JP4318573B2 - Luminance data correction apparatus and luminance data correction method - Google Patents

Description

  The present invention relates to correction of image data input from a video camera device or the like, and more particularly to an apparatus and method for correcting luminance data.

  Input / output conversion characteristic curves (relationship between input and output conversion) when displaying images on a display device that uses a plasma display panel (PDP) or liquid crystal display panel (LCD (Liquid Crystal Display) panel) as the display panel Many video signal correction circuits that perform correction (for example, gamma correction) of an input video signal with correction data corresponding to (conversion curve representing) are disclosed.

  Japanese Patent Laid-Open No. 2000-287104 (Patent Document 1) discloses a video signal correction circuit that performs correction for increasing the resolution of a video for M% (for example, 90%) of the entire frequency distribution of luminance levels of an input video signal. Is disclosed. This video signal correction circuit is a video signal correction circuit that corrects an input video signal with correction data corresponding to an input / output conversion characteristic curve, and detects a frequency distribution of luminance levels based on the input video signal. A luminance level for detecting luminance levels a1 and a2 at both ends of a distribution region that occupies M% (0 <M <100) of the entire frequency distribution based on the frequency number of luminance levels detected by the detection unit and the histogram detection unit Correction data corresponding to the input / output conversion characteristic curve that maximizes the slope between the luminance levels a1 and a2 for the plurality of luminance levels a1 and a2 is stored in advance and detected by the luminance level detection unit The correction data storage unit from which the corresponding correction data is read out using the luminance levels a1 and a2 as addresses, and the correction data read out from the correction data storage unit are input. And a picture quality correcting unit that corrects the image signal.

According to this video signal correction circuit, a histogram detection unit, a luminance level detection unit, a correction data storage unit, and an image quality correction unit are provided, and a frequency distribution of luminance levels is detected based on an input video signal. Based on the frequency number, luminance levels a1 and a2 at both ends of the distribution region occupying M% (for example, 90%) of the entire frequency distribution are detected, and the detected luminance levels a1 and a2 are used as addresses from the correction data storage unit. Corresponding correction data is read out, and the input video signal is corrected according to the input / output conversion characteristic curve corresponding to the correction data to become an output video signal. For this reason, it is possible to perform correction based on the luminance levels a1 and a2 at both ends of the distribution area that occupies M% of the entire frequency distribution, and in particular, correction to increase the video resolution of the input video signal having a narrow distribution area. be able to. As a result, it is possible to perform correction for increasing the resolution of both a dark image and a bright image on the entire screen.
JP 2000-287104 A

  However, this video signal correction circuit cannot perform good luminance correction processing for the following image data. In this video signal correction circuit, the luminance levels at both ends of the distribution area occupying 90% of the entire frequency distribution are detected, and processing is performed while paying attention to data within the range. At this time, the luminance correction processing is performed on data in the range of 90% even if the luminance distribution in the histogram is not one peak value as in the normal distribution but has two peak values. Therefore, the luminance correction is performed in a state where the luminance peaks are dispersed, and there is a case where the correction of the portion where the luminance distribution is concentrated is not as expected.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a luminance data correction apparatus and luminance data correction method capable of accurately performing luminance correction regardless of the form of the luminance distribution. Is to provide.

  According to a first aspect of the present invention, there is provided a luminance data correction apparatus, a unit for calculating a frequency distribution of luminance levels based on an input image signal, a unit for storing a threshold for the frequency frequency of the frequency distribution, Centering on the maximum point of the distribution, means for calculating a luminance value on the dark region side having a frequency frequency equal to or higher than the threshold value, and a luminance value on the bright region side having a frequency equal to or higher than the threshold value; A first luminance region from the side to the luminance value on the dark region side, a second luminance region from the luminance value on the dark region side to the luminance value on the bright region side, and a third from the luminance value on the bright region side And a correction means for correcting the luminance separately.

  According to the first invention, the luminance value on the dark region side and the luminance value on the bright region side having a frequency equal to or higher than a predetermined threshold value are obtained around the maximum value of the frequency in the luminance distribution. At this time, even if there are a plurality of peaks, the maximum value is determined as one, so that one luminance value on the dark region side and one luminance value on the bright region side are determined. Based on the determined luminance value, a first luminance region, a second luminance region, and a third luminance region are defined. The second luminance region defined in this way is a region having a high frequency in the luminance distribution. For example, in this second luminance region, if the brighter portion is corrected to be brighter and the darker portion is darker, the luminance can be sharpened in the region where the luminance distribution is concentrated. As a result, it is possible to provide a luminance data correction apparatus capable of accurately correcting the luminance regardless of the form of the luminance distribution.

  In the luminance data correction apparatus according to the second invention, in addition to the configuration of the first invention, the correction means includes means for correcting the luminance so that the corrected luminance is continuous in the three luminance regions. .

  According to the second aspect of the present invention, luminance data that can realize continuous luminance correction in any of the first luminance region (dark region), the second luminance region (intermediate region), and the third luminance region (bright region). A correction device can be provided.

  In the luminance data correction apparatus according to the third invention, in addition to the configuration of the first or second invention, the correction means includes a linear first correction line for correcting the luminance to be dark in the first region, A third linear correction line in which luminance is corrected brightly in the third area, and a second correction line in which the first correction line and the third correction line are linearly connected in the second area. Means for correcting the luminance by the three correction lines.

  According to the third invention, the first luminance region is corrected so as to be darker, and the second luminance region is corrected so that the bright part is brighter and the darker part is darker. In the luminance region 3, the correction is performed so that it becomes brighter. Accordingly, it is possible to provide a luminance data correction apparatus that can appropriately correct the luminance in a region where the luminance distribution is concentrated, and that does not cause reversal of the brightness of the image because continuous correction lines are used.

  A luminance data correction method according to a fourth aspect of the present invention includes a step of calculating a frequency distribution of luminance levels based on an input image signal, a step of preparing a threshold for the frequency frequency of the frequency distribution in advance, and a maximum of the frequency distribution A step of calculating a luminance value on a dark area side having a frequency frequency equal to or higher than a threshold and a luminance value on a bright area side having a frequency equal to or higher than the threshold from the dark luminance side, A first luminance region up to the luminance value on the side, a second luminance region from the luminance value on the dark region side to the luminance value on the bright region side, and a third luminance region from the luminance value on the bright region side. And a correction step of correcting the luminance.

  According to the fourth invention, the luminance value on the dark region side and the luminance value on the bright region side having a frequency equal to or higher than a predetermined threshold value are obtained around the maximum value of the frequency in the luminance distribution. At this time, even if there are a plurality of peaks, the maximum value is determined as one, so that one luminance value on the dark region side and one luminance value on the bright region side are determined. Based on the determined luminance value, a first luminance region, a second luminance region, and a third luminance region are defined. The second luminance region defined in this way is a region having a high frequency in the luminance distribution. For example, in this second luminance region, if the brighter portion is corrected to be brighter and the darker portion is darker, the luminance can be sharpened in the region where the luminance distribution is concentrated. As a result, it is possible to provide a luminance data correction method capable of accurately correcting the luminance regardless of the form of the luminance distribution.

  In the luminance data correction method according to the fifth invention, in addition to the configuration of the fourth invention, the correction step includes a step of correcting the luminance so that the corrected luminance is continuous in the three luminance regions.

  According to the fifth aspect of the present invention, luminance data that can realize continuous luminance correction in any of the first luminance region (dark region), the second luminance region (intermediate region), and the third luminance region (bright region). A correction method can be provided.

  In the luminance data correction method according to the sixth aspect of the invention, in addition to the configuration of the fourth or fifth aspect of the invention, the correction step includes a linear first correction line in which the luminance is corrected to be dark in the first region, A third linear correction line in which luminance is corrected brightly in the third area, and a second correction line in which the first correction line and the third correction line are linearly connected in the second area. The step of correcting the luminance by the three correction lines is included.

  According to the sixth aspect of the invention, the first luminance region is corrected to be darker, and the second luminance region is corrected to be brighter and the darker portion darker. In the luminance region 3, the correction is performed so that it becomes brighter. As a result, it is possible to provide a luminance data correction method in which luminance can be corrected appropriately in a region where the luminance distribution is concentrated, and a continuous correction line is used, so that no reversal of the brightness of the image occurs.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the same parts are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

  With reference to FIG. 1, a control block of the image processing apparatus according to the present embodiment will be described.

  As shown in FIG. 1, the image processing apparatus 100 is connected to a video signal input unit 110 to which a video signal is input from an external video camera device or the like, and a video signal input unit 110 to create a simple histogram of luminance data. A simple histogram creation unit 120 that receives the video signal and the brightness correction unit 130 that corrects the luminance of the video signal and the brightness correction unit 130 to perform image data compression processing. A JPEG (Joint Photographic coding Experts Group) processing unit 140 and a video signal output unit 150 connected to the luminance correction unit 130 and outputting image data whose luminance has been corrected to an external monitor or the like are included. Further, the compressed image signal is output from the JPEG processing unit 140 to an external computer or the like.

  The simple histogram creation unit 120 and the luminance correction unit 130 are connected to a CPU (Central Processing Unit) 200. The CPU 200 also controls the JPEG processing unit 140.

  The biggest feature of the image processing apparatus 100 according to the embodiment of the present invention is that a simple histogram representing a frequency distribution of luminance is created for a video signal input via the video signal input unit 110, and the simple histogram Based on this correction line, a correction line for correcting the luminance is created, and the luminance correction unit 130 corrects the image data of the video signal based on the correction line. Such processing is realized by executing a program in the CPU 200. That is, the simple histogram distribution of the luminance of the image data included in the video signal is corrected. Obtain the left and right spread from the maximum luminance peak value, determine the dividing point, and based on the dividing point, expand the main part of the luminance histogram in either the dark direction or the bright direction to create a continuous histogram distribution . By doing so, sharpness in a region where the luminance is concentrated in the luminance histogram can be more clearly given. Hereinafter, this characteristic function will be described in detail.

  A control structure of a program executed by CPU 200 in FIG. 1 will be described with reference to FIG.

  In step (hereinafter, step is abbreviated as S) 100, CPU 200 acquires a simple histogram created from input video data from simple histogram creation unit 120. In S200, CPU 200 calculates intersections H (1) and H (2) with a predetermined threshold value in the acquired simple histogram. At this time, the intersection on the dark area side is defined as an intersection H (1), and the intersection on the bright area side is defined as an intersection H (2).

  In S300, CPU 200 calculates a luminance correction curve having intersections H (1) and H (2) as inflection points. At this time, it may be a straight line instead of a curved line. In particular, digital signal processing can be simplified by using a straight line. In S400, CPU 200 determines intersections H (1) and H (2), the slope and intercept of the brightness correction line in the maximum area, the slope and intercept of the brightness correction line in the intermediate area, and the slope and intercept of the brightness correction line in the minimum area. Is output to the luminance correction unit 130.

  An operation related to luminance correction in the image processing apparatus according to the present embodiment based on the above-described structure and flowchart will be described.

  First, FIG. 3 shows a diagram representing image data to be subjected to luminance correction of image data processing apparatus 100 according to the present embodiment.

  As shown in FIG. 3, this image data is data of 640 pixels × 480 pixels called VGA (Video Graphics Array) data. This image data is divided into 16 pixels × 16 pixels. At this time, pixel blocks of 16 pixels × 16 pixels are arranged in 40 columns in the horizontal direction and 30 rows in the vertical direction. Luminance data at the intersection (shown by black circles in FIG. 3) of the pixel block of 16 pixels × 16 pixels is obtained, and a simple histogram representing the luminance distribution of the luminance data is created by the simple histogram creation unit 120. That is, the distribution of luminance data at a total of 1200 intersections of 40 in the horizontal direction and 30 in the vertical direction is expressed as a frequency by a simple histogram.

  FIG. 4 shows a simple histogram created by the simple histogram creation unit 120. In the following description, in order to shorten the processing time of the digital image data, the luminance gradation is set to 255 gradations, and further, as shown in FIG. 4, the luminance area is a discrete area of 16 gradations. It is divided into. That is, a simple histogram is created by dividing the luminance of 255 gradations into 16 parts. In the histogram shown in FIG. 4, the horizontal axis represents luminance and the vertical axis represents frequency. By adding all the frequencies in FIG. 4, 1200 data are obtained. As shown in FIG. 4, the frequency in 64/255 to 80/255 is the largest.

  The CPU 200 acquires a simple histogram as shown in FIG. 4 from the simple histogram creation unit 120 (S100). In the simple histogram, intersections H (1) and H (2) with a predetermined threshold are calculated (S200). At this time, as shown in FIG. 5, the intersection H (1) (dark region side) and the intersection H (2) with the luminance having the maximum value as the center and not less than the threshold value and the smallest frequency among them. ) (Bright area side). The threshold value is 128 in FIG. 5, but is not limited thereto. Further, in the histograms shown in FIGS. 4 and 5, if the upper limit value is set at 255 for the luminance indicating the frequency exceeding 255, the upper limit of the memory can be set, and it is necessary to secure a useless memory area. Disappears.

  A luminance correction curve (straight line) is calculated with the intersection H (1) (dark region side) and the intersection H (2) (bright region side) as inflection points (S300). At this time, a correction curve (straight line) is determined as shown in FIG. As shown in FIG. 6, in the first region up to the intersection H (1), the correction curve has the intersection H (1) to the intersection H so that the corrected luminance is darker than the original luminance. In the second region determined by (2), the original luminance is darkened on the dark region side and is corrected to be brighter than the original luminance in the bright region. In the third region, which is a region brighter than the intersection H (2), the luminance is corrected so as to be brighter than the original luminance. In FIG. 6, for example, 50% luminance is set to be reduced at the intersection H (2), and 50% luminance is set to be increased at the intersection H (2). In addition, this 50% shown in FIG. 6 is an example, and is not limited to this.

  The intersection H (1), the intersection H (2), the slope and intercept of the correction line in the third area which is the maximum area, the slope and intercept of the correction line in the second area which is the intermediate area, and the first area which is the minimum area The slope and intercept of the correction straight line in the region are output to the luminance correction unit 130 (S400). In the brightness correction unit 130, the brightness of the image data input via the simple histogram creation unit 120 is corrected according to the brightness correction line shown in FIG. The image data corrected in this way by the brightness correction unit is subjected to compressed image processing by the JPEG processing unit 140 and output to a computer or output to a video monitor or the like via the video signal output unit 150.

  As described above, the image data processing apparatus according to the present embodiment creates a simple histogram representing the luminance distribution of the image data of the original data, and sets a frequency threshold for the simple histogram. Keep it. The luminance on the dark region side and the luminance on the bright region side that are equal to or higher than the frequency threshold are calculated. The correction is determined so that the original luminance becomes brighter in the brightness on the bright region side, so that the original luminance becomes darker in the luminance on the dark region side. The intersection points are connected in a straight line, and a correction line composed of three correction lines is created. The luminance data of the image data is corrected based on such a correction straight line. As a result, the luminance on the dark region side and the luminance on the bright region side having a frequency equal to or higher than the threshold value are obtained around the local maximum value in the luminance histogram, and three luminance regions are defined. Since a linear and continuous luminance correction line is set in each of the three luminance regions, the luminance can be sharpened in the region where the luminance distribution is concentrated. Moreover, since it is linear, continuous brightness correction can be realized. As a result, it is possible to correct the luminance appropriately in the region where the luminance distribution is concentrated, and it is possible to realize correction of the luminance data that does not cause reversal of luminance due to continuous correction lines.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is a control block diagram of an image processing apparatus. It is a flowchart which shows the control structure of the program performed with CPU of FIG. It is a figure showing the image of a process target. It is a figure (the 1) showing a brightness | luminance histogram. It is a figure (the 2) showing a brightness | luminance histogram. It is a figure showing a correction line.

Explanation of symbols

  100 image processing device, 110 video signal input unit, 120 simple histogram creation unit, 130 brightness correction unit, 140 JPEG processing unit, 150 video signal output unit, 200 CPU.

Claims (6)

Means for calculating a frequency distribution of luminance levels based on an input image signal;
Means for storing a threshold for the frequency of the frequency distribution;
Means for calculating a luminance value on the dark region side having a frequency frequency equal to or higher than the threshold value and a luminance value on the bright region side having a frequency value equal to or higher than the threshold value with the local maximum point of the frequency distribution as a center. When,
A first luminance region from a dark luminance side to a luminance value on the dark region side; a second luminance region from a luminance value on the dark region side to a luminance value on the bright region side; and A brightness data correction apparatus including correction means for correcting the brightness divided into a third brightness area from the brightness value.   The brightness data correction apparatus according to claim 1, wherein the correction means includes means for correcting the brightness so that the correction brightness is continuous in three brightness areas.   The correction means includes a linear first correction line whose luminance is corrected to be dark in the first region, a linear third correction line whose luminance is corrected to be bright in the third region, And means for correcting the luminance by three correction lines, ie, a second correction line in which the first correction line and the third correction line are linearly connected in the second region. Item 3. The luminance data correction apparatus according to Item 1 or 2. Calculating a luminance level frequency distribution based on the input image signal;
Preparing in advance a threshold for the frequency of the frequency distribution;
Centering on the maximum point of the frequency distribution, calculating a luminance value on the dark region side having a frequency frequency equal to or higher than the threshold value, and a luminance value on the bright region side having a frequency equal to or higher than the threshold value;
A first luminance region from a dark luminance side to a luminance value on the dark region side; a second luminance region from a luminance value on the dark region side to a luminance value on the bright region side; and A luminance data correction method including a correction step of correcting the luminance separately from the third luminance region from the luminance value.   The luminance data correction method according to claim 4, wherein the correcting step includes a step of correcting the luminance so that the corrected luminance is continuous in the three luminance regions.   In the correction step, a linear first correction line in which luminance is corrected to be dark in the first region, a linear third correction line in which luminance is corrected to be bright in the third region, 5. The step of correcting the luminance by using three correction lines of a second correction line in which the first correction line and the third correction line are linearly connected in the second region. Or the brightness | luminance data correction method of 5.

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