JP2008017321A - Image processing apparatus and image processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve a follow-up capability of gradation correction while keeping suitable gradation correction for a moving image. <P>SOLUTION: When detecting a luminance histogram in a moving image and changing a gradation correction property in accordance with a result of the detection, an allowable value for a change of the correction amount is dynamically generated from the luminance histogram information. Thus, the follow-up capability of gradation correction can be improved while keeping the suitable gradation correction for the moving image and motion picture display can be performed with much higher image quality. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image processing apparatus, an image processing method, and a program, and more particularly to a technique suitable for use in tone correction in a moving image.

  2. Description of the Related Art Conventionally, in a display, a television, or the like, it has been performed to automatically adjust the image quality of a displayed image by detecting the characteristics of the displayed image. As one of the methods, there is known a method of detecting a luminance histogram of an image and changing a gradation correction characteristic according to the result, and various inventions have been made so far.

  As a basic method, a luminance histogram of an image is detected, and at a level where the histogram is large, a large number of gradations are assigned by, for example, increasing the gain with respect to the input. Conversely, when the histogram is small, the gain is reduced with respect to the input so that a small number of gradations is assigned. As a result, the luminance histogram of the image after gradation correction is flattened compared to the input, and the gradation expression can be used more effectively and the image can be more easily viewed.

  Inventions that further improve this method have also been made. For example, in the invention disclosed in Patent Document 1, generation of gradation correction characteristics is improved by simultaneously using dynamic range information in addition to image histogram information. In the invention disclosed in Patent Document 2, image quality correction is applied to a moving image by changing the correction amount with time, thereby enabling high-quality moving images.

Japanese Patent Laid-Open No. 2002-27285 JP 2002-262303 A

  In the above-described technique, the image quality correction amount is changed temporally in order to deal with moving images. At this time, if the change amount of the correction amount is too large, a difference in the image quality between the frame images becomes large and a problem such as flickering is eliminated. However, since the limit width at this time is a constant value, there is a limit to the followability to moving images.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to improve the follow-up performance of gradation correction while maintaining appropriate gradation correction for a moving image.

The image processing apparatus according to the present invention divides the luminance level of the input image into a plurality of regions, and obtains a luminance histogram of each region for each frame, and according to the luminance histogram acquired by the histogram acquiring unit. A gradation correction characteristic generation unit that generates a gradation correction characteristic, a gradation correction unit that performs gradation correction of the input image in accordance with the gradation correction characteristic generated by the gradation correction characteristic generation unit, The amount of change between the gradation correction characteristic of the current frame generated by the gradation correction characteristic generation unit and the gradation correction characteristic of the previous frame is calculated for each luminance level region, and the amount of change is limited according to the luminance histogram. And a gradation correction characteristic change restricting means.
Another feature of the image processing apparatus of the present invention is that the luminance level of the input image is divided into a plurality of areas, and a histogram acquisition means for acquiring a luminance histogram of each area for each frame, and the histogram acquisition Gradation correction characteristic generation means for generating gradation correction characteristics according to the luminance histogram acquired by the means, and gradation correction of the input image according to the gradation correction characteristics generated by the gradation correction characteristic generation means For each luminance level region, and calculating the amount of change between the gradation correction characteristic of the current frame and the gradation correction characteristic of the previous frame generated by the gradation correction characteristic generation unit A gradation correction characteristic for calculating an allowable value of the change amount from a histogram and limiting the change amount to the allowable value when the change amount exceeds the allowable value And having a further limiting means.

An image processing method according to the present invention is an image processing method for correcting gradation of an input image, wherein the luminance level of the input image is divided into a plurality of regions, and a luminance histogram of each region is obtained for each frame. An acquisition step, a gradation correction characteristic generation step for generating a gradation correction characteristic according to the luminance histogram acquired at the histogram acquisition step, and a gradation correction characteristic generated at the gradation correction characteristic generation step. A luminance level area is used to indicate a change amount between the gradation correction step for performing gradation correction of the input image and the gradation correction characteristic of the current frame and the gradation correction characteristic of the previous frame generated in the gradation correction characteristic generation step. A gradation correction characteristic change limiting step of calculating for each and limiting the change amount according to the luminance histogram. To.
Another feature of the image processing method of the present invention is that a luminance level of an input image is divided into a plurality of areas, and a histogram acquisition step of acquiring a luminance histogram of each area for each frame, and the histogram acquisition A gradation correction characteristic generating step for generating a gradation correction characteristic according to the luminance histogram acquired in the step; and a gradation correction of the input image according to the gradation correction characteristic generated in the gradation correction characteristic generation step. And a change amount between the gradation correction characteristic of the current frame generated in the gradation correction characteristic generation step and the gradation correction characteristic of the previous frame generated in the gradation correction characteristic generation step for each luminance level region and the luminance An allowable value of the change amount is calculated from a histogram, and when the change amount exceeds the allowable value, the change amount is calculated as the allowable value. And having a gradation correction characteristic changing limiting step of limiting the.

  A program according to the present invention causes each step of the method described above to be executed by a computer.

  According to the present invention, when a luminance histogram is detected in a moving image and the gradation correction characteristic is changed according to the result, an allowable value of the amount of change in the correction amount is dynamically generated from the luminance histogram information. As a result, it is possible to improve the follow-up performance of the gradation correction while maintaining an appropriate gradation correction for the moving image, and display a moving image with higher image quality.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. In the present embodiment, a liquid crystal display will be described as an example. FIG. 1 is a block diagram illustrating a functional configuration example inside the liquid crystal display according to the present embodiment.

  First, it is assumed that a video signal that is an NTSC video video signal is input to the video input unit 1 as a video input. In the video input unit 1, an input signal which is an analog composite signal is first digitized by A / D conversion with 720 pixels in the horizontal direction and 240 lines in the vertical direction. Next, the digitized signal is subjected to Y / C separation processing, and the Y / C separated signal is subjected to conversion processing into an RGB signal. It is output to the histogram acquisition unit 4.

  In the image adjusting unit 2, the digital image signal which is an interlaced signal is subjected to I / P conversion which doubles the number of lines to 480 lines and is made progressive. Here, as an I / P conversion method, an average value of data on the upper and lower lines of a line to be generated is used. On the other hand, for example, a method such as a so-called three-dimensional I / P conversion is used in which motion components between the preceding and following fields that are different in time and the current field are detected and data is generated using the data of the preceding and following fields. You may do it.

  Next, here, it is assumed that the number of pixels of the liquid crystal panel 9 is 1024 pixels in the horizontal direction and 768 pixels in the vertical direction. In order to match the progressive resolution of 720 pixels in the horizontal direction and 480 pixels in the vertical direction with the number of pixels of the liquid crystal panel 9, the resolution is converted.

The converted image signal is temporarily written and stored in the frame memory 3 here.
Then, the image signal stored in the frame memory 3 is read again to the image adjustment unit 2 at a timing synchronized with the driving timing of the liquid crystal panel 9. The image signal is subjected to image adjustment processing such as contrast adjustment, brightness adjustment, color adjustment, edge enhancement, and noise reduction processing in the image adjustment unit 2, and then transmitted to the gradation correction unit 7.

  On the other hand, the digital image signal is also input to the histogram acquisition unit 4. The histogram acquisition unit 4 calculates the luminance from the digital image signal data. Here, assuming that the luminance is L and X, Y, and Z are coefficients, the luminance L is calculated by the following equation (1).

Here, the coefficients X, Y, and Z are determined from the system configuration such as individual optical systems. For example, these coefficients are determined by a procedure such as measuring R, G, and B luminances when the apparatus is assembled.

  Next, the histogram acquisition unit 4 divides the luminance level into 16 regions and measures the luminance histogram H (K) of each region for each frame. Since the digital image signal is composed of 720 pixels in the horizontal direction and 240 lines in the vertical direction, the total number of pixels is 172800 pixels. Then, the number of pixels is counted for each area divided into 16, and when counting for one frame is completed, a value obtained by dividing the count number by 675 is set to H (K). An example of the result of this processing is shown in FIG. The input luminance is divided into 16 areas to obtain respective histogram values. Here, for example, it is assumed that the values are as shown in Table 1 below.

  Next, the luminance histogram H (K) data measured by the histogram acquisition unit 4 is transmitted to the gradation correction characteristic generation unit 5. The gradation correction characteristic generation unit 5 generates gradation correction characteristics by integrating the received luminance histogram H (K) data from a low input luminance area. If the gradation correction characteristic for each luminance region is γ (K), the result shown in Table 2 below is calculated from the result shown in Table 1.

  Here, by counting all 172800 pixels and dividing by 675 at the end, the total of the histogram values is H (0) + H (1) +... + H (15) = 256. As a result, γ (16) is always 256. By doing so, the number of bits of the gradation correction circuit can be fixed, and the size can be reduced.

  Note that the gradation correction characteristic γ (K) is obtained by connecting the points shown in Table 2 with straight lines. The graph is shown in FIG. In this way, in the region where the histogram is large, the gradient is increased and the gradation is stretched. Conversely, in the region where the histogram is small, the gradient is decreased and the gradation is compressed.

  In the present embodiment, the luminance histogram H (K) data is accumulated from the low input luminance region to generate the gradation correction characteristic. However, for example, a steep characteristic is provided by setting an upper limit value or a lower limit value for the integrated amount. Of course, processing such as prevention of crushing may be performed. The gradation correction characteristic γ (K) data and the luminance histogram H (K) data generated by the gradation correction characteristic generation unit 5 in this way are transmitted to the gradation correction characteristic change amount restriction unit 6.

  The gradation correction characteristic change amount limiting unit 6 stores the gradation correction characteristic γp (K) data of the previous frame. First, | Δγ (K) | = | γ (K) −γp (K) |, which is the absolute value of the amount of change between the tone correction characteristics of the current frame and the tone correction characteristics of the previous frame, is calculated. Here, it is assumed that γp (K) has a value shown in Table 3 below.

  From the results shown in Table 2 and Table 3, | Δγ (K) | is a value shown in Table 4 below.

  Next, an allowable value MAX (H (K)) of the change amount of the gradation correction characteristic is calculated from the luminance histogram H (K) data. Here, for example, MAX (X) is represented by the following formula 2.

  The relationship between X in formula (2) and MAX (X) is shown in FIG. According to the equation (2), the allowable value MAX (X) of the change amount takes the maximum value 6 when the histogram is the minimum 0, and takes the minimum value 1 when the histogram is 32 or more.

  This means that if the histogram is small, the area displayed on the screen is small. Therefore, even if the change in the gradation correction characteristic between frames is large, it is difficult to stand out. On the contrary, if the histogram is large, the display area in the screen is large. Therefore, if the change in gradation correction characteristics between frames is large, it may become noticeable and flicker. Accordingly, since it is necessary to suppress a change in gradation correction characteristics between frames, such characteristics are provided.

  In the present embodiment, the description has been given using the expression (2). However, MAX (X) has a large value when the histogram is small, and various monotonic decreasing functions that decrease as the histogram increases. It goes without saying that the formula can be applied.

Next, MAX (H (K)) is calculated from Table 1 and Equation (2).
In addition, rounding processing shall be performed after the decimal point of the calculation result. The calculation results are shown in Table 5 below.

  Here, if | Δγ (K) |> MAX (H (K)), | Δγ (K) | is changed to MAX (H (K)). In the present embodiment, from the results shown in Tables 4 and 5, K = 5, 6, 8, 9, 10, 11, 12, 13, and 14 correspond to the respective | Δγ (K) | It is changed to (H (K)). The results are shown in Table 6 below.

  Based on the results shown in Table 6, the tone correction characteristic γ (K) is updated by the following equation (3).

  From Tables 3, 6 and (3), γ (K) is the result shown in Table 7 below.

  The updated tone correction characteristic γ (K) is transmitted to the tone correction unit 7. The gradation correction unit 7 performs gradation correction on the digital image signal from the image adjustment unit 2 according to the received gradation correction characteristic γ (K). A correction value is calculated by linear interpolation calculation between 16 points of γ (K).

  Specifically, assuming that the signal input level is Yin (having a value in the range of 0 to 255) and the corrected level is Yout (having a value in the range of 0 to 255), the following equation 4 To calculate Yout.

  In the present embodiment, the correction value is calculated by linear interpolation calculation as shown in Equation (4), but it goes without saying that various other interpolation methods can be applied. Then, Yout is transmitted to the panel drive signal generator 8. The panel drive signal generation unit 8 generates a panel drive signal synchronized with the received image signal, and outputs the image signal and the panel drive signal to the liquid crystal panel 9. Then, an image signal is formed on the liquid crystal panel 9.

  As described above, in the present embodiment, when a luminance histogram is detected in a moving image and the gradation correction characteristic is changed according to the result, an allowable value of the change amount of the correction amount is dynamically generated from the luminance histogram information. I did it. As a result, it is possible to improve the follow-up performance of the gradation correction while maintaining an appropriate gradation correction for the moving image, and display a moving image with higher image quality.

(Second Embodiment)
Hereinafter, this embodiment will be described. In this embodiment, a portable liquid crystal display will be described as an example. In this apparatus, a moving image stored in a memory or a hard disk in the apparatus is subjected to image processing by a built-in microcontroller (not shown) and reproduced on a liquid crystal screen. The video playback process performed by the microcontroller will be described below. Note that the functional configuration in this embodiment is the same as that in FIG. 1, and thus the description of the functional configuration is omitted.

  First, the microcontroller reads out the compressed video from the frame memory 3 or the like and performs a decoding process. Next, resolution conversion is performed to match the size to be displayed on the liquid crystal panel 9. Note that the display size is determined by the menu setting on the screen, so that the magnification is set according to the value and enlarged or reduced. Next, each image adjustment process such as contrast adjustment, brightness adjustment, color adjustment, edge enhancement, and noise reduction process is performed. Then, gradation correction processing is performed.

FIG. 5 is a flowchart showing an example of the gradation correction processing procedure in the present embodiment. Note that the details of the processing are the same as those in the first embodiment, and thus detailed description thereof is omitted.
First, in step S501, gradation correction processing is started. Next, in step S502, the luminance level is divided into a plurality of regions, and the luminance histogram H (K) of each region is measured for each frame.

In step S503, the luminance correction characteristics are generated by integrating the luminance histogram H (K) data from the low input luminance region. Next, in step S504, a change amount Δγ (K) between the gradation correction characteristic of the current frame and the gradation correction characteristic of the previous frame is calculated.
In step S505, an allowable value MAX (H (K)) of the change amount of the gradation correction characteristic is calculated from the luminance histogram H (K) data and compared with | Δγ (K) |. If | Δγ (K) |> MAX (H (K)) as a result of this comparison, the process proceeds to step S506. On the other hand, as a result of the comparison in step S505, if not, the process proceeds to step S507. In step S507, | Δγ (K) | is changed to MAX (H (K)), and the gradation correction characteristic γ (K) is updated.

  In step S508, tone correction is performed on the image signal using the updated tone correction characteristic γ (K). In step S509, the tone correction process is terminated. Then, an image signal is formed on the liquid crystal panel 9 for the image subjected to the gradation correction processing.

  As described above, in the present embodiment, it is possible to improve the follow-up performance of gradation correction while maintaining appropriate gradation correction for a moving image, and display a moving image with higher image quality.

(Other embodiments according to the present invention)
Each means constituting the image processing apparatus and each step of the image processing method in the embodiment of the present invention described above can be realized by operating a program stored in a RAM or ROM of a computer. This program and a computer-readable recording medium recording the program are included in the present invention.

  Further, the present invention can be implemented as, for example, a system, apparatus, method, program, or recording medium. Specifically, the present invention may be applied to a system including a plurality of devices. The present invention may be applied to an apparatus composed of a single device.

  In the present invention, a software program (in the embodiment, a program corresponding to the flowchart shown in FIG. 5) for realizing the functions of the above-described embodiments is directly or remotely supplied to the system or apparatus. This includes the case where the system or the computer of the apparatus is also achieved by reading and executing the supplied program code.

  Accordingly, since the functions of the present invention are implemented by computer, the program code installed in the computer also implements the present invention. In other words, the present invention includes a computer program itself for realizing the functional processing of the present invention.

  In that case, as long as it has the function of a program, it may be in the form of object code, a program executed by an interpreter, script data supplied to the OS, or the like.

  Examples of the recording medium for supplying the program include a floppy (registered trademark) disk, a hard disk, an optical disk, and a magneto-optical disk. Further, there are MO, CD-ROM, CD-R, CD-RW, magnetic tape, nonvolatile memory card, ROM, DVD (DVD-ROM, DVD-R) and the like.

  As another program supply method, there is a method of connecting to a homepage on the Internet using a browser of a client computer. The computer program itself of the present invention or a compressed file including an automatic installation function can be downloaded from the homepage by downloading it to a recording medium such as a hard disk.

  It can also be realized by dividing the program code constituting the program of the present invention into a plurality of files and downloading each file from a different homepage. That is, a WWW server that allows a plurality of users to download a program file for realizing the functional processing of the present invention on a computer is also included in the present invention.

  As another method, the program of the present invention is encrypted, stored in a recording medium such as a CD-ROM, distributed to users, and encrypted from a homepage via the Internet to users who have cleared predetermined conditions. Download the key information to be solved. It is also possible to execute the encrypted program by using the key information and install the program on a computer.

  Further, the functions of the above-described embodiments are realized by the computer executing the read program. Furthermore, based on the instructions of the program, an OS or the like running on the computer performs part or all of the actual processing, and the functions of the above-described embodiments can be realized by the processing.

  As another method, the program read from the recording medium is first written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer. Then, based on the instructions of the program, the CPU or the like provided in the function expansion board or function expansion unit performs part or all of the actual processing, and the functions of the above-described embodiments are also realized by the processing.

It is a block diagram which shows the function structural example inside the liquid crystal display in the 1st Embodiment of this invention. It is a figure which shows an example of the brightness | luminance histogram in the 1st Embodiment of this invention. It is a figure which shows an example of the gradation correction characteristic in the 1st Embodiment of this invention. It is a figure which shows an example of the allowable value of the variation | change_quantity of the gradation correction characteristic in the 1st Embodiment of this invention. It is a flowchart which shows an example of the gradation correction process sequence in the 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image input part 2 Image adjustment part 3 Frame memory 4 Histogram acquisition part 5 Gradation correction characteristic production | generation part 6 Gradation correction characteristic change amount restriction | limiting part 7 Gradation correction part 8 Panel drive signal generation part 9 Liquid crystal panel

Claims (8)

Histogram acquisition means for dividing the luminance level of the input image into a plurality of areas and acquiring a luminance histogram of each area for each frame;
Gradation correction characteristic generation means for generating gradation correction characteristics in accordance with the luminance histogram acquired by the histogram acquisition means;
Gradation correction means for performing gradation correction of the input image in accordance with the gradation correction characteristic generated by the gradation correction characteristic generation means;
A change amount between the gradation correction characteristic of the current frame and the gradation correction characteristic of the previous frame generated by the gradation correction characteristic generation unit is calculated for each luminance level region, and the change amount is calculated according to the luminance histogram. An image processing apparatus comprising a gradation correction characteristic change restricting means for restricting.   The image processing apparatus according to claim 1, wherein the gradation correction characteristic change limiting unit limits the change amount to a small value as the value of the luminance histogram increases. Histogram acquisition means for dividing the luminance level of the input image into a plurality of areas and acquiring a luminance histogram of each area for each frame;
Gradation correction characteristic generation means for generating gradation correction characteristics in accordance with the luminance histogram acquired by the histogram acquisition means;
Gradation correction means for performing gradation correction of the input image in accordance with the gradation correction characteristic generated by the gradation correction characteristic generation means;
A change amount between the gradation correction characteristic of the current frame and the gradation correction characteristic of the previous frame generated by the gradation correction characteristic generation unit is calculated for each luminance level region, and the allowable value of the change amount is calculated from the luminance histogram. An image processing apparatus comprising: gradation correction characteristic change limiting means for limiting the change amount to the allowable value when the change amount exceeds the allowable value.   The image processing apparatus according to claim 3, wherein the allowable value of the change amount is a monotone decreasing function. An image processing method for correcting gradation of an input image,
A histogram acquisition step of dividing the luminance level of the input image into a plurality of regions and acquiring a luminance histogram of each region for each frame;
A gradation correction characteristic generation step for generating a gradation correction characteristic according to the luminance histogram acquired in the histogram acquisition step;
A gradation correction step for performing gradation correction of the input image in accordance with the gradation correction characteristic generated in the gradation correction characteristic generation step;
A change amount between the gradation correction characteristic of the current frame and the gradation correction characteristic of the previous frame generated in the gradation correction characteristic generation step is calculated for each luminance level region, and the change amount is calculated according to the luminance histogram. An image processing method comprising: a gradation correction characteristic change limiting step for limiting.   6. The image processing method according to claim 5, wherein, in the gradation correction characteristic change limiting step, the change amount is limited to a small value as the value of the luminance histogram increases. A histogram acquisition step of dividing the luminance level of the input image into a plurality of areas and acquiring a luminance histogram of each area for each frame;
A gradation correction characteristic generation step for generating a gradation correction characteristic according to the luminance histogram acquired in the histogram acquisition step;
A gradation correction step for performing gradation correction of the input image in accordance with the gradation correction characteristic generated in the gradation correction characteristic generation step;
A change amount between the gradation correction characteristic of the current frame and the gradation correction characteristic of the previous frame generated in the gradation correction characteristic generation step is calculated for each luminance level region, and the allowable value of the change amount is calculated from the luminance histogram. And a gradation correction characteristic change limiting step for limiting the change amount to the allowable value when the change amount exceeds the allowable value.   A program that causes a computer to execute each step of the method according to claim 5 or 7.

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