KR100843817B1 - Tone correcting apparatus, mobile terminal, image capturing apparatus, mobile phone, and tone correcting method - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for correcting the gradation of a digitized image and is used in portable terminal equipment and the like. When the conventional image gradation correction technique is applied to backlight correction, there is a limit in improving local contrast in bright areas or dark areas. In the present invention, the block timing generator 102 divides one screen into a plurality of blocks, and the average luminance calculator 103 calculates an average luminance level in units of blocks designated by the member 102. The unit correction amount calculating unit 104 calculates the direction and correction amount of the correction from the average luminance level in blocks, and the pixel unit correction amount calculating unit 105 interpolates the correction amount in blocks by the correction amount in each pixel unit in the block. The gradation converter 107 reads the final correction amount from the gradation conversion table 108 and performs gradation conversion using the correction amount in units of pixels and the luminance data of the pixel read out from the storage unit 106 as addresses.

Description

Gradation correction device, mobile terminal device, imaging device, mobile phone and gradation correction method {TONE CORRECTING APPARATUS, MOBILE TERMINAL, IMAGE CAPTURING APPARATUS, MOBILE PHONE, AND TONE CORRECTING METHOD}

The present invention relates to a technique for correcting the gradation of a digitized image.

In the prior art for correcting the gradation of an image, a luminance value or a density value of each pixel is calculated over the entire screen of the input image, and the same partitioned into pixels having the same gradation value or divided into sections smaller than the quantization number of the gradation. The "histogram equalization method" which generally produces a histogram indicating the frequency of appearance of pixels included in a section and performs a gradation correction process for optimizing the shape of the created histogram over the entire screen is generally well known (e.g., non-patent). See Document 1). By using the histogram equalization method of correcting the gradation of the image using this histogram, when the gradation in the screen is at an arbitrary level, the gradation characteristics of the entire screen can be improved by optimizing the distribution of the gradations.

Moreover, the technique which applied such a "histogram equalization method" to the backlight correction is also proposed (for example, refer patent document 1 and patent document 2). In these techniques, the backlight state is determined based on the histogram of the entire screen, and gradation correction is performed so as to be close to the optimum histogram.

On the other hand, a technique using a "local contrast correction method" that divides the inside of the screen into a plurality of blocks instead of the entire screen and corrects local contrast, which is a local contrast, based on the average luminance value in the divided blocks, is also proposed. (For example, refer patent document 3). By using this "local contrast correction method" and using the gradient O'Brien effect, which causes illusions due to the characteristics of the human eye when the contour has a luminance gradient, It is possible to expand the dynamic range pseudo-intentionally.

(Patent Document 1) Japanese Unexamined Patent Publication No. 2003-69825

(Patent Document 2) Japanese Unexamined Patent Publication No. 2003-299107

(Patent Document 3) Japanese Unexamined Patent Publication No. Hei 9-65252

(Non-Patent Document 1) ANIL K. JAIN, "Fundamentals of Digital Image Processing", Prentice-Hall International, Inc. Pub. 1989, pp.241-244

However, when the "histogram equalization method" or "local contrast correction method", which is a conventional technique for correcting the gradation of the image described above, is applied to backlight correction as it is, there is a limit to improving local contrast in a bright area or a dark area. There is a problem that occurs. The reason for this point is described in detail below.

That is, in the conventional technique using the "histogram equalization method", since the same gradation correction curve is used throughout the entire screen, as long as the slope of the gradation correction curve does not have a negative value, or Unless a discontinuous gradation correction curve is used, the vertical relationship of gradation levels does not change in one screen. For example, as shown in FIG. 10, when the histogram of the input image is concentrated in the vicinity of the specific gradation, respectively, the gradation correction is performed using the "histogram equalization method". It has the same distribution as the solid line. That is, the histogram 601 of the low luminance region becomes a wider gradation distribution 611 after conversion, and the local contrast in the low luminance region increases. Similarly, the histogram 602 of the high luminance region also becomes wider gradation distribution 612 after the conversion, so that the local contrast in the high luminance region is increased. However, all of the above prior arts are such that the histogram 621 of the low luminance region and the histogram 622 of the high luminance region, as shown in Fig. 12, cause the inversion of the vertical relationship of the gradation levels in some gradations, respectively. It was impossible to do the conversion. Therefore, when the dark part of the bright area in one screen is brighter than the bright part of the other dark area in the same screen, the upper and lower relations of the gradation levels are preserved even after correction. The dark side of the bright area in one screen was either brighter or rounded to the same as the other dark areas in the same screen. For this reason, there exists a limit of the correction amount between the dark part of the bright area and the dark part of the dark area, and a limit is inevitably generated when the local contrast in the bright area in the screen or in the dark area in the screen is improved.

In addition, in the conventional technique using the "local contrast correction method", although there may be an inversion phenomenon of the up-down relationship of the gradation level depending on the place, in order to make the effect of the local contrast correction over the entire gradation appear, the average luminance of the local region is Since it acts to maintain a value to an arbitrary degree, the backlight correction effect as whole bright area or whole dark area has a limit. For example, when the bright area or the dark area is continuous over an area exceeding the size of the divided block or the predetermined size of the divided block size determined according to the filter shape of the block unit, the continuous The gradation level is maintained even after correction for the average luminance level of the entire bright or dark region, and since the average luminance level after the correction does not change significantly compared to before the correction, the contrast of the local region is improved, but the whole or dark region is improved. There was a limit to the backlight correction effect as a whole region.

In addition, since the conventional technique using the "local contrast correction method" brings about the effect of local contrast correction over the entire gradation, when the correction method is applied to backlight correction, it remains in a dark area or a bright area as it is. In order to increase the correction effect, the local contrast of the block of the halftone level, which is not the original purpose, is also raised, so that the local contrast can be improved only to the extent that the halftone level is not overcorrected.

This invention is made | formed in order to solve the above-mentioned subject, The objective is to make it possible to further improve local contrast in a bright area | region or a dark area | region at the time of backlight correction.

A subject of the present invention is a gradation correction device for performing gradation correction after dividing an inside of one screen of a digital image into a plurality of local areas, the average of obtaining an average luminance for each local area over the one screen of the digital image. A luminance calculator, a correction amount calculator for calculating a correction amount for each local area by the average luminance of each local area, an interpolation unit for interpolating from the correction amount for each local area to the correction amount for each pixel unit, and the local Preliminarily prepared based on the magnitude of the correction amount for each region and the correction amount corresponding to the median value of the entire luminance gradation level, or the magnitude of the correction amount for each pixel unit and the correction amount corresponding to the median value of the overall luminance gradation level One gradation conversion function is selected from a plurality of gradation conversion functions, and the correction amount and image for each local area are selected. And either one of the correction amount of each pixel by the parameter, characterized in that it includes parts of gradation conversion performed by the tone correction for correcting the gradation conversion function is selected the the brightness of each pixel.

The subject matter of the present invention exhibits the effects of 1) to 3) described below.

1) After the screen is divided into a plurality of local regions (for example, blocks), the amount of change from the average luminance level of the local region to the corrected luminance level is controlled by the average luminance level of the local region. While improving the above-mentioned, there is an effect that a good gradation correction result can be obtained as a whole even in a portion where the same level of gradation level, such as a bright area or a dark area, is widely continuous in area.

2) Since the average luminance level of each local area is controlled to be raised when the average luminance level of the local area is low, even in the entire area where the dark area is continuously continuous, good overall gray level correction results are obtained. There is an effect that can be obtained.

3) Since the average luminance level of each local area is controlled to be lowered when the average luminance level of the local area is high, even in the entire area where the bright area is continuously continuous, good overall gray level correction results are obtained. There is an effect that can be obtained.

The objects, features, aspects, and advantages of the present invention will become apparent from the following detailed description and the accompanying drawings.

1 is a block diagram showing a configuration example of a gradation correction device according to a first embodiment of the present invention;

2 is a diagram illustrating block division of an image;

3 is a diagram illustrating control of a correction amount based on a block average luminance value;

4 is a diagram showing a form of interpolation for obtaining a correction amount for each pixel;

5 is a diagram illustrating a gray scale conversion curve in a low luminance region;

6 is a diagram illustrating a gray scale conversion curve in a high luminance region;

7 is a flowchart illustrating a gradation correction method according to Embodiment 1 of the present invention;

8 is a block diagram showing a configuration example of a gradation correction device according to a second embodiment of the present invention;

9 is a flowchart illustrating a gradation correction method according to a second embodiment of the present invention;

10 is a diagram showing a histogram of an input image;

11 is a diagram showing a histogram of an image after conversion;

12 is a diagram showing a histogram of an image after conversion;

13 is a block diagram showing a configuration example of a gradation correction device according to a third embodiment of the present invention;

14 is a diagram showing a mapping curve according to a third embodiment of the present invention;

15 is a diagram illustrating a mapping curve of straight lines.

(Example 1)

The characteristic point of this embodiment is that after dividing the screen into a plurality of blocks, the amount of change from the average luminance level of each local region divided as a block to the luminance level after the correction is controlled by the average luminance level of the local region. Is in. In particular, the feature of this embodiment is that the average brightness level of each local area is controlled to be raised when the average brightness level of the local area is relatively lower than the median value of the entire brightness gradation level. On the contrary, the feature of the present embodiment lies in that the average brightness level of each local area is controlled to decrease when the average brightness level of the local area is relatively higher than the median value of the entire brightness gradation level. In addition, the characteristic point of this embodiment is that (1) when the average luminance level of the local region is relatively lower than the median value of the overall luminance gradation level, the correction amount in the luminance correction of the local region is greatly controlled, and (2) the average luminance. Even when the level is higher than the median of the entire luminance gradation levels, the amount of correction in the luminance correction of the local region is largely controlled, and (3) when the average luminance level of the local region is medium (about the entire luminance gradation level), The point of control is to reduce the amount of correction in the luminance correction of the local area. Alternatively, in the present embodiment, when the average luminance level of the local region is lower than the median of all luminance gradation levels, the amount of correction in the luminance correction of the local region is increased, and when the average luminance level is medium, the luminance correction of the local region is medium. The amount of correction is reduced, and when the average luminance level is higher than the median of all luminance gradation levels, the amount of correction in the luminance correction of the local area is controlled to be about medium. EMBODIMENT OF THE INVENTION Hereinafter, the characteristic point of this embodiment is described in detail based on an accompanying drawing.

1 is a block diagram showing a configuration or a functional part of a gradation correction device according to the present embodiment. In Fig. 1, the digital image data input to the gradation correction device is input to the correction amount calculation unit 101 and the storage unit 106. The correction amount calculation unit 101 performs a block unit (local area unit) processing under the control of the nested block timing generation unit 102. First, (1) the average brightness calculator 103 calculates an average brightness value in units of blocks from the input image data. Next, (2) the block unit correction amount calculating unit 104 calculates a correction amount in block units from the input average luminance value in block units. (3) The pixel unit correction amount calculating section 105 calculates the correction amount in units of pixels from the input block unit correction amount. In other words, the pixel unit correction amount calculation unit 105 functions as an "interpolation unit" which interpolates from the correction amount for each block unit to the correction amount based on the pixel unit.

The gray level conversion unit 107 uses the correction amount input from the pixel unit correction amount calculation unit 105 and the conversion table value of the gray level conversion table 108 based on the control signal output from the block timing generation unit 102. Then, the same member 107 performs gradation conversion on the image data (luminance value data) read out from the storage unit 106.

Next, the detailed operation of each processing block will be described. First, the storage unit 106 will be described. Since the delay amount by one or several block lines occurs as the correction amount calculation unit 101 as a whole, the storage unit 106 is usually configured with a line memory that generates delays of equivalent one to several block lines. If a delay in units of frames occurs on the correction amount calculating unit 101 side, the storage unit 106 also includes a frame memory that generates delays in units of equivalent frames.

On the other hand, with respect to the image data input into the correction amount calculation unit 101, for each block number generated by the block timing generation unit 102, the average luminance calculation unit 103 performs an average luminance value in units of blocks ('average average luminance in blocks). (Also called '). If the image data format is not set to the luminance / color difference format when the image data is input to the average luminance calculating section 103, it is necessary to perform format conversion to the luminance / color difference format before obtaining the average luminance. . In that case, a block or a functional unit for performing such a format conversion is provided in the previous step of the correction amount calculation unit 101. On the other hand, if the input image data is used in the RGB format, the average brightness calculator 103 may determine the average value of RGB pseudoly as an "average brightness value in units of blocks", but in the following description, After the digital image data is converted into the luminance / color difference format in advance, it is assumed that the digital image data is input into the correction amount calculation unit 101.

In addition, the block timing generator 102, 1) When the digital image input into the correction amount calculation unit 101 is a television video signal or an imaging signal of a digital camera module, each member is synchronized with the synchronization signal of the image signal. The first to fourth control signals for controlling the processing of (103, 104, 105, 107) are output. In contrast, 2) a digital image to be input to the correction amount calculating unit 101 is already stored in an arbitrary memory (not shown), and the digital image is read by the CPU (not shown), and the correction amount calculating unit 101 In the case of inputting into the, the block timing generating unit 102 controls the processing of the respective members 103, 104, 105, and 107 in synchronization with the read start clock of the memory of the CPU. Output a control signal.

Here, a block for dividing one screen, which is designated by an instruction (first control signal) of the block timing generator 102, will be described with reference to FIG. 2 is a diagram illustrating block division of an image. In FIG. 2, reference numeral 501 denotes the entirety of one screen, and the entirety of one screen 501 is divided into a plurality of blocks by a boundary line 502 extending vertically and horizontally. When performing backlight correction, for example, if there are considerably bright areas and considerably dark areas in the input image, the block 503 included in the bright areas in the image and the block 504 included in the dark areas in the image are 1; It is present in the entire screen 501.

The average luminance calculation unit 103 calculates the average luminance value in units of blocks by accumulating and adding the luminance value of the input image data in the same block area and finally dividing by the number of pixels in the block. Here, for the sake of simplicity of division, the number of pixels of powers of 2 in both vertical and horizontal directions is usually used for the block size. Since the block 503 in FIG. 2 is a bright area, the average luminance value of each block 503 obtained by the average luminance calculator 103 becomes a relatively high value. On the contrary, since the block 504 in FIG. 2 is a dark area, the average luminance value of each block 504 obtained by the average luminance calculation unit 103 becomes a relatively low value.

In addition, the "pixel number information" in the said process object block (the block number is designated by the said 1st control signal) of the said member 103 is 1) for each block, when it is variable information. "Pixel number information" is applied to both members 102 and 103 from the CPU (not shown). On the other hand, when 2) it is a fixed value, the fixed "pixel number information" is applied to both members 102; , 103).

The average luminance value in units of blocks obtained by the average luminance calculator 103 is input to the block unit correction amount calculator 104. The block unit correction amount calculating unit (also referred to simply as the 'compensation amount calculating unit') 104 is performed in units of blocks in accordance with the timing (process start timing indicated by the second control signal) generated by the block timing generating unit 102. The direction of correction and the amount of correction are calculated. The correction amount calculation method is as follows. That is, when the average luminance value of any block (unit) to be processed in one screen input to the block unit correction amount calculation unit 104 is relatively lower than the median value of the entire luminance gradation levels, as shown in FIG. The unit correction amount calculation unit 104 sets a large correction amount with respect to the average luminance value of the block (unit) (in this case, sets the direction of correction to a positive value), and applies the relatively large block (unit) generated in this way. Output the correction amount for On the contrary, in the case where the average luminance value of the block unit input to the block unit correction amount calculation unit 104 is relatively higher than the median value, as shown in FIG. 3, the block unit correction amount calculation unit 104 of the block (unit) The correction amount for the average luminance value is set small (in this case, the direction of correction is set to minus), and the correction amount in the relatively small block unit thus produced is output. Here, as an example, the case where the calculation formula for controlling the correction amount by the inputted average luminance value in the block is a straight line is shown, but instead of such a straight line, a curve may be used for the correction calculation formula. However, if the control curve of the curve is used, since the throughput in the block unit correction amount calculation unit 104 is increased, the block unit correction amount calculation unit 104 usually uses a straight line or a combination of straight lines to calculate the correction. In this way, the processing operations of the correction direction and the correction amount are executed. In addition, when the "direction of correction" calculated by the block unit correction amount calculation unit 104 is set in reverse, it is necessary to reverse the setting of the correction curve (FIGS. 5 and 6) described later.

The correction amount of the block (the current processing target block designated by the first control signal) (block unit) outputted from the block unit correction amount calculation unit 104 is input to the pixel unit correction amount calculation unit 105 and the pixels in the block Interpolation is performed for each correction amount. That is, the pixel unit correction amount calculating unit 105 includes a block unit correction amount input from the block unit correction amount calculating unit 104, and the "block number" and the "in-block offset position" input together from the block timing generating unit 102. Based on the information of " the offset position in the block " is the position of each pixel belonging to the block defined by the position coordinate axis in which one of the four corners of each block is set as the origin. Correction amount ”is calculated. The interpolation form for obtaining the correction amount for each pixel at that time is shown in FIG. 4 as an example. In Fig. 4, reference numeral 221 denotes the position 225 of the "focus pixel" that is the interpolation target (the positional relationship itself with respect to the center of gravity of the block of the pixel position 225 of interest is the corresponding block to which the pixel of interest belongs. Is the correction amount of the block whose center is located at the upper left of the (left) defined in accordance with the offset position in the circuit. Similarly, reference numeral 222 is located at the upper right of the pixel of interest 225, reference numeral 223 is located at the lower left of the pixel of interest 225, and reference 224 is centered at the lower right of the pixel of interest 225. It is the correction amount of each block. The correction amount 226 at the position 225 of the pixel of interest is linearly interpolated from the correction amount in units of blocks in the surrounding four blocks using the offset position in the block input from the block timing generation unit 102. Obtained by For example, if the offset coordinate of the center position of the block to which the reference numeral 221 belongs is set to (0, 0), since the offset coordinate of the center position of the other three surrounding blocks is also defined on the basis of the offset coordinate, these 4 Based on the two offset coordinates, the copper member 105 can obtain the coefficient value of the linear interpolation, and accordingly, the copper member 105 can calculate the correction amount of the pixel of interest at the position 225. The process of calculating the correction amount by linear interpolation is performed for all the pixels of interest in the block to which the position 225 belongs. In addition, although the example of simple linear interpolation was shown here, the pixel unit correction amount calculation part 105 may use the spline interpolation, the multi-order polynomial interpolation, or the interpolation method using other curves. .

In the above description, a "block unit" that defines one block as a "local area" is employed. Instead, an integer multiple of a block size based on a block unit, or one times that integer, or an integer portion thereof May be used as one unit of the processing in the members 103 and 104. In that sense, these units at the time of dividing one screen of a digital image into a plurality are defined as "local areas". Therefore, in other words, one screen of the digital image is divided into a plurality of local areas under the designated control by the block timing generating unit 102, and then the calculation of each member 103, 104 is performed at the timing in units of local areas. It can be said.

Similarly, as a unit of the processing operation of the pixel unit correction amount calculating unit 105, the point that has been expressed as "pixel unit" so far is an integer multiple of the pixel size based on the pixel unit, or one times the integer, or an integer thereof. The integral multiple of minutes may be set to "one unit" in the processing operation of the member 105.

The correction amount for each pixel unit output from the pixel unit correction amount calculation unit 105 is input to the gradation converter 107. The gray scale conversion unit 107 is configured to read the correction amount of the pixel unit of the pixel and the correction unit 107 read out from the storage unit 106 with respect to the pixel designated by the block timing generation unit 102. By using the luminance level of the pixel as an address of the gradation conversion table section 108 prepared in advance, the luminance data after correction is obtained by reading the corresponding data from the gradation conversion table section 108. In the gradation conversion table 108, (A) when the correction amount obtained by the pixel unit correction amount calculation unit 105 is relatively higher than the median of all luminance gradation levels, the gradation of the low luminance part shown in FIG. The first conversion curve that broadens the dynamic range of the luminance unit is stored. (B) In contrast, when the correction amount determined by the pixel unit correction amount calculation unit 105 is low, for example, the gray scale of the high luminance unit shown in FIG. The second conversion curve that widens the range is stored. Here, although the gradation conversion curve of the curve as shown in FIG. 5 and FIG. 6 is illustrated, the combination of the straight lines for simplifying the calculation to suppress the circuit scale and power consumption or to improve the processing speed is used for the gradation conversion. May be applied. Alternatively, instead of the present embodiment in which the tone conversion table unit 108 is prepared in advance, the tone conversion unit 107 may be configured so as to obtain the conversion table itself by sequential calculation, or without using the conversion table. The converter 107 may be modified to perform correction by direct calculation from the input correction amount. In that sense, the gradation conversion table unit 108 may be referred to as any component, rather than an essential component. In addition, as described above, in the case of the deformation in which the graph of the correction amount shown in FIG. 3 is inverted plus and minus, such a modification also reverses the gray scale conversion characteristics of FIGS. 5 and 6, It becomes equivalent to this embodiment. The gradation conversion table section 108 is configured by, for example, a storage device or a gate circuit.

7 is a flowchart showing the principle of the gradation correction process described above. 7 shows each processing procedure in a program of software executable by a computer. First, in the average luminance calculation step 301, the average luminance value is calculated in units of blocks with respect to the input image, and in the next block unit correction amount calculation step 302, the average luminance value is calculated based on the direction of correction from the average luminance value. In the next pixel unit correction amount calculation step 303, after calculating (interpolating) the pixel correction amount from the input block unit correction amount in step 303, the final gray level conversion step 304 is calculated. The gray level conversion for each final pixel is performed using the input correction amount in pixel units.

The direction of correction and the amount of correction in units of blocks are controlled by the average luminance value in units of blocks of the input image, for example, as shown in FIG. 3. And calculation of the correction amount of a pixel unit from the correction amount of a block unit is performed by linear interpolation shown, for example in FIG. In the tone conversion step 304, for example, the tone is converted using a mapping curve as shown in Fig. 5 or 6.

At this time, when the average luminance value of any local region formed by dividing the input image into a plurality of blocks is lower than the median value of the entire luminance gradation levels as shown in block 504 shown in FIG. 2, the mapping curve shown in FIG. Is selected and used. In this case, among the all pixels in the block 504, the pixel level at which the correction amount in the pixel unit calculated in the functional unit 105 or step 303 is equal to the average luminance value 201 of the block also corresponds to the level ( The luminance level 202 corresponds to the gradation level higher than 201. Similarly, with respect to the other pixels in which the correction amount in units of pixels calculated by the functional unit 105 is near the average luminance value 201, by applying the application of FIG. 5, the gradation levels are respectively converted to higher gradation levels. In this regard, in the method disclosed in the conventional patent document 3, since the average luminance level in the block is preserved, the average luminance of the low luminance region of the image is also saved, and the entire low luminance region of the image is dark even after the gray scale conversion. It was as it was. On the other hand, in the method shown in the present embodiment, since the average luminance level in the block is also changed as described above, the low luminance region of the image is also brightly converted as a whole, thereby improving the recognition of intuitive dark portions. That is, it is possible to heighten the effect of backlight correction.

Conversely, when the average luminance value of any local region formed by dividing the input image into a plurality of blocks is as high as the block 503 shown in FIG. 2, the mapping curve shown in FIG. 6 is selected and used, and the block is selected. Of all the pixels in 503, the average luminance value 203 of the block also applies to pixels whose correction amount in units of pixels calculated in the functional unit 105 or step 303 is equal to the average luminance value 203 of the block. Is converted to the luminance level 204 corresponding to the gradation level lower than the level 203. Similarly, the gradation level near the average luminance value 203 is also converted to a lower gradation level, respectively. In this respect, in the method disclosed in the conventional patent document 3, since the average luminance level in a block is preserve | saved, the average luminance of the high luminance area | region of an image is also preserve | saved, and the high luminance area | region of an image remains bright after gradation conversion as a whole. It was. On the other hand, in the method shown in the present embodiment, since the average luminance level in the block is also changed as described above, the high luminance region of the image is also darkened as a whole, thereby improving the recognition of the intuitively bright portions. That is, it is possible to heighten the effect of backlight correction.

Here, the correction amount at the time of performing the tone correction using the mapping curves shown in Figs. 5 and 6 is that when the average luminance value of the local region formed by dividing the input image into blocks is in the middle, that is, the overall luminance tone When in the vicinity of the center of the level, the average luminance value is low, i.e., near the lower limit of the overall luminance gradation level, and when the average luminance value is high, i.e., near the upper limit of the overall luminance gradation level, so as to be smaller. Set it. By this setting, the visibility of the dark areas is greatly improved while the influence of the correction is reduced in the area of the halftone level where the original gradation level was appropriate. It is possible to obtain the effect that the visibility can be improved while reducing the subjective adverse effects.

In addition, it is more preferable to make the absolute value of the correction amount when the average luminance value is lower than the absolute value of the correction amount when the average luminance value is high. This is particularly effective when applied to backlight correction, and is particularly effective for securing a correction amount in a dark region while looking more natural with respect to a bright region such as an image of a daytime sky.

In addition, in the method shown in the present embodiment, the image is processed after partitioning the image into small regions (local regions) of a plurality of blocks as shown in FIG. Since the correction amount is independently assigned to each pixel by FIG. 7 and the mapping curve for tonal correction is independently selected for each pixel in the following tone conversion step 304 (FIG. 7), if the locations are different, Even if it is originally the same gradation level, it can be output as another gradation level after gradation conversion.

For example, with respect to the histogram of the input image, as shown in FIG. 10, when the low luminance region 601 and the high luminance region 602 are each concentrated in the vicinity of a specific gradation, the conventional histogram equalization method is used. The distribution of the solid line shown in FIG. 11 is obtained, and the histogram 611 of the low luminance region and the histogram 612 of the high luminance region after conversion do not cause the vertical relationship inversion of the gradation level in some gradations, respectively. However, in the case of using the method shown in the present embodiment, as shown in Fig. 12, the histogram 621 of the low luminance region and the histogram 622 of the high luminance region are each one of the upper and lower relations of the gradation levels at some gradations. There may be cases of reversal.

This means that the local dynamic range is further expanded in the conventional method of using a mapping curve without the same gray level inversion over the entire one screen, as compared with the case where there is no change of the order of gray levels depending on the place. In other words, by dividing one screen of an image into a plurality of blocks, the above-described series of processes are executed, so that an optimal mapping curve can be used for the low luminance region and the high luminance region of the image, so that the low luminance region of the image is obtained. In this case, the dynamic range can be expanded without being aware of the deterioration of the gradation characteristics of the high luminance region, and the dynamic range can be expanded without being aware of the deterioration of the gradation characteristics of the low luminance region for the high luminance region of the image. That is, the effect of backlight correction can be enhanced. In addition, the degree of freedom in setting the mapping curve is increased, so that additional processing for compromise in both the low luminance region and the high luminance region can be omitted.

This also means that the method shown in the present embodiment does not merely change the backlight compensation method of the entire screen using the conventional histogram equalization method to the backlight compensation process in units of blocks. In other words, if the conventional technique of detecting the backlight state in the screen and correcting the backlight state in the screen based on the histogram of the entire screen is simply changed in units of blocks, the backlight state in the block is detected to correct the backlight state in the block. . However, in the above-described manner employed by the apparatus according to the present embodiment, the backlight state in the block is not detected and the backlight state in the block is not corrected. This method corrects the backlight state between a plurality of blocks on the basis of the average luminance value in the block. Thus, the backlight backlight state of the entire screen can be corrected without creating a histogram.

In addition, according to the method shown in the present embodiment, since the entire screen can be corrected simply by using the information of the local area one by one, there is no need to wait until the entire processing of one screen is completed. It is possible to perform real-time processing without a frame delay by only using a line memory of the extent to which a block is included or a line memory of about 2 to 3 times that of a block is contained without requiring a frame memory in.

As described above, the screen is divided into a plurality of blocks, and when the average luminance level of the local region divided into blocks is low, the amount of correction in luminance correction of the local region is increased. Since the correction amount in the luminance correction is made small, the visibility of the dark region can be improved while reducing the effect of the correction in the region of the halftone level where the original gradation level was appropriate.

In addition, the screen is divided into a plurality of blocks, and when the average luminance level of the local region divided into blocks is low, the amount of correction in the luminance correction of the local region is increased. When the average luminance level is medium, the luminance correction of the local region is made. Since the correction amount in the region is small and the average luminance level is high, the correction amount in the luminance correction of the local region is increased, so that the effect of the correction is small in the region of the halftone level where the original gradation level was appropriate. The visibility of dark areas and bright areas can be improved.

Alternatively, the screen is divided into a plurality of blocks, and when the average luminance level of the local region divided into blocks is low, the amount of correction in the luminance correction of the local region is increased, and when the average luminance level is medium, the luminance correction of the local region is medium. In the case where the correction amount is small and the average luminance level is high, the correction amount in the luminance correction of the local region may be set to about medium. At this time, in the area of the halftone level where the original gradation level was appropriate, the effect of correction is reduced, the visibility of the dark area is greatly improved, and in the bright area, the visibility is reduced while the subjective adverse effect of the human due to the decrease in brightness is reduced. There is an advantage that it can also be improved.

(Example 2)

The characteristic point of this embodiment is that the amount of change from the average luminance level of the local area to the luminance level after correction is also controlled by the average color difference vector of the local area. The present embodiment also has a feature point in that the amount of change from the average luminance level of the local area to the luminance level after correction is controlled so as to be small when the average color difference vector of the local area is approximately around the skin color. Hereinafter, the characteristic point of this embodiment is explained in full detail based on an accompanying drawing.

8 is a block diagram showing the block configuration of the gradation correction device according to the present embodiment. The difference of the structure of FIG. 8 from the structure of FIG. 1 is only each member 109 and 110 in FIG. 8, The other components are the same as the corresponding component in FIG.

In Fig. 8, the image data input to the gradation correction device is input to the correction amount calculation unit 101A and the storage unit 106. In the correction amount calculation unit 101A, the block timing generation unit 102 performs block-by-block processing. First, in the average luminance calculation unit 103, an average luminance value in units of blocks is obtained from the image data. In parallel, the average color calculation unit 109 obtains an average color in units of blocks from the image data. Next, in the block unit correction amount calculation unit 110, a block unit correction amount is obtained from the average luminance value and the average color in the unit of blocks. Further, in the pixel unit correction amount calculating unit 105, the pixel unit correction amount is obtained from the block unit correction amount. In the tone conversion unit 107, the tone conversion is performed on the image data read out from the storage unit 106 using the correction amount from the pixel unit correction amount calculating unit 105 and the tone conversion table 108.

Next, the detailed operation of each processing block will be described. First, the storage unit 106 will be described. Since the delay amount by one or several block lines occurs in the correction amount calculation unit 101A as a whole, the storage unit 106 is usually constituted by a line memory which generates a delay of equivalent one to several block lines. If a delay in units of frames occurs in the correction amount calculation unit 101A, the storage unit 106 also includes a frame memory for generating delays in units of equivalent frames.

On the other hand, for the image data input to the correction amount calculation unit 101A, the average luminance within the block is calculated by the average luminance calculation unit 103 for each block number generated by the block timing generation unit 102. Similarly, in the average color calculator 109, the average color in the block is obtained. If the image data format is not in the luminance / color difference format when the image data is input to the average luminance calculating section 103, format conversion is performed in the luminance / color difference format before obtaining the average luminance and the average color. If the RGB format is used as it is, the average value of RGB may be used pseudo-wise as the luminance value, but in the following description, it is assumed that image data has been input in the luminance / color difference format in advance.

Here, a block generated by the block timing generator 102 will be described with reference to FIG. 2. In Fig. 2, reference numeral 501 denotes an entire screen, and the entirety of one screen 501 is divided into a plurality of blocks by the boundary line 502. In FIG. When performing backlight correction, for example, when there are considerably bright areas and dark areas in the input image, there are blocks 503 included in the bright areas in the image and blocks 504 included in the dark areas in the image. .

The average brightness calculator 103 calculates the average brightness in the block by accumulating and adding the brightness value of the input image data in the same block area and finally dividing by the number of pixels in the block. Here, for the sake of simplification of division, usually, the number of pixels of power of 2 in both vertical and horizontal directions is often used as the block size. Since the block 503 in FIG. 2 is a bright area, the average luminance value output from the average luminance calculator 103 becomes a high value. In addition, since the block 504 in FIG. 2 is a dark area, the average luminance value output from the average luminance calculation part 103 becomes a low value.

The average color calculator 109 calculates the average color in the block by accumulating and adding the color of the input image data in the same block area and finally dividing by the number of pixels in the block. Here, for the sake of simplicity of division, that is, the number of pixels of powers of 2 in both vertical and horizontal directions is often used as the block size. As color data for obtaining the average color, the color difference in the luminance / color difference format is usually used. When the luminance and color difference format is, for example, Y, Cb and Cr, the average value for each of Cb and Cr is obtained using two components of Cb and Cr, and a color vector composed of two components of the average value of Cb and the average value of Cr obtained. Outputs However, hereinafter, this color vector will be referred to simply as the average color.

Here, when only the components of a specific color, such as skin color, are used as the color information, the scalar amount of the difference between the specific color and the average color in the block is obtained in advance, so that a specific color degree is used instead of the color vector. May be output as a scalar value. In addition, the difference is not determined after obtaining the average color in the block, but more precisely, for example, the difference between the specific color and the color of the pixel is determined in pixel units, and finally, the average of the difference value is determined to determine the difference value. You may output as a scalar value of a color grade. A scalar value of a specific color degree is also referred to simply as an average color in the following similar to the color vector.

Here, only the color difference is used to obtain the average color. However, in the case where only a light skin color is used, for example, the average color including luminance information may also be obtained using both the color difference and the luminance. Since the correction unit calculates the correction amount using both information of the average luminance obtained from the luminance and the average color obtained from the color difference, the block unit correction amount calculating unit 110 at the later stage. ), The luminance information and the color difference information may be synthesized. However, when it is better to combine the luminance information and the color difference information in pixel units in advance, the average color calculator 109 uses both the color difference and the luminance to obtain luminance. The average color, which also contains information, is obtained in advance.

The average luminance value in the block determined by the average luminance calculator 103 and the average color obtained by the average color calculator 109 are input to the block unit correction amount calculator 110. The block unit correction amount calculation unit 110 calculates a correction amount in units of blocks at the timing specified by the block timing generation unit 102. When the intra-block average luminance value input to the block unit correction amount calculation unit 110 is low, as shown in FIG. 3, the correction amount output from the block unit correction amount calculation unit 110 is increased. On the contrary, when the average intra-block luminance value input to the block unit correction amount calculation unit 110 is high, as shown in FIG. 3, the correction amount output from the block unit correction amount calculation unit 110 is reduced. Here, although FIG. 3 shows the case where the calculation formula for controlling the correction amount according to the inputted average luminance value in the block is a straight line, this straight line may be a curve. However, if the control curve of the curve is used, since the throughput is increased, the control is usually performed by a straight line or a combination of straight lines. In addition, when the direction of correction is set in reverse here, it is necessary to also reverse the correction curve mentioned later.

On the other hand, when the average color input from the average color calculator 109 is about skin color, the correction amount output from the block unit correction amount calculator 110 is made small as in the case of the luminance average value. On the contrary, when the average color input from the average color calculator 109 is separated from the skin color on the chromaticity diagram, the correction amount output from the block unit correction amount calculator 110 is increased. This calculation formula may also be a straight line, a combination of straight lines, or a curve, but since the throughput increases when a control curve of a curve is used, the control is usually performed by a straight line or a combination of straight lines.

The block unit correction amount output from the block unit correction amount calculator 110 is input to the pixel unit correction amount calculator 105. In the pixel unit correction amount calculation unit 105, the block unit correction amount calculation unit 110 inputs a block unit correction amount, a block number input from the block timing generation unit 102, and an intra-block offset position. Calculate the correction amount. 4 shows a form of interpolation for obtaining the correction amount for each pixel. Reference numeral 221 denotes a correction amount of the block where the center of gravity is located at the upper left of the pixel position 225 of interest. Similarly, reference numeral 222 is at the upper right of the pixel of interest 225, reference numeral 223 is at the lower left of pixel of interest 225, and reference 224 is at the lower right of pixel of interest 225, respectively. The correction amount of the located block. When obtaining the correction amount 226 at the pixel position 225 of interest, it is calculated | required by linear interpolation using the in-block offset position input from the block timing generation part 102 from the correction amount of four surrounding blocks. Although examples of simple linear interpolation are shown here, spline interpolation, multi-order polynomial interpolation, or other interpolation methods using curves may be used. In addition, although expressed in block units here, one unit may be an integer multiple of a block size, an integer multiple of an integer number, or an integer multiple of an integer number based on a block unit. Similarly, the viscosity expressed in pixel units, an integer multiple of the pixel size based on the pixel unit, an integer multiple of the integer portion, or an integer multiple of the integer portion may be one unit.

The correction amount in units of pixels output from the pixel unit correction amount calculating unit 105 is input to the gray scale conversion unit 107. The gray scale conversion unit 107 reads the correction amount in units of pixels and the luminance level of the pixel read out from the storage unit 106 as an address of the gray scale conversion table 108 prepared in advance, thereby obtaining data after correction. have. In the gradation conversion table 108, when the correction amount is high, for example, a conversion curve for increasing the gradation of the low luminance part shown in FIG. 5 to broaden the dynamic range of the low luminance part is stored. The conversion curve which raises the tonality of the high luminance part to show and widens the dynamic range of the high luminance part is memorize | stored. Here, although the gray scale conversion curve of the curve is shown in Figs. 5 and 6, a combination of straight lines may be used to simplify the calculation to suppress the circuit scale and power consumption, or to improve the processing speed. In addition, although the example which prepares a conversion table beforehand was shown here, you may be comprised so that a conversion table may be calculated | required by sequential calculation, and you may correct | amend by direct calculation directly from a correction amount, without using a conversion table. In addition, when the graph of the correction amount shown in FIG. 3 is positively reversed, it becomes equivalent by also inverting the characteristic of FIG. 5 and FIG.

9 is a flowchart showing the principle of gradation correction processing according to the present embodiment. Only the following steps 305 and 302 are different from the processing in the flowchart of FIG. That is, in the average brightness and average color calculation step 305, the average brightness value and the average color are calculated in units of blocks with respect to the input image, and in the block unit correction amount calculation step 302, the average brightness value and the average color are calculated. From the correction amount in the input block unit, and in the gradation conversion step 304, the correction amount in the input pixel unit is calculated. Gradation conversion is performed using.

The correction amount in units of blocks is controlled by the average luminance value in units of blocks of the input image as shown in FIG. 3, and is also controlled by the average color in units of the blocks as well. When the correction amount in units of pixels is calculated from the correction amount in units of blocks, linear interpolation shown in FIG. 4 is used.

In the gradation conversion step 304, when performing gradation conversion, for example, a mapping curve as shown in Figs. 5 and 6 is used. At this time, when the average luminance value of each local area formed by dividing the input image into a plurality of blocks is as low as the block 504 shown in FIG. 2, the mapping curve shown in FIG. 5 is used, and an arbitrary pixel unit. When the correction amount of is equal to the average luminance value of the block to which the pixel belongs, the average luminance value 201 of the block is converted to the level of the luminance value 202 having a higher gradation level. Similarly, the gradation levels near the average luminance value are also converted to higher gradation levels, respectively.

In the method disclosed in the conventional patent document 3, since the average luminance level in a block is preserve | saved, the average luminance of the low luminance area | region of an image is also preserve | saved, and as a whole, the low luminance area | region of an image remained dark even after gradation conversion.

On the other hand, in the method shown in the present embodiment, the average luminance level in the block is also changed, so that the whole low luminance region of the image is also brightly converted, thereby improving the recognition of intuitive dark portions. That is, the effect of backlight correction can be enhanced.

On the contrary, even when the average luminance value of the local region formed by dividing the input image into blocks is relatively high as in block 503 shown in FIG. 2, the mapping curve shown in FIG. 6 is used, and the average luminance value 203 of the block is used. Is converted to the level of the luminance value 204 having a gradation level lower than that level. Similarly, the gradation levels near the average luminance value are also converted to lower gradation levels, respectively.

In the method described in the conventional patent document 3, since the average luminance level in a block is preserve | saved, the average luminance of the high luminance area | region of an image is also preserve | saved with it, and as a whole the high luminance area | region of an image remained bright even after gradation conversion.

On the other hand, in the method shown in the present embodiment, the average luminance level in the block is also changed, so that the entire high luminance region of the image is also darkened, thereby improving the recognition of the intuitively bright portions. That is, the effect of backlight correction can be enhanced.

Here, the correction amount at the time of performing correction using the mapping curve shown in FIG. 5 and FIG. 6 is the mean when the average luminance value of the area | region which divided the input image into blocks is about the middle, ie, the center of all luminance gradation levels. In the vicinity, the average luminance value is set to be smaller than when the average luminance value is low, i.e., near the lower limit of the entire luminance gradation level, and when the average luminance value is high, ie, when the average luminance value is near the upper limit of the overall luminance gradation level. As a result, in the region of the halftone level where the original gradation level was appropriate, the effect of correction is made small while the visibility of the dark region is greatly improved, and the visibility is also improved while reducing the subjective adverse effects of human beings due to the decrease in luminance in the bright region. It is said to be able to do it.

Further, it is more preferable to set the absolute value of the correction amount when the average luminance value is lower than the absolute value of the correction amount when the average luminance value is high. This is particularly effective when applied to backlight correction, and is particularly effective for securing a correction amount in a dark region while looking more natural with respect to a bright region such as an image of a daytime sky.

In addition, the method shown in this embodiment divides an image into small areas of a plurality of blocks, as shown in Fig. 2, and performs the processing. Further, the correction amount is calculated independently for each pixel by the pixel unit correction amount calculation step 303. Since the mapping curve for gradation correction is selected for each pixel independently in the subsequent gradation conversion step 304 in the subsequent gradation conversion step 304, even if the location is different, even if it is the same gradation level originally, it can be output as another gradation level after gradation conversion. have.

For example, when the histogram of the input image is concentrated in the vicinity of the specific gradation, respectively, as shown in FIG. 10, when the low luminance region and the high luminance region are concentrated, the same distribution as the solid line shown in FIG. 11 when the conventional histogram equalization method is used. When the histogram 611 of the low luminance region and the histogram 612 of the high luminance region after conversion did not cause the inversion of the vertical relationship of the gradation levels in some gradations, respectively, the figure shown in FIG. As shown in Fig. 12, the histogram 621 of the low luminance region and the histogram 622 of the high luminance region may cause inversion of the vertical relationship of the gradation levels in some gradations, respectively.

This means that the local dynamic range is further expanded in the conventional method of using a mapping curve without the same gray level inversion over the entire one screen, as compared with the case where there is no change of the order of gray levels depending on the place. In other words, by dividing the image into blocks and processing them, an optimal mapping curve can be used for the low luminance region and the high luminance region of the image, so that the low luminance region of the image is aware of deterioration of the gradation characteristics of the high luminance region. It is possible to expand the dynamic range without increasing the dynamic range, and the dynamic range can be enlarged in the high luminance region of the image without being aware of the deterioration of the gradation characteristics of the low luminance region. That is, the effect of backlight correction can be enhanced. In addition, the degree of freedom in setting the mapping curve is increased, and the additional processing for the compromise between the low luminance region and the high luminance region can be omitted.

This also means that the method shown in the present embodiment does not merely change the backlight compensation method of the entire screen using the conventional histogram equalization method to the block backlight compensation process. That is, conventionally, if the backlight state in the screen is detected based on the histogram of the entire screen and the backlight state in the screen is corrected in units of blocks, the backlight state in the block is detected to correct the backlight state in the block. do. However, the method shown in this embodiment does not detect the backlight state in a block, nor does it correct the backlight state in a block. Since the method shown in this embodiment corrects the backlight state between a plurality of blocks based on the luminance average value in the block, it is possible to correct the backlight state of the entire screen without creating a histogram.

In addition, in the method shown in the present embodiment, since the entire screen can be corrected simply by using the information of the local area one by one, there is no need to wait until the entire processing of one entire screen is completed. It is possible to perform real-time processing without a frame delay by only using a line memory that includes a block or a line memory that is about twice or three times that does not require a memory.

Moreover, in the method shown in Example 1, since the color information was not used for the correction process, there was a problem that the correction was excessively applied to the specific color. In the method shown in the present embodiment, the correction amount is defined as the average color difference of the local area. Since the control is also performed by the vector, there is an effect that the subjective effect that a human feels due to the gradation correction for a region having a specific color can be controlled.

Since the subjective effect that a human feels is particularly noticeable with respect to the skin color of a person, when the average color difference vector of the local area is approximately around the skin color, if the correction amount is set to be small, even if the image contains a portrait, It is effective that the subjective effect which a human feels on a human skin burn can be reduced.

As described above, according to the present embodiment, the screen is divided into a plurality of blocks so that the amount of change from the average luminance level of the local region divided into blocks to the corrected luminance level is also controlled by the average color difference vector of the local region. Therefore, there is an advantage that the subjective influence of the human feeling due to the gradation correction can be controlled in the whole part such that the area having a specific color is continuously wide in area.

Since the screen is divided into a plurality of blocks, the amount of change from the average luminance level of the local region divided into blocks to the luminance level after correction is controlled so as to become small when the average color difference vector of the local region is approximately around the skin color. Therefore, there is an advantage that the subjective effect of the human on the human skin burn due to the gradation correction can be reduced.

(Example 3)

In Example 1, when the tone conversion unit 107 obtains the luminance data after correction from the correction amount in units of pixels, a method of performing conversion with a conversion table corresponding to the number of levels of the correction amount has been described. Conversion is performed using only two types of conversion data tables.

Fig. 13 is a block diagram showing the block configuration of the gradation correction device according to the present embodiment. The configuration of FIG. 13 is different from the configuration of FIG. 1 in the apparatus configuration of a portion for performing gradation conversion. The gray scale conversion is performed by the first tone conversion unit 107A having the first conversion table unit 108A, the second tone conversion unit 107B having the second conversion table unit 108B, and the tone interpolation unit 107C. It consists of). As shown in FIG. 14, in the 1st conversion table part 108A, the mapping curve 246 in the case where the correction amount becomes the maximum value in a positive direction is prepared previously, and the 2nd conversion table part 108B is provided. ), A mapping curve 247 is prepared in the case where the correction amount reaches a maximum value in the negative direction.

Since operations other than the gradation conversion are the same as those in the first embodiment, only the operation of the gradation conversion in the present embodiment will be described below.

In FIG. 13, the luminance level for each pixel is input from the storage unit 106 to the first gray level conversion unit 107A and the second gray level conversion unit 107B. The first tone conversion unit 107A refers to the first conversion table unit 108A and obtains an output value corresponding to 241 shown in FIG. 14. On the other hand, the second tone conversion unit 107B refers to the second conversion table unit 108B to obtain an output value corresponding to the reference numeral 242 shown in FIG. 14. The gradation interpolation unit 107C which has received these two outputs interpolates the gradation according to the correction amount by performing a weighted average with the correction amount of the pixel unit output from the pixel unit correction amount calculation unit 105. An output level corresponding to 243 is obtained.

In this method, a conversion table adapted to the gradation characteristics of the system can be used. Since the conversion tables are reduced to two types, the circuit size or program size can be reduced.

Although described in the first embodiment, a combination of straight lines may be used for the gray level conversion in order to simplify the calculation to suppress the circuit scale and power consumption, or to improve the processing speed, instead of the gray level conversion curve of the curve. Alternatively, instead of preparing the gradation conversion table in advance, the gradation conversion unit may be configured to obtain the conversion table by sequential calculation itself, or the gradation conversion unit is corrected by direct calculation from the input correction amount without using the conversion table. The modification may be performed to execute.

For example, by using the straight lines 256 to 259 shown in FIG. 15 as the mapping curve, the calculations are compared with the calculation of the straight lines without using the first and second conversion table portions 108A and 108B shown in FIG. The circuit size or program size can be reduced by the circuit. Specifically, after the conversion of the input data when the gray scale conversion by input is performed by the straight line 256 and the straight line 257, and the smaller output result is the maximum correction amount in the forward direction (the first gray level conversion section). Output), and similarly, the larger the conversion result by the linear expressions 258, 259 can be used as the post-conversion gradation (output of the second gradation conversion section) when the correction amount in the negative direction is maximum. In this method, the degree of freedom of the gradation characteristics is lowered by fixing the conversion table as a calculation formula, but the circuit scale or program size can be further reduced than the above method.

(Bookkeeping)

As mentioned above, although the Example of this invention was disclosed and described in detail, the above description illustrates the applicable aspect of this invention, and this invention is not limited to this. In other words, various modifications and variations to the above described aspects can be considered without departing from the scope of the present invention.

For example, the gradation correction device according to the present invention implemented in the first or second embodiment can be realized not only as a hardware device but also by software processing as function execution of each part by a program. The example of FIG. 7 or FIG. 9 of this application also shows the example of application of such a program.

The present invention can be applied to the correction processing of an image photographed in a backlit state by the imaging device, but the grayscale is partially underexposed or overexposed even when not in a backlit state. It can also be applied to an image correction process. In addition, the present invention can be applied to improve the visibility of a display device lacking contrast. Moreover, even if it does not comprise an imaging device or a display apparatus, this invention can be applied as long as it is an apparatus which correct | amends an image.

More specifically, the gradation correction device according to the present invention can be applied to digital devices such as portable terminal devices such as mobile phones and PDAs and personal computers.

Claims (17)

A block timing generator for controlling timing in local area units after dividing one screen of an input digital image into a plurality of local areas; An average luminance calculator for calculating an average luminance of each of the plurality of local regions with respect to the one screen of the input digital image; A correction amount calculating section for obtaining a direction and an amount of correction of each local region in luminance correction from the average luminance of each local region; An interpolation unit for interpolating the correction amount based on the pixel unit from the direction and amount of correction of the respective local regions; Gradation converter for performing gradation correction of the input digital image by using the correction amount based on the pixel unit Provided with The correction amount calculation unit, For the low luminance portion where the average luminance of each local region is lower than the center of the entire luminance gradation level, the direction and amount of correction of each local region are obtained so as to raise the luminance of the local region, Further, for the high luminance portion where the average luminance of each local region is higher than the center of the overall luminance gradation level, the direction and amount of correction of each local region are calculated so as to lower the luminance of the local region. Gradation correction device, characterized in that. A gradation correction device for performing gradation correction after dividing the inside of one screen of a digital image into a plurality of local areas, An average brightness calculator that calculates an average brightness for each of the local areas over the one screen of the digital image; A correction amount calculating section for obtaining a correction amount for each local region from the average brightness for each local region; An interpolation unit for interpolating the correction amount for each local region from the correction amount for each pixel unit; Based on the magnitude of the correction amount for each local region and the correction amount corresponding to the median value of the entire luminance gradation level, or the magnitude of the correction amount for the pixel unit and the correction amount corresponding to the median value of the overall luminance gradation level, One gradation conversion function is selected from a plurality of gradation conversion functions prepared in advance, and one of the correction amount for each local region and the correction amount for each pixel unit is used as a parameter, and the luminance for each pixel is selected by the selected gradation conversion function. Gradation conversion section for performing gradation correction Provided with The plurality of gradation conversion functions comprise a first conversion function having a function of increasing the gradation of the low luminance portion and a second conversion function having a function of increasing the gradation of the high luminance portion Gradation correction device, characterized in that. The method of claim 1, An average color calculator for calculating an average color for each of the local areas; The correction amount calculating unit calculates a luminance correction amount for each of the local areas by using the average luminance and the average color. Gradation Correction Device. The method of claim 3, wherein And the correction amount calculating unit changes a variation range due to correction when the average color is in the vicinity of a predetermined color. The method of claim 4, wherein And the specific color set in advance is a skin color. The method of claim 5, wherein And the correction amount calculating unit decreases the variation range caused by the correction when the average color is near the skin color. It has the said gradation correction apparatus in any one of Claims 1-6, The portable terminal apparatus characterized by the above-mentioned. It has the said gradation correction device in any one of Claims 1-6, The imaging device characterized by the above-mentioned. The mobile telephone which has the said imaging device of Claim 8. A dividing step of dividing the inside of one screen of the input digital image into a plurality of local regions; An average brightness calculating step of obtaining an average brightness of each local area of the plurality of local areas with respect to the one screen of the input digital image; From the average brightness of each local area, each local area in luminance correction is made to raise the brightness of the local area for a low luminance portion where the average brightness of each local area is lower than the center of the entire luminance gradation level. Calculating the direction and amount of correction of each local area so as to lower the luminance of the local area for the high luminance portion whose average brightness is higher than the center of the overall luminance gradation level. Correction amount calculating step, An interpolation step of performing interpolation from the direction and amount of correction of each local region to a correction amount based on a pixel unit; A gradation conversion step of performing gradation correction on the input digital image using the correction amount based on the pixel unit. Gray level correction method comprising a. A dividing step of dividing the inside of one screen of the digital image into a plurality of local regions; An average brightness calculation step of obtaining an average brightness for each of the local areas over the one screen of the digital image; A correction amount calculating step of obtaining a correction amount for each local region from the average luminance for each local region; An interpolation step of performing interpolation from the correction amount for each local region to the correction amount for each pixel, A plurality of previously prepared based on the magnitude of the correction amount for each local region and the correction amount corresponding to the median value of the entire luminance gradation level or the magnitude of the correction amount for each pixel unit and the correction amount corresponding to the median value of the overall luminance gradation level One gray level conversion function is selected from the gray level conversion function, and the luminance for each pixel is corrected by the selected gray level conversion function using either the correction amount for each local region or the correction amount for each pixel unit as a parameter. Transformation steps With The plurality of gradation conversion functions comprise a first conversion function having a function of increasing the gradation of the low luminance portion and a second conversion function having a function of increasing the gradation of the high luminance portion Tonal correction method characterized in that. The method of claim 10, An average color calculation step of obtaining an average color for each of the local areas; In the calculating of the correction amount, the luminance correction amount for each of the local areas is calculated using the average luminance and the average color. Gradation correction method. The method of claim 12, The step of calculating the amount of correction is characterized in that, when the average color is approximately in the vicinity of the skin color, the variance caused by the correction is reduced. delete delete delete delete

Images