JP2008016962A - Video signal processing circuit, video display apparatus, and video signal processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology of preventing a bit dropout when an image receiving side applies inverse gamma correction (gamma back) to a video signal with a gamma characteristic wherein a gain of an output signal level is high with respect to an input signal level. <P>SOLUTION: In the case of applying the inverse gamma correction processing to the input video signal, a video display apparatus calculates an inverse gamma curve 33 when the level of the input video signal is 0 or over, a straight line 31 when the level of the input video signal is 0 or over and around a black level, and a transition curve 32 for smoothly connecting the inverse gamma curve 33 and the straight line 31 for a range including part before and after a cross point 34 between the inverse gamma curve 33 and the straight line 31. Further, the video display apparatus generates an inverse gamma correction characteristic by using the straight line 31 for a range including from the input video signal level 0 to a signal level wherein a bit dropout takes place on the inverse gamma curve 33, the inverse gamma curve 33 for a range at a level higher than a bit dropout generating level, and the transition curve 32 for the connected part between the straight line 31 and the inverse gamma curve 33. The video display apparatus executes inverse gamma processing on the basis of the inverse gamma characteristic generated in this way. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a video signal processing circuit that performs inverse gamma correction on an input video signal, a video display device that displays a video signal subjected to inverse gamma correction, and a video signal processing method.

  2. Description of the Related Art Conventionally, a technique is known in which light emission output characteristics (non-linear characteristics) on the receiver side are taken into consideration and correction is performed in advance on the transmission side in consideration of the characteristics. For example, many television receivers use a cathode ray tube (CRT) as a display device, and this CRT also has non-linear characteristics. Such a non-linear characteristic is called a gamma characteristic (γ characteristic). The non-linear characteristic on the image receiving side is represented by X for input and Y for output.

と表せるから、送像側で予め加えるガンマ特性は、

The gamma characteristic added in advance on the image transmission side is

となる。

It becomes.

  A broadcast station that provides a video signal broadcasts the video signal by performing a gamma correction process that cancels the gamma characteristics of the CRT on the receiving side. Accordingly, the television receiver can perform linear display with the CRT gamma characteristic corrected.

  The gamma value used for the gamma correction is determined for each use, that is, for each color expression standard. For example, in a CRT television receiver, a gamma value (γ) representing a gamma characteristic (gamma curve) = 2.2, which is defined by ITU (International Telecommunication Union) 709. In addition, sRGB is a color space standard established to ensure color reproducibility between different environments such as a personal computer, a display, and a printer. Here, a gamma value (γ) = 2.4 is specified. Yes. Further, the gamma curve in the DCDM (D-Cinema Distribution Master) of the digital cinema distribution master has a gamma value (γ) = 2.6 in all levels (all sections).

  Examples of these three gamma curves are shown in FIG. FIG. 6 is a partially enlarged view of the three gamma curves shown in FIG. In FIG. 5, the vertical axis and the horizontal axis represent the signal levels of the input video signal and the output video signal, respectively. When “0”, the signal level is 0%, and when “1”, the signal level is 100%. . In this example, for example, when the input video signal is digitized by 8 bits, the input 0% level is the black quantization level of 16 quantization levels (logical level, shown in the figure as a digital code when digitized). The level of 100% input corresponds to the 235 quantization level. When digitized with 8 bits, it is possible to express up to an input minus (−) 7% level corresponding to the 0 quantization level, which is not shown here.

  The gamma curve 101 according to the ITU 709 standard is composed of a straight line in addition to a curve. If the input is X and the output is Y, the gamma curve 101 is expressed by the following equation.

  The gamma curve 102 according to the sRGB standard is also composed of a curve and a straight line. If the input is X and the output is Y, the gamma curve 102 is expressed by the following equation.

  Since the gamma curves 101 and 102 according to the ITU 709 and sRGB standards are approximated by a straight line having a low gain near the black level where the signal level is low (see FIG. 6), a large word length ( (In the case of hardware) is not necessary, and the problem does not become apparent in terms of characteristics and hardware scale.

  For example, as an example of the inverse gamma correction process, there is a technique as described in Patent Document 1. This Patent Document 1 discloses a straight line having a predetermined slope from gradation 0 to a predetermined gradation in the input gradation as an inverse gamma correction characteristic representing the relationship between the output gradation and the input gradation set in the inverse gamma correction circuit. An image display apparatus is disclosed that includes a portion that exceeds a predetermined gradation as a curve connected to a straight line, and is provided with switching means for switching the inverse gamma correction characteristics as a whole by varying the slope of the straight line. According to this image display device, the state of the displayed image can be effectively changed (see, for example, Patent Document 1).

Japanese Patent No. 3562707

  On the other hand, in the DCDM standard, the gamma characteristic is composed only of a curve. If the input is X and the output is Y, it is expressed by the following equation.

  Thus, the entire section of the gamma curve 103 has a gamma value (γ) = 1 / 2.6, and the gain is very high near the black level where the signal level is low (see FIG. 6). If the video signal processing circuit conforming to the DCDM standard is configured by hardware according to the conventional word length (for example, 8 bits), a bit drop will inevitably occur. If the word length is increased in order to prevent this, the subsequent processing will be affected and the circuit scale will be greatly increased. Although the signal level near the black level is very low (within 1%), once a bit drop occurs, reproduction is impossible in the subsequent processing, and the video quality is greatly deteriorated. As described above, when realizing LSI (Large Scale Integration) in conformity with the DCDM standard, there is a problem in that the conventional method cannot avoid bit dropping to some extent.

  The present invention has been made in view of such a point. When a video signal having a gamma characteristic having a high output signal level gain with respect to an input signal level is subjected to inverse gamma correction (gamma return) on the image receiving side. The purpose is to prevent bit dropping.

  In order to solve the above problems, the present invention calculates an inverse gamma curve when an input signal level of a video signal is 0 or more and performs input gamma signal input when performing an inverse gamma correction process on the input video signal. A straight line is calculated when the signal level is 0 or more, and a transition curve that smoothly connects the reverse gamma curve and the straight line is calculated in the preceding and following sections including the input signal level at the intersection of the reverse gamma curve and the straight line. Then, the straight line is used in the section including the signal level where the input signal level of the video signal is 0 and the bit drop occurs in the reverse gamma curve, and the reverse gamma curve is used in the section higher than the signal level in which the bit drop occurs. In addition, an inverse gamma correction characteristic is created by using a transition curve at the connection portion between the straight line and the inverse gamma curve. A reverse gamma correction process is performed based on an inverse gamma correction characteristic composed of the straight line, the reverse gamma curve, and the transition curve.

  According to the above-described configuration, the inverse gamma correction process using a single inverse gamma curve, such as a video signal that has been subjected to a gamma correction process with a high gamma value, is achieved by configuring the black level vicinity as a straight line and securing the signal level after level conversion. Bit dropping can be prevented for a steep input video signal in which bit dropping occurs in a low level region (near the black level).

  According to the present invention, bit loss is prevented from occurring when reverse gamma correction (gamma return) is performed on the image receiving side for a video signal having a gamma characteristic with a high gain of the output signal level with respect to the input signal level. Can do. Therefore, it is possible to suppress a decrease in video quality when displayed on the display.

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

  FIG. 1 is a block diagram of a video display apparatus according to an example of an embodiment of the present invention. In FIG. 1, a video display device 1 is a video signal processing circuit of the present invention, for example, a display 16 such as a liquid crystal panel or PDP (Plasma Display Panel) as shown in FIG. A reverse gamma correction circuit 11 that performs reverse gamma correction corresponding to the gamma correction characteristics of the display 16, and a signal in a linear region such as a 3 × 3 matrix process for the video signal that has been subjected to the reverse gamma correction by the reverse gamma correction circuit 11. Linear region signal processing 12 for processing, gamma correction processing 13 for performing gamma processing again according to the display on the video signal processed by the linear region signal processing circuit 12, and video signal that has been gamma corrected by the gamma correction circuit 13 An error diffusion / dither processing circuit 14 that performs error diffusion processing and dither processing, and an error diffusion / dither processing circuit 14 A display driving circuit 15 is provided for driving the display 16 based on the processed video signal and displaying the video on the display 16. Since the linear area signal processing 12, the gamma correction processing 13, the error diffusion / dither processing circuit 14, the display driving circuit 15 and the display 16 are well-known techniques and are not essential parts of the present invention, detailed description thereof will be omitted. To do.

  The inverse gamma correction circuit 11 of the video display device 1 receives, for example, a DCDM R (red) system video signal represented by 8 bits. The DCDM standard stipulates that inverse gamma correction according to a gamma correction curve (γ value = 2.6) expressed by Equation (5) is applied to a video signal. Therefore, the inverse gamma correction circuit 11 converts the level of the input video signal so that the reverse gamma correction is performed on the input video signal as the video signal to be sent to the display 16. Specifically, the inverse gamma correction circuit 11 has a signal level corresponding to the inverse gamma correction characteristic calculated based on the inverse characteristic curve of the gamma correction curve (“inverse gamma correction curve” or simply “inverse gamma curve”). Perform conversion. For example, in the case of a video signal composed of three primary color signals of R (red), G (green), and B (blue), this series of processing is performed for each of the three channels of RGB.

  In this example, the input video signal is added to the inverse gamma correction circuit 11 after being added with a black level (specified level) and subjected to gamma correction (γ = 2.6). In the (inverse gamma correction) process, the black level is subtracted before performing the process. Further, the gamma return processing of this example is performed separately according to the signal level of the input video signal. As shown in FIG. 3, the input signal level is functionally large, and the interval (negative interval) from the signal level (input -7%) corresponding to code 0 of the input video signal to the black level (input 0%, code 16). From the black level to the normal inverse gamma correction, the section including the signal level where the bit drop occurs (straight section), the section having a predetermined width from the end point of the straight section (transition section), and higher than the end point of the transition section It is divided into four sections (inverse gamma curve sections) on the level side, in which gamma return is performed along the reverse gamma curve of the normal rule (DCDM standard, γ = 2.6 in this example). FIG. 4 is an enlarged view of the inverse gamma correction characteristic of FIG.

  Next, the inverse gamma correction circuit 11 that performs level conversion corresponding to the inverse gamma correction characteristics will be described. A block configuration of the inverse gamma correction circuit 11 is shown in FIG. As shown in FIG. 2, the inverse gamma correction circuit 11 includes a negative side calculation unit 21, a straight line calculation unit 22, a transition calculation unit 23, an inverse gamma curve calculation unit 24, a selector 25 to which an output signal of each calculation unit is supplied, A memory 26, a control unit 27, and an encoder 28 are provided. The video signal input to the inverse gamma correction circuit 11 is first input to each of the negative side calculation unit 21, the straight line calculation unit 22, the transition calculation unit 23, and the reverse gamma curve calculation unit 24. In this example, as described above, the black level of the video signal input to the inverse gamma correction circuit 11 has already been subtracted, and the negative max value is set to − (minus) black level.

  The negative side calculation unit 21 generates a predetermined curve with respect to the input video signal when the signal level is less than 0% from the -black level, and performs signal level conversion. This section is narrow as a whole, and since the priority is lower than a value of 0 or more, the curve is generated by polygonal line approximation.

  The straight line calculation unit 22 performs a straight line calculation (Y = aX + b; X is an input signal level, Y is an output signal level, a, b based on a straight line 31 shown in FIG. 4 in a section where the signal level of the input video signal is 0% or more. Is a constant) and performs signal level conversion. It is assumed that the straight line at this time has a slope that intersects with the inverse gamma correction curve around the signal level where the bit drop occurs.

  The inverse gamma curve calculation unit 24 generates an inverse gamma correction curve 33 (see FIG. 4) conforming to a predetermined standard (DCDM standard in this example) when the signal level of the input video signal is 0% or more, and converts the signal level. I do. In this example, a cubic interpolation calculation is performed that can generate a curve that is relatively accurate with less setting parameters and that is closer to the ideal than the polygonal line approximation. The inverse gamma curve calculation unit 24 holds a predetermined number of sample data after inverse gamma correction in advance, restores the inverse gamma correction curve by performing cubic interpolation calculation based on these sample data, and restores the restored gamma correction Video signal level conversion is performed according to the curve. The level conversion process in the inverse gamma curve calculation unit 24 will be briefly described below.

  The inverse gamma curve calculation unit 24 divides the signal level of the input video signal from the minimum value (= 0) to the maximum value (= max) into equal intervals at an arbitrary interval, so that the dynamic range of the input video signal is obtained. Set multiple sample points on top. The inverse gamma curve calculation unit 24 holds the signal level on the inverse gamma correction curve at the sample point as sample data. That is, the sample data is the signal level after performing inverse gamma correction on the signal level when the input video signal is at the signal level of the sample point.

  When a video signal of a certain arbitrary signal level is input, the inverse gamma curve calculation unit 24 has two sample points located near the high level side and near the low level side with respect to the input signal level. Two sample points located are detected. Then, four sample data corresponding to the detected four sample points are selected. The inverse gamma curve calculation unit 24 performs cubic interpolation calculation based on the selected four sample data, and calculates a corrected signal level corresponding to the signal level of the input video signal. The inverse gamma correction circuit 11 performs level conversion of the signal level of the input video signal as described above.

  Cubic interpolation is an interpolation algorithm using a cubic polynomial called a kernel function. For example, “George Wolberg“ Digital Image Warping ”, IEEE Computer Society Press, ISBN 0-8186-8944-7, 1990. "It is described in.

  The transition calculation unit 23 generates a transition curve 32 (see FIG. 4) that is substantially centered at the intersection 34 of the straight line calculated by the straight line calculation unit 22 and the reverse gamma correction curve calculated by the reverse gamma curve calculation unit 24. The chamfering is performed by smoothly connecting the inverse gamma correction curve. In this example, a transition curve is generated by broken line approximation, and a smooth curve with a wide transition section to a curve with a narrow transition section and a slightly inferior smoothness can be selected by setting.

  The signals whose signal levels have been converted by the respective arithmetic units 21 to 24 are supplied to selectors (switching units) 25, respectively. The selector 25 switches the output of each calculation unit based on a control signal input from an encoder 28 described later.

  On the other hand, the video signal input to the inverse gamma correction circuit 11 is also input to the memory (storage unit) 26. The memory 26 stores setting information 26a to 26d of the minimum value and the maximum value of the signal level in each of the negative interval, the straight interval, the transition interval, and the inverse gamma curve interval of the inverse gamma correction characteristic. That is, these setting information shows the handling section of each calculating part 21-24.

  For example, in the example of the inverse gamma correction characteristics shown in FIGS. 3 and 4, the setting information 26 a corresponding to the straight section is stored in the memory 26 from input −7% (code 0) to input 0% (code 16). The setting information 26b corresponding to the straight section is a predetermined signal level Ta on the higher level side from the bit drop portion due to the gamma curve from the input 0%, and the setting information 26c corresponding to the transition section is the straight line 31 from the signal level Ta. The predetermined signal level Tb located on the high level side with the intersection 34 of the inverse gamma curve 33 as the center, and the setting information 26d corresponding to the inverse gamma curve section is the value of each signal level from the signal level Tb to 100% input. Is held.

  In the inverse gamma correction circuit 11, the memory 26 may be constituted by a RAM or a ROM. In the case of the RAM, the interval condition of the inverse gamma correction characteristic can be appropriately stored from an external controller.

  The controller 27 is an example of a control unit, and includes an arithmetic processing device such as a CPU (Central Processing Unit). The controller 27 has a function of instructing the memory 26 to specify the type of input signal used for the inverse gamma correction process, that is, the output signal constituting the inverse gamma correction characteristic. For example, as shown in FIG. 3, when the inverse gamma correction processing is performed using all of the negative side calculation unit 21, the straight line calculation unit 22, the transition calculation unit 23, and the reverse gamma curve calculation unit 24, the controller 27 stores the memory 26. An ON signal is output with respect to each setting information 26a to 26d.

  When there is an output signal that is not used for the inverse gamma correction characteristic, the control signal for the setting information corresponding to the calculation unit of the output signal is turned off. For example, when the black level is not subtracted from the input video signal, an off signal is sent to the setting information 26a, and a straight line (straight line section), a transition curve (transition section), and a negative section curve are excluded. It is also possible to construct an inverse gamma correction characteristic from an inverse gamma curve (inverse gamma curve section).

  In the memory 26, for each output signal selected by the controller 27, it is determined which of the sections stored in the memory 26 the input signal level of the video signal corresponds to, and the determination result is output to the encoder 28. For example, when the signal level at a certain moment of the input video signal corresponds to a straight section (that is, a straight line), a signal set with a flag “1” indicating that it corresponds to a straight section (setting information 26b), another section ( For the setting information 26a, 26c, 26d), a signal “0” is output to the encoder 28. Further, for example, when the input signal level increases and the signal level shifts from the straight section and corresponds to the transition section, that is, the setting information 26c, the signal with the flag “1” indicating that is set, and other sections A “0” signal is output to the encoder 28.

  Regarding the selection of the type of output signal that constitutes the inverse gamma correction characteristic, for example, the controller 27 specifies the standard of the video signal from management information included in the input video signal, and performs the reverse gamma correction based on the standard. It may be configured to automatically determine the characteristics and select setting information to be referred to and output an on / off signal to the memory 26. Alternatively, based on the operation signal input by the user operating the operation unit (not shown) installed in the video display device, the controller 27 uses the output signal from any of the operation units to perform inverse gamma. You may determine whether correction processing is performed.

  The encoder (encoder) 28 performs a predetermined encoding process on the signal supplied from the memory 26 and supplies the signal to the selector 25. The selector 25 switches the output signals of the arithmetic units 21 to 24 based on the signal supplied from the encoder 28, converts the input video signal into a substantially linear characteristic, and converts the input video signal into a circuit at a later stage, in this example, error diffusion. Output to the dither processing circuit 12

  Based on the video signal that has been subjected to error diffusion processing and dither processing by the error diffusion / dither processing circuit 14, the display drive circuit 15 drives the display 16 to display the video on the display 16.

  With the above-described configuration, even in a steep input video signal in which a bit drop occurs in the vicinity of the black level in the inverse gamma correction process using the inverse gamma curve 33 alone, the vicinity of the black level is constituted by the straight line 31 and the level is converted. As a result, the signal level can be secured and bit loss can be prevented. Strictly speaking, the color reproduction is different from the ideal data, but it is displayed on the display by executing such video signal processing while ensuring a word length (for example, lower 8 bits) that can be suppressed to a very low level. It is possible to minimize the influence on the displayed image. Note that the number of bits of the word length is not limited to this example.

  For example, the straight section of the inverse gamma correction characteristic shown in FIGS. 3 and 4 requires a large word length and is not realistic if an ideal process is to be realized by hardware. If floating point arithmetic is performed as one method, accuracy can be ensured, but the circuit scale becomes large in hardware, which is very difficult to implement. Bit loss occurs when the word length is as small as conventional, which does not burden the hardware. Once a bit drop occurs, the data becomes “0” and cannot be restored in the subsequent processing. In addition, the video level in the vicinity where the bit drop occurs is important, and the processing of the video signal having no gradation such as “blackout” significantly deteriorates the video quality. The present invention can solve the above-mentioned problem by performing a linear approximation for the section where the bit loss occurs, and executing the inverse gamma correction process without setting the video level to “0” although it includes some errors. . Therefore, in the video display device equipped with this video signal processing circuit, the video quality particularly near the black level is improved.

  In addition, the inverse gamma correction characteristic is divided into a plurality of sections, and the type and section of the output signal constituting the reverse gamma correction characteristics can be changed from the controller 27, so that the reverse gamma correction curve alone or the straight line is reversed. Various inverse gamma correction characteristics (inverse gamma return curves) such as those with mixed gamma correction curves can be created with high accuracy. Therefore, on the image receiving side, video signals (gamma characteristics) that comply with various standards such as the DCDM standard, ITU709, and sRGB can be handled. When the output signal constituting the inverse gamma correction characteristic is changed, it is necessary to change the setting of the signal level range of the setting information 26a to 26b.

  Also, as shown in FIGS. 3 and 4, a transition section is provided between a straight section approximating the straight line of the reverse gamma correction characteristic and the reverse gamma curve section, and the vicinity of the intersection 34 between the straight line 31 and the reverse gamma correction curve 33. The connecting part is rounded. By generating such a gentle curve, the straight line 31 and the inverse gamma correction curve 33 are smoothly connected, and a steep level change of the video signal that causes a reduction in image quality can be eliminated.

  Note that the video display apparatus in the above-described embodiment performs a reverse gamma correction process on the input gamma-processed video signal and displays it, and has a configuration for achieving the object of the present invention. Needless to say, it may be provided with the inverse gamma correction circuit 11 (video signal processing circuit), and various other modifications and changes are possible.

  Moreover, although the example which performs a cubic interpolation calculation was demonstrated in the said embodiment as a gamma return process implemented in the reverse gamma correction circuit 11, other nonlinear interpolation processes, for example, the method of using a look-up table, and the method of approximating with a polynomial Etc. may be applied.

  In the above embodiment, the case where the number of gradation bits representing the signal level of the video signal input to the inverse gamma correction circuit 11 is set to 8 bits. However, the present invention is not limited to 8 bits, and other bits may be used. Of course it is good.

It is a block block diagram of the video display apparatus concerning one Embodiment of this invention. It is a block block diagram of the reverse gamma correction circuit which concerns on one Embodiment of this invention. It is a diagram which shows the example of the reverse gamma correction characteristic which concerns on one Embodiment of this invention. FIG. 4 is a partially enlarged view of FIG. 3. It is a diagram which shows the gamma correction characteristic in each standard. It is the elements on larger scale of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Video display apparatus, 11 ... Reverse gamma correction circuit, 12 ... Linear area signal processing circuit, 13 ... Gamma correction processing circuit, 14 ... Error diffusion / dither processing circuit, 15 ... Display drive circuit, 16 ... Display, 21 ... Negative Side calculation unit, 22 ... straight line calculation unit, 23 ... transition calculation unit, 24 ... inverse gamma curve calculation unit, 25 ... selector, 26 ... memory, 27 ... controller, 28 ... encoder, 31 ... straight line, 32 ... transition curve, 33 ... Inverse gamma curve, 34 ... Intersection

Claims (6)

In the video signal processing circuit that performs inverse gamma correction processing on the input gamma processed video signal,
An inverse gamma curve calculation unit for calculating an inverse gamma curve in accordance with a predetermined standard when the input signal level of the video signal is 0 or more;
A straight line calculation unit for calculating a straight line when the input signal level of the video signal is 0 or more;
A transition calculation unit that calculates a transition curve connecting the inverse gamma curve and the straight line in a section before and after the input signal level at the intersection of the inverse gamma curve and the straight line;
The straight line in a section including a signal level in which a bit drop occurs in the inverse gamma curve from 0 to the input signal level of the video signal, the inverse gamma curve in a section higher than the signal level in which the bit drop occurs, and A video signal processing circuit, wherein an inverse gamma correction characteristic is generated from the transition curve connecting the straight line and the inverse gamma curve, and an inverse gamma correction process is performed based on the inverse gamma correction specification. A switching unit that switches an output signal supplied from the straight line calculation unit, the transition calculation unit, and the inverse gamma curve calculation unit according to an instruction and outputs the output signal to the outside;
A storage unit that stores a minimum value and a maximum value setting of the signal level in each of the straight interval, the transition interval, and the inverse gamma curve interval of the inverse gamma correction characteristic;
A control unit for instructing the type of output signal constituting the inverse gamma correction characteristic;
For each output signal selected by the control unit, it is determined which of the sections stored in the storage unit the input signal level of the video signal corresponds to, and the determination result is input to the switching unit. The video signal processing circuit according to claim 1. A negative-side arithmetic unit that calculates a predetermined curve in a negative interval where the input signal level of the video signal is less than 0 and supplies an output signal to the switching unit; and the storage unit has a negative interval of the inverse gamma correction characteristic The video signal processing circuit according to claim 2, wherein settings of a minimum value and a maximum value of the signal level in the are stored. The video signal processing circuit according to claim 2, wherein the control unit selects a type of an output signal constituting the inverse gamma correction characteristic according to a gamma value used for the gamma processing. In a video display device that performs reverse gamma correction processing on an input gamma processed video signal and displays it,
An inverse gamma curve calculation unit for calculating an inverse gamma curve in accordance with a predetermined standard when the input signal level of the video signal is 0 or more;
A straight line calculation unit for calculating a straight line when the input signal level of the video signal is 0 or more;
In a section before and after including the input signal level at the intersection of the inverse gamma curve and the straight line, the transition calculation unit is configured to calculate a transition curve connecting the reverse gamma curve and the straight line,
The straight line in a section including a signal level in which a bit drop occurs in the inverse gamma curve from 0 to the input signal level of the video signal, the inverse gamma curve in a section higher than the signal level in which the bit drop occurs, and An image display device comprising: an image signal processing circuit that generates an inverse gamma correction characteristic from the transition curve connecting the straight line and the inverse gamma curve, and performs an inverse gamma correction process based on the inverse gamma correction characteristic. In a video signal processing method for performing an inverse gamma correction process on an input gamma processed video signal,
Calculating an inverse gamma curve in accordance with a predetermined standard when the input signal level of the video signal is 0 or more;
Calculating a straight line when the input signal level of the video signal is 0 or more;
Calculating a transition curve connecting the inverse gamma curve and the straight line in a section before and after the input signal level at the intersection of the inverse gamma curve and the straight line;
The straight line in a section including a signal level in which a bit drop occurs in the inverse gamma curve from 0 to the input signal level of the video signal, the inverse gamma curve in a section higher than the signal level in which the bit drop occurs, and Generating an inverse gamma correction characteristic from the transition curve connecting the straight line and the inverse gamma curve;
And a step of performing a reverse gamma correction process on the video signal based on the reverse gamma correction characteristic.

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