JP2003046807A - Image display device and image display method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that, in the case where a correction is made in correspondence to a maximum value and a minimum value of a brightness signal on the whole of a display screen, when a dynamic range of a process system has already been used up on the whole of the screen, a sufficient correction effect cannot be attained. SOLUTION: A marked pixel neighboring area brightness detection circuit 2 sequentially sets one pixel out of an input image brightness signal 1 to a marked pixel in input order, and a maximum value detection circuit 3 and a minimum value detection circuit 4 detect a maximum value and a minimum value of an image brightness signal in a neighboring area of the marked pixel, respectively. Each pixel of the input image brightness signal 1 is corrected based on such a characteristic that, based on a characteristic corresponding to the such-detected maximum value and minimum value, the maximum value of an input signal in the neighboring area is converted into the maximum value of the dynamic range of the process system, and the minimum value of the input signal in the neighboring area is converted into the minimum value of the dynamic range of the process system.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image display device and an image display method, and more particularly to an image display device and an image display method for dynamically correcting gradation according to the characteristics of an input video luminance signal. .

[0002]

2. Description of the Related Art There is an image display device which realizes high image quality by gradation correction and contour correction of a video luminance signal in video equipment. Conventionally, this type of image display device uses a sampling window in almost the entire effective display period of the display screen, and creates a correction table from a combination of a maximum value, a minimum value, and an average brightness level (hereinafter referred to as APL). For the same field, the input video luminance signal is corrected for the same field based on the same correction table to realize high image quality.

For example, the minimum and maximum values of the video luminance signal within the effective display period are detected field by field or frame by frame, and the detected maximum value of the input signal is the maximum value of the dynamic range of the video signal processing system ( In 8-bit processing, it is changed to 255), and the minimum value of the detected input signal is converted to the minimum value (usually 0) of the dynamic range of the video signal processing system, and between the minimum value and the maximum value of the input luminance signal. There was a method called black expansion and white expansion in which all values of were linearly interpolated and corrected so that the dynamic range of the processing system could be used up for any input signal. For example, the method described in Japanese Patent Laid-Open No. 10-248024 can be given as an example.

[0004]

However, in this conventional method, since the correction table is calculated based on the information of the entire screen, the correction effect may be insufficient.
For example, in a movie-like scene in which a dark scene occupies most of the effective display period, the maximum value of the dynamic range of the processing system (255 in 8-bit processing) exists even for only one pixel. In this case, no correction is made by stretching in the white direction. Also, in the case of a video source that uses up the dynamic range from top to bottom like a personal computer signal, no correction is performed in either the white direction or the black direction, resulting in sufficient gradation expression and image quality with a sense of contrast. There was a problem that could not be realized.

Therefore, an object of the present invention is to obtain a sufficient correction effect when performing gradation correction and contour correction of a video luminance signal without being influenced by the characteristics of the video signal, and as a result, sufficient correction effect is obtained. An object of the present invention is to provide an image display device and an image display method capable of realizing an image quality with gradation expression and a sense of contrast.

[0006]

A first aspect of the present invention is an image display device which dynamically corrects gradation according to the characteristics of an input video luminance signal, and a pixel of the input video luminance signal The target pixel neighboring area feature detecting means for sequentially detecting the features of the input video luminance signal in the neighboring area of the target pixel, and the luminance of the target pixel based on the features detected by the target pixel neighboring area feature detecting means And a correction means for sequentially correcting the levels.

As described above, according to the first aspect of the present invention, the pixel of interest is corrected according to the characteristics (for example, maximum brightness, minimum brightness, average brightness, and variance value) in each neighboring area. Therefore, a larger correction effect can be obtained as compared with the case where correction is performed based on the features extracted from the entire effective display area. Further, even when the correction effect is not so obtained when the correction is performed based on the features extracted from the entire effective display area, a sufficient correction effect can be obtained for each area.

In a second aspect based on the first aspect, the target pixel neighboring area feature detecting means detects maximum and minimum luminance levels in the neighboring area of the target pixel, respectively. The correcting means includes the means, and the correcting means determines the maximum value and the minimum value based on the maximum value detected by the maximum value detecting means and the minimum value detected by the minimum value detecting means, respectively, based on the maximum dynamic range of the signal processing system. It is characterized in that the brightness level of the pixel of interest is sequentially corrected on the basis of the correction characteristic such that the value and the minimum value are converted.

As described above, according to the second aspect of the present invention, the target pixel is corrected in accordance with the MAX value and the MIN value of the luminance signal in each neighboring area, so that it is always within the neighboring area of the target pixel. A signal that uses the entire dynamic range is output. Therefore, even if the dynamic range of the processing system is used up on the entire screen, by performing gradation correction of white expansion and black expansion for each area near the pixel of interest, sufficient gradation can be used until the dynamic range is used up for each area. Correction is possible.

In a third aspect based on the second aspect, the correction means uses a first subtraction circuit for subtracting the minimum value from the maximum value and a denominator for the output of the first subtraction circuit, and the corrected luminance A division circuit that performs division using the maximum value as a numerator, a second subtraction circuit that subtracts the minimum value from the luminance level of the pixel of interest, and a multiplication circuit that multiplies the output of the second subtraction circuit and the output of the division circuit. Including.

As described above, according to the third invention, the correction means can be easily realized.

In a fourth aspect based on the first aspect, the target pixel neighboring area feature detecting means includes an average luminance detecting means for detecting an average luminance level in a neighboring area of the target pixel, and the correcting means includes The brightness level of the target pixel is sequentially corrected according to the difference between the brightness level and the average brightness detected by the average brightness detection means.

As described above, according to the fourth aspect of the present invention, the correction is performed based on the difference between the average luminance level (APL) and the target pixel for each target pixel neighboring area, so that there is a local sense of contrast. Gradation correction is possible.

According to a fifth aspect of the present invention, in the fourth aspect, the correction means focuses on the pixel when the difference between the luminance level of the pixel of interest and the average luminance detected by the average luminance detection means is smaller than a predetermined value. If the brightness level of the pixel is not corrected and the difference between the brightness level and the average brightness is larger than a predetermined value,
It is characterized in that the brightness level of the pixel of interest is corrected so that the brightness level is farther from the average brightness according to this difference.

As described above, according to the fifth invention, the AP
When the difference between L and the pixel of interest is smaller than a predetermined value, no correction is performed, and when the difference is larger than a predetermined value, correction is performed according to the difference, so that in a continuous scene where adjacent pixels are connected, It is possible to perform correction such as emphasizing contrast in a scene in which adjacent pixels are not connected and there is no need to maintain gradation while maintaining the gradation.

In a sixth aspect based on the fifth aspect, the correction means comprises a subtraction circuit for subtracting the average brightness from the brightness level of the pixel of interest, and a gain amount calculation circuit for calculating the gain amount based on the output of the subtraction circuit. And a multiplication circuit for multiplying the luminance level of the pixel of interest and the output of the gain amount calculation circuit.

As described above, according to the sixth aspect, the correction means can be easily realized.

In a seventh aspect based on the first aspect, the target pixel neighboring area feature detecting means includes a variance value detecting means for detecting a variance value of the brightness level in the neighboring area of the target pixel, and the correcting means comprises the variance value. When the variance value detected by the value detecting means is relatively large, the luminance level of the pixel of interest is sequentially corrected so as to emphasize the contrast, while when the variance value is relatively small, the pixel of interest is maintained to maintain the gradation. It is characterized in that the luminance levels of are sequentially corrected.

As described above, according to the seventh aspect, the degree of continuity of the scene is locally judged according to the variance value within the area for each target pixel neighboring area, and the correction is performed based on the judgment result. As a result, it becomes possible to perform the correction that achieves both good gradation and high contrast.

In an eighth aspect based on the seventh aspect, the target pixel neighboring area feature detecting means further includes an average luminance detecting means for detecting an average luminance level in the neighboring area of the target pixel, and the correcting means comprises a variance value. Is greater than a predetermined value, the brightness level of the pixel of interest is set so that the brightness level of the pixel of interest becomes farther from the average brightness detected by the average brightness detection means. The feature is that the correction is performed sequentially.

As described above, according to the eighth aspect of the invention, it is possible to perform gradation correction with a local contrast feeling by performing correction based on the local APL.

In a ninth aspect based on the eighth aspect, the correction means comprises a gain amount calculation circuit for calculating a gain amount based on the variance value and the average luminance, and a luminance level of the pixel of interest and an output of the gain amount calculation circuit. And a multiplication circuit for multiplying and.

As described above, according to the ninth aspect, the correction means can be easily realized.

A tenth aspect of the present invention is an image display method in which gradation is dynamically corrected according to the characteristics of an input video luminance signal, and one pixel of the input video luminance signal is sequentially set as a target pixel, and the vicinity of this target pixel is set. A target pixel neighboring area feature detecting step of sequentially detecting features of the input video luminance signal in the area, and a correction step of sequentially correcting the luminance level of the target pixel based on the features detected by the target pixel neighboring area feature detecting step. .

As described above, according to the tenth aspect, the pixel of interest is corrected according to the characteristics (for example, the maximum luminance, the minimum luminance, the average luminance, and the variance value) in each neighboring area. Therefore, a larger correction effect can be obtained as compared with the case where correction is performed based on the features extracted from the entire effective display area. Further, even when the correction effect is not so obtained when the correction is performed based on the features extracted from the entire effective display area, a sufficient correction effect can be obtained for each area.

An eleventh invention is the tenth invention, wherein
The target pixel neighboring area feature detecting step includes a maximum value detecting step and a minimum value detecting step of detecting the maximum value and the minimum value of the brightness level in the neighboring area of the target pixel, respectively, and the correction step is detected by the maximum value detecting step. Based on the minimum value detected by the maximum and minimum value detection step, the maximum value and the minimum value are converted into the maximum value and the minimum value of the dynamic range of the signal processing system, respectively. It is characterized in that the brightness levels of the pixels are sequentially corrected.

As described above, according to the eleventh aspect, the target pixel is the MAX of the luminance signal in each neighboring area.
Since the correction is performed according to the value and the MIN value, a signal that uses the entire dynamic range is always output within the area near the pixel of interest. Therefore, even if the dynamic range of the processing system is used up on the entire screen, by performing gradation correction of white expansion and black expansion for each area near the pixel of interest, sufficient gradation can be used until the dynamic range is used up for each area. Correction is possible.

The twelfth invention is the eleventh invention, wherein
The correction step includes a first subtraction step of subtracting the minimum value from the maximum value, a division step in which the calculation result of the first subtraction step is used as a denominator, and a maximum value of the corrected brightness is used as a numerator for division. A second subtraction step of subtracting the minimum value from the luminance level of 1. and a multiplication step of multiplying the calculation result of the second subtraction step by the calculation result of the division step.

As described above, according to the twelfth aspect, the correction step can be easily realized.

A thirteenth invention is the tenth invention, wherein
The target pixel neighborhood area feature detection step includes an average luminance detection step of detecting an average luminance level in the neighborhood area of the attention pixel, and the correction step includes a luminance level of the attention pixel and an average luminance detected by the average luminance detection step. The brightness level of the target pixel is sequentially corrected according to the difference.

As described above, according to the thirteenth aspect of the present invention, the correction is performed based on the difference between the average luminance level (APL) and the target pixel for each target pixel neighboring area, so that there is a local sense of contrast. Gradation correction is possible.

A fourteenth invention is the thirteenth invention, wherein
If the difference between the brightness level of the pixel of interest and the average brightness detected by the average brightness detection step is smaller than a predetermined value, the correction step does not correct the brightness level of the pixel of interest and sets the brightness level and the average brightness. If the difference is larger than a predetermined value, the brightness level of the pixel of interest is corrected according to this difference so that the brightness level is farther from the average brightness.

As described above, according to the fourteenth invention, A
When the difference between PL and the pixel of interest is smaller than a predetermined value, no correction is performed, and when the difference is larger than the predetermined value, correction is performed according to the difference, so that in a continuous scene where adjacent pixels are connected, originally It is possible to perform correction such as emphasizing contrast in a scene in which adjacent pixels are not connected and there is no need to maintain gradation while maintaining the gradation.

A fifteenth invention is the fourteenth invention, wherein
The correction step includes a subtraction step of subtracting the average brightness from the brightness level of the pixel of interest, a gain amount calculation step of calculating a gain amount based on the calculation result of the subtraction step, and a calculation of the brightness level of the pixel of interest and the gain amount calculation step. A multiplication step for multiplying the result with.

As described above, according to the fifteenth invention, the correction step can be easily realized.

A sixteenth invention is the tenth invention according to the tenth invention.
The target pixel neighborhood area feature detection step includes a variance value detection step of detecting a variance value of the brightness level in the neighborhood area of the target pixel, and the correction step has a variance value detected by the variance value detection step larger than a predetermined value. In this case, the luminance level of the pixel of interest is sequentially corrected so as to enhance the contrast, while the luminance level of the pixel of interest is sequentially corrected so as to maintain the gradation when the variance value is smaller than a predetermined value. Characterize.

As described above, according to the sixteenth aspect, the degree of continuity of the scene is locally judged according to the variance value within the area for each target pixel neighboring area, and the correction is performed based on the judgment result. As a result, it becomes possible to perform the correction that achieves both good gradation and high contrast.

The seventeenth invention is the sixteenth invention, wherein
The target pixel neighboring area feature detecting step further includes an average luminance detecting step of detecting an average luminance level in the neighboring area of the target pixel, and the correcting step includes determining that the luminance level of the target pixel is when the variance value is larger than a predetermined value. It is characterized in that the luminance level of the pixel of interest is sequentially corrected so that the farther from the average luminance detected by the average luminance detecting step, the further the luminance level becomes from this average luminance.

As described above, according to the seventeenth aspect of the invention, it is possible to perform gradation correction with a local contrast feeling by performing correction based on the local APL.

An eighteenth invention is the seventeenth invention, wherein
The correction step includes a gain amount calculation step of calculating a gain amount based on the variance value and the average luminance, and a multiplication step of multiplying the luminance level of the pixel of interest by the calculation result of the gain amount calculation step.

As described above, according to the eighteenth invention, the correction step can be easily realized.

[0042]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Various embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 is a block diagram showing the arrangement of an image display apparatus according to the first embodiment of the present invention. Figure 1
In the image display device, the image display device includes the pixel-of-interest neighborhood area brightness detection circuit 2, the first subtraction circuit 5, and the second subtraction circuit 6.
And a division circuit 7 and a multiplication circuit 8. The target pixel neighboring area brightness detection circuit 2 includes a maximum value detection circuit 3 and a minimum value detection circuit 4. The input video luminance signal 1 is input to the image display device, and the input video luminance signal 1 is input to the image display device.
To output the output video luminance signal 9. The operation of the image display device will be described below.

The input video luminance signal 1 is input to the target pixel neighboring area luminance detection circuit 2. The target pixel neighboring area brightness detection circuit 2 sequentially sets one pixel of the input video brightness signal 1 as a target pixel in the order of input (for example, sequentially from the upper left pixel to the lower right pixel of the display screen, the target pixel). The maximum value and the minimum value of the video luminance signal in the area near the pixels are detected by the maximum value detection circuit 3 and the minimum value detection circuit 4, respectively. In this way, the maximum value and the minimum value in the neighboring area are sequentially detected for all the pixels of the input video luminance signal 1.

The size of the neighboring area, that is, the size of the detection area is preferably determined according to the type of input signal. Generally, in the case of a source having a lot of character information such as a PC signal, it is preferable to narrow the area, and for example, an area of horizontal 3 pixels × vertical 3 lines with the pixel of interest at the center. On the other hand, in the case of a natural image such as a video signal, it is preferable to make it wide, for example, horizontal 5 pixels × vertical 5 with the pixel of interest as the center.
The area of the line.

The rate to be detected may be for each field or may be further thinned out. If necessary, an appropriate filter may be applied to the detected value. When detecting the maximum value and the minimum value in the neighborhood area, a line memory may be used if there are few vertical detection lines, or a frame memory may be used if there are many detection lines.

The maximum value MAX in the target pixel neighborhood area thus detected is input to the first subtraction circuit 5. On the other hand, the similarly detected minimum value MIN is input to the first subtraction circuit 5 and the second subtraction circuit 6. The first subtraction circuit 5 calculates (MAX-MIN) based on the maximum value MAX and the minimum value MIN. The division circuit 7 is based on the calculation result (MAX-MIN) by the first subtraction circuit and the maximum value MAX ′ of the corrected luminance signal, MAX ′ /
Calculate (MAX-MIN). The second subtraction circuit 6
(L-MIN) is calculated based on the minimum value MIN and the input video luminance signal 1 (L). The outputs of the division circuit 7 and the second subtraction circuit 6 are both input to the multiplication circuit 8, and the multiplication circuit 8 outputs MAX ′ based on these outputs.
The calculation of / (MAX-MIN) * (L-MIN) is performed.
The calculation result of the multiplication circuit 8 is output as the output video luminance signal 9.

Filters may be inserted in the outputs of the maximum value detection circuit 3 and the minimum value detection circuit 4 as described above, or similarly, filters may be inserted between the arithmetic circuits or in the output of the multiplication circuit 8. You may.

The relationship between these inputs and outputs will be described with reference to FIG. Each pixel of the input video luminance signal 1 has a maximum value MAX and a minimum value MIN of the input signal in the vicinity area thereof.
Is corrected based on the characteristics according to. This characteristic is shown in FIG. 2 as the corrected characteristic. As shown in FIG. 2, each pixel is
The maximum value MAX of the input signal in the neighboring area is converted into the maximum value MAX ′ of the dynamic range of the processing system (corresponding to 255 in the 8BIT processing), and the minimum value MIN of the input signal in the neighboring area is the minimum value of the dynamic range of the processing system. It is converted to MIN '(normally 0), and the value between the maximum value MAX and the minimum value MIN is corrected based on the characteristic that it maps between the maximum value MAX' and the minimum value MIN '.

As described above, the input image luminance signals within the effective display period are set as the target pixels in the order of input, and the target pixels are
MAX value and M of the luminance signal in each neighboring area
Since the correction is performed according to the IN value, a signal that uses the entire dynamic range is always output in the area near the pixel of interest. MAX value and MIN detected on the entire screen
When the same correction is performed using the value, there is no correction effect when the input video luminance signal uses up the dynamic range. However, even in such a case, the dynamic range is not used up in the area near the pixel of interest, and there is room for correction. In this embodiment,
Since the correction is performed based on the local information, it is possible to output an image having a sufficient gradation for each area.

(Second Embodiment) FIG. 3 shows a second embodiment of the present invention.
It is a block diagram showing a configuration of an image display device according to the embodiment of. In FIG. 3, the image display device includes a target pixel neighboring area luminance detection circuit 10, a subtraction circuit 12, a gain amount calculation circuit 13, and a multiplication circuit 14. The target pixel neighboring area brightness detection circuit 10 includes an average brightness detection circuit 11. The input video luminance signal 1 is input to the image display device, and the image display device corrects the input video luminance signal 1 and outputs the output video luminance signal 9. The operation of the image display device will be described below.

The input video luminance signal 1 is input to the target pixel neighborhood area luminance detection circuit 10. The target pixel neighboring area luminance detection circuit 10 sequentially sets one pixel of the input video luminance signal 1 as a target pixel in the order of input, and determines the average luminance level of the video luminance signal in the neighboring area of the target pixel from the average luminance detection circuit. 11 to detect. In this way, the average brightness level in all the pixels of the input video brightness signal 1 is sequentially detected in the vicinity area.

The size of the neighborhood area, that is, the size of the detection area is preferably determined according to the type of the input signal. Generally, in the case of a source having a lot of character information such as a PC signal, it is preferable to narrow the area, and for example, an area of horizontal 3 pixels × vertical 3 lines with the pixel of interest at the center. On the other hand, in the case of a natural image such as a video signal, it is preferable to set it to a large value.
The area of the line.

The detected rate may be for each field or may be further thinned out. If necessary, an appropriate filter may be applied to the detected value. When detecting the average luminance level in the detection area, a line memory may be used if there are few vertical detection lines, or a frame memory may be used if there are many detection lines.

The average luminance level in the target pixel neighborhood area thus detected is input to the subtraction circuit 12. The subtraction circuit 12 calculates the average brightness level (APL),
Difference from the input video luminance signal 1 (L) (L-AP
L). The gain amount calculation circuit 13 uses the subtraction circuit 1
Based on the output of 2, the correction gain amount for the input video luminance signal 1 is calculated. An example of the calculation of the correction gain amount will be described with reference to FIG.

The output signal of the average luminance detection circuit 11 is set to AP
L, input video luminance signal 1 is L, output video luminance signal is L '
Then, the input of the gain amount calculation circuit 13 (L-APL)
And the output L '/ L are as shown in FIG. When the brightness level of the pixel of interest is sufficiently higher than the APL in the area near the pixel of interest, the larger the brightness level, the more the brightness difference of the pixel of interest with the other pixels in the area of proximity.
In such a case, the gradation is not required because it is a continuous scene, and the gain-up correction is performed based on the judgment that it is better to raise the brightness sufficiently to bring out the contrast because it is discontinuous. Similarly, when the input luminance signal level is sufficiently smaller than that of APL, it is judged that it is better to output the contrast, so that the gain down correction is performed. On the other hand, the brightness level of the pixel of interest and the AP in the vicinity area
When L is close to the above, contrary to the above determination, the gain 1 is maintained and the correction is not performed because it is determined that the gradation should be maintained rather than the contrast is produced.

As described above, when a large number of pixels having a brightness close to that of the target pixel exist in the target pixel neighboring area, the brightness of the target pixel and the APL of the neighboring area are close to each other, and it is determined that the gradation is necessary, and the gradation Elongation is suppressed. On the other hand, when the difference between the brightness of the target pixel and the APL of the neighboring area is sufficiently large, the target pixel and the peripheral pixels are discontinuous, and the brightness of the target pixel is set so as to increase the contrast feeling rather than maintaining the gradation. Performs a correction that stretches the image closer to white or black.

The gain amount calculated as described above is
The multiplication circuit 14 multiplies the input video luminance signal 1 by
It is output as the output video luminance signal 9.

As described above, according to the present embodiment, by performing the above-described correction, the original gradation is maintained in a continuous scene in which adjacent pixels are connected, and there is no connection between adjacent pixels. In scenes that do not require key retention,
It is possible to improve the contrast by performing correction so that pixels having brightness levels farther away from the neighboring pixels in the white and black directions are made closer to white and black, respectively.

Although the characteristic for calculating the gain amount is the characteristic shown in FIG. 4 in the present embodiment, the characteristic is not limited to this. For example, in the characteristic shown in FIG. 4, L-APL =
The range in which L / L 'is 1 is set to be wide enough in the vicinity of 0, but the gain becomes 1 only at one point of L-APL = 0, and immediately before or after L-APL = 0, it rises or falls. May have a gain other than 1. Further, for example, the characteristic shown in FIG. 4 is linear, but other curves such as a quadratic function may be used. Further, the upper limit value and the lower limit value of the gain amount are not limited to 2 and 0, respectively.

(Third Embodiment) FIG. 5 shows a third embodiment of the present invention.
It is a block diagram showing a configuration of an image display device according to the embodiment of. In FIG. 5, the image display device includes a target pixel neighboring area luminance detection circuit 15, a gain amount calculation circuit 17,
And a multiplication circuit 14. The target pixel neighboring area brightness detection circuit 15 includes an average brightness detection circuit 11 and a variance value detection circuit 16. The input video luminance signal 1 is input to the image display device, and the image display device corrects the input video luminance signal 1 and outputs the output video luminance signal 9. In FIG. 5, the same components as those shown in FIG. 3 are designated by the same reference numerals and the description thereof will be omitted. The operation of the image display device will be described below.

The input image brightness signal 1 is input to the target pixel neighborhood area brightness detection circuit 15. The target pixel neighboring area luminance detection circuit 15 sequentially sets one pixel of the input video luminance signal 1 as a target pixel in the order of input, and determines the average luminance level and the variance value of the luminance level in the neighboring area of the target pixel as the average luminance. Detection circuit 11 and variance value detection circuit 1
6, respectively.

The size of the neighborhood area, that is, the size of the detection area is preferably determined according to the type of the input signal. Generally, in the case of a source having a lot of character information such as a PC signal, it is preferable to narrow the area, and for example, an area of horizontal 3 pixels × vertical 3 lines with the pixel of interest at the center. On the other hand, in the case of a natural image such as a video signal, it is preferable to make it wide, for example, horizontal 5 pixels × vertical 5 with the pixel of interest as the center.
The area of the line.

The detected rate may be frame by frame or may be further thinned out. If necessary, an appropriate filter may be applied to the detected value. When detecting the average luminance level and the variance value in the detection area, a line memory may be used if there are few vertical detection lines,
If there are many detection lines, a frame memory may be used.

The average brightness level and the variance value in the target pixel neighborhood area detected in this way are the gain amount calculation circuit 1
Input to 7. The gain amount calculation circuit 17 calculates a correction gain amount for the input video luminance signal 1 based on the average luminance level and the variance value. An example of the calculation of the correction gain amount will be described with reference to FIG.

The gain amount calculation circuit 17 calculates the correction gain amount from the table shown in FIG. 6 based on the average brightness level and the variance value. When the output signal of the average brightness detection circuit 11 is APL and the input video brightness signal 1 is L, the relationship between the output signal of the variance value detection circuit 16 and the output signal of the gain amount calculation circuit 17 is as shown in FIG. . When the output of the variance value detection circuit 16, that is, when the variance value is B1 or less, it indicates that pixels having luminance levels close to each other are gathered in the area near the pixel of interest. In this case, continuous scenes between adjacent pixels are shown. Therefore, the output of the gain amount calculation circuit 17 is set to 1 in order to maintain the current gradation. On the other hand, when the variance value is B1 or more, it indicates that pixels having different luminance levels are gathered in the area near the pixel of interest. In this case, it is determined that there is a discontinuous scene between adjacent pixels. Therefore, it is preferable in terms of image quality to increase the contrast rather than maintain the current gradation. Therefore, the output of the gain amount calculation circuit 17 is linearly changed from 1 to 0 or 2 according to the increase of the variance value. When L> APL, it is determined that the pixel of interest is brighter than the neighboring area, and the gain amount calculation circuit 17
Is output between 1 and 2, and when L <APL, the target pixel is determined to be darker than the neighboring area, and the output of the gain amount calculation circuit 17 is output between 1 and 0. Fork point B
1 should be selected optimally while watching various scenes.

In the present embodiment, the output of the gain amount calculation circuit 17 when the variance value is B1 or more is changed by a linear function, but the optimum curve should be selected while observing various images. is there.

The gain amount calculated as described above is
The multiplication circuit 14 multiplies the input video luminance signal 1 by
It is output as the output video luminance signal 9.

As described above, according to the present embodiment, by performing the above-described correction, the original gradation is maintained in a continuous scene in which adjacent pixels are connected, and there is no connection between adjacent pixels. In scenes that do not require key retention,
Good contrast and high contrast are achieved by improving the contrast by correcting pixels with luminance levels farther in the white and black directions than the neighboring pixels so that they are closer to white and black, respectively. be able to.

Although the characteristic for calculating the gain amount is the characteristic shown in FIG. 6 in the present embodiment, the characteristic is not limited to this. For example, in the characteristic shown in FIG. 6, the variance value is B1.
In the above case, the output of the gain amount calculation circuit 17 is changed in a linear function, but other curves such as a quadratic function may be used, and the optimum curve should be selected while observing various images. is there. Further, the upper limit value and the lower limit value of the gain amount are not limited to 2 and 0, respectively.

The light valve type display device such as liquid crystal or DLP has a problem of insufficient contrast due to black floating due to leaked light as compared with the CRT type display device. Therefore, the various embodiments described above are different from the light valve type display device. It is particularly effective for a display device of the type.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an image display device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a correction characteristic at the time of brightness correction in the first embodiment.

FIG. 3 is a block diagram showing a configuration of an image display device according to a second embodiment of the present invention.

FIG. 4 is a gain amount calculation circuit 13 according to the second embodiment.
It is a figure which shows the input-output relationship of.

FIG. 5 is a block diagram showing a configuration of an image display device according to a third embodiment of the present invention.

FIG. 6 is a gain amount calculation circuit 17 according to the third embodiment.
It is a figure which shows the input-output relationship of.

[Explanation of symbols]

1 ... Input video luminance signal 2 ... Luminance detection circuit near the target pixel 3 ... Maximum value detection circuit 4 ... Minimum value detection circuit 5 ... First subtraction circuit 6 ... Second subtraction circuit 7 ... Division circuit 8 ... Multiplier circuit 9 ... Output video brightness signal 10 ... Luminance detection circuit for area around target pixel 11 ... Average luminance detection circuit 12 ... Subtraction circuit 13 ... Gain amount calculation circuit 14 ... Multiplier circuit 15 ... Luminance detection circuit for area near target pixel 16 ... Dispersion value detection circuit 17 ... Gain amount calculation circuit

Claims (18)

[Claims] 1. An image display device that dynamically corrects gradations according to the characteristics of an input video luminance signal, wherein one pixel of the input video luminance signal is sequentially set as a pixel of interest, and the pixel in the area near the pixel of interest is selected. A target pixel neighboring area feature detecting unit that sequentially detects the features of the input video luminance signal, and a correction unit that sequentially corrects the luminance level of the target pixel based on the features detected by the target pixel neighboring area feature detecting unit. An image display device provided. 2. The target pixel neighboring area feature detecting means includes a maximum value detecting means and a minimum value detecting means for detecting a maximum value and a minimum value of a brightness level in the neighboring area of the target pixel, respectively, and the correcting means. , Based on the maximum value detected by the maximum value detection means and the minimum value detected by the minimum value detection means, the maximum value and the minimum value are respectively set to the maximum value and the minimum value of the dynamic range of the signal processing system. 2. The brightness level of the pixel of interest is sequentially corrected based on a correction characteristic such as conversion.
The image display device according to. 3. The correction means divides the first subtraction circuit that subtracts the minimum value from the maximum value, the output of the first subtraction circuit as a denominator, and the maximum value of the corrected brightness as a numerator. And a second subtraction circuit that subtracts the minimum value from the luminance level of the pixel of interest, and a multiplication circuit that multiplies the output of the second subtraction circuit and the output of the division circuit. The image display device according to claim 2. 4. The target pixel neighboring area feature detecting means includes an average luminance detecting means for detecting an average luminance level in the neighboring area of the target pixel, and the correcting means includes a luminance level of the target pixel and the average luminance. The image display device according to claim 1, wherein the brightness level of the pixel of interest is sequentially corrected according to the difference from the average brightness detected by the detection means. 5. The correcting unit corrects the brightness level of the pixel of interest when the difference between the brightness level of the pixel of interest and the average brightness detected by the average brightness detecting unit is smaller than a predetermined value. If the difference between the brightness level and the average brightness is larger than the predetermined value, the brightness level of the pixel of interest is set to a brightness level further away from the average brightness according to the difference. The image display device according to claim 4, characterized in that 6. The correction unit, a subtraction circuit that subtracts the average brightness from the brightness level of the pixel of interest, a gain amount calculation circuit that calculates a gain amount based on the output of the subtraction circuit, and The image display device according to claim 5, further comprising: a multiplication circuit that multiplies a luminance level and an output of the gain amount calculation circuit. 7. The target pixel neighboring area feature detecting means includes a variance value detecting means for detecting a variance value of luminance levels in the neighboring area of the target pixel, and the correcting means is detected by the variance value detecting means. When the dispersion value is larger than a predetermined value, the brightness level of the pixel of interest is sequentially corrected so as to enhance the contrast, while the gradation is maintained when the dispersion value is smaller than the predetermined value. The image display device according to claim 1, wherein the brightness level of the pixel of interest is sequentially corrected. 8. The target pixel neighboring area feature detecting means further includes an average luminance detecting means for detecting an average luminance level in the neighboring area of the target pixel, and the correcting means has the variance value larger than a predetermined value. In this case, the luminance level of the pixel of interest is sequentially corrected so that the farther the luminance level of the pixel of interest is from the average luminance detected by the average luminance detecting means, the more the luminance level of the pixel becomes. The image display device according to claim 7, wherein: 9. The correcting means calculates a gain amount based on the dispersion value and the average luminance, and a multiplication for multiplying a luminance level of the pixel of interest by an output of the gain amount arithmetic circuit. The image display device according to claim 8, further comprising a circuit. 10. An image display method for dynamically correcting gradation according to a characteristic of an input video luminance signal, wherein one pixel of the input video luminance signal is sequentially set as a target pixel, and the pixel in the area near the target pixel is selected. A target pixel neighboring area feature detecting step of sequentially detecting features of the input video luminance signal; and a correction step of sequentially correcting the luminance level of the target pixel based on the features detected by the target pixel neighboring area feature detecting step. An image display method provided. 11. The target pixel neighboring area feature detecting step includes a maximum value detecting step and a minimum value detecting step of respectively detecting a maximum value and a minimum value of a brightness level in the neighboring area of the target pixel, and the correcting step includes , Based on the maximum value detected by the maximum value detection step and the minimum value detected by the minimum value detection step, the maximum value and the minimum value, respectively, to the maximum value and the minimum value of the dynamic range of the signal processing system. 11. The image display method according to claim 10, wherein the brightness level of the pixel of interest is sequentially corrected based on a correction characteristic such as conversion. 12. The correction step includes a first subtraction step of subtracting the minimum value from the maximum value, a denominator of a calculation result of the first subtraction step, and a maximum value of luminance after correction as a numerator. A division step of performing division, a second subtraction step of subtracting the minimum value from the luminance level of the pixel of interest, and a multiplication step of multiplying the operation result of the second subtraction step by the operation result of the division step. The image display method according to claim 11, further comprising: 13. The target pixel neighboring area feature detecting step includes an average luminance detecting step of detecting an average luminance level in the neighboring area of the target pixel, and the correcting step includes a luminance level of the target pixel and the average luminance. The image display method according to claim 10, wherein the brightness level of the pixel of interest is sequentially corrected according to the difference from the average brightness detected by the detection step. 14. The correction step, when the difference between the brightness level of the pixel of interest and the average brightness detected by the average brightness detection step is smaller than a predetermined value,
When the brightness level of the pixel of interest is not corrected and the difference between the brightness level and the average brightness is larger than the predetermined value, the brightness level is further away from the average brightness according to the difference. 14. The image display method according to claim 13, wherein the brightness level of the pixel of interest is corrected as described above. 15. The correction step comprises a subtraction step of subtracting the average brightness from the brightness level of the pixel of interest, a gain amount calculation step of calculating a gain amount based on the calculation result of the subtraction step, and the pixel of interest. 15. The image display method according to claim 14, further comprising: a multiplication step of multiplying the brightness level of 1. by the calculation result of the gain amount calculation step. 16. The target pixel neighboring area feature detecting step includes a variance value detecting step of detecting a variance value of luminance levels in the neighboring area of the target pixel, and the correcting step is detected by the variance value detecting step. When the dispersion value is larger than a predetermined value, the brightness level of the pixel of interest is sequentially corrected so as to enhance the contrast, while the gradation is maintained when the dispersion value is smaller than the predetermined value. 11. The image display method according to claim 10, further comprising sequentially correcting the brightness level of the pixel of interest. 17. The target pixel neighboring area feature detecting step further includes an average luminance detecting step of detecting an average luminance level in the neighboring area of the target pixel, and the correcting step includes the variance value being larger than a predetermined value. In this case, the luminance level of the pixel of interest is sequentially corrected so that the farther the luminance level of the pixel of interest is from the average luminance detected by the average luminance detection step, the luminance level of the pixel of interest becomes farther from the average luminance. The image display method according to claim 16, wherein: 18. The correction step multiplies a gain amount calculation step of calculating a gain amount based on the variance value and the average luminance, and a luminance level of the pixel of interest and a calculation result of the gain amount calculation step. The image display method according to claim 17, further comprising a multiplication step.