JP2012058523A - Image display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image display device that achieves display with high picture quality with low power consumption at low cost.SOLUTION: The image display device according to an embodiment of the present invention comprises a light source section, an optical modulation element section, a light source luminance calculation section, a light source luminance allocation section, and a control section. The light source section includes a first white light source and a second white light source. The luminous efficiency and color gamut of the first white light source are different from the luminous efficiency and color gamut of the second white light source, and each luminance of the first white light source and the second white light source can be controlled. The optical modulation element section can modulate light transmittance or reflectance according to a display image signal. The light source luminance calculation section calculates the luminance of a pair of white light sources that includes the first white light source and the second white light source on the basis of a pixel value of an input image signal and generates a light source luminance signal. The light source luminance allocation section generates a first light source luminance allocation signal that indicates the luminance of the first white light source and a second light source luminance allocation signal that indicates the luminance of the second white light source. The control section generates the display image signal for controlling the optical modulation element on the basis of the input image signal and generates a luminance control signal for controlling the luminance of the first white light source and the second white light source on the basis of the first light source luminance allocation signal and the second light source luminance allocation signal.

Description

  Embodiments described herein relate generally to an image display apparatus.

  In recent years, as represented by a liquid crystal display device, an image display device including a light source and a light modulation element that modulates the intensity of light incident from the light source has been widely used. In such an image display device, a bright and high dynamic range display can be realized by increasing the number of light sources. In addition, by using a light source having a wide color gamut (color reproduction range), a vivid color display can be realized.

  However, when the number of light sources is increased, there is a problem that member costs and power consumption increase. In addition, a light source with a wide color gamut generally has a lower luminous efficiency than a light source with a narrow color gamut, and it is necessary to provide more light sources in order to display a bright image. There is a problem that power consumption increases. Therefore, it is difficult to simultaneously realize high image quality, low cost, and low power consumption in the image display device.

  As an example of an image display device that displays an image with high image quality while suppressing cost and power consumption, Patent Document 1 discloses a first light source for high-luminance display and a color gamut based on the first light source, depending on the use environment. Has disclosed a liquid crystal display device that uses a second light source for wide, high-quality display. This liquid crystal display device uses a first light source to display an image with high brightness in bright places such as outdoors, and displays a vivid image using a second light source in dark places such as indoors. ing.

  However, since the optimum image quality differs depending on the image (video), the method of determining whether the luminance priority or the image quality priority depends on the use environment or the like as in Patent Document 1 cannot display the image faithfully.

JP 2007-264659 A

  Therefore, image display devices are required to display images with high image quality while suppressing cost and power consumption. The present disclosure has been made to solve the above-described problems, and an object thereof is to provide an image display device that realizes high-quality display at low cost and low power consumption.

  The image display apparatus according to the present embodiment includes a light source unit, a light modulation element unit, a light source luminance calculation unit, a light source luminance allocation unit, and a control unit. The light source unit includes first and second white light sources having different light emission efficiencies and color gamuts, and can control the luminances of the first and second white light sources, respectively. The light modulation element unit can modulate the light transmittance or reflectance according to the display image signal. The light source luminance calculation unit calculates the luminance of a set of white light sources including one each of the first and second white light sources based on the pixel value of the input image signal, and generates a light source luminance signal. The light source luminance allocation unit allocates the light source luminance signal to the first and second white light sources, and generates first and second light source luminance allocation signals indicating the respective luminances of the first and second white light sources. . The control unit generates a display image signal for controlling the light modulation element unit based on the input image signal, and the first and second white light sources based on the first and second light source luminance assignment signals. A brightness control signal for controlling the brightness is generated.

1 is a block diagram schematically showing an image display device according to a first embodiment. The graph which shows an example which produces | generates the 1st and 2nd light source luminance allocation signal from a light source luminance signal. The graph which shows the other example which produces | generates the 1st and 2nd light source luminance allocation signal from a light source luminance signal. The figure which shows the characteristic of three types of white light sources with which the image display apparatus of 2nd Embodiment is provided. (A) is a figure which shows an example of a 1st-3rd light source luminance allocation signal, (b) is a figure which shows the other example of a 1st-3rd light source luminance allocation signal. The block diagram which shows schematically the image display apparatus which concerns on 3rd Embodiment. The figure explaining the division area set to the backlight of FIG. The graph which shows the luminance distribution when one light source in the backlight of FIG. 6 light-emits. The graph which shows the luminance distribution when the some light source in the backlight of FIG. 6 light-emits. The block diagram which shows the light source luminance distribution calculation part of FIG. 6 in detail. The block diagram which shows schematically the image display apparatus which concerns on 4th Embodiment. The block diagram which shows the light source brightness correction | amendment part of FIG. 11 in detail. The graph which shows an example of the relationship between the average brightness | luminance currently hold | maintained at LUT of FIG. 12, and a correction coefficient. 13 is a graph showing another example of the relationship between the average luminance and the correction coefficient held in the LUT in FIG. (A) is a graph which shows an example which produces | generates a light source luminance signal from light source luminance, (b) is a graph which shows the relationship between the light source luminance and display luminance at the time of the relationship shown to (a). (A) is a graph which shows the other example which produces | generates a light source luminance signal from light source luminance, (b) is a graph which shows the relationship between light source luminance and display luminance at the time of the relationship shown to (a). (A) is a graph which shows the further another example which produces | generates a light source luminance signal from light source luminance, (b) is a graph which shows the relationship between the light source luminance and display luminance at the time of the relationship shown to (a). . The block diagram which shows roughly the image display apparatus which concerns on 6th Embodiment. The block diagram which shows the light source luminance allocation part of FIG. 18 in detail. (A) is a graph which shows an example of the 1st, 2nd, and 3rd light source luminance allocation signal in case saturation is high, (b) is the 1st, 2nd, and 3rd in case saturation is low. It is a graph which shows an example of a light source luminance allocation signal. The figure which shows the characteristic of a white light source in case the 1st light source contains a several light source in FIG.

  Hereinafter, an image display device according to an embodiment will be described with reference to the drawings as necessary.

(First embodiment)
FIG. 1 schematically shows an image display apparatus according to the first embodiment. The image display apparatus includes a light source luminance calculation unit 101, a light source luminance allocation unit 102, a control unit 103, and an image display unit 104.

  The image display unit 104 is a liquid crystal display unit including a liquid crystal panel 105 serving as a light modulation element unit and a backlight 106 serving as a light source unit disposed opposite to the back surface of the liquid crystal panel 105. The liquid crystal panel 105 displays an image in the display area by modulating the light transmittance. The backlight 106 is provided with two types of white light sources, that is, a first light source 111 and a second light source 112 having different light emission efficiency and color gamut (color reproduction range). As an example, the first and second light sources 111 and 112 are arranged on the surface of the backlight 106 facing the back surface of the liquid crystal panel 105. In the present embodiment, the brightness of the first and second light sources 111 and 112 is controlled as a set.

  Note that the backlight 106 is not limited to the example in which the two types of white light sources 111 and 112 shown in FIG. 1 are provided, and may include three or more types of white light sources having different light emission efficiency and color gamut. For example, when the backlight 106 is provided with three types of white light sources, the luminance of these three types of white light sources is controlled as one set. The case where three or more types of white light sources are provided in the backlight 106 will be described in the second embodiment.

  In the image display apparatus of FIG. 1, the input image signal 10 is input to the light source luminance calculation unit 101 and the control unit 103. The input image signal 10 is a moving image or a still image, and is input in units of frames, for example. The light source luminance calculation unit 101 calculates the light source luminance based on the input image signal 10 and generates the light source luminance signal 11. This light source luminance indicates the luminance of a set of white light sources. The light source luminance signal 11 is sent to the light source luminance assigning unit 102.

  The light source luminance allocation unit 102 allocates the light source luminance signal 11 to the first and second light sources 111 and 112, and indicates the luminance of the first light source luminance allocation signal 12 indicating the luminance of the first light source 111 and the luminance of the second light source 112. A second light source luminance assignment signal 13 is generated. The first and second light source luminance assignment signals 12 and 13 are sent to the control unit 103.

  The control unit 103 drives and controls the image display unit 104 based on the input image signal 10 and the first and second light source luminance assignment signals 12 and 13 from the light source luminance assignment unit 102. More specifically, the control unit 103 generates a display image signal 14 for driving the liquid crystal panel 105 based on the input image signal 10, and sends the display image signal 14 to the liquid crystal panel 105. First and second light source luminance control signals 15 and 16 for driving the first and second light sources 111 and 112 are generated based on the first and second light source luminance allocation signals 12 and 13, respectively. Second light source luminance control signals 15 and 16 are sent to the backlight 106.

  In the image display unit 104, the display image signal 14 is written to the liquid crystal panel 105, and the first and second light sources 111 and 112 in the backlight 106 have luminances according to the first and second light source luminance assignment signals 12 and 13, respectively. Flashes on. In this way, an image corresponding to the input image signal 10 is displayed on the image display unit 104.

Next, each part of the image display apparatus of FIG. 1 will be described in more detail.
For example, upon receiving the input image signal 10, the light source luminance calculation unit 101 first calculates the maximum gradation value L _max from the input image signal 10. The input image signal 10 has a plurality of pixels, and each pixel has red, green, and blue gradation values. The maximum value among the gradation values of the input image signal 10 is calculated as the maximum gradation value L _max .

Thereafter, the light source luminance calculation unit 101 calculates the light source luminance I from the calculated maximum gradation value L _max . As an example, when the input image signal 10 is an image expressed by 8 bits, that is, when the input image signal 10 has gradation values from 0 gradation to 255 gradations, the light source luminance I is expressed by the formula (1). ).

Here, γ is a gamma value, and 2.2 is generally used. That is, the light source luminance calculation unit 101 obtains a maximum gradation value _{L max} of the input image signal 10, the maximum gradation value _{L max,} the maximum gradation value by the input image signal 10 possible (255 in this example) The light source luminance I is calculated by dividing and further correcting with the gamma value γ. The calculated light source luminance I is a relative value from 0 to 1. A light source luminance signal 11 indicating the light source luminance I is sent to the light source luminance assigning unit 102.

Note that the light source luminance calculation unit 101 may calculate the light source luminance I using a look-up table (LUT) instead of calculating the light source luminance I by calculation according to Equation (1). That is, a relationship between the maximum gradation value L _max and the light source luminance I is obtained in advance, and an LUT describing the relationship is stored in a memory such as a ROM (Read Only Memory). after obtaining a gradation value _{L max,} it may be determined light intensity I with reference to the LUT in maximum gradation value _{L max.}

  When the light source luminance allocation unit 102 receives the light source luminance signal 11 from the light source luminance calculation unit 101, the light source luminance allocation unit 102 allocates the light source luminance signal 11 to the first and second light sources 111 and 112, and the first and second light source luminance allocation signals 12, 13 is generated. More specifically, the light source luminance assigning unit 102 determines the luminance of each of the first and second light sources 111 and 112 in order to cause each set of white light sources to emit light with luminance according to the light source luminance signal 11. First and second light source luminance assignment signals 12 and 13 indicating the luminances of the determined first and second light sources 111 and 112 are generated.

  FIG. 2 shows an example of a method in which the light source luminance assignment unit 102 generates the first and second light source luminance assignment signals 12 and 13 from the light source luminance signal 11. In FIG. 2, the horizontal axis indicates the normalized input value, and the vertical axis indicates the normalized output value. In the graph of the light source luminance signal, the input value indicates the light source luminance calculated by the light source luminance calculation unit 101, and the output value indicates the light source luminance signal 11. In the graph of the first light source luminance allocation signal, the input value indicates the light source luminance signal 11 and the output value indicates the first light source luminance allocation signal 12. In the graph of the second light source luminance allocation signal, the input value indicates the light source luminance signal 11 and the output value indicates the second light source luminance allocation signal 13.

  In FIG. 2, the light source luminance signal 11 increases in proportion to the light source luminance. The first light source luminance allocation signal 12 increases in proportion to the light source luminance signal 11 when the light source luminance signal 11 is 0 to 0.5 or less, and is a constant value (maximum output) when the light source luminance signal is 0.5 to 1 or less. That is, 1.0). On the other hand, the second light source luminance allocation signal 13 becomes a constant value (minimum output, that is, zero) when the light source luminance signal 11 is 0 to 0.5 or less, and the light source luminance signal 11 is 0.5 to 1 or less. Then, the light source luminance signal 11 increases linearly. Therefore, when the light source luminance signal 11 is 0 to 0.5 or less, the first light source 111 emits light alone with the luminance according to the first light source luminance allocation signal 12, and the light source luminance signal 11 is 0.5 to 1. In the following cases, the first light source 111 emits light with constant luminance (for example, with maximum luminance), and the second light source 112 emits light with luminance according to the second light source luminance assignment signal 13.

  FIG. 3 shows another example of a method in which the light source luminance allocation unit 102 generates the first and second light source luminance allocation signals 12 and 13 from the light source luminance signal 11. In FIG. 3, the vertical axis and the horizontal axis of each graph are the same as those shown in FIG. In FIG. 3, the light source luminance signal 11 increases in proportion to the light source luminance. The first light source luminance allocation signal 12 is a constant value (zero) when the light source luminance signal 11 is 0 to 0.5 or less, and increases linearly to the light source luminance signal 11 when the light source luminance signal is 0.5 to 1 or less. To do. On the other hand, the second light source luminance allocation signal 13 increases in proportion to the light source luminance signal 11 when the light source luminance signal 11 is 0 to 0.5 or less, and is constant when the light source luminance signal is 0.5 to 1 or less. Value (1.0). Therefore, when the light source luminance signal 11 is 0 to 0.5 or less, the first light source 111 emits light alone at a luminance according to the first light source luminance allocation signal 12, and the light source luminance signal 11 is from 0.5. When it is 1 or less, the first light source 111 emits light with a constant luminance (for example, with maximum luminance), and the second light source 112 emits light with luminance according to the second light source luminance assignment signal 13.

  As shown in FIG. 2 or 3, when the light source luminance signal 11 is assigned to the first and second light sources 111 and 112, and the light source luminance is low, any of the first and second light sources 111 and 112 is used. On the other hand, since the second light source 112 in the case of FIG. 2 and the first light source 111 in the case of FIG. 3 emit light alone, power consumption can be suppressed. When the light source luminance is high, both the first and second light sources 111 and 112 emit light, so that a bright image can be displayed on the image display unit 104.

  As an example, the first light source 111 is a light source that emits white light with low light emission efficiency and a wide color gamut, and the second light source 112 has higher light emission efficiency and a narrow color gamut than the first light source 111. In the case of a light source that emits white light, the light source luminance assigning unit 102 uses the first light source 111 when the light source luminance is low and the first light source 111 when the light source luminance is high, as shown in FIG. First and second light source luminance assignment signals 12 and 13 are generated so as to be used in combination with the second light source 112. Therefore, when the light source brightness is low, it is possible to display an image with high saturation by using the first light source 111 having a wide color gamut. When the light source brightness is high, the first light source 111 and the light emission efficiency are high. By using the second light source 112 in combination, a brighter image can be displayed.

  The control unit 103 receives the input image signal 10 and further receives the first and second light source luminance assignment signals 12 and 13 from the light source luminance assignment unit 102. The control unit 103 controls the timing of writing the input image signal 10 to the liquid crystal panel 105 and the timing of applying the first and second light source luminance allocation signals 12 and 13 to the backlight 106.

  In the control unit 103, several synchronization signals (horizontal synchronization signal, vertical synchronization signal, etc.) necessary for driving the liquid crystal panel 105 generated in the control unit 103 based on the input image signal 10 are input image signals. 10 is generated, and the display image signal 14 is transmitted to the liquid crystal panel 105. Further, in the control unit 103, first and second light source luminance control signals 15 and 16 for causing the first and second light sources 111 and 112 to emit light with luminance according to the first and second light source luminance assignment signals 12 and 13. Is generated and sent to the backlight 106.

  The light source luminance control signal (each of the first and second light source luminance control signals 15 and 16) varies depending on the type of light source installed in the backlight 106. In general, a cold cathode tube, a light-emitting diode (LED), or the like is used as a light source of the backlight 106 of the liquid crystal display device. These light sources can modulate the luminance by controlling the applied voltage and current. However, in general, pulse width modulation (PWM) control is used in which the luminance is modulated by switching the ratio between the light emission period and the non-light emission period at high speed. In the present embodiment, an LED light source whose emission intensity is relatively easy to control is used as the first and second light sources 111 and 112 of the backlight 106, and the luminance of the LED light source is modulated by PWM control. In this case, the control unit 103 generates the first and second PWM control signals as the first and second light source luminance control signals 15 and 16 based on the first and second light source luminance allocation signals 12 and 13, It is sent to the light 106.

  In the image display unit 104, the display image signal 14 from the control unit 103 is written to the liquid crystal panel 105, and the backlight 106 is turned on according to the first and second light source luminance control signals 15 and 16 from the control unit 103. Thus, an image corresponding to the input image signal 10 is displayed. As described above, in the present embodiment, an LED light source is used as the light source of the backlight 106 (that is, the first and second light sources 111 and 112).

  As described above, the image display apparatus according to the present embodiment includes two types of white light sources having different color gamuts (color reproduction ranges) and light emission efficiencies, and according to the input image signal 10, among these two types of light sources. By causing one or both of these to emit light, an image can be displayed with high image quality while suppressing an increase in power consumption as much as possible. The image display apparatus according to the present embodiment suppresses an increase in power consumption as much as possible by using the first light source 111 having a wide color gamut when displaying the input image signal 10 having a low maximum gradation value. However, when the input image signal 10 having a high maximum gradation value can be displayed, a bright image can be displayed by using the second light source 112 having a high luminous efficiency. Can do.

(Second Embodiment)
The second embodiment is a modification of the first embodiment. In the second embodiment, the backlight 106 in FIG. 1 is provided with three or more types of white light sources having different color gamuts and luminous efficiencies. An example will be described.

  The image display apparatus according to the present embodiment has the same configuration as that of the first embodiment shown in FIG. 1, but three or more types of white light sources are provided in the backlight 106, whereby the light source luminance allocation unit 102. The method of assigning the light source luminance signal 11 to each white light source is different from the first embodiment. In the present embodiment, the light source luminance allocation unit 102 will be described in detail, and the other configurations are the same as those in the first embodiment, and thus the description thereof will be omitted.

First, an example in which three types of white light sources are provided in the backlight 106 will be described with reference to FIGS. 4 and 5A and 5B.
FIG. 4 shows the characteristics of three types of white light sources (first light source, second light source, and third light source) provided in the backlight 106. The white light emitted from the first light source has the widest color gamut, the white light emitted from the second light source has a narrower color gamut than the first light source, and the white light emitted from the third light source has the narrowest color gamut. On the other hand, the first light source has the lowest light emission efficiency, the second light source has higher light emission efficiency than the first light source, and the third light source has the highest light emission efficiency. Thus, the color gamut is wide in the order of the third light source, the second light source, and the first light source, and the luminous efficiency is high in the order of the first light source, the second light source, and the third light source.

  FIG. 5A shows an example of a method in which the light source luminance assignment unit 102 generates the first, second, and third light source luminance assignment signals from the light source luminance signal 11. In FIG. 5A, the horizontal axis represents the normalized input value (light source luminance signal 11), and the vertical axis represents the normalized output value (the first, second, and third light source luminances). , Second and third light source luminance control signals).

  In FIG. 5A, the first light source luminance allocation signal increases in proportion to the light source luminance signal 11 when the light source luminance signal 11 is from 0 to a predetermined first signal value (for example, 0.33) or less. When the light source luminance signal 11 is 1 or less from the first signal value, a constant value (1.0) is obtained. The second light source luminance allocation signal 13 becomes a constant value (zero) when the light source luminance signal 11 is 0 to the first signal value or less, and the light source luminance signal 11 is a predetermined second signal value from the first signal value ( For example, when 0.67) or less, the light source luminance signal 11 increases linearly, and when the light source luminance signal is 1 or less from the second signal value, it becomes a constant value (1.0). Further, the third light source luminance allocation signal becomes a constant value (zero) when the light source luminance signal 11 is 0 to the second signal value or less, and when the light source luminance signal 11 is 1 or less from the second signal value, the light source luminance signal 11. Increases linearly with respect to. Therefore, when the light source luminance signal 11 is from 0 to the first signal value or less, the first light source 112 emits light at a luminance according to the first light source luminance allocation signal, and the light source luminance signal 11 is second from the first signal value. When the signal value is less than or equal to the signal value, the first light source emits light with a constant luminance, and the second light source emits light with a luminance according to the first light source luminance assignment signal 12. Further, when the light source luminance signal 11 is equal to or higher than the second signal value, the first and second light sources emit light with a constant luminance, and the third light source emits light with luminance according to the third light source luminance assignment signal.

  FIG. 5A shows an example in which the first signal value is 0.33 and the second signal value is 0.67. The first and second signal values may be set to any values as long as the second signal value is larger than the first signal value. For example, as shown in FIG. 5B, the first signal value can be set to 0.25 and the second signal value can be set to 0.5.

  When four or more types of white light sources are provided in the backlight 106, in the same manner as described above, when the light source luminance signal 11 is equal to or lower than the first signal value, the first light source having the widest color gamut is caused to emit light. The light source luminance signal 11 is changed from a low value to a high value so that the second light source having the second largest color gamut is emitted in addition to the first light source until the first signal value is exceeded and the first signal value is not more than the first signal value. Accordingly, light is emitted in order from a white light source with a wide color gamut.

  As described above, according to the second embodiment, as the light source luminance signal 11 is changed from a low value to a high value, an input image having a low maximum gradation value is used in order from a white light source with a wide color gamut. When the signal 10 is displayed, a higher saturation image can be displayed, and when the input image signal 10 having a higher maximum gradation value is displayed, a brighter image can be displayed.

  Each type of white light source may be a single light source that emits white light alone, such as a white LED, or a plurality of light sources that emit light of different colors, such as red light. The light source may include a red LED, a green LED that emits green light, and a blue LED that emits blue light, and may emit white light by mixing the light of each color. When a white light source includes a plurality of light sources and mixes light of a plurality of colors to generate white light, the number of light sources increases, resulting in a decrease in luminous efficiency, but an increase in the color gamut of the white light source. Can do. As an example, as shown in FIG. 21, by using the first light source 111 having the widest color gamut as a light source including a red LED, a green LED, and a blue LED, an image with higher saturation can be displayed on the image display unit 104. It becomes possible.

(Third embodiment)
An image display apparatus according to the third embodiment will be described with reference to FIGS.
FIG. 6 schematically shows an image display apparatus according to the third embodiment. In FIG. 6, the same reference numerals as those shown in FIG. 1 are attached to the same portions and the same portions, and the overlapping description is omitted as appropriate, and the portions different from the first embodiment will be described in detail. This embodiment is different from the first embodiment in that the luminance of the first and second light sources 111 and 112 can be modulated for each divided region set in the backlight 106.

  The image display apparatus of FIG. 6 includes a light source luminance distribution calculation unit 601 and a gradation conversion unit 602 in addition to the image display apparatus of FIG. The input image signal 10 is sent to the light source luminance calculation unit 101 and the gradation conversion unit 602.

  The light source luminance calculation unit 101 calculates the light source luminance for each divided region based on the input image signal 10 and generates a light source luminance signal 11 indicating the light source luminance for each divided region. The light source luminance signal 11 is sent to the light source luminance assigning unit 102 and the light source luminance distribution calculating unit 601.

  The light source luminance distribution calculation unit 601 estimates the backlight luminance distribution when all the light sources emit light according to the light source luminance signal 11 based on the light emission luminance distribution shape when one light source of the backlight 106 emits alone. The light source luminance distribution signal 60 is generated. The light source luminance distribution signal 60 is sent to the gradation conversion unit 602.

  The gradation converting unit 602 converts the gradation of each pixel of the input image signal 10 based on the light source luminance distribution signal 60 and generates a converted image signal 62. The converted image signal 62 is sent to the control unit 103.

  The light source luminance assignment unit 102 assigns the light source luminance signal 11 to the first and second light sources 111 and 112 for each divided region, and generates the first and second light source luminance assignment signals 12 and 13.

  The control unit 103 controls the timing of the converted image signal 62 from the gradation conversion unit 602 and the first and second light source luminance assignment signals 12 and 13 from the light source luminance assignment unit 102. More specifically, the control unit 103 generates a display image signal 14 based on the converted image signal 62 instead of the input image signal 10, sends the display image signal 14 to the liquid crystal panel 105, and First and second light source luminance control signals 15 and 16 are generated based on each of the first and second light source luminance allocation signals 12 and 13, and the first and second light source luminance control signals 15 and 16 are supplied to the backlight 106. Send it out.

  In the image display unit 104, the display image signal 14 is written to the liquid crystal panel 105, and the first and second light sources 111 and 112 in the backlight 106 have luminances according to the first and second light source luminance assignment signals 12 and 13, respectively. By emitting light at, an image corresponding to the input image signal 10 is displayed.

Next, each part of the image display apparatus of FIG. 6 will be described in detail.
Upon receiving the input image signal 10, the light source luminance calculation unit 101 first divides the input image signal 10 into a plurality of pixel blocks (small regions) in association with the divided regions of the backlight 106, and inputs the input image for each pixel block. The maximum gradation value of the signal 10 is calculated. As an example, as shown in FIG. 7, when the set of the first and second light sources 111 and 112 is provided in the backlight 106 by 5 in the horizontal direction and 4 in the vertical direction, the backlight 106 is It is divided into 5 × 4 divided areas. In this example, the light source luminance calculation unit 101 divides the input image signal 10 into 5 × 4 pixel blocks so as to correspond to the divided areas of the backlight 106, and calculates a maximum gradation value for each pixel block.

Thereafter, the light source luminance calculation unit 101 calculates the light source luminance of each divided region from the maximum gradation value of each pixel block. For example, when the input image signal 10 is an image expressed by 8 bits (0 gradation to 255 gradation), the maximum gradation value of the i-th pixel block is L _max (i), and the i-th The light source luminance I (i) of the divided areas is calculated by the equation (2).

  Here, γ is a gamma value, and 2.2 is generally used. The light source luminance signal 11 of the present embodiment includes the light source luminance for each divided region.

  Thus, by calculating the light source luminance for each divided region, the light source luminance of the first and second light sources 111 and 112 corresponding to the pixel block having a small gradation value in the input image is reduced. Electric power can be reduced.

  In the present embodiment, an example in which one set of white light sources is included in each divided region is described. However, the present invention is not limited to this. For example, each divided region includes a plurality of sets of white light sources. The backlight 106 may be divided into a plurality of areas. Further, the pixel blocks of the input image signal 10 are not limited to the example in which the pixel blocks of the input image signal 10 are equally divided by the number of divided regions as shown in FIG. A block may be set.

  When the light source luminance distribution calculation unit 601 receives the light source luminance signal 11 from the light source luminance calculation unit 101, the light source luminance distribution calculation unit 601 calculates the actual luminance distribution of the backlight 106 based on the light source luminance calculated for each divided region.

  FIG. 8 schematically shows a luminance distribution when one light source in the backlight 106 emits light. In FIG. 8, for ease of explanation, the luminance distribution is expressed in one dimension, the horizontal axis indicates the position, and the vertical axis indicates the luminance. FIG. 8 shows a luminance distribution when a light source is installed at a position indicated by a circle indicated below the horizontal axis, and one of the light sources at the center indicated by a white circle is lit alone. As can be seen from FIG. 8, the luminance distribution (hereinafter referred to as “emission luminance distribution”) when one light source emits light spreads to nearby light source positions.

  The light source luminance distribution calculation unit 601 calculates a luminance distribution when one light source emits light with luminance according to the light source luminance signal 11 in order to perform gradation conversion based on the luminance distribution of the backlight 106 in the gradation conversion unit 602. By adding together, the actual luminance distribution (backlight luminance distribution) of the backlight 106 is calculated.

  FIG. 9 schematically shows a luminance distribution when a plurality of light sources of the backlight 106 are turned on. FIG. 9 is expressed in one dimension as in FIG. When the light sources at the positions indicated by the circles below the horizontal axis in FIG. 9 are turned on, each light source has a light emission luminance distribution as indicated by a broken line in FIG. The backlight luminance distribution as shown by the solid line in FIG. 9 is calculated by obtaining the emission luminance distributions of all the first and second light sources 111 and 112 in the backlight 106 and adding all the emission luminance distributions. .

  The light emission luminance distribution as shown in FIG. 8 is obtained by actually emitting a light source alone and measuring the luminance. In this embodiment, an LUT 1002 (shown in FIG. 10) describing the relationship between the distance from the light source and the luminance obtained based on the measurement is stored in advance in a recording medium such as a ROM. In another example, the light emission luminance distribution can be obtained as an approximate function related to the distance from the light source based on the measurement, and is stored in the light source luminance distribution calculation unit 601.

  FIG. 10 shows the light source luminance distribution calculation unit 601 in more detail. In the light source luminance distribution calculation unit 601, the light source luminance signal 11 is sent to the light source luminance distribution acquisition unit 1001. The light source luminance distribution acquisition unit 1001 acquires the light emission luminance distribution from the LUT 1002. Thereafter, the light source luminance distribution acquisition unit 1001 obtains the luminance distribution for each divided region by multiplying the light emission luminance distribution by the light source luminance for each divided region. Specifically, the light source luminance distribution acquisition unit 1001 first allocates the light source luminance signal 11 to the first and second light sources 111 and 112 in the same manner as the light source luminance allocation unit 102, and first and second light sources 111. , 112 is obtained for each divided region. Subsequently, the light source luminance distribution acquisition unit 1001 obtains the luminance distribution of each of the first and second light sources 111 and 112 and adds them to obtain the luminance distribution for each divided region. In another example, although not shown, the light source luminance distribution acquisition unit 1001 receives the first and second light source luminance allocation signals 12 and 13 from the light source luminance allocation unit 102 instead of receiving the light source luminance signal 11, and The luminance distribution may be obtained for each divided region based on the second light source luminance assignment signals 12 and 13. The luminance distribution 61 for each divided area is sent to the luminance distribution synthesis unit 1003.

  The luminance distribution synthesizing unit 1003 calculates the backlight luminance distribution as shown in FIG. 9 by adding, that is, synthesizing the luminance distribution 61 for each divided region, and calculates the backlight luminance distribution based on the light source luminance signal 11. A light source luminance distribution signal 60 is generated.

  The gradation converting unit 602 receives the input image signal 10 and further receives the light source luminance distribution signal 60 from the light source luminance distribution calculating unit 601. The gradation conversion unit 602 converts the gradation value of each pixel of the input image signal 10 based on the light source luminance distribution signal 60 and generates a converted image signal 62.

Since the luminance of the light source calculated by the light source luminance calculation unit 101 is reduced, the transmittance of the liquid crystal panel 105, that is, the gradation value of the input image signal 10 is converted in order to obtain a desired brightness. There is a need to. The gradation values of the red, green, and blue sub-pixels at the pixel position (x, y) of the input image signal 10 are set to L _R (x, y), L _G (x, y), and L _B (x, y), respectively. ), Gradation values L _R ′ (x, y), L _G ′ (x, y), and L _B ′ (L _B ′ ( x, y) is calculated as follows.

Here, I _d (x, y) indicates the luminance at the pixel position (x, y) in the backlight luminance distribution calculated by the light source luminance distribution calculating unit 601.

Note that the gradation value after gradation conversion may be obtained by calculation according to Equation (3), but in this embodiment, the gradation value L, the light source luminance distribution _Id, and the converted gradation value L ′ are calculated. An LUT describing the relationship is prepared in advance, and the tone conversion unit 602 refers to the LUT with the tone value L (x, y) and the light source luminance distribution I _d (x, y) of the input image signal 10, The converted gradation value L ′ (x, y) is obtained.

Further, in Equation (3), the value of the gradation value L and the light source luminance distribution I _d, when occurs the gradation value after conversion L'exceeds "255" which is the maximum gradation value of the liquid crystal panel 105 . In such a case, for example, the gradation value after conversion may be saturated with “255”, but gradation loss occurs in the gradation value subjected to saturation processing. Therefore, the changed tone value held by the LUT may be corrected in advance so as to change gently in the vicinity of the saturated tone value.

  The light source luminance calculation unit 101 and the light source luminance distribution calculation unit 601 calculate the light source luminance and the light source luminance distribution using all the gradation values of the input image signal 10 of one frame. Therefore, at the timing when the input image signal 10 is input to the gradation conversion unit 602, the light source luminance distribution corresponding to the input image signal 10 of the frame has not been calculated yet. Therefore, the gradation conversion unit 602 includes a frame memory (not shown), temporarily holds the input image signal 10 in the frame memory, and delays, for example, one frame period, and then corresponds to the light source corresponding to the held input image signal 10. A converted image signal 62 is generated based on the luminance distribution signal 60.

  In general, the input image signal 10 is continuous to some extent in time, and therefore, the correlation between temporally continuous images is high, and the backlight luminance distribution between consecutive images is substantially the same. Can be considered. For this reason, the gradation conversion unit 602 may generate the converted image signal 62 based on the backlight luminance distribution obtained for the current input image with respect to the input image one frame before. In this case, since it is not necessary to delay the input image by one frame period in the gradation conversion unit 602, it is not necessary to mount a frame memory, and the circuit scale can be reduced.

  The light source luminance assigning unit 102 receives the light source luminance signal 11 indicating the light source luminance for each divided region. The light source luminance assigning unit 102 determines the luminance of each of the first and second light sources 111 and 112 for each divided region based on the light source luminance signal 11, and the first and second light sources 111, First and second light source luminance assignment signals 12 and 13 indicating the luminance of each of 112 are generated.

  The control unit 103 according to the present embodiment receives the converted image signal 62 from the gradation converting unit 602 instead of the input image signal 10. In addition, the control unit 103 receives the first and second light source luminance assignment signals 12 and 13 from the light source luminance assignment unit 102. The control unit 103 controls the timing of writing the display image signal 14 to the liquid crystal panel 105 and the timing of applying the first and second light source luminance assignment signals 12 and 13 to the backlight 106.

  The control unit 103 displays the converted image signal 62 together with some synchronization signals (such as a horizontal synchronization signal and a vertical synchronization signal) necessary for driving the liquid crystal panel 105 generated in the control unit 103. 14 is sent to the liquid crystal panel 105. At the same time, the controller 103 controls the first and second light source luminance control signals 15 and 16 for turning on the light sources 111 and 112 of the backlight 106 with luminance based on the first and second light source luminance allocation signals 12 and 13. Is transmitted to the backlight 106. The first and second light sources 111 and 112 of this embodiment are, for example, white LED light sources, and are subjected to luminance modulation by PWM control.

  As described above, the image display apparatus according to the present embodiment has the same effect as that of the first embodiment, and further modulates the luminance of the first and second light sources 111 and 112 for each divided region. High image quality and low power consumption can be realized.

(Fourth embodiment)
An image display apparatus according to the fourth embodiment will be described with reference to FIGS.
FIG. 11 schematically shows an image display apparatus according to the fourth embodiment. In FIG. 11, the same reference numerals as those shown in FIGS. 1 and 6 are attached to the same portions and the same portions, and repeated description is omitted as appropriate, and portions different from the third embodiment will be described in detail. In the present embodiment, the average value or sum of the luminances of all the sets of white light sources is obtained from the light source luminance signal 11 indicating the light source luminance for each divided region calculated by the light source luminance calculating unit 101, and this average value or sum is calculated. The difference from the third embodiment is that the light source luminance signal 11 is corrected with a correction coefficient that decreases as the value increases. Specifically, the image display apparatus of FIG. 11 includes a light source luminance correction unit 1101 in addition to the image display apparatus of FIG.

  The light source luminance correction unit 1101 corrects the light source luminance for each divided region calculated by the light source luminance calculation unit 101 and generates a corrected light source luminance signal 70. Specifically, as shown in FIG. 12, the light source luminance correction unit 1101 describes a correction coefficient calculation unit 1201 that calculates a correction coefficient for correcting the light source luminance for each divided region, and describes the relationship between the average luminance and the correction coefficient. The LUT 1202 includes a correction coefficient multiplication unit 1203 that calculates the correction light source luminance by multiplying the light source luminance by the correction coefficient for each divided region.

The correction coefficient calculation unit 1201 calculates an average value for a predetermined period (for example, one frame period) from the light source luminance for each divided region. In the present embodiment, one set of light sources 111 and 112 is included for each divided region. When the number of sets of the first and second light sources 111 and 112 is n, the average luminance in one frame period is calculated as follows.

Here, I (i) represents the i-th light source luminance, and I _ave represents the average luminance. The number n of pairs of the first and second light sources 111 and 112 is a very small value compared to the number of pixels of the input image signal 10, and the processing cost is much higher than when calculating the average luminance from the entire image. Can be reduced.

Next, the correction coefficient calculation unit 1201 obtains a correction coefficient G for the light source luminance with reference to the LUT 1202 in which the correction coefficient is held with the calculated average luminance I _ave . There are various possible relationships between the average luminance I _ave held in the LUT 1202 and the correction coefficient G, but the correction coefficient is set to increase as the average luminance decreases.

FIG. 13 shows the relationship between the average luminance I _ave held in the LUT 1202 and the correction coefficient G in the present embodiment. In FIG. 13, when the average brightness is less than a predetermined first set value, the correction coefficient is 1.0, and when the average brightness is equal to or higher than the first set value and less than the predetermined second set value, the correction coefficient is an average. When the average luminance decreases more than the second set value according to the luminance, the correction coefficient is 0.5. In this embodiment, it is assumed that the light source luminance can be controlled by 10 bits, and in this case, the maximum value of the average luminance is 1023. In FIG. 13, when the average luminance is 1023 which is the maximum value, the correction coefficient is 0.5.

In this embodiment, the correction coefficient is held in the LUT 1202. However, the correction coefficient calculation unit 1201 holds the relationship between the average luminance I _ave and the correction coefficient G as a function, and calculates the calculated average luminance I _ave from the calculated average luminance I _ave. The correction coefficient G may be calculated.

Further, the correction coefficient calculation unit 1201 may calculate the correction coefficient G by _obtaining the sum I _sum of the light source luminances by setting n in the denominator of Equation (4) to 1, instead of calculating the average luminance I _ave. .

Information 71 of the correction coefficient G calculated by the correction coefficient calculation unit 1201 is sent to the correction coefficient multiplication unit 1203. The correction coefficient multiplier 1203 calculates the correction light source luminance by multiplying the light source luminance of each divided region by the correction coefficient G, for example, according to Equation (5).

Here, I _c (i) indicates the i-th corrected light source luminance. When the correction coefficient G is 1.0, the light source luminance calculated by the light source luminance calculation unit 101 is output as it is as the correction light source luminance. When the correction coefficient is 0.5, a value half the light source luminance is used as the correction light source luminance. Is output.

If the average luminance I _ave is large, the correction coefficient is 0.5. Therefore, the first and second light sources 111 and 112 of the backlight 106 are lit at half the brightness, and as a result, glare is suppressed. Is done. For example, when the screen brightness when all the first and second light sources 111 and 112 of the backlight 106 are turned on is 1,000 cd / m ² , the screen brightness is 500 cd / m when the correction coefficient is 0.5. ² .

On the other hand, when the average luminance I _ave is small, the correction coefficient G is 1.0. Therefore, it is assumed that the first and second light sources 111 and 112 have a maximum screen luminance of 1,000 cd / m ^2. It will emit light. As a result, the first and second light sources 111 and 112 set with high luminance are lit brightly, and display with a high dynamic range is possible, such that a bright image region is bright and a dark image region is dark.

Further, from the viewpoint of power consumption, assuming that the power consumption when the average luminance is 1023 and correction is not performed (that is, G = 1) is 1.0, the average luminance I _ave is 1023 and the correction coefficient G The power consumption when N is 0.5 is 0.5 × 1023/1023 = 0.5. On the other hand, when the average luminance I _ave is small, for example, when the average luminance I _ave is 100, even if the correction coefficient G is 1.0, the average luminance I _ave is small, so the power consumption is 1.0 × 100/1023 = 0.1. Therefore, the maximum brightness of the screen even if the display as 1,000 cd / ^{m 2} corresponds, can be the maximum luminance compared to 500 cd / ^{m 2} corresponds, to significantly reduce power consumption.

Furthermore, the correction coefficient G is calculated so that the power consumption is always 0.5 or less, with 0.5 being the power consumption when the average luminance I _ave is “1023” as the maximum power consumption of the backlight 106. You can also. Specifically, the correction coefficient G is calculated so as to satisfy the following formula.

FIG. 14 shows the relationship between the maximum value of the correction coefficient G that satisfies Equation (6) and the average luminance I _ave . By setting the correction coefficient G as shown in FIG. 14, it is possible to realize a display with a screen luminance equivalent to a maximum of 1000 cd / m ² with a power consumption equal to or lower than the power consumption corresponding to a maximum of 500 cd / m ² .

  The light source luminance assigning unit 102 of this embodiment receives the corrected light source luminance signal 70 from the light source luminance correcting unit 1101 instead of receiving the light source luminance signal 11 from the light source luminance calculating unit 101. The light source luminance assignment unit 102 assigns the corrected light source luminance signal 70 to the first light source 111 and the second light source 112 in the same manner as described in the first embodiment, and the first light source luminance assignment signal and the second light source luminance. Set the assignment signal.

  When the backlight 106 is provided with three or more types of white light sources, the light source luminance assigning unit 102 determines the predetermined light source luminance based on the corrected light source luminance signal 70 as described in the second embodiment. Up to one signal value, the light source luminance signal is low so that the first light source having the widest color gamut emits light, and the light source luminance signal equal to or greater than this threshold also emits the second light source having the second largest color gamut. As the value increases, the white light source emits light in the order of wide color gamut.

  As described above, the image display apparatus according to the present embodiment can reduce power consumption by correcting the light source luminance to be small when the average luminance of the input image signal is high. Similarly to the first and third embodiments, when the input image signal 10 is bright and vivid, it is possible to display a vivid color image by using the first light source 111 having a wide color gamut. When the maximum gradation value of the input image signal 10 is low, in addition to the first light source 111 having a wide color gamut, the second light source 112 having a high light emission efficiency is used, thereby improving the luminance and displaying the image. It is possible to display. Accordingly, it is possible to realize a display with a high dynamic range with a high level of glitter while suppressing power consumption.

(Fifth embodiment)
With reference to FIGS. 15A to 17B, an image display apparatus according to a fifth embodiment will be described.
In the fifth embodiment, a method in which the light source luminance assignment unit 102 generates the first and second light source luminance assignment signals 12 and 13 based on the light source luminance signal will be described. As described in the first to fourth embodiments, a plurality of white light sources, for example, first and second light sources 111 and 112 having different luminous efficiencies are used as the light source of the backlight 106. Therefore, even if the light source luminance signal 11 (corrected light source luminance signal 70 in the fourth embodiment) increases at a constant rate, the luminance emitted from the image display unit 104 is a constant rate due to the difference in light emission efficiency of the light source. Does not increase. This will be described with reference to FIGS. 15 (a) and 15 (b). FIG. 15B shows the relationship between the light source luminance and the display luminance, the horizontal axis shows the light source luminance, and the vertical axis shows the display luminance.

  For example, as shown in FIG. 15A, the first light source 111 having a low light emission efficiency is used until the light source luminance signal is 0.5, and light is emitted from the first light source 111 when the light source luminance signal is 0.5 or more. Consider a case where the second light source 112 whose efficiency is 1.2 times higher, for example, is also used. At this time, since the luminous efficiency is different between the first light source 111 and the second light source 112, the first light source 111 is switched to the combined use of the first and second light sources 111 and 112 as shown in FIG. Sometimes, a discontinuity of brightness occurs in the actually displayed brightness. That is, the increase rate (slope) of the display luminance changes with the light source luminance being 0.5.

  Therefore, the light source luminance assigning unit 102 of the fifth embodiment linearly increases the luminance of the light source with respect to the constant increase of the light source luminance signal or the corrected light source luminance signal (in the case of the fourth embodiment). Thus, the first and second light source luminance assignment signals 12 and 13 are generated. Specifically, the light source luminance allocation unit 102 outputs the second light source luminance allocation signal 13 with a reduced size or outputs the first light source luminance allocation signal 12 with a ratio of the luminous efficiency.

  FIGS. 16A and 16B show luminance signals that make the display luminance constant by weakening the luminance of the second light source 112 having high luminous efficiency when the light source luminance is between 0.5 and 1.0. Shows how to generate. FIGS. 17A and 17B show a method of generating a luminance signal that makes the display luminance constant by increasing the luminance of the first light source with low luminous efficiency. In FIGS. 17A and 17B, the first and second light sources 111 and 112 are used together even when the light source luminance is less than 0.5.

  As described above, the image display apparatus according to this embodiment uses the first and second light source luminance assignment signals in accordance with the ratio of the light emission efficiency in the light source luminance assignment unit 102 even when a plurality of light sources having different light emission efficiencies are used. By controlling the intensities 12 and 13, the luminance can be increased linearly with respect to the light source luminance without generating a luminance discontinuity, and a natural image can be displayed.

(Sixth embodiment)
With reference to FIG. 18, an image display apparatus according to a sixth embodiment will be described.
FIG. 18 schematically shows an image display apparatus according to the sixth embodiment. The image display apparatus of this embodiment has the same configuration as that of the first embodiment, and includes a light source luminance calculation unit 101, a light source luminance allocation unit 1801, a control unit 103, and an image display unit 104. Unlike the light source luminance assignment unit 102 in FIG. 1, the light source luminance assignment unit 1801 assigns the light source luminance signal 11 to the first and second light sources 111 and 112 using the input image signal 10. Specifically, the light source luminance assignment unit 1801 includes a saturation calculation unit 1901, a saturation determination unit 1902, and a light source luminance assignment setting unit 1903 as shown in FIG.

  In the light source luminance allocation unit 1801, the input image signal 10 is sent to the saturation calculation unit 1901. The saturation calculation unit 1901 calculates the saturation of the input image signal 10. The saturation determination unit 1902 determines whether the saturation calculated by the saturation calculation unit 1901 is equal to or less than a predetermined value or exceeds a predetermined value. Information on whether the saturation is equal to or less than a predetermined value is sent to the light source luminance assignment setting unit 1903.

  When the saturation exceeds a predetermined value, the light source luminance assignment setting unit 1903 causes the white light source to emit light in the order of wide color gamut as the light source luminance signal 11 changes from a low value to a high value. Set the light source luminance allocation signal. On the other hand, when the saturation is equal to or lower than the predetermined value, the light source luminance assigning unit 1903 causes the white light source to emit light in order of narrow color gamut as the light source luminance signal 11 changes from a low value to a high value. First and second light source luminance assignment signals are set. 20A and 20B show the first, second, and third light source luminance assignment signals when the saturation exceeds a predetermined value and when the saturation is not more than the predetermined value, respectively. . These first, second and third light sources have the characteristics shown in FIG. As described above, when the saturation of the input image signal 10 is high, the first light source having a wide color gamut is preferentially used to display a colorful image, and when the saturation is low, power consumption is suppressed. In addition, the third light source having high luminous efficiency is preferentially used.

  In the present embodiment, an example in which the first, second, and third light sources are used in combination has been shown. However, the first light source is used without using the second and third light sources for images with high saturation. For a low-saturation image, the third light source may be used without using the first and second light sources.

  As described above, according to the present embodiment, it is possible to display a colorful image efficiently by preferentially using a light source with a wide color gamut for an image with high saturation. By using a light source with high light emission efficiency preferentially for an image with low power consumption, it becomes possible to display an image with reduced power consumption.

  In the above-described embodiment, the example in which the image display unit 104 is a transmissive liquid crystal display device in which the liquid crystal panel 105 and the backlight 106 are combined has been described. However, the present invention is not limited to this. As an example, the image display unit 104 may be a projection-type liquid crystal display device that combines a liquid crystal panel and a light source such as a halogen light source. In another example, the image display unit 104 uses a halogen light source as a light source unit, and uses a digital micromirror device that displays an image by controlling reflection of light from the halogen light source as a light modulation element. It may be a projection type image display unit.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 10 ... Input image signal, 11 ... Light source luminance signal, 12 ... Light source luminance allocation signal, 13 ... Light source luminance allocation signal, 14 ... Display image signal, 15 ... First light source luminance control signal, 16 ... Second light source luminance control signal, DESCRIPTION OF SYMBOLS 60 ... Light source luminance distribution signal, 62 ... Conversion image signal, 70 ... Correction light source luminance signal, 101 ... Light source luminance calculation part, 102 ... Light source luminance allocation part, 103 ... Control part, 104 ... Image display part, 105 ... Liquid crystal panel, 106 ... Backlight, 111 ... First light source, 112 ... Second light source, 601 ... Light source luminance distribution calculation unit, 602 ... Tone conversion unit, 1001 ... Light source luminance distribution acquisition unit, 1002, 1202 ... LUT, 1003 ... Luminance distribution Synthesis unit, 1101... Light source luminance correction unit, 1201... Correction coefficient calculation unit, 1203... Correction coefficient multiplication unit, 1801... Light source luminance allocation unit, 1901. Tough, 1903 ... light source luminance assignment setting unit.

Claims (7)

A light source unit including first and second white light sources having different light emission efficiencies and color gamuts, each capable of controlling the luminance of the first and second white light sources;
A light modulation element unit capable of modulating light transmittance or reflectance according to a display image signal;
A light source luminance calculating unit that calculates a luminance of a set of white light sources each including the first and second white light sources, and generates a light source luminance signal, based on a pixel value of an input image signal;
A light source luminance assigning unit for assigning the light source luminance signal to the first and second white light sources and generating first and second light source luminance assignment signals indicating the respective luminances of the first and second white light sources;
A display image signal for controlling the light modulation element unit is generated based on the input image signal, and the luminances of the first and second white light sources are controlled based on the first and second light source luminance allocation signals. A control unit for generating a brightness control signal;
An image display device comprising: The first white light source has a higher color gamut and lower luminous efficiency than the second white light source,
The light source luminance allocating unit causes the first white light source to emit light when the light source luminance signal is less than a predetermined signal value, and when the light source luminance signal is equal to or greater than a predetermined signal value, The image display apparatus according to claim 1, wherein the light source luminance signal is assigned to the first and second white light sources so as to emit a white light source.   The light source luminance assigning unit assigns the light source luminance signal to the first and second white light sources so that the luminance of the one set of white light sources increases linearly with respect to the constant increase of the light source luminance signal. The image display device according to claim 2, which is assigned to the image display device.   The light source luminance allocating unit calculates a saturation of the input image signal based on a pixel value of the input image signal, and when the saturation is smaller than a predetermined value, One of the two white light sources that emits light is given priority, and when the saturation is equal to or higher than a predetermined value, the other light source that emits light with priority is given priority. 3. The image according to claim 2, further comprising: a light source luminance assignment setting unit that assigns the light source luminance signal to the first and second white light sources and generates the first and second light source luminance assignment signals. Display device.   Each of the first and second white light sources is a single light source that emits white light alone, or includes a plurality of light sources that emit light of different colors. The image display device according to claim 1, wherein the image display device is a light source that emits light of a predetermined amount. A light modulation element unit capable of displaying an image in the display region by modulating light transmittance or reflectance; and
A light source that has a plurality of sets of first and second white light sources that have different light emission efficiency and color gamut, each of which can control luminance, and that irradiates light to a divided area obtained by virtually dividing the display area for each set. And
The input image signal is divided into a plurality of blocks corresponding to the divided areas, and the luminance of the white light source of the set of the first and second white light sources is calculated based on the pixel value in the block, and the light source luminance A light source luminance calculation unit for generating a signal;
A light source luminance distribution calculating unit that estimates a light source luminance distribution when the light source unit emits light according to the light source luminance signal;
A gradation converter that generates a converted image signal obtained by converting the input image signal based on the light source luminance distribution;
For each set, the calculated light source luminance signal is assigned to the first and second white light sources, and first and second light source luminance assignment signals indicating the respective luminances of the first and second white light sources are assigned. A light source luminance allocation unit to be generated;
A display image signal for controlling the light modulation element unit is generated based on the converted image signal, and luminances of the first and second white light sources are controlled based on the first and second light source luminance allocation signals. A control unit for generating a brightness control signal;
An image display device comprising: A correction coefficient calculation unit that calculates a correction coefficient that becomes a smaller value as the sum of the light source luminance signals calculated for each of the divided areas is larger;
A correction coefficient multiplier that corrects the light source luminance signal by multiplying the light source luminance signal by the correction coefficient, and generates a corrected light source luminance signal;
Further comprising
The image display device according to claim 6, wherein the light source luminance allocation unit generates the first and second light source luminance allocation signals based on the light source luminance signal instead of the light source luminance signal.

Images