by dividing the display area spatially finer than the illumination area obtained by virtually dividing the display area corresponding to the spatial arrangement of the plurality of light sources and coarser than the pixels. A first calculation unit for calculating a second emission intensity assigned to each of the small regions based on
Based on the positional relationship between the illumination area and the plurality of small areas including at least one small area that does not overlap at least partially spatially with the illumination area, the illumination area is assigned to the plurality of small areas. A second calculation unit that calculates a combination of the plurality of second light emission intensities and calculates the first light emission intensity assigned to each of the plurality of light sources;
A controller that turns on each of the plurality of light sources according to the first emission intensity;
A video display device comprising:   The second calculation unit uses the weighting coefficient given based on the positional relationship between the illumination area and the plurality of small areas to calculate the first light emission from the weighted average of the plurality of second light emission intensities. The video display device according to claim 1, wherein the intensity is calculated.   The video display device according to claim 2, wherein the weighting factor decreases as a spatial distance from the center of the illumination area to the small area increases.   4. The video according to claim 3, wherein the first calculation unit calculates each of the plurality of second light emission intensities based on a maximum value of a plurality of video signals included in a calculation region corresponding to each of the small regions. Display device.   The first calculation unit is configured to calculate the plurality of second light emission intensities based on a central value between a maximum value and a minimum value of brightness in a plurality of video signals included in a calculation region corresponding to each of the small regions. The video display device according to claim 3, wherein each of them is calculated.   The video display device according to claim 3, wherein the first calculation unit calculates each of the second light emission intensities based on an average value of luminance in a plurality of video signals included in each of the small regions.

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