JP2019101241A - Signal processing apparatus - Google Patents

Abstract

To control display luminance while keeping continuity of a derivative of a control function so as not to generate a pseudo contour visually even in the case in which the gain control is performed so as to lower the drive current only in a bright area by dividing the signal value into the bright area and the dark area for each subpixel of RGB.SOLUTION: The signal processing apparatus connected to a display having Hybrid log gamma characteristics includes an EOTF conversion part 11 including a control function for converting an input signal to a first output signal, a parameter calculation part 12 for calculating a parameter value for adjusting a coefficient of the control function for converting the input signal of the bright area out of the bright and dark areas set in advance on the basis of the first output signal, and a signal processing part 13 for outputting a second output signal by converting the input signal of the bright area, using a control function of which the coefficient is adjusted by a parameter value calculated by the parameter calculation part 12.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a signal processing apparatus for controlling the gray level of a display.

  High dynamic range (HDR) display, which is a display technology used in displays, is a technology for expanding the range of light and dark of an image that can be expressed, and a scene with a large difference in contrast as compared with conventional standard dynamic range (SDR) It is possible to reproduce bright scenes etc. more faithfully.

  In particular, a hybrid log gamma method compatible with the standard dynamic range (SDR) display standard is suitable as a high dynamic range (HDR) method used for broadcasting. The HDR display can sufficiently obtain its effect by using a display capable of high brightness display.

  However, due to the problems of luminous efficiency and lifetime of the device, a large screen and high luminance organic EL display does not currently exist.

  In addition, the organic EL element is a current drive element, and emits light by flowing a current. A display using this organic EL element as a display element controls the brightness according to the current. When a large screen display is realized by an organic EL element, a very large current is required, and therefore, power consumption increases when high-brightness display is performed over the entire screen. In general, when a large screen organic EL display has a bright screen over a large area, control is performed so that the power consumption is suppressed to a certain value or less by displaying with the luminance lowered.

In addition, in an image display apparatus using LEDs or OLEDs as light sources, it is known that adaptive luminance (power) control is performed on input signals for the purpose of power saving, element protection, etc. Document 1, Patent Document 2, Patent Document 3). In this method, feedback gain control is used which calculates a feature quantity such as an average signal level APL (Average Picture Level) from an input video signal and adjusts an input signal. It is known that this technique makes it possible to suppress the light emission luminance so that the power consumption of the panel does not exceed the allowable range of the drive circuit.
However, image display devices tend to have higher resolution, larger panels, higher luminance, and faster driving, and a further increase in drive power is expected. An increase in driving power causes a temperature rise of the light emitting element, which degrades the element characteristics and the life. In particular, in order to realize reduction in thickness and flexibility, a device structure without a cooling mechanism is desirable, and a significant reduction in drive power is required.

JP 2007-147868 A JP, 2010-156974, A International Publication No. 2015/111118

In this respect, as shown in FIGS. 7 and 8, the display luminance is reduced by applying a constant gain g (<1) to all pixels, or by clipping a high luminance portion to a constant luminance. , And processing to reduce the power consumption of the entire display. However, in the existing control method for suppressing the video signal by uniform gain control, loss of gradation and degradation of the SN ratio in the dark area become factors causing deterioration of the image quality. In addition, when clipping the high brightness part to a constant brightness, the image in the low brightness area can be appropriately represented, but since the high brightness area is fixed to a constant value, the gray level of the high brightness level is There was a problem that it was not possible to express appropriately.
Therefore, it is conceivable to divide the video signal into the bright area and the dark area and to lower the drive current only in the bright area. However, when performing gain control by dividing the signal value for each sub-pixel of RGB If the derivative of the control function does not have continuity, a pseudo contour is visually generated. The pseudo contour is a phenomenon in which a step is formed in the density due to quantization at a portion where the density is originally changing smoothly and the contour appears to exist in a pseudo manner.
For this reason, even when gain control is performed such that the drive current is reduced only in the bright area, the signal value is divided into the bright area and the dark area for each sub-pixel of RGB, and the pseudo contour is visually determined. It is required to control the display brightness while maintaining the continuity of the derivative of the control function so as not to generate.

  Therefore, the present invention divides the video signal into a dark area and a bright area when displaying an HDR signal of the hybrid log gamma method on a display capable of high luminance display, such as an organic EL display, and in any display Is set so that substantially the same luminance can be displayed, and when reducing the signal in the bright area, even when the signal value is divided for each RGB sub-pixel and gain control is performed, An object of the present invention is to provide a signal processing device capable of suppressing drive power without visually generating a pseudo contour by controlling display luminance while maintaining continuity of a derivative.

  (1) A signal processing apparatus according to the present invention is a signal processing apparatus connected to a display, which has a hybrid log gamma characteristic and includes an EOTF conversion unit including a control function for converting an input signal into a first output signal. And a bright area including a signal corresponding to a signal level equal to or higher than a preset threshold value based on the first output signal, and a signal level lower than the threshold value or lower than the threshold value. A parameter calculation unit that calculates a parameter value for adjusting a coefficient of the control function that converts an input signal of the bright region in a dark region formed of a signal, and a coefficient based on the parameter value calculated by the parameter calculator And a signal processing unit that outputs a second output signal by converting the input signal in the bright area using the control function adjusted to .

  (2) In the signal processing device according to (1), the parameter calculating unit calculates a feature amount dependent on power consumption at the time of video display based on the first output signal, and the parameter calculation unit calculates the feature amount based on the feature amount. Parameter values may be calculated.

  (3) In the signal processing device according to (1) or (2), a 50% level of the input signal may be used as the threshold.

  (4) In the signal processing device described in (1) to (3), the input signal may be a video signal, and the first output signal and the second output signal may be luminance signals.

  (5) The video processing apparatus according to the present invention may include the signal processing apparatus described in (1) to (4).

  According to the present invention, when an HDR signal of the hybrid log gamma system is displayed on a display capable of high luminance display, the signal value is divided into a bright area and a dark area and the drive current is reduced only in the bright area. When gain control is performed, it is possible to suppress the power consumption of the display to a certain value or less, and to appropriately display the gray level in both the dark area and the bright area of the video signal while not generating a false contour visually Become.

It is a functional block diagram of a signal processing device concerning an embodiment of the present invention. In embodiment of this invention, it is a graph which shows the whole gain value in the control example at the time of making APL = 10% into a threshold value. It is a graph which shows the division | segmentation method of a video signal. It is a graph which shows the outline | summary of the brightness control by the signal processing apparatus which concerns on embodiment of this invention. It is a graph which shows the difference of the brightness control by linear control, and the brightness control by nonlinear control. It is a flowchart which shows the signal processing method which the signal processing apparatus which concerns on embodiment of this invention performs. It is a figure which shows the outline | summary of the luminance control method performed with the signal processing apparatus in a prior art. It is a figure which shows the outline | summary of the luminance control method performed with the signal processing apparatus in a prior art.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 6.

[1. Outline of the Invention]
A signal processing device according to an embodiment of the present invention processes and outputs a video signal as a signal optimum as display luminance in a video display device. Further, the signal processing device calculates a feature amount dependent on power consumption at the time of display from the video signal, and adjusts the signal so as to be optimal for the setting determined from the structure and performance of the video display device.

[2. Constitution of the Invention]
FIG. 1 is a functional block diagram of a signal processing device 1 according to an embodiment of the present invention. The signal processing device 1 is a device connected to a display and used to convert a video signal as an input signal into a luminance signal as an output signal, and includes an EOTF converter 11, a parameter calculator 12 and signal processing. And a unit 13. Here, the “display” may be, for example, a 4K or 8K organic EL display, but is not limited thereto.

  In the following description, a region including a signal corresponding to a signal level equal to or lower than a preset threshold is referred to as a dark region, and a region including a signal corresponding to a signal level exceeding the preset threshold is referred to as a bright region. Note that the video signal or the output signal of the video signal converted by the EOTF converter 11 described later is generically called a signal, and the dark area includes a video signal corresponding to a signal level equal to or lower than a preset threshold. A region or a region including an output signal converted by the EOTF converter 11 of the video signal is collectively referred to. Similarly, the bright region generally refers to a region including a video signal corresponding to a signal level exceeding a preset threshold or a region including an output signal converted by the EOTF converter 11 of the video signal.

  The EOTF conversion unit 11 has a hybrid log gamma characteristic related to Electro Optical Transfer Function (EOTF) known to those skilled in the art, and performs gamma conversion of the hybrid log gamma to display an image signal as an input signal as a output signal. Convert to a signal. Hereinafter, a function in the EOTF conversion unit 11 for converting an input video signal into an output signal is referred to as a control function. Specifically, as described later, the control function indicates a function represented by Equation 1 according to the case where the signal belongs to the dark area and the case where the signal belongs to the bright area.

The parameter calculation unit 12 estimates the power consumption when displaying an image on the display based on the output signal converted by the EOTF conversion unit 11, and calculates the feature amount depending on the power consumption. As the feature amount dependent on the power consumption, for example, it is possible to use APL (Average Picture Level) which is an average value of the output signal as described later, but another feature amount may be used.
Next, the parameter calculation unit 12 converts the coefficient of the control function that converts the video signal of the bright area into an output signal when the feature amount dependent on the power consumption calculated by the parameter calculation unit 12 exceeds a predetermined threshold set in advance. Calculate a parameter value k for adjustment. Specifically, the control function (the control function after adjustment) whose coefficient is adjusted by the parameter value k is, as will be described later, the expression 5 according to the case where the signal belongs to the dark area and the case where it belongs to the bright area. Points to the function represented by
The derivative of the control function after adjustment maintains continuity, and the feature value dependent on the power consumption of the display, which is calculated based on the output signal converted by the control function after adjustment, has a preset predetermined threshold value It does not exceed. The control function after adjustment makes it possible to control the display brightness so as to suppress the power consumption of the display to a predetermined value or less and not to generate a pseudo outline visually.
The specific calculation method of the feature amount depending on the power consumption and the parameter value will be described later.

The signal processing unit 13 converts the entire video signal into the same value as the output signal converted by the EOTF conversion unit 11 for the entire video signal, and the parameter calculation unit 12 calculates only the video signal for the bright region. Convert by the control function whose coefficient is adjusted by the value and output.
By having the above configuration, the signal processing device 1 suppresses the power consumption of the display to a certain value or less, and maintains continuity of the derivative of the control function, and in any video signal, the dark region is Display can be performed with substantially the same gradation characteristics, and the display luminance can be controlled by suppressing the luminance in the bright area.
Although the description concerning the basic configuration of the signal processing device 1 is as described above, the details of the signal processing method by the signal processing device 1 will be described below.

[3. Signal processing method]
[3.1 Threshold value for dividing dark and light areas]
As shown in FIG. 3, first, the threshold value for dividing the video signal into the video signal in the bright area and the video signal in the dark area is set to 0.5 (50%) of the video signal.

[3.2 Method of calculating parameter values used for bright area control]
First, the video signal E ′ {R ′, G ′, B ′} is converted into luminance signals E {R, G, B} using the equation 1 in the EOTF converter 11.

  However, it is set as a = 0.17883277, b = 1-4a, c = 0.5-a * ln (4a).

Next, for example, in the E {R, G, B} converted by the EOTF conversion unit 11, the parameter calculation unit 12 calculates maxE {R, G, B} that is the maximum value of the sub-pixel RGB of each pixel. Substituting into 2, the APL is calculated as the feature amount dependent on the power consumption.
As shown in Equation 2, since APL is 100% when maxE {R, G, B} in all pixels is 1 as the maximum value, it should be adopted as a feature dependent on the power consumption of the display. Can.

ここで、式２は、輝度信号が８Ｋ信号の場合の数式である。輝度信号が例えば４Ｋ信号の場合には、分母が３８４０×２１６０となる。また、式２において、消費電力に依存する特徴量（ＡＰＬ）を算出する際に、Ｅ｛Ｒ，Ｇ，Ｂ｝の最大値であるｍａｘＥ｛Ｒ，Ｇ，Ｂ｝を適用したが、これに限られない。例えば、Ｅ｛Ｒ，Ｇ，Ｂ｝の最大値ｍａｘＥ｛Ｒ，Ｇ，Ｂ｝の代わりに、Ｅ｛Ｒ，Ｇ，Ｂ｝の平均値を適用してもよい。

Here, Equation 2 is an equation in the case where the luminance signal is an 8K signal. When the luminance signal is, for example, a 4K signal, the denominator is 3840 × 2160. In addition, maxE {R, G, B} which is the maximum value of E {R, G, B} is applied when calculating the feature amount (APL) depending on power consumption in Equation 2. It is not limited. For example, instead of the maximum value maxE {R, G, B} of E {R, G, B}, an average value of E {R, G, B} may be applied.

Next, the threshold value of the feature amount APL is used as a threshold value for setting the upper limit of the power consumption of the display.
FIG. 2 shows overall gain values in a control example where APL = 10% is a threshold value. In the example of FIG. 2, the overall gain m is
M = 1 if APL ≦ 10%
M = 10 / APL when APL> 10%
The signal processing device 1 performs signal processing so that
That is, in the example of FIG. 2, the video whose APL is 10% or less is not subjected to luminance control, and is output after being EOTF converted.
In the following, as an example, a control example in the case of adopting a threshold value 10% of the feature amount APL as a threshold value for setting the upper limit of the power consumption of the display, and a parameter value k used when controlling only the bright region The calculation method will be described.

  As shown in FIG. 3, the parameter calculation unit 12 divides the video signal into a video signal of the bright area and a video signal of the dark area. Here, the threshold for dividing the video signal of the bright area and the video signal of the dark area is set to 0.5 (50%) of the video signal. However, the division threshold is not limited to 0.5 (50%).

  At this time, in order to control only the bright region, a parameter value k is set to be a ‘= 0.17883277 / k.

  The signal processing unit 13 converts the video signal using the control function (control function after adjustment) whose coefficient is adjusted by the parameter value k, as shown in Equation 3, and outputs an output signal.

  However, b '= 1-4a', c '= 0.5-a'.ln (4a').

  FIG. 4 shows the relationship between the video signal and the signal value of the luminance signal when the value of k is k = 1, 2/3, 0 in Equation 3. It can be seen from FIG. 4 that setting of the parameter value k controls only the bright region and that the brightness of the bright region decreases as k approaches 1 to 0. That is, by reducing the value of the parameter value k, it is possible to lower the luminance of only the bright area.

Here, assuming that the average value of the luminance signal in the bright area is APL _high , the ratio of the bright area is R _high , the average value of the luminance signal in the dark area is APL _low , and the ratio of the dark area is R _low. And the parameter value k can be obtained from Eq.

However, APL in Equation 4 is calculated for the video signal E ′ before EOTF conversion.
When trying to expand for k contained in a ′ using Equation 4, since k is also contained in b and c, the expansion equation becomes k nonlinear equation and analytically finds a solution of k It is difficult.

Therefore, the left side of Equation 4 is approximated by the left side of Equation 5.

  The reason why the left side of Equation 4 can be approximated by the left side of Equation 5 will be described later.

Based on Equation 5, the parameter value k is calculated by Equation 6.

The signal processing apparatus 1 uses k of Equation 6 as the parameter value k of the control function of Equation 3 and controls only the brightness of the bright region to obtain 10% of the feature amount APL dependent on the power consumption of the display. In order not to exceed, that is, the luminance can be lowered as much as gain control of the whole luminance signal with the above-mentioned overall gain m. Specifically, the dark area is displayed with substantially the same gradation characteristics, and by controlling only the brightness of the bright area, the power consumption of the display is suppressed to a certain value or less, and the dark area and the bright area of the video signal The gradation can be displayed properly in both of the above.
In addition, the control function whose coefficient is adjusted by the parameter value k shown in Equation 3 (The derivative of the control function after adjustment maintains continuity, so the display brightness is controlled so as not to generate a pseudo contour visually) It is possible to

3.3 Approximate relationship between overall gain m and parameter value k
In principle, the relationship between the overall gain m and the parameter value k can be obtained from Equation 4.
As described above, when trying to expand with respect to k contained in a ′ using equation 4, since k is contained in b and c, the expansion equation becomes k nonlinear equation, and analytically It is difficult to find the solution of k.
However, when the value calculated by the control function of Equation 3 is compared with the value calculated by the control function of Equation 7 (g = k), as shown in FIG. It can be seen that the case of = 0.4 is similar. Here, FIG. 5 shows the relationship between the video signal and the display luminance in the case of non-linear control as a solid line, and the relationship between the video signal and the display luminance in the case of linear control as a dotted line. FIG. 5 shows that g in Equation 7 is k, and how much the display luminance differs with the same k value.

Referring to FIG. 5, when the solid line and the dotted line are compared, although the details are different, the dotted line follows the solid line, and it can be said that the solid line can be approximately represented by the dotted line. Basically, the power consumption to be evaluated in the embodiment of the present invention is only an approximate value depending on the average value (APL) of all the pixels, so the accuracy of the dotted line and solid line in FIG. 5 can be sufficiently evaluated.
Then, the left side of Equation 4 can be approximated by the left side of Equation 5.

[3.4 Operation flow]
Next, a signal processing method by the signal processing device 1 will be described. FIG. 6 is a flowchart showing a signal processing method by the signal processing device 1.

  In step S1, the EOTF converter 11 EOTF-converts the video signal into an output signal by using, for example, Equation 1.

  In step S2, the parameter calculation unit 12 calculates the APL based on the output signal converted by the EOTF conversion unit 11 by using, for example, Equation 2.

  In step S3, the parameter calculation unit 12 adjusts the coefficient of the control function for converting the video signal of the bright area into the output signal by using, for example, the equation 4 based on the APL calculated by itself. Calculate k.

  In step S4, the signal processing unit 13 converts the video signal into an output signal using the control function (Equation 3) whose coefficient is adjusted by the parameter value k calculated by the parameter calculation unit 12, and outputs this luminance signal Control the brightness.

  Note that the above flow is just an example, and the present invention is not limited to this. For example, it is possible to change the order of the steps.

[4 Effects of Embodiments of the Present Invention]
When an HDR signal of the hybrid log gamma system is displayed on a display capable of high luminance display, the signal processing device 1 according to the embodiment of the present invention divides the signal value into a bright area and a dark area, and By controlling the gain to lower the drive current only, the power consumption of the display can be reduced to a fixed value or less, and the gray level can be displayed visually in both the dark area and the bright area of the video signal. It is possible not to generate
Further, by controlling the display luminance, it is possible to maintain the gradation expression of the dark part and to suppress the driving power without generating a false contour.

[5 Modification 1]
In the above embodiment, when calculating the APL, the maximum values of the R signal, the G signal, and the B signal among the RGB signals are used, but the present invention is not limited to this. For example, it is possible to calculate APL using the average value of R signal, G signal, and B signal.

[6 Modification 2]
The signal processing device according to the above embodiments may be incorporated in the display and integrated with the display.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to embodiment mentioned above. Further, the effects described in the present embodiment only list the most preferable effects arising from the present invention, and the effects according to the present invention are not limited to those described in the present embodiment.

1 Signal Processing Device 11 EOTF Converter 12 Parameter Calculator 13 Signal Processor

Claims (5)

A signal processor connected to the display,
An EOTF converter having a hybrid log gamma characteristic and including a control function for converting an input signal to a first output signal;
Based on the first output signal, a bright area including a signal corresponding to a signal level equal to or higher than a predetermined threshold value and a signal corresponding to a signal level lower than the threshold value or lower than the threshold value A parameter calculation unit that calculates a parameter value for adjusting a coefficient of the control function that converts an input signal of the bright area among the dark areas,
A signal processing unit that outputs a second output signal by converting an input signal of the bright area using the control function whose coefficient is adjusted by the parameter value calculated by the parameter calculation unit Processing unit. The parameter calculation unit
The signal processing apparatus according to claim 1, wherein a feature quantity dependent on power consumption at the time of video display is calculated based on the first output signal, and the parameter value is calculated based on the feature quantity.   The signal processing apparatus according to claim 1, wherein a 50% level of the input signal is used as the threshold.   The signal processing apparatus according to any one of claims 1 to 3, wherein the input signal is a video signal, and the first output signal and the second output signal are luminance signals.   An image display apparatus comprising the signal processing apparatus according to any one of claims 1 to 4.

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