JP2015203798A - Display device and display method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress an increase in power consumption while suppressing a decline in picture quality.SOLUTION: A display device comprises: a table holding unit for holding a table in which a plurality of input values, for which there are provided a first section in which the input values are placed in a row at prescribed intervals and a second section in which the input values are placed in a row at closer intervals than in the first section, are correlated with converted values of the plurality of input values that are converted by a first function; a signal conversion unit for referencing the table, specifying a section in which the input value of an input signal is located, accepting input of the input value of the input signal to a second function derived from the converted values located at both ends of the specified section, and converting the input value into an output signal; and an image display panel for outputting an image on the basis of the output signal.

Description

  The present technology relates to a display device and a display method.

  A display device including a liquid crystal display panel converts an input image signal into an output image signal corresponding to the input image signal using a graph indicating gamma characteristics of the liquid crystal display panel, and based on the converted output image signal Display an image.

  Further, the display device can use a graph (linear interpolation graph) obtained by linear interpolation between a plurality of coordinates (adjustment points) on the graph indicating the gamma characteristic for the conversion of the image signal (for example, , See Patent Document 1).

  Such a linear interpolation graph approximates the graph showing the gamma characteristic, and the error from the graph showing the gamma characteristic can be reduced as the number of adjustment points is increased.

JP 2011-209523 A

  However, when the number of adjustment points is increased, the linear interpolation graph increases the circuit size (area) and the power consumption because the number of circuits that hold the adjustment points increases. there were.

  On the other hand, if the number of adjustment points is decreased in order to suppress an increase in circuit scale, an error between the linear interpolation graph and the graph indicating the gamma characteristic increases. As a result, there is a problem in that a desired image quality cannot be obtained from an image displayed based on the output image signal converted by the linear interpolation graph.

  The technology of the present disclosure has been made in view of such a point, and provides a display device and a display method that suppress a decrease in image quality while suppressing an increase in power consumption.

  According to one aspect of the present invention, a plurality of input values provided with a first section in which input values are arranged at predetermined intervals and a second section in which input values are arranged at a denser interval than the first section, and the plurality of input values A table holding unit that holds a table that associates the converted values converted by the first function with reference to the table, specifies a section where the input value of the input signal is located, and is positioned at both ends of the specified section A display device comprising: a signal conversion unit that inputs an input value of the input signal to a second function derived from the converted value to be converted into an output signal; and an image display panel that outputs an image based on the output signal It is.

It is a figure which shows the display apparatus in 1st Embodiment. It is a figure which shows the hardware structural example of the display apparatus in 2nd Embodiment. It is a figure which shows the pixel array example of the image display panel contained in the display apparatus in 2nd Embodiment. It is a figure which shows the structural example of the planar light source device contained in the display apparatus in 2nd Embodiment. It is a figure which shows the structural example of the function with which the display apparatus in 2nd Embodiment is provided. It is a conceptual diagram of reproduction HSV color space reproducible with the display apparatus in 2nd Embodiment. It is a figure which shows the function example with which the signal processing part of the display apparatus in 2nd Embodiment is provided. It is a figure for demonstrating the reverse gamma conversion of the display apparatus in 2nd Embodiment. It is a figure which shows the example of a division | segmentation of the gradation value of the graph of an inverse gamma characteristic in 2nd Embodiment. It is a figure which shows an example of the look-up table contained in the display apparatus in 2nd Embodiment. It is a figure which shows the circuit structural example of the inverse gamma conversion part contained in the display apparatus in 2nd Embodiment.

Embodiments will be described below 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 modifications 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 clarity of explanation, but are merely examples, and the interpretation of the present invention may be It is not limited.

  In addition, in the present specification and each drawing, the same elements as those described above with reference to the previous drawings are denoted by the same reference numerals, and detailed description may be omitted as appropriate.

[First Embodiment]
The display device of the first embodiment will be described with reference to FIG.

  FIG. 1 is a diagram illustrating a display device according to the first embodiment.

  FIG. 1A shows a configuration example included in the display device 1, and FIG. 1B shows an example of a table included in the display device 1. FIG. 1C is a graph showing a converted signal obtained by converting the input signal by the first function with respect to the input signal. FIG. 1D is a graph showing the input signal converted by the second function with respect to the input signal. The graphs showing the output signals are shown respectively. In both FIG. 1C and FIG. 1D, the horizontal axis represents the input signal, and the vertical axis represents the converted / output signal obtained by converting the input signal by the first and second functions.

  As illustrated in FIG. 1A, the display device 1 includes a table holding unit 2, a signal conversion unit 3, and an image display panel 4.

  The table holding unit 2 includes a plurality of input values provided with a first section in which input values are arranged at predetermined intervals, and a second section in which input values are arranged at intervals closer to the first section, and a plurality of input values. A table in which conversion values converted by one function are associated is held. For example, in the table 2a illustrated in FIG. 1B held by the table holding unit 2, the input values a0 to a6 and the converted values b0 to b6 converted from the input values a0 to a6 are associated with each other. . The converted values b0 to b6 are converted from the input values a0 to a6 by, for example, a function F1 as shown in FIG. Note that coordinates A0 to A6 are coordinates based on the input values a0 to a6 and the converted values b0 to b6 of the function F1 (FIG. 1C). The input values a0 to a6 are extracted from the values indicated by the horizontal axis in FIG. The interval between the input values a0 and a1 arranged in the section (a0 ≦ X <a1) is narrower (fine) than the interval between the input values a1 and a2 arranged in the section (a1 ≦ X <a2). Similarly, the interval (a1 ≦ X <a2) is narrower than the interval (a2 ≦ X <a3). The interval (a2 ≦ X <a3) is narrower than the interval (a3 ≦ X <a4). The interval (a3 ≦ X <a4) is wider (sparse) than the interval (a4 ≦ X <a5). The interval (a4 ≦ X <a5) is wider than the interval (a5 ≦ X <a6). The interval between such sections is set, for example, by extracting the input values a1 to a6 so that the larger the absolute value of the slope of the function F1, the denser, and the smaller the absolute value of the slope, the sparse. The The table holding unit 2 can hold a plurality of tables 2a in accordance with the type of the function F1 as well as the one type of table 2a shown in FIG.

  The signal conversion unit 3 refers to the table 2a, identifies a section where the input value of the input signal is located, and inputs the input value of the input signal to the second function derived from the conversion values located at both ends of the identified section. To convert it to an output signal. Such a signal conversion unit 3 converts an input signal into an output signal according to, for example, display characteristics (gamma value) of an image display panel 4 described later. For example, when the signal conversion unit 3 refers to the table 2a (FIG. 1B) and specifies that the input value of the input signal is located in the section (a0 ≦ X <a1), the signal conversion section 3 is located at both ends of the section. The input signal is converted into an output signal by a function F2a (FIG. 1D) derived from the conversion values b0 and b1 (coordinates A0 and A1). The function F2a is derived from the coordinates A0 and A1 on the function F1, and approximates the function F1 in the section (a0 ≦ X <a1). Similarly, the function F2b is an interval (a1 ≦ X <a2), the function F2c is an interval (a2 ≦ X <a3), the function F2d is an interval (a3 ≦ X <a4), and the function F2e is an interval The function F2f of (a4 ≦ X <a5) approximates each function F1 of the section (a5 ≦ X <a6). When the table holding unit 2 holds a plurality of tables 2a in accordance with a plurality of types of functions F1, the signal conversion unit 3 selects the table 2a corresponding to the previously specified type of function F1. The above conversion can be performed using the selected table 2a.

  The image display panel 4 outputs an image based on the output signal (converted by the signal conversion unit 3).

  Next, a display method of the display device 1 including such a configuration will be described.

  In the display device 1, when the input value of the input signal is input, the signal conversion unit 3 refers to the table 2 a held by the table holding unit 2 and identifies the section of the input values a 0 to a 6 where the input value is located. To do. At this time, for example, when the signal conversion unit 3 specifies that the input value is located in the section (a0 ≦ X <a1), as shown in FIG. 1D, the conversion values b0 at both ends of the section are displayed. , B1 (coordinates A0, A1), an input signal is converted into an output signal by a function F2a (a0 ≦ X <a1).

  In this way, the signal conversion unit 3 converts the input signal into the output signal by the functions F2a to F2f in accordance with the section where the input value of the input signal is input, and the image display panel 4 is converted. An image is displayed based on the output signal.

  The functions F2a to F2f (second function) are derived from the converted values (coordinates) of the function F1 (first function) located at both ends of each section as described above, and approximate the function F1 in each section. To do. The input value indicated by the horizontal axis in FIG. 1C is such that the interval between each section is sparser as the absolute value of the slope of the function F1 is larger and denser, and as the absolute value of the slope of the function F1 is smaller. Extracting. For this reason, in particular, when the functions F2a to F2f are linear functions that pass through the converted values (coordinates) of the function F1 (first function) located at both ends of each section, the functions F2a to F2 that approximate the function F1. F2f reduces the error from the function F1 without increasing the number of input values to be extracted. Therefore, since the increase in the number of input values to be extracted is suppressed, the display device 1 can suppress the increase in the number of circuits and the circuit area, thereby suppressing an increase in power consumption. Further, the image displayed based on the output signal converted from the input signal by the functions F2a to F2f approximating the function F1 with the error from the function F1 reduced is close to the image of the output signal converted by the function F1. Image quality is maintained.

[Second Embodiment]
In the second embodiment, the first embodiment will be described more specifically as one form of the first embodiment.

  First, the hardware configuration of the display device according to the second embodiment will be described with reference to FIG.

  FIG. 2 is a diagram illustrating a hardware configuration example of the display device according to the second embodiment.

  The display device 100 includes a control unit 100a, a display driver IC (Integrated Circuit) 100b, an LED (Light Emitting Diode) driver IC 100c, an input / output interface 100d, and a communication interface 100e, and is mutually connected via a bus 100f. Are connected so that signals can be input and output. Further, the display device 100 includes an image display panel 200 and a planar 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, an LED 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 LED driver IC 100c is connected to each light source 303 of the sidelight light source 302 included in the planar light source device 300 described later with reference to FIG. The LED driver IC 100c drives the light source 303 according to the light source control signal, and controls the luminance of the planar 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 a pixel array example of an image display panel included in the display device according to the second embodiment.

  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 planar 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 planar light source device included in the display device according to the second embodiment.

  The planar light source device 300 is disposed on the back surface of the image display panel 200 shown in FIG. 3 and illuminates the image display panel 200 by irradiating light toward the image display panel 200. Such a planar 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. A planar light source device driving unit 500 that drives the sidelight 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 planar light source device driving unit 500 has at least part of its functions realized by the LED driver IC 100 c and is connected to each light source 303 of the sidelight light source 302. The planar light source device driving unit 500 controls the light amount of the light source 303 by adjusting the current or duty ratio supplied to the light source 303 based on the light source control signal, and the luminance (light intensity) of the planar light source device 300. To control.

  Next, functions of the display device 100 including the image display panel 200 and the planar 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 according to the second embodiment.

  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 planar 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 x _{1 (p, q)} for the first primary color, an input signal value x _{2 (p, q) for} the second primary color, and an input signal value x _{3 (p, q)} for the third primary color. Is included. In the second embodiment, 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 planar light source device driving unit 500 that drives the planar light source device 300. The signal processing unit 120 determines an index (or an index for reducing the luminance of the planar light source device 300) for adjusting the luminance of the pixels of the image display panel 200 according to the input signal SRGB, and the planar shape according to the index. Luminance information for each pixel of the light source device 300 is calculated and reflected in an output signal SRGBW (for example, the number of display gradation bits is 8 bits) to control image display on the image display panel 200. The output signal SRGBW includes the output signal value X _{1 (p, q)} of the first sub-pixel 202R, the output signal value X _{2 (p, q) of} the second sub-pixel 202G, and the output signal value X of the third sub-pixel 202B. _{In addition to 3 (p, q)} , the output signal value X _{4 (p, q) of} the fourth sub-pixel 202W that displays the fourth color is included. In the second embodiment, it is assumed 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, the light source control signal SBL is generated and sent to the LED 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 LED 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 planar 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 the display device according to the second embodiment.

  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. Note that H represents hue, S represents saturation, and V represents lightness (Value).

  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 for 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 an 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 subpixel 202W can be increased, and the luminance 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 surface light source device 300 is reduced 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, X _{1 (p, q)} that is the output signal of the _first subpixel 202R, the output signal of X _{2 (p, q)} that is the output signal of the second subpixel 202G, and the output signal of the third subpixel 202B. A certain X _{3 (p, q)} can be expressed as follows using the expansion coefficient α and the constant χ. χ will be described later.

X _{1 (p, q)} = α · x _{1 (p, q)} −χ · X _{4 (p, q)} (1)

X _{2 (p, q)} = α · x _{2 (p, q)} −χ · X _{4 (p, q)} (2)

X _{3 (p, q)} = α · x _{3 (p, q)} −χ · X _{4 (p, q)} (3)

Further, the output signal value X _{4 (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 of the first sub-pixel _{202R x 1 (p, q)} , the input signal value x _{2 (p, q)} of the second sub-pixel 202G and the input signal of the third sub-pixel 202B It is the minimum value among the values _{x3 (p, q)} . Specifically, the output signal value X _{4 (p, q)} can be obtained based on the following equation (4).

X _{4 (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. The expansion coefficient α is determined for each image display frame.

  Hereinafter, these points will be described.

Generally, in the (p, q) -th pixel, the input signal value x _{1 (p, q)} of the first sub-pixel 202R, the input signal value x _{2 (p, q) of} the second sub-pixel 202G, and the third sub-pixel Based on the input signal SRGB including the input signal value x3 _{(p, q)} of the pixel 202B, the saturation S _{(p, q)} and the lightness V (S) _{(p, q)} in the HSV color space of the cylinder are It can be obtained from (5) and (6).

S _{(p, q)} = (Max _{(p, q)} −Min _{(p, q)} ) / Max _{(p, q)} (5)

V (S) _{(p, q)} = Max _{(p, q)} (6)

Incidentally, Max _{(p, q)} is the input signal value of the first sub-pixel _{202R x 1 (p, q)} , the input signal value of the second subpixel 202G x _{2 (p, q)} and the third sub-pixel 202B This is the maximum value of the input signal values x _{3 (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 subpixel 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 X _{4 (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 It can represent with Formula (7) and (8).

If S ≦ S ₀ ,
Vmax (S) = (χ + 1) · (2 ⁿ −1) (7)

If S ₀ <S ≦ 1,
Vmax (S) = (2 ⁿ −1) · (1 / S) (8)
Here, S ₀ = 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 for 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 according to the second embodiment.

  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 (gamma conversion) the input signal SRGB so that the luminance (lightness) with respect to the input signal value (gradation value) when the input signal SRGB is input changes linearly. 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 planar 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 for 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. . Details of the inverse gamma conversion unit 600 will be described later.

  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.

  Next, the inverse gamma conversion unit 600 will be described.

  First, an inverse gamma characteristic when the inverse gamma conversion unit 600 performs conversion will be described with reference to FIG.

  FIG. 8 is a diagram for explaining the inverse gamma conversion of the display device according to the second embodiment. FIG. 8A shows an example of a graph of the inverse gamma characteristic related to a predetermined gamma value. B) shows graphs relating to the slope of the graph of FIG. 8A and 8B, the horizontal axis indicates the gradation value (for example, the output signal value of the output signal SRGBW), and the vertical axis indicates the normalized luminance value in FIG. 8A. B) represents the inclination.

  The inverse gamma conversion unit 600 performs inverse gamma conversion so that the output signal value (gradation value) of the output signal SRGBW becomes a luminance value obtained from the graph function (inverse gamma conversion function) shown in FIG. I do.

  The look-up table held by the LUT holding unit 630 included in the inverse gamma conversion unit 600 is a table in which correspondences between values before and after conversion by the inverse gamma conversion function are tabulated.

  Note that the inverse gamma conversion function has a different slope for each gradation value, as shown in FIG. As shown in FIG. 8B, the slopes with respect to the gradation values of 0-8192 and 57344-65536 are particularly large. On the other hand, the gradient of the inverse gamma conversion function with respect to the gradation values of 8192 to 57344, which is between them, is small.

  Next, the lookup table held by the LUT holding unit 630 in the case of the graph shown in FIG. 8A will be described with reference to FIGS. 9 and 10.

  FIG. 9 is a diagram illustrating an example of classification of gradation values in the inverse gamma characteristic graph according to the second embodiment. FIG. 10 is a diagram illustrating an example of a look-up table included in the display device according to the second embodiment. FIG. 10A illustrates the LUT_0 in FIG. ) Represents the case of LUT_13.

  As shown in FIG. 8B, the inverse gamma conversion function has a difference in the magnitude of the inclination (absolute value). Therefore, the lookup table is divided by decreasing the gradation value extraction interval as the inverse gamma conversion function has a larger inclination, and increasing the gradation value extraction interval as the inclination is smaller.

  As an example of the division shown in FIG. 9, when the gradation value is from 0 to 15, the gradient of the inverse gamma conversion function is large, so the interval is set to 1 and the gradation value range is LUT_0. As another example, when the gradation value is 16384 to 32767, since the gradient of the inverse gamma conversion function is small, the interval is set to 2048 (wider than the interval of LUT_0), and the gradation value range of LUT_13 is set. As described above, a range of gradation values of LUT_m (where m is 0 to 18) is set in accordance with the magnitude of the gradient of the inverse gamma conversion function.

  In such a lookup table, for example, in LUT_0, as shown in FIG. 10A, gradation values 0 to 15 (interval is 1) and gradation values 0 to 15 are converted by an inverse gamma conversion function. The brightness values (LUT_0 (n) (where n is 0 to 15 of the gradation value with an interval of 1)) obtained in this manner are associated with each other in a table form. In the LUT_13, as shown in FIG. 10B, the gradation values 16384 to 32767 (interval is 2048) and the luminance values (LUT_13 (n) obtained by converting the gradation values 16384 to 32767 with an inverse gamma conversion function. ) (Where n is a gradation value 16384 to 32767 with an interval of 2048)).

  The inverse gamma conversion unit 600 refers to such a lookup table, and specifies a section of the lookup table where the gradation value of the output signal SRGBW is located. The inverse gamma conversion unit 600 performs linear interpolation based on the luminance value of the inverse gamma conversion function at both ends of the specified section, generates a function (approximation function) that approximates the inverse gamma conversion function in the specified section, and outputs the function using the approximation function. The signal SRGBW is converted.

  Here, linear interpolation in the case of the second embodiment will be described.

  An approximate function obtained by linear interpolation using the luminance value of the inverse gamma conversion function at both ends of the section of the lookup table where the gradation value of the output signal SRGBW is located is calculated by the following equation.

Approximate function = [LUT_m (n + d) −LUT_m (n)] * X / d + LUT_m (n)
(10)
(Where m is an LUT number (m = 0 to 18), n is a gradation value, d is an interval of gradation values, and X is an output signal value (gradation value) of the output signal SRGBW− n (0 ≦ X <d).)

  For example, the approximate function when the output signal value (gradation value) of the output signal SRGBW is 2.5 is expressed as follows using Expression (10).

  Approximate function = [LUT — 0 (3) −LUT — 0 (2)] * (0.5) + LUT — 0 (2)

  Alternatively, the approximate function when the output signal value (gradation value) of the output signal SRGBW is 24580 is expressed as follows using Expression (10).

  Approximate function = [LUT — 13 (26624) −LUT — 13 (24576)] * (4/2048) + LUT — 13 (24576)

  Next, a specific example of such an inverse gamma conversion unit 600 will be described with reference to FIG.

  FIG. 11 is a diagram illustrating a circuit configuration example of the inverse gamma conversion unit included in the display device according to the second embodiment.

  The inverse gamma conversion unit 600 includes a gamma value selection unit 610, selectors 621-0 to 621-18, 622-0 to 622-18, 623-0 to 623-18 (collectively these are selectors 620), Converters 631-0 to 631-18, 632-0 to 632-18, 633-0 to 633-18, and a selector 640 are included. Further, inverse gamma conversion unit 600 includes storage units 650, 660, 670, multiplier 680, and adder 690.

  The gamma value selection unit 610 is preset with a gamma value to be subjected to inverse gamma conversion, and outputs a selection instruction signal for the gamma value.

  When the output signal SRGBW is input to the selector 620, the selectors 621-0 to 621-18, 622-0 to 622-18, 623-0 selected based on the selection instruction signal of the gamma value selector 610. The output signal SRGBW is output from ˜623-18.

  The converters 631-0 to 631-18, 632-0 to 632-18, 633-0 to 633-18 respectively convert LUT_0 to LUT_18 for each gamma value (for example, the gamma values are 2.2, γA, and γB). Hold. The converters 631-0 to 631-18, 632-0 to 632-18, 633-0 to 633-18 refer to the LUT — 0 to LUT — 18 for each held gamma value, and output output from the selector 620. The section (n, n + d) of the lookup table number (m) where the signal SRGBW is located is specified. The converters 631-0 to 631-18, 632-0 to 632-18, 633-0 to 633-18 are LUT_m (n) and LUT_m (n + d), which are values located at both ends of the specified section, and X / D is output.

  Based on the gamma value selection instruction signal from the gamma value selection unit 610, the selector 640 converts the converters 631-0 to 631-18, 632-0 to 632-18, 633-0 corresponding to the gamma value. Select 633-18. The selector 640 includes LUT_m (n) and LUT_m (n + d) output from the selected converters 631-0 to 631-18, 632-0 to 632-18, 633-0 to 633-18, and X / d Are output to the storage units 650, 660, and 670.

The storage unit 650 stores X output from the converter selected by the selector 640.
The storage unit 660 stores the difference between the LUT_m (n) and the LUT_m (n + d) output from the converter selected by the selector 640.
The storage unit 670 stores LUT_m (n) output from the converter selected by the selector 640.

Multiplier 680 multiplies X stored in storage unit 650 and LUT_m (n + d) −LUT_m (n) stored in storage unit 660.
Adder 690 adds LUT_m (n) stored in storage unit 670 and the multiplication result multiplied by multiplier 680 and outputs output signal SRGBW.

  With this configuration, the inverse gamma conversion unit 600 shares the storage units 650, 660, and 670, the multiplier 680, and the adder 690, and outputs an output signal according to the above equation (10) according to the designated gamma value. Inverse gamma conversion can be performed on SRGBW. For this reason, the inverse gamma conversion unit 600 can suppress an increase in circuit scale (number of circuits and circuit formation area).

  As described above, the approximation function is derived from the luminance values of the inverse gamma conversion function located at both ends of the gradation value interval, as described above, and approximates the inverse gamma conversion function in each interval. The output signal value (scale) of the output signal SRGBW is such that the interval between each section becomes denser as the absolute value of the gradient of the inverse gamma conversion function is larger and sparser as the absolute value of the gradient of the inverse gamma transformation function is smaller. Key value). Therefore, when the approximate function is a linear function that passes through the luminance values of the inverse gamma conversion function located at both ends of each section, the approximate function that approximates the inverse gamma conversion function is the number of output signal values to be extracted. The error with the inverse gamma conversion function is reduced without increasing. The interval between the sections can be set so that the error between the approximate function and the inverse gamma conversion function falls within a predetermined range. In general, a person is likely to notice a change in the image on the low gradation value side, and difficult to notice on the high gradation value side. For example, when there is an upper limit on the number of gradation value sections to be extracted using such a property, the floor is extracted so that it is dense on the low gradation value side and sparse on the high gradation value side. Try to balance the interval of the key value.

  Therefore, since the increase in the number of output signal values to be extracted is suppressed, the display device 100 can suppress an increase in circuit scale and an increase in power consumption. In addition, the image displayed based on the output signal SRGBW converted from the input signal SRGB by the approximation function with the error from the inverse gamma conversion function reduced is close to the image quality of the output signal converted by the inverse gamma conversion function. Is maintained.

  The above processing functions 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. Examples of the optical disc include a DVD (Digital Versatile Disc), a DVD-RAM (Random Access Memory), a CD-ROM (Compact Disc Read Only Memory), and a CD-R (Recordable) / RW (ReWritable). Magneto-optical recording media include MO (Magneto-Optical disk).

  When distributing the program, for example, portable recording media such as a DVD and a CD-ROM in which the program is recorded are 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 this embodiment, the case of a liquid crystal display device is illustrated, but as other application examples, other flat panel type devices such as other self-luminous display devices or electronic paper display devices having an electrophoretic element or the like are used. A display device is mentioned. Moreover, it cannot be overemphasized that it can apply, without specifically limiting from a small size to a large size.

  Within the scope of the idea of the present technology, 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 technology. For example, those in which the person skilled in the art appropriately added, deleted, or changed the design for each of the above-described embodiments, or added the process, omitted, or changed the conditions are also included in the present technology. As long as the gist is provided, it is included in the scope of the present technology.

  In addition, it is understood that other functions and effects brought about by the aspects described in the present embodiment are obvious from the description of the present specification, or can be appropriately conceived by those skilled in the art, brought about by the present technology. The

(1) One aspect of the disclosed invention includes a plurality of input values provided with a first section in which input values are arranged at a predetermined interval and a second section in which input values are arranged at a denser interval than the first section; A table holding unit that holds a table that associates the converted values obtained by converting the plurality of input values with a first function;
Referring to the table, the section where the input value of the input signal is located is specified, the input value of the input signal is input to the second function derived from the converted values located at both ends of the specified section, and the output signal A signal converter for converting into
An image display panel for outputting an image based on the output signal;
It is a display apparatus which has.

  (2) In one aspect of the disclosed invention, in the table, the absolute value of the slope of the first function in the second section is larger than the absolute value of the slope of the first function in the first section ( 1) The display device described above.

  (3) One aspect of the disclosed invention is the display device according to (1) or (2), wherein the second function is a linear function that passes through conversion values located at both ends of the specified section. .

  (4) According to one aspect of the disclosed invention, the second function is derived by linear interpolation using conversion values located at both ends of the specified section. It is a display device.

  (5) In one aspect of the disclosed invention, the table holding unit holds a plurality of the tables corresponding to a plurality of types of the first functions. Display device.

  (6) One aspect of the disclosed invention is the display device according to (5), wherein the signal conversion unit selects a table corresponding to the specified type of the first function from the table holding unit.

(7) In one embodiment of the disclosed invention, the input value is a gradation value,
The display device according to any one of (1) to (6), wherein the gradation value of the second section is denser than the gradation value of the first section.

  (8) One embodiment of the disclosed invention is the display device according to any one of (1) to (7), in which the input signal is adjusted based on an index for adjusting luminance of a pixel of the image display panel. It is.

(9) One embodiment of the disclosed invention is a display method of a display device including a table holding unit and a signal conversion unit.
The signal converter is
A plurality of input values provided with a first section in which input values are arranged at a predetermined interval and a second section in which input values are arranged at a denser interval than the first section, and the plurality of input values are converted by a first function. Refer to the table held by the table holding unit in association with the conversion value,
Identify the section where the input value of the input signal is located, input the input value of the input signal to the second function derived from the conversion values located at both ends of the identified section, and convert it to an output signal,
Based on the output signal, an image is output.
It is a display method.

  DESCRIPTION OF SYMBOLS 1 ... Display apparatus 2 ... Table holding | maintenance part 2a ... Table 3 ... Signal conversion part 4 ... Image display panel

Claims (9)

A plurality of input values provided with a first section in which input values are arranged at a predetermined interval and a second section in which input values are arranged at a denser interval than the first section, and the plurality of input values are converted by a first function. A table holding unit for holding a table in which conversion values are associated with each other;
Referring to the table, the section where the input value of the input signal is located is specified, the input value of the input signal is input to the second function derived from the converted values located at both ends of the specified section, and the output signal A signal converter for converting into
An image display panel for outputting an image based on the output signal;
A display device.   2. The display device according to claim 1, wherein in the table, the absolute value of the slope of the first function in the second section is larger than the absolute value of the slope of the first function in the first section.   The display device according to claim 1, wherein the second function is a linear function that passes through conversion values located at both ends of the specified section.   The display device according to claim 1, wherein the second function is derived by linear interpolation using conversion values located at both ends of the specified section.   The display device according to claim 1, wherein the table holding unit holds a plurality of the tables corresponding to a plurality of types of the first functions.   The display device according to claim 5, wherein the signal conversion unit selects a table corresponding to the designated type of the first function from the table holding unit. The input value is a gradation value,
The display device according to claim 1, wherein the gradation value in the second section is denser than the gradation value in the first section.   The display device according to claim 1, wherein the input signal is adjusted based on an index for adjusting luminance of a pixel of the image display panel. In a display method of a display device having a table holding unit and a signal conversion unit,
The signal converter is
A plurality of input values provided with a first section in which input values are arranged at a predetermined interval and a second section in which input values are arranged at a denser interval than the first section, and the plurality of input values are converted by a first function. Refer to the table held by the table holding unit in association with the conversion value,
Identify the section where the input value of the input signal is located, input the input value of the input signal to the second function derived from the conversion values located at both ends of the identified section, and convert it to an output signal,
Based on the output signal, an image is output.
Display method.

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