WO2019039111A1 - Video processing device, display appartus, video processing method, control program, and recording medium - Google Patents

Video processing device, display appartus, video processing method, control program, and recording medium Download PDF

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Publication number
WO2019039111A1
WO2019039111A1 PCT/JP2018/025554 JP2018025554W WO2019039111A1 WO 2019039111 A1 WO2019039111 A1 WO 2019039111A1 JP 2018025554 W JP2018025554 W JP 2018025554W WO 2019039111 A1 WO2019039111 A1 WO 2019039111A1
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value
gradation
luminance level
gradation value
maximum
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PCT/JP2018/025554
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French (fr)
Japanese (ja)
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神田　貴史
下田　裕紀
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シャープ株式会社
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    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G5/00—Control arrangements or circuits for visual indicators common to cathode-ray tube indicators and other visual indicators
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G5/00—Control arrangements or circuits for visual indicators common to cathode-ray tube indicators and other visual indicators
    • G09G5/10—Intensity circuits
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G5/00—Control arrangements or circuits for visual indicators common to cathode-ray tube indicators and other visual indicators
    • G09G5/36—Control arrangements or circuits for visual indicators common to cathode-ray tube indicators and other visual indicators characterised by the display of a graphic pattern, e.g. using an all-points-addressable [APA] memory
    • G09G5/39—Control of the bit-mapped memory
    • G09G5/391—Resolution modifying circuits, e.g. variable screen formats
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N5/00—Details of television systems
    • H04N5/14—Picture signal circuitry for video frequency region
    • H04N5/20—Circuitry for controlling amplitude response
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N5/00—Details of television systems
    • H04N5/66—Transforming electric information into light information

Definitions

  • One aspect of the present invention relates to an image processing apparatus or the like that converts a gradation value of an HDR signal.
  • HDR High Dynamic Range
  • SDR Standard Dynamic Range
  • the SDR signal is manufactured on the premise of reproduction in an reproduction environment (hereinafter referred to as “SDR environment”) having an EOTF (Electro-Optical Transfer Function) of ⁇ 2.2 or the like, while the HDR signal is And SMPTE-ST 2084 (hereinafter, abbreviated as "ST2084") and the like, and is manufactured on the premise of regeneration in a reproduction environment (hereinafter, described as "SDR environment”) having an EOTF.
  • SDR environment SDR environment
  • the luminance of the obtained image is different from the luminance intended by the producer.
  • Patent Document 1 discloses a liquid crystal display device that performs light adjustment control of a backlight by changing the change width of the average luminance level before and after the expansion of the dynamic range according to the average luminance level of the input video signal and the ⁇ adjustment value. It is done.
  • Patent Document 2 discloses a scan conversion unit that scans and converts an input video signal into a signal having a predetermined number of scanning lines, a gamma correction unit that performs gamma correction on the signal from the scan conversion unit, and a signal level from the input video signal.
  • a plasma display is disclosed that includes a level detection unit that detects and controls a gamma correction unit based on the detection signal, and controls average brightness according to an input signal level.
  • the EOTF of the HDR signal is different from that of the SDR signal. Therefore, when attempting to map the entire EOTF domain for the HDR signal to the EOTF domain for the SDR signal when converting the grayscale values taken by each pixel with the HDR signal, the tone values are degraded (different floors It may occur that tone values are mapped to the same tone value).
  • the number of gradations per unit luminance difference is particularly large in the low luminance region in order to express a slight difference between light and dark in the dark part. Therefore, when the gradation value taken by each pixel is converted with the HDR signal by such mapping, degeneration of the gradation value is likely to occur in the low luminance region.
  • the range corresponding to the luminance level equal to or lower than the maximum luminance level of the content is mapped to the EOTF domain for the SDR signal.
  • the HDR signal includes metadata called MAX_CLL (Maximum Content Light Level) that represents the maximum luminance of the content. The maximum brightness of the content can be specified by referring to this metadata.
  • the maximum intensity level of the content is the intensity level of a particular pixel of a particular frame of a particular scene. Therefore, in frames other than this specific frame or scenes other than this specific scene, gradation values that are not actually used are mapped to the domain of the EDR for the SDR signal. That is, in the method of mapping the range corresponding to the luminance level equal to or lower than the maximum luminance level of the content in the EOTF definition area for the HDR signal to the EOTF definition area for the SDR signal, There is room to further suppress the degeneracy of the regulation.
  • the present invention has been made in view of the above problems, and an object thereof is a gradation value conversion device for converting gradation values of an HDR signal, wherein degeneration of gradation values that may occur in a low luminance region To realize the gradation value conversion device further suppressed.
  • a video processing apparatus converts the gradation value taken by each pixel in a video signal according to a second video format having a wider luminance range than the first video format.
  • Image processing apparatus wherein a virtual maximum luminance level not exceeding the maximum luminance level indicated by the metadata included in the video signal is set by referring to the gradation value taken by each pixel in the video signal.
  • a luminance level setting unit and, among the gradation values taken by each pixel in the video signal, the gradation values corresponding to the respective luminance levels below the virtual maximum luminance level are converted to be larger than the virtual maximum luminance level and And a tone value conversion unit for converting a tone value corresponding to each brightness level lower than the maximum brightness level into a value higher than the brightness value corresponding to the virtual maximum brightness level.
  • a video processing method is a video processing method for converting a gradation value taken by each pixel in a video signal according to a second video format having a wider luminance range than the first video format.
  • Virtual maximum luminance level setting step of setting a virtual maximum luminance level not exceeding the maximum luminance level indicated by the metadata included in the video signal by referring to the gradation value taken by each pixel in the video signal;
  • the gradation values corresponding to each luminance level equal to or lower than the virtual maximum luminance level are converted to be larger than the virtual maximum luminance level and equal to or lower than the maximum luminance level
  • a tone value conversion step of converting the tone value corresponding to the brightness level into a value equal to or greater than the brightness value corresponding to the virtual maximum brightness level.
  • a gradation value conversion device in which degeneration of gradation values that may occur in a low luminance region is further suppressed.
  • Embodiment 1 (Display 1) A display device 1 provided with a gradation value conversion device (video processing device) 2 according to a first embodiment of the present invention will be described with reference to FIGS. 1 and 2.
  • FIG. FIG. 1 is a block diagram showing a configuration of a display device 1 provided with a tone value conversion device 2 according to the present embodiment.
  • FIG. 2 is a perspective view showing the appearance of the display device 1. As shown in FIG. 1, the display device 1 includes a gradation value conversion device 2, a panel control unit 6, and a display panel 7.
  • the gradation value conversion device 2 is a device for converting the gradation value of each pixel of the HDR signal (video signal according to the second video format), and the video data acquisition unit 3, virtual maximum luminance level setting unit 4, and floor A tuning conversion unit 5 is provided.
  • the video data acquisition unit 3 acquires an HDR signal.
  • the HDR signal acquired by the video data acquisition unit 3 is an HDMI signal based on the HDMI (registered trademark) (High-Definition Multimedia Interface) standard, a Tuner signal (a signal received by the tuner), and a CVBS. (Composite Video, Blanking, and Sync: composite video signal) signals and the like.
  • the HDR signal is also included as metadata such as MAX_CLL indicating the maximum luminance level of the content, in addition to the gradation value taken by each pixel.
  • the virtual maximum luminance level setting unit 4 refers to the gradation value or metadata included in the HDR signal acquired by the video data acquisition unit 3 and sets the virtual maximum luminance level smaller than the maximum luminance level indicated by MAX_CLL for each frame Or set for each scene.
  • the gradation value conversion unit 5 refers to the virtual maximum luminance level set by the virtual maximum luminance level setting unit 4 and determines the gradation value to be taken by each pixel in the HDR signal from the first gradation value to the second gradation.
  • the gradation value conversion unit 5 selects the gradation value corresponding to each luminance level equal to or lower than the virtual maximum luminance level set by the virtual maximum luminance level setting unit 4 among the gradation values that each pixel can take in the HDR signal. Is used to correspond to each gradation value in the definition area of the EOTF for the SDR signal (video signal according to the first video format).
  • the panel control unit 6 controls the luminance of each pixel of the display panel 7 to a luminance value corresponding to the gradation value obtained by the gradation value conversion unit 5 in the SDR EOTF. As a result, the video represented by the HDR signal is displayed on the display panel 7 at the original luminance.
  • the display panel 7 may be realized by any device capable of displaying an image, but as a specific example, a liquid crystal display, an organic EL (Electro Luminescence) display, a plasma display, etc. Can be mentioned.
  • FIG. 3 is a flowchart showing the flow of tone conversion processing.
  • FIG. 4 is a graph showing the contents of tone conversion processing.
  • the tone value conversion device 2 executes the steps S0 to S4 described below for each frame to obtain the tone value of each pixel constituting the HDR signal from the first tone value. Convert to the second tone value.
  • the video data acquisition unit 3 acquires an HDR signal (step S0).
  • the video data acquisition unit 3 supplies, to the virtual maximum luminance level setting unit 4 and the gradation value conversion unit 5, the gradation value taken by each of the pixels constituting the processing target frame in the acquired HDR signal.
  • the virtual maximum luminance level setting unit 4 acquires, from the video data acquisition unit 3, the gradation value to be taken by each pixel constituting the processing target frame, and acquires the maximum value of the acquired gradation values (maximum gradation value in frame) ) Is set as the virtual maximum luminance level (step S1).
  • FIG. 4A shows the correspondence (OETF) between the luminance value and the gradation value in the HDR signal.
  • the in-frame maximum luminance value corresponding to the in-frame maximum gradation value is lower than the maximum luminance level of the content indicated by MAX_CLL. Therefore, the virtual maximum brightness level set in this step is lower than the maximum brightness level of the content indicated by MAC_CLL.
  • the virtual maximum brightness level setting unit 4 supplies the set virtual maximum brightness level to the tone value conversion unit 5.
  • the gradation value conversion unit 5 acquires, from the video data acquisition unit 3, the gradation value to be taken by each of the pixels constituting the processing target frame, and the acquired gradation value from the first gradation value to the second. It converts into a gradation value (step S2). For this conversion, the gradation value conversion unit 5 acquires the virtual maximum luminance level from the virtual maximum luminance level setting unit 4, and among the gradation values that each pixel can take for the HDR signal, the acquired virtual maximum luminance A mapping is used in which the gradation value x corresponding to each luminance level y below the level is made to correspond to each gradation value X in the EOTF definition area for the SDR signal.
  • MAX_y represents a virtual maximum luminance level
  • MAX_Y represents a maximum value (corresponding to a maximum luminance level of a display device) of a range of EOTF for SDR signal.
  • (B) in FIG. 4 is a graph showing the relationship between the luminance value x before conversion and the gradation value y (OETF for HDR signal), and (c) in FIG. It is a graph showing the relationship with gradation value Y (OETF for SDR signal).
  • the tone value conversion unit 5 supplies, to the panel control unit 6, the tone value after conversion which each pixel constituting the processing target frame takes.
  • the panel control unit 6 acquires, from the gradation value conversion unit 5, gradation values after conversion which each pixel constituting the processing target frame takes, and converts the acquired gradation values into luminance values (step S3). ).
  • the panel control unit 6 uses an EDR for SDR, for example, an EOTF equivalent to ⁇ 2.2. This conversion is also called tone mapping, and the correspondence between tone values and luminance values in this conversion is also called tone curve.
  • the panel control unit 6 controls the luminance of each pixel constituting the display panel 7 to the luminance value obtained by tone mapping. As a result, the processing target frame is displayed on the display panel 7 (step S4).
  • the range corresponding to the luminance value equal to or lower than the virtual maximum luminance level in the domain of EOTF for HDR signal is defined as the domain of EOTF for SDR signal.
  • Use mapping to correspond Since the virtual maximum brightness level is lower than the maximum brightness level indicated by MAC_CLL, the definition of the EOTF for SDR signal in the range corresponding to the brightness value equal to or less than the maximum brightness level indicated by MAX_CLL within the definition area of EOTF for HDR signal In comparison with the case of using the mapping corresponding to the area, it is possible to suppress the black crushing and the gradation value degeneration.
  • the gradation value conversion process is performed for every frame, and the intra-frame maximum luminance value of each frame is set as the virtual maximum luminance level
  • the present embodiment is not limited to this.
  • tone value conversion processing is performed for each scene, and the in-scene maximum luminance value of each scene (the in-frame maximum of all the frames constituting that scene).
  • the maximum value of the luminance values is the virtual maximum luminance level. In this case, before starting the tone value conversion of the first frame constituting the processing target scene, the gradation values taken by the pixels constituting all the frames constituting the processing target scene are acquired, and the maximum luminance value in the scene is obtained.
  • the virtual maximum luminance level is set with reference to this metadata. With such a configuration, it is possible to perform gradation value conversion processing not only on the HDR signal recorded in the recorder or the like but also on the HDR signal received by the tuner or the like.
  • an arrangement may be adopted in which the temporal average value of the intra-frame maximum luminance values of each frame is set as the virtual maximum luminance level.
  • the temporal average value of the intra-frame maximum luminance values of each frame is set as the virtual maximum luminance level.
  • a well-known time average filter may be used to calculate the time average value of the in-frame luminance value of each frame.
  • step S1 the virtual maximum luminance level setting unit 4 sets the luminance value (in-frame maximum luminance value) or the luminance value corresponding to the acquired maximum value of the gradation values (maximum in-frame gradation value or in-scene maximum gradation value).
  • the configuration for setting the in-scene maximum luminance value) to the virtual maximum luminance level has been described.
  • the virtual maximum brightness level set by the virtual maximum brightness level setting unit 4 in step S1 is not limited to the in-frame maximum brightness value or the in-scene maximum brightness value. More specifically, the virtual maximum brightness level set by the virtual maximum brightness level setting unit 4 may be a value that does not exceed the maximum brightness level (MAX_CLL) indicated by the metadata included in the video signal.
  • MAX_CLL maximum brightness level
  • step S1 the virtual maximum brightness level setting unit 4 sets the virtual maximum brightness level to a brightness value lower than the in-frame maximum brightness value or the in-scene maximum brightness value.
  • step S3 the panel control unit 6 converts the gradation value acquired from the gradation value conversion unit 5 into a luminance value as described above.
  • the gradation values corresponding to the respective luminance levels larger than the virtual maximum luminance level and lower than the maximum luminance level (MAX_CLL) are Convert to a value greater than the luminance value corresponding to the virtual maximum luminance level.
  • step S4 the panel control unit 6 controls the luminance of each pixel constituting the display panel 7 to a luminance value obtained by tone mapping or a value greater than or equal to the luminance value corresponding to the virtual maximum luminance level.
  • FIG. (A) and (b) of FIG. 5 are graphs showing the relationship between the luminance value X and the gradation value Y after the conversion of step S2 (partly, the OETF for the SDR signal).
  • the panel control unit 6 sets each of the luminance values larger than the virtual maximum luminance level and lower than the maximum luminance level (MAX_CLL) among the gradation values acquired by the video data acquisition unit 3 in step S0.
  • the gradation value corresponding to the level may be regarded as a constant gradation value as shown in FIG. 5A, and may be converted into a constant luminance value corresponding to the virtual maximum luminance level.
  • the gradation value corresponding to each luminance level larger than the virtual maximum luminance level and lower than the maximum luminance level (MAX_CLL) is converted to a constant luminance value, and thus the image displayed by the converted luminance value
  • the effect is obtained that the gradation expression of the gradation value before conversion is not greatly impaired.
  • step S3 the panel control unit 6 determines that the gradation value acquired by the video data acquisition unit 3 in step S0 is greater than the virtual maximum luminance level and not higher than the maximum luminance level (MAX_CLL). Assuming that the gradation value corresponding to each luminance level gradually increases as the luminance value increases as (b) in FIG. 5 shows, the luminance value corresponding to the virtual maximum luminance level is equal to or higher than It may be converted to the value of As a result, in step S3, in the graph of the gradation value before conversion and the luminance value after conversion, panel control unit 6 gradually increases the luminance value after conversion as the gradation value before conversion increases.
  • MAX_CLL maximum luminance level
  • the gradation values corresponding to the luminance levels larger than the virtual maximum luminance level and lower than the maximum luminance level correspond to the virtual maximum luminance level so as to be larger. Convert to a value greater than the luminance value.
  • the size of the luminance value after conversion is a value according to the size of the gradation value before conversion, so that even in the image displayed with the luminance value after conversion, the floor of the gradation value before conversion is An effect is obtained that the tone expression is not significantly impaired.
  • the same configuration as the above-described configuration can be adopted even when the in-frame maximum luminance value or the in-scene maximum luminance value exceeds MAX_CLL.
  • the panel control unit 6 determines that the gradation value acquired by the video data acquisition unit 3 in step S0 is greater than the virtual maximum luminance level and is the maximum luminance value in the frame or the maximum in the scene.
  • the gradation value corresponding to each luminance level lower than the luminance value may be converted to a value higher than the luminance value corresponding to the virtual maximum luminance level.
  • the display device 1 including the tone value conversion device 2 shown in FIG. 1 is used as in the first embodiment.
  • FIG. 6 is a flowchart showing the flow of tone value conversion processing executed by the tone value conversion device 2 according to the present embodiment. Detailed descriptions of steps similar to those of the image processing method according to the first embodiment will be omitted.
  • step S10 the video data acquisition unit 3 acquires an HDR signal (step S0).
  • step S11 the virtual maximum luminance level setting unit 4 generates a histogram of luminance values corresponding to the gradation values taken by each of the pixels constituting the processing target frame, and obtains the histogram maximum value from the generated histogram.
  • the histogram maximum value here will be described later.
  • step S12 the virtual maximum brightness level setting unit 4 sets the virtual maximum brightness level to the histogram maximum value obtained in step S11.
  • the gradation value conversion unit 5 sets the virtual maximum luminance level (virtual maximum luminance level setting unit) among the gradation values (obtained from the video data acquisition unit 3) that each pixel can take for the HDR signal. 4) to convert the gradation value corresponding to each luminance level below into each gradation value within the definition range of the EDR for the SDR signal.
  • step S14 the panel control unit 6 adds the step of converting the gradation value acquired from the gradation value conversion unit 5 into the luminance value as in step S3 described above, and the video data acquisition unit 3 performs the step.
  • the gradation values acquired in S10 are the luminance values corresponding to the virtual maximum luminance level or more. Convert to a value
  • step S14 panel control unit 6 sets the gradation value corresponding to each luminance level larger than the virtual maximum luminance level and lower than the maximum luminance level (MAX_CLL) to the luminance corresponding to the virtual maximum luminance level. It may be converted to a value (constant luminance value). Further, in the graph of the gradation value before conversion and the luminance value after conversion, the panel control unit 6 causes the luminance value after conversion to gradually increase as the gradation value before conversion increases. The gradation value corresponding to each luminance level larger than the virtual maximum luminance level and lower than the maximum luminance level (MAX_CLL) may be converted to a value larger than the luminance value corresponding to the virtual maximum luminance level.
  • MAX_CLL maximum luminance level
  • the panel control unit 6 determines whether the image data acquisition unit 3 acquires the gradation value acquired in step S10. Among them, the gray level value corresponding to each brightness level larger than the virtual maximum brightness level (hist maximum value) and smaller than the in-frame maximum brightness value or the in-scene maximum brightness value is the brightness value corresponding to the virtual maximum brightness level. It may be converted to the above values.
  • step S15 panel control unit 6 corresponds the luminance of each pixel constituting display panel 7 to the luminance value obtained by tone mapping in step S14 or the virtual maximum luminance level. Control to a value greater than the luminance value.
  • the above-described histogram maximum value is the maximum value of the luminance values excluding specifically large luminance values among the luminance values corresponding to the gradation values taken by the pixels constituting the processing target frame, and the average value of the histogram It is an amount that can be calculated from the value M and the standard deviation ⁇ .
  • M + 3 ⁇ is a typical example of the histogram maximum.
  • FIG. 7 An example of the histogram generated in step S11 is shown in FIG.
  • some pixels have a uniquely large luminance value close to the maximum luminance level indicated by MAX_CLL.
  • the gradation value conversion step The area between the specifically large luminance value and the maximum value of the luminance values excluding the specifically large luminance value in S13 is uselessly associated with the range of the EDR for SDR.
  • the histogram maximum value of the luminance value corresponding to the gradation value taken by the pixels constituting the processing target frame is set as the virtual maximum luminance level, the luminance value excluding the specifically large luminance value In the tone value conversion step S13, the value range of the SDR EOTF can be associated without waste.
  • a configuration has been described in which a histogram of luminance values is created for each frame, and the intra-frame histogram maximum value of each frame is set as the virtual maximum luminance level, but the present embodiment is not limited to this.
  • a histogram of luminance values is executed for each scene and the in-scene histogram maximum value of each scene is a virtual maximum luminance level. It is.
  • a histogram of luminance values corresponding to the tone values taken by pixels making up all the frames making up the processing target scene is created And set the in-scene histogram maximum value to the virtual maximum luminance level.
  • the metadata indicating the in-scene histogram maximum value of each scene is included in the HDR signal, it is also possible to adopt a configuration in which the virtual maximum luminance level is set with reference to this metadata. With such a configuration, it is possible to perform gradation value conversion processing not only on the HDR signal recorded in the recorder or the like but also on the HDR signal received by the tuner or the like.
  • the intra-frame intra-histo maximum value of each frame may be temporally averaged to be the virtual maximum luminance level.
  • a well-known time average filter or the like may be used to calculate the time average value of the in-frame maximum values of the respective frames.
  • the display device 1 including the tone value conversion device 2 shown in FIG. 1 is used as in the first embodiment.
  • FIG. 8 is a flowchart showing the flow of tone value conversion processing executed by the tone value conversion device according to the present embodiment. Detailed descriptions of steps similar to those of the image processing method according to the first embodiment will be omitted.
  • step S100 the video data acquisition unit 3 acquires an HDR signal (step S0).
  • step S101 the virtual maximum luminance level setting unit 4 generates a histogram of luminance values corresponding to the gradation value taken by each pixel constituting the processing target frame, and obtains the histogram maximum value from the generated histogram.
  • the definition of the histogram maximum is similar to that given in the second embodiment.
  • the virtual maximum brightness level setting unit 4 sets a limit value lower by a predetermined value than the maximum brightness level indicated by MAC_CLL.
  • the predetermined value is an arbitrary value, and may be set at the time of factory shipment, or may be set by the user after factory shipment.
  • step S103 the virtual maximum luminance level setting unit 4 determines whether the histogram maximum value calculated in step S101 is lower than the limit value calculated in step S102.
  • the virtual maximum brightness level setting unit 4 sets the virtual maximum brightness level as the limit value (step S104). If the histogram maximum value is equal to or more than the limit value, the virtual maximum luminance level setting unit 4 sets the virtual maximum luminance level to the histogram maximum value (step S105).
  • the gradation value conversion unit 5 sets the virtual maximum luminance level (limit value) among the gradation values (obtained from the video data acquisition unit 3) that each pixel can take for the HDR signal.
  • the gradation value corresponding to each luminance level lower than the maximum value of the histogram is converted into each gradation value within the definition range of the EDR for the SDR signal (step S106).
  • step S107 the panel control unit 6 adds the step of converting the gradation value acquired from the gradation value conversion unit 5 into the luminance value as in step S3 described above, and the video data acquisition unit 3 performs the step.
  • the gradation value corresponding to each luminance level larger than the virtual maximum luminance level (limit value or maximum value of the histogram) and lower than the maximum luminance level (MAX_CLL) among the gradation values acquired in S100 is the virtual maximum luminance. Convert to a value greater than the luminance value corresponding to the level.
  • step S107 panel control unit 6 sets the gradation value corresponding to each luminance level larger than the virtual maximum luminance level (limit value or maximum value of the histogram) and not higher than the maximum luminance level (MAX_CLL). It may be converted to a luminance value (constant luminance value) corresponding to the virtual maximum luminance level. Further, in the graph of the gradation value before conversion and the luminance value after conversion, the panel control unit 6 causes the luminance value after conversion to gradually increase as the gradation value before conversion increases.
  • step S107 the panel control unit 6 determines whether the image data acquisition unit 3 acquires the gradation value acquired in step S100.
  • the gradation value corresponding to each luminance level which is larger than the virtual maximum luminance level (limit value or the maximum histogram value) and smaller than the in-frame maximum luminance value or the in-scene maximum luminance value corresponds to the virtual maximum luminance level. You may convert into the value more than the brightness value to be.
  • step S108 the panel control unit 6 corresponds the luminance of each pixel constituting the display panel 7 to the luminance value obtained by tone mapping in step S107 or the virtual maximum luminance level. Control to a value greater than the luminance value.
  • FIG. (A) and (c) in FIG. 9 show histograms of luminance values corresponding to the gradation values taken by the pixels constituting the processing target frame, and (b) and (d) in FIG. It is a graph showing the relationship between the luminance value X after conversion and the gradation value Y (OETF for SDR signal).
  • the virtual maximum brightness level setting unit 4 sets the virtual maximum brightness level to the limit value. In this case, as shown in (b) of FIG.
  • step S106 a range equal to or less than the limit value in the domain of the OETF for HDR signal is mapped to the entire domain of the OETF for SDR signal. Note that the process of step S107 described above is performed for the gradation value in the range larger than the limit value in the definition area of the OETF for the HDR signal.
  • step S105 when the histogram maximum value is equal to or more than the limit value, the virtual maximum luminance level setting unit 4 sets the virtual maximum luminance level to the histogram maximum value in step S105.
  • step S106 a range equal to or less than the maximum value of the histogram is mapped to the entire range of the EDRF for SDR in the range of EOTF for HDR signal. Note that the process of step S107 described above is performed for the gradation value in the range larger than the maximum value of the histogram within the range of the EOTF for the HDR signal.
  • the virtual maximum luminance can be generated when the histogram maximum value becomes extremely small by providing the limit value to the virtual maximum luminance level It is possible to prevent the deterioration of the image quality caused by the large fluctuation of the level.
  • Embodiment 4 The fourth embodiment of the present invention is described below with reference to the drawings.
  • the display device 1 including the tone value conversion device 2 shown in FIG. 1 is used as in the first embodiment.
  • the flow of tone value conversion processing executed by the tone value conversion device 2 according to the present embodiment is the same as the tone conversion processing performed by the tone value conversion device 2 according to the third embodiment, as shown in FIG. It is expressed by the flowchart shown in FIG. However, in the present embodiment, the limit value setting process S102 in the third embodiment is replaced with the limit value setting process S109 described below.
  • step S109 the virtual maximum brightness level setting unit 4 sets a predetermined ratio between the difference obtained by subtracting the limit value from the maximum brightness level indicated by MAX_CLL and the difference obtained by subtracting the maximum value of the histogram in the brightness histogram from the limit value.
  • the predetermined ratio is an arbitrary ratio, and may be set at the time of factory shipment, or may be set by the user after factory shipment.
  • step S104 when the histogram maximum value is lower than the limit value, the virtual maximum luminance level setting unit 4 sets the virtual maximum luminance level to the limit value in step S104.
  • step S106 a range equal to or less than the limit value in the domain of the OETF for HDR signal is mapped to the entire domain of the OETF for SDR signal. Note that the process of step S107 described above is performed for the gradation value in the range larger than the limit value in the definition area of the OETF for the HDR signal.
  • the virtual maximum luminance level setting unit 4 sets the virtual maximum luminance level to the histogram maximum value in step S105.
  • the range of the EOTF for the HDR signal in the range of the EOTF for the HDR signal, the range equal to or less than the maximum value of the histogram is mapped to the entire range of the EDR for the SDR signal. Note that the process of step S107 described above is performed for the gradation value in the range larger than the maximum value of the histogram within the range of the EOTF for the HDR signal.
  • the virtual maximum luminance can be generated when the histogram maximum value becomes extremely small by providing the limit value to the virtual maximum luminance level It is possible to prevent the deterioration of the image quality caused by the large fluctuation of the level.
  • the luminance value (maximum luminance value in a frame) corresponding to the maximum value (maximum gradation value in a frame) of the gradation value taken by each pixel constituting the processing target frame by the virtual maximum luminance level setting unit 4 Is described to set the virtual maximum brightness level. According to this configuration, it is possible to convert the gradation value according to the peak luminance which is the greatest advantage of HDR.
  • the tone value conversion device 11 converts the tone values of the low tone value region among the tone values converted by the tone value conversion unit 5.
  • the gradation value taken by each pixel constituting each frame or each scene in the video signal is adjusted so as to have a lifting portion.
  • the low gradation value area indicates a gradation value area near the origin (a point at which the gradation value and the corresponding luminance value are zero) in the converted gradation value.
  • the low gradation value area indicates an area of about one-fifth the gradation value when the gradation value is quantized with 8 bits (256 gradations (0 to 255)). (Area in which the gradation value is 0 to 51).
  • the area of the gradation value having the gradation value larger than the largest gradation value in the low gradation value area as the lowest gradation value is taken as the middle gradation value area, and the largest floor in the middle gradation value area.
  • a region of tone values having a tone value larger than a tone value as the lowest tone value is defined as a high tone value region.
  • “having a lifting portion in the gradation value of the low gradation value region” means the low floor caused by converting the gradation value by the gradation value conversion method described in the first embodiment. It means raising the tone value of the low tone region to improve the relative drop (blackout) of the tone value of the tone value region.
  • FIG. 11 is a block diagram showing a configuration of a display device 10 provided with the gradation value conversion device (video processing device) 11 according to the present embodiment. As shown in FIG. 11, the gradation value conversion device 11 further includes a gradation value adjustment unit 12 in addition to the configuration of the gradation value conversion device 2 according to the first embodiment.
  • the gradation value adjustment unit 12 adjusts the gradation value of the low gradation value region to have a lifting part among the gradation values converted by the gradation value conversion unit 5.
  • FIG. 12 is a flowchart showing the flow of tone value conversion processing.
  • the gradation value conversion process is performed for each frame and the maximum luminance value in each frame is set as the virtual maximum luminance level, the gradation value conversion process is performed for each scene, The same applies to a configuration in which the in-scene maximum luminance value of each scene is set as the virtual maximum luminance level.
  • the video data acquisition unit 3 acquires the HDR signal (step S20).
  • the video data acquisition unit 3 sets the gradation value taken by each pixel constituting the processing target frame in the acquired HDR signal to the virtual maximum luminance level setting unit 4 and the gradation value converter 5.
  • the virtual maximum luminance level setting unit 4 acquires, from the video data acquisition unit 3, the gradation value to be taken by each pixel constituting the processing target frame, and acquires the maximum value of the acquired gradation values (maximum gradation value in frame) ) Is set as the virtual maximum luminance level (step S21).
  • the gradation value conversion unit 5 acquires, from the video data acquisition unit 3, the gradation value to be taken by each pixel constituting the processing target frame, and among the acquired gradation values, the virtual maximum luminance level setting unit 4 The gradation value corresponding to each luminance level lower than the set virtual maximum luminance level is converted from the first gradation value to the second gradation value (step S22).
  • the gradation value adjustment unit 12 adjusts the gradation value of the low gradation value region to have a lifting part among the gradation values converted by the gradation value conversion unit 5 (step S23).
  • a specific example of the method of adjusting the gradation value by the gradation value adjustment unit 12 will be described later.
  • the tone value adjusted by the tone value adjusting unit 12 is preferably larger in the low tone value region than the tone value indicated by the predetermined format.
  • ST2084 can be mentioned.
  • the panel control unit 6 acquires, from the gradation value adjustment unit 12, the adjusted gradation values taken by the pixels constituting the processing target frame, and converts the acquired gradation values into luminance values (step S24). ) (Tone mapping).
  • the panel control unit 6 controls the luminance of each pixel constituting the display panel 7 to the luminance value obtained by tone mapping. As a result, the processing target frame is displayed on the display panel 7 (step S25).
  • FIG. 13 is a graph showing the relationship between the gradation value after conversion in step S22 and the corresponding luminance value.
  • Region A in FIG. 13 indicates the above-described low gradation value region, the dotted line indicates a curve before adjustment, and the solid line indicates a curve after adjustment.
  • the gradation value adjustment unit 12 adjusts the gradation value after conversion so that the gradation value in the region A has a lifting part (adjusts from a dotted curve to a solid curve).
  • the gradation value adjustment unit 12 adjusts the gradation value of the low gradation value region by adding a value of about 10% of the gradation value.
  • the gradation value to be adjusted is a gradation value according to ST2084
  • the gradation value adjustment unit 12 graphs the gradation value corresponding to the gradation value and the luminance value corresponding to the gradation value in the low gradation value region. If so, the curve in the graph is adjusted to be equal to the curve of ⁇ 2.2.
  • the gradation value adjustment unit 12 may change the low gradation value region with reference to the average value of the luminance levels corresponding to the gradation value converted by the gradation value conversion unit 5.
  • the low gradation value region can be set in accordance with the distribution of the luminance levels, so that the gradation values can be adjusted in accordance with the distribution of the luminance levels.
  • the average value of the luminance levels to which the tone value adjusting unit 12 refers may be calculated by the tone value adjusting unit 12 itself, or may be obtained from the outside.
  • the gradation value adjustment unit 12 also calculates the gradation value of the low gradation value region and the gradation value of the high gradation value region.
  • the tone values of the middle tone value region may be further adjusted so that.
  • step S21 the virtual maximum brightness level setting unit 4 sets the brightness value (maximum brightness value in a frame) corresponding to the maximum value of the acquired tone values (maximum tone value in a frame) to the virtual maximum brightness level.
  • Configuration has been described.
  • the virtual maximum brightness level set by the virtual maximum brightness level setting unit 4 in step S21 is not limited to the in-frame maximum brightness value.
  • the virtual maximum brightness level set by the virtual maximum brightness level setting unit 4 may be a value that does not exceed the maximum brightness level (MAX_CLL) indicated by the metadata included in the video signal. And each process in such composition is the same as each process explained by the modification of Embodiment 1.
  • step S24 the panel control unit 6 adds the gradation value adjusted by the gradation value adjustment unit 12 in step S23 to the luminance value, and the video data acquisition unit 3 performs the step.
  • the gradation values corresponding to each luminance level larger than the virtual maximum luminance level and lower than the maximum luminance level are the luminance values corresponding to the virtual maximum luminance level or more.
  • the panel control unit 6 sets each of the steps to a specific example, which is larger than the virtual maximum luminance level and lower than the maximum luminance level (MAX_CLL).
  • the gradation value corresponding to the luminance level may be converted into a luminance value (constant luminance value) corresponding to the virtual maximum luminance level. Further, in the graph of the gradation value before conversion and the luminance value after conversion, the panel control unit 6 causes the luminance value after conversion to gradually increase as the gradation value before conversion increases.
  • the gradation value corresponding to each luminance level larger than the virtual maximum luminance level and lower than the maximum luminance level (MAX_CLL) may be converted to a value larger than the luminance value corresponding to the virtual maximum luminance level.
  • the tone value conversion device 11 sets the virtual maximum brightness level to the maximum value of the brightness level, converts the tone value with reference to the set virtual maximum brightness level, Among the converted tone values, the tone value in the low tone value region is adjusted to have a lifting portion.
  • the tone value of the region By setting the virtual maximum luminance level to the maximum value of the luminance level, the fidelity of the peak feeling included in the video signal can be maintained, and the low gradation value among the converted gradation values can be maintained.
  • By adjusting the tone value of the region to have a raised portion it is possible to prevent blackout due to the decrease of the tone value of the low tone value region and improve the tone expression power of the low tone value region. .
  • the control block (in particular, the video data acquisition unit 3, the virtual maximum luminance level setting unit 4 and the gradation value conversion unit 5) of the gradation value conversion device 2 is a logic circuit (hardware) formed in an integrated circuit (IC chip) or the like. And may be realized by software using a CPU (Central Processing Unit).
  • a CPU Central Processing Unit
  • the gradation value conversion device 2 is a CPU that executes instructions of a program that is software that realizes each function, a ROM (Read Only) in which the program and various data are readably recorded by a computer (or CPU). Memory or storage device (these are referred to as “recording media”), and RAM (Random Access Memory) for developing the program.
  • the object of the present invention is achieved by the computer (or CPU) reading the program from the recording medium and executing the program.
  • the recording medium a “non-transitory tangible medium”, for example, a tape, a disk, a card, a semiconductor memory, a programmable logic circuit or the like can be used.
  • the program may be supplied to the computer via any transmission medium (communication network, broadcast wave, etc.) capable of transmitting the program.
  • the present invention can also be realized in the form of a data signal embedded in a carrier wave, in which the program is embodied by electronic transmission.
  • a video processing apparatus (2, 11) according to aspect 1 of the present invention is a video processing apparatus that converts a gradation value taken by each pixel in a video signal according to a second video format wider in luminance range than the first video format. And a virtual maximum brightness level setting unit that sets a virtual maximum brightness level not exceeding the maximum brightness level indicated by the metadata included in the video signal by referring to the gray scale value taken by each pixel in the video signal.
  • the gradation values corresponding to each luminance level below the virtual maximum luminance level are converted, and are larger than the virtual maximum luminance level, and And a gradation value conversion unit (5) for converting the gradation value corresponding to each luminance level lower than the maximum luminance level into a value higher than the luminance value corresponding to the virtual maximum luminance level.
  • the gradation value conversion unit determines whether the gradation value of each pixel in the image signal is higher than the virtual maximum luminance level A gradation value corresponding to each luminance level which is large and equal to or less than the maximum luminance level may be converted into a luminance value corresponding to the virtual maximum luminance level.
  • the gradation value corresponding to each luminance level larger than the virtual maximum luminance level and lower than the maximum luminance level is converted to a constant luminance value, the luminance values after conversion are displayed. Also in the image, the gradation expression of the gradation value before conversion is not significantly impaired.
  • the gradation value conversion unit is configured to generate the gradation value before conversion and the luminance value after conversion before the conversion.
  • the gradation value of each pixel in the video signal is larger than the virtual maximum luminance level and the maximum luminance level so that the luminance value after conversion gradually increases as the gradation value of the pixel increases.
  • the gradation values corresponding to the following luminance levels may be converted to values equal to or higher than the luminance value corresponding to the virtual maximum luminance level.
  • the size of the luminance value after conversion is a value corresponding to the size of the gradation value before conversion, so even in the image displayed with the luminance value after conversion, the floor before conversion is Do not significantly reduce the tone expression of the key value.
  • the gradation value conversion unit (5) takes each pixel in a second video format according to the video signal.
  • the image It converts the gradation value that each pixel takes in the signal.
  • the display quality of the video can be further improved.
  • the first video format is a format in which the EOTF is equivalent to ⁇ 2.2
  • the second video format is the EOTF Is a format that is SMPTE-ST2084.
  • the virtual maximum luminance level setting unit is a floor taken by each pixel constituting each frame or each scene in the video signal.
  • the virtual maximum luminance level is set by referring to the adjustment value.
  • the virtual maximum luminance level setting unit (4) determines that the virtual maximum luminance level corresponds to each frame or each scene in the video signal. Are set to the maximum value of the luminance level corresponding to the gradation value to be taken by each of the pixels constituting the image.
  • the gradation value in the low gradation value region has a lifting portion.
  • a tone value adjustment unit (12) for adjusting the image in the above-mentioned aspect 7, among the gradation values converted by the gradation value conversion section, the gradation value in the low gradation value region has a lifting portion. And a tone value adjustment unit (12) for adjusting the image.
  • the gradation value adjustment unit refers to the average value of the luminance levels corresponding to the gradation value converted by the gradation value conversion unit. Then, the low gradation value area is changed.
  • the low gradation value region can be set according to the distribution of the luminance level, it becomes possible to adjust the gradation value according to the distribution of the luminance level.
  • the gradation value adjustment unit is a graph of the gradation value converted by the gradation value conversion unit and the corresponding luminance level.
  • the tone values in the middle tone value area are further adjusted so that the tone values in the low tone value area and the tone values in the high tone value area change continuously.
  • the gradation value adjusted by the gradation value adjustment unit is the second image format in the low gradation value region. Greater than the indicated tone value.
  • the video image conversion device of the above aspects 8 to 10 can be suitably used.
  • the virtual maximum luminance level setting unit (4) takes each pixel constituting each frame or each scene in the video signal. A histogram of luminance levels corresponding to gradation values is created, and the virtual maximum luminance level is set by referring to the histogram.
  • the virtual maximum luminance level setting unit (4) configures each frame or each scene in the video signal with the virtual maximum luminance level.
  • the effective maximum value of the luminance level corresponding to the gradation value taken by each pixel is set to the effective maximum value defined by a constant multiple of the standard deviation of the histogram.
  • the virtual maximum luminance level setting unit (4) sets a limit value lower than the maximum luminance level by a predetermined value, and the video signal
  • the effective maximum value of the luminance level corresponding to the gradation value taken by each pixel constituting each frame or each scene in the image, and the effective maximum value defined by a constant multiple of the standard deviation of the histogram is higher than the limit value If it is low, the virtual maximum brightness level is set to the value of the limit value, and if the effective maximum value is equal to or more than the limit value, the virtual maximum brightness level is set to the effective maximum value.
  • the virtual maximum luminance level setting unit (4) is a difference obtained by subtracting the limit value from the maximum luminance level.
  • the effective maximum value of the luminance level corresponding to the gradation value taken by each pixel constituting each frame or each scene in the video signal, which is defined by a constant multiple of the standard deviation of the histogram The virtual maximum luminance level is set to the value of the limit value when the effective maximum value is lower than the limit value, and the difference obtained by subtracting the difference from the value is a predetermined ratio, and the effective maximum value is set. Is greater than or equal to the limit value, the virtual maximum brightness level is set to the effective maximum value.
  • the limit value can be set to a desired value.
  • the virtual maximum luminance level setting unit determines that the virtual maximum luminance level corresponds to each frame or each pixel forming each scene in the video signal.
  • the effective maximum value of the luminance level corresponding to the gradation value to be taken is set to a time average value of the effective maximum value defined by a constant multiple of the standard deviation of the histogram.
  • the video quality can be improved.
  • the display device (1, 10) according to aspect 17 of the present invention includes the video processing device according to any one of the above aspects 1 to 16.
  • a video processing method is a video processing method for converting the gradation value taken by each pixel in a video signal according to a second video format having a wider luminance range than the first video format, Virtual maximum luminance level setting step of setting a virtual maximum luminance level not exceeding the maximum luminance level indicated by the metadata included in the video signal by referring to the gradation value taken by each pixel in the video signal; and the video signal
  • the gradation value corresponding to each luminance level below the virtual maximum luminance level among the gradation values taken by each pixel is converted, and each luminance level larger than the virtual maximum luminance level and below the maximum luminance level
  • a tone value conversion step of converting the tone value corresponding to ⁇ to a value greater than or equal to the brightness value corresponding to the virtual maximum brightness level.
  • the display device may be realized by a computer.
  • the display device is realized by the computer by operating the computer as each unit (software element) included in the display device.
  • a control program of a display device and a computer readable recording medium recording the same also fall within the scope of the present invention.
  • tone value adjustment unit 1
  • 10 display device 2 11 Tone value converter 3
  • Video data acquisition unit 4 Virtual Maximum Brightness Level Setting Unit 5 Tone value converter 6
  • Panel control unit 7 Display panel 12 tone value adjustment unit

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Abstract

The present invention efficiently converts, even in a display apparatus that supports an SDR signal, a gradation characteristic indicated by an HDR signal into a gradation characteristic suitable to the display apparatus to improve display quality. A video processing device (2) is provided with: a virtual maximum luminance level setting unit (4) which sets a virtual maximum luminance level that does not exceed a maximum luminance level indicated by metadata included in a video signal; and a gradation value conversion unit (5) which converts gradation values corresponding to luminance levels lower than or equal to the virtual maximum luminance level among gradation values taken by respective pixels in the video signal.

Description

映像処理装置、表示装置、映像処理方法、制御プログラム、および記録媒体VIDEO PROCESSING DEVICE, DISPLAY DEVICE, VIDEO PROCESSING METHOD, CONTROL PROGRAM, AND RECORDING MEDIUM
　本発明の一様態は、ＨＤＲ信号の階調値を変換する映像処理装置等に関する。 One aspect of the present invention relates to an image processing apparatus or the like that converts a gradation value of an HDR signal.
　近年、高画質化技術の１つとして、ＳＤＲ（Standard Dynamic Range）信号よりも、階調数（取り得る階調値の個数）が多く、かつ、より高輝度の情報を含むＨＤＲ（High Dynamic Range）信号が注目を集めている。ＨＤＲ信号を用いることより、従来よりも高輝度かつ高コントラストな迫力のある映像を得ることができる。 In recent years, as one of the image quality improvement techniques, HDR (High Dynamic Range) that includes more gradations (number of possible gradation values) and higher luminance information than SDR (Standard Dynamic Range) signals. ) Signal has attracted attention. By using the HDR signal, it is possible to obtain a powerful video with high brightness and high contrast as compared with the conventional case.
　ＳＤＲ信号は、γ２．２相当等のＥＯＴＦ（Electro-Optical Transfer Function）を有する再生環境（以下、「ＳＤＲ環境」と記載）での再生を前提として製作されているのに対して、ＨＤＲ信号は、ＳＭＰＴＥ－ＳＴ２０８４（以下、「ＳＴ２０８４」と略記）等のＥＯＴＦを有する再生環境（以下、「ＳＤＲ環境」と記載）での再生を前提として製作されている。このため、ＳＤＲ環境でＨＤＲ信号を再生すると、得られる映像の輝度が製作者の意図した輝度と異なってしまう。 The SDR signal is manufactured on the premise of reproduction in an reproduction environment (hereinafter referred to as “SDR environment”) having an EOTF (Electro-Optical Transfer Function) of γ2.2 or the like, while the HDR signal is And SMPTE-ST 2084 (hereinafter, abbreviated as "ST2084") and the like, and is manufactured on the premise of regeneration in a reproduction environment (hereinafter, described as "SDR environment") having an EOTF. For this reason, when the HDR signal is reproduced in the SDR environment, the luminance of the obtained image is different from the luminance intended by the producer.
　このような問題を回避するための方法としては、例えば、ＳＤＲ環境でＨＤＲ信号を表示する前に、ＨＤＲ信号で各画素が取る階調値を、ＨＤＲ環境において作成者の意図した輝度に対応する第１の階調値から、ＳＤＲ環境において作成者の意図した輝度に対応する第２の階調値に変換することなどが考えられる。例えば、ＨＤＲ環境におけるＥＯＴＦをｆ、ＳＤＲ環境におけるＥＯＴＦをｇとすると、この変換は、第１の階調値ｘを、第２の階調値ｙ＝ｇ－１（ｆ（ｘ））に対応させるマッピングとなる。 As a method for avoiding such a problem, for example, before displaying the HDR signal in the SDR environment, the gradation value taken by each pixel in the HDR signal corresponds to the luminance intended by the creator in the HDR environment. It is conceivable to convert the first tone value to a second tone value corresponding to the luminance intended by the creator in the SDR environment. For example, assuming that the EOTF in the HDR environment is f and the EOTF in the SDR environment is g, this conversion corresponds to the first tone value x and the second tone value y = g −1 (f (x)) It will be mapping that
　再生環境のＥＯＴＦ又はガンマカーブに関連する技術を開示した文献としては、例えば、特許文献１～２が挙げられる。特許文献１には、入力映像信号の平均輝度レベル及びγ調整値によりダイナミックレンジ拡大前後の平均輝度レベルの変化幅を毎フレーム変化させることにより、バックライトの調光制御を行う液晶表示装置が開示されている。 Examples of documents disclosing techniques related to EOTF or gamma curves in a reproduction environment include, for example, Patent Documents 1 and 2. Patent Document 1 discloses a liquid crystal display device that performs light adjustment control of a backlight by changing the change width of the average luminance level before and after the expansion of the dynamic range according to the average luminance level of the input video signal and the γ adjustment value. It is done.
　特許文献２には、入力映像信号を所定の走査線数を有する信号に走査変換する走査変換部と、この走査変換部からの信号をガンマ補正するガンマ補正部と、入力映像信号から信号レベルを検出し、この検出信号によりガンマ補正部を制御するレベル検出部とを備え、入力信号レベルに応じて平均輝度を制御するプラズマディスプレイが開示されている。 Patent Document 2 discloses a scan conversion unit that scans and converts an input video signal into a signal having a predetermined number of scanning lines, a gamma correction unit that performs gamma correction on the signal from the scan conversion unit, and a signal level from the input video signal. A plasma display is disclosed that includes a level detection unit that detects and controls a gamma correction unit based on the detection signal, and controls average brightness according to an input signal level.
日本国特許公開公報「特開２００２－１０８３０５号公報（２００２年４月１０日公開）」Japanese Patent Laid-Open Publication No. 2002-108305 (Apr. 10, 2002) 日本国特許公開公報「特開２００２－３５４３７８号公報（２００２年１２月６日公開）」Japanese Patent Laid-Open Publication No. 2002-354378 (disclosed on December 6, 2002)
　上述したように、ＨＤＲ信号は、ＳＤＲ信号よりも高輝度の情報を含むように構成されているため、ＨＤＲ信号のＥＯＴＦは、ＳＤＲ信号のものと異なる。したがって、ＨＤＲ信号で各画素が取る階調値を変換する際に、ＨＤＲ信号用のＥＯＴＦの定義域全体をＳＤＲ信号用のＥＯＴＦの定義域にマッピングしようとすると、階調値の縮退（異なる階調値が同一の階調値にマッピングされることを指す）が生じることがある。特に、ＳＭＰＴＥ－ＳＴ２０８４等のＨＤＲ用のＥＯＴＦでは、暗部における僅かな明暗の違いを表現するべく、単位輝度差あたり階調数が低輝度領域において特に大きくなっている。このため、このようなマッピングによりＨＤＲ信号で各画素が取る階調値を変換すると、低輝度領域において階調値の縮退が生じ易い。 As described above, since the HDR signal is configured to include information of higher luminance than the SDR signal, the EOTF of the HDR signal is different from that of the SDR signal. Therefore, when attempting to map the entire EOTF domain for the HDR signal to the EOTF domain for the SDR signal when converting the grayscale values taken by each pixel with the HDR signal, the tone values are degraded (different floors It may occur that tone values are mapped to the same tone value). In particular, in the HDR EOTF such as SMPTE-ST 2084, the number of gradations per unit luminance difference is particularly large in the low luminance region in order to express a slight difference between light and dark in the dark part. Therefore, when the gradation value taken by each pixel is converted with the HDR signal by such mapping, degeneration of the gradation value is likely to occur in the low luminance region.
　このような問題を解決するための方法としては、ＨＤＲ信号用のＥＯＴＦの定義域のうち、コンテンツの最大輝度レベル以下の輝度レベルに対応する範囲を、ＳＤＲ信号用のＥＯＴＦの定義域にマッピングする方法が考えられる。ＨＤＲ信号で各画素は１００００ｃｄ/ｍ２以下の輝度に対応する階調値を取り得るが、これらの階調値の全部が実際のコンテンツで使われるわけではない。このため、このようなマッピングによりＨＤＲ信号で各画素が取る画素値を変換すれば、黒潰れの抑制、階調値の縮退の抑制を行うことができる。なお、ＨＤＲ信号には、ＭＡＸ＿ＣＬＬ（Maximum Content Light Level）と呼ばれる、コンテンツの最大輝度を表すメタデータが含まれている。コンテンツの最大輝度は、このメタデータを参照することにより特定することが可能である。 As a method for solving such a problem, in the EOTF domain for the HDR signal, the range corresponding to the luminance level equal to or lower than the maximum luminance level of the content is mapped to the EOTF domain for the SDR signal. I can think of a method. Although each pixel in the HDR signal can take gradation values corresponding to a luminance of 10000 cd / m 2 or less, not all of these gradation values are used in actual content. Therefore, by converting the pixel value taken by each pixel with the HDR signal by such mapping, it is possible to suppress the black crushing and the degeneration of the gradation value. The HDR signal includes metadata called MAX_CLL (Maximum Content Light Level) that represents the maximum luminance of the content. The maximum brightness of the content can be specified by referring to this metadata.
　しかしながら、コンテンツの最大輝度レベルは、ある特定のシーンの、ある特定のフレームの、ある特定の画素の輝度レベルである。したがって、この特定のフレーム以外のフレーム、あるいは、この特定のシーン以外のシーンでは、実際に使われない階調値がＳＤＲ信号用のＥＯＴＦの定義域にマッピングされてしまっていることになる。すなわち、ＨＤＲ信号用のＥＯＴＦの定義域のうち、コンテンツの最大輝度レベル以下の輝度レベルに対応する範囲を、ＳＤＲ信号用のＥＯＴＦの定義域にマッピングする方法には、低輝度領域において生じ得る階調値の縮退を更に抑制する余地が残されている。 However, the maximum intensity level of the content is the intensity level of a particular pixel of a particular frame of a particular scene. Therefore, in frames other than this specific frame or scenes other than this specific scene, gradation values that are not actually used are mapped to the domain of the EDR for the SDR signal. That is, in the method of mapping the range corresponding to the luminance level equal to or lower than the maximum luminance level of the content in the EOTF definition area for the HDR signal to the EOTF definition area for the SDR signal, There is room to further suppress the degeneracy of the regulation.
　本発明は、前記の問題点に鑑みてなされたものであり、その目的は、ＨＤＲ信号の階調値を変換する階調値変換装置であって、低輝度領域において生じ得る階調値の縮退を更に抑制された階調値変換装置を実現することである。 The present invention has been made in view of the above problems, and an object thereof is a gradation value conversion device for converting gradation values of an HDR signal, wherein degeneration of gradation values that may occur in a low luminance region To realize the gradation value conversion device further suppressed.
　上記の課題を解決するために、本発明の一態様に係る映像処理装置は、第１の映像フォーマットよりも輝度範囲の広い第２の映像フォーマットに従う映像信号において各画素が取る階調値を変換する映像処理装置であって、上記映像信号において各画素が取る階調値を参照することによって、上記映像信号に含まれるメタデータが示す最大輝度レベルを超えない仮想最大輝度レベルを設定する仮想最大輝度レベル設定部と、上記映像信号において各画素が取る階調値のうち、上記仮想最大輝度レベル以下の各輝度レベルに対応する階調値を変換し、上記仮想最大輝度レベルより大きく、かつ、上記最大輝度レベル以下の各輝度レベルに対応する階調値を、上記仮想最大輝度レベルに対応する輝度値以上の値に変換する階調値変換部と、を備えている。 In order to solve the above problems, a video processing apparatus according to an aspect of the present invention converts the gradation value taken by each pixel in a video signal according to a second video format having a wider luminance range than the first video format. Image processing apparatus, wherein a virtual maximum luminance level not exceeding the maximum luminance level indicated by the metadata included in the video signal is set by referring to the gradation value taken by each pixel in the video signal. A luminance level setting unit and, among the gradation values taken by each pixel in the video signal, the gradation values corresponding to the respective luminance levels below the virtual maximum luminance level are converted to be larger than the virtual maximum luminance level and And a tone value conversion unit for converting a tone value corresponding to each brightness level lower than the maximum brightness level into a value higher than the brightness value corresponding to the virtual maximum brightness level. To have.
　また、本発明の一態様に係る映像処理方法は、第１の映像フォーマットよりも輝度範囲の広い第２の映像フォーマットに従う映像信号において各画素が取る階調値を変換する映像処理方法であって、上記映像信号において各画素が取る階調値を参照することによって、上記映像信号に含まれるメタデータが示す最大輝度レベルを超えない仮想最大輝度レベルを設定する仮想最大輝度レベル設定ステップと、上記映像信号において各画素が取る階調値のうち、上記仮想最大輝度レベル以下の各輝度レベルに対応する階調値を変換し、上記仮想最大輝度レベルより大きく、かつ、上記最大輝度レベル以下の各輝度レベルに対応する階調値を、上記仮想最大輝度レベルに対応する輝度値以上の値に変換する階調値変換ステップと、を含んでいる。 Further, a video processing method according to an aspect of the present invention is a video processing method for converting a gradation value taken by each pixel in a video signal according to a second video format having a wider luminance range than the first video format. Virtual maximum luminance level setting step of setting a virtual maximum luminance level not exceeding the maximum luminance level indicated by the metadata included in the video signal by referring to the gradation value taken by each pixel in the video signal; Among the gradation values taken by each pixel in the video signal, the gradation values corresponding to each luminance level equal to or lower than the virtual maximum luminance level are converted to be larger than the virtual maximum luminance level and equal to or lower than the maximum luminance level And a tone value conversion step of converting the tone value corresponding to the brightness level into a value equal to or greater than the brightness value corresponding to the virtual maximum brightness level.
　本発明によれば、低輝度領域において生じ得る階調値の縮退を更に抑制された階調値変換装置を実現することができる。 According to the present invention, it is possible to realize a gradation value conversion device in which degeneration of gradation values that may occur in a low luminance region is further suppressed.
本発明の実施形態１、２および３に係る階調値変換装置を備えた表示装置の構成を示すブロック図である。It is a block diagram which shows the structure of the display apparatus provided with the gradation value converter which concerns on Embodiment 1, 2 and 3 of this invention. 上記表示装置の外観を示す図である。It is a figure which shows the external appearance of the said display apparatus. 本発明の実施形態１に係る階調値変換方法を説明するフローチャートである。It is a flowchart explaining the gradation value conversion method concerning Embodiment 1 of this invention. 本発明の実施形態１に係る階調値変換方法を説明するための図である。It is a figure for demonstrating the gradation value conversion method which concerns on Embodiment 1 of this invention. 本発明の実施形態１に係る階調値変換方法の変形例を説明するための図である。It is a figure for demonstrating the modification of the gradation value conversion method which concerns on Embodiment 1 of this invention. 本発明の実施形態２に係る階調値変換方法を説明するフローチャートである。It is a flowchart explaining the gradation value conversion method concerning Embodiment 2 of this invention. 本発明の実施形態２に係る階調値変換方法を説明するための図である。It is a figure for demonstrating the gradation value conversion method which concerns on Embodiment 2 of this invention. 本発明の実施形態３に係る階調値変換方法を説明するフローチャートである。It is a flowchart explaining the gradation value conversion method concerning Embodiment 3 of this invention. 本発明の実施形態３に係る階調値変換方法を説明するための図である。It is a figure for demonstrating the gradation value conversion method which concerns on Embodiment 3 of this invention. 本発明の実施形態４に係る階調値変換方法を説明するための図である。It is a figure for demonstrating the gradation value conversion method which concerns on Embodiment 4 of this invention. 本発明の実施形態５に係る階調値変換装置を備えた表示装置の構成を示すブロック図である。It is a block diagram which shows the structure of the display apparatus provided with the gradation value converter which concerns on Embodiment 5 of this invention. 本発明の実施形態５に係る階調値変換方法を説明するフローチャートである。It is a flowchart explaining the gradation value conversion method concerning Embodiment 5 of this invention. 本発明の実施形態５に係る階調値変換方法を説明するための図である。It is a figure for demonstrating the gradation value conversion method which concerns on Embodiment 5 of this invention.
　以下、本発明の実施形態について、詳細に説明する。ただし、本実施形態に記載されている構成は、特に特定的な記載がない限り、この発明の範囲をそれのみに限定する趣旨ではなく、単なる説明例に過ぎない。 Hereinafter, embodiments of the present invention will be described in detail. However, the configuration described in the present embodiment is not intended to limit the scope of the present invention to only that, unless specifically described otherwise, and is merely an illustrative example.
　〔実施形態１〕
　（表示装置１）
　本発明の第１の実施形態に係る階調値変換装置（映像処理装置）２を備えた表示装置１について、図１および図２を参照して説明する。図１は、本実施形態に係る階調値変換装置２を備えた表示装置１の構成を示すブロック図である。また、図２は、表示装置１の外観を示す斜視図である。図１が示すように、表示装置１は、階調値変換装置２、パネル制御部６、および表示パネル７を備えている。 Embodiment 1
(Display 1)
A display device 1 provided with a gradation value conversion device (video processing device) 2 according to a first embodiment of the present invention will be described with reference to FIGS. 1 and 2. FIG. FIG. 1 is a block diagram showing a configuration of a display device 1 provided with a tone value conversion device 2 according to the present embodiment. FIG. 2 is a perspective view showing the appearance of the display device 1. As shown in FIG. 1, the display device 1 includes a gradation value conversion device 2, a panel control unit 6, and a display panel 7.
　（階調値変換装置２）
　階調値変換装置２は、ＨＤＲ信号（第２の映像フォーマットに従う映像信号）の各画素の階調値を変換する装置であり、映像データ取得部３、仮想最大輝度レベル設定部４、および階調値変換部５を備えている。映像データ取得部３は、ＨＤＲ信号を取得する。なお、映像データ取得部３が取得するＨＤＲ信号は、ＨＤＭＩ（登録商標）（High-Definition Multimedia Interface：高精細度マルチメディアインターフェース）規格に基づくＨＤＭＩ信号、Ｔｕｎｅｒ信号（チューナーによって受信した信号）およびＣＶＢＳ（Composite Video, Blanking, and Sync：コンポジット映像信号）信号等であり得る。また、ＨＤＲ信号には、各画素が取る階調値の他に、コンテンツの最大輝度レベルを示すＭＡＸ＿ＣＬＬ等のメタデータとして含まれる。仮想最大輝度レベル設定部４は、映像データ取得部３が取得したＨＤＲ信号に含まれる階調値またはメタデータを参照し、ＭＡＸ＿ＣＬＬが示す最大輝度レベルよりも値の小さい仮想最大輝度レベルをフレーム毎またはシーン毎に設定する。階調値変換部５は、仮想最大輝度レベル設定部４が設定した仮想最大輝度レベルを参照し、ＨＤＲ信号において各画素が取る階調値を、第１の階調値から第２の階調値に変換する。この際、階調値変換部５は、ＨＤＲ信号において各画素が取り得る階調値のうち、仮想最大輝度レベル設定部４が設定した仮想最大輝度レベル以下の各輝度レベルに対応する階調値を、ＳＤＲ信号（第１の映像フォーマットに従う映像信号）用のＥＯＴＦの定義域内の各階調値に対応させるマッピングが用いられる。 (Tone value converter 2)
The gradation value conversion device 2 is a device for converting the gradation value of each pixel of the HDR signal (video signal according to the second video format), and the video data acquisition unit 3, virtual maximum luminance level setting unit 4, and floor A tuning conversion unit 5 is provided. The video data acquisition unit 3 acquires an HDR signal. The HDR signal acquired by the video data acquisition unit 3 is an HDMI signal based on the HDMI (registered trademark) (High-Definition Multimedia Interface) standard, a Tuner signal (a signal received by the tuner), and a CVBS. (Composite Video, Blanking, and Sync: composite video signal) signals and the like. The HDR signal is also included as metadata such as MAX_CLL indicating the maximum luminance level of the content, in addition to the gradation value taken by each pixel. The virtual maximum luminance level setting unit 4 refers to the gradation value or metadata included in the HDR signal acquired by the video data acquisition unit 3 and sets the virtual maximum luminance level smaller than the maximum luminance level indicated by MAX_CLL for each frame Or set for each scene. The gradation value conversion unit 5 refers to the virtual maximum luminance level set by the virtual maximum luminance level setting unit 4 and determines the gradation value to be taken by each pixel in the HDR signal from the first gradation value to the second gradation. Convert to a value At this time, the gradation value conversion unit 5 selects the gradation value corresponding to each luminance level equal to or lower than the virtual maximum luminance level set by the virtual maximum luminance level setting unit 4 among the gradation values that each pixel can take in the HDR signal. Is used to correspond to each gradation value in the definition area of the EOTF for the SDR signal (video signal according to the first video format).
　（その他の部材）
　パネル制御部６は、表示パネル７の各画素の輝度を、ＳＤＲ用のＥＯＴＦにおいて階調値変換部５が得た階調値に対応する輝度値に制御する。これにより、ＨＤＲ信号が表す映像が本来の輝度で表示パネル７に表示される。表示パネル７は、映像の表示が可能な表示装置であればどのような装置によって実現されてもよいが、具体的な例としては、液晶ディスプレイ、有機ＥＬ（Electro Luminescence）ディスプレイ、およびプラズマディスプレイ等が挙げられる。 (Other components)
The panel control unit 6 controls the luminance of each pixel of the display panel 7 to a luminance value corresponding to the gradation value obtained by the gradation value conversion unit 5 in the SDR EOTF. As a result, the video represented by the HDR signal is displayed on the display panel 7 at the original luminance. The display panel 7 may be realized by any device capable of displaying an image, but as a specific example, a liquid crystal display, an organic EL (Electro Luminescence) display, a plasma display, etc. Can be mentioned.
　（階調値変換方法）
　本実施形態に係る階調値変換装置２により実行される階調変換処理（映像処理方法）の流れを、図３及び図４を参照して説明する。図３は、階調変換処理の流れを示すフローチャートである。図４は、階調変換処理の内容を示すグラフである。 (Tonal value conversion method)
The flow of tone conversion processing (image processing method) executed by the tone value conversion device 2 according to the present embodiment will be described with reference to FIGS. 3 and 4. FIG. 3 is a flowchart showing the flow of tone conversion processing. FIG. 4 is a graph showing the contents of tone conversion processing.
　本実施形態に係る階調値変換装置２は、以下に説明するステップＳ０～Ｓ４をフレーム毎に実効することによって、ＨＤＲ信号を構成する各画素の階調値を、第１の階調値から第２の階調値に変換する。 The tone value conversion device 2 according to the present embodiment executes the steps S0 to S4 described below for each frame to obtain the tone value of each pixel constituting the HDR signal from the first tone value. Convert to the second tone value.
　まず、映像データ取得部３は、ＨＤＲ信号を取得する（ステップＳ０）。映像データ取得部３は、取得したＨＤＲ信号において処理対象フレームを構成する各画素が取る階調値を仮想最大輝度レベル設定部４及び階調値変換部５に供給する。 First, the video data acquisition unit 3 acquires an HDR signal (step S0). The video data acquisition unit 3 supplies, to the virtual maximum luminance level setting unit 4 and the gradation value conversion unit 5, the gradation value taken by each of the pixels constituting the processing target frame in the acquired HDR signal.
　次に、仮想最大輝度レベル設定部４は、処理対象フレームを構成する各画素が取る階調値を映像データ取得部３から取得し、取得した階調値の最大値（フレーム内最大階調値）に対応する輝度値（フレーム内最大輝度値）を仮想最大輝度レベルに設定する（ステップＳ１）。図４の（ａ）に、ＨＤＲ信号における輝度値と階調値との対応関係（ＯＥＴＦ）を示す。図４の（ａ）に示すように、フレーム内最大階調値に対応するフレーム内最大輝度値は、ＭＡＸ＿ＣＬＬが示すコンテンツの最大輝度レベルよりも低くなる。したがって、本ステップにおいて設定される仮想最大輝度レベルは、ＭＡＣ＿ＣＬＬが示すコンテンツの最大輝度レベルよりも低くなる。仮想最大輝度レベル設定部４は、設定した仮想最大輝度レベルを階調値変換部５に供給する。 Next, the virtual maximum luminance level setting unit 4 acquires, from the video data acquisition unit 3, the gradation value to be taken by each pixel constituting the processing target frame, and acquires the maximum value of the acquired gradation values (maximum gradation value in frame) ) Is set as the virtual maximum luminance level (step S1). FIG. 4A shows the correspondence (OETF) between the luminance value and the gradation value in the HDR signal. As shown in (a) of FIG. 4, the in-frame maximum luminance value corresponding to the in-frame maximum gradation value is lower than the maximum luminance level of the content indicated by MAX_CLL. Therefore, the virtual maximum brightness level set in this step is lower than the maximum brightness level of the content indicated by MAC_CLL. The virtual maximum brightness level setting unit 4 supplies the set virtual maximum brightness level to the tone value conversion unit 5.
　次に、階調値変換部５は、処理対象フレームを構成する各画素が取る階調値を映像データ取得部３から取得し、取得した階調値を第１の階調値から第２の階調値に変換する（ステップＳ２）。この変換のために、階調値変換部５は、仮想最大輝度レベルを仮想最大輝度レベル設定部４から取得し、ＨＤＲ信号用において各画素が取り得る階調値のうち、取得した仮想最大輝度レベル以下の各輝度レベルｙに対応する階調値ｘを、ＳＤＲ信号用のＥＯＴＦの定義域内の各階調値Ｘに対応させるマッピングを用いる。より具体的に言うと、仮想最大輝度レベル以下の各輝度レベルｙに対応する階調値ｘを、ＳＤＲ信号用のＥＯＴＦにおいて輝度レベルＹ＝（ＭＡＸ＿Ｙ／ＭＡＸ＿ｙ）ｙに対応する階調値Ｘに対応させるマッピングを用いる。ここで、ＭＡＸ＿ｙは、仮想最大輝度レベルを表し、ＭＡＸ＿Ｙは、ＳＤＲ信号用のＥＯＴＦの値域の最大値（表示装置の最大輝度レベルに相当）を表す。図４の（ｂ）は、変換前の輝度値ｘと階調値ｙとの関係（ＨＤＲ信号用のＯＥＴＦ）を表すグラフであり、図４の（ｃ）は、変換後の輝度値Ｘと階調値Ｙとの関係（ＳＤＲ信号用のＯＥＴＦ）を表すグラフである。階調値変換部５は、処理対象フレームを構成する各画素が取る変換後の階調値をパネル制御部６に供給する。 Next, the gradation value conversion unit 5 acquires, from the video data acquisition unit 3, the gradation value to be taken by each of the pixels constituting the processing target frame, and the acquired gradation value from the first gradation value to the second. It converts into a gradation value (step S2). For this conversion, the gradation value conversion unit 5 acquires the virtual maximum luminance level from the virtual maximum luminance level setting unit 4, and among the gradation values that each pixel can take for the HDR signal, the acquired virtual maximum luminance A mapping is used in which the gradation value x corresponding to each luminance level y below the level is made to correspond to each gradation value X in the EOTF definition area for the SDR signal. More specifically, the gray scale value x corresponding to each brightness level y lower than the virtual maximum brightness level is set to the gray scale value X corresponding to the brightness level Y = (MAX_Y / MAX_y) y in the EDR for the SDR signal. Use the corresponding mapping. Here, MAX_y represents a virtual maximum luminance level, and MAX_Y represents a maximum value (corresponding to a maximum luminance level of a display device) of a range of EOTF for SDR signal. (B) in FIG. 4 is a graph showing the relationship between the luminance value x before conversion and the gradation value y (OETF for HDR signal), and (c) in FIG. It is a graph showing the relationship with gradation value Y (OETF for SDR signal). The tone value conversion unit 5 supplies, to the panel control unit 6, the tone value after conversion which each pixel constituting the processing target frame takes.
　次に、パネル制御部６は、処理対象フレームを構成する各画素が取る変換後の階調値を階調値変換部５から取得し、取得した階調値を輝度値に変換する（ステップＳ３）。この変換のために、パネル制御部６は、ＳＤＲ用のＥＯＴＦ、例えば、γ２．２相当のＥＯＴＦを用いる。この変換は、トーンマッピングとも呼ばれ、この変換における階調値と輝度値との対応関係は、トーンカーブとも呼ばれる。パネル制御部６は、表示パネル７を構成する各画素の輝度を、トーンマッピングにより得られた輝度値に制御する。これにより、処理対象フレームが表示パネル７に表示される（ステップＳ４）。 Next, the panel control unit 6 acquires, from the gradation value conversion unit 5, gradation values after conversion which each pixel constituting the processing target frame takes, and converts the acquired gradation values into luminance values (step S3). ). For this conversion, the panel control unit 6 uses an EDR for SDR, for example, an EOTF equivalent to γ2.2. This conversion is also called tone mapping, and the correspondence between tone values and luminance values in this conversion is also called tone curve. The panel control unit 6 controls the luminance of each pixel constituting the display panel 7 to the luminance value obtained by tone mapping. As a result, the processing target frame is displayed on the display panel 7 (step S4).
　以上のように、本実施形態に係る階調値変換処理では、ＨＤＲ信号用のＥＯＴＦの定義域のうち、仮想最大輝度レベル以下の輝度値に対応する範囲をＳＤＲ信号用のＥＯＴＦの定義域に対応付けるマッピングを用いる。仮想最大輝度レベルは、ＭＡＣ＿ＣＬＬが示す最大輝度レベルよりも低いので、ＨＤＲ信号用のＥＯＴＦの定義域のうち、ＭＡＸ＿ＣＬＬが示す最大輝度レベル以下の輝度値に対応する範囲をＳＤＲ信号用のＥＯＴＦの定義域に対応付けるマッピングを用いる場合と比べて、黒潰れの抑制、階調値の縮退の抑制を行うことができる。 As described above, in the gradation value conversion process according to the present embodiment, the range corresponding to the luminance value equal to or lower than the virtual maximum luminance level in the domain of EOTF for HDR signal is defined as the domain of EOTF for SDR signal. Use mapping to correspond. Since the virtual maximum brightness level is lower than the maximum brightness level indicated by MAC_CLL, the definition of the EOTF for SDR signal in the range corresponding to the brightness value equal to or less than the maximum brightness level indicated by MAX_CLL within the definition area of EOTF for HDR signal In comparison with the case of using the mapping corresponding to the area, it is possible to suppress the black crushing and the gradation value degeneration.
　なお、ここでは、階調値変換処理をフレーム毎に実行し、各フレームのフレーム内最大輝度値を仮想最大輝度レベルとする構成について説明したが、本実施形態はこれに限定されない。例えば、レコーダ等に記録されたＨＤＲ信号を再生する場合には、階調値変換処理をシーン毎に実行し、各シーンのシーン内最大輝度値（そのシーンを構成する全てのフレームのフレーム内最大輝度値の最大値）を仮想最大輝度レベルとする構成を採用することも可能である。この場合、処理対象シーンを構成する最初のフレームの階調値変換を開始する前に、処理対象シーンを構成する全てのフレームを構成する画素が取る階調値を取得し、シーン内最大輝度値を仮想最大輝度レベルに設定することになる。また、各シーンのシーン内最大輝度値を示すメタデータがＨＤＲ信号に含まれている場合は、このメタデータを参照して仮想最大輝度レベルを設定する構成を採用することもできる。このような構成であれば、レコーダ等に記録されたＨＤＲ信号のみならず、チューナ等で受信したＨＤＲ信号に対しても階調値変換処理を施すことが可能である。 Here, although the gradation value conversion process is performed for every frame, and the intra-frame maximum luminance value of each frame is set as the virtual maximum luminance level, the present embodiment is not limited to this. For example, when an HDR signal recorded in a recorder or the like is reproduced, tone value conversion processing is performed for each scene, and the in-scene maximum luminance value of each scene (the in-frame maximum of all the frames constituting that scene). It is also possible to adopt a configuration in which the maximum value of the luminance values) is the virtual maximum luminance level. In this case, before starting the tone value conversion of the first frame constituting the processing target scene, the gradation values taken by the pixels constituting all the frames constituting the processing target scene are acquired, and the maximum luminance value in the scene is obtained. To the virtual maximum brightness level. In addition, when the metadata indicating the in-scene maximum luminance value of each scene is included in the HDR signal, a configuration may be adopted in which the virtual maximum luminance level is set with reference to this metadata. With such a configuration, it is possible to perform gradation value conversion processing not only on the HDR signal recorded in the recorder or the like but also on the HDR signal received by the tuner or the like.
　また、各フレームのフレーム内最大輝度値そのものを仮想最大輝度レベルとする構成の代わりに、各フレームのフレーム内最大輝度値の時間平均値を仮想最大輝度レベルとする構成を採用してもよい。これにより、各フレームのフレーム内最大輝度値そのものを仮想最大輝度レベルとする構成を採用した場合に生じ得る画面のちらつきを効果的に抑制することが可能である。なお、各フレームのフレーム内輝度値の時間平均値の算出にあたっては、例えば公知の時間平均フィルタなどを用いればよい。 Also, instead of setting the intra-frame maximum luminance value itself of each frame as the virtual maximum luminance level, an arrangement may be adopted in which the temporal average value of the intra-frame maximum luminance values of each frame is set as the virtual maximum luminance level. Thereby, it is possible to effectively suppress the flickering of the screen which may occur when the configuration in which the intra-frame maximum luminance value itself of each frame is set to the virtual maximum luminance level is adopted. Note that, for example, a well-known time average filter may be used to calculate the time average value of the in-frame luminance value of each frame.
　（変形例）
　上述のステップＳ１では、仮想最大輝度レベル設定部４が、取得した階調値の最大値（フレーム内最大階調値又はシーン内最大階調値）に対応する輝度値（フレーム内最大輝度値又はシーン内最大輝度値）を仮想最大輝度レベルに設定する構成について説明した。しかし、ステップＳ１で、仮想最大輝度レベル設定部４が設定する仮想最大輝度レベルは、フレーム内最大輝度値又はシーン内最大輝度値に限定されない。より詳細には、仮想最大輝度レベル設定部４が設定する仮想最大輝度レベルは、映像信号に含まれるメタデータが示す最大輝度レベル（ＭＡＸ＿ＣＬＬ）を超えない値であればよい。 (Modification)
In step S1 described above, the virtual maximum luminance level setting unit 4 sets the luminance value (in-frame maximum luminance value) or the luminance value corresponding to the acquired maximum value of the gradation values (maximum in-frame gradation value or in-scene maximum gradation value). The configuration for setting the in-scene maximum luminance value) to the virtual maximum luminance level has been described. However, the virtual maximum brightness level set by the virtual maximum brightness level setting unit 4 in step S1 is not limited to the in-frame maximum brightness value or the in-scene maximum brightness value. More specifically, the virtual maximum brightness level set by the virtual maximum brightness level setting unit 4 may be a value that does not exceed the maximum brightness level (MAX_CLL) indicated by the metadata included in the video signal.
　そのような構成を以下で説明する。まず、ステップＳ１で、仮想最大輝度レベル設定部４は、フレーム内最大輝度値又はシーン内最大輝度値よりも低い輝度値に仮想最大輝度レベルを設定する。次に、ステップＳ２を上述の方法で同様に実行したあとに、ステップＳ３において、パネル制御部６は、上述の通り、階調値変換部５から取得した階調値を輝度値に変換する工程に加えて、映像データ取得部３がステップＳ０で取得した階調値のうち、仮想最大輝度レベルより大きく、かつ、最大輝度レベル（ＭＡＸ＿ＣＬＬ）以下の各輝度レベルに対応する階調値を、当該仮想最大輝度レベルに対応する輝度値以上の値に変換する。そして、ステップＳ４において、パネル制御部６は、表示パネル７を構成する各画素の輝度を、トーンマッピングにより得られた輝度値、又は仮想最大輝度レベルに対応する輝度値以上の値に制御する。 Such an arrangement is described below. First, in step S1, the virtual maximum brightness level setting unit 4 sets the virtual maximum brightness level to a brightness value lower than the in-frame maximum brightness value or the in-scene maximum brightness value. Next, after step S2 is performed in the same manner as described above, in step S3, the panel control unit 6 converts the gradation value acquired from the gradation value conversion unit 5 into a luminance value as described above. In addition to the above, of the gradation values acquired by the video data acquisition unit 3 in step S0, the gradation values corresponding to the respective luminance levels larger than the virtual maximum luminance level and lower than the maximum luminance level (MAX_CLL) are Convert to a value greater than the luminance value corresponding to the virtual maximum luminance level. Then, in step S4, the panel control unit 6 controls the luminance of each pixel constituting the display panel 7 to a luminance value obtained by tone mapping or a value greater than or equal to the luminance value corresponding to the virtual maximum luminance level.
　上記の構成の具体例を、図５を参照して説明する。図５の（ａ）及び（ｂ）は、ステップＳ２の変換後の輝度値Ｘと階調値Ｙとの関係（一部、ＳＤＲ信号用のＯＥＴＦ）を表すグラフである。例えば、上述のステップＳ３において、パネル制御部６は、映像データ取得部３がステップＳ０で取得した階調値のうち、仮想最大輝度レベルより大きく、かつ、最大輝度レベル（ＭＡＸ＿ＣＬＬ）以下の各輝度レベルに対応する階調値を、図５の（ａ）が示すように、一定の階調値とみなして、当該仮想最大輝度レベルに対応する一定の輝度値に変換してもよい。これにより、仮想最大輝度レベルより大きく、かつ、最大輝度レベル（ＭＡＸ＿ＣＬＬ）以下の各輝度レベルに対応する階調値は、一定の輝度値に変換されるため、変換後の輝度値で表示した映像においても、変換前の階調値の階調表現を大きく損なわないという効果を奏する。 A specific example of the above configuration will be described with reference to FIG. (A) and (b) of FIG. 5 are graphs showing the relationship between the luminance value X and the gradation value Y after the conversion of step S2 (partly, the OETF for the SDR signal). For example, in the above-described step S3, the panel control unit 6 sets each of the luminance values larger than the virtual maximum luminance level and lower than the maximum luminance level (MAX_CLL) among the gradation values acquired by the video data acquisition unit 3 in step S0. The gradation value corresponding to the level may be regarded as a constant gradation value as shown in FIG. 5A, and may be converted into a constant luminance value corresponding to the virtual maximum luminance level. As a result, the gradation value corresponding to each luminance level larger than the virtual maximum luminance level and lower than the maximum luminance level (MAX_CLL) is converted to a constant luminance value, and thus the image displayed by the converted luminance value In the above, the effect is obtained that the gradation expression of the gradation value before conversion is not greatly impaired.
　また、例えば、上述のステップＳ３において、パネル制御部６は、映像データ取得部３がステップＳ０で取得した階調値のうち、仮想最大輝度レベルより大きく、かつ、最大輝度レベル（ＭＡＸ＿ＣＬＬ）以下の各輝度レベルに対応する階調値を、図５の（ｂ）が示すように輝度値が大きくなるのに従って階調値が次第に大きくなるものとみなして、仮想最大輝度レベルに対応する輝度値以上の値に変換してもよい。結果として、ステップＳ３において、パネル制御部６は、変換前の階調値と変換後の輝度値とのグラフにおいて、当該変換前の階調値が大きくなるのに従って当該変換後の輝度値が次第に大きくなるように、映像信号において各画素が取る階調値のうち、仮想最大輝度レベルより大きく、かつ、最大輝度レベル以下の各輝度レベルに対応する階調値を、仮想最大輝度レベルに対応する輝度値以上の値に変換する。これにより、変換後の輝度値の大きさは、変換前の階調値の大きさに応じた値となるため、変換後の輝度値で表示した映像においても、変換前の階調値の階調表現を大きく損なわないという効果を奏する。 In addition, for example, in step S3 described above, the panel control unit 6 determines that the gradation value acquired by the video data acquisition unit 3 in step S0 is greater than the virtual maximum luminance level and not higher than the maximum luminance level (MAX_CLL). Assuming that the gradation value corresponding to each luminance level gradually increases as the luminance value increases as (b) in FIG. 5 shows, the luminance value corresponding to the virtual maximum luminance level is equal to or higher than It may be converted to the value of As a result, in step S3, in the graph of the gradation value before conversion and the luminance value after conversion, panel control unit 6 gradually increases the luminance value after conversion as the gradation value before conversion increases. Among the gradation values taken by each pixel in the video signal, the gradation values corresponding to the luminance levels larger than the virtual maximum luminance level and lower than the maximum luminance level correspond to the virtual maximum luminance level so as to be larger. Convert to a value greater than the luminance value. As a result, the size of the luminance value after conversion is a value according to the size of the gradation value before conversion, so that even in the image displayed with the luminance value after conversion, the floor of the gradation value before conversion is An effect is obtained that the tone expression is not significantly impaired.
　また、別の変形例において、フレーム内最大輝度値又はシーン内最大輝度値がＭＡＸ＿ＣＬＬを超える場合についても、上記の構成と同様の構成を採用することができる。より詳細には、ステップＳ３において、パネル制御部６は、映像データ取得部３がステップＳ０で取得した階調値のうち、仮想最大輝度レベルより大きく、かつ、フレーム内最大輝度値又はシーン内最大輝度値以下の各輝度レベルに対応する階調値を、当該仮想最大輝度レベルに対応する輝度値以上の値に変換してもよい。 Furthermore, in another modification, the same configuration as the above-described configuration can be adopted even when the in-frame maximum luminance value or the in-scene maximum luminance value exceeds MAX_CLL. More specifically, in step S3, the panel control unit 6 determines that the gradation value acquired by the video data acquisition unit 3 in step S0 is greater than the virtual maximum luminance level and is the maximum luminance value in the frame or the maximum in the scene. The gradation value corresponding to each luminance level lower than the luminance value may be converted to a value higher than the luminance value corresponding to the virtual maximum luminance level.
　〔実施形態２〕
　本発明の第２の実施形態について、図面に基づいて説明すれば、以下のとおりである。なお、本実施形態では、図１に示す階調値変換装置２を備える表示装置１を、第１の実施形態と同様に用いる。 Second Embodiment
The second embodiment of the present invention is described below with reference to the drawings. In the present embodiment, the display device 1 including the tone value conversion device 2 shown in FIG. 1 is used as in the first embodiment.
　以下で、本実施形態に係る階調値変換装置２による画像処理方法について、図６を参照して、詳細に説明する。図６は、本実施形態に係る階調値変換装置２により実行される階調値変換処理の流れを示すフローチャートである。なお、実施形態１に係る画像処理方法と同様の工程については、詳細な説明は省略する。 Hereinafter, an image processing method by the tone value conversion device 2 according to the present embodiment will be described in detail with reference to FIG. FIG. 6 is a flowchart showing the flow of tone value conversion processing executed by the tone value conversion device 2 according to the present embodiment. Detailed descriptions of steps similar to those of the image processing method according to the first embodiment will be omitted.
　まず、ステップＳ１０において、映像データ取得部３は、ＨＤＲ信号を取得する（ステップＳ０）。次に、ステップＳ１１において、仮想最大輝度レベル設定部４は、処理対象フレームを構成する各画素が取る階調値に対応する輝度値のヒストグラムを生成し、生成したヒストグラムからヒスト最大値を求める。ここにおけるヒスト最大値については後述する。 First, in step S10, the video data acquisition unit 3 acquires an HDR signal (step S0). Next, in step S11, the virtual maximum luminance level setting unit 4 generates a histogram of luminance values corresponding to the gradation values taken by each of the pixels constituting the processing target frame, and obtains the histogram maximum value from the generated histogram. The histogram maximum value here will be described later.
　そして、ステップＳ１２において、仮想最大輝度レベル設定部４は、仮想最大輝度レベルをステップＳ１１にて求めたヒスト最大値に設定する。 Then, in step S12, the virtual maximum brightness level setting unit 4 sets the virtual maximum brightness level to the histogram maximum value obtained in step S11.
　次に、ステップＳ１３において、階調値変換部５は、ＨＤＲ信号用において各画素が取り得る階調値（映像データ取得部３から取得）のうち、仮想最大輝度レベル（仮想最大輝度レベル設定部４から取得）以下の各輝度レベルに対応する階調値を、ＳＤＲ信号用のＥＯＴＦの定義域内の各階調値に変換する。 Next, in step S13, the gradation value conversion unit 5 sets the virtual maximum luminance level (virtual maximum luminance level setting unit) among the gradation values (obtained from the video data acquisition unit 3) that each pixel can take for the HDR signal. 4) to convert the gradation value corresponding to each luminance level below into each gradation value within the definition range of the EDR for the SDR signal.
　次に、ステップＳ１４において、パネル制御部６は、上述のステップＳ３と同様に階調値変換部５から取得した階調値を輝度値に変換する工程に加えて、映像データ取得部３がステップＳ１０で取得した階調値のうち、仮想最大輝度レベルより大きく、かつ、最大輝度レベル（ＭＡＸ＿ＣＬＬ）以下の各輝度レベルに対応する階調値を、当該仮想最大輝度レベルに対応する輝度値以上の値に変換する。 Next, in step S14, the panel control unit 6 adds the step of converting the gradation value acquired from the gradation value conversion unit 5 into the luminance value as in step S3 described above, and the video data acquisition unit 3 performs the step. Among the gradation values acquired in S10, the gradation values corresponding to each luminance level larger than the virtual maximum luminance level and lower than the maximum luminance level (MAX_CLL) are the luminance values corresponding to the virtual maximum luminance level or more. Convert to a value
　なお、ステップＳ１４においても、パネル制御部６は、仮想最大輝度レベルより大きく、かつ、最大輝度レベル（ＭＡＸ＿ＣＬＬ）以下の各輝度レベルに対応する階調値を、当該仮想最大輝度レベルに対応する輝度値（一定の輝度値）に変換してもよい。また、パネル制御部６は、変換前の階調値と変換後の輝度値とのグラフにおいて、当該変換前の階調値が大きくなるのに従って当該変換後の輝度値が次第に大きくなるように、仮想最大輝度レベルより大きく、かつ、最大輝度レベル（ＭＡＸ＿ＣＬＬ）以下の各輝度レベルに対応する階調値を、仮想最大輝度レベルに対応する輝度値以上の値に変換してもよい。また、別の変形例において、フレーム内最大輝度値又はシーン内最大輝度値がＭＡＸ＿ＣＬＬを超える場合、ステップＳ１４において、パネル制御部６は、映像データ取得部３がステップＳ１０で取得した階調値のうち、仮想最大輝度レベル（ヒスト最大値）より大きく、かつ、フレーム内最大輝度値又はシーン内最大輝度値以下の各輝度レベルに対応する階調値を、当該仮想最大輝度レベルに対応する輝度値以上の値に変換してもよい。 Also in step S14, panel control unit 6 sets the gradation value corresponding to each luminance level larger than the virtual maximum luminance level and lower than the maximum luminance level (MAX_CLL) to the luminance corresponding to the virtual maximum luminance level. It may be converted to a value (constant luminance value). Further, in the graph of the gradation value before conversion and the luminance value after conversion, the panel control unit 6 causes the luminance value after conversion to gradually increase as the gradation value before conversion increases. The gradation value corresponding to each luminance level larger than the virtual maximum luminance level and lower than the maximum luminance level (MAX_CLL) may be converted to a value larger than the luminance value corresponding to the virtual maximum luminance level. In another modification, when the in-frame maximum luminance value or the in-scene maximum luminance value exceeds MAX_CLL, in step S14, the panel control unit 6 determines whether the image data acquisition unit 3 acquires the gradation value acquired in step S10. Among them, the gray level value corresponding to each brightness level larger than the virtual maximum brightness level (hist maximum value) and smaller than the in-frame maximum brightness value or the in-scene maximum brightness value is the brightness value corresponding to the virtual maximum brightness level. It may be converted to the above values.
　ステップＳ１４の次の工程として、ステップＳ１５において、パネル制御部６は、表示パネル７を構成する各画素の輝度を、ステップＳ１４でトーンマッピングにより得られた輝度値、又は仮想最大輝度レベルに対応する輝度値以上の値に制御する。 As a process following step S14, in step S15, panel control unit 6 corresponds the luminance of each pixel constituting display panel 7 to the luminance value obtained by tone mapping in step S14 or the virtual maximum luminance level. Control to a value greater than the luminance value.
　ここで、上述のヒスト最大値とは、処理対象フレームを構成する画素が取る階調値に対応する輝度値のうち、特異的に大きな輝度値を除く輝度値の最大値であり、ヒストグラムの平均値Ｍと標準偏差σとから算出できる量である。例えば、Ｍ＋３σは、ヒスト最大値の典型例である。 Here, the above-described histogram maximum value is the maximum value of the luminance values excluding specifically large luminance values among the luminance values corresponding to the gradation values taken by the pixels constituting the processing target frame, and the average value of the histogram It is an amount that can be calculated from the value M and the standard deviation σ. For example, M + 3σ is a typical example of the histogram maximum.
　ステップＳ１１に生成されるヒストグラムの例を図７に示す。図７に示す例では、幾つかの画素がＭＡＸ＿ＣＬＬが示す最大輝度レベルに近い特異的に大きな輝度値を取る。このような場合、処理対象フレームを構成する画素が取る階調値に対応する輝度値の最大値を仮想最大輝度レベルとする構成（第１の実施形態参照）を採用すると、階調値変換ステップＳ１３において特異的に大きな輝度値と特異的に大きな輝度値を除く輝度値の最大値との間の領域が、ＳＤＲ用のＥＯＴＦの値域に無駄に対応付けられることになる。これに対して、処理対象フレームを構成する画素が取る階調値に対応する輝度値のヒスト最大値を仮想最大輝度レベルとする構成を採用すれば、特異的に大きな輝度値を除く輝度値を、階調値変換ステップＳ１３においてＳＤＲ用のＥＯＴＦの値域に無駄なく対応付けることができる。 An example of the histogram generated in step S11 is shown in FIG. In the example shown in FIG. 7, some pixels have a uniquely large luminance value close to the maximum luminance level indicated by MAX_CLL. In such a case, if a configuration (see the first embodiment) in which the maximum value of the luminance values corresponding to the gradation values taken by the pixels constituting the processing target frame is the virtual maximum luminance level is adopted, the gradation value conversion step The area between the specifically large luminance value and the maximum value of the luminance values excluding the specifically large luminance value in S13 is uselessly associated with the range of the EDR for SDR. On the other hand, if a configuration is adopted in which the histogram maximum value of the luminance value corresponding to the gradation value taken by the pixels constituting the processing target frame is set as the virtual maximum luminance level, the luminance value excluding the specifically large luminance value In the tone value conversion step S13, the value range of the SDR EOTF can be associated without waste.
　なお、ここでは、輝度値のヒストグラムをフレーム毎に作成し、各フレームのフレーム内ヒスト最大値を仮想最大輝度レベルとする構成について説明したが、本実施形態はこれに限定されない。例えば、レコーダ等に記録されたＨＤＲ信号を再生する場合には、輝度値のヒストグラムをシーン毎に実行し、各シーンのシーン内ヒスト最大値を仮想最大輝度レベルとする構成を採用することも可能である。この場合、処理対象シーンを構成する最初のフレームの階調値変換を開始する前に、処理対象シーンを構成する全てのフレームを構成する画素が取る階調値に対応する輝度値のヒストグラムを作成し、シーン内ヒスト最大値を仮想最大輝度レベルに設定することになる。また、各シーンのシーン内ヒスト最大値を示すメタデータがＨＤＲ信号に含まれている場合は、このメタデータを参照して仮想最大輝度レベルを設定する構成を採用することもできる。このような構成であれば、レコーダ等に記録されたＨＤＲ信号のみならず、チューナ等で受信したＨＤＲ信号に対しても階調値変換処理を施すことが可能である。 Here, a configuration has been described in which a histogram of luminance values is created for each frame, and the intra-frame histogram maximum value of each frame is set as the virtual maximum luminance level, but the present embodiment is not limited to this. For example, in the case of reproducing an HDR signal recorded in a recorder or the like, it is possible to adopt a configuration in which a histogram of luminance values is executed for each scene and the in-scene histogram maximum value of each scene is a virtual maximum luminance level. It is. In this case, before starting tone value conversion of the first frame making up the processing target scene, a histogram of luminance values corresponding to the tone values taken by pixels making up all the frames making up the processing target scene is created And set the in-scene histogram maximum value to the virtual maximum luminance level. Further, when the metadata indicating the in-scene histogram maximum value of each scene is included in the HDR signal, it is also possible to adopt a configuration in which the virtual maximum luminance level is set with reference to this metadata. With such a configuration, it is possible to perform gradation value conversion processing not only on the HDR signal recorded in the recorder or the like but also on the HDR signal received by the tuner or the like.
　また、各フレームのフレーム内ヒスト最大値そのものを仮想最大輝度レベルとする構成の代わりに、各フレームのフレーム内ヒスト最大値の時間平均値を仮想最大輝度レベルとする構成を採用してもよい。これにより、各フレームのフレーム内ヒスト最大値そのものを仮想最大輝度レベルとする構成を採用した場合に生じ得る画面のちらつきを効果的に抑制することが可能である。なお、各フレームのフレーム内ヒスト最大値の時間平均値の算出にあたっては、例えば公知の時間平均フィルタなどを用いればよい。 Also, instead of using the intra-histo intra-site histogram maximum value of each frame as the virtual maximum luminance level, the intra-frame intra-histo maximum value of each frame may be temporally averaged to be the virtual maximum luminance level. As a result, it is possible to effectively suppress the flickering of the screen which may occur when the configuration in which the intra-histo maximum value itself of each frame is used as the virtual maximum luminance level is adopted. Note that, for example, a well-known time average filter or the like may be used to calculate the time average value of the in-frame maximum values of the respective frames.
　〔実施形態３〕
　本発明の第３の実施形態について、図面に基づいて説明すれば、以下のとおりである。なお、本実施形態では、図１に示す階調値変換装置２を備える表示装置１を第１の実施形態と同様に用いる。 Third Embodiment
The third embodiment of the present invention is described below with reference to the drawings. In the present embodiment, the display device 1 including the tone value conversion device 2 shown in FIG. 1 is used as in the first embodiment.
　以下で、本実施形態に係る階調値変換装置２による画像処理方法について、図８を参照して、詳細に説明する。図８は、本実施形態に係る階調値変換装置により実行される階調値変換処理の流れを示すフローチャートである。なお、実施形態１に係る画像処理方法と同様の工程については、詳細な説明は省略する。 Hereinafter, an image processing method by the tone value conversion device 2 according to the present embodiment will be described in detail with reference to FIG. FIG. 8 is a flowchart showing the flow of tone value conversion processing executed by the tone value conversion device according to the present embodiment. Detailed descriptions of steps similar to those of the image processing method according to the first embodiment will be omitted.
　まず、ステップＳ１００において、映像データ取得部３は、ＨＤＲ信号を取得する（ステップＳ０）。次に、ステップＳ１０１において、仮想最大輝度レベル設定部４は、処理対象フレームを構成する各画素が取る階調値に対応する輝度値のヒストグラムを生成し、生成したヒストグラムからヒスト最大値を求める。ヒスト最大値の定義は、第２の実施形態において与えたものと同様である。 First, in step S100, the video data acquisition unit 3 acquires an HDR signal (step S0). Next, in step S101, the virtual maximum luminance level setting unit 4 generates a histogram of luminance values corresponding to the gradation value taken by each pixel constituting the processing target frame, and obtains the histogram maximum value from the generated histogram. The definition of the histogram maximum is similar to that given in the second embodiment.
　次に、ステップＳ１０２において、仮想最大輝度レベル設定部４は、ＭＡＣ＿ＣＬＬが示す最大輝度レベルよりも所定の値だけ低いリミット値を設定する。ここで、所定の値は、任意の値であり、工場出荷時に設定されたものであってもよいし、工場出荷後にユーザが設定したものであってもよい。 Next, in step S102, the virtual maximum brightness level setting unit 4 sets a limit value lower by a predetermined value than the maximum brightness level indicated by MAC_CLL. Here, the predetermined value is an arbitrary value, and may be set at the time of factory shipment, or may be set by the user after factory shipment.
　次に、ステップＳ１０３において、仮想最大輝度レベル設定部４は、ステップＳ１０１で算出したヒスト最大値がステップＳ１０２で算出したリミット値よりも低いか否かを判定する。ここで、ヒスト最大値がリミット値よりも低い場合、仮想最大輝度レベル設定部４は、仮想最大輝度レベルをリミット値に設定する（ステップＳ１０４）。ヒスト最大値がリミット値以上の場合、仮想最大輝度レベル設定部４は、仮想最大輝度レベルをヒスト最大値に設定する（ステップＳ１０５）。 Next, in step S103, the virtual maximum luminance level setting unit 4 determines whether the histogram maximum value calculated in step S101 is lower than the limit value calculated in step S102. Here, when the histogram maximum value is lower than the limit value, the virtual maximum brightness level setting unit 4 sets the virtual maximum brightness level as the limit value (step S104). If the histogram maximum value is equal to or more than the limit value, the virtual maximum luminance level setting unit 4 sets the virtual maximum luminance level to the histogram maximum value (step S105).
　ステップＳ１０４又はステップＳ１０５の次の工程として、階調値変換部５は、ＨＤＲ信号用において各画素が取り得る階調値（映像データ取得部３から取得）のうち、仮想最大輝度レベル（リミット値またはヒスト最大値）以下の各輝度レベルに対応する階調値を、ＳＤＲ信号用のＥＯＴＦの定義域内の各階調値に変換する（ステップＳ１０６）。 As a process following step S104 or step S105, the gradation value conversion unit 5 sets the virtual maximum luminance level (limit value) among the gradation values (obtained from the video data acquisition unit 3) that each pixel can take for the HDR signal. Alternatively, the gradation value corresponding to each luminance level lower than the maximum value of the histogram) is converted into each gradation value within the definition range of the EDR for the SDR signal (step S106).
　次に、ステップＳ１０７において、パネル制御部６は、上述のステップＳ３と同様に階調値変換部５から取得した階調値を輝度値に変換する工程に加えて、映像データ取得部３がステップＳ１００で取得した階調値のうち、仮想最大輝度レベル（リミット値またはヒスト最大値）より大きく、かつ、最大輝度レベル（ＭＡＸ＿ＣＬＬ）以下の各輝度レベルに対応する階調値を、当該仮想最大輝度レベルに対応する輝度値以上の値に変換する。 Next, in step S107, the panel control unit 6 adds the step of converting the gradation value acquired from the gradation value conversion unit 5 into the luminance value as in step S3 described above, and the video data acquisition unit 3 performs the step. The gradation value corresponding to each luminance level larger than the virtual maximum luminance level (limit value or maximum value of the histogram) and lower than the maximum luminance level (MAX_CLL) among the gradation values acquired in S100 is the virtual maximum luminance. Convert to a value greater than the luminance value corresponding to the level.
　なお、ステップＳ１０７においても、パネル制御部６は、仮想最大輝度レベル（リミット値またはヒスト最大値）より大きく、かつ、最大輝度レベル（ＭＡＸ＿ＣＬＬ）以下の各輝度レベルに対応する階調値を、当該仮想最大輝度レベルに対応する輝度値（一定の輝度値）に変換してもよい。また、パネル制御部６は、変換前の階調値と変換後の輝度値とのグラフにおいて、当該変換前の階調値が大きくなるのに従って当該変換後の輝度値が次第に大きくなるように、仮想最大輝度レベル（リミット値又はヒスト最大値）より大きく、かつ、最大輝度レベル（ＭＡＸ＿ＣＬＬ）以下の各輝度レベルに対応する階調値を、仮想最大輝度レベルに対応する輝度値以上の値に変換してもよい。また、別の変形例において、フレーム内最大輝度値又はシーン内最大輝度値がＭＡＸ＿ＣＬＬを超える場合、ステップＳ１０７において、パネル制御部６は、映像データ取得部３がステップＳ１００で取得した階調値のうち、仮想最大輝度レベル（リミット値又はヒスト最大値）より大きく、かつ、フレーム内最大輝度値又はシーン内最大輝度値以下の各輝度レベルに対応する階調値を、当該仮想最大輝度レベルに対応する輝度値以上の値に変換してもよい。 Also in step S107, panel control unit 6 sets the gradation value corresponding to each luminance level larger than the virtual maximum luminance level (limit value or maximum value of the histogram) and not higher than the maximum luminance level (MAX_CLL). It may be converted to a luminance value (constant luminance value) corresponding to the virtual maximum luminance level. Further, in the graph of the gradation value before conversion and the luminance value after conversion, the panel control unit 6 causes the luminance value after conversion to gradually increase as the gradation value before conversion increases. Converts the gradation value corresponding to each luminance level that is larger than the virtual maximum luminance level (limit value or histo maximum value) and less than the maximum luminance level (MAX_CLL) to a value higher than the luminance value corresponding to the virtual maximum luminance level You may In another modification, when the in-frame maximum luminance value or the in-scene maximum luminance value exceeds MAX_CLL, in step S107, the panel control unit 6 determines whether the image data acquisition unit 3 acquires the gradation value acquired in step S100. Among them, the gradation value corresponding to each luminance level which is larger than the virtual maximum luminance level (limit value or the maximum histogram value) and smaller than the in-frame maximum luminance value or the in-scene maximum luminance value corresponds to the virtual maximum luminance level. You may convert into the value more than the brightness value to be.
　ステップＳ１０７の次の工程として、ステップＳ１０８において、パネル制御部６は、表示パネル７を構成する各画素の輝度を、ステップＳ１０７でトーンマッピングにより得られた輝度値、又は仮想最大輝度レベルに対応する輝度値以上の値に制御する。 As a process following step S107, in step S108, the panel control unit 6 corresponds the luminance of each pixel constituting the display panel 7 to the luminance value obtained by tone mapping in step S107 or the virtual maximum luminance level. Control to a value greater than the luminance value.
　以下で、本実施形態に係る階調値変換装置により実行される階調値変換処理の具体例について、図９を参照して説明する。図９の（ａ）および（ｃ）は、処理対象フレームを構成する各画素が取る階調値に対応する輝度値のヒストグラムを示し、図９の（ｂ）および（ｄ）は、ステップＳ１０６における変換後の輝度値Ｘと階調値Ｙとの関係（ＳＤＲ信号用のＯＥＴＦ）を表すグラフである。図９の（ａ）に示すように、ヒスト最大値がリミット値よりも低い場合、ステップＳ１０４において、仮想最大輝度レベル設定部４は、仮想最大輝度レベルをリミット値に設定する。この場合、図９の（ｂ）に示すように、ステップＳ１０６において、ＨＤＲ信号用のＯＥＴＦの定義域のうち、リミット値以下の範囲がＳＤＲ信号用のＯＥＴＦの定義域全体にマッピングされる。なお、ＨＤＲ信号用のＯＥＴＦの定義域のうち、リミット値より大きい範囲の階調値については、上述のステップＳ１０７の処理が行われる。 Hereinafter, a specific example of the gradation value conversion process performed by the gradation value conversion device according to the present embodiment will be described with reference to FIG. (A) and (c) in FIG. 9 show histograms of luminance values corresponding to the gradation values taken by the pixels constituting the processing target frame, and (b) and (d) in FIG. It is a graph showing the relationship between the luminance value X after conversion and the gradation value Y (OETF for SDR signal). As shown in (a) of FIG. 9, when the histogram maximum value is lower than the limit value, in step S104, the virtual maximum brightness level setting unit 4 sets the virtual maximum brightness level to the limit value. In this case, as shown in (b) of FIG. 9, in step S106, a range equal to or less than the limit value in the domain of the OETF for HDR signal is mapped to the entire domain of the OETF for SDR signal. Note that the process of step S107 described above is performed for the gradation value in the range larger than the limit value in the definition area of the OETF for the HDR signal.
　一方、図９の（ｃ）に示すように、ヒスト最大値がリミット値以上である場合、仮想最大輝度レベル設定部４は、ステップＳ１０５において、仮想最大輝度レベルをヒスト最大値に設定する。この場合、図９の（ｄ）に示すように、ステップＳ１０６において、ＨＤＲ信号用のＥＯＴＦの値域のうち、ヒスト最大値以下の範囲がＳＤＲ信号用のＥＯＴＦの値域全体にマッピングされる。なお、ＨＤＲ信号用のＥＯＴＦの値域のうち、ヒスト最大値より大きい範囲の階調値については、上述のステップＳ１０７の処理が行われる。 On the other hand, as shown in (c) of FIG. 9, when the histogram maximum value is equal to or more than the limit value, the virtual maximum luminance level setting unit 4 sets the virtual maximum luminance level to the histogram maximum value in step S105. In this case, as shown in (d) of FIG. 9, in step S106, a range equal to or less than the maximum value of the histogram is mapped to the entire range of the EDRF for SDR in the range of EOTF for HDR signal. Note that the process of step S107 described above is performed for the gradation value in the range larger than the maximum value of the histogram within the range of the EOTF for the HDR signal.
　本実施形態に係る階調値変換装置２の階調値変換方法によれば、仮想最大輝度レベルにリミット値を設けることにより、ヒスト最大値が極端に小さくなった場合に生じ得る、仮想最大輝度レベルの大きな変動に伴う映像品位の低下を防ぐことができる。 According to the gradation value conversion method of the gradation value conversion device 2 according to the present embodiment, the virtual maximum luminance can be generated when the histogram maximum value becomes extremely small by providing the limit value to the virtual maximum luminance level It is possible to prevent the deterioration of the image quality caused by the large fluctuation of the level.
　〔実施形態４〕
　本発明の第４の実施形態について、図面に基づいて説明すれば、以下のとおりである。なお、本実施形態では、図１に示す階調値変換装置２を備える表示装置１を第１の実施形態と同様に用いる。 Embodiment 4
The fourth embodiment of the present invention is described below with reference to the drawings. In the present embodiment, the display device 1 including the tone value conversion device 2 shown in FIG. 1 is used as in the first embodiment.
　本実施形態に係る階調値変換装置２により実行される階調値変換処理の流れは、第３の実施形態に係る階調値変換装置２により実行される階調変換処理と同様、図８に示すフローチャートにより表現される。ただし、本実施形態においては、第３の実施形態におけるリミット値設定処理Ｓ１０２は、以下に説明するリミット値設定処理Ｓ１０９に置き換えられる。 The flow of tone value conversion processing executed by the tone value conversion device 2 according to the present embodiment is the same as the tone conversion processing performed by the tone value conversion device 2 according to the third embodiment, as shown in FIG. It is expressed by the flowchart shown in FIG. However, in the present embodiment, the limit value setting process S102 in the third embodiment is replaced with the limit value setting process S109 described below.
　すなわち、ステップＳ１０９において、仮想最大輝度レベル設定部４は、ＭＡＸ＿ＣＬＬが示す最大輝度レベルからリミット値を減算した差と、リミット値から輝度ヒストグラムにおけるヒスト最大値を減算した差とが所定の比になるようリミット値を設定する。ここで、所定の比は、任意の比であり、工場出荷時に設定されたものであってもよいし、工場出荷後にユーザが設定したものであってもよい。 That is, in step S109, the virtual maximum brightness level setting unit 4 sets a predetermined ratio between the difference obtained by subtracting the limit value from the maximum brightness level indicated by MAX_CLL and the difference obtained by subtracting the maximum value of the histogram in the brightness histogram from the limit value. Set the limit value. Here, the predetermined ratio is an arbitrary ratio, and may be set at the time of factory shipment, or may be set by the user after factory shipment.
　図１０の（ａ）に示すように、ヒスト最大値がリミット値よりも低い場合、ステップＳ１０４において、仮想最大輝度レベル設定部４は、仮想最大輝度レベルをリミット値に設定する。この場合、図１０の（ｂ）に示すように、ステップＳ１０６において、ＨＤＲ信号用のＯＥＴＦの定義域のうち、リミット値以下の範囲がＳＤＲ信号用のＯＥＴＦの定義域全体にマッピングされる。なお、ＨＤＲ信号用のＯＥＴＦの定義域のうち、リミット値より大きい範囲の階調値については、上述のステップＳ１０７の処理が行われる。 As shown in (a) of FIG. 10, when the histogram maximum value is lower than the limit value, the virtual maximum luminance level setting unit 4 sets the virtual maximum luminance level to the limit value in step S104. In this case, as shown in (b) of FIG. 10, in step S106, a range equal to or less than the limit value in the domain of the OETF for HDR signal is mapped to the entire domain of the OETF for SDR signal. Note that the process of step S107 described above is performed for the gradation value in the range larger than the limit value in the definition area of the OETF for the HDR signal.
　一方、図１０の（ｃ）に示すように、ヒスト最大値がリミット値以上である場合、仮想最大輝度レベル設定部４は、ステップＳ１０５において、仮想最大輝度レベルをヒスト最大値に設定する。この場合、図１０の（ｄ）に示すように、ステップＳ１０６において、ＨＤＲ信号用のＥＯＴＦの値域のうち、ヒスト最大値以下の範囲がＳＤＲ信号用のＥＯＴＦの値域全体にマッピングされる。なお、ＨＤＲ信号用のＥＯＴＦの値域のうち、ヒスト最大値より大きい範囲の階調値については、上述のステップＳ１０７の処理が行われる。 On the other hand, as shown in (c) of FIG. 10, when the histogram maximum value is equal to or larger than the limit value, the virtual maximum luminance level setting unit 4 sets the virtual maximum luminance level to the histogram maximum value in step S105. In this case, as shown in (d) of FIG. 10, in the range of the EOTF for the HDR signal, the range equal to or less than the maximum value of the histogram is mapped to the entire range of the EDR for the SDR signal. Note that the process of step S107 described above is performed for the gradation value in the range larger than the maximum value of the histogram within the range of the EOTF for the HDR signal.
　本実施形態に係る階調値変換装置２の階調値変換方法によれば、仮想最大輝度レベルにリミット値を設けることにより、ヒスト最大値が極端に小さくなった場合に生じ得る、仮想最大輝度レベルの大きな変動に伴う映像品位の低下を防ぐことができる。 According to the gradation value conversion method of the gradation value conversion device 2 according to the present embodiment, the virtual maximum luminance can be generated when the histogram maximum value becomes extremely small by providing the limit value to the virtual maximum luminance level It is possible to prevent the deterioration of the image quality caused by the large fluctuation of the level.
　〔実施形態５〕
　本発明の第５の実施形態について、図面に基づいて説明すれば、以下のとおりである。なお、説明の便宜上、実施形態１にて説明した部材と同じ機能を有する部材については、同じ符号を付記し、その説明を省略する。 Fifth Embodiment
The fifth embodiment of the present invention is described below with reference to the drawings. In addition, about the member which has the same function as the member demonstrated in Embodiment 1 for convenience of explanation, the same code | symbol is appended and the description is abbreviate | omitted.
　実施形態１において、仮想最大輝度レベル設定部４が、処理対象フレームを構成する各画素が取る階調値の最大値（フレーム内最大階調値）に対応する輝度値（フレーム内最大輝度値）を仮想最大輝度レベルに設定することを説明した。当該構成により、ＨＤＲの最大の利点であるピーク輝度に応じて、階調値を変換することができる。 In the first embodiment, the luminance value (maximum luminance value in a frame) corresponding to the maximum value (maximum gradation value in a frame) of the gradation value taken by each pixel constituting the processing target frame by the virtual maximum luminance level setting unit 4 Is described to set the virtual maximum brightness level. According to this configuration, it is possible to convert the gradation value according to the peak luminance which is the greatest advantage of HDR.
　しかし、このように階調値を変換すると、輝度値に対する低階調値領域の階調値が相対的に低下してしまう（黒つぶれ）。これにより、画像を表示したときに、低階調値領域内の階調値で表示された画像内の領域は、真っ暗になり、表現不足となってしまう。 However, when the gradation value is converted in this way, the gradation value in the low gradation value region relative to the luminance value is relatively lowered (blackout). As a result, when the image is displayed, the area in the image displayed with the gradation value in the low gradation value area is completely dark and the expression is insufficient.
　上記のような問題を解決するために、本実施形態に係る階調値変換装置１１は、階調値変換部５が変換した後の階調値のうち、低階調値領域の階調値に持ち上げ部を有するように、映像信号において各フレーム又は各シーンを構成する各画素が取る階調値を調整する。 In order to solve the problems as described above, the tone value conversion device 11 according to the present embodiment converts the tone values of the low tone value region among the tone values converted by the tone value conversion unit 5. The gradation value taken by each pixel constituting each frame or each scene in the video signal is adjusted so as to have a lifting portion.
　なお、本願明細書において、低階調値領域とは、変換後の階調値において、原点（階調値および対応する輝度値がゼロの点）近傍の階調値領域を示す。例えば、低階調値領域とは、階調値が８ビットで量子化されている場合（２５６階調（０～２５５））、その５分の１程度の階調値の領域のことを示す（階調値が０～５１である領域）。また、低階調値領域における最大の階調値よりも大きい階調値を最低の階調値として有する階調値の領域を、中階調値領域とし、中階調値領域における最大の階調値よりも大きい階調値を最低の階調値として有する階調値の領域を、高階調値領域として定義する。 In the specification of the present application, the low gradation value area indicates a gradation value area near the origin (a point at which the gradation value and the corresponding luminance value are zero) in the converted gradation value. For example, the low gradation value area indicates an area of about one-fifth the gradation value when the gradation value is quantized with 8 bits (256 gradations (0 to 255)). (Area in which the gradation value is 0 to 51). In addition, the area of the gradation value having the gradation value larger than the largest gradation value in the low gradation value area as the lowest gradation value is taken as the middle gradation value area, and the largest floor in the middle gradation value area. A region of tone values having a tone value larger than a tone value as the lowest tone value is defined as a high tone value region.
　また、本願明細書において、「低階調値領域の階調値に持ち上げ部を有する」とは、実施形態１で説明した階調値変換方法によって階調値を変換することにより生じる、低階調値領域の階調値の相対的な低下（黒つぶれ）を改善するために、低階調領域の階調値を上昇させることを意味する。 Further, in the specification of the present application, “having a lifting portion in the gradation value of the low gradation value region” means the low floor caused by converting the gradation value by the gradation value conversion method described in the first embodiment. It means raising the tone value of the low tone region to improve the relative drop (blackout) of the tone value of the tone value region.
　（階調値変換装置１１）
　図１１は、本実施形態に係る階調値変換装置（映像処理装置）１１を備えている表示装置１０の構成を示すブロック図である。図１１が示すように、階調値変換装置１１は、実施形態１に係る階調値変換装置２の構成に加えて、階調値調整部１２をさらに備えている。 (Tone value converter 11)
FIG. 11 is a block diagram showing a configuration of a display device 10 provided with the gradation value conversion device (video processing device) 11 according to the present embodiment. As shown in FIG. 11, the gradation value conversion device 11 further includes a gradation value adjustment unit 12 in addition to the configuration of the gradation value conversion device 2 according to the first embodiment.
　階調値調整部１２は、階調値変換部５が変換した階調値のうち、低階調値領域の階調値に持ち上げ部を有するように調整する。 The gradation value adjustment unit 12 adjusts the gradation value of the low gradation value region to have a lifting part among the gradation values converted by the gradation value conversion unit 5.
　（階調値変換方法）
　本実施形態に係る階調値変換装置１１により実行される階調値変換処理の流れを、図１２を参照して説明する。図１２は、階調値変換処理の流れを示すフローチャートである。なお、以下では、階調値変換処理をフレーム毎に実行し、各フレームのフレーム内最大輝度値を仮想最大輝度レベルとする構成について説明するが、階調値変換処理をシーン毎に実行し、各シーンのシーン内最大輝度値を仮想最大輝度レベルとする構成についても同様である。 (Tonal value conversion method)
A flow of tone value conversion processing executed by the tone value conversion device 11 according to the present embodiment will be described with reference to FIG. FIG. 12 is a flowchart showing the flow of tone value conversion processing. In the following description, although the gradation value conversion process is performed for each frame and the maximum luminance value in each frame is set as the virtual maximum luminance level, the gradation value conversion process is performed for each scene, The same applies to a configuration in which the in-scene maximum luminance value of each scene is set as the virtual maximum luminance level.
　まず、映像データ取得部３は、ＨＤＲ信号を取得する（ステップＳ２０）映像データ取得部３は、取得したＨＤＲ信号において処理対象フレームを構成する各画素が取る階調値を仮想最大輝度レベル設定部４及び階調値変換部５に供給する。 First, the video data acquisition unit 3 acquires the HDR signal (step S20). The video data acquisition unit 3 sets the gradation value taken by each pixel constituting the processing target frame in the acquired HDR signal to the virtual maximum luminance level setting unit 4 and the gradation value converter 5.
　次に、仮想最大輝度レベル設定部４は、処理対象フレームを構成する各画素が取る階調値を映像データ取得部３から取得し、取得した階調値の最大値（フレーム内最大階調値）に対応する輝度値（フレーム内最大輝度値）を仮想最大輝度レベルに設定する（ステップＳ２１）。 Next, the virtual maximum luminance level setting unit 4 acquires, from the video data acquisition unit 3, the gradation value to be taken by each pixel constituting the processing target frame, and acquires the maximum value of the acquired gradation values (maximum gradation value in frame) ) Is set as the virtual maximum luminance level (step S21).
　次に、階調値変換部５は、処理対象フレームを構成する各画素が取る階調値を映像データ取得部３から取得し、取得した階調値のうち、仮想最大輝度レベル設定部４が設定した仮想最大輝度レベル以下の各輝度レベルに対応する階調値を、第１の階調値から第２の階調値に変換する（ステップＳ２２）。 Next, the gradation value conversion unit 5 acquires, from the video data acquisition unit 3, the gradation value to be taken by each pixel constituting the processing target frame, and among the acquired gradation values, the virtual maximum luminance level setting unit 4 The gradation value corresponding to each luminance level lower than the set virtual maximum luminance level is converted from the first gradation value to the second gradation value (step S22).
　次に、階調値調整部１２は、階調値変換部５が変換した階調値のうち、低階調値領域の階調値に持ち上げ部を有するように調整する（ステップＳ２３）。階調値調整部１２が階調値を調整する方法の具体的な例は後述する。なお、階調値調整部１２が調整した階調値は、低階調値領域において、所定のフォーマットが示す階調値よりも大きいことが好ましい。当該所定のフォーマットの例として、ＳＴ２０８４が挙げられる。 Next, the gradation value adjustment unit 12 adjusts the gradation value of the low gradation value region to have a lifting part among the gradation values converted by the gradation value conversion unit 5 (step S23). A specific example of the method of adjusting the gradation value by the gradation value adjustment unit 12 will be described later. The tone value adjusted by the tone value adjusting unit 12 is preferably larger in the low tone value region than the tone value indicated by the predetermined format. As an example of the predetermined format, ST2084 can be mentioned.
　次に、パネル制御部６は、処理対象フレームを構成する各画素が取る調整後の階調値を階調値調整部１２から取得し、取得した階調値を輝度値に変換する（ステップＳ２４）（トーンマッピング）。 Next, the panel control unit 6 acquires, from the gradation value adjustment unit 12, the adjusted gradation values taken by the pixels constituting the processing target frame, and converts the acquired gradation values into luminance values (step S24). ) (Tone mapping).
　次に、パネル制御部６は、表示パネル７を構成する各画素の輝度を、トーンマッピングにより得られた輝度値に制御する。これにより、処理対象フレームが表示パネル７に表示される（ステップＳ２５）。 Next, the panel control unit 6 controls the luminance of each pixel constituting the display panel 7 to the luminance value obtained by tone mapping. As a result, the processing target frame is displayed on the display panel 7 (step S25).
　（階調値調整部１２が階調値を調整する方法の例）
　図１３は、ステップＳ２２で変換した後の階調値と対応する輝度値との関係を示すグラフである。図１３の領域Ａは、上述の低階調値領域を示し、点線は調整前のカーブ、実線は調整後のカーブを示す。階調値調整部１２は、ステップＳ２３において、変換後の階調値を、領域Ａにおける階調値に持ち上げ部を有するように調整する（点線のカーブから実線のカーブに調整する）。 (Example of a method in which the tone value adjustment unit 12 adjusts the tone value)
FIG. 13 is a graph showing the relationship between the gradation value after conversion in step S22 and the corresponding luminance value. Region A in FIG. 13 indicates the above-described low gradation value region, the dotted line indicates a curve before adjustment, and the solid line indicates a curve after adjustment. In step S23, the gradation value adjustment unit 12 adjusts the gradation value after conversion so that the gradation value in the region A has a lifting part (adjusts from a dotted curve to a solid curve).
　例えば、階調値調整部１２は、低階調値領域の階調値に対して、当該階調値の１０％程度の値を付加することによって調整する。または、調整する階調値がＳＴ２０８４に従う階調値である場合、階調値調整部１２は、低階調値領域の階調値に対して、当該階調値と対応する輝度値とをグラフにした場合、当該グラフにおけるカーブがγ２．２のカーブと同等になるように調整する。 For example, the gradation value adjustment unit 12 adjusts the gradation value of the low gradation value region by adding a value of about 10% of the gradation value. Alternatively, when the gradation value to be adjusted is a gradation value according to ST2084, the gradation value adjustment unit 12 graphs the gradation value corresponding to the gradation value and the luminance value corresponding to the gradation value in the low gradation value region. If so, the curve in the graph is adjusted to be equal to the curve of γ2.2.
　また、階調値調整部１２は、階調値変換部５が変換した階調値に対応する輝度レベルの平均値を参照して、上記低階調値領域を変更してもよい。これにより、輝度レベルの分布に応じて、低階調値領域を設定することができるため、輝度レベルの分布に応じた階調値の調整が可能となる。なお、階調値調整部１２が参照する輝度レベルの平均値は、階調値調整部１２自体が算出してもよいし、外部から取得してもよい。 Further, the gradation value adjustment unit 12 may change the low gradation value region with reference to the average value of the luminance levels corresponding to the gradation value converted by the gradation value conversion unit 5. Thus, the low gradation value region can be set in accordance with the distribution of the luminance levels, so that the gradation values can be adjusted in accordance with the distribution of the luminance levels. The average value of the luminance levels to which the tone value adjusting unit 12 refers may be calculated by the tone value adjusting unit 12 itself, or may be obtained from the outside.
　また、階調値調整部１２は、階調値変換部が変換した階調値と対応する輝度レベルとのグラフにおいて、低階調値領域の階調値と、高階調値領域の階調値とが連続的に変化するように、中階調値領域の階調値をさらに調整してもよい。これにより、調整後の階調値で表示した画像において、低階調値領域の階調値と高階調値領域の階調値との差異による不自然さを解消することができる。 In the graph of the gradation value converted by the gradation value conversion unit and the corresponding luminance level, the gradation value adjustment unit 12 also calculates the gradation value of the low gradation value region and the gradation value of the high gradation value region. The tone values of the middle tone value region may be further adjusted so that. As a result, in the image displayed with the adjusted gradation value, it is possible to eliminate the unnaturalness due to the difference between the gradation value of the low gradation value region and the gradation value of the high gradation value region.
　（変形例）
　上述のステップＳ２１では、仮想最大輝度レベル設定部４が、取得した階調値の最大値（フレーム内最大階調値）に対応する輝度値（フレーム内最大輝度値）を仮想最大輝度レベルに設定する構成について説明した。しかし、ステップＳ２１で、仮想最大輝度レベル設定部４が設定する仮想最大輝度レベルは、フレーム内最大輝度値に限定されない。実施形態１と同様に、仮想最大輝度レベル設定部４が設定する仮想最大輝度レベルは、映像信号に含まれるメタデータが示す最大輝度レベル（ＭＡＸ＿ＣＬＬ）を超えない値であればよい。そして、そのような構成における各工程は、実施形態１の変形例で説明した各工程と同様である。重要な点だけ説明すると、ステップＳ２４において、パネル制御部６は、ステップＳ２３で階調値調整部１２が調整した階調値を輝度値に変換する工程に加えて、映像データ取得部３がステップＳ２０で取得した階調値のうち、仮想最大輝度レベルより大きく、かつ、最大輝度レベル（ＭＡＸ＿ＣＬＬ）以下の各輝度レベルに対応する階調値を、当該仮想最大輝度レベルに対応する輝度値以上の値に変換する。当該工程の具体例を挙げると、パネル制御部６は、映像データ取得部３がステップＳ２０で取得した階調値のうち、仮想最大輝度レベルより大きく、かつ、最大輝度レベル（ＭＡＸ＿ＣＬＬ）以下の各輝度レベルに対応する階調値を、当該仮想最大輝度レベルに対応する輝度値（一定の輝度値）に変換してもよい。また、パネル制御部６は、変換前の階調値と変換後の輝度値とのグラフにおいて、当該変換前の階調値が大きくなるのに従って当該変換後の輝度値が次第に大きくなるように、仮想最大輝度レベルより大きく、かつ、最大輝度レベル（ＭＡＸ＿ＣＬＬ）以下の各輝度レベルに対応する階調値を、仮想最大輝度レベルに対応する輝度値以上の値に変換してもよい。 (Modification)
In step S21 described above, the virtual maximum brightness level setting unit 4 sets the brightness value (maximum brightness value in a frame) corresponding to the maximum value of the acquired tone values (maximum tone value in a frame) to the virtual maximum brightness level. Configuration has been described. However, the virtual maximum brightness level set by the virtual maximum brightness level setting unit 4 in step S21 is not limited to the in-frame maximum brightness value. As in the first embodiment, the virtual maximum brightness level set by the virtual maximum brightness level setting unit 4 may be a value that does not exceed the maximum brightness level (MAX_CLL) indicated by the metadata included in the video signal. And each process in such composition is the same as each process explained by the modification of Embodiment 1. To explain only the important points, in step S24, the panel control unit 6 adds the gradation value adjusted by the gradation value adjustment unit 12 in step S23 to the luminance value, and the video data acquisition unit 3 performs the step. Among the gradation values acquired in S20, the gradation values corresponding to each luminance level larger than the virtual maximum luminance level and lower than the maximum luminance level (MAX_CLL) are the luminance values corresponding to the virtual maximum luminance level or more. Convert to a value Among the gradation values acquired by the video data acquisition unit 3 in step S20, the panel control unit 6 sets each of the steps to a specific example, which is larger than the virtual maximum luminance level and lower than the maximum luminance level (MAX_CLL). The gradation value corresponding to the luminance level may be converted into a luminance value (constant luminance value) corresponding to the virtual maximum luminance level. Further, in the graph of the gradation value before conversion and the luminance value after conversion, the panel control unit 6 causes the luminance value after conversion to gradually increase as the gradation value before conversion increases. The gradation value corresponding to each luminance level larger than the virtual maximum luminance level and lower than the maximum luminance level (MAX_CLL) may be converted to a value larger than the luminance value corresponding to the virtual maximum luminance level.
　（実施形態５のまとめ）
　以上のように、本実施形態に係る階調値変換装置１１は、仮想最大輝度レベルを、輝度レベルの最大値に設定し、設定した仮想最大輝度レベルを参照して階調値を変換し、変換した階調値のうち、低階調値領域の階調値に持ち上げ部を有するように調整する。当該構成では、仮想最大輝度レベルを輝度レベルの最大値に設定することにより、映像信号が含むピーク感の忠実性を保持することができ、また、変換した階調値のうち、低階調値領域の階調値に持ち上げ部を有するように調整することにより、低階調値領域の階調値の低下による黒つぶれを防ぎ、低階調値領域の階調表現力を改善することができる。 (Summary of Embodiment 5)
As described above, the tone value conversion device 11 according to the present embodiment sets the virtual maximum brightness level to the maximum value of the brightness level, converts the tone value with reference to the set virtual maximum brightness level, Among the converted tone values, the tone value in the low tone value region is adjusted to have a lifting portion. In this configuration, by setting the virtual maximum luminance level to the maximum value of the luminance level, the fidelity of the peak feeling included in the video signal can be maintained, and the low gradation value among the converted gradation values can be maintained. By adjusting the tone value of the region to have a raised portion, it is possible to prevent blackout due to the decrease of the tone value of the low tone value region and improve the tone expression power of the low tone value region. .
　〔ソフトウェアによる実現例〕
　階調値変換装置２の制御ブロック（特に映像データ取得部３、仮想最大輝度レベル設定部４および階調値変換部５）は、集積回路（ＩＣチップ）等に形成された論理回路（ハードウェア）によって実現してもよいし、ＣＰＵ（Central Processing Unit）を用いてソフトウェアによって実現してもよい。 [Example of software implementation]
The control block (in particular, the video data acquisition unit 3, the virtual maximum luminance level setting unit 4 and the gradation value conversion unit 5) of the gradation value conversion device 2 is a logic circuit (hardware) formed in an integrated circuit (IC chip) or the like. And may be realized by software using a CPU (Central Processing Unit).
　後者の場合、階調値変換装置２は、各機能を実現するソフトウェアであるプログラムの命令を実行するＣＰＵ、上記プログラムおよび各種データがコンピュータ（またはＣＰＵ）で読み取り可能に記録されたＲＯＭ（Read Only Memory）または記憶装置（これらを「記録媒体」と称する）、上記プログラムを展開するＲＡＭ（Random Access Memory）などを備えている。そして、コンピュータ（またはＣＰＵ）が上記プログラムを上記記録媒体から読み取って実行することにより、本発明の目的が達成される。上記記録媒体としては、「一時的でない有形の媒体」、例えば、テープ、ディスク、カード、半導体メモリ、プログラマブルな論理回路などを用いることができる。また、上記プログラムは、該プログラムを伝送可能な任意の伝送媒体（通信ネットワークや放送波等）を介して上記コンピュータに供給されてもよい。なお、本発明は、上記プログラムが電子的な伝送によって具現化された、搬送波に埋め込まれたデータ信号の形態でも実現され得る。 In the latter case, the gradation value conversion device 2 is a CPU that executes instructions of a program that is software that realizes each function, a ROM (Read Only) in which the program and various data are readably recorded by a computer (or CPU). Memory or storage device (these are referred to as "recording media"), and RAM (Random Access Memory) for developing the program. The object of the present invention is achieved by the computer (or CPU) reading the program from the recording medium and executing the program. As the recording medium, a “non-transitory tangible medium”, for example, a tape, a disk, a card, a semiconductor memory, a programmable logic circuit or the like can be used. The program may be supplied to the computer via any transmission medium (communication network, broadcast wave, etc.) capable of transmitting the program. The present invention can also be realized in the form of a data signal embedded in a carrier wave, in which the program is embodied by electronic transmission.
　〔まとめ〕
　本発明の態様１に係る映像処理装置（２、１１）は、第１の映像フォーマットよりも輝度範囲の広い第２の映像フォーマットに従う映像信号において各画素が取る階調値を変換する映像処理装置であって、上記映像信号において各画素が取る階調値を参照することによって、上記映像信号に含まれるメタデータが示す最大輝度レベルを超えない仮想最大輝度レベルを設定する仮想最大輝度レベル設定部（４）と、上記映像信号において各画素が取る階調値のうち、上記仮想最大輝度レベル以下の各輝度レベルに対応する階調値を変換し、上記仮想最大輝度レベルより大きく、かつ、上記最大輝度レベル以下の各輝度レベルに対応する階調値を、上記仮想最大輝度レベルに対応する輝度値以上の値に変換する階調値変換部（５）と、を備えている。 [Summary]
A video processing apparatus (2, 11) according to aspect 1 of the present invention is a video processing apparatus that converts a gradation value taken by each pixel in a video signal according to a second video format wider in luminance range than the first video format. And a virtual maximum brightness level setting unit that sets a virtual maximum brightness level not exceeding the maximum brightness level indicated by the metadata included in the video signal by referring to the gray scale value taken by each pixel in the video signal. (4) Among the gradation values taken by each pixel in the video signal, the gradation values corresponding to each luminance level below the virtual maximum luminance level are converted, and are larger than the virtual maximum luminance level, and And a gradation value conversion unit (5) for converting the gradation value corresponding to each luminance level lower than the maximum luminance level into a value higher than the luminance value corresponding to the virtual maximum luminance level. .
　上記の構成によれば、上記映像信号が表す映像を、上記映像信号が従う第２の映像フォーマットよりも輝度のダイナミックレンジの狭い第１の映像フォーマットに対応した表示装置に表示する際に、低輝度領域において生じ得る階調値の縮退を抑制することができる。これにより、映像の表示品位を向上することができる。 According to the above configuration, when displaying the video represented by the video signal on the display device compatible with the first video format having a narrower dynamic range of luminance than the second video format followed by the video signal, Degeneracy of gradation values that may occur in the luminance region can be suppressed. Thereby, the display quality of the video can be improved.
　本発明の態様２に係る映像処理装置（２、１１）は、上記態様１において、上記階調値変換部は、上記映像信号において各画素が取る階調値のうち、上記仮想最大輝度レベルより大きく、かつ、上記最大輝度レベル以下の各輝度レベルに対応する階調値を、上記仮想最大輝度レベルに対応する輝度値に変換してもよい。 In the video processing device (2, 11) according to aspect 2 of the present invention, in the aspect 1, the gradation value conversion unit determines whether the gradation value of each pixel in the image signal is higher than the virtual maximum luminance level A gradation value corresponding to each luminance level which is large and equal to or less than the maximum luminance level may be converted into a luminance value corresponding to the virtual maximum luminance level.
　上記の構成によれば、仮想最大輝度レベルより大きく、かつ、最大輝度レベル以下の各輝度レベルに対応する階調値は、一定の輝度値に変換されるため、変換後の輝度値で表示した映像においても、変換前の階調値の階調表現を大きく損なわない。 According to the above configuration, since the gradation value corresponding to each luminance level larger than the virtual maximum luminance level and lower than the maximum luminance level is converted to a constant luminance value, the luminance values after conversion are displayed. Also in the image, the gradation expression of the gradation value before conversion is not significantly impaired.
　本発明の態様３に係る映像処理装置（２、１１）は、上記態様１において、上記階調値変換部は、変換前の階調値と変換後の輝度値とのグラフにおいて、当該変換前の階調値が大きくなるのに従って当該変換後の輝度値が次第に大きくなるように、上記映像信号において各画素が取る階調値のうち、上記仮想最大輝度レベルより大きく、かつ、上記最大輝度レベル以下の各輝度レベルに対応する階調値を、上記仮想最大輝度レベルに対応する輝度値以上の値に変換してもよい。 In the video processing device (2, 11) according to aspect 3 of the present invention, in the aspect 1, the gradation value conversion unit is configured to generate the gradation value before conversion and the luminance value after conversion before the conversion. The gradation value of each pixel in the video signal is larger than the virtual maximum luminance level and the maximum luminance level so that the luminance value after conversion gradually increases as the gradation value of the pixel increases. The gradation values corresponding to the following luminance levels may be converted to values equal to or higher than the luminance value corresponding to the virtual maximum luminance level.
　上記の構成によれば、変換後の輝度値の大きさは、変換前の階調値の大きさに応じた値となるため、変換後の輝度値で表示した映像においても、変換前の階調値の階調表現を大きく損なわない。 According to the above configuration, the size of the luminance value after conversion is a value corresponding to the size of the gradation value before conversion, so even in the image displayed with the luminance value after conversion, the floor before conversion is Do not significantly reduce the tone expression of the key value.
　本発明の態様４に係る映像処理装置（２、１１）は、上記態様１～３において、上記階調値変換部（５）は、上記映像信号が従う第２の映像フォーマットにおいて各画素が取り得る階調値のうち、上記仮想最大輝度レベル以下の各輝度レベルに対応する階調値を、上記第１の映像フォーマットにおいて各画素が取り得る階調値に対応させるマッピングを用いて、上記映像信号において各画素が取る階調値を変換する。 In the video processing device (2, 11) according to aspect 4 of the present invention, in the above aspects 1 to 3, the gradation value conversion unit (5) takes each pixel in a second video format according to the video signal. Among the obtained gradation values, using the mapping that corresponds the gradation value corresponding to each luminance level equal to or lower than the virtual maximum luminance level to the gradation value that each pixel can take in the first image format, the image It converts the gradation value that each pixel takes in the signal.
　上記の構成によれば、映像の表示品位をさらに向上することができる。 According to the above configuration, the display quality of the video can be further improved.
　本発明の態様５に係る映像処理装置（２、１１）は、上記態様４において、上記第１の映像フォーマットは、ＥＯＴＦがγ２．２相当のフォーマットであり、上記第２の映像フォーマットは、ＥＯＴＦがＳＭＰＴＥ－ＳＴ２０８４であるフォーマットである。 In the video processing device (2, 11) according to aspect 5 of the present invention, in the aspect 4, the first video format is a format in which the EOTF is equivalent to γ2.2, and the second video format is the EOTF Is a format that is SMPTE-ST2084.
　上記の構成によれば、上記映像信号がＨＤＲ信号であるときに、ＳＤＲ再生環境における映像の表示品位を向上することができる。 According to the above configuration, when the video signal is an HDR signal, it is possible to improve the display quality of the video in the SDR reproduction environment.
　本発明の態様６に係る映像処理装置（２、１１）は、上記態様１～５において、上記仮想最大輝度レベル設定部は、上記映像信号において各フレーム又は各シーンを構成する各画素が取る階調値を参照することによって、上記仮想最大輝度レベルを設定する。 In the video processing device (2, 11) according to aspect 6 of the present invention, in the above aspects 1 to 5, the virtual maximum luminance level setting unit is a floor taken by each pixel constituting each frame or each scene in the video signal. The virtual maximum luminance level is set by referring to the adjustment value.
　上記の構成によれば、映像信号が含む階調値に即して、効率的に階調値を変換することができる。 According to the above configuration, it is possible to efficiently convert the gradation value in accordance with the gradation value included in the video signal.
　本発明の態様７に係る映像処理装置（２、１１）は、上記態様６において、上記仮想最大輝度レベル設定部（４）は、上記仮想最大輝度レベルを、上記映像信号において各フレーム又は各シーンを構成する各画素が取る階調値に対応する輝度レベルの最大値に設定する。 In the video processing device (2, 11) according to aspect 7 of the present invention, in the above-mentioned aspect 6, the virtual maximum luminance level setting unit (4) determines that the virtual maximum luminance level corresponds to each frame or each scene in the video signal. Are set to the maximum value of the luminance level corresponding to the gradation value to be taken by each of the pixels constituting the image.
　上記の構成によれば、映像信号が含む階調値に即して、効率的に階調値を変換することができる。 According to the above configuration, it is possible to efficiently convert the gradation value in accordance with the gradation value included in the video signal.
　本発明の態様８に係る映像処理装置（１１）は、上記態様７において、上記階調値変換部が変換した階調値のうち、低階調値領域の階調値に持ち上げ部を有するように調整する階調値調整部（１２）をさらに備えている。 In the video processing apparatus (11) according to aspect 8 of the present invention, in the above-mentioned aspect 7, among the gradation values converted by the gradation value conversion section, the gradation value in the low gradation value region has a lifting portion. And a tone value adjustment unit (12) for adjusting the image.
　上記の構成によれば、低階調値領域の階調値の低下による黒つぶれを防ぎ、低階調値領域の階調表現力を改善することができる。 According to the above configuration, it is possible to prevent blackout due to a decrease in tone value in the low tone value region, and to improve the tone expression capability in the low tone value region.
　本発明の態様９に係る映像処理装置（１１）は、上記態様８において、上記階調値調整部は、上記階調値変換部が変換した階調値に対応する輝度レベルの平均値を参照して、上記低階調値領域を変更する。 In the video processing device (11) according to aspect 9 of the present invention, in the aspect 8, the gradation value adjustment unit refers to the average value of the luminance levels corresponding to the gradation value converted by the gradation value conversion unit. Then, the low gradation value area is changed.
　上記の構成によれば、輝度レベルの分布に応じて、低階調値領域を設定することができるため、輝度レベルの分布に応じた階調値の調整が可能となる。 According to the above configuration, since the low gradation value region can be set according to the distribution of the luminance level, it becomes possible to adjust the gradation value according to the distribution of the luminance level.
　本発明の態様１０に係る映像処理装置（１１）は、上記態様８または９において、上記階調値調整部は、上記階調値変換部が変換した階調値と対応する輝度レベルとのグラフにおいて、低階調値領域の階調値と、高階調値領域の階調値とが連続的に変化するように、中階調値領域の階調値をさらに調整する。 In the video processing device (11) according to aspect 10 of the present invention, in the aspect 8 or 9, the gradation value adjustment unit is a graph of the gradation value converted by the gradation value conversion unit and the corresponding luminance level. The tone values in the middle tone value area are further adjusted so that the tone values in the low tone value area and the tone values in the high tone value area change continuously.
　上記の構成によれば、調整後の階調値で表示した画像において、低階調値領域の階調値と高階調値領域の階調値との差異による不自然さを解消することができる。 According to the above configuration, it is possible to eliminate the unnaturalness due to the difference between the gradation value of the low gradation value region and the gradation value of the high gradation value region in the image displayed by the adjusted gradation values. .
　本発明の態様１１に係る映像処理装置（１１）は、上記態様８～１０において、上記階調値調整部が調整した階調値は、低階調値領域において、上記第２の映像フォーマットが示す階調値よりも大きい。 In the video processing device (11) according to aspect 11 of the present invention, in the above aspects 8 to 10, the gradation value adjusted by the gradation value adjustment unit is the second image format in the low gradation value region. Greater than the indicated tone value.
　上記の構成によれば、上記態様８～１０の映像変換装置を好適に用いることができる。 According to the above configuration, the video image conversion device of the above aspects 8 to 10 can be suitably used.
　本発明の態様１２に係る映像処理装置（２）は、上記態様１～６において、上記仮想最大輝度レベル設定部（４）は、上記映像信号において各フレーム又は各シーンを構成する各画素が取る階調値に対応する輝度レベルのヒストグラムを作成し、上記ヒストグラムを参照することによって、上記仮想最大輝度レベルを設定することを特徴とする。 In the video processing apparatus (2) according to aspect 12 of the present invention, in the above-mentioned aspects 1 to 6, the virtual maximum luminance level setting unit (4) takes each pixel constituting each frame or each scene in the video signal. A histogram of luminance levels corresponding to gradation values is created, and the virtual maximum luminance level is set by referring to the histogram.
　上記の構成によれば、映像信号が含む階調値に即して、さらに効率的に階調値を変換することができる。 According to the above configuration, it is possible to more efficiently convert the gradation value in accordance with the gradation value included in the video signal.
　本発明の態様１３に係る映像処理装置（２）は、上記態様１２において、上記仮想最大輝度レベル設定部（４）は、上記仮想最大輝度レベルを、上記映像信号において各フレーム又は各シーンを構成する各画素が取る階調値に対応する輝度レベルの実効最大値であって、上記ヒストグラムの標準偏差の定数倍により定義される実効最大値に設定する。 In the video processing device (2) according to aspect 13 of the present invention, in the aspect 12, the virtual maximum luminance level setting unit (4) configures each frame or each scene in the video signal with the virtual maximum luminance level. The effective maximum value of the luminance level corresponding to the gradation value taken by each pixel is set to the effective maximum value defined by a constant multiple of the standard deviation of the histogram.
　上記の構成によれば、映像信号が含む階調値に即して、さらに効率的に階調値を変換することができる。 According to the above configuration, it is possible to more efficiently convert the gradation value in accordance with the gradation value included in the video signal.
　本発明の態様１４に係る映像処理装置（２）は、上記態様１２において、上記仮想最大輝度レベル設定部（４）は、上記最大輝度レベルから所定値低いリミット値を設定すると共に、上記映像信号において各フレーム又は各シーンを構成する各画素が取る階調値に対応する輝度レベルの実効最大値であって、上記ヒストグラムの標準偏差の定数倍により定義される実効最大値が上記リミット値よりも低い場合、上記仮想最大輝度レベルを上記リミット値の値に設定し、上記実効最大値が上記リミット値以上である場合、上記仮想最大輝度レベルを上記実効最大値に設定する。 In the video processing device (2) according to aspect 14 of the present invention, in the aspect 12, the virtual maximum luminance level setting unit (4) sets a limit value lower than the maximum luminance level by a predetermined value, and the video signal The effective maximum value of the luminance level corresponding to the gradation value taken by each pixel constituting each frame or each scene in the image, and the effective maximum value defined by a constant multiple of the standard deviation of the histogram is higher than the limit value If it is low, the virtual maximum brightness level is set to the value of the limit value, and if the effective maximum value is equal to or more than the limit value, the virtual maximum brightness level is set to the effective maximum value.
　上記の構成によれば、仮想最大輝度レベルにリミット値を設けることにより、仮想最大輝度レベルの大きな変動を防ぎ、輝度およびヒストグラムの大きな変動による映像品位の低下を防ぐことができる。 According to the above configuration, by setting the limit value to the virtual maximum brightness level, it is possible to prevent large fluctuation of the virtual maximum brightness level and to prevent deterioration of the image quality due to large fluctuation of the brightness and the histogram.
　本発明の態様１５に係る映像処理装置（２）は、上記態様１２において、上記仮想最大輝度レベル設定部（４）は、リミット値を、上記最大輝度レベルから当該リミット値を減算した差と、上記映像信号において各フレーム又は各シーンを構成する各画素が取る階調値に対応する輝度レベルの実効最大値であって、上記ヒストグラムの標準偏差の定数倍により定義される実効最大値を上記リミット値から減算した差とが所定の比になるように設定すると共に、上記実効最大値が上記リミット値よりも低い場合、上記仮想最大輝度レベルを上記リミット値の値に設定し、上記実効最大値が上記リミット値以上である場合、上記仮想最大輝度レベルを上記実効最大値に設定する。 In the video processing device (2) according to aspect 15 of the present invention, in the above aspect 12, the virtual maximum luminance level setting unit (4) is a difference obtained by subtracting the limit value from the maximum luminance level. The effective maximum value of the luminance level corresponding to the gradation value taken by each pixel constituting each frame or each scene in the video signal, which is defined by a constant multiple of the standard deviation of the histogram The virtual maximum luminance level is set to the value of the limit value when the effective maximum value is lower than the limit value, and the difference obtained by subtracting the difference from the value is a predetermined ratio, and the effective maximum value is set. Is greater than or equal to the limit value, the virtual maximum brightness level is set to the effective maximum value.
　上記の構成によれば、リミット値を所望の値に設定することができる。 According to the above configuration, the limit value can be set to a desired value.
　本発明の態様１６に係る映像処理装置（２）は、上記態様１２において、上記仮想最大輝度レベル設定部は、上記仮想最大輝度レベルを、上記映像信号において各フレーム又は各シーンを構成する各画素が取る階調値に対応する輝度レベルの実効最大値であって、上記ヒストグラムの標準偏差の定数倍により定義される実効最大値の時間平均値に設定する。 In the video processing device (2) according to aspect 16 of the present invention, in the aspect 12, the virtual maximum luminance level setting unit determines that the virtual maximum luminance level corresponds to each frame or each pixel forming each scene in the video signal. The effective maximum value of the luminance level corresponding to the gradation value to be taken is set to a time average value of the effective maximum value defined by a constant multiple of the standard deviation of the histogram.
　上記の構成によれば、映像品位を向上させることができる。 According to the above configuration, the video quality can be improved.
　本発明の態様１７に係る表示装置（１、１０）は、上記態様１～１６の何れか１つの映像処理装置を備えている。 The display device (1, 10) according to aspect 17 of the present invention includes the video processing device according to any one of the above aspects 1 to 16.
　上記の構成によれば、上記映像処理装置が上記各態様において奏する効果を上記表示装置において得ることができる。 According to the above configuration, it is possible to obtain, in the display device, the effects obtained by the video processing device in the above aspects.
　本発明の態様１８に係る映像処理方法は、第１の映像フォーマットよりも輝度範囲の広い第２の映像フォーマットに従う映像信号において各画素が取る階調値を変換する映像処理方法であって、上記映像信号において各画素が取る階調値を参照することによって、上記映像信号に含まれるメタデータが示す最大輝度レベルを超えない仮想最大輝度レベルを設定する仮想最大輝度レベル設定ステップと、上記映像信号において各画素が取る階調値のうち、上記仮想最大輝度レベル以下の各輝度レベルに対応する階調値を変換し、上記仮想最大輝度レベルより大きく、かつ、上記最大輝度レベル以下の各輝度レベルに対応する階調値を、上記仮想最大輝度レベルに対応する輝度値以上の値に変換する階調値変換ステップと、を含んでいる。 A video processing method according to aspect 18 of the present invention is a video processing method for converting the gradation value taken by each pixel in a video signal according to a second video format having a wider luminance range than the first video format, Virtual maximum luminance level setting step of setting a virtual maximum luminance level not exceeding the maximum luminance level indicated by the metadata included in the video signal by referring to the gradation value taken by each pixel in the video signal; and the video signal The gradation value corresponding to each luminance level below the virtual maximum luminance level among the gradation values taken by each pixel is converted, and each luminance level larger than the virtual maximum luminance level and below the maximum luminance level And a tone value conversion step of converting the tone value corresponding to に to a value greater than or equal to the brightness value corresponding to the virtual maximum brightness level.
　上記の構成によれば、上記態様１の映像処理装置と同様の効果を奏することができる。 According to the above configuration, the same effect as that of the video processing device of aspect 1 can be achieved.
　本発明の各態様に係る表示装置は、コンピュータによって実現してもよく、この場合には、コンピュータを上記表示装置が備える各部（ソフトウェア要素）として動作させることにより上記表示装置をコンピュータにて実現させる表示装置の制御プログラム、およびそれを記録したコンピュータ読み取り可能な記録媒体も、本発明の範疇に入る。 The display device according to each aspect of the present invention may be realized by a computer. In this case, the display device is realized by the computer by operating the computer as each unit (software element) included in the display device. A control program of a display device and a computer readable recording medium recording the same also fall within the scope of the present invention.
　本発明は上述した各実施形態に限定されるものではなく、請求項に示した範囲で種々の変更が可能であり、異なる実施形態にそれぞれ開示された技術的手段を適宜組み合わせて得られる実施形態についても本発明の技術的範囲に含まれる。さらに、各実施形態にそれぞれ開示された技術的手段を組み合わせることにより、新しい技術的特徴を形成することができる。 The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims, and embodiments obtained by appropriately combining the technical means disclosed in the different embodiments. Is also included in the technical scope of the present invention. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment.
　１、１０　表示装置　
　２、１１　階調値変換装置　
　３　映像データ取得部　
　４　仮想最大輝度レベル設定部　
　５　階調値変換部　
　６　パネル制御部　
　７　表示パネル　
　１２　階調値調整部 1, 10 display device
2, 11 Tone value converter
3 Video data acquisition unit
4 Virtual Maximum Brightness Level Setting Unit
5 Tone value converter
6 Panel control unit
7 Display panel
12 tone value adjustment unit

Claims (20)

  1. 　第１の映像フォーマットよりも輝度範囲の広い第２の映像フォーマットに従う映像信号において各画素が取る階調値を変換する映像処理装置であって、
    　上記映像信号において各画素が取る階調値を参照することによって、上記映像信号に含まれるメタデータが示す最大輝度レベルを超えない仮想最大輝度レベルを設定する仮想最大輝度レベル設定部と、
    　上記映像信号において各画素が取る階調値のうち、上記仮想最大輝度レベル以下の各輝度レベルに対応する階調値を変換し、上記仮想最大輝度レベルより大きく、かつ、上記最大輝度レベル以下の各輝度レベルに対応する階調値を、上記仮想最大輝度レベルに対応する輝度値以上の値に変換する階調値変換部と、を備えていることを特徴とする、映像処理装置。     A video processing apparatus that converts a gradation value to be taken by each pixel in a video signal according to a second video format having a luminance range wider than the first video format.
    A virtual maximum brightness level setting unit that sets a virtual maximum brightness level not exceeding the maximum brightness level indicated by the metadata included in the video signal by referring to the gray scale value taken by each pixel in the video signal;
    The gradation value corresponding to each luminance level equal to or lower than the virtual maximum luminance level among the gradation values taken by each pixel in the video signal is converted to be larger than the virtual maximum luminance level and equal to or lower than the maximum luminance level A video processing apparatus comprising: a grayscale value conversion unit configured to convert a grayscale value corresponding to each luminance level to a value equal to or higher than a luminance value corresponding to the virtual maximum luminance level.
  2. 　上記階調値変換部は、上記映像信号において各画素が取る階調値のうち、上記仮想最大輝度レベルより大きく、かつ、上記最大輝度レベル以下の各輝度レベルに対応する階調値を、上記仮想最大輝度レベルに対応する輝度値に変換することを特徴とする、請求項１に記載の映像処理装置。 The gradation value conversion unit is configured to, of the gradation values taken by each pixel in the video signal, the gradation values corresponding to each luminance level larger than the virtual maximum luminance level and lower than the maximum luminance level. The image processing apparatus according to claim 1, wherein the image processing apparatus converts the luminance value corresponding to the virtual maximum luminance level.
  3. 　上記階調値変換部は、変換前の階調値と変換後の輝度値とのグラフにおいて、当該変換前の階調値が大きくなるのに従って当該変換後の輝度値が次第に大きくなるように、上記映像信号において各画素が取る階調値のうち、上記仮想最大輝度レベルより大きく、かつ、上記最大輝度レベル以下の各輝度レベルに対応する階調値を、上記仮想最大輝度レベルに対応する輝度値以上の値に変換することを特徴とする、請求項１に記載の映像処理装置。 In the graph of the gradation value before conversion and the luminance value after conversion, the gradation value conversion unit causes the luminance value after conversion to gradually increase as the gradation value before conversion increases. The gradation value corresponding to each luminance level larger than the virtual maximum luminance level and lower than the maximum luminance level among the gradation values taken by each pixel in the video signal is the luminance corresponding to the virtual maximum luminance level The image processing apparatus according to claim 1, wherein the image processing apparatus converts the value into a value greater than or equal to the value.
  4. 　上記階調値変換部は、上記映像信号が従う第２の映像フォーマットにおいて各画素が取り得る階調値のうち、上記仮想最大輝度レベル以下の各輝度レベルに対応する階調値を、上記第１の映像フォーマットにおいて各画素が取り得る階調値に対応させるマッピングを用いて、上記映像信号において各画素が取る階調値を変換する、
    ことを特徴とする請求項１～３の何れか１項に記載の映像処理装置。     The gradation value conversion unit is configured to select, from among the gradation values that can be taken by each pixel in the second video format according to the video signal, the gradation values corresponding to each luminance level lower than the virtual maximum luminance level. Converting the gradation value to be taken by each pixel in the above-mentioned video signal using the mapping corresponding to the gradation value that each pixel can take in one video format,
    The video processing apparatus according to any one of claims 1 to 3, characterized in that:
  5. 　上記第１の映像フォーマットは、ＥＯＴＦがγ２．２相当のフォーマットであり、
    　上記第２の映像フォーマットは、ＥＯＴＦがＳＭＰＴＥ（Ｓｏｃｉｅｔｙ　ｏｆ　Ｍｏｔｉｏｎ　Ｐｉｃｔｕｒｅ　ａｎｄ　Ｔｅｌｅｖｉｓｉｏｎ　Ｅｎｇｉｎｅｅｒｓ）－ＳＴ２０８４であるフォーマットである、
    ことを特徴とする請求項４に記載の映像処理装置。     In the first video format, the EOTF is a format equivalent to γ2.2,
    The second video format is a format in which the EOTF is SMPTE (Society of Motion Picture and Television Engineers) -ST2084.
    The video processing apparatus according to claim 4, wherein
  6. 　上記仮想最大輝度レベル設定部は、上記映像信号において各フレーム又は各シーンを構成する各画素が取る階調値を参照することによって、上記仮想最大輝度レベルを設定することを特徴とする請求項１～５の何れか１項に記載の映像処理装置。 The virtual maximum luminance level setting unit sets the virtual maximum luminance level by referring to a gradation value taken by each pixel constituting each frame or each scene in the video signal. The video processing device according to any one of items 1 to 5.
  7. 　上記仮想最大輝度レベル設定部は、上記仮想最大輝度レベルを、上記映像信号において各フレーム又は各シーンを構成する各画素が取る階調値に対応する輝度レベルの最大値に設定する、ことを特徴とする請求項６に記載の映像処理装置。 The virtual maximum luminance level setting unit sets the virtual maximum luminance level to the maximum value of the luminance level corresponding to the gradation value taken by each pixel constituting each frame or each scene in the video signal. The video processing apparatus according to claim 6.
  8. 　上記階調値変換部が変換した階調値のうち、低階調値領域の階調値に持ち上げ部を有するように調整する階調値調整部をさらに備えていることを特徴とする、請求項７に記載の映像処理装置。 Among the gradation values converted by the gradation value conversion unit, the present invention further comprises a gradation value adjustment unit for adjusting the gradation value of the low gradation value region to have a lifting part. Item 8. The video processing device according to Item 7.
  9. 　上記階調値調整部は、上記階調値変換部が変換した階調値に対応する輝度レベルの平均値を参照して、上記低階調値領域を変更することを特徴とする、請求項８に記載の映像処理装置。 The gradation value adjustment unit changes the low gradation value region with reference to an average value of luminance levels corresponding to the gradation value converted by the gradation value conversion unit. 8. The video processing device according to 8.
  10. 　上記階調値調整部は、上記階調値変換部が変換した階調値と対応する輝度レベルとのグラフにおいて、低階調値領域の階調値と、高階調値領域の階調値とが連続的に変化するように、中階調値領域の階調値をさらに調整することを特徴とする、請求項８または９に記載の映像処理装置。 The gradation value adjustment unit is configured to adjust the gradation value of the low gradation value region and the gradation value of the high gradation value region in the graph of the gradation value converted by the gradation value conversion unit and the corresponding luminance level. 10. The video processing apparatus according to claim 8, further comprising: adjusting the gradation value of the middle gradation value area so that .DELTA. Changes continuously.
  11. 　上記階調値調整部が調整した階調値は、低階調値領域において、上記第２の映像フォーマットが示す階調値よりも大きいことを特徴とする、請求項８～１０の何れか１項に記載の映像処理装置。 The tone value adjusted by the tone value adjusting unit is larger in the low tone value region than the tone value indicated by the second video format. An image processing apparatus according to claim 1.
  12. 　上記仮想最大輝度レベル設定部は、上記映像信号において各フレーム又は各シーンを構成する各画素が取る階調値に対応する輝度レベルのヒストグラムを作成し、上記ヒストグラムを参照することによって、上記仮想最大輝度レベルを設定することを特徴とする請求項１～６の何れか１項に記載の映像処理装置。 The virtual maximum brightness level setting unit creates a histogram of brightness levels corresponding to gradation values taken by each pixel constituting each frame or each scene in the video signal, and refers to the histogram to obtain the virtual maximum. The image processing apparatus according to any one of claims 1 to 6, wherein a luminance level is set.
  13. 　上記仮想最大輝度レベル設定部は、上記仮想最大輝度レベルを、上記映像信号において各フレーム又は各シーンを構成する各画素が取る階調値に対応する輝度レベルの実効最大値であって、上記ヒストグラムの標準偏差の定数倍により定義される実効最大値に設定する、ことを特徴とする請求項１２に記載の映像処理装置。 The virtual maximum brightness level setting unit is an effective maximum value of the brightness level corresponding to a gray level value taken by each pixel constituting each frame or each scene in the video signal, and the virtual maximum brightness level setting unit The image processing apparatus according to claim 12, wherein the effective maximum value is defined by a constant multiple of the standard deviation of.
  14. 　上記仮想最大輝度レベル設定部は、上記最大輝度レベルから所定値低いリミット値を設定すると共に、上記映像信号において各フレーム又は各シーンを構成する各画素が取る階調値に対応する輝度レベルの実効最大値であって、上記ヒストグラムの標準偏差の定数倍により定義される実効最大値が上記リミット値よりも低い場合、上記仮想最大輝度レベルを上記リミット値の値に設定し、上記実効最大値が上記リミット値以上である場合、上記仮想最大輝度レベルを上記実効最大値に設定することを特徴とする請求項１２に記載の映像処理装置。 The virtual maximum brightness level setting unit sets a limit value lower by a predetermined value from the maximum brightness level, and the brightness level corresponding to the gradation value taken by each pixel constituting each frame or each scene in the video signal is effective. If the maximum value and the effective maximum value defined by a constant multiple of the standard deviation of the histogram is lower than the limit value, the virtual maximum luminance level is set to the value of the limit value, and the effective maximum value is 13. The video processing apparatus according to claim 12, wherein the virtual maximum luminance level is set to the effective maximum value when it is equal to or more than the limit value.
  15. 　上記仮想最大輝度レベル設定部は、リミット値を、上記最大輝度レベルから当該リミット値を減算した差と、上記映像信号において各フレーム又は各シーンを構成する各画素が取る階調値に対応する輝度レベルの実効最大値であって、上記ヒストグラムの標準偏差の定数倍により定義される実効最大値を上記リミット値から減算した差とが所定の比になるように設定すると共に、上記実効最大値が上記リミット値よりも低い場合、上記仮想最大輝度レベルを上記リミット値の値に設定し、上記実効最大値が上記リミット値以上である場合、上記仮想最大輝度レベルを上記実効最大値に設定することを特徴とする請求項１２に記載の映像処理装置。 The virtual maximum luminance level setting unit is a luminance corresponding to a difference obtained by subtracting the limit value from the maximum luminance level and a gradation value taken by each pixel constituting each frame or each scene in the video signal. The effective maximum value of the level is set such that the effective maximum value defined by a constant multiple of the standard deviation of the histogram minus the limit value is a predetermined ratio, and the effective maximum value is If lower than the limit value, set the virtual maximum luminance level to the value of the limit value, and if the effective maximum value is equal to or higher than the limit value, set the virtual maximum luminance level to the effective maximum value. The image processing apparatus according to claim 12, characterized in that:
  16. 　上記仮想最大輝度レベル設定部は、上記仮想最大輝度レベルを、上記映像信号において各フレーム又は各シーンを構成する各画素が取る階調値に対応する輝度レベルの実効最大値であって、上記ヒストグラムの標準偏差の定数倍により定義される実効最大値の時間平均値に設定する、ことを特徴とする請求項１２に記載の映像処理装置。 The virtual maximum brightness level setting unit is an effective maximum value of the brightness level corresponding to a gray level value taken by each pixel constituting each frame or each scene in the video signal, and the virtual maximum brightness level setting unit The image processing apparatus according to claim 12, wherein the time average value is set to a time average value of effective maximum values defined by a constant multiple of a standard deviation of.
  17. 　請求項１～１６の何れか１項に記載の映像処理装置を備えている表示装置。 A display device comprising the video processing device according to any one of claims 1 to 16.
  18. 　第１の映像フォーマットよりも輝度範囲の広い第２の映像フォーマットに従う映像信号において各画素が取る階調値を変換する映像処理方法であって、
    　上記映像信号において各画素が取る階調値を参照することによって、上記映像信号に含まれるメタデータが示す最大輝度レベルを超えない仮想最大輝度レベルを設定する仮想最大輝度レベル設定ステップと、
    　上記映像信号において各画素が取る階調値のうち、上記仮想最大輝度レベル以下の各輝度レベルに対応する階調値を変換し、上記仮想最大輝度レベルより大きく、かつ、上記最大輝度レベル以下の各輝度レベルに対応する階調値を、上記仮想最大輝度レベルに対応する輝度値以上の値に変換する階調値変換ステップと、を含んでいることを特徴とする、映像処理方法。     A video processing method for converting the gradation value taken by each pixel in a video signal according to a second video format having a wider luminance range than the first video format,
    Virtual maximum brightness level setting step of setting a virtual maximum brightness level not exceeding the maximum brightness level indicated by the metadata included in the video signal by referring to the gray scale value taken by each pixel in the video signal;
    The gradation value corresponding to each luminance level equal to or lower than the virtual maximum luminance level among the gradation values taken by each pixel in the video signal is converted to be larger than the virtual maximum luminance level and equal to or lower than the maximum luminance level And G. converting the gradation value corresponding to each luminance level to a value equal to or higher than the luminance value corresponding to the virtual maximum luminance level.
  19. 　請求項１に記載の映像処理装置としてコンピュータを機能させるための制御プログラムであって、上記仮想最大輝度レベル設定部および上記階調値変換部としてコンピュータを機能させるための制御プログラム。 A control program for causing a computer to function as the video processing apparatus according to claim 1, wherein the control program causes the computer to function as the virtual maximum luminance level setting unit and the gradation value conversion unit.
  20. 　請求項１９に記載の制御プログラムを記録したコンピュータ読み取り可能な記録媒体。 A computer readable recording medium recording the control program according to claim 19.
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