JP2008176111A - Image display device and image display method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently change a black display ratio without causing degradation in the picture quality due to flicker. <P>SOLUTION: The image display method in one embodiment of the present invention comprises switching a display period and a non-display period in one frame period of an input image, and is characterized in steps of: inputting an input image; calculating the length of a target non-display period in the frame to be currently displayed; calculating the variation width of brightness from a plurality of frames; calculating the allowable maximum variation width of the length in the non-display period based on the variation width of brightness; calculating the length of a non-display period closest to the length of the target non-display period from the length of the non-display period of the preceding displayed frame, so as not to exceed the above maximum variation width; calculating variation suppressing information to suppress variation in the display brightness due to the variation in the length of the non-display period; and displaying an image in the display period on the basis of the variation suppressing information and the frame to be currently displayed, while stopping the image display in the non-display period. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image display device and an image display method.

  Conventionally, in liquid crystal display devices, the display brightness of the liquid crystal panel and the backlight is dynamically controlled according to the image to be displayed for the purpose of improving the quality of moving images, reducing flicker, reducing power consumption, improving contrast, and the like. .

  For example, Japanese Patent Laid-Open No. 2006-189661 (Patent Document 1) inserts a black image between successive frames in order to improve motion blur in a hold-type display device such as a liquid crystal display device. The display ratio of the black image is changed according to the magnitude of the image movement.

  When the black display ratio of the liquid crystal panel is increased, the screen brightness becomes dark. Therefore, in Patent Document 1, the backlight brightness is also changed at the same time so as to compensate for the change in the display brightness of the liquid crystal panel accompanying the change in the black display ratio. Yes.

  However, even if the black display ratio and the backlight luminance are changed so that the luminance does not change, if the black display ratio and the backlight luminance change suddenly, flicker occurs at that moment and the image quality deteriorates. Therefore, in Patent Document 1, the occurrence of flicker is suppressed by limiting the black display ratio and the change width of the backlight luminance to a certain fixed value or less.

However, in this method, since the black display ratio and the backlight luminance can be changed only slowly, the effect of changing the black display ratio cannot be sufficiently obtained.
JP 2006-189661 A

  The present invention provides an image display device and an image display method capable of efficiently changing the black display ratio and the backlight luminance without causing image quality degradation due to flicker.

An image display device according to an aspect of the present invention includes:
An image display device capable of switching between a display period and a non-display period in one frame period of an input image,
An image input unit for inputting an input image;
A target non-display period calculator that calculates the length of the non-display period to be targeted for the frame to be displayed this time,
A brightness change width calculation unit for calculating a brightness change width between a plurality of frames;
A maximum change width calculation unit that calculates an allowable maximum change width of the length of the non-display period based on the change width of the brightness;
A non-display period calculation unit that calculates the length of the non-display period that is closest to the target non-display period length so as not to exceed the maximum change width from the length of the non-display period of the previously displayed frame. When,
A fluctuation suppression information calculation unit that calculates fluctuation suppression information for suppressing fluctuations in display luminance due to fluctuations in the length of the non-display period;
An image display unit that performs image display based on the fluctuation suppression information and the frame to be displayed this time in the display period, and stops the image display in the non-display period;
Is provided.

An image display method as one aspect of the present invention includes:
An image display method for switching between a display period and a non-display period in one frame period of an input image,
Enter the input image,
Calculate the length of the hidden period that should be targeted for the frame that should be displayed this time,
Calculate the brightness change from multiple frames,
Calculating an allowable maximum change width of the length of the non-display period based on the change width of the brightness;
Calculate the length of the non-display period that is closest to the length of the non-display period that should be the target so as not to exceed the maximum change width from the length of the non-display period of the previously displayed frame,
Calculating fluctuation suppression information for suppressing fluctuations in display luminance due to fluctuations in the length of the non-display period;
Performing image display based on the fluctuation suppression information and the frame to be displayed this time in the display period, and stopping the image display in the non-display period;
It is characterized by that.

  According to the present invention, it is possible to efficiently change the black display ratio and the backlight luminance without causing image quality degradation due to flicker.

  Exemplary embodiments of an image display apparatus and method according to the present invention will be explained below in detail with reference to the accompanying drawings.

(First embodiment)
An image display device according to a first embodiment of the present invention will be described with reference to FIGS.

(1) Configuration of Image Display Device FIG. 1 shows the configuration of the image display device according to the present embodiment.

  The image display apparatus according to the present embodiment includes a brightness change width calculation unit 1, a maximum black display ratio change width calculation unit 2, a black display ratio calculation unit 3, a backlight luminance calculation unit 4, a target black display ratio calculation unit 5, a back light It comprises a light 6, a liquid crystal panel 7, a frame memory 8 and a memory 9.

を算出する。黒表示比率算出部３は、黒表示比率の変化幅の上限ΔＢ_ｍａｘと、黒表示比率の目標値

と、過去に算出した黒表示比率Ｂ_{｛ｎ−１｝}とから、各画像フレームＩ_ｎの表示に適用する黒表示比率Ｂ_ｎを算出する。過去に算出した黒表示比率Ｂ_{｛ｎ−１｝}はメモリ９に格納されている。黒表示比率算出部３は、算出した黒表示比率Ｂ_ｎをバックライト輝度算出部４に送り、また、黒表示比率Ｂ_ｎに基づいた制御信号を液晶パネル７に送る。液晶パネル７は、入力画像と、黒表示比率算出部３からの制御信号とに基づきフレーム間に黒表示を内挿した映像信号を表示する。バックライト輝度算出部４では、入力された黒表示比率Ｂ_ｎにしたがってバックライト６の光源を制御するバックライト輝度制御信号をバックライト６に送る。バックライト６は、受け取ったバックライト輝度制御信号に基づいた輝度で発光する。 The input image is stored in the frame memory 8. Brightness change width calculation unit 1 calculates the brightness variation ΔI lightness (gradation) of the input image I _n and I _n the past input to the image display device the image I from _{n-1}. The maximum black display ratio change width calculation unit 2 calculates the upper limit ΔB _max of the change width of the black display ratio applied between the frames from the brightness change width ΔI. The target black display ratio calculation unit 5 calculates the target value of the black display ratio from the input image.

Is calculated. The black display ratio calculation unit 3 determines the upper limit ΔB _max of the change width of the black display ratio and the target value of the black display ratio.

If, from the calculated past black display ratio B _{n-1}, it calculates a black display ratio B _n applied to the display of each image frame I _n. The black display ratio B _{n−1} calculated in the past is stored in the memory 9. The black display ratio calculation unit 3 sends the calculated black display ratio _Bn to the backlight luminance calculation unit 4 and sends a control signal based on the black display ratio _Bn to the liquid crystal panel 7. The liquid crystal panel 7 displays a video signal in which black display is interpolated between frames based on the input image and the control signal from the black display ratio calculation unit 3. The backlight luminance calculation unit 4 sends a backlight luminance control signal for controlling the light source of the backlight 6 to the backlight 6 according to the input black display ratio _Bn . The backlight 6 emits light with luminance based on the received backlight luminance control signal.

  Details of each part are described below.

(2-1) Brightness change width calculation unit 1
FIG. 3 is a block diagram of the brightness change width calculation unit 1.

Brightness change width calculation section 1 are the brightness from the brightness of the input image I _n and I _n from input to the image display apparatus in the past image I _{{n-1} (usually} using a previous frame In) A change width ΔI is calculated.

The brightness Y (x, y) at the coordinates (x, y) of the input image I is calculated by the brightness calculation unit as shown in Equation 1.

In Equation 1, I _r , I _g , and I _b are a red component, a green component, and a blue component, respectively, included in I (x, y).

The brightness change width calculation unit calculates the average absolute value within the frame of the interframe difference as ΔI. That is, the brightness at the coordinates (x, y) of I _n and I _{n−1} is Y _n (x, y) and Y _{n−1} (x, y), respectively, and ΔI is Calculated.

  In Equation 2, N is the total number of pixels in the image, W is the number of horizontal pixels, and H is the number of vertical pixels.

Alternatively, ΔI may be calculated as an RMS (Root Mean Square) within a frame of the interframe difference. That is, ΔI may be calculated as shown in Equation 3.

  Experiments have confirmed that there is no significant difference in the effect of the present invention regardless of whether absolute value averaging or RMS is used in the calculation of ΔI.

In calculating ΔI, ΔI may be calculated according to Equation 2 or Equation 3 after applying a known linear band pass filter (Gaussian filter or the like) to each of I _n and I _{{n−1} in} advance. Since human brightness perception is insensitive to high frequency components, this makes it possible to make ΔI closer to human brightness change perception.

The brightness change width ΔI may be calculated from a set of a plurality of I _n and I _{n−1} . For example, it can be calculated as a linear sum of a plurality of brightness change widths. That, I _n, may be calculated brightness change width calculated as _{I {n-1}} from the equation 2 or the equation 3 as number 4 as [Delta] I _n.

In Equation 4, w _n is a weight for ΔI _n . The influence of the brightness change of the input image on human vision has temporal band transmission characteristics. Therefore, by calculating a weighted linear sum of changes in brightness between a plurality of frames, ΔI can be made closer to a human brightness change perception.

  ΔI calculated as described above is considered to represent the amount of change in brightness between input image frames.

(2-2) Maximum Black Display Ratio Change Width Calculation Unit The maximum black display ratio change width calculation unit 2 calculates the upper limit ΔB _max of the black display ratio change width applied between the frames.

  It has been confirmed by experiments by the present inventors that the smaller the change width ΔB of the black display ratio applied between the frames, the smaller the change in display luminance when the image is actually observed. The smaller the change width ΔI of the brightness of the input image, the more easily the change in display luminance due to flicker is perceived. Accordingly, if the change width ΔB of the black display ratio is decreased as the brightness change width ΔI of the input image is smaller, the driving can be performed without conspicuous flicker.

The maximum black display ratio change width calculation unit 2 calculates the upper limit ΔB _max of the change width of ΔB as shown in Equation 5.

In this way, the smaller ΔI is, the smaller ΔB _max is, so that the driving can be performed without conspicuous flicker.

The maximum black value of .DELTA.B _max to be outputted from the display ratio change width calculation unit 2 is not necessary that the values and time-synchronization ΔI is taken using the calculation of .DELTA.B _max, if necessary, past frame A value calculated from the above may be output. In this case, the calculated ΔB _max value may be output after buffering it in a memory or the like (not shown).

(2-3) Black display ratio calculating unit black display ratio calculating unit 3 calculates the black display ratio B _n applied to the display of each image frame I _n. The black display ratio corresponds to, for example, the length of the non-display period, and “1-black display ratio” corresponds to, for example, the length of the display period. The length of the non-display period and the length of the display period may be expressed as a ratio in one frame period, or may be expressed as an actual length of time. A calculation example of the black display ratio _Bn is shown in FIG.

More specifically, black display ratio calculating unit 3 includes an image frame black display ratio applied to a display of the I black display ratio applicable to the display of _n B _n and the image frame _{I {n-1} B {} n-1} _Bn is calculated such that the change width ΔB _n of the black display ratio during the period is smaller than ΔB _{{max, n−1}} calculated by the maximum black display ratio change width calculation unit 2 in the frame I _n−1 . . That is, B _n is calculated so as to satisfy Equation 6 (see FIG. 2). In Equation 6, ΔB _{{max, n}} can be used instead of ΔB _{{max, n−1}} . In other words, the brightness change width obtained from the frame to be displayed this time and one or more frames input in the past, or the brightness obtained from a plurality of frames input in the past from the frame to be displayed this time. The maximum black display ratio change width obtained from the change width of the height can be used.

6 is a constraint for B _n, of from 6 can not immediately determine Bn.

から数７のように算出する。

The calculation of B _n is performed by calculating the target value of the black display ratio calculated by the target black display ratio calculation unit 5 based on information such as the amount of motion of the input image.

Is calculated as shown in Equation (7).

に近い値が設定される。 In Equation 7, sgn (x) is a function that returns the sign of x, and min (x, y) is a function that returns the smaller value of x and y. That is, B _n has the most target value within a range where the change width of the black display ratio does not exceed ΔB _{{max, n−1}.}

A value close to is set.

In this way, by setting the black display ratio to a value closest to the target value within a range where the change width does not exceed ΔB _max , the black display ratio can be changed quickly without making the flicker noticeable.

を算出する。 (2-4) Target Black Display Ratio Calculation Unit The target black display ratio calculation unit 5 is a target value of the black display ratio.

Is calculated.

  The target black display ratio can be determined from the viewpoint of moving image quality (blur), flicker, power consumption, and the like. For example, as described in paragraphs 0028 to 0067, 0104, 0110 to 0136 in JP-A 2006-189658, and as described in paragraphs 0028 to 0036, paragraphs 0100 to 0130 and paragraph 0134 in JP-A 2006-189661, Motion vector is calculated by motion detection from images of multiple frames that have been input (frames to be displayed this time and one or more frames that have been input in the past, or frames that have been input in the past from frames that are displayed this time). Then, from the obtained motion vector, the speed of motion, the direction of motion, the contrast of the moving object, the spatial frequency of the moving object are calculated, and based on these information (from the linear sum of each value, etc.), it becomes the target The black display ratio can be determined.

(2-5) Liquid Crystal Panel The liquid crystal panel 7 is of an active matrix type in this embodiment, and as shown in FIG. 4, a plurality of signal lines 21 and a plurality of signal lines crossing the signal line 21 are arranged on the array substrate 24. The scanning line 22 is disposed via an insulating film (not shown), and a pixel 23 is formed at each intersection of both lines. The end of the signal line 21 is connected to the signal line driving circuit 25, and the end of the scanning line 22 is connected to the scanning line driving circuit 26.

  In the pixel 23, a switch element 31 composed of a thin film transistor (TFT) is a switch element for writing a video signal, its gate is commonly connected to the scanning line 22 for each horizontal line, and the source is a signal for each vertical line. The line 21 is connected in common. Further, the drain is connected to the pixel electrode 32 and is also connected to an auxiliary capacitor 33 arranged in parallel with the pixel electrode 32.

  The pixel electrode 32 is formed on the array substrate 24, and the counter electrode 34 electrically opposed to the pixel electrode 32 is formed on a counter substrate (not shown). A predetermined counter voltage is applied to the counter electrode 34 from a counter voltage generation circuit (not shown). A liquid crystal layer 35 is held between the pixel electrode 32 and the counter electrode 34, and the periphery of the array substrate 24 and the counter substrate is sealed with a sealing material (not shown). Although any liquid crystal material may be used for the liquid crystal layer 35, as will be described later, the liquid crystal panel 7 according to the present embodiment needs to write two image signals of image display and black display in one frame period. Therefore, it is desirable to respond relatively quickly. For example, a ferroelectric liquid crystal, an OCB (Optically Compensated Bend) mode liquid crystal, or the like is preferable.

  The scanning line driving circuit 26 includes a shift register, a level shifter, a buffer circuit, and the like (not shown). The scanning line driving circuit 26 outputs a row selection signal to each scanning line 22 based on the vertical start signal and the vertical clock signal output as part of the control signal from the black display ratio calculation unit 3.

  The signal line driving circuit 25 includes an analog switch, a shift register, a sample hold circuit, a video bus, and the like (not shown). The signal line driving circuit 25 is supplied with a horizontal start signal and a horizontal clock signal output as part of the control signal from the black display ratio calculation unit 3 and a video signal.

  Next, the operation of the liquid crystal panel 7 according to the present embodiment will be described.

  FIG. 5 shows a timing chart of the liquid crystal display panel when the black display ratio is 50%. A display signal output from the signal line driving circuit 25, a driving waveform of the scanning line signal output from the scanning line driving circuit 26, and an image display state on the liquid crystal panel 7 are shown. Here, an example in which the number of vertical scanning lines V = 8 is shown. In FIG. 5, a blanking period is not shown for simplicity of explanation, but a typical liquid crystal panel drive signal usually has horizontal and vertical blanking periods.

  The signal line drive circuit 25 outputs an image display signal in the first half of one horizontal scanning period and a black display signal in the second half. In the scanning line driving circuit 26, a scanning line corresponding to each pixel to which an image display signal is to be supplied is selected in the first half of one horizontal scanning period, and a scanning line corresponding to each pixel to which a black display signal is to be supplied is subjected to one horizontal scanning. Select later in the line period.

  When the first scanning line is selected in the first half of one horizontal scanning period and an image display signal is supplied to the corresponding pixel, the V / 2 + 1th scanning line is selected in the second half of the one horizontal scanning period. A black display signal is supplied to the pixels to be processed. Similarly, when the second scanning line is selected in the first half of one horizontal scanning period, the V / 2 + 2th scanning line is selected in the second half of one horizontal scanning period. Similarly, the next scanning line is sequentially selected in the first half and the second half of one horizontal scanning period, and the V-th scanning line is selected in the first half of one horizontal scanning period, and an image is displayed on the corresponding pixel. When the signal is supplied, the V / 2 scanning line is selected in the second half of one horizontal scanning period, and the black display signal is supplied to the corresponding pixel.

  FIG. 6 shows a display state on the liquid crystal panel 7 when the black display ratio is 50%. FIG. 6A shows a display state when the writing of the image display signal of the nth frame is completed up to the V / 2 + 1 line and the black display signal is written in the first line. FIG. 6B shows a display state when the image display signal of the nth frame is written up to the V / 2 + 2 line and the black display signal is written in the second line. FIG. 6C shows a display state when an image display signal of the nth frame is written in the V line and a black display signal is written in the V / 2-1 line. FIG. 6D shows a display state when the image display signal of the (n + 1) th frame is written in the first line and the black display signal is written in the V / 2 + 1 line. FIG. 6E shows a display state when the image display signal of the (n + 1) th frame is written on the V / 2 line and the black display signal is written on the V line.

  FIG. 6 shows the case where the black display rate is 50%. Similarly, the black display period can be set by changing the black display signal writing start timing, that is, by changing the scanning line signal timing. It is. Therefore, the black display ratio is calculated by the black display ratio calculation unit 3, and the writing start timing of the black display signal is input to the liquid crystal panel 7 as a control signal, so that an image is displayed on the liquid crystal panel 7 with an arbitrary black display ratio. It becomes possible.

(2-6) Backlight Luminance Calculation Unit The backlight luminance calculation unit 4 outputs a backlight luminance control signal for controlling the light source of the backlight 6 using the input black display ratio information. That is, if the light source of the backlight 6 is an analog modulation LED, an analog voltage signal is output, and if it is a pulse width modulation (PWM) LED, a pulse width modulation signal is output. If the light source is a cold cathode tube, an analog voltage input to the inverter for lighting the cold cathode tube is output.

  In the present embodiment, a pulse width modulation type LED light source capable of obtaining a large luminance dynamic range with a relatively simple configuration is used. The relationship between the pulse width input to the LED light source and the luminance of the backlight 6 is measured in advance and stored in the backlight luminance calculation unit 4. As data to be held, for example, when the above relationship can be expressed by a function, the function may be held.

  Further, it may be held in a ROM or the like as a LUT (Look-up Table).

  Further, if the LED light source is configured to display white by mixing the three primary colors of red, green, and blue, it is desirable to retain the data of each LED.

  Further, in the above description, the method of holding the relationship between the pulse width and the backlight luminance as data has been shown. However, on the liquid crystal panel 7 displayed at various black display ratios, The pulse width relationship may be maintained.

  That is, a white image is displayed on the liquid crystal panel 7 at a certain black display ratio, and the backlight luminance is controlled so that the luminance after passing through the liquid crystal panel becomes a predetermined value, and the pulse input to the LED light source at that time Find the width. The above operation is performed at various black display ratios, and the relationship between the black display ratio and the pulse width is obtained and stored as data. By referring to the data with the input black display ratio information, the luminance of the backlight 6 is controlled, and the luminance on the liquid crystal panel 7 can be kept constant with respect to an arbitrary black display ratio.

  In addition to the above, a method may be used in which a photodiode or the like is installed in the backlight 6 and feedback is performed while the luminance of the backlight 6 is measured by the photodiode or the like to control the luminance of the LED light source. In particular, since the light emission characteristic of an LED light source varies depending on temperature, a configuration in which feedback is performed using a photodiode or the like as described above is effective.

  FIG. 7 shows the relationship between the black display ratio, the liquid crystal panel relative transmittance, the backlight relative brightness, and the liquid crystal display relative brightness when the black display ratio is set in the range of 0% to 50%. is there.

  The horizontal axis represents the black display rate, the left vertical axis represents the relative transmittance with respect to the transmittance of the liquid crystal panel 7 when the black display rate is 0%, and the right vertical axis represents the backlight when the black display rate is 50%. The relative luminance with respect to the luminance of 6 is shown. The liquid crystal panel 7 used in the present embodiment linearly decreases in transmittance as the black display ratio increases, so that the luminance of the backlight 6 increases as the black display ratio increases, and the relative luminance of the liquid crystal display device is increased. That is, the luminance of the backlight 6 is controlled so that the luminance after passing through the liquid crystal panel is constant. That is, there is a relationship of liquid crystal panel relative transmittance × backlight relative luminance = liquid crystal display device relative luminance. From FIG. 7, the relationship between the black display rate and the relative luminance of the backlight 6 can be obtained, and further, the relationship between the black display rate and the pulse width can be obtained from the relationship between the backlight relative luminance and the pulse width input to the LED light source. . Therefore, the backlight luminance setting signal represented by the pulse width can be obtained from the black display rate obtained by the black display ratio calculation unit 3.

  Note that, on the liquid crystal panel 7 displayed at various black display ratios, the luminance is controlled so as to be always constant during one frame period. Control may be performed to suppress fluctuations in luminance within the range. In other words, the object of the present embodiment can be achieved if the control suppresses fluctuations in luminance within a range where flicker is not felt when viewed with the human eye.

(2-7) Backlight Although the backlight 6 can be comprised by various light sources as mentioned above, in this embodiment, it was set as the direct type | mold backlight which used LED as the light source. However, the configuration of the backlight is not limited to the above. For example, an edge light type backlight using a light guide plate may be used. The brightness of the backlight 6 is controlled by the backlight brightness control signal output from the backlight brightness calculation unit 4.

(2-8) Modification Example 1 of Brightness Change Width Calculation Unit
FIG. 8 is a block diagram illustrating a configuration of the brightness change width calculation unit according to the first modification.

  The brightness change width calculation unit 1a includes a cut point detection unit 1d that detects a cut point.

  The brightness change width calculation unit 1a wants to calculate the amount of change in brightness that a person feels when viewing the image. For this reason, the brightness change width calculation unit 1 in FIG. 3 uses the absolute value average, RMS, or the like in the frame of the interframe difference for calculation of the change amount. However, when a moving object is present in the image, the brightness change width calculated in this way is not necessarily proportional to the brightness change width perceived by a person. When a moving object is present in an image, the images of the two frames do not match, so that the inter-frame difference value generally increases. On the other hand, when a person views the image, the eyeball follows the moving body in the image, so that the image as the retina image does not change much. Accordingly, there is a difference between the calculated brightness change width and the brightness change width perceived by a person.

  The brightness change width calculation unit 1a of the present modification has a cut point detection unit 1d in order to take this deviation into consideration.

  The cut point detection unit 1d detects a cut point from the input image In and an image I {n−1} (usually using a frame immediately before In) input to the image display device in the past. The cut point detection may be performed using a known cut point detection method (surface luminance method, frequency distribution method, chromatic frequency distribution method, chi-square test method, etc.).

  When the cut point is detected by the cut point detection unit 1d, the brightness change width calculation unit 1a according to the present modification outputs ΔI calculated as expressed by Equation 2 or Equation 3 as an output value. When the cut point is not detected by the cut point detection unit 1d, a sufficiently small value (for example, ΔI = 0) is set as the output value.

  By doing so, it is possible to avoid a malfunction when a moving object is included in the input image.

(2-9) Modification Example 2 of Brightness Change Width Calculation Unit
The brightness change width calculation unit may be configured as follows in order to ignore the influence of motion.

  FIG. 9 is a block diagram illustrating a configuration of the brightness change width calculation unit 1e according to the second modification.

The brightness change width calculation unit 1e according to the second modification includes a Fourier transform unit 1f. The Fourier transform unit 1 f performs Fourier transform on the brightness of the input image to obtain F (u, v) (Fourier component), and calculates its amplitude | F (u, v) |. That is, the amplitude | F (u, v) |

The lightness change width calculation unit in FIG. 3 performs processing on the lightness of the input image, but the lightness change width calculation unit 1e in FIG. 9 performs processing on this | F (u, v) |. That is, ΔI is calculated based on an equation in which Y in Equation 2 or 3 is replaced with | F |, x is replaced with u, and y is replaced with v. That is, ΔI is calculated as shown in Equation 9 or Equation 10.

  Any image can be represented as the sum of sine waves of different frequencies. An image F (u, v) (this value is obtained as a complex number) obtained by Fourier transform of the image Y (x, y) is a vertical frequency u and a horizontal frequency v included in the image Y (x, y). Represents the amplitude and phase of the sine wave. F (u, v) is a vector having a magnitude and direction, the absolute value of F (u, v) represents the amplitude of the sine wave, and the declination of F (u, v) represents the phase of the sine wave. Yes.

  The RMS can also be obtained from the image F (u, v) obtained by Fourier transform, and the obtained value is the same as the RMS obtained from the original image Y (x, y).

  By the way, since the phase component included in F (u, v) represents the position of the wave, it is considered that the position information of the original image Y (x, y) is approximately represented. Therefore, ignoring the phase component of F (u, v) and obtaining the RMS value from only the amplitude component of F (u, v) (that is, the absolute value of F (u, v)) is approximately. Therefore, the RMS value is calculated by ignoring the position information of the image. Therefore, ΔI calculated in this way is calculated with almost no influence from the movement of the object, and therefore even if a moving object is present in the input image, a value close to the brightness change seen by human eyes is obtained. Can be calculated.

Further, in calculating ΔI, the values of F _{n (u, v)} and F _{{n−1} (u, v)} are emphasized or attenuated according to the frequency (u, v) in advance, and then according to Equation 9 or Equation 10. ΔI may be calculated. Since human brightness perception is insensitive to high-frequency components, ΔI can be made closer to human brightness change perception.

  By doing so, it is possible to avoid a malfunction when a moving object is included in the input image.

(2-10) Modification Example 3 of Brightness Change Width Calculation Unit
The brightness change width calculation unit may be configured as follows in order to ignore the influence of motion.

  FIG. 10 is a block diagram illustrating the configuration of the brightness change width calculation unit according to the third modification.

The brightness change width calculation unit 1g according to this modification includes a motion compensation unit 1h. The motion compensation unit 1h performs alignment between the brightness images Y _n and Y _{n−1}, and obtains a displacement vector field d _n (x, y) for each coordinate (x, y) on the image. . Displacement vector field d _{n (x,} y) may be performed using a known registration method (block matching or the like).

The brightness change calculation unit 1c according to the present modification calculates ΔI using the displacement vector field calculated by the motion compensation unit 1h. That is, ΔI is calculated as shown in Equation 11 or Equation 12.

In Equation 11, the number _{12, d {x, n}} , d {y, n} from _{Y {n-1}} obtained between the luminosity image _{Y {n-1}} and _{Y n} to _{Y n} and x and y components of the displacement vector field d _n.

  Also by doing this, it is possible to avoid a malfunction when a moving object is included in the input image.

(2-11) Modification Example 4 of Brightness Change Width Calculation Unit
The brightness change width calculation unit may be configured as follows in order to reduce the required memory capacity.

  FIG. 11 is a block diagram illustrating the configuration of the brightness change width calculation unit according to the fourth modification.

The brightness change width calculation unit 1j according to the present modification includes a one-dimensional histogram calculation unit 1k. A one-dimensional histogram calculation unit 1k adds the brightness of the input image in the vertical direction and the horizontal direction to generate a one-dimensional histogram. That is, the vertical projection histogram Hv (x) and the horizontal projection histogram Hh (y) are obtained from the input image Y (x, y) as shown in Equations 13 and 14.

The lightness change calculation unit in FIG. 3 performs processing on the lightness of the input image, but the lightness change width calculation unit 1j in FIG. 11 performs processing on each of the vertical and horizontal projection histograms to calculate an average value. . That is, ΔI is calculated as shown in Equation 15 or 16.

  By doing so, the amount of calculation and the required memory capacity can be reduced.

(3) Effect of Image Display Device FIG. 12 is a diagram for explaining the effect of the image display device according to the present embodiment.

  The display luminance of the liquid crystal panel 7 or the luminance of the backlight 6 determined according to the black display ratio or the black display ratio is determined from the viewpoint of the amount of movement in the input image, the amount of flicker caused by impulse light emission, power consumption, contrast, etc. It is desirable that the optimum value is always controlled according to the content of the image to be displayed.

  However, in the conventional method, when the display brightness of the liquid crystal panel or the brightness of the backlight, which is determined according to the black display ratio or the black display ratio, is rapidly changed, the change in display brightness accompanying the change is perceived as flicker. In order to prevent this, these values were always controlled so as not to change rapidly. As a result, the values of the black display ratio that is actually applied, the display brightness of the liquid crystal panel or the brightness of the backlight, and the like, greatly deviate from the target values determined to be optimal.

  On the other hand, according to the proposed image display apparatus, the black display ratio, the display brightness of the liquid crystal panel 7 determined according to the maximum change width in which the flicker is not perceived, or the backlight 6 or the backlight 6 according to the input image. The brightness can be changed. In other words, depending on the image to be displayed, flicker may not be noticeable even when the black display ratio or backlight brightness is suddenly changed (for example, in the case of a video with a sharp change in brightness). The black display ratio and backlight brightness can be changed. Conversely, in an image where flicker is conspicuous, image quality deterioration due to flicker can be avoided by reducing the change rate of the black display ratio and backlight luminance. Therefore, it is possible to change the black display ratio and the backlight luminance more quickly than in the conventional method, and it is possible to control more efficiently.

  Thus, according to the present embodiment, the black display ratio and the backlight luminance can be efficiently changed without causing image quality degradation due to flicker.

(Second Embodiment)
FIG. 13 shows a main configuration of a liquid crystal display device according to the second embodiment of the present invention.

  The basic configuration of the liquid crystal display device according to the second embodiment is the same as that of the first embodiment, but the black of the input image displayed on the liquid crystal panel 7 by controlling the light emission and extinction of the backlight 6. The display ratio is controlled.

  From the input video, the black display ratio is calculated in the black display ratio calculation unit 3 in the same manner as in the first embodiment. The calculated black display ratio is input to the backlight luminance control unit 51 as black display ratio information. The backlight luminance control unit 51 determines the light emission period of the backlight 6 and the light emission luminance of the backlight 6 on the basis of the black display ratio information, and outputs the backlight light emission ratio control signal and the backlight luminance control signal to the backlight 6. input. The backlight 6 emits light based on the input backlight emission ratio control signal and backlight luminance control signal.

  Next, operations of the liquid crystal panel 7 and the backlight 6 will be described.

  FIG. 14 is a diagram for explaining the operation of the liquid crystal panel 7 and the backlight 6. In FIG. 14, the horizontal axis indicates time, and the vertical axis indicates the vertical display position of the liquid crystal panel 7. Usually, on the liquid crystal display panel 7, video is written line-sequentially from the top toward the screen.

  Therefore, in writing to the liquid crystal panel 7, as shown in FIG. 14, an image is written to the liquid crystal panel 7 while gradually shifting the writing time from the top toward the screen. In general, writing to the liquid crystal panel 7 is performed over one frame period (generally 1/60 second). However, in this embodiment, in order to secure a light emission period of the backlight 6 described later, one frame is used. Writing is performed in a period shorter than the period, 1/4 frame period (1/240 seconds). After the lowermost line of the liquid crystal panel 7 is written, the backlight 6 emits light in accordance with the backlight emission ratio control signal after a predetermined period until the response of the liquid crystal is completed.

  Note that the light emission luminance of the backlight 6 is determined by the backlight light emission period, and is controlled so that the product of the backlight light emission period and the backlight light emission luminance is approximately constant.

  The backlight 6 is preferably extinguished during the writing period to the liquid crystal panel 7 and the liquid crystal response period. This is because a part of the image of the previous frame is displayed on the liquid crystal panel 7 in the writing period to the liquid crystal panel 7 and the response period of the liquid crystal. This is because the frames are mixed and presented to the observer.

  By controlling the light emission period of the backlight 6 as described above, the black display ratio of the liquid crystal display device can be controlled as in the first embodiment.

  As described above, according to the liquid crystal display device according to the present embodiment, it is possible to improve the image quality of the displayed input video while suppressing an increase in power consumption. Furthermore, it is possible to suppress as much as possible flicker that occurs due to a sudden change in the black display ratio. In addition, a stable black display ratio can be obtained for various images.

(Third embodiment)
FIG. 15 shows a configuration of a liquid crystal display device according to the third embodiment of the present invention.

  The basic configuration of the liquid crystal display device according to the third embodiment is the same as that of the second embodiment, but the light emitting area of the backlight 6a is divided, and the light emitting areas of the backlight emit light at different timings. It is possible to make it.

  An example of the structure of the backlight 6a according to the present embodiment is shown in FIG.

  The structure of the backlight 6 a is called a direct type backlight, and cold cathode tubes 320 are arranged as light sources, and each cold cathode tube is surrounded by a reflector 321. A diffusion plate 322 is installed above the cold cathode tube and diffuses light from the cold cathode tube to realize a uniform surface light source. In this embodiment, the light emission timing of each cold cathode tube is different.

  FIG. 17 is a diagram for explaining the operation of the liquid crystal panel 7 and the backlight 6a. In FIG. 17, the backlight 6a is divided into four in the horizontal direction, and the timing of light emission and extinction can be controlled independently in each region. In the second embodiment, the light emission timing of the backlight is a certain period after the bottom line of the liquid crystal panel is written, but in this embodiment, the timing of the liquid crystal panel 7 corresponding to each divided region is set. After the bottom line is written, after the response period of the liquid crystal, light is emitted according to the light emission ratio control signal of the backlight 6a. When the light emission area of the backlight is divided in this way, the light emission period of the backlight can be lengthened compared to the second embodiment, and the black display ratio can be controlled in a larger range.

  As described above, according to the liquid crystal display device according to the present embodiment, it is possible to improve the image quality of the displayed input video while suppressing an increase in power consumption. Furthermore, it is possible to suppress as much as possible flicker that occurs due to a sudden change in the black display ratio. In addition, a stable black display ratio can be obtained for various images.

(Fourth embodiment)
FIG. 18 shows a configuration of an organic EL display according to the fourth embodiment of the present invention.

  The basic configuration of the organic EL display according to the fourth embodiment is the same as that of the first embodiment, but the image display unit is configured by the organic EL panel 61.

  FIG. 19 shows an example of the configuration of the organic EL panel 61. The organic EL panel 61 includes a switch element 341 and a switch element 342 made of two thin film transistors, a voltage holding capacitor 344 for holding a voltage supplied from the signal line 343, and a pixel 346 including an organic EL element 345, and a signal line 343 and the end of the power supply line 347 are connected to the signal line driver circuit 348, and the scanning line 349 in a direction orthogonal to the signal line 343 and the power supply line 347 is connected to the scanning line driver circuit 350.

  Next, the operation will be described.

  The scanning line drive signal in the ON state is applied to the switch element 341 from the scanning line drive circuit 350 via the scanning line 349, and the switch element 341 becomes conductive, and the signal line drive output from the signal line drive circuit 348 at that time A signal is written into the voltage holding capacitor 344 through the signal line 343. The conduction state of the switch element 342 is determined according to the amount of charge accumulated in the voltage holding capacitor 344, current is supplied from the power supply line 347 to the organic EL element 345, and the organic EL element 345 emits light. Even when the scanning line drive signal is turned off, the voltage that determines the conduction state of the switch element 342 is accumulated in the voltage holding capacitor 344, so that current is supplied from the power supply line 347 to the organic EL element 345. It will continue to be done.

  Therefore, as in FIG. 5 of the first embodiment, the video signal is output from the signal line driving circuit 348 in the first half of one horizontal scanning period and the black video signal is output from the signal line driving circuit 348 in the second half of the horizontal scanning period, and the video line is written. The scanning line drive signal in the ON state synchronized with the first half of one horizontal scanning period is applied to 349, and the scanning line drive in the ON state synchronized with the latter half of one horizontal scanning period is applied to the scanning line 349 for writing the black video signal. By applying the signal, the video display period and the black video display period of the organic EL panel can be controlled as in the first embodiment.

  That is, based on the black display ratio determined by the black display ratio calculation unit 3, the scanning line driving circuit 350 is controlled in the same manner as in the first embodiment. However, since the organic EL panel 61 is a self-luminous element, the brightness of the image during the period in which the image is displayed is controlled according to the black display ratio to control the luminance during one frame period to be substantially constant. There is a need.

  Therefore, in the present embodiment, the brightness of the image is digitally controlled using the signal line driving circuit 348 having an output accuracy of 10 bits. The state where the brightness of the image is most necessary is a state in which the black display ratio is maximized in a predetermined control range. That is, since the black display ratio is large, the video display period is short, and in order to make the luminance of one frame period substantially constant, it is necessary to increase the brightness of the video.

Therefore, in the predetermined black display ratio control range, the maximum display gradation (maximum display brightness) of the video at the maximum black display ratio is set as 1020 gradations, and as the black display ratio decreases, the video The maximum brightness during the video display period was controlled by setting the maximum display gradation to a small value. In other words, when the gamma value of the input video is γ, the maximum gradation of the input video is 8 bits (255 gradations), and the black display ratio to be set with respect to the luminance of the video display period at the maximum black display ratio in the black display ratio control range. Assuming that the luminance ratio of the video display period is I, the maximum gradation L _max set at the luminance ratio I is expressed by Equation 17.

  After obtaining the maximum gradation according to the black display ratio according to Expression 17, a compensation image (compensation frame) is generated by requantizing all the gradations of the image, and this is displayed, thereby displaying the image display period. Can control the brightness.

  The organic EL panel 61 can also control the brightness by controlling the current value supplied from the power line 347. Therefore, the current value supplied from the power supply line 347 may be controlled so that the luminance in one frame period becomes substantially constant in accordance with the black display ratio.

  As described above, according to the organic EL display device according to the present embodiment, it is possible to improve the image quality of the displayed input video while suppressing an increase in power consumption. Furthermore, it is possible to suppress as much as possible flicker that occurs due to a sudden change in the black display ratio. In addition, a stable black display ratio can be obtained for various images.

It is a figure which shows the structure of the image display apparatus in the 1st Embodiment of this invention. It is a figure which shows the process of calculating the black display ratio in 1st Embodiment. It is a figure which shows the structure of the brightness change width calculation part in 1st Embodiment. It is a figure which shows the structure of the liquid crystal panel in 1st Embodiment. It is a figure which shows operation | movement of the liquid crystal panel in 1st Embodiment. It is a figure which shows the mode of a display of the image display apparatus in 1st Embodiment. It is a figure which shows the relationship between the black display ratio of 1st Embodiment, a liquid crystal panel relative transmittance | permeability, the relative luminance of a backlight, and the relative luminance of a liquid crystal display device. It is a figure which shows the structure of the example 1 of a change of the brightness variation calculation part in 1st Embodiment. It is a figure which shows the structure of the example 2 of a change of the brightness variation calculation part in 1st Embodiment. It is a figure which shows the structure of the example 3 of a change of the brightness variation calculation part in 1st Embodiment. It is a figure which shows the structure of the example 4 of a change of the brightness variation calculation part in 1st Embodiment. It is a figure for demonstrating the effect of the image display apparatus in 1st Embodiment. It is a figure which shows the structure of the image display apparatus in the 2nd Embodiment of this invention. It is a figure which shows the operation | movement in 2nd Embodiment. It is a figure which shows the structure of the image display apparatus in the 3rd Embodiment of this invention. It is a figure which shows the structure of the backlight in 3rd Embodiment. It is a figure which shows the operation | movement in 3rd Embodiment. It is a figure which shows the structure of the image display apparatus of Embodiment 4 in this invention. It is a figure which shows the structure of the organic electroluminescent panel in 4th Embodiment.

Explanation of symbols

1: Brightness change width calculation unit 2: Maximum black display ratio change width calculation unit 3: Black display ratio calculation unit 4: Backlight luminance calculation unit 5: Target display ratio calculation unit 6, 6a: Backlight 7: Liquid crystal panel 8 : Frame memory 9: Memory 1 b: Lightness calculation unit 1 c: Lightness change width calculation unit 1 d: Cut point detection unit 1 f: Fourier transform unit 1 h: Motion compensation unit 1 k: One-dimensional histogram calculation unit 51: Backlight luminance control unit 61: Organic EL panel

Claims (22)

An image display device capable of switching between a display period and a non-display period in one frame period of an input image,
An image input unit for inputting an input image;
A target non-display period calculator that calculates the length of the non-display period to be targeted for the frame to be displayed this time,
A brightness change width calculation unit for calculating a brightness change width between a plurality of frames;
A maximum change width calculation unit that calculates an allowable maximum change width of the length of the non-display period based on the change width of the brightness;
A non-display period calculation unit that calculates the length of the non-display period that is closest to the length of the non-display period that should be the target within a range that does not exceed the maximum change width from the length of the non-display period of the previously displayed frame. When,
A fluctuation suppression information calculation unit that calculates fluctuation suppression information for suppressing fluctuations in display luminance in one frame period due to fluctuations in the length of the non-display period;
An image display unit that performs image display based on the variation suppression information and the frame to be displayed this time in the display period, and stops the image display in the non-display period;
An image display device comprising:   The image display device according to claim 1, wherein the image display unit stops the image display by displaying a black image during the non-display period.   The maximum change width calculation unit is a change width of brightness obtained from the frame to be displayed this time and one or more frames input in the past, or input from the past in the frame to be displayed this time. The image display apparatus according to claim 1, wherein brightness change widths obtained from a plurality of frames are used.   The image display device according to claim 1, wherein the maximum change width calculation unit decreases the maximum change width as the brightness change width is smaller.   5. The brightness change width calculation unit calculates an average absolute value of a difference in brightness of each pixel in a frame between two frames as the brightness change width. The image display device according to item.   The brightness change width calculation unit calculates a root mean square (RMS) of a difference in brightness of each pixel in a frame between two frames as the brightness change width. Item 5. The image display device according to any one of Items 1 to 4.   The image display device according to claim 5, wherein the brightness change width calculation unit calculates the brightness change width after performing linear band transmission filtering on each of the two frames.   The brightness change width calculation unit performs Fourier transform on each of the two frames, and calculates an absolute value average of amplitude differences of Fourier components obtained by the Fourier transform from the two frames as the brightness change width. The image display device according to claim 1, wherein:   The brightness change width calculation unit performs Fourier transform on each of two frames, and calculates a root mean square (RMS: Root Mean Square :) of the difference in amplitude of Fourier components obtained from the two frames by the Fourier transform. The image display apparatus according to claim 1, wherein the image display apparatus calculates the brightness change width.   The brightness change width calculation unit performs weighting for enhancing or attenuating the amplitude of each Fourier component obtained by Fourier transform from the frame according to the frequency of the Fourier component, and the brightness from the two weighted frames. The image display device according to claim 8, wherein a change width is calculated.   The brightness change width calculation unit aligns images between two frames, and uses the average absolute value of the differences in brightness of the corresponding pixels between the two aligned frames as the brightness change width. The image display device according to claim 1, wherein the image display device is calculated.   The brightness change width calculation unit aligns images between two frames, and calculates a root mean square (RMS) of a difference in brightness between corresponding pixels between the two frames. 5 is calculated as the brightness change width. 5. The image display device according to claim 1, wherein the brightness change width is calculated.   The brightness change width calculation unit generates a vertical histogram and a horizontal histogram by adding each pixel included in the frame in the vertical direction and the horizontal direction in each of the two frames, and generates the vertical histogram between the two frames. 5. The image display device according to claim 1, wherein an average of a difference between histograms and an average of differences between the horizontal histograms is calculated as the brightness change width. 6.   The brightness change width calculation unit generates a vertical histogram and a horizontal histogram by adding each pixel included in the frame in the vertical direction and the horizontal direction in each of the two frames, and generates the vertical histogram between the two frames. The average of the root mean square (RMS) of the difference of the histogram and the root mean square of the difference of the horizontal histogram (RMS: Root Mean Square :) is calculated as the brightness change width. The image display apparatus as described in any one of Claim 1 thru | or 4. A cut point detection unit for detecting a cut point from the frame to be displayed this time and a frame input in the past;
The image according to any one of claims 1 to 14, wherein when the cut point is detected, the maximum change width calculation unit sets the maximum change width to zero or suppresses it within a predetermined threshold. Display device. The image display unit includes a liquid crystal panel and a backlight that is installed on the back surface of the liquid crystal panel and irradiates the liquid crystal panel from the back surface,
The fluctuation suppression information calculation unit calculates information on the emission luminance of the backlight necessary for suppressing fluctuations in the display luminance due to fluctuations in the length of the non-display period as the fluctuation suppression information,
5. The image display unit according to claim 1, wherein the image display unit controls the light emission luminance of the backlight based on the information on the light emission luminance, and writes the frame to be displayed this time on the liquid crystal panel. The image display device according to one item.   The image display device according to claim 16, wherein the image display unit causes the backlight to emit light during the display period and extinguishes during the non-display period. The backlight is configured to be capable of switching between light emission and extinction for each unit horizontal light emitting region divided into a plurality of vertical directions of the screen of the liquid crystal panel.
The image display unit inputs the frame data line by line from the vertical end of the screen to the liquid crystal panel for each horizontal line, and enters the display area of the liquid crystal panel corresponding to the unit horizontal light emitting area. 17. The image display according to claim 16, wherein after the frame data is written, the unit horizontal light emitting area is caused to emit light during the display period, and the unit horizontal light emitting area is extinguished during the non-display period. apparatus. The image display unit has an organic EL panel,
The fluctuation suppression information calculation unit calculates, as the fluctuation suppression information, information on the maximum display brightness necessary for suppressing fluctuations in the display luminance due to fluctuations in the length of the non-display period.
The image display unit generates a compensation frame that compensates for the frame to be displayed this time from the information on the maximum display brightness, and displays the generated compensation frame on the organic EL panel. The image display device according to any one of the above. The image display unit has an organic EL panel,
The fluctuation suppression information calculation unit calculates, as the fluctuation suppression information, a current value to be supplied to the organic EL panel in order to suppress fluctuations in the display luminance due to fluctuations in the length of the non-display period.
5. The image display device according to claim 1, wherein the image display unit supplies the frame to be displayed this time and the current of the current value to the organic EL panel. 6. An image display method for switching between a display period and a non-display period in one frame period of an input image,
Enter the input image,
Calculate the length of the hidden period that should be targeted for the frame that should be displayed this time,
Calculate the brightness change from multiple frames,
Calculating an allowable maximum change width of the length of the non-display period based on the change width of the brightness;
Calculate the length of the non-display period that is closest to the length of the non-display period that should be the target so as not to exceed the maximum change width from the length of the non-display period of the previously displayed frame,
Calculating fluctuation suppression information for suppressing fluctuations in display luminance due to fluctuations in the length of the non-display period;
Performing image display based on the fluctuation suppression information and the frame to be displayed this time in the display period, and stopping the image display in the non-display period;
Image display method.   The image display method according to claim 21, wherein the image display is stopped by displaying a black image during the non-display period.

Images