WO2015129667A1

WO2015129667A1 - Image display device and image display method

Info

Publication number: WO2015129667A1
Application number: PCT/JP2015/055156
Authority: WO
Inventors: 秀紀桑島; 文隆関
Original assignee: シャープ株式会社
Priority date: 2014-02-28
Filing date: 2015-02-24
Publication date: 2015-09-03

Abstract

　The present invention provides an image display device in which the display quality of a display image is not degraded. This image display device (101) is provided with an image processing unit (4) for applying, to an input image (S1), a normalization parameter (S3) obtained from image analysis information (S2) derived by analyzing a frequency distribution or cumulative frequency distribution obtained from the number of pixels per luminance of an image obtained by filtering the input image (S1), and generating a normalized image (S4).

Description

Image display device and image display method

The present invention relates to an image display apparatus and an image display method for generating an image for display from an input image and displaying the image.

Conventionally, in an image display device that displays an image using a backlight, the maximum luminance value that can be expressed by the image display device is m (for example, in the case of a display device that expresses 8 bits, the maximum luminance value is 255). For example, when displaying input image data that does not have a value as bright as m, for example, the entire image data is normalized (converted) so that the maximum luminance value n of the input image data becomes the maximum luminance value m. As a result, the entire image data is brightened. That is, in the conventional image display device, the converted image data is generally brightened by m / n compared to the input image data. Further, at the same time as the image data is brightened, the amount of light of the backlight is reduced by the amount that the image data is brightened. That is, the brightness of the backlight is lowered by m / n.

As a result of the above combination (brightening the image data and lowering the brightness of the backlight), the power consumption of the backlight is reduced without changing the brightness of the apparent display image. This method is known and is called a so-called CABC (Contents Adaptive Backlight Control).

However, in CABC, if there is a pixel having a luminance value n ′ close to the maximum luminance value m in the input image data, the image data can hardly be converted brightly. That is, in such a case, since m / n ′ is as close to 1 as possible, the luminance of the backlight cannot be effectively reduced, and a power consumption reduction effect cannot be expected.

In order to solve the above problem, for example, in Patent Document 1, when a bright pixel having a certain luminance or more is present in the input image data, the pixel is ignored (allowed) and the entire image is displayed. CABC is applied.

Japanese Patent Registration “Patent No. 4996623 (registered on May 18, 2012)”

However, although the technique disclosed in Patent Document 1 can reduce power consumption, there is no disclosure or suggestion of a measure for suppressing a reduction in display quality of a display image. For example, since the allowable value is determined numerically based on the histogram result of the entire image, for example, even if a small number of pixels are ignored (allowed), an image whose display quality is significantly deteriorated is ignored. However, since CABC is applied uniformly, the display quality of the display image is deteriorated.

Here, an example of an image that is not preferable when CABC is applied by ignoring even a small number of pixels will be described. If the pixels around the bright and protruding pixels are dark pixels, even if CABC is applied by allowing the luminance of this pixel to be lowered, a certain degree of contrast can be secured, so the display quality will not be lowered so much. If the surrounding pixels are also bright pixels to some extent, if the brightness of the protruding bright pixels is reduced, the contrast with the surrounding pixels is significantly lowered, resulting in an adverse effect on the display quality. For example, when the entire image data is calculated using the brightness value n ′ of the protruding bright pixel as a normalized value, the image is hardly brightened as described above, and as a result, the amount of light of the backlight cannot be reduced. Normalization is performed with a luminance value n that has decreased to some extent. Then, in calculation, the luminance value n ′ of the pixel is n ′ × (m / n). However, when the maximum luminance value m is exceeded, the luminance value of the pixel becomes m (saturated. End up). Since the luminance value n is normalized, the backlight luminance is n / m, but since the luminance value n ′ of the original pixel is m, the apparent brightness of this pixel is m × n. / M = n, resulting in the pixel appearing dark.

Therefore, as described in Patent Document 1, when a display image is generated by paying attention only to a specific luminance of a pixel of the input image, there is a possibility that the display quality of the display image cannot be maintained. That is, in the technique disclosed in Patent Document 1, the display image is generated without considering the image feature (contrast presence / absence) of the input image, so that the display quality of the display image is degraded depending on the image feature. Will do.

The present invention has been made in view of the above-described problems, and an object of the present invention is to generate an image for display in consideration of image characteristics of an input image, thereby preventing image display from deteriorating the display quality of the image for display. An apparatus and an image display method are provided.

In order to solve the above problems, an image display device according to an aspect of the present invention includes a filter processing unit that performs a filtering process on an input image in an image display device that generates a display image from an input image and displays the image. An information recording unit that records in the memory unit image analysis information obtained by analyzing a frequency distribution or cumulative frequency distribution obtained from the number of pixels for each luminance in the input image filtered by the filter processing unit, and the memory unit And an image processing unit that generates the display image by applying the image analysis information recorded in the input image to the input image.

According to one aspect of the present invention, the display image is generated in consideration of the image characteristics of the input image, so that the display quality of the display image is not deteriorated.

1 is a schematic configuration block diagram of an image display apparatus according to Embodiment 1 of the present invention. It is a schematic block diagram of the image analysis part with which the image display apparatus shown in FIG. 1 is provided. It is a figure which shows an example of the digital filter used with the filter part with which the image analysis part shown in FIG. 2 is provided. It is a histogram which shows the frequency distribution which shows the relationship between the brightness | luminance in an input image, and the number of pixels. It is a histogram which shows the cumulative frequency distribution which shows the relationship between the brightness | luminance in an input image, and the number of pixels. It is a histogram which shows the cumulative frequency distribution which shows the relationship between the brightness | luminance and the number of pixels in a filter-processed input image. It is a figure which shows the example of an input image. It is a histogram which shows the cumulative frequency distribution which shows the relationship between the brightness | luminance in the input image shown in FIG. 7, and the number of pixels. It is a figure which shows an example of the digital filter used by the filter process with respect to the input image shown in FIG. It is a figure which shows the example of an image at the time of filtering the input image shown in FIG. 7 with the digital filter shown in FIG. 10 is a histogram showing a cumulative frequency distribution indicating the relationship between the luminance and the number of pixels in an image when the input image shown in FIG. 7 is filtered by the digital filter shown in FIG. 9. It is a figure which shows the example of the image which applied CABC with respect to the image at the time of filtering the input image shown in FIG. 7 with the digital filter shown in FIG. It is a figure which shows the other example of the digital filter used by the filter process with respect to the input image shown in FIG. It is a figure which shows the example of an image at the time of filtering the input image shown in FIG. 7 with the digital filter shown in FIG. It is a graph which shows the relationship between the input value of a liquid crystal display device used in the image display apparatus which concerns on Embodiment 2 of this invention, and an output value. It is a schematic block diagram of an image display device according to Embodiment 3 of the present invention. It is a figure which shows an example of the digital filter used with the filter part with which the image-analysis part shown in FIG.

Embodiment 1
An embodiment of the present invention will be described as follows.

(General description of the image display device)
FIG. 1 is a block diagram illustrating a schematic configuration of an image display apparatus 101 according to the present embodiment.

As shown in FIG. 1, the image display device 101 includes a display device 6 such as a liquid crystal display panel (LCD), a light source 7 such as a backlight, an image control of the display device 6, and a light source control of the light source 7. And a control unit 1 for controlling the whole. The control unit 1 performs parameter determination to create a normalization parameter S3 for performing appropriate light source control and image control from the image analysis unit 2 that analyzes the image of the input image S1 and the image analysis information S2 of the image analysis unit 2. The image processing unit 4 that generates the normalized image S4 by applying the normalization parameter S3 to the unit 3, and the light source control signal S5 for adjusting the luminance of the light source 7 by applying the normalization parameter S3 in the same manner And a light source control unit 5 that performs the operation.

In the image display apparatus 101 configured as described above, the input image S1 is assumed to be a YUV signal, and is processed based on the luminance component Y in particular. When the input image S1 has another signal format such as RGB, a conversion processing unit can be provided before and after the input image S1 to perform the same processing. In the present embodiment, the input image S1 is expressed by 8 bits, and 0 is the darkest signal and 255 is the brightest signal.

(Explanation of image analysis unit)
FIG. 2 is a schematic block diagram illustrating an example of the image analysis unit 2.

As shown in FIG. 2, the image analysis unit 2 performs a filter process (filter process) on the input image S1, and the input image S1 (processed input) filtered by the filter process unit 21. And an image recording information 22 for recording image analysis information S2 obtained by analyzing the frequency distribution or cumulative frequency distribution obtained from the number of pixels for each luminance in the image S1 ′) in the memory unit 23 (image analysis information recording step). The memory unit 23 is not necessarily provided in the image analysis unit 2, and may be provided outside the image analysis unit 2, outside the control unit 1, and further outside the image display device 101. Well, there are no particular restrictions on the location.

That is, the image analysis unit 2 configured as described above does not directly obtain the frequency distribution or the cumulative frequency distribution from the number of images for each luminance of the input image S1, but the processed input image S1 ′ once filtered by the filter processing unit 21. The frequency distribution and cumulative frequency distribution are obtained from the number of images for each luminance. This is a feature of the present invention.

(Digital filter)
FIG. 3 is a conceptual diagram of a 3 × 3 digital filter (low-pass filter) for filtering the input image S1 in the filter processing unit 21.

In the digital filter, the luminance value of the 3 × 3 central pixel of the input image S1 is S1 (x, y), and this luminance value S1 (x, y) is the luminance value of the calculation target pixel (target pixel). The luminance values of the eight pixels around the pixel of interest, that is, the luminance values S1 (x−1, y−1) to S1 (x + 1, y + 1) of the surrounding pixels are also used for calculating the luminance value of the pixel of interest. It is done. When the filtered input image S1 is a processed input image S1 ′, and the luminance value of the target pixel of the processed input image S1 ′ is S1 ′ (x, y), the following expression (1) is expressed. Can do. Here, F0 to F8 are the coefficients of the filter. That is, F0 is a coefficient of S1 (x-1, y-1), F1 is a coefficient of S1 (x, y-1), F2 is a coefficient of S1 (x + 1, y-1), and F3 is S1 (x-1 , Y), F4 is a coefficient of S1 (x, y) (target pixel), F5 is a coefficient of S1 (x + 1, y), F6 is a coefficient of S1 (x-1, y + 1), and F7 is S1 (x , Y + 1) and F8 is a coefficient of S1 (x + 1, y + 1).

S1 ′ (x, y) = F0 × S1 (x−1, y−1) + F1 × S1 (x, y−1)
+ F2 × S1 (x + 1, y−1) + F3 × S1 (x−1, y)
+ F4 × S1 (x, y) + F5 × S1 (x + 1, y)
+ F6 × S1 (x−1, y + 1) + F7 × S1 (x, y + 1)
+ F8 × S1 (x + 1, y + 1) (1)
By changing each filter coefficient, an appropriate filter calculation can be performed and, as a result, an appropriate image analysis result can be obtained. For example, consider the case where the filter coefficient F4 of the target pixel is 0.6 and the filter coefficients F0 to F3 and F5 to F8 of other pixels of the surrounding pixels are 0.05.

Here, when the input image S1 is an image having protruding bright pixels and clear contrast, the luminance value S1 (x, y) of the pixel of interest is close to 255, and the luminance value S1 of the surrounding pixels. (X-1, y-1) to S1 (x + 1, y + 1) are values close to zero. For example, if the luminance value S1 (x, y) of the target pixel is 240 and the luminance values S1 (x−1, y−1) to S1 (x + 1, y + 1) of the surrounding pixels are all 30, As a result of 1), the luminance value S1 ′ (x, y) after filtering of the pixel of interest is 156, which is somewhat smaller than the original luminance value.

Further, when the input image S1 is an image that protrudes and has bright pixels and the surrounding pixels are bright and the contrast is not clear, for example, the luminance value S1 (x, y) of the target pixel is 240, and the luminance of the surrounding pixels Assuming that the values S1 (x−1, y−1) to S1 (x + 1, y + 1) are all 220, the luminance value S1 ′ (x, y) after filtering of the target pixel is obtained as a result of Expression (1). 232, which is not much less than the original luminance value.

From the above two calculation examples, when such a filter coefficient is used, the higher the brightness value S1 ′ (x, y) after the filter processing of the target pixel is, the brighter the image is, but the lower the contrast is. I can judge.

In the above example, the 3 × 3 low-pass filter is used as the digital filter, but the present invention is not limited to this, and a 5 × 5 low-pass filter or a 3 × 3 high-pass filter may be used. In addition, when generating the input image S1 ′ filtered by the filter processing unit 21, a digital circuit such as a linear function (R ′ = α × R) circuit, for example, is used in addition to the digital filter as described above. It may be used.

The information recording unit 22 causes the filter processing unit 21 to store the input image S1 ′ that has been filtered using Expression (1) in the memory unit 23, and creates a frequency distribution and a cumulative frequency distribution from the input image S1 ′. From the result, image analysis information S2 described later is created. Of course, as usual, the data of the input image S1 may also be created as another frequency distribution or cumulative frequency distribution and reflected in the image analysis information S2.

(Image analysis information S2)
The creation of the image analysis information S2 will be described below. FIGS. 4 and 5 show image diagrams of a general frequency distribution and a cumulative frequency distribution in the input image S1, respectively. FIG. 6 shows an image of the cumulative frequency distribution of the processed input image S1 ′ that is the filtered input image from the cumulative frequency distribution shown in FIG. For example, since the digital filter as shown in FIG. 3 is a low-pass filter that lowers the image spatial frequency, the pixel value of the processed input image S1 ′ is an intermediate value compared to the pixel value of the input image S1. It is easy to become.

The memory unit 23 in the image analysis unit 2 stores the processed input image S1 'that has been filtered and the frequency distribution of the input image S1.

An example of how to create the frequency distribution F is shown below. First, before inputting the input image S1 for one screen, the frequency distribution memory F (0 to 255) is cleared to zero. Then, while the luminance values of all the pixels S1 'for one screen are input, the following equation (2) is calculated. Then, when all input pixels for one screen are calculated, a frequency distribution F is created. Also, the memory F is cleared to 0 before the next screen is input.

F (S1 ′ (x, y)) = F (S1 ′ (x, y)) + 1 (2)
The cumulative frequency distribution C is represented by the following formula (3). In this example, since the luminance value is 256 gradations, the maximum value of i is 255.

In any case, the frequency distribution F and the cumulative frequency distribution C may be obtained by any method. As described above, the image analysis information S2 having the image characteristics of the input image S1 is obtained by performing the filtering process and taking the frequency distribution.

The image analysis information S2 created as described above is sent to the parameter determination unit 3 at the subsequent stage.

(Normalization parameter S3)
The parameter determination unit 3 generates a normalization parameter S3 appropriate for the input image S1 from the image analysis information S2. For example, the parameter determination unit 3 sets the normalization parameter S3 low if the high numerical value is relatively small in the frequency distribution of the processed input image S1 ′, and conversely if the numerical value of the processed input image S1 ′ is high, Control is performed such that the normalization parameter S3 is set to a high value.

The normalization parameter S3 thus obtained is sent to the subsequent image processing unit 4 and the light source control unit 5.

(Display image generation processing)
In the following, the image analysis information S2 recorded in the memory unit 23 is used as a light source 7 (backlight) for irradiating the display device 6 (liquid crystal display panel) for displaying a display image generated by the image processing unit 4 from the back side. ) Will be described. Note that the description of the light amount control corresponds to the CABC technique which is a known technique, and thus the description will be simplified.

The image processing unit 4 uses the normalized parameter S3 received from the parameter determining unit 3 to create a normalized image S4 that brightens the input image S1 (image processing step).

Here, as an example, a method of creating the normalized image S4 when the normalization parameter S3 is n is shown in the following equation (4).

S4 (x, y) = (255 / n) × S1 (x, y) (4)
Note that when obtaining the normalized image S4, the calculation may be performed in consideration of not only the normalization by the above-described simple expression (4) but also a parameter peculiar to the display device 6, such as the γ characteristic of the liquid crystal.

Thus, by creating the normalized image S4 that is brighter than the input image S1, the light source control unit 5 performs control to lower the luminance of the light source 7 by the amount that is brighter than the input image S1. Here, assuming that the normalization parameter S3 is n, the luminance of the light source 7 before correcting the processed input image S1 ′ with n is Y, and the luminance of the light source 7 after correction is Y ′, the luminance Y ′ is It calculates | requires by the following formula | equation (5). Then, the light source control signal S5 output from the light source control unit 5 to the light source 7 is controlled to have the luminance Y '.

Y ′ = (n / 255) × Y (5)
As described above, by controlling the luminance Y ′, it is possible to reduce the power consumed by the light source 7 without changing the brightness of the image displayed on the image display apparatus 101.

(CABC processing control)
Depending on the input image S1, CABC processing may be performed to reduce display quality. As described above, if the input image S1 whose display quality deteriorates even if the CABC process is performed can be specified, the display quality can be prevented from being lowered by adjusting so as to reduce the effectiveness of the CABC process. In addition, when the input image S1 whose display quality deteriorates even if the CABC process is performed can be specified, the CABC process itself may not be performed.

Hereinafter, a description will be given for determining whether or not an input image is suitable for CABC processing.

7A is a diagram illustrating an example of an image S1a having gradation as the input image S1, and FIG. 7B is a diagram illustrating an example of an image S1b having a high contrast as the input image S1. An image S1b shown in FIG. 7B is an image in which the gradation of the gradient image S1a shown in FIG.

When the cumulative frequency distribution indicating the relationship between the pixels of the images S1a and S1b shown in FIGS. 7A and 7B and the luminance value is created, the results are as shown in FIGS. 8A and 8B.

As described above, the image S1a and the image S1b have exactly the same relationship between the number of pixels and the luminance value, except that the position of the image data (luminance value) is different. Accordingly, the cumulative frequency distributions shown in FIGS. 8A and 8B are the same.

By simply taking the cumulative frequency, the difference between the image S1a shown in FIG. 7A and the image S1b shown in FIG. 7B is not clear, so which is the image suitable for the CABC process? It is difficult to judge.

Therefore, as in this embodiment, after the filter processing unit 21 of the image analysis unit 2 performs the filtering process on the input image S1, the cumulative frequency distribution of the processed input image S1 'after the filtering process is created.

For example, as a filter used in the filter processing unit 21, a 3 × 3 low-pass filter shown in FIG. 3 is used, and the input image S1 is filtered by this filter. As shown in FIG. 9, the low-pass filter is set with filter coefficients F0 to F8 (FIG. 3). Here, the filter coefficient F4 (x, y) for the center pixel of interest is set to 0.6, and the filter coefficients F0 to F3 and F5 to F8 for the surrounding pixels are all set to 0.05.

10 (a) and 10 (b) are diagrams showing the high-contrast image S1b shown in FIG. 7 (b) with luminance values corresponding to pixels. FIGS. 10C to 10E are diagrams showing the gradation image S1a shown in FIG. 7A with luminance values corresponding to pixels.

Using the low-pass filter having the filter coefficient shown in FIG. 9, the image S1 shown in (a) to (e) of FIG. 10 is filtered to obtain a processed input image S1 '. The processed input image S1 'is obtained by the above equation (1). Accordingly, in the case of the image shown in FIG. 10A, the luminance value S ′ (x, y) of the center pixel of the processed input image S1 ′ is 178.7, which is the case of the image shown in FIG. The luminance value S ′ (x, y) of the central pixel of the processed input image S1 ′ is 89.75. In the case of the image shown in FIG. 10C, the luminance value of the central pixel of the processed input image S1 ′. S ′ (x, y) is 254, and in the case of the image shown in FIG. 10D, the luminance value S ′ (x, y) of the central pixel of the processed input image S1 ′ is 128, which is shown in FIG. In the case of the image shown in e), the luminance value S ′ (x, y) of the center pixel of the processed input image S1 ′ is 10. Similarly, in each image, a processed input image S1 'for each peripheral pixel is obtained.

When there are many high values in the processed input image S1 'after the filter processing, it is necessary to control so that the normalized value (value of the normalized parameter S3) at the time of CABC processing is not lowered too much. In such an image, if the normalized value at the time of CABC processing is lowered too much, the image quality deteriorates significantly.

As described above, the results of obtaining the cumulative frequency distribution of the processed input image S1 'obtained from the input image S1 are as shown in FIGS.

(A) in FIG. 11 shows a cumulative frequency distribution after the image S1a having the gradation shown in (a) in FIG. 7 is filtered. As described above, in the case of the image S1a having the gradation shown in FIG. 7A, saturation of the cumulative frequency distribution is not seen even when the low-pass filter is applied. In such a case, if the CABC process is strongly performed (the normalized value is greatly reduced), the image quality is significantly reduced. Therefore, the image S1a having the gradation shown in FIG. 7A can be said to be an image not suitable for CABC processing.

On the other hand, FIG. 11B shows a cumulative frequency distribution after the high-contrast image S1b shown in FIG. 7B is filtered. As described above, in the case of the image S1a having the gradation shown in FIG. 7B, if the low-pass filter is applied, the luminance value S ′ of the pixel of the processed input image S1 ′ becomes an intermediate value as a whole. That is, there is no high value and it is saturated with a low S1 'value. In such a case, even if the normalized value is lowered somewhat, it is difficult to cause a reduction in image quality. Therefore, the image S1b having a high contrast shown in FIG. 7B can be said to be an image suitable for CABC processing.

However, it is only an index for determining whether or not the above result is an image suitable for CABC processing.

12A and 12B, CABC processing is performed on the processed input images S1a ′ and S1b ′ obtained by performing filtering on the images S1a and S1b in FIGS. 7A and 7B, respectively. An image of when. Here, the CABC process is performed with the normalized value set to 192 for the image after the filter process.

From the image shown in FIG. 12 (a), it can be seen that the contrast is lost in the portion with a high luminance value, the image is crushed, and the image quality is significantly lowered compared to the input image S1a shown in FIG. 7 (a).

On the other hand, although the maximum luminance value is reduced to 192 from the image shown in FIG. 12B, the change in contrast is not so much seen. For the purpose of viewing, the input image S1b shown in FIG. Therefore, it can be seen that the image quality has not deteriorated so much.

From the above, according to the image display apparatus 101 according to the present embodiment, the image analysis information S2 is applied to the input image S1, thereby normalizing in consideration of the image features (contrast level, etc.) of the input image S1. By generating the rear image S4 (display image) and applying the image analysis information S2 to the light source control unit 5, a light source control signal S5 that provides a backlight light amount suitable for the generated display image is generated. Therefore, the power consumption by the backlight is reduced, and the display quality of the display image is not deteriorated.

(Filter processing: 5 × 5 low-pass filter)
In the above description, the digital filter used in the filter processing unit 21 has been described using a 3 × 3 low-pass filter, but a 5 × 5 low-pass filter may be used.

FIG. 13 shows filter coefficients of a 5 × 5 low-pass filter. Here, the filter coefficient of the center pixel (target pixel) is set to 0.4, and the filter coefficient of the peripheral pixels is set to 0.02.

When the processed input image S1 ′ in the case of good contrast shown in FIG. 14A is obtained using the 5 × 5 low-pass filter, the luminance value S1 ′ (x, y) = 143.4 of the central pixel is obtained. Thus, when the processed input image S1 ′ when there is no contrast as shown in FIG. 14B is obtained, the luminance value S1 ′ (x, y) of the center pixel is 194.4.

In the above case as well, as in the case of the 3 × 3 low-pass filter, it can be determined that the higher the obtained luminance value S1 ', the brighter and the less the contrast.

Thus, when the number of target pixels that can be processed is increased from 3 × 3 to 5 × 5, more detailed image analysis can be performed. In particular, when a display device with high resolution is used, more appropriate image analysis information can be obtained. However, if the number of target pixels that can be processed is increased, the circuit scale increases and the cost increases. Therefore, it is preferable to set the number of target pixels that can be processed by balancing the image quality finally obtained (or the image quality desired by the user) with the circuit scale. Note that the number of target pixels that can be processed may be 7 × 7 or more.

[Embodiment 2]
Another embodiment of the present invention will be described as follows. For convenience of explanation, members having the same functions as those described in the first embodiment are given the same reference numerals, and descriptions thereof are omitted.

(Γ correction)
In the present embodiment, when the display device 6 of the image display device 101 shown in the first embodiment is a liquid crystal display device (LCD), the normalized image is taken into account in consideration of the γ characteristic (γ curve) of the liquid crystal display device. An example of correcting S4 will be described.

Generally, in a liquid crystal display device, the relationship between an input value (luminance value) X and an output value (luminance value) Y is a γ curve (γ value = 2.2 or the like) indicated by a solid line in FIG. Further, an ideal relationship between the input value X and the output value Y in the display device is a straight line (γ value = 1.0) indicated by a broken line in FIG.

Therefore, in the display device 6, when the normalized image S4 output from the image processing unit 4 of the control unit 1 is an input value X, the input value X is multiplied by the γ curve shown in FIG. Correction (γ correction) for obtaining the output value Y is performed, and an image is displayed with the corrected output value Y.

From the above, since the image displayed on the display device 6 takes into account the LCD characteristics, that is, the γ characteristics, the image quality can be further improved. Therefore, according to the image display apparatus 101 according to the present embodiment, it is possible to maintain or improve image quality while reducing power consumption.

In the first and second embodiments, it is assumed that the CABC process is performed. However, the present invention is not limited to the CABC process, and can be applied to other processes. For example, the present invention can be applied to edge enhancement processing for enhancing the edge of an image. In the following third embodiment, an example in which the present invention is applied to edge enhancement processing will be described.

[Embodiment 3]
The following will describe still another embodiment of the present invention. For convenience of explanation, members having the same functions as those described in the first embodiment are given the same reference numerals, and descriptions thereof are omitted.

(General description of the image display device)
FIG. 16 is a block diagram schematically illustrating the configuration of the image display apparatus 201 according to the present embodiment.

The image display device 201 has substantially the same configuration as the image display device 101 of the first embodiment. The difference from the image display apparatus 101 is that the parameter determination unit 3 is not provided in the control unit 1 and an edge enhancement processing unit 8 is provided instead of the image processing unit 4.

Image analysis information S2 from the image analysis unit 2 is input to the edge enhancement processing unit 8. Then, the edge enhancement processing unit 8 performs edge enhancement processing on the input image S1 based on the input image analysis information S2, and outputs the image subjected to the edge enhancement processing to the display device 6 as an edge enhanced image S6. It is supposed to be.

(Filter processing: 3 × 3 high-pass filter)
The image analysis unit 2 illustrated in FIG. 16 has the same configuration as the image analysis unit 2 illustrated in FIG. 2 of the first embodiment, and includes a filter processing unit 21, an information recording unit 22, and a memory unit 23. The difference is the digital filter used in the filter processing unit 21. That is, in the first embodiment, the filter processing unit 21 uses a low-pass filter, but in the present embodiment, the edge enhancement processing unit 8 performs the edge enhancement processing in order to perform the filter processing in the image analysis unit 2. The unit 21 performs a filtering process using a high-pass filter.

FIG. 17 is a diagram showing filter coefficients in the 3 × 3 high-pass filter used in the present embodiment. Usually, in the case of the image (gradation image) without contrast shown in FIG. 7A of the first embodiment, since the edge is not clear, it is necessary to emphasize the edge strongly, but FIG. In the case of an image with good contrast, since the edge is clear, it is better to emphasize the edge weakly or not to emphasize the edge.

The edge emphasis processing unit 8 adjusts the degree of edge emphasis according to whether the input image S1 is a gradation image shown in FIG. 7A or a high contrast image shown in FIG. 7B. . A guideline for this is image analysis information S2 output from the image analysis unit 2. The image analysis information S2 includes information obtained by analyzing the cumulative frequency distribution of the processed input image S1 'filtered by the filter processing unit 21. That is, the image analysis information S2 includes information for adjusting the degree of edge enhancement of the input image S1 according to the value of the processed input image S1 '.

For example, by using a high-pass filter having a filter coefficient shown in FIG. 16, the image S1 shown in FIGS. 10A to 10E shown in the first embodiment is subjected to filter processing to obtain a processed input image S1 ′. Ask. The processed input image S1 'is obtained by the above equation (1). In the case of the image shown in FIG. 10A, the luminance value S1 ′ (x, y) of the processed input image S1 ′ is 76.35. In the case of the image shown in FIG. The luminance value S1 ′ (x, y) of S1 ′ is 38.25. In the case of the image shown in FIG. 10C, the luminance value S1 ′ (x, y) of the processed input image S1 ′ is 0. In the case of the image shown in FIG. 10D, the luminance value S1 ′ (x, y) of the processed input image S1 ′ is 0, and in the case of the image shown in FIG. 10E, the processed input image S1 ′. The luminance value S1 ′ (x, y) of the pixel is 0. Similarly, in each image, the luminance value S1 'of the processed input image S1' of each peripheral pixel is obtained.

From the above, in the image with good (high) contrast (image with many edges), the luminance value of the processed input image S1 ′ is large ((a) and (b) in FIG. 10) and the contrast is not good (low). It can be seen that in the image (image with few edges), the luminance value of the processed input image S1 ′ is small ((c) to (e) in FIG. 10).

Therefore, in the image analysis unit 2, for an image having a large luminance value of the processed input image S1 ′, information for instructing to adjust the degree of edge enhancement to a low level, an image having a small value of the processed input image S1 ′ In contrast, image analysis information S2 including information instructing to adjust the degree of edge enhancement to a high level is created.

[Example of software implementation]
The control unit 1 of the

image display apparatuses

101 and 201 may be realized by a logic circuit (hardware) formed in an integrated circuit (IC chip) or the like, or realized by software using a CPU (Central Processing Unit). May be.

In the latter case, the

image display devices

101 and 201 include a CPU that executes instructions of a program that is software that realizes each function, and a ROM (Read Only Memory) or a storage device (these are referred to as “recording media”), a RAM (Random Access Memory) for expanding the program, and the like. And the objective of this invention is achieved when a computer (or CPU) reads the said program from the said recording medium and runs it. As the recording medium, a “non-temporary tangible medium” such as a tape, a disk, a card, a semiconductor memory, a programmable logic circuit, or the like can be used. The program may be supplied to the computer via an arbitrary transmission medium (such as a communication network or a broadcast wave) that can transmit the program. The present invention can also be realized in the form of a data signal embedded in a carrier wave in which the program is embodied by electronic transmission.

[Summary]
The image display device according to the first aspect of the present invention includes a filter processing unit 21 that performs a filtering process on an input image S1, and luminance in the input image (processed input image S1 ′) that has been filtered by the filter processing unit 21. The information recording unit 22 for recording the image analysis information S2 obtained by analyzing the frequency distribution or cumulative frequency distribution obtained from the number of pixels for each memory in the memory unit 23, and the image analysis information S2 recorded in the memory unit 23 for the input image And an image processing unit 4 that generates a display image by applying to S1.

According to the above configuration, the image analysis information is information obtained by analyzing the frequency distribution or cumulative frequency distribution obtained from the number of pixels for each luminance in the input image filtered by the filter processing unit. Image features (such as the presence or absence of contrast and the presence or absence of edges) are revealed. If such image analysis information is applied to the input image to generate a display image, the generated display image is an image that takes into account the image characteristics of the input image.

Therefore, since the display image is generated in consideration of the image characteristics of the input image, as compared with the conventional case where the display image is generated by paying attention only to the specific luminance of the pixel of the input image, The display quality of the display image is not deteriorated.

The image display device according to aspect 2 of the present invention is characterized in that, in the aspect 1, the filter processing unit 21 performs a filtering process by a low-pass filter on the input image S1.

According to the above configuration, by performing the filtering process using the low-pass filter on the input image S1, the higher the contrast, the higher the luminance is, and the image having the cumulative frequency distribution saturated with the lower luminance (the processed input image). S1 ′), the lower the contrast (gradation image), the higher the luminance remains and the image (processed input image S1 ′) having a cumulative frequency distribution in which the luminance is not saturated as a whole. As described above, in an image having a cumulative frequency distribution in which high luminance disappears and is saturated at low luminance, even if the normalized value is slightly reduced, the image quality does not deteriorate, but high luminance remains and the luminance is not saturated as a whole. In an image having a cumulative frequency distribution, if the normalized value is lowered, the image quality is significantly lowered.

Therefore, by performing filter processing using a low-pass filter, it is possible to determine whether or not it is preferable to perform so-called CABC processing that lowers the normalized value, so that CABC processing can be performed appropriately. It becomes.

Examples of low-pass filters include the following 3 × 3, 5 × 5, and 7 × 7 filters.

In the image display device according to aspect 3 of the present invention, in the aspect 2, the low-pass filter calculates the luminance value of the target pixel to be processed from the luminance values of the surrounding eight pixels centered on the target pixel. The desired 3 × 3 digital filter is preferable.

In the image display device according to aspect 4 of the present invention, in the aspect 2, the low-pass filter calculates the luminance value of the target pixel to be processed from the luminance values of 24 pixels around the target pixel. The desired 5 × 5 digital filter is preferable.

In the image display device according to aspect 5 of the present invention, in the aspect 2, the low-pass filter calculates the luminance value of the target pixel to be processed from the luminance values of 48 pixels around the target pixel. A 7 × 7 digital filter to be obtained is preferable.

If the number of target pixels that can be processed is increased to 3 × 3, 5 × 5, and 7 × 7, more detailed image analysis can be performed. In particular, when a display device with high resolution is used, more appropriate image analysis information can be obtained. However, if the number of target pixels that can be processed is increased, the circuit scale increases and the cost increases. Therefore, it is preferable to set the number of target pixels that can be processed by balancing the image quality finally obtained (or the image quality desired by the user) with the circuit scale.

The image display device according to aspect 6 of the present invention is characterized in that, in aspect 1, the filter processing unit 21 performs a filtering process with a high-pass filter on the input image S1.

According to the above configuration, the input image S1 is filtered with a high-pass filter, so that the input image S1 is an image with high contrast (image with many edges) or an image with low contrast (image with few edges). Can be determined.

As a result, the edge enhancement processing is weakened for images with many edges and the edge enhancement processing is strengthened for images with few edges, so that excessive edge enhancement processing is not performed. There will be no degradation of image quality associated with processing.

The image display device according to aspect 7 of the present invention is the image display device according to aspect 2, in which the image analysis information S2 recorded in the memory unit 23 is irradiated from the back surface to the liquid crystal display panel (display device 6) that displays the display image. It is preferable to apply to the light amount control of the backlight (light source 7).

According to the above configuration, when displaying an image on the liquid crystal display panel that does not degrade the image quality even if the normalized value is lowered, control is performed so that the amount of light from the backlight is lowered by the amount that the normalized value is lowered. By doing so, power consumption by the backlight can be reduced without degrading the image quality. Specifically, the following image display device is obtained.

An image display device according to an aspect 8 of the present invention is the liquid crystal display panel (display device 6) for displaying the display image and the backlight for illuminating the liquid crystal display panel (display device 6) from the back surface in the aspect 7. (Light source 7).

An image display method according to an aspect 9 of the present invention is an image display method for generating an image for display from an input image S1 and displaying the image. An image analysis information recording step for recording in the memory unit 23 image analysis information S2 obtained by analyzing the frequency distribution or cumulative frequency distribution obtained from the number of pixels for each luminance in the input image filtered and recorded in the memory unit 23 The image analysis information S2 is applied to the input image S1 to generate an image for display, and is characterized by including an image processing step. According to said structure, there exists an effect similar to the said aspect 1. FIG.

The control unit 1 provided in the image display apparatus according to each aspect of the present invention may be realized by a computer. In this case, the control unit 1 is operated by causing the computer to operate as each unit provided in the control unit 1. The control program of the control unit 1 for realizing the above in a computer and a computer-readable recording medium on which the control program is recorded also fall within the scope of the present invention.

The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention. Furthermore, a new technical feature can be formed by combining the technical means disclosed in each embodiment.

The present invention can be suitably used for all kinds of display devices such as mobile phones, smartphones, tablet terminals, personal computers equipped with displays, televisions of various sizes, projectors, and the like.

1 control unit, 2 image analysis unit, 3 parameter determination unit, 4 image processing unit, 5 light source control unit, 6 display device (liquid crystal display panel), 7 light source (backlight), 8 edge enhancement processing unit, 21 filter processing unit , 22 information recording unit, 23 memory unit, 101 image display device, 201 image display device, S1 input image, S1 ′ processed input image, S2 image analysis information, S3 normalization parameter, S4 post-normalization image, S5 light source control Signal, image after S6 edge enhancement

Claims

In an image display device that generates a display image from an input image and displays an image,
A filter processing unit that performs a filtering process on the input image;
An information recording unit that records in a memory unit image analysis information obtained by analyzing a frequency distribution or a cumulative frequency distribution obtained from the number of pixels for each luminance in the input image filtered by the filter processing unit;
An image processing unit that generates image for display by applying the image analysis information recorded in the memory unit to the input image;
An image display device comprising:
The image display device according to claim 1, wherein the filter processing unit performs a filtering process using a low-pass filter on the input image.
3. The image display according to claim 1, wherein the image analysis information recorded in the memory unit is applied to a light amount control of a backlight that irradiates a liquid crystal display panel that displays the display image from the back side. apparatus.
A liquid crystal display panel for displaying the display image;
The image display apparatus according to claim 3, further comprising a backlight that irradiates the liquid crystal display panel from the back.
In an image display method for generating a display image from an input image and displaying the image,
A filtering process for filtering the input image;
An image analysis information recording step for recording in a memory unit image analysis information obtained by analyzing a frequency distribution or a cumulative frequency distribution obtained from the number of pixels for each luminance in the input image filtered in the filter processing step;
An image processing step of generating image for display by applying the image analysis information recorded in the memory unit to the input image;
An image display method comprising: