JP2009053217A - Image processing apparatus and image display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide technique for performing high-quality image display by preferably adjusting brightness of a screen and reducing luminance fluctuation. <P>SOLUTION: The image processing apparatus is equipped with an ABL section 1 and a luminance fluctuation compensation section 2. The ABL section 1 corrects image data according to the mean luminance level for one screen portion of the image data. The luminance fluctuation compensation section 2 corrects the image data based on the integrated value of the maximum value of each line of the image data. More specifically, the luminance fluctuation compensation section 2 includes an Lmax detection section 6 which detects the maximum value of each line of the image data, an integrating section 7 which calculates the integrated value s by subjecting the detected maximum value to the one-screen portion integration, a gain determination section 8 which determines a gain g from the integrated value s, and a multiplication section 9 which multiplies the image data by the gain g. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a technique for controlling the luminance of a display panel of an image display device.

ABL (Automatic) is a method for controlling screen display brightness in accordance with input image brightness.
Brightness Limiter). ABL controls display luminance in accordance with an average luminance level (hereinafter referred to as APL (Average Picture Level)) for one screen of an input image. When a bright image is input, that is, when the APL is high, the ABL decreases the display brightness of the entire screen, and when a dark image is input, that is, when the APL is low, the display brightness of the entire screen is not decreased much. To do. Accordingly, it is possible to perform suitable luminance control without causing the user to feel glare in a bright scene and maintaining dark part reproducibility in a dark scene.

On the other hand, as a luminance control technique for a display panel that performs line sequential driving, there is a technique called “high luminance driving method”. The high luminance driving method is a method of determining the length of the scanning period of each horizontal line according to the maximum luminance in one horizontal line in order to increase the display luminance of the entire screen (see Patent Document 1).
JP 2003-228317 A

  In the high-intensity driving method, the scanning period of each horizontal line is optimized by shortening the scanning period of a horizontal line having a small maximum luminance and assigning that period to a horizontal line having a large maximum luminance. However, the following problems may occur in an image display apparatus that employs the high brightness driving method.

  As a characteristic of the high brightness driving method, an image in which bright pixels are distributed in the horizontal direction can display the screen brightly, and an image in which bright pixels are distributed in the vertical direction cannot be displayed as brightly as an image distributed in the horizontal direction. Therefore, in the high brightness driving method, the display brightness differs depending on whether the bright pixels are distributed in the horizontal direction or the vertical direction.

  FIG. 6 is a diagram for explaining this phenomenon. (A-1) and (a-2) in the figure represent original images. Here, the processing results of these two types of original images will be described as an example. These images are a single frame in a video in which a light-colored pendulum swings in a single-color background. The APLs of the original images (a-1) and (a-2) are almost the same. Images (b-1) and (b-2) are images obtained by displaying the original images (a-1) and (a-2) by the high brightness driving method.

  Since the original image (a-1) has bright pixels distributed in the horizontal direction, the overall display luminance is increased due to the characteristics of the high luminance driving method. As a result, it may be displayed brighter than the preferred luminance. On the other hand, in the original image (a-2), bright pixels are distributed in the vertical direction, and in this case, the effect of the high luminance driving method is difficult to appear, so that it cannot be displayed as brightly as the image (a-1).

  Since the APLs of the original images (a-1) and (a-2) are substantially the same, it is preferable to display them with close luminance. However, in the image display apparatus using the display panel having the characteristic of the high brightness driving method, a difference occurs in the display brightness as shown in the images (b-1) and (b-2). Such luminance fluctuations are not desirable because they give the viewer a sense of incongruity.

  An object of the present invention is to provide a technique for performing high-quality image display by preferably adjusting the brightness of a screen and reducing luminance fluctuations.

An image processing apparatus according to the present invention includes:
Correction means for outputting corrected image data to a display panel that determines the length of the scanning period of the horizontal line according to the maximum luminance in one horizontal line;
The image processing apparatus is characterized in that the correction means corrects the image data based on an integrated value of maximum values of each line of the image data.

An image display device according to the present invention includes:
The image processing device;
A display panel for displaying an image based on image data output from the image processing device;
An image display apparatus comprising:

  According to the present invention, it is possible to perform high-quality image display by preferably adjusting the brightness of the screen and reducing variations in luminance.

  Exemplary embodiments of the present invention will be described in detail below with reference to the drawings.

<First Embodiment>
FIG. 1 is a block diagram of an image processing apparatus according to the first embodiment. The image processing apparatus includes an ABL unit 1 (second correction unit) and a luminance fluctuation compensation unit 2 (correction unit). The ABL unit 1 is provided before the luminance fluctuation compensation unit 2, and the output of the ABL unit 1 is input to the luminance fluctuation compensation unit 2. The ABL unit 1 includes an APL detection unit 3, an APL / gain conversion unit 4, and a multiplication unit 5. The luminance fluctuation compensation unit 2 includes an Lmax detection unit 6 (line maximum value detection unit), an integration unit 7, a gain determination unit 8 (coefficient calculation unit), and a multiplication unit 9 (adjustment unit).

  A TV signal processing unit (a tuner, a decoder, a resolution conversion unit, a color space conversion unit, etc.) (not shown) is provided before the ABL unit 1, and a display panel (not shown) is provided after the luminance fluctuation compensation unit 2. The TV signal processing unit, the image processing unit, and the display panel constitute an image display device (TV device). The display panel of the present embodiment is a line-sequentially driven panel and has at least a driving mode by the above-described high-intensity driving method. For example, a display panel using an electron-emitting device such as a surface conduction electron-emitting device or a field emission device as a display device can be preferably used.

(ABL part)
The ABL unit 1 is a block that performs processing (ABL processing) for correcting the luminance of input image data in accordance with the average luminance level for one screen of image data.

  The APL detection unit 3 detects an average luminance level (APL) for one screen of input image data. As the average luminance level, for example, an average of RGB data for one screen can be considered. However, other representative values (statistics) such as an intermediate value and a mode value may be used as the average luminance level without being limited to the addition average. The APL / gain converter 4 obtains an ABL gain from the APL value input from the APL detector 3. For the conversion from the APL value to the ABL gain, a table may be used or a predetermined arithmetic expression may be used. The multiplication unit 5 performs luminance control by multiplying each of the input image data R, G, and B by the ABL gain.

  When a bright image is input, that is, an image with a high APL, display luminance is lowered by uniformly multiplying image data for one screen by an ABL gain smaller than 1. On the other hand, when a dark image is input, that is, an image with a low APL, the image data is uniformly multiplied by 1 or an ABL gain close to 1, and displayed without significantly reducing the luminance.

(Brightness fluctuation compensation section)
The brightness fluctuation compensation unit 2 is a block that performs a process of correcting the brightness of the image data (brightness fluctuation compensation process) based on the integrated value of the maximum value of each line of the image data. This process is a process for reducing the luminance fluctuation caused by the high luminance driving method.

  The Lmax detection unit 6 is a block that detects the largest value Lmax (maximum line value) in the data of one horizontal line of the image data input to the luminance fluctuation compensation unit 2. For example, when an image of 1920 × 1080 pixels having a full high-definition (hereinafter referred to as FHD) resolution is input, there are 1080 Lmax on one screen. Lmax (i) in the i-th row represents the maximum value among all 1920 × 3 (R, G, B) = 5760 image data of RGB existing in the i-th row.

The integrating unit 7 integrates Lmax detected by the Lmax detecting unit 6 for one screen and outputs an integrated value s. For example, when an FHD image is input, 1080 Lmax values are integrated. The integrated value s is expressed as Equation 1.

  The gain determining unit 8 estimates how much luminance is displayed by the high luminance driving method on the display panel from the integrated value s calculated by the integrating unit 7, and calculates the luminance variation compensation gain g (coefficient). Ask. In this example, a table is used when the luminance fluctuation compensation gain g is obtained from the integrated value s. An example of the table is shown in FIG. It is estimated that the smaller the integrated value s, the brighter the display because the effect of the high brightness driving method is higher. Therefore, as shown in FIG. 3, the table is such that the luminance fluctuation compensation gain g decreases as the integrated value s decreases. However, for conversion from the integrated value s to the luminance fluctuation compensation gain g, an arithmetic expression or the like may be used instead of a table.

  The multiplication unit 9 multiplies each of the image data R, G, and B by the obtained luminance fluctuation compensation gain g. Note that the same gain g is uniformly multiplied with respect to image data for one screen.

  Next, the flow of processing will be described using actual image data as an example with reference to FIG.

  (A-1) and (a-2) in FIG. 2 represent two types of original images. Here, the processing results of these two types of original images will be described as an example. These images are a single frame in a video in which a light-colored pendulum swings in a single-color background.

For the image input to the ABL unit 1, an APL value for one screen is calculated by the APL detection unit 3. Here, an average value of RGB image data is defined as an APL value. The APL / gain converter 4 calculates an ABL gain according to the APL value. In this example, it is assumed that the APL values of the original images (a-1) and (a-2) are the same. In this case, the original images (a-1) and (a-2) are preferably displayed with the same level of screen luminance, and the multiplication unit 5 multiplies the same ABL gain. Output images of the ABL unit 1 are shown in (b-1) and (b-2) of FIG. Images (b-1) and (b-2) also have the same APL value.

  The images (b-1) and (b-2) whose luminance is controlled by the ABL unit 1 are input to the luminance variation compensating unit 2. The Lmax detector 6 detects Lmax of the images (b-1) and (b-2). The integration unit 7 integrates Lmax of all lines to obtain an integrated value s. In the image (b-1), since bright pixels (pendulum portions) are distributed in the horizontal direction, the integrated value s is smaller than that in the image (b-2).

  In this example, the image data is 8-bit data of 0 to 255 gradations, and the image resolution is 1920 × 1080. At this time, the possible range of the integrated value s is 0 to 275400 (= 255 × 1080). Assume that the integrated value s of the image (b-1) is 260000, and the integrated value of the image (b-2) is 100,000.

  As the integrated value s is larger, that is, an image in which bright pixels are distributed in the vertical direction, the effect of the high luminance drive method is less, and thus the image is displayed with lower luminance. Further, as the integrated value s is smaller, that is, an image in which bright pixels are not distributed in the vertical direction is displayed with higher luminance by the high luminance driving method. Therefore, when the images (b-1) and (b-2) are displayed on the display panel, the image (b-1) is displayed brighter than the image (b-2).

  If the integrated value s can be detected, it is possible to estimate how much luminance fluctuation is caused by the high luminance driving method. Therefore, the luminance fluctuation compensation unit 2 estimates the luminance fluctuation by the high luminance driving method from the integrated value s, multiplyes the image data in advance by a gain for compensating (reducing) the luminance fluctuation, and the corrected image data. Is output to the display panel.

  The gain determination unit 8 estimates the luminance fluctuation by the high luminance driving method from the integrated value s, and obtains the luminance fluctuation compensation gain g. In this example, the luminance variation compensation gain g is obtained from the integrated value s by a table (see FIG. 3). However, for calculating the luminance fluctuation compensation gain g from the integrated value s (that is, estimating the luminance fluctuation), a predetermined arithmetic expression (estimation expression) may be used instead of a table.

  Since the integrated value s of the image (b-1) is 100,000, the luminance variation compensation gain g is 0.6. On the other hand, since the integrated value s of the image (b-2) is 260000, the luminance variation compensation gain g is 1.

  The multiplier 9 multiplies each of the RGB image data by the luminance variation compensation gain g. Output images of the multiplication unit 9 are shown in (c-1) and (c-2) of FIG. The output image (c-1) of the multiplication unit 9 is an overall darker image than the image (c-2).

  The output images (c-1) and (c-2) of the luminance fluctuation compensation unit 2 are output to the display panel. A display panel drive circuit (not shown) drives each display element based on the image data Rout, Gout, and Bout received from the luminance fluctuation compensation unit 2. In the high luminance driving method, the driving circuit increases the display luminance of the entire screen by optimizing the scanning period of each line according to the maximum luminance in each horizontal line. In the image (c-1), the effect of the high brightness driving method is large, and the increase in brightness is large. On the other hand, the image (c-2) has little effect by the high brightness driving method, and the brightness does not increase so much. As a result, the actually displayed image has substantially the same luminance as shown in (d-1) and (d-2).

  FIG. 4 is a diagram for explaining the effect of the luminance variation compensation of the present embodiment.

4A and 4C show the display brightness of the conventional device (when the output of the ABL unit 1 is input to the display panel), and FIGS. 4B and 4D show the display brightness of the present embodiment. ing. In each graph, the horizontal axis represents the APL value of the input image, and the vertical axis represents the display luminance. Also, the curve 20 in the figure represents the desired luminance (preferred display luminance) that is originally desired to be displayed.

  Assume that original images such as (a-1) and (a-2) in FIG. 2 are input. In the case of the conventional apparatus, the image (a-1) is displayed brightly by the high luminance driving method, and the image (a-2) is not as bright as the image (a-1) because the effect of the high luminance driving method is small. Points 21 and 22 in FIG. 4A indicate such a display state. That is, the point 21 represents the display luminance of the original image (a-1), and the point 22 represents the display luminance of the original image (a-2). Since the original images (a-1) and (a-2) are equivalent APLs, they are preferably displayed with substantially the same luminance. However, the luminance fluctuation as shown by points 21 and 22 in FIG. In addition, the original image (a-1) is displayed brighter than the desired luminance 20.

  According to the present embodiment, this luminance variation can be reduced as shown in FIG. The original image (a-1) is reduced to the luminance at the point 23 in FIG. 4B by the luminance variation compensation gain g, and the original image (a-2) is displayed at the luminance at the point 22 as in the conventional case. Thereby, the luminance of the original image (a-1) is adjusted to a preferable state, and the difference in display luminance between the original images (a-1) and (a-2) is also reduced.

  FIGS. 4C and 4D are diagrams in the case where luminance fluctuation occurs in a range higher than the desired luminance 20. A point 31 in FIG. 4C shows a case where the luminance is increased by the high luminance driving method, and a point 32 shows a case where the effect of the high luminance driving method is low and the luminance does not increase. According to the present embodiment, in such a case, each image data is multiplied by the luminance variation compensation gain g so that the two original images have substantially the same luminance. As a result, both images are displayed with a brightness close to the desired brightness 20 (see point 33). As a result, luminance fluctuation can be reduced and display can be performed with preferable luminance.

  As described above, according to the present embodiment, it is possible to preferably adjust the brightness of the screen and reduce the luminance fluctuation caused by the high luminance driving method. Thereby, a suitable image according to APL can be displayed.

Second Embodiment
Next, a second embodiment of the present invention will be described.

  FIG. 5 is a block diagram of an image processing apparatus according to the second embodiment. Blocks having the same functions as those in the first embodiment are denoted by the same reference numerals. Reference numerals 40 and 41 in FIG. 5 denote multipliers.

  The APL detection unit 3 detects the APL values of the input image data R, G, B. The APL / gain conversion unit 4 (first coefficient calculation unit) obtains an ABL gain (first coefficient) from the APL value. The ABL gain is output to the first multiplier 40 and the second multiplier 41.

  The Lmax detector 6 (line maximum value detector) detects the maximum value Lmax of each line of the input image data R, G, B. The integrating unit 7 integrates Lmax for one screen and outputs an integrated value s.

  The multiplier 40 multiplies the integrated value s and the ABL gain. The output s1 of the multiplier 40 is equal to the integrated value obtained from the image data after ABL control (that is, the integrated value s output from the integrating unit 7 in FIG. 1).

The gain determination unit 8 (second coefficient calculation unit) obtains the luminance variation compensation gain g (second coefficient) from the output s1 of the multiplier 40. Similarly to the first embodiment, the gain determination unit 8 may obtain the luminance fluctuation compensation gain g using the table of FIG. 3 or may obtain the luminance fluctuation compensation gain g using a predetermined arithmetic expression.

  The multiplier 41 multiplies the ABL gain and the luminance variation compensation gain g and outputs a gain g1. The multiplication unit 9 (adjustment unit) multiplies the image data R, G, and B by the gain g1. As a result, it is possible to simultaneously perform the ABL processing and the luminance variation compensation processing for the high luminance driving method.

  In the configuration of the second embodiment, the same effect as that of the first embodiment can be obtained.

1 is a block diagram of an image processing apparatus according to a first embodiment. It is a figure for demonstrating the process of 1st Embodiment. It is a figure which shows the table used by a gain determination part. It is a figure for demonstrating the effect of the process of 1st Embodiment. It is a block diagram of the image processing apparatus of 2nd Embodiment. It is a figure for demonstrating the brightness | luminance fluctuation | variation resulting from the high brightness drive method.

Explanation of symbols

1 ABL section (correction means)
2 Luminance fluctuation compensation unit (second correction means)
3 APL detection unit 4 APL / gain conversion unit (first coefficient calculation unit)
5 Multiplying unit 6 Lmax detecting unit (line maximum value detecting unit)
7 Accumulation unit 8 Gain determination unit (coefficient calculation unit; second coefficient calculation unit)
9 Multiplying unit (adjusting unit)
20 Desired luminance characteristics (preferred luminance characteristics)
40 multiplier (first multiplier)
41 multiplier (second multiplier)

Claims (7)

Correction means for outputting corrected image data to a display panel that determines the length of the scanning period of the horizontal line according to the maximum luminance in one horizontal line;
The image processing apparatus according to claim 1, wherein the correction means corrects the image data based on an integrated value of maximum values of the respective lines of the image data. The correction means includes
A line maximum value detection unit for detecting a maximum value of each line of the image data;
An integration unit for calculating the integrated value by integrating the detected maximum value for one screen;
A coefficient calculation unit for obtaining a coefficient from the integrated value;
An adjusting unit for adjusting the image data by the coefficient;
The image processing apparatus according to claim 1, further comprising: The image processing apparatus according to claim 2, wherein the adjustment unit is a multiplication unit that multiplies the image data by the coefficient. A second correction means is provided upstream of the correction means;
The image according to any one of claims 1 to 3, wherein the second correction unit corrects the image data in accordance with an average luminance level of one screen of the image data. Processing equipment. The correction means includes
An APL detector that detects an average luminance level for one screen of image data;
A first coefficient calculation unit for obtaining a first coefficient from the detected average luminance level;
A line maximum value detection unit for detecting a maximum value of each line of the image data;
An integration unit for calculating the integrated value by integrating the detected maximum value for one screen;
A first multiplier for multiplying the integrated value by the first coefficient;
A second coefficient calculation unit for obtaining a second coefficient from the output of the first multiplier;
A second multiplier for multiplying the first coefficient by a second coefficient;
An adjustment unit that adjusts the image data according to an output of the second multiplier;
The image processing apparatus according to claim 1, further comprising: The image processing apparatus according to claim 5, wherein the adjustment unit is a multiplication unit that multiplies the output of the second multiplier by image data. The image processing apparatus according to any one of claims 1 to 6,
A display panel for displaying an image based on image data output from the image processing device;
An image display device comprising:

Images