JP2016130781A - Display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce power consumption.SOLUTION: A display device comprises an image signal output part that outputs a first image signal, and a conversion part that converts the first image signal into a second image signal. The conversion part includes a function to extend the luminance of the second image signal beyond RGBW color spaces of a display panel.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a display device.

  In recent years, liquid crystal panel displays employing the RGBW method have been developed. In this configuration, one pixel is configured by adding W (white) pixels to R (red), G (green), and B (blue) pixels. As a result, the luminance of the light source device that illuminates the liquid crystal panel from the back surface or the like can be lowered by the amount of improvement in the luminance of the W pixel, and the power consumption of the entire device can be reduced.

  On the other hand, there is a demand for further reduction of power consumption in the display method as described above. As a technique for reducing power consumption, for example, a technique for reducing the power consumption by changing the spatial light quantity distribution of light emitted from a light emitting diode of a backlight corresponding to image information has been proposed (patent). Reference 1).

JP 2006-339047 A

  The present invention provides a display device in which power consumption is reduced. Alternatively, a display device with improved visibility is provided.

  One embodiment of the present invention displays a first subpixel that displays a first color, a second subpixel that displays a second color, a third subpixel that displays a third color, and a fourth color A display panel having a fourth subpixel, an image signal output unit for outputting a first image signal having input signal values of the first subpixel to the third subpixel, and an extension of the first image signal And a conversion unit that converts the output signal value of the first subpixel to the fourth subpixel into a second image signal, and the conversion unit converts the luminance of the first image signal, A first mode that expands into a first color space in which color does not change and converts it into the second image signal, and a luminance of the first image signal that exceeds the first color space. And a second mode for expanding into a second color space and converting it to the second image signal.

It is a figure which shows the structural example of a display apparatus. It is a figure which shows the hardware structural example of a display apparatus. It is a figure which shows the pixel array example of the image display panel contained in a display apparatus. It is a figure which shows the structural example of the light source device contained in a display apparatus. It is a figure which shows the structural example of the function with which a display apparatus is provided. It is a conceptual diagram of the reproduction HSV color space which can be reproduced with a display apparatus. It is a figure which shows the function example with which the signal processing part of a display apparatus is provided. It is a figure which shows RGBW color space. It is a figure which shows RGBW color space. It is a figure which shows the function curve which comprises RGBW color space. It is a figure which shows RGBW color space. It is a figure which shows the extended virtual RGBW color space. It is a figure which shows RGBW boost color space. It is a figure which shows RGBW boost color space. A state in which the luminance is increased in the RGBW boost color space is shown. It is a figure which shows the output brightness | luminance on RGBW boost color space. It is a figure which shows the output brightness | luminance on RGBW boost color space. It is a figure which shows the output brightness | luminance on RGBW boost color space. It is a figure which shows the output brightness | luminance on RGBW boost color space. It is a figure which shows the output brightness | luminance on RGBW boost color space. It is a figure which shows the output brightness | luminance on RGBW boost color space. It is a figure which shows the structural example of a display apparatus.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  It should be noted that the disclosure is merely an example, and those skilled in the art can easily conceive of appropriate changes while maintaining the gist of the invention are naturally included in the scope of the present invention. In addition, the drawings may be schematically represented with respect to the width, thickness, shape, and the like of each part in comparison with actual aspects for the sake of clarity of explanation, but are merely examples, and the interpretation of the present invention is not limited. It is not limited.

  In the present invention and each drawing, the same reference numerals are given to the same elements as those described above with reference to the previous drawings, and the detailed description may be omitted as appropriate.

  FIG. 1 is a diagram illustrating a configuration example of a display device. The display device 1 includes an image signal output unit 1a, a conversion unit 1b, and a display panel 200. The image signal output unit 1a outputs an image signal d1 (first image signal). The display panel 200 includes a first subpixel, a second subpixel, a third subpixel, and a fourth subpixel that display the first color, the second color, the third color, and the fourth color. . In the present embodiment, for example, the first color is red (R), the second color is green (G), the third color is blue (B), and the fourth color is white (W). Note that the fourth color may be a color other than white, such as yellow (Y), as long as it has a higher luminance than the first to third colors.

  The converter 1b expands the image signal d1 and converts it into an image signal d2 (second image signal). For example, when the image signal d1 has input signal values of the first subpixel to the third subpixel, the conversion unit 1b converts the image signal d1 and outputs the output signal values of the first subpixel to the fourth subpixel. An image signal d2 having the same is generated. In addition, the conversion unit 1b extends the luminance of the image signal d2 beyond a color space where the original color does not change even when a fourth subpixel (W subpixel in the present embodiment) is added.

  Here, FIG. 1 shows a color space expressed from saturation and luminance, where the horizontal axis represents saturation and the vertical axis represents luminance (the luminance of the image signal d2). A color space (extended color space) in which the original color does not change even if the fourth subpixel (W subpixel in the present embodiment) is added is shown by a graph ga. In the graph ga, the luminance of the image signal d2 at the saturation Sa0 is the luminance br1 (can be output up to the luminance br1).

  On the other hand, the conversion unit 1b extends the luminance of the image signal d2 beyond a color space where the original color does not change even when a white (W) subpixel is added. For example, the conversion unit 1b extends the luminance of the image signal d2 at the saturation Sa0 to the luminance br2 (> br1).

  A color space (virtual extended color space) expanded beyond a color space in which the original color does not change even when such a white (W) subpixel is added is shown by a dotted line graph gb in the drawing. The graph gb can be regarded as a virtual color space obtained by expanding the color space of the graph ga. The conversion unit 1b extends the luminance of the image signal beyond the color space in which the original color does not change even if a white (W) subpixel is added within the expanded virtual color space.

  As described above, the display device 1 has a function of extending the luminance of the image signal d2 beyond the color space of the RGBW panel. When the luminance of the image signal d2 is expanded, the luminance of the light source that illuminates the display panel is reduced according to the expansion amount.

  As a result, the luminance of the light source such as a backlight that illuminates the display panel can be lowered by the amount corresponding to the increase in the luminance of the image signal, so that power consumption can be reduced. Alternatively, since the image brightness increases, it becomes possible to improve visibility (particularly outdoor visibility).

  Next, details of the operation of the present invention will be described. First, the configuration of the RGBW display device and the HSV color space reproduced by the display device will be described in detail.

  FIG. 2 is a diagram illustrating a hardware configuration example of the display device. The display device 100 includes a control unit 100a, a display driver IC (Integrated Circuit) 100b, a light source driver IC 100c, an input / output interface 100d, and a communication interface 100e, and signals are input / output to / from each other via a bus 100f. Connected as possible. Further, the display device 100 includes an image display panel 200 and a light source device 300.

  The control unit 100a includes a CPU (Central Processing Unit) 100a1, and the CPU 100a1 controls the entire apparatus. Such a control unit 100a further includes a RAM (Random Access Memory) 100a2 and a ROM (Read Only Memory) 100a3, to which a plurality of peripheral devices are connected.

  The RAM 100a2 is used as a main storage device of the display device 100. The RAM 100a2 temporarily stores at least part of an OS (Operating System) program and application programs to be executed by the CPU 100a1. The RAM 100a2 stores various data necessary for processing by the CPU 100a1.

  The ROM 100a3 is a read-only semiconductor storage device that stores an OS program, application programs, and fixed data that is not rewritten. Further, instead of the ROM 100a3 or in addition to the ROM 100a3, a semiconductor storage device such as a flash memory can be used as a secondary storage device.

  For example, a display driver IC 100b, a light source driver IC 100c, an input / output interface 100d, and a communication interface 100e are connected to the control unit 100a as peripheral devices.

  An image display panel 200 is connected to the display driver IC 100b. When the input signal is input, the display driver IC 100b executes a predetermined process to generate an output signal. The display driver IC 100b causes the image display panel 200 to display an image by outputting a control signal corresponding to the generated output signal to the image display panel 200.

  The light source driver IC 100c is connected to each light source 303 of the sidelight light source 302 included in the light source device 300 described later with reference to FIG. The light source driver IC 100 c drives the light source 303 according to the light source control signal and controls the luminance of the light source device 300.

  An input device for inputting user instructions is connected to the input / output interface 100d. For example, it is connected to an input device such as a keyboard, a mouse used as a pointing device, or a touch panel. The input / output interface 100d transmits a signal sent from the input device to the CPU 100a1 via the bus 100f.

  The communication interface 100e is connected to the network 1000. The communication interface 100e transmits / receives data to / from other computers or communication devices via the network 1000.

  The display device 100 can realize the processing functions of the present embodiment, for example, with the above hardware configuration.

  Next, the image display panel 200 included in the display device 100 will be described with reference to FIG. FIG. 3 is a diagram illustrating an example of a pixel array of an image display panel included in the display device.

  As shown in FIG. 3, the image display panel 200 has pixels 201 arranged in a two-dimensional matrix. The pixel 201 includes a first subpixel 202R, a second subpixel 202G, a third subpixel 202B, and a fourth subpixel 202W. In the case shown in FIG. 3, the first subpixel 202R displays red, the second subpixel 202G displays green, the third subpixel 202B displays blue, and the fourth subpixel 202W displays white. The colors of the first sub-pixel 202R, the second sub-pixel 202G, and the third sub-pixel 202B are not limited to this, and it is sufficient that colors such as complementary colors are different. Further, the color of the fourth sub-pixel 202W is not limited to white, and may be yellow, for example, and white is particularly effective for reducing power. The fourth subpixel 202W is preferably brighter than the first subpixel 202R, the second subpixel 202G, and the third subpixel 202B when irradiated with the same light source lighting amount. Hereinafter, when it is not necessary to distinguish the first subpixel 202R, the second subpixel 202G, the third subpixel 202B, and the fourth subpixel 202W, they are referred to as subpixels 202.

  More specifically, the image display panel 200 is a transmissive color liquid crystal display panel, and a red color is provided between the first sub-pixel 202R, the second sub-pixel 202G, the third sub-pixel 202B, and the image observer. Color filters that pass green, blue are disposed. Further, no color filter is disposed between the fourth sub-pixel 202W and the image observer. The fourth subpixel 202W may be provided with a transparent resin layer instead of the color filter. By providing the transparent resin layer in this way, it is possible to suppress the occurrence of a large step in the fourth subpixel 202W by not providing the color filter in the fourth subpixel 202W.

  The image display panel 200 including such a configuration is connected to the image display panel driving unit 400, and the image display panel 200 is controlled by the image display panel driving unit 400.

  The image display panel driving unit 400 has at least a part of its functions realized by the display driver IC 100b, and includes a signal output circuit 410 and a scanning circuit 420.

  The signal output circuit 410 and the scanning circuit 420 are electrically connected to the first to fourth subpixels 202R, 202G, 202B, and 202W of the image display panel 200 through the signal line DTL and the signal line SCL, respectively. . The sub-pixel 202 is connected to the signal line DTL and is connected to the signal line SCL via a switching element (for example, a thin film transistor TFT). The image display panel driving unit 400 controls the operation (light transmittance) of the sub-pixel 202 by selecting the sub-pixel 202 by the scanning circuit 420 and sequentially outputting output signals from the signal output circuit 410.

  Next, the light source device 300 included in the display device 100 will be described with reference to FIG. FIG. 4 is a diagram illustrating a configuration example of a light source device included in the display device.

  The light source device 300 (backlight) is disposed on the back surface of the image display panel 200 illustrated in FIG. 3 and illuminates the image display panel 200 by irradiating light toward the image display panel 200. Such a light source device 300 includes a light guide plate 301, a sidelight light source 302 in which at least one side surface of the light guide plate 301 is an entrance surface E, and a plurality of light sources 303 are arranged at positions facing the entrance surface E, and a sidelight A light source device driving unit 500 that drives the light source 302. The plurality of light sources 303 are light-emitting diodes (LEDs) of the same color (for example, white), and can control the current or the duty ratio independently of each other. The light sources 303 are arranged along one side surface of the light guide plate 301. When the direction in which the light sources 303 are arranged is the light source arrangement direction LY, the light source 303 is directed from the incident surface E toward the light incident direction LX orthogonal to the light source arrangement direction LY. Incident light from the light source 303 enters the light guide plate 301.

  The light source device driving unit 500 has at least a part of its functions realized by the light source driver IC 100 c and is connected to each light source 303 of the sidelight light source 302. The light source device driving unit 500 controls the light amount of the light source 303 and the luminance (light intensity) of the light source device 300 by adjusting the current or duty ratio supplied to the light source 303 based on the light source control signal.

  Next, functions of the display device 100 including the image display panel 200 and the light source device 300 will be described with reference to FIG.

  FIG. 5 is a diagram illustrating a configuration example of functions provided in the display device. The display device 100 includes an image output unit 110 and a signal processing unit 120, and inputs an output signal SRGBW to the image display panel drive unit 400 and a light source control signal SBL to the light source device drive unit 500, respectively.

  The image output unit 110 outputs the input signal SRGB (for example, the display gradation bit number is 8 bits) to the signal processing unit 120. The input signal SRGB includes an input signal value x1 (p, q) for the first primary color, an input signal value x2 (p, q) for the second primary color, and an input signal value x3 (p, q) for the third primary color. . Assume that the first primary color is red, the second primary color is green, and the third primary color is blue.

  The signal processing unit 120 supplies signals to the image display panel driving unit 400 that drives the image display panel 200 and the light source device driving unit 500 that drives the light source device 300. The signal processing unit 120 determines an index for adjusting the luminance of the pixels of the image display panel 200 (or an index for reducing the luminance of the light source device 300) according to the input signal SRGB, and the signal processing unit 120 of the light source device 300 according to the index. Luminance information for each pixel is calculated and reflected in an output signal SRGBW (for example, the display gradation bit number is 8 bits) to control image display on the image display panel 200. The output signal SRGBW includes an output signal value X1 (p, q) of the first subpixel 202R, an output signal value X2 (p, q) of the second subpixel 202G, and an output signal value X3 (p of the third subpixel 202B). , Q), the output signal value X4 (p, q) of the fourth sub-pixel 202W that displays the fourth color is included. Assume that the fourth color is white. An index for adjusting the luminance of the pixel will be described later.

  Such processing operation of the signal processing unit 120 is realized by the display driver IC 100b or the CPU 100a1 shown in FIG.

  When the display driver IC 100b is used, the input signal SRGB is input to the display driver IC 100b via the CPU 100a1. The display driver IC 100b generates an output signal SRGBW and controls the image display panel 200. Further, a light source control signal SBL is generated and sent to the light source driver IC 100c via the bus 100f.

  When realized by the CPU 100a1, the output signal SRGBW is input from the CPU 100a1 to the display driver IC 100b. The light source control signal SBL is also generated by the CPU 100a1 and sent to the light source driver IC 100c via the bus 100f.

  Next, the case where the expansion coefficient α is used as an index as an index for improving the luminance of the pixel or the index for reducing the luminance of the light source device 300 will be described with reference to FIG.

  FIG. 6 is a conceptual diagram of a reproduction HSV color space that can be reproduced by a display device. In the display device 100, by providing the pixel 201 with the fourth sub-pixel 202 </ b> W that outputs the fourth color (white), the dynamic range of brightness in the reproduction HSV color space that can be reproduced by the display device 100 can be expanded. H represents hue, S represents saturation, and V represents lightness (Value (also referred to as Value of Brightness in this specification)).

  The reproduction HSV color space to which the fourth color is added is a cylindrical shape that can be displayed by the first subpixel 202R, the second subpixel 202G, and the third subpixel 202B, as shown in FIG. The HSV color space has a shape in which a solid body having a substantially trapezoidal shape in which the maximum value of the lightness V decreases as the saturation S increases. The signal processing unit 120 stores a maximum value Vmax (S) of lightness V with the saturation S in the reproduction HSV color space expanded by adding the fourth color as a variable. That is, the signal processing unit 120 stores the value of the maximum value Vmax (S) of the brightness V for each of the coordinates (values) of the saturation S and the hue H with respect to the three-dimensional shape of the reproduction HSV color space shown in FIG. Yes.

  Since the input signal SRGB is a signal having input signal values corresponding to the first primary color, the second primary color, and the third primary color, the HSV color space of the input signal SRGB has a cylindrical shape, that is, FIG. The same shape as the cylindrical portion of the reproduction HSV color space shown in FIG. Therefore, the output signal SRGBW can be calculated as an expanded image signal obtained by expanding the input signal SRGB with respect to the reproduction HSV color space. This expanded image signal is expanded by the expansion coefficient α determined by comparing the lightness levels in the reproduction HSV color space. By expanding the signal level of the input image signal by the expansion coefficient α, the value of the fourth sub-pixel 202W can be increased, and the brightness of the entire image can be improved. At this time, since the luminance of the entire image is improved by the expansion coefficient α, the luminance of the light source device 300 is lowered to 1 / α, so that it is possible to display with the same luminance as the input signal SRGB.

  In the signal processing unit 120, when χ is a constant depending on the display device 100, the (p, q) -th pixel (or the first sub-pixel 202R, the second sub-pixel 202G, the third sub-pixel 202B, X1 (p, q) that is the output signal of the first subpixel 202R, X2 (p, q) that is the output signal of the second subpixel 202G, and X3 that is the output signal of the third subpixel 202B (P, q) can be expressed as follows using the expansion coefficient α and the constant χ. χ will be described later.

  X1 (p, q) = [alpha] .x1 (p, q)-[chi] .X4 (p, q) (1)

  X2 (p, q) = [alpha] .x2 (p, q)-[chi] .X4 (p, q) (2)

  X3 (p, q) = [alpha] .x3 (p, q)-[chi] .X4 (p, q) (3)

  Further, the output signal value X4 (p, q) can be obtained based on the product of Min (p, q) and the expansion coefficient α. Min (p, q) is the input signal value x1 (p, q) of the first subpixel 202R, the input signal value x2 (p, q) of the second subpixel 202G, and the input signal value x3 of the third subpixel 202B. It is the minimum value of (p, q). Specifically, the output signal value X4 (p, q) can be obtained based on the following equation (4).

  X4 (p, q) = Min (p, q) · α / χ (4)

  In Equation (4), the product of Min (p, q) and the expansion coefficient α is divided by χ, but the present invention is not limited to this. Further, the expansion coefficient α is determined for each image display frame.

  Hereinafter, these points will be described. In general, in the (p, q) th pixel, the input signal value x1 (p, q) of the first subpixel 202R, the input signal value x2 (p, q) of the second subpixel 202G, and the third subpixel 202B. The saturation S (p, q) and lightness V (S) (p, q) in the cylindrical HSV color space are based on the input signal SRGB including the input signal value x3 (p, q) of ), (6).

S (p, q) = (Max (p, q) −Min (p, q)) / Max (p, q)
... (5)

  V (S) (p, q) = Max (p, q) (6)

Note that Max (p, q) is the input signal value x1 (p, q) of the first subpixel 202R, the input signal value x2 (p, q) of the second subpixel 202G, and the input signal of the third subpixel 202B. It is the maximum value among the values x3 (p, q). Min (p, q) is the minimum value of the input values of the three sub-pixels as described above. The saturation S can take a value from 0 to 1, and the lightness V (S) can take a value from 0 to (2 ⁿ −1). n is the number of display gradation bits.

Here, no color filter is disposed in the fourth sub-pixel 202W that displays white. When the fourth sub-pixel 202W displaying the fourth color is irradiated with the same light source lighting amount, the first sub-pixel 202R displaying the first primary color, the second sub-pixel 202G displaying the second primary color, and the third sub-pixel 202G. Brighter than the third sub-pixel 202B displaying the primary color. A signal having a value corresponding to the maximum signal value of the output signal of the first subpixel 202R is input to the first subpixel 202R, and the signal value corresponding to the maximum signal value of the output signal of the second subpixel 202G is input to the second subpixel 202G. A first subpixel 202R included in the group of pixels 201 when a signal having a value is input and a signal having a value corresponding to the maximum signal value of the output signal of the third subpixel 202B is input to the third subpixel 202B. The luminance of the aggregate of the second subpixel 202G and the third subpixel 202B is BN _1-3 . Further, when the fourth luminance subpixel 202W when the signal having a value corresponding to the maximum signal value of the output signal of the fourth sub-pixel 202W included in the group of pixels 201 or the pixel 201 is input to the BN ₄ Suppose. That is, the first sub-pixel 202R, white maximum luminance is displayed by the aggregate of the second sub-pixel 202G and the third sub-pixel 202B, the luminance of the white is represented by BN _1-3. Then, the constant χ depending on the display device 100 is expressed by χ = BN ₄ / BN _1-3 .

  By the way, when the output signal value X4 (p, q) is given by the above equation (4), the maximum value Vmax (S) of the brightness V with the saturation S in the reproduction HSV color space as a variable is expressed by the following equation: (7) and (8).

If S ≦ S0,
Vmax (S) = (χ + 1) · (2 ⁿ −1) (7)

When S0 <S ≦ 1,
Vmax (S) = (2 ⁿ −1) · (1 / S) (8)
Here, S0 = 1 / (χ + 1), and the saturation is such that the lightness V in FIG.

  The maximum value Vmax (S) of the lightness V with the saturation S in the reproduction HSV color space obtained by adding the fourth color as a variable is, for example, a kind of lookup for the signal processing unit 120. Stored as a table. Alternatively, the maximum value Vmax (S) of the lightness V with the saturation S in the reproduction HSV color space as a variable is obtained in the signal processing unit 120 each time.

  The expansion coefficient α is a coefficient for expanding the lightness V (S) in the HSV color space to the reproduction HSV color space, and can be expressed by the following equation (9).

  α (S) = Vmax (S) / V (S) (9)

  In the expansion calculation, for example, the expansion coefficient α is determined based on α (S) obtained in the plurality of pixels 201.

  Next, a configuration example of functions included in the signal processing unit 120 will be described with reference to FIG.

  FIG. 7 is a diagram illustrating an example of functions provided in the signal processing unit of the display device. The signal processing unit 120 of the display device 100 includes an image input I / F (interface) unit 121, a frame memory 122, a gamma conversion unit 123, an expansion coefficient generation unit 124, an RGBW generation unit 125, and an inverse gamma conversion unit. 600, a D / A converter (DAC) 126, and an output amplifier 127.

  The image input I / F unit 121 receives an input signal SRGB and performs input interface processing.

  The frame memory 122 stores the input signal SRGB in units of frames. The input signal SRGB read from the frame memory 122 is output to the gamma conversion unit 123.

  The gamma conversion unit 123 converts the input signal SRGB (gamma conversion) so that the brightness with respect to the input signal value (gradation value) when the input signal SRGB is input changes linearly. In this specification, the brightness after gamma conversion is referred to as luminance. When the RGBW generation unit 125 described later generates an output signal SRGBW from the input signal SRGB to increase the luminance, if the input signal SRGB does not have linearity, the generated output signal SRGBW is appropriately generated. I can't. Therefore, the input signal SRGB is converted so as to have linearity. The gamma converted input signal SRGB is output to the expansion coefficient generation unit 124 and the RGBW generation unit 125.

  The expansion coefficient generation unit 124 first converts the input signal SRGB into a signal in the HSV space, performs gamma conversion of the input signal in the HSV space, and calculates the expansion coefficient α from the image signal in the HSV space after the gamma correction. The calculated expansion coefficient α is output to the RGBW generator 125 and the light source device driver 500.

  The RGBW generation unit 125 outputs an output signal SRGBW (for example, the number of display gradation bits is 16 bits) using the expansion coefficient α output from the expansion coefficient generation unit 124 with respect to the input signal SRGB.

  The inverse gamma conversion unit 600 includes an LUT holding unit 630 that holds a lookup table (LUT) for each gamma value. The inverse gamma conversion unit 600 refers to a lookup table corresponding to the gamma value to be converted, and converts the output signal SRGBW to a state before the input signal SRGB is converted by the gamma conversion unit 123 (inverse gamma conversion). For example, the inverse gamma conversion unit 600 can convert the output signal SRGBW having a display gradation bit number of 16 bits into an 8-bit output signal SRGBW that is the display gradation bit number before the gamma conversion of the input signal SRGB. .

  The D / A converter 126 converts the output signal SRGBW output from the inverse gamma conversion unit 600 into an analog image signal.

  The output amplifier 127 amplifies the level of the analog image signal and outputs it to the image display panel driving unit 400.

  Hereinafter, problems to be solved by the present invention will be described. As described above, in the RGBW system display device, the color space as shown in FIG. 6 is defined, and the luminance (brightness) of the screen is improved so that the saturation falls within the area of the color space. An image quality equivalent to that of a general RGB panel not including W pixels is realized.

  On the other hand, in such an RGBW-type display device, the luminance of the light source device that illuminates the liquid crystal panel is lowered by the amount that improves the luminance of each RGBW pixel, thereby reducing the power consumption of the entire device. Even if the image quality is slightly reduced, there are many requests for further reduction of power consumption.

  The present invention has been made in view of these points, and performs display control that promotes reduction of power consumption. In addition, display control is performed to improve visibility.

  Next, the display device of the present invention will be described below. First, the RGBW color space that can be reproduced by the display device will be described.

  8 and 9 are diagrams showing the RGBW color space. The horizontal axis is saturation and the vertical axis is luminance. The RGBW color space shown in FIG. 8 corresponds to the cross-sectional view of the HSV space in FIG. 6, and is a color space expressed by saturation and luminance.

  Note that the luminance Lx is the maximum luminance that the RGBW color space can output. The luminance L0 is the maximum luminance that can be output in an RGB color space that does not include W pixels.

  8 and 9, the horizontal axis represents saturation and the vertical axis represents luminance. A graph g11 shows a normal RGBW color space, and a graph g12 shows an image analysis result when luminance is analyzed for a certain image. Further, the graph g13 shows α-fold luminance obtained by expanding the luminance of the image analysis result by the expansion coefficient α.

  In the graph g11, the color of the lower region surrounded by the straight line ka having a constant luminance in the range from 0 to Sa1 and the variable luminance curve kb in the range from the Sa1 to 256 does not change in color. An area in which the luminance can be changed in a state where it does not collapse is shown. A lower area surrounded by the straight line ka and the curve kb is a color space defined by the RGBW display device.

  In the RGBW color space, the luminance is usually set and used in a state that does not exceed the luminance of the straight line ka and the curve kb. Therefore, for example, when it is desired to brighten the screen even if the image quality is lowered, it is possible to deal with it by increasing the luminance to a point exceeding the curve kb.

  Here, in the low saturation region of the RGBW color space, more W pixels can be used than in the high saturation region. For this reason, even if the maximum luminance that can be output in the RGB color space is L0, in the RGBW color space, it is possible to output up to a larger luminance Lx (> L0). Therefore, in the low saturation region of the RGBW color space, the luminance that can be displayed on the RGBW panel can be raised to the limit luminance Lx.

  For this reason, in the low saturation region, the luminance cannot be further increased beyond the luminance Lx corresponding to the straight line ka. Therefore, if the luminance is increased beyond the luminance Lx, the gradation cannot be maintained. High gradation collapse will occur.

  On the other hand, in the medium saturation region to the high saturation region, it is not possible to increase the luminance while maintaining the color, but if the color retention is not taken into consideration, it is possible to increase the output luminance while maintaining the gradation. .

  For example, the current maximum luminance of the saturation Sa2 having the intermediate saturation region is the luminance L1, but when the change of the color of the saturation Sa2 is allowed, the luminance L1 is maintained exceeding the curve kb while maintaining the gradation. It is possible to raise it. In the example of FIG. 8, the luminance L1 is increased to the luminance L2, but in this case, even if the color changes, the luminance gradation can remain.

  In FIG. 8, the α-fold luminance of the graph g13 is stored in the RGBW color space of the graph g11, and shows a state where the luminance is increased within a range not exceeding the RGBW color space.

  On the other hand, in FIG. 9, the α-fold luminance of the graph g13 protrudes from the RGBW color space of the graph g11, and shows a state where the luminance is increased beyond the RGBW color space.

  In this case, since the luminance protrudes from the RGBW color space, the color changes. However, since the luminance is increased within the range not exceeding the maximum luminance Lx, the luminance gradation can be expressed.

  FIG. 9 shows a range in which the luminance can be increased. With respect to the RGBW color space shown in FIG. 8, in the medium saturation region to the high saturation region, a portion where there is room for increasing the luminance while maintaining the gradation even if there is a color change is shown as a region r0.

Next, the virtual RGBW color space expanded by the present invention will be described. The RGBW color space of the present invention is an RGBW color space in which the original color does not change even when W pixels are added (corresponding to the virtual extended color space gb in FIG. 1).
FIG. 10 is a diagram showing function curves constituting the RGBW color space. The horizontal axis is saturation and the vertical axis is luminance. The graph g1 corresponds to the straight line ka in FIG. 8, and the graph g2 corresponds to the curve kb in FIG.

  If the function of the graph g1 is G1 and the function of the graph g2 is G2, the functions G1 and G2 can be expressed by the following equations (10) and (11).

  G1 = 1 + χ (10)

  G2 = 1 / (Vmax−β × Vmin) (11)

  Some of the parameters in the equation have been described above, but briefly described again. Χ is the ratio of the luminance of the W pixel to the luminance of the R, G, and B pixels. That is, χ = (brightness of W pixel) / {(brightness of R pixel) + (brightness of G pixel) + (brightness of B pixel)}.

  Further, Vmax is the maximum value of each luminance of R, G, and B in a certain pixel, and Vmin is the minimum value of each luminance of R, G, and B in a certain pixel.

  Furthermore, the coefficient β is an arbitrary value given from the outside (such as a host CPU), and is a coefficient that determines the value of the W pixel when generating the W pixel from the R, G, and B pixels. For example, in the normal RGBW color space, when β = 1, the minimum luminance value Vmin of the R, G, and B pixels is directly replaced with the luminance value of the W pixel.

  That is, β = 1 corresponds to the maximum replacement in which the minimum luminance value Vmin of the R, G, and B pixels is replaced by 100% with the luminance value of the W pixel. On the other hand, when β is decreased from 1, the replacement amount decreases as 100% replacement amount, for example, 95% replacement amount and 90% replacement amount.

  FIG. 11 is a diagram showing the RGBW color space. The horizontal axis is saturation and the vertical axis is luminance. On the graphs g1 and g2 shown in FIG. 10, the RGBW color space defined by the above formulas (10) and (11) is indicated by a thick solid line. As an example of the RGBW color space, a case where χ = 1 and β = 1 is shown.

  FIG. 12 is a diagram showing an extended virtual RGBW color space. The horizontal axis is saturation and the vertical axis is luminance. On the graphs g1 and g2 shown in FIG. 10, the expanded virtual RGBW color space defined and formed by the above equations (10) and (11) is indicated by a thick solid line.

  Here, in the RGBW color space shown in FIG. 8, the saturation range of the straight line ka is from saturation 0 to saturation Sa1, but for example, saturation Sa1 = 50.

  On the other hand, in the virtual RGBW color space shown in FIG. 12, the saturation range of the straight line kaa corresponding to the straight line ka is from saturation 0 to saturation Sa1a, but saturation Sa1a = 240.

  That is, in the color space shown in FIG. 12, the luminance of the intermediate saturation region or the luminance from the intermediate saturation region to the high saturation region can be output by changing the parameter setting (specifically, setting of the coefficient β). An extended RGBW color space is formed that can be increased to the maximum luminance level.

  Hereinafter, expanding the RGBW color space as described above is referred to as boost. The expanded virtual RGBW color space is called an RGBW boost color space.

  13 and 14 are diagrams showing the RGBW boost color space. The horizontal axis is saturation and the vertical axis is luminance. The graph g11 shows the RGBW color space, and the graphs g20a and g20b show the RGBW boost color space.

  The coefficient β of the normal RGBW color space can range from 0 to 1, but by setting the coefficient β to a value larger than 1, the RGBW color space is expanded to generate the RGBW boost color space. . The RGBW boost color space changes the size of the space to be boosted by changing the value of the coefficient β.

  The RGBW boost color space of the graph g20a shown in FIG. 13 is for β = 15, and the RGBW boost color space of the graph g20b shown in FIG. 14 is for β = 150. In this way, by increasing the value of the coefficient β, the RGBW boost color space becomes wider by extending the horizontal straight line portion parallel to the x-axis.

  FIG. 15 shows a state in which the luminance is increased in the RGBW boost color space. The horizontal axis is saturation and the vertical axis is luminance. The graph g20 shows the RGBW boost color space. Further, the graph g12 is an image analysis result, and the graph g13 is α-times luminance.

  By calculating the expansion coefficient α in the RGBW boost color space, it is possible to obtain the maximum value of the expansion coefficient α that can maintain the gradation although the color changes. That is, it is possible to set the maximum α-fold luminance that falls within the RGBW boost color space.

  In this way, the luminance of the intermediate saturation region or the luminance from the intermediate saturation region to the high saturation region is increased to a level equivalent to the luminance level that the low saturation region can output.

  The color space when such luminance expansion is performed can be regarded as an RGBW boost color space that is a virtual RGBW color space obtained by extending the normal RGBW color space of the display panel. Then, the image luminance is expanded in the range of the RGBW boost color space beyond the RGBW color space.

  By performing the control as described above, it is possible to increase the RGBW luminance while maintaining the luminance gradation in the intermediate saturation region or the intermediate saturation region to the high saturation region.

  Therefore, by increasing the expansion coefficient α in the RGBW boost color space and increasing the image brightness, the brightness of the light source device can be reduced more than before, and the power consumption can be further reduced. become. Further, since the image brightness is increased, it is possible to improve the visibility in the outdoors.

  Here, output luminance (maximum luminance Vmax and minimum luminance Vmin) in different saturation regions on the RGBW boost color space will be described.

  16 and 17 are diagrams showing output luminance in the RGBW boost color space. The horizontal axis is the input gradation, and the vertical axis is the luminance. The state before and after extending | stretching a brightness | luminance with the expansion | extension coefficient (alpha) in case saturation is zero (Vmax = Vmin) is shown. Note that the input gradation is in the range of 0 to 256.

  FIG. 16 shows a state before the luminance is expanded by the expansion coefficient α. When the saturation = 0, the input gradation increases as the luminance of the graph gv increases.

  FIG. 17 shows a state after the luminance is expanded by the expansion coefficient α. It can be seen that the luminance of the graph gva expanded α times with the expansion coefficient α is collapsed on the high gradation side as the luminance value increases when the saturation = 0.

  18 and 19 are diagrams showing output luminance in the RGBW boost color space. The horizontal axis is the input gradation, and the vertical axis is the luminance. The state before and after extending | stretching a brightness | luminance with the expansion | extension coefficient (alpha) in case saturation is intermediate | middle saturation (Vmax> Vmin) is shown. Note that the input gradation is in the range of 0 to 256.

  FIG. 18 shows a state before the luminance is expanded by the expansion coefficient α. In the case of intermediate saturation, as the maximum luminance (Vmax) of the graph gmax1 and the minimum luminance (Vmin) of the graph gmin1 increase, The gradation is also increasing.

  FIG. 19 shows a state after the luminance is expanded by the expansion coefficient α. The maximum luminance of the graph gmax1a expanded by α times with the expansion coefficient α is crushed on the high gradation side as the luminance value increases in the case of intermediate saturation.

  On the other hand, the minimum luminance of the graph gmin1a expanded by α times with the expansion coefficient α is intermediate gradation, and as the luminance value increases, gradation collapse does not occur and the luminance gradation remains. .

  20 and 21 are diagrams showing output luminance in the RGBW boost color space. The horizontal axis is the input gradation, and the vertical axis is the luminance. The state before and after extending | stretching a brightness | luminance by the expansion | extension coefficient (alpha) in case saturation is the maximum (Vmin = 0) is shown. Note that the input gradation is in the range of 0 to 256.

  FIG. 20 shows a state before the luminance is expanded by the expansion coefficient α. In the case of maximum saturation, the input gradation increases as the maximum luminance (Vmax) of the graph gmax2 increases.

  FIG. 21 shows a state after the luminance is expanded by the expansion coefficient α. When the maximum luminance of the graph gmax2a expanded α times with the expansion coefficient α is the maximum saturation, the high gradation side is crushed as the luminance value increases.

  Next, switching control to the extended mode of the RGBW color space will be described. As a switching control between the mode using the RGBW color space (first mode) and the mode using the RGBW boost color space (second mode), for example, a normal mode in which the RGBW color space is displayed by user setting To the boost mode for displaying the RGBW boost color space.

  That is, it is configured to switch from the RGBW color space to the preset RGBW boost color space based on a manual operation from the user.

  Such control makes it possible to easily switch to the low power consumption mode by a user operation. Note that it is possible to switch from the RGBW boost color space to the RGBW color space according to user settings.

  Alternatively, the conversion unit 1b monitors the luminance of the light source device, and displays the RGBW boost color space from the normal mode for displaying the RGBW color space when the luminance of the light source device exceeds a predetermined threshold. Switch to boost mode. Such control makes it possible to automatically switch to the low power consumption mode.

  In addition, when the brightness | luminance of a light source device is less than a threshold value, it is also possible to switch from the boost mode which displays RGBW boost color space to the normal mode which displays RGBW color space.

  Next, variable setting of the luminance expansion amount will be described. In the present invention, as shown in FIGS. 13 and 14, by setting the coefficient β to a value larger than 1, the luminance expansion amount is variably set.

  For example, the first expansion amount corresponds to the RGBW boost color space when the saturation range of the straight line kaa (FIG. 12) is from saturation = 0 to saturation = 200, and this is the boost mode level. Let Lv1.

  Further, the second expansion amount corresponds to the RGBW boost color space when the saturation range of the straight line kaa is changed from saturation = 0 to saturation = 220, and this is the boost mode level Lv2.

  Further, the third expansion amount corresponds to the RGBW boost color space when the saturation range of the straight line kaa is changed from saturation = 0 to saturation = 240, and this is set as the boost mode level Lv3 ( Saturation values are an example).

  Thus, a plurality of boost modes can be set, and the RGBW boost color space can be set flexibly by switching to a desired boost mode.

  In addition, as switching control between boost modes, it can be set as the structure switched from one boost mode to the other boost mode by a user setting.

  For example, the boost mode level Lv1 is switched to the boost mode level Lv2 based on a manual operation from the user (the reverse switching from the boost mode level Lv2 to the boost mode level Lv1 is also possible).

  Alternatively, the converter 1b may be configured to monitor the luminance of the light source device and switch the boost mode level step by step by comparing a plurality of threshold values having different values with the monitor value.

  For example, when the monitor value of the luminance of the light source device exceeds the first threshold value, the boost mode level Lv1 is set, and when the monitor value exceeds the second threshold value (> first threshold value). Is control to shift to the boost mode level Lv2.

  Note that if the monitor value transitions to a state where it is below the second threshold and exceeds the first threshold, the boost mode level Lv2 is switched to the boost mode level Lv1.

  Such control makes it possible to adaptively and efficiently switch to the low power consumption mode based on the luminance of the light source device.

  Next, simulation results comparing the PWM (Pulse Width Modulation) value of the light source device in the RGBW color space and the PWM value of the light source device in the RGBW boost color space will be described.

  The luminance of the light source device is controlled by the PWM value and is changed according to the displayed image. Further, when the brightness of the RGBW pixel is increased to increase the screen brightness, the PWM value is reduced, and the brightness of the light source device is decreased accordingly to maintain the original screen brightness.

  Here, in a normal RGBW color space as shown in FIG. 8, when 1020 images are displayed, the average of the PWM values of each image and 1020 images for the RGBW boost color space. A value obtained by simulating the PWM value of each image when displayed was obtained by simulation.

  In a normal RGBW color space, the average value of the PWM values of each image when displaying 1020 images was 162.12. This value of 162.12 is assumed to be 100% power consumption.

  On the other hand, first to third RGBW boost color spaces were set as the RGBW boost color spaces. The second RGBW boost color space is obtained by boosting the spatial region wider than the first RGBW boost color space, and the third RGBW boost color space is wider than the second RGBW boost color space. It is a boosted one.

  That is, the luminance expansion amount in the third RGBW boost color space is the largest, the luminance expansion amount in the second RGBW boost color space is the next largest, and the luminance expansion in the first RGBW boost color space is The amount is the smallest.

  Then, when the average PWM value of each image when displaying 1020 images in the first RGBW boost color space was obtained, it was 140.69. The power consumption at this time is 86.78%.

  Further, when the average value of the PWM values of each image when displaying 1020 images in the second RGBW boost color space is obtained, it is 138.09 and the power consumption is 85.18%. Further, when the average value of the PWM values of each image when displaying 1020 images in the third RGBW boost color space is obtained, it is 136.42, and the power consumption is 84.03%.

  Thus, the power consumption in the first RGBW boost color space is approximately -13% lower than the power consumption in the normal RGBW color space. In addition, in the second RGBW boost color space, a low power consumption of about −15% is achieved, and in the third RGBW boost color space, a low power consumption of about −16% is achieved. I understand.

  Next, the configuration of the display device having the RGBW boost control function of the present invention will be described. FIG. 24 is a diagram illustrating a configuration example of a display device. The display device 10 includes a gamma (γ) conversion unit 11, an image processing unit 12, an inverse gamma (1 / γ) conversion unit 13, a display panel control unit 14, a display panel 15, a light source device control unit 16, and a light source device (for example, Backlight) 17 is provided.

  The gamma conversion unit 11 includes the function of the image signal output unit 1a in FIG. The image processing unit 12 includes the function of the conversion unit 1b in FIG.

  For example, each of R (first subpixel), G (second subpixel), and B (third subpixel) gamma-converts an 8-bit input RGB signal, A 16-bit RGB signal (first image) is output.

  When the image processing unit 12 receives the RGB signal output from the gamma conversion unit 11, the image processing unit 12 calculates the expansion coefficient α (for example, 10 bits, 8 bits after the decimal point) and further controls the luminance of the light source device 17. A control signal (PWM value) is generated.

  Further, the image processing unit 12 generates a W (fourth subpixel) signal based on the expansion coefficient α, and each of R, G, B, and W is, for example, a 16-bit RGBW signal (second image). Is output. Note that, as described above, the image processing unit 12 has a function of extending the luminance of the second image beyond the color space of the RGBW panel. Further, when the luminance of the RGBW signal is expanded, the image processing unit 12 generates a PWM value for reducing the luminance of the light source device 17 according to the expansion amount.

  The inverse gamma conversion unit 13 performs inverse gamma conversion on the RGBW signal output from the image processing unit 12, and each of R, G, B, and W generates, for example, an 8-bit RGBW signal. The display panel control unit 14 D / A converts the output signal from the inverse gamma conversion unit 13 to generate an analog signal, and causes the display panel 15 to optically output an image signal based on the voltage of the analog signal.

  The light source device control unit 16 generates a drive signal for causing the light source device 17 to emit light based on the PWM value output from the image processing unit 12 and supplies the drive signal to the light source device 17.

  Note that the processing functions of the display device of the present invention described above can be realized by a computer. In that case, a program describing the processing contents of the functions that the display device should have is provided. By executing the program on a computer, the above processing functions are realized on the computer. The program describing the processing contents can be recorded on a computer-readable recording medium.

  Examples of the computer-readable recording medium include a magnetic storage device, an optical disk, a magneto-optical recording medium, and a semiconductor memory. Examples of the magnetic storage device include a hard disk drive (HDD), a flexible disk (FD), and a magnetic tape. Optical discs include DVD (Digital Versatile Disc), DVD-RAM, CD-ROM (Compact Disc ROM), CD-R (Recordable) / RW (Rewritable), and the like. Magneto-optical recording media include MO (Magneto-Optical disk).

  When distributing the program, for example, a portable recording medium such as a DVD or a CD-ROM in which the program is recorded is sold. It is also possible to store the program in a storage device of a server computer and transfer the program from the server computer to another computer via a network.

  The computer that executes the program stores, for example, the program recorded on the portable recording medium or the program transferred from the server computer in its own storage device.

  Then, the computer reads the program from its own storage device and executes processing according to the program. The computer can also read the program directly from the portable recording medium and execute processing according to the program. In addition, each time a program is transferred from a server computer connected via a network, the computer can sequentially execute processing according to the received program.

  In addition, at least a part of the above processing functions can be realized by an electronic circuit such as a DSP (Digital Signal Processor), an ASIC (Application Specific Integrated Circuit), or a PLD (Programmable Logic Device).

  In the scope of the idea of the present invention, those skilled in the art can conceive various changes and modifications, and it is understood that these changes and modifications also belong to the scope of the present invention. For example, those in which the person skilled in the art has appropriately added, deleted, or changed the design of the above-described embodiments, or those in which processes have been added, omitted, or changed conditions are also included in the gist of the present invention. As long as it is included in the scope of the present invention.

(1) One aspect of the disclosed invention is
A first subpixel that displays the first color, a second subpixel that displays the second color, a third subpixel that displays the third color, and a fourth subpixel that displays the fourth color. A display panel having
An image signal output unit that outputs a first image signal having input signal values of the first subpixel to the third subpixel;
A conversion unit that decompresses the first image signal and converts the first image signal into a second image signal having output signal values of the first to fourth subpixels;
With
The converter is
A first mode in which the luminance of the first image signal is expanded into a first color space in which color does not change and converted into the second image signal;
A second mode in which the luminance of the first image signal is expanded into a virtual second color space exceeding the first color space and converted into the second image signal;
It is a display apparatus which has.

(2) One aspect of the disclosed invention is as follows:
The conversion unit generates the virtual second color space increased to a maximum level that can be output by the display panel;
The display device according to (1).

(3) One aspect of the disclosed invention is as follows:
The conversion unit variably sets a luminance expansion amount of the second image signal;
The display device according to (1).

(4) One aspect of the disclosed invention is as follows:
A light source for illuminating the display panel;
When the luminance of the second image signal is expanded, the conversion unit reduces the luminance of the light source according to the expansion amount.
The display device according to (1).

(5) One aspect of the disclosed invention is
The display panel;
A light source for illuminating the display panel;
An expansion coefficient is calculated from the first image for the first subpixel, the second subpixel, and the third subpixel, a luminance control signal for controlling the luminance of the light source is generated, and based on the expansion coefficient An image processing unit for generating a second image having the first subpixel, the second subpixel, the third subpixel, and the fourth subpixel;
A light source control unit that generates a drive signal for controlling the light source based on the luminance control signal and supplies the drive signal to the light source;
The display device according to (1).

  DESCRIPTION OF SYMBOLS 1 ... Display apparatus, 1a ... Image signal output part, 1b ... Conversion part, d1 ... 1st image signal, d2 ... 2nd image signal, ga ... Extended color space, gb ... Virtual extension Color space, Sa0 ... saturation, br1, br2 ... luminance

Claims (5)

A first subpixel that displays the first color, a second subpixel that displays the second color, a third subpixel that displays the third color, and a fourth subpixel that displays the fourth color. A display panel having
An image signal output unit that outputs a first image signal having input signal values of the first subpixel to the third subpixel;
A conversion unit that decompresses the first image signal and converts the first image signal into a second image signal having output signal values of the first to fourth subpixels;
With
The converter is
A first mode in which the luminance of the first image signal is expanded into a first color space in which color does not change and converted into the second image signal;
A second mode in which the luminance of the first image signal is expanded into a virtual second color space exceeding the first color space and converted into the second image signal;
A display device. The conversion unit generates the virtual second color space increased to a maximum level that can be output by the display panel;
The display device according to claim 1. The conversion unit variably sets a luminance expansion amount of the second image signal;
The display device according to claim 1. A light source for illuminating the display panel;
When the luminance of the second image signal is expanded, the conversion unit reduces the luminance of the light source according to the expansion amount.
The display device according to claim 1. The display panel;
A light source for illuminating the display panel;
An expansion coefficient is calculated from the first image for the first subpixel, the second subpixel, and the third subpixel, a luminance control signal for controlling the luminance of the light source is generated, and based on the expansion coefficient An image processing unit for generating a second image having the first subpixel, the second subpixel, the third subpixel, and the fourth subpixel;
A light source control unit that generates a drive signal for controlling the light source based on the luminance control signal and supplies the drive signal to the light source;
The display device according to claim 1.

Images