Image display method, image display apparatus, and program

Abstract

To make luminance change accompanying dimming control of an image display image inconspicuous.SOLUTION: An image display method includes: calculating a weighted sum value weighted such that at least one of weight of a high gradation value and weight of a low gradation value becomes large with respect to gradation values of pixels constituting an image; determining a first control value used for dimming control of a light source of an image display device using the weighted sum value; determining a second control value used for extension processing of extending the number of gradations of the image using the first control value; and displaying an image after the extension processing obtained by applying the extension processing on the image using the second control value by controlling the light source using the first control value.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an image display method, an image display device, and a program.

Background Art

[0002] Conventionally, in an image display device, a technique for reducing power consumption by performing dimming is known. For example, Patent Document 1 discloses a technique for determining a dimming rate based on the average value of the gradation values of image data to be displayed and correcting the luminance value of the image data in order to reduce the luminance change due to dimming. According to this, it is said that power consumption can be reduced while suppressing luminance change.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, the influence of performing dimming on the displayed image varies depending on the gradation of the pixels. Therefore, when dimming is performed based on the average value of the gradation values, the luminance change becomes conspicuous in some pixels, which may affect the display quality.

Means for Solving the Problems

[0005] One aspect of the present disclosure includes calculating a weighted total value in which at least one of the weight of a high gradation value and the weight of a low gradation value is increased with respect to the gradation value of a pixel constituting an image, determining a first control value for use in dimming control of a light source of an image display device using the weighted total value, determining a second control value for use in an expansion process of expanding the number of gradations of the image using the first control value, and displaying an image after the expansion process in which the expansion process is performed on the image using the second control value by controlling the light source using the first control value.

[0006] Another aspect of the present disclosure includes a light source and at least one processor. The at least one processor calculates a weighted total value in which at least one of the weight of a high gradation value and the weight of a low gradation value is increased with respect to the gradation value of a pixel constituting an image, determines a first control value for use in dimming control of the light source using the weighted total value, determines a second control value for use in an expansion process of expanding the number of gradations of the image using the first control value, and displays an image after the expansion process in which the expansion process is performed on the image using the second control value by controlling the light source using the first control value.

[0007] Yet another aspect of the present disclosure is a program executed by a processor, which causes the processor to obtain a weighted total value in which at least one of the weight of a high gradation value and the weight of a low gradation value is increased with respect to the gradation value of a pixel constituting an image, determine a first control value for use in dimming control of a light source of an image display device using the weighted total value, determine a second control value for use in an expansion process of expanding the number of gradations of the image using the first control value, and display an image after the expansion process in which the expansion process is performed on the image using the second control value by controlling the light source using the first control value.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

MODE FOR CARRYING OUT THE INVENTION

[0009] [1. Configuration of Projector] Hereinafter, the present embodiment will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration example of the projector according to the present embodiment. The projector 1 projects a projection image P onto the screen SC. The projector 1 is an example of a display device, and the projection of the projection image P by the projector 1 is an example of display. The projection image P may be a still image or a video.

[0010] The projector 1 includes a control unit 10 that controls the projector 1, a projection unit 20, and a drive unit 30 that drives the projection unit 20.

[0011] The control unit 10 includes a processor 11 and a storage unit 13. The processor 11 is an arithmetic processing device composed of a CPU (Central Processing Unit), an MPU (Micro-Processing Unit), or other processors. The processor 11 may be composed of a single processor, or a configuration in which a plurality of processors function as the processor 11.

[0012] The memory unit 13 includes a volatile memory device and a non-volatile memory device. The volatile memory device is constituted by, for example, a RAM (Random Access Memory). The non-volatile memory device is constituted by, for example, a ROM (Read Only Memory), a flash memory, or an EEPROM (Electrically Erasable Programmable Read-Only Memory). The volatile memory device is used as an arithmetic area of the processor 11. The non-volatile memory device stores programs and data executed by the processor 11 in a non-volatile manner. For example, the memory unit 13 stores a control program 15 executed by the processor 11.

[0013] The control unit 10 may be a SoC integrating the processor 11, the memory unit 13, and other circuits. The processor 11 may be constituted by a combination of a CPU that executes programs and a DSP (Digital Signal Processor) that executes predetermined arithmetic processing. Further, all functions of the processor 11 may be implemented in hardware, or it may be configured using a programmable device.

[0014] The projection unit 20 forms an optical image and projects the image onto the screen SC. The projection unit 20 includes a light source 21, a light modulation device 23, and an optical system unit 25. The drive unit 30 includes a light source drive unit 31 and a light modulation device drive unit 33.

[0015] The light source 21 is constituted by a lamp light source, a solid light source, or other light emitters. The lamp light source is, for example, a halogen lamp, a xenon lamp, or an ultra-high pressure mercury lamp. The solid light source is, for example, an LED (Light Emitting Diode) or a laser light source.

[0016] The light source driving unit 31 includes, for example, a power supply circuit that supplies power to the light source 21 according to the control of the control unit 10. The light source driving unit 31 supplies a current to the light source 21 according to the control of the control unit 10, and turns on and off the light source 21.

[0017] The light source driving unit 31 has a dimming function of adjusting the light amount of the light source 21 according to the control of the control unit 10. The control unit 10 causes the light source driving unit 31 to execute the dimming function, thereby adjusting the light amount emitted by the light source 21 by the light source driving unit 31. The light amount of the light source 21 can also be referred to as the emission amount or brightness.

[0018] For example, when the light source 21 is a lamp light source, the light source driving unit 31 adjusts the light amount of the light source 21 by adjusting the current or voltage supplied to the light source 21. Also, for example, when the light source 21 is a solid light source, the light amount is adjusted by adjusting the duty or current of the pulse in PWM (Pulse Wave Modulation) control. With the dimming function, the power consumption of the light source 21 can be reduced, and the power consumption of the projector 1 can be reduced.

[0019] In the following description, the operation of reducing the light amount of the light source 21 is referred to as dimming control. The dimming control includes the control of the light source driving unit 31 by the control unit 10. The dimming control may include the operation in which the light source driving unit 31 actually reduces the light amount of the light source 21.

[0020] The light emitted by the light source 21 is modulated by the light modulation device 23 and enters the optical system unit 25. The optical system unit 25 includes lenses, mirrors, and other optical elements. The optical system unit 25 projects the projection image P onto the screen SC by emitting the light modulated by the light modulation device 23 toward the screen SC.

[0021] In this embodiment, as an example, a configuration is given in which the optical modulation device 23 includes three transmissive liquid crystal panels 27. These three liquid crystal panels 27 include a liquid crystal panel 27 that modulates red light, a liquid crystal panel 27 that modulates blue light, and a liquid crystal panel 27 that modulates green light. In this configuration, the light emitted from the light source 21 is separated into three color lights of red light, green light, and blue light by an optical element (not shown) disposed in the optical path between the light source 21 and the optical modulation device 23. These color lights are incident on each of the three liquid crystal panels 27 and are modulated by passing through the liquid crystal panel 27. The image light modulated by the liquid crystal panel 27 is synthesized by a synthetic optical system such as a cross dichroic prism and is emitted to the optical system unit 25.

[0022] The configuration of the optical modulation device 23 is not limited to a configuration including three transmissive liquid crystal panels 27. For example, the optical modulation device 23 may have a configuration in which light is modulated by one liquid crystal panel 27. Further, for example, the optical modulation device 23 may have a configuration including a reflective liquid crystal panel, or may have a configuration including a digital micromirror device (DMD).

[0023] The optical modulation device driving unit 33 drives the optical modulation device 23. The optical modulation device driving unit 33 includes, for example, a liquid crystal driver circuit that drives each of the three liquid crystal panels 27 included in the optical modulation device 23.

[0024] The projector 1 includes an image processing unit 41, a frame memory 43, an image interface 45, an input interface 47, and a remote control light receiving unit 49. The control unit 10, the image processing unit 41, the image interface 45, and the input interface 47 are connected to each other via a bus 40 so as to be capable of data communication.

[0025] The input interface 47 receives inputs for the projector 1. For example, an operation panel (not shown) is connected to the input interface 47. This operation panel is provided on the housing surface of the projector 1 and includes various buttons and switches. When the buttons and switches on the operation panel are operated by the user, operation signals corresponding to the operated buttons and switches are input from the operation panel to the input interface 47.

[0026] A remote control light receiving unit 49 is connected to the input interface 47. The projector 1 includes a remote control 2. The remote control 2 is a device for the user to operate the projector 1. The remote control light receiving unit 49 receives the infrared signal transmitted from the remote control 2. The remote control light receiving unit 49 decodes the received infrared signal to generate an operation signal and outputs the generated operation signal to the input interface 47.

[0027] The input interface 47 outputs the operation signals input from the operation panel or the remote control light receiving unit 49 to the control unit 10. The configuration in which the remote control 2 and the remote control light receiving unit 49 transmit and receive infrared signals is an example. For example, a configuration in which the remote control 2 and the remote control light receiving unit 49 transmit and receive operation signals by performing short-range wireless communication such as Bluetooth may be used. Bluetooth is a registered trademark.

[0028] The image interface 45 is a device for inputting image data from an image supply device (not shown) to the projector 1. The image supply device is, for example, a PC (Personal Computer), a smartphone, a video playback device, a DVD (Digital Versatile Disc) player, a Blu-ray Disc player, a hard disk recorder, a television tuner device, or a video game console.

[0029] The image interface 45 is connected to the image supply device via a cable. The image interface 45 includes, for example, a connector to which a cable can be connected and an interface circuit that inputs and outputs signals via the connector. The image interface 45 may be configured to receive image data by performing wireless communication with the image supply device. In this case, the image interface 45 includes an antenna and a wireless communication circuit such as an RF (Radio Frequency) circuit.

[0030] The image processing unit 41 can be configured by, for example, an integrated circuit. The integrated circuit is configured by, for example, LSI (Large Scale Integration). More specifically, the image processing unit 41 is configured by an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), etc. The PLD includes, for example, an FPGA (Field-Programmable Gate Array). Also, an analog circuit may be included in a part of the configuration of the integrated circuit, or it may be a combination of a processor and an integrated circuit. The combination of a processor and an integrated circuit is called a microcontroller (MCU), a SoC (System-on-a-Chip), a system LSI, a chipset, etc.

[0031] A frame memory 43 is connected to the image processing unit 41. The frame memory 43 is configured by, for example, SDRAM (Synchronous Dynamic Random Access Memory).

[0032] The control unit 10 causes the image processing unit 41 to acquire the image data input from the image interface 45 or the image data stored in the control program 15, and thereby projects the projection image P onto the screen SC based on the above image data.

[0033] The image processing unit 41 acquires image data according to the control of the control unit 10, and expands the acquired image data in the frame memory 43. The image processing unit 41 executes image processing on the image data expanded in the frame memory 43. The image processing that the image processing unit 41 can execute is, for example, resolution conversion processing, geometric correction processing, digital zoom processing, image correction processing for adjusting the color and brightness of the image, and the like. Further, in the following description, the image processing unit 41 performs a process of expanding the pixel values of the pixels constituting the image data expanded in the frame memory 43. This process is particularly called an expansion process. The pixel value of a pixel can be a gradation value as will be described later.

[0034] The image processing unit 41 inputs the image data expanded in the frame memory 43 to the light modulation device driving unit 33. The light modulation device driving unit 33 receives image data corresponding to each primary color of red, blue, and green from the image processing unit 41. The light modulation device driving unit 33 converts the image data input from the image processing unit 41 into a signal for driving the liquid crystal panel 27. The light modulation device driving unit 33 applies a voltage to the pixels constituting each of the three liquid crystal panels 27 based on the converted signal, thereby drawing an image on the liquid crystal panel 27. As a result, the projection image P based on the image data processed by the image processing unit 41 is projected.

[0035] [2. Operation of the Projector] FIG. 2 is a flowchart showing an operation example of the projector 1. The operation of the projector 1 will be described according to this flowchart. Steps S1 to S6 are executed by the processor 11.

[0036] The operation shown in FIG. 2 is a series of operations related to the dimming control of the projector 1. When dimming control is performed, the light amount of the light source 21 decreases, so the brightness of the projection image P decreases. The projector 1 corrects the pixel values of the pixels of the projection image P so as to compensate for the decrease in the light amount, so that the decrease in the brightness of the projection image P is not noticeable. This correction of the pixel value is a process of expanding the number of gradations of the input image, which is the above-described expansion process.

[0037] In this embodiment, the color space of the image data of the input image is set to the YUV color space composed of luminance Y and color differences U and V. Then, in the operation of FIG. 2, the projector 1 performs processing on the gradation value of the Y component among the pixel values. The gradation value of luminance Y affects the brightness of the image. Therefore, by performing processing on the gradation value of the Y component, a sufficient effect can be obtained with respect to the brightness of the projected image P, and the efficiency is higher than when processing all the values of YUV. Accordingly, hereinafter, as an example of the processing for the pixel values, the processing regarding the gradation value of the Y component will be described. These processes are also applicable to the gradation values of the U component and the V component, and are also applicable to the pixel values in the RGB color space.

[0038] [2-1. Average value calculation process] In step S1, the projector 1 executes an average value calculation process to calculate the average value APL of the gradation values of the input image. The input image is the image acquired by the image processing unit 41 and developed in the frame memory 43. When the projector 1 displays a video, the input image is one frame constituting the video. In the following description, a rectangular input image is assumed, and the pixels constituting the input image are specified by the x coordinate and the y coordinate. That is, an X-Y orthogonal coordinate system including the X axis with the upper left corner of the input image as the origin and the right direction of the input image as the positive direction, and the Y axis with the downward direction of the input image as the positive direction is set for the input image. Then, the position of the pixel is indicated as (x, y) by x indicating the coordinate on the X axis and y indicating the coordinate on the Y axis.

[0039] The calculation of the average value APL in step S1 is performed, for example, by the operation of the following formula (1).

[0040] [Equation]

[0041] In formula (1), Nx is the number of pixels in the x direction of the input image, Ny is the number of pixels in the y direction of the input image, and i(x, y) is the gradation value of the pixel located at the coordinate (x, y). In this embodiment, the projector 1 calculates the average value APL of the gradation values for all the pixels constituting the input image.

[0042] The projector 1 may perform processing on a part of the pixels constituting the input image. For example, processing may be performed on a plurality of pixels located at preset coordinates in the input image, or a preset number of representative pixels may be selected in the input image, and processing may be performed on the selected plurality of pixels. Similarly for steps S2 to S4, in this embodiment, an example of processing all the pixels constituting the input image is described, but the projector 1 may perform processing on a part of the pixels constituting the input image.

[0043] [2-2. Weighted sum calculation processing] In step S2, the projector 1 executes weighted sum calculation processing. The weighted sum calculation processing is processing for calculating the sum of the gradation values of the entire input image by performing weighting according to the gradation values.

[0044] As a first example of weighting, it can be mentioned that weighting is performed on the gradation values such that the weight increases as the gradation value increases. In other words, the projector 1 assigns a first weight to the first gradation value, and assigns a weight to the second gradation value that is higher in gradation than the first gradation value, and the second weight is larger than the first weight.

[0045] High-gradation pixels tend to be visually recognized as having lower brightness when the light source 21 is dimmed, so the brightness decrease of high-gradation pixels is likely to be noticeable along with dimming control. The projector 1 according to the present disclosure suppresses the dimming amount of the light source 21 when the input image contains many high-gradation pixels in order to make the brightness decrease of the pixels less noticeable. The dimming amount refers to the ratio of decreasing the light amount of the light source 21 in dimming control. To achieve this, in step S2, the projector 1 obtains a weighted total value that serves as an index of how many high-gradation pixels the input image contains.

[0046] Examples of methods for obtaining a weighted sum value include a method using a polynomial and a method using a pre-created LUT (Look Up Table). The quadratic polynomial and the LUT are stored in advance in the storage unit 13, for example. For example, as shown in the following formula (2), the projector 1 w , B w , C w calculates the weighted sum value w(i(x,y)) using a quadratic polynomial with these as coefficients.

[0047]

Equation

[0048] As described above, the purpose of obtaining the weighted sum value w(i(x,y)) is to extract the tone value i(x,y) of high-tone pixels where brightness reduction is likely to be prominent. Therefore, as a first condition, the weighted sum value w(i(x,y)) should be a positive value for high-tone pixels.

[0049] Among high-tone parts, the closer the tone value i(x,y) is to the maximum value, the more prominent the brightness reduction is. Therefore, as a second condition, the closer the tone value i(x,y) is to the maximum value, the larger the weighted sum value w(i(x,y)) should be. In other words, the second condition means that the weighted sum value w(i(x,y)) monotonically increases in the high-tone part.

[0050] The coefficients A w , B w , C w of formula (2) are determined to satisfy both the above first condition and second condition.

[0051] For example, when i(x,y) is in the range of 0 to 1023, the high-tone part is defined as the range i(x,y) > 800. In this case, in the region where i(x,y) > 800, the coefficients A w , B w , C w are determined so as to satisfy the following formula (3). Formula (3) represents satisfying both the above first condition and second condition.

[0052] [Number]

[0053] Furthermore, by distinguishing between the high-tone part and the low-tone part, which is the area other than the high-tone part, the influence of the tone value of the low-tone part can be excluded from the weighted total value. For example, as shown in the following formula (4), the boundary value i B between the high-tone part and the low-tone part is determined, and a method of performing a case-by-case operation using the boundary value i B can be mentioned. In the present embodiment, w´(i(x, y)) obtained by the formula (4) is used as the weighted total value.

[0054] [Number]

[0055] Coefficient A w , B w , C w and i B are not limited to fixed values. For example, the coefficients A w , B w , C w and i B may be determined from the average value APL. The boundary value i B between the high-tone part and the low-tone part is not limited to 800, and may be appropriately set according to the range of the tone value of the input image.

[0056] FIG. 3 is a chart showing an example of the correlation between the tone value i(x, y) of the input image and the weighted total value w´(i(x, y)). In the example of FIG. 3, the coefficients A w , B w , C w and i B are determined using the average value APL. Specifically, as shown in the following formula (5), i B is set to the average value APL. And the weighted total value w´(APL) at the tone value i(x, y) = i B is 0, and i(x, y)>iB The coefficients A w , B w , C w are determined such that the weighted sum value w´(i(x, y)) increases monotonically in the region of

[0057] i B = APL ···(5)

[0058] As shown in FIG. 3, when the coefficients A w , B w , C w and i B are determined, the weighted sum value can be obtained only for the pixels where the gradation value i(x, y) exceeds the average value APL.

[0059] The projector 1 obtains the weighted total sum s of the entire input image by using the weighted sum value w´(i(x, y)) through an operation shown in, for example, the following formula (6). Thereby, the total sum of the gradation values reflecting how much the input image includes pixels in the high gradation portion can be obtained.

[0060]

Equation

[0061] [2-3. Light source dimming amount calculation process] In step S3, the projector 1 executes a light source dimming amount calculation process for obtaining the dimming amount of the light source 21. The projector 1 obtains the dimming amount l of the light source 21 based on the average value APL. For example, the projector 1 uses the coefficients A l , B l , C l to obtain the dimming amount l by a quadratic polynomial.

[0062]

Equation

[0063] The projector 1 uses the coefficients A l , Bl , C l is determined such that the light reduction amount l decreases monotonically with respect to the average value APL. That is, the relationship is such that the larger the average value APL, the smaller the light reduction amount l. As a result, for an input image with a large average value APL, the light reduction amount l is small, and for an input image with a small average value APL, the light reduction amount l is large. Since an input image with a large average value APL is an image with many high-tone parts, the decrease in luminance due to light reduction is likely to be noticeable. Since an input image with a small average value APL is an image with few high-tone parts, the decrease in luminance due to light reduction is less likely to be noticeable. Therefore, by making the light reduction amount l decrease monotonically with respect to the average value APL, the decrease in luminance of an input image with a large average value APL can be made less noticeable, and the light reduction amount of an input image with a small average value APL can be increased to enhance the power consumption reduction effect.

[0064] The projector 1 obtains the light reduction gain g based on the weighted sum s. For example, as shown in the following formula (8), the projector 1 g , B g , C g obtains the light reduction gain g using a quadratic polynomial with coefficients A, B, and C. Furthermore, the projector 1 obtains the final light reduction amount l' using the light reduction gain g. This process can be said to be a process of correcting the light reduction amount l obtained from the average value APL by the light reduction gain g obtained based on the weighted sum s, and the light reduction amount l' is the light reduction amount after correction. For example, as shown in the following formula (9), the projector 1 obtains the light reduction amount l' by multiplying the light reduction amount l by the light reduction gain g.

[0065]

Equation

[0066] Figure 4 is a chart showing an example of the correlation between the weighted sum s and the light reduction gain g. The example shown in Fig. 4 corresponds to an example where the amount of light reduction decreases monotonically as the weighted sum increases, and the characteristic that the light reduction gain g decreases as the weighted sum s increases appears. In this example, the larger the weighted sum s, the smaller the light reduction gain g. Therefore, the more high-tone pixels the input image contains, the smaller the amount of light reduction tends to be. Accordingly, an effect of making the luminance reduction of the input image less noticeable can be expected.

[0067] [2-4. Image Expansion Amount Calculation Process] In step S4, the projector 1 executes an image expansion amount calculation process for obtaining the image expansion amount. The image expansion amount is a coefficient for converting the gradation value in the expansion process.

[0068] The projector 1 obtains the magnification r based on the amount of light reduction l´. For example, the projector 1 uses coefficients A r , B r , C r to obtain the magnification r by a quadratic polynomial.

[0069] [Equation]

[0070] The magnification r is a value that determines the image expansion amount. The larger the magnification r, the larger the expansion amount of the image, that is, the increase amount of the gradation value. When the magnification r = 0, the image expansion amount is 0.

[0071] The coefficients A r , B r , C r of Equation (10) are set so as to compensate for the luminance reduction due to light reduction without excess or deficiency. As a method for obtaining the coefficients A r , B r , C r , for example, a method of making the average value of the gradation values before the expansion process equal to the average value of the effective gradation values after the expansion process can be mentioned.

[0072] For example, assuming that the gradation value after the stretching process is o(x, y), the conditional expression of the following formula (11) can be defined. In formula (11), α indicates the brightness that a person feels about the projection image P when the light quantity of the light source 21 is multiplied by (1 - l´). α can be defined as in the following formula (12), and in this case, the value of γ is γ = 2.2 based on the visual characteristics of humans.

[0073] [Number]

[0074] o(x, y) depends on the magnification factor r. Therefore, formula (11) can be solved for r. For example, for sample images with various light attenuation amounts l´, the correlation between the light attenuation amount l´ and the magnification factor r is plotted on a graph, and the coefficients A r , B r , C r can be determined so that the quadratic polynomial approximating this correlation satisfies formula (11).

[0075] The amount of image stretching for compensating for the decrease in the luminance of the projection image P due to the light attenuation of the light source 21 can be referred to as the compensation amount for luminance decrease. When the light attenuation amount l´ is large, it is desirable to increase the compensation amount for luminance decrease, and when the light attenuation amount l´ is small, it is appropriate to set the compensation amount for luminance decrease to a small value. That is, when an appropriate compensation amount for luminance decrease is determined, a correlation is obtained in which the magnification factor r increases monotonically with respect to the light attenuation amount l´.

[0076] [2-5. Light attenuation control and stretching process] In step S5, the projector 1 executes light attenuation control. The projector 1 reduces the light quantity of the light source 21 by the amount of light attenuation l´ calculated in step S3 using the dimming function of the light source driving unit 31.

[0077] In step S6, the projector 1 executes a stretching process. The projector 1 performs an expansion process using the expansion magnification r obtained by the above calculation. For example, as shown in the following formula (13), the projector 1 obtains the value of the image expansion amount e(i(x, y)) by multiplying the reference expansion amount F(i(x, y)) by the expansion magnification r. For example, the projector 1 can obtain the reference expansion amount F(i(x, y)) by a quadratic polynomial using the input gradation value i(x, y) as a variable, as shown in formula (13).

[0078] [Number]

[0079] In formula (13), the coefficients A F , B F , C F of the quadratic polynomial for obtaining the reference expansion amount F(i(x, y)) are defined in advance.

[0080] For example, as shown in the following formula (14), the projector 1 determines the final output gradation value o(x, y) by adding e(i(x, y)) to i(x, y). Formula (14) corresponds to the process of expanding the gradation number of the input image.

[0081] [Number]

[0082] Figure 5 is a chart showing an example of the correlation between the output gradation value o(x, y) after the expansion process and the gradation value i(x, y) of the input image. The dashed line in Figure 5 shows the correlation between the output gradation value o(x, y) and the gradation value i(x, y) of the input image when the expansion magnification r is a constant, specifically zero. The curve in Figure 5 shows the correlation between the output gradation value o(x, y) and the gradation value i(x, y) of the input image when the expansion process according to formulas (13) and (14) is executed.

[0083] The coefficient A of formula (13) F , B F , C FIt is defined such that the reference elongation amount F(i(x, y)) changes in a shape having a peak at a middle tone, that is, an intermediate gradation. In this case, the magnification factor r corresponding to the gradation value i(x, y) of the middle tone becomes larger than those of the low tone part and the high tone part. For this reason, as shown by the curve in FIG. 5, the gradation value of the middle tone is stretched more greatly than those of the low tone part and the high tone part.

[0084] The image processing unit 41 reads out the image data after the stretching process from the frame memory 43, and causes the projection unit 20 to display an image based on the read image data.

[0085] In the present embodiment, the execution order of step S5 and step S6 may be reversed. Also, the arithmetic expressions, coefficients, and other values used by the projector 1 in the arithmetic processing in steps S1 to S6 are preset and stored in the storage unit 13. A part of these arithmetic expressions, coefficients, and other values may be calculated each time the projector 1 executes the operation of FIG. 2 or at a predetermined timing.

[0086] In the above embodiment, the light reduction amount l´ corresponds to an example of the first control value, and the magnification factor r corresponds to an example of the second control value. The value of the boundary i B corresponds to an example of the first value.

[0087] [3. First Modification Example] As a first modification example of the above embodiment, another example of the weighted sum calculation process in step S2 will be described.

[0088] In the above embodiment, when calculating the weighted total value, in order to eliminate the influence of the gradation value of the low tone part, as shown in Equation (4), a method of performing a conditional operation using the boundary value i B between the high tone part and the low tone part has been described.

[0089] By the way, even in low-tone pixels, the influence of the light source 21 dimming may appear. Specifically, due to the influence of dimming control and stretching processing, banding may occur in an input image with many low-tone pixels, and an event may occur where the low-tone pixels become too bright. In order to suppress these events, it is conceivable to perform weighting so that the weights of both the high-tone part and the low-tone part increase.

[0090] Therefore, as a first modification example, an example of suppressing the circumstances that cause deterioration of image quality in the low-tone part will be described in the process of calculating the weighted sum s.

[0091] In the first modification example, weighting is performed so that the weight of the low-tone part becomes larger than that of the middle tone. In this case, in the projector 1, the boundary value i B between the high-tone part and the non-high-tone part, and the boundary value i BL between the low-tone part and the non-low-tone part are determined. The boundary value i BL may be appropriately set corresponding to the range of the tone values of the input image.

[0092] The projector 1 obtains the weighted total value w L (i(x, y)) of the input image using, for example, a quadratic polynomial with A wL , B wL , C wL as coefficients, as shown in the following formula (15).

[0093]

Equation

[0094] The coefficients A wL , B wL , C wL of formula (15) are determined so that the weighted total value becomes larger as the tone value is lower. Specifically, the coefficients A wL , B wL , C wL are determined to satisfy the following two conditions. The first condition is that the weighted total value w LIt is that (i(x, y)) becomes a positive value in the low-tone part. The second condition is that the weighted total value w L (i(x, y)) monotonically decreases in the low-tone part, that is, the lower the tone value, the larger the weighted total value w L (i(x, y)) becomes.

[0095] Then, the projector 1 distinguishes the high-tone part, the low-tone part, and the region different from the high-tone part and the low-tone part, and obtains the weighted total value w L ´(i(x, y)). The weighted total value w L ´(i(x, y)) is a value used in place of the weighted total value w´(i(x, y)) described in the above embodiment, and reflects only the high-tone part and the low-tone part.

[0096] For example, as shown in the following formula (16), the projector 1 performs a case-by-case operation using the boundary value i B and the boundary value i BL and calculates the weighted total value w L ´(i(x, y)).

[0097]

Equation

[0098] Figure 6 is a chart showing an example of the correlation between the tone value i(x, y) of the input image in the first modified example and the weighted total value w´(i(x, y)). The correlation in Figure 6 shows the case where the weighted total value w´(i(x, y)) is calculated using formula (16).

[0099] In the example of Figure 6, the boundary i B is the average value APL. In the region where the tone value is larger than the boundary i B , the weighted total value monotonically increases, and the higher the tone value, the larger the weighted total value. Also, in the region where the tone value is lower than the boundary i BL , the weighted total value monotonically decreases, and the lower the tone value, the larger the weighted total value. In other words, the tone value is the boundary i BLIn the region lower than [a certain value], the higher the gradation value, the smaller the weighted total value. And the weighted total value in the region different from the high-gradation part and the low-gradation part is 0. Here, the boundary i BL The value of may be a pre-specified value or may be determined based on the average value APL. The boundary i BL The value of corresponds to an example of the second value.

[0100] Thus, in the first modification example, since the gradation values in the regions different from the high-gradation part and the low-gradation part are not included, the projector 1 can obtain the weighted total value reflecting only the high-gradation part and the low-gradation part. Furthermore, in the first modification example, the region to be weighted may be only the pixels in the low-gradation part. That is, weighting may be performed so that the weight of the pixels in the low-gradation part becomes large, and the weighted total value in the regions other than the low-gradation part may be made small or zero. For example, in the example of FIG. 6, the weighted total value in the region where the gradation value is larger than the boundary i B is set to 0. In this case, the event that the pixels in the low gradation become too bright can be suppressed.

[0101] Instead of the above formula (6), the projector 1 can calculate the weighted total s from the weighted total value w L ´(i(x,y)) by performing the operation of the following formula (17). The projector 1 can use the weighted total s calculated by the formula (17) in the processing of steps S2 to S4 of the above embodiment.

[0102] [4. Second Modification Example]

[0103] In the above embodiment, in the weighted total calculation process, weights are assigned to the gradation values of each pixel of the input image to calculate the weighted total of the entire input image. In the weighted total calculation process, weights are assigned to the gradation values of each pixel of the input image to calculate the weighted total of the entire input image. On the one hand, histogram calculation is used as a method for obtaining the distribution of pixel values of the entire image. Therefore, as a method for obtaining the weighted sum of the entire input image, a method using histogram calculation will be described as a second modification example.

[0104] In the second modification example, instead of assigning weights to each pixel of the input image, weights are assigned to the histogram calculation results. For example, the projector 1 executes histogram calculation for the gradation values of each pixel of the input image and creates a histogram showing the distribution of the gradation values of each pixel. The class values, the number of classes, and the class width of the histogram are appropriately determined according to the range of the gradation value i(x, y). A predetermined weight is assigned to each class of the histogram.

[0105] The weight assigned to the histogram preferably satisfies either of the following conditions (1) and (2). Condition (1) is that in the high-gradation part where the gradation value is high, the closer the gradation value is to the maximum value, the greater the weight, that is, the weight monotonically increases in the high-gradation part. Condition (2) is that in addition to condition (1), in the low-gradation part where the gradation value is low, the closer the gradation value is to the minimum value, the greater the weight, that is, the weight monotonically decreases in the low-gradation part. The high-gradation part and the low-gradation part refer to the ranges described in the embodiment and the first modification example.

[0106] The projector 1 obtains the weighted frequency w´(h) by multiplying the frequency, the class value, and the weight for each class of the histogram. The projector 1 obtains the sum of the obtained weighted frequencies w´(h) by the following formula (18).

[0107]

Equation

[0108] In this way, if histogram calculation is adopted in the process of calculating the weighted sum of the entire input image, the weighted sum can be efficiently calculated by using existing resources such as software and hardware for histogram calculation. The projector 1 can use the weighted sum s calculated by the formula (18) in the processes of steps S2 to S4 of the above embodiment.

[0109] [5. Other Embodiments] The above-described embodiment is a preferred embodiment. However, it is not limited to the above-described embodiment, and various modifications can be made without departing from the gist.

[0110] In this embodiment, an example in which the processing is performed on the Y component of the pixel value for the pixels constituting the input image has been described. The present disclosure is not limited to this. For example, it is also possible to include the U component and the V component as processing targets. For example, the projector 1 may calculate the average value APL and the weighted total value w'(i(x,y)) for each of the Y component, the U component, and the V component, and obtain the weighted sum s as the sum of the weighted total values w'(i(x,y)) of the Y component, the U component, and the V component.

[0111] In this embodiment, the projector 1 has been exemplified and described as an example of the image display device. However, the display device to which the present disclosure is applicable is not limited to the projector 1. For example, the image display device may be a flat panel display. For example, when the image display device is a liquid crystal display having a light source such as a backlight device and a transmissive liquid crystal display panel, the present disclosure may be applied to perform dimming control of the light source and stretching processing.

[0112] Each functional unit shown in FIG. 1 shows a functional configuration, and the specific implementation form is not particularly limited. That is, it is not necessarily required to implement hardware corresponding to each functional unit individually, and it is also possible to adopt a configuration in which one processor executes a program to realize the functions of a plurality of functional units. Further, in the above embodiment, a part of the functions realized by software may be realized by hardware, or a part of the functions realized by hardware may be realized by software. In addition, the specific detailed configuration of each part of the projector 1 can also be arbitrarily changed without departing from the spirit.

[0113] The processing units of the flowchart shown in FIG. 2 are divided according to the main processing contents in order to facilitate the understanding of the processing of the control unit 10 of the projector 1. The way and name of the division of the processing units shown in the flowchart of FIG. 2 are not limited, and according to the processing contents, it can be further divided into more processing units, or one processing unit can be divided to include more processes. In addition, the processing order of the above flowchart is not limited to the illustrated example.

[0114] The control method of the display device of the present disclosure can be realized by causing the processor 11 provided in the projector 1 to execute a control program 15 corresponding to the control method of the projector 1 in the projector 1. The control program 15 can also be recorded on a recording medium that can be read by a computer. As the recording medium, a magnetic or optical recording medium or a semiconductor memory device can be used. Specifically, portable or fixed recording media such as flexible disks, HDDs, CD-ROMs (Compact Disk Read Only Memories), DVDs, Blu-ray (registered trademark) Discs, magneto-optical disks, flash memories, and card-type recording media can be mentioned. Further, the recording medium may be a non-volatile storage device such as a RAM, ROM, or HDD that is an internal storage device provided in the projector 1. The control method of the projector 1 can also be realized by storing the control program 15 in a server device or the like and downloading the control program 15 from the server device to the projector 1.

[0115] [6. Supplementary Note] Hereinafter, a summary of the present disclosure will be appended. (Supplementary Note 1) Calculating a weighted total value in which at least one of the weights of high gradation values and the weights of low gradation values is increased with respect to the gradation values of the pixels constituting the image; determining a first control value for use in dimming control of the light source of the image display device using the weighted total value; determining a second control value for use in an expansion process of expanding the number of gradations of the image using the first control value; and displaying an image after the expansion process in which the expansion process is performed on the image using the second control value by controlling the light source using the first control value. An image display method including:

[0116] Thereby, when performing dimming control of the light source in the image display device, it is possible to make the luminance change of at least one of the pixels with high gradation values and low gradation values less noticeable. Thereby, it is possible to perform dimming control of the light source while suppressing the influence on the display quality of the image display device and reducing the power consumption of the image display device.

[0117] (Appendix 2) The weighted total value includes at least one of the weighted total value calculated from the gradation values of each pixel among at least some of the pixels constituting the image whose gradation value is equal to or greater than a first value, and the weighted total value calculated from the gradation values of each pixel whose gradation value is equal to or less than a second value smaller than the first value. The image display method according to Appendix 1.

[0118] Thereby, for at least one of the pixels with high gradation values and the pixels with low gradation values among at least some of the pixels constituting the image, dimming control and stretching processing can be executed using the total value obtained by weighting the gradation values. Therefore, the change in pixel luminance when performing dimming control of the light source can be made less noticeable, and the influence of dimming control on the display quality can be further suppressed.

[0119] (Appendix 3) Calculating the weighted total value includes determining the weighted total value such that the weighted total value monotonically increases as the gradation value increases in a range where the gradation value is equal to or greater than a first value. The image display method according to Appendix 1.

[0120] Thereby, in response to the fact that when performing dimming control, the luminance change of pixels with higher gradation values is more likely to be noticeable, weighting can be performed. Therefore, the luminance change of pixels when performing dimming control of the light source can be made even less noticeable.

[0121] (Appendix 4) The first value is the average value of the gradation values of some of the pixels constituting the image. The image display method according to Appendix 2 or Appendix 3.

[0122] Thereby, for pixels with gradation values higher than the average value of the displayed image, the luminance change can be made less noticeable. Also, since the average value is obtained for some of the pixels, the processing load can be reduced.

[0123] (Appendix 5) The image display method according to Supplementary Note 2 or Supplementary Note 3, wherein the first value is an average value of gradation values of all pixels constituting the image.

[0124] Accordingly, for pixels having gradation values higher than the average value of the displayed image, the luminance change can be made less conspicuous. Further, by using the average value obtained for all pixels, the luminance change of pixels when performing dimming control of the light source can be made more surely less conspicuous.

[0125] (Supplementary Note 6) The image display method according to Supplementary Note 1, wherein the first control value is a value indicating the dimming amount of the light source, and determining the first control value includes determining the first control value such that the dimming amount monotonically decreases as the weighted total value increases.

[0126] Accordingly, as the number of pixels having high gradation values increases, the dimming amount of the light source is reduced, so that the luminance change of pixels when performing dimming control of the light source can be made even less conspicuous.

[0127] (Supplementary Note 7) Determining the first control value includes obtaining the dimming amount of the light source from the average value of gradation values of at least some of the pixels constituting the image, obtaining the dimming gain of the light source using the weighted total value, and correcting the dimming amount by the dimming gain, the image display method according to Supplementary Note 1.

[0128] Accordingly, since the dimming amount obtained from the gradation value of the pixel is corrected by the dimming gain obtained by weighting the gradation value of the pixel, the dimming amount can be determined in response to the presence of pixels where the luminance change is likely to be conspicuous. For this reason, the luminance change of pixels when performing dimming control of the light source can be made even less conspicuous.

[0129] (Supplementary Note 8) An image display device including a light source and at least one processor, wherein the at least one processor calculates a weighted total value in which at least one of the weight of a high gradation value and the weight of a low gradation value is increased with respect to the gradation value of a pixel constituting an image, determines a first control value used for dimming control of the light source using the weighted total value, determines a second control value used for an expansion process of expanding the number of gradations of the image using the first control value, and displays an image after the expansion process obtained by performing the expansion process on the image using the second control value by controlling the light source using the first control value.

[0130] According to the image display device described in Supplementary Note 8, the same effect as the method for determining the correction value described in Supplementary Note 1 can be obtained.

[0131] (Supplementary Note 9) A program executed by a processor, which causes the processor to obtain a weighted total value in which at least one of the weight of a high gradation value and the weight of a low gradation value is increased with respect to the gradation value of a pixel constituting an image, determine a first control value used for dimming control of a light source of an image display device using the weighted total value, determine a second control value used for an expansion process of expanding the number of gradations of the image using the first control value, and display an image after the expansion process obtained by performing the expansion process on the image using the second control value by controlling the light source using the first control value.

[0132] According to the program described in Supplementary Note 9, the same effect as the method for determining the correction value described in Supplementary Note 1 can be obtained.

Explanation of Signs

[0133] 1... Projector (image display device), 2... Remote control, 10... Control unit, 11... Processor, 13... Memory unit, 15... Control program, 20... Projection unit, 21... Light source, 23... Light modulation device, 25... Optical system unit, 27... Liquid crystal panel, 30... Driving unit, 31... Light source driving unit, 33... Light modulation device driving unit, 40... Bus, 41... Image processing unit, 43... Frame memory, 45... Image interface, 47... Input interface, 49... Remote control light receiving unit, P... Projected image, SC... Screen.

Claims

1. Calculating a weighted total value in which at least one of the weight of the high gradation value and the weight of the low gradation value is increased with respect to the gradation value of the pixel constituting the image; Determining a first control value used for dimming control of the light source of the image display device using the weighted total value; Determining a second control value used for an expansion process of expanding the gradation number of the image using the first control value; Displaying an image after the expansion process obtained by subjecting the image to the expansion process using the second control value by controlling the light source using the first control value; An image display method.

2. The weighted total value includes at least one of the weighted total value calculated from the gradation values of each pixel having a gradation value of a first value or more among at least a part of the pixels constituting the image, and the weighted total value calculated from the gradation values of each pixel having a gradation value smaller than the first value and equal to or less than a second value. The image display method according to claim 1.

3. Calculating the weighted total value includes determining the weighted total value such that the weighted total value monotonically increases as the gradation value increases in a range where the gradation value is equal to or more than the first value. The image display method according to claim 1.

4. The first value is an average value of gradation values of a part of the pixels constituting the image. The image display method according to claim 2 or claim 3.

5. The first value is an average value of gradation values of all the pixels constituting the image. The image display method according to claim 2 or claim 3.

6. The first control value is a value indicating the dimming amount of the light source, Determining the first control value includes determining the first control value such that the dimming amount monotonically decreases as the weighted total value increases. The image display method according to claim 1.

7. Determining the first control value includes Obtaining the dimming amount of the light source from the average value of gradation values of at least a part of the pixels constituting the image; Obtaining a dimming gain of the light source using the weighted total value; Correcting the dimming amount by the dimming gain. The image display method according to claim 1.

8. A light source, Including at least one processor, The at least one processor is Calculating a weighted total value in which at least one of the weights of high gradation values and the weights of low gradation values is increased with respect to the gradation values of the pixels constituting the image; Determining a first control value used for dimming control of the light source using the weighted total value; Determining a second control value used for an expansion process of expanding the number of gradations of the image using the first control value; Displaying an image after the expansion process in which the expansion process is performed on the image using the second control value by controlling the light source using the first control value; Executing; An image display device.

9. A program executed by a processor, causing the processor to obtain a weighted total value in which at least one of the weights of high gradation values and the weights of low gradation values is increased with respect to the gradation values of the pixels constituting the image; determine a first control value used for dimming control of a light source of an image display device using the weighted total value; determine a second control value used for an expansion process of expanding the number of gradations of the image using the first control value; display an image after the expansion process in which the expansion process is performed on the image using the second control value by controlling the light source using the first control value; execute; A program.

Images