JPH10198801A - Picture quality improving method, edge intensity calculating method and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To emphasize both local and global contrasts and to improve the image quality by simply calculating without needing a user's judgment. SOLUTION: In this method, the mean value Vmean of an entire luminance value of an image is founed, the average value Vave of neighborhood luminance values vl to vi of each pixel of the image is found, positive pixel variable δposi is founed by multiplying a relative value of the value Vave of a positive image by a coefficient that corresponds to the ratio of the value Vmean to the value Vave , negative pixel variable δnega is founed by multiplying the relative value of the value Vave of a negative image by the coefficient, the variable δposi is corrected by adding it to the relative value of the pixel of the positive image, the variable δnega is corrected by adding it to the relative value of the pixel of the negative image, the luminance value (v) of the pixel is corrected by the logarithm of the ratio of each modified absolute value and normalizes a corrected result k (v) within the output range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a local contrast and a global contrast for an input image from an image sensor, a digital camera, or the like while emphasizing a subtle change in luminance value between a bright portion and a dark portion. And an image quality improving method, an edge strength calculating method and a device capable of simultaneously outputting the image data in accordance with the output range.

[0002]

2. Description of the Related Art Generally, in the field of visual technology involving image processing or image display, higher definition images are required.
There is a need for an image quality improvement method that converts an input image into an image with the highest possible accuracy without using a special human operation.

As this kind of image quality improvement method, there are a method of linearly converting each pixel value of an image, an exponential conversion method represented by gamma correction, and a logarithmic conversion method. When an extreme enhancement of an image is desired, there is a method of contrast enhancement of pixel values of the image by histogram flattening.

Further, according to the luminance sensitivity characteristic curve of a person,
The range is divided into several sections, a line segment approximating a curve is obtained for each section, and those line segments are combined to convert a pixel value. There is a piecewise linear conversion method (Takagi, Shimoda ( Supervision) "Image Analysis Handbook", University of Tokyo Press, 1991
Year).

[0005] Here, in the method using the linear transformation, FIG.
As shown in (1), the section of the pixel value I of the input image is divided into several sections, and by changing the slope of the line segment in each section, the dynamic range of the output is increased or decreased in a piecewise manner to emphasize the contrast. ing.

In the logarithmic conversion method, as shown in FIG. 16, the pixel value I of the input image is converted to a value that increases the entirety. As shown in the figure, since the smaller the pixel value has the larger increment, it can be understood that the contrast of the dark portion is mainly emphasized.

Further, in the method using the exponential conversion, FIG.
As shown in (1), when the exponent is smaller than 1, a conversion curve similar to logarithmic conversion is drawn, and conversion is performed to increase the pixel value as a whole. Therefore, the contrast of the dark part is enhanced. on the other hand,
If the exponent is greater than 1, the pixel value is converted to a value that reduces the pixel value as a whole, as shown in FIG. Therefore, the contrast of the bright part is enhanced.

In the method based on the piecewise linear conversion, the section is subdivided to improve the degree of approximation of the curve, so that a considerable degree of contrast enhancement is possible.

The histogram flattening method is a technique of appropriately dispersing a cluster of pixel value distributions around and performing contrast enhancement in accordance with the distribution, and is actually an enhancement method among various image enhancement methods. It is a method with a remarkable effect.

[0010] In addition to the above, as an image enhancement method excellent in resolution improvement, an image quality improvement method and apparatus in which contrast is suppressed to a certain extent in an intermediate portion having good visibility and contrast is enhanced in a bright portion and a dark portion, are particularly characteristic. Fairness 8
-21079.

[0011]

However, the above-described image quality improving method has the following problems.

The method using the linear transformation has a problem in that it has no generality because the user determines the segmentation section while visually judging each image to be processed and determines the slope in each section.

In the method based on logarithmic conversion, the contrast in a section having a small pixel value is emphasized, but there is a problem that the contrast in a section having a large pixel value is suppressed.

In the method based on the exponential conversion, it takes time and effort for the user to determine the index by judging each image. When the index is smaller than 1, the contrast of the section having a small pixel value is emphasized, but the section having a large pixel value is emphasized. There is a problem that the contrast is suppressed. When the index is larger than 1, the contrast in the section where the pixel value is large is emphasized,
There is a problem that the contrast in a section having a small pixel value is suppressed.

Further, the piecewise linear conversion method has a problem that the amount of calculation is enormous and is not realistic.

The histogram flattening method has a problem in that while the effect of enhancing the global contrast is remarkable, a relatively small local contrast indicating a change or the like within the region is suppressed.

Further, in the method described in Japanese Patent Publication No. 8-21079, a sharp image is locally obtained due to a high local contrast enhancement effect, while the global contrast tends to be reduced. .

The present invention has been made in consideration of the above-described circumstances, and enhances both local and global contrasts by simple calculations without requiring user judgment to improve image quality. An object of the present invention is to provide an improvement method, an edge strength calculation method and an apparatus.

[0019]

A first gist of the present invention will be described. The technique disclosed in Japanese Patent Publication No. 8-21079 uses an inverse S-shaped conversion to linearly correct an S-shaped response characteristic in human vision.
As described above, while the local contrast is enhanced, the global contrast tends to be reduced.

In order to improve this tendency, in the present invention, the ratio of the local brightness (the average value v _ave of the brightness in the vicinity of the pixel) to the brightness of the entire image (the average value v _mean of the entire brightness) is set. By obtaining the corresponding coefficient and emphasizing the difference between the overall brightness and the local brightness, the global contrast is improved while maintaining the local contrast.

In addition, the present invention takes into account that the receptive field in the human side suppression mechanism is substantially concentric, so that the local brightness of the image is indicated by the average value v _ave of the brightness in the vicinity of the pixel. The local contrast itself is also improved.

Next, the second gist of the present invention will be described.

In order to further enhance the global contrast in the first gist, the overall brightness of the image is reduced to the average value v of the brightness values by taking into account the light-dark adaptation mechanism.
_mean , and a correction value k (v
_mean ) is made to correspond to the intermediate value V _mid of the output range of the display system, and the linear contrast is executed so as to adapt to the output range before and after the average luminance, thereby enhancing the global contrast.

Next, the third gist of the present invention will be described.

In the above-described first gist, the change of the dark section and the change of the bright section are emphasized by using the differential equation of the inverse S-shaped conversion, so that the edge emphasizing effect in both the bright portion and the dark portion is obtained. We are improving. In addition, in the change of the section,
The maximum gradient value dv (v) between neighboring pixels is used.

Now, based on the gist of the present invention described above,
Specifically, the following solution is realized.

The invention corresponding to claim 1, the average value v _{me an,} the luminance value v of the pixels in the entire image, for each pixel of the image, the i number in the vicinity of the pixel luminance value v
An average value v _{ave of 1} to vi is obtained, and the average value v
A coefficient corresponding to the ratio between _mean and the average value v _{ave of the} neighborhood is obtained, and the coefficient is multiplied by a relative value of the average value v _ave of the neighborhood in a positive image to obtain a positive pixel variable δ _posi, and the coefficient _Is multiplied by the relative value of the average value v _ave of the neighborhood in the negative image to obtain a negative pixel variable δ
_{Finding nega} , correcting the relative value by adding the positive pixel variable δ _posi to the relative value of the luminance value of the pixel in the positive image, and the negative pixel variable δ _nega the luminance value of the pixel in the negative image In addition to this relative value, the relative value is corrected, the luminance value v of the pixel is corrected by the logarithm of the ratio of the corrected relative value, and the correction result k
This is an image quality improvement method in which (v) is normalized within the range of the output range.

According to a second aspect of the present invention, in the image quality improving method according to the first aspect, as the normalization, the correction result k (v _mean ) of the overall average value v _mean is used as the output range. _Is an image quality improvement method executed so as to correspond to the intermediate value V _mid of.

Further, according to a third aspect of the present invention, an average value v _mean of luminance values v of all pixels of an image is obtained, and for each pixel of the image, i luminance values v 1 in the vicinity of the pixel are determined. To the average value v _ave of
_mean the calculated coefficients corresponding to the ratio between the average value v _{av e} of the proximity, the determined positive pixel variable [delta] _posi multiplied by the coefficient relative value of the average value v _ave of the vicinity of a positive image, the The coefficient is multiplied by the relative value of the average value v _ave of the neighborhood in the negative image to obtain a negative pixel variable δ
_nega , the positive pixel variable δ _posi is added to the relative value of the luminance value v of the pixel in the positive image to correct this relative value, and the negative pixel variable δ _nega
Is added to the relative value of the luminance value v of the pixel in the negative image, and the relative value is corrected.
The maximum gradient value dv (v) indicating the maximum among the absolute values of the gradients along the direction is obtained, and this maximum gradient value dv (v) is divided by the correction result of the relative value in the positive image to obtain the positive image. The edge strength value is obtained, and the maximum gradient value dv (v) is divided by the correction result of the relative value in the negative image to obtain the edge strength value of the negative image. Is calculated, and the calculation result dk (v) is normalized within an output range.

[0030] Further, the invention according to claim 4 provides [a]
Image input means for inputting an image, [b] an overall average calculating means for calculating an overall average value v _mean by averaging luminance values of all pixels of the image input by the image input means;
[C] neighboring image extracting means for extracting, for each pixel of the image input by the image input means, the luminance value v of the pixel and the luminance values v1 to vi of i pixels in the vicinity thereof, [d] A neighborhood average calculation means for calculating a neighborhood average value v _ave by averaging the luminance values v1 to vi of the neighborhood pixels extracted by the neighborhood image extraction means, and [e] an overall average value calculated by the overall average calculation means v and coefficient calculating means for calculating a coefficient corresponding to the ratio of the _mean and the neighboring average calculation means near the average value v _{av e} calculated by, [f] the luminance value of the pixel extracted by the neighborhood image extracting unit v, the overall average value v _mean calculated by the overall average calculation means, the neighborhood average value v _ave calculated by the neighborhood average calculation means, and the coefficient calculated by the coefficient calculation means. A positive image pixel value variable determining means for determining the pixel value variable δ _posi of [g], the luminance value v of the pixel extracted by the neighboring image extracting means, and the overall average value v calculated by the overall average calculating means. _mean , a neighborhood average value v _ave calculated by the neighborhood average calculation unit, and a coefficient calculated by the coefficient calculation unit, based on the pixel value variation δ _nega of the negative image, a negative image pixel value variation determination unit, , [h] of each said pixel based on each determined pixel value variable [delta] _{ne ga} by pixel value variable [delta] _{po si} and the negative image pixel value variable determining means which is determined by the positive image pixel value variable determining means A pixel value correction means for correcting the luminance value v, calculating a logarithm of a ratio of each correction result to calculate a pixel correction value k (v), and [j] calculating a pixel correction value by the pixel correction means. And all of the pixel correction value k (v), the correction value maximum and minimum value calculating means for calculating the maximum value k _max and the minimum value k _min was,
[L] A pixel correction value k (v) calculated by the pixel value correction means based on the maximum value k _max and the minimum value _kmin calculated by the correction value maximum / minimum value calculation means within an output range. Pixel value normalizing means for calculating a normalized conversion value V (v) by normalizing to [m] based on the normalized conversion value V (v) of each pixel calculated by the pixel value normalizing means. An image quality improving apparatus comprising: an image output unit configured to output an entire image.

According to a fifth aspect of the present invention, there is provided the image quality improving apparatus according to the fourth aspect, wherein the pixel value normalizing means and the image output means are replaced by [a] the overall average calculating means. The obtained overall average value v _mean , the neighborhood average value v _ave calculated by the neighborhood average calculation means,
And an overall average correction value calculation unit that calculates a correction value k (v _mean ) of the overall average value v _mean based on the coefficient calculated by the coefficient calculation unit, and [b] a pixel value correction unit that calculates the correction value k (v _mean ). The pixel correction value k (v) of each pixel and the correction value k calculated by the overall average correction value calculation means.
(V _mean ), and when k (v) <k (v _mean ), the pixel correction value k (v) is set to the intermediate value V within the output range.
linearly converted to an output range section smaller than _mid , k (v)
= K (v _mean ), the pixel correction value k (v) is converted to an intermediate value V _mid of the output range, and k (v)> k (v _mean )
In the case of, the pixel correction value k (v) is linearly converted into an output range section larger than the intermediate value V _mid in the output range, thereby normalizing each pixel correction value k (v) within the output range. A pixel correction value conversion means for calculating a normalized conversion value V (v), and [c] an entire image based on the normalized conversion value V (v) of each pixel calculated by the pixel correction value conversion means. And a normalized image output means for outputting the image.

Further, the invention corresponding to claim 6 is:
[A] image input means for inputting an image, and [b] overall average calculation means for calculating an overall average value v _mean by averaging luminance values of all pixels of the image input by the image input means. [C] neighboring image extracting means for extracting, for each pixel of the image input by the image input means, the luminance value v of the pixel and the luminance values v1 to vi of i pixels in the vicinity thereof, [d] By averaging the luminance values v1 to vi of the neighboring pixels extracted by the neighboring image extracting means, a neighborhood average value v
a neighborhood average calculation means for calculating _ave , and [e] a coefficient corresponding to a ratio between the overall average value v _mean calculated by the overall average calculation means and the neighborhood average value v _ave calculated by the neighborhood average calculation means. A coefficient calculating means for calculating; [f] a luminance value v of the pixel extracted by the neighboring image extracting means, an overall average value v _mean calculated by the overall average calculating means, calculated by the neighboring average calculating means. based on the coefficient calculated by the neighboring average value v _{av e,} and said coefficient calculating means, a positive image pixel value variable determining means for determining a pixel value variable [delta] _posi positive image, by [g] said neighboring image extracting means luminance value v of the extracted the pixel, the entire overall calculated by the average calculating means averages v _mean, near the average value v _ave calculated by the neighborhood average calculating unit, and the engaging Based on the coefficient calculated by the calculating means, and a negative image pixel value variable determining means for determining a pixel value variable [delta] _nega negative image, [h] the luminance values of the neighboring pixels extracted by the neighboring image extracting unit v1 A maximum pixel gradient value calculating means for calculating the maximum gradient value dv (v) indicating the maximum among the absolute values of the gradients along the four directions of up, down, left, right, left diagonal, and right diagonal between vi; ] The pixel value variation δ _posi determined by the positive image pixel value variation determining means is added to the relative value of the luminance value v of the pixel in the positive image to correct the relative value and calculate the maximum gradient value of the neighboring pixels. Means for calculating a positive image edge strength value by dividing the maximum gradient value dv (v) calculated by the means by the correction result; The pixel value variation δ _nega determined by the image pixel value variation determining means is added to the relative value of the luminance value v of the pixel in the negative image to correct the relative value, and calculated by the neighboring pixel maximum gradient value calculating means. A negative image edge intensity value calculating means for calculating a negative image edge intensity value by dividing the maximum gradient value dv (v) thus obtained by the correction result; and [m] a positive image edge intensity value calculating means calculated by the positive image edge intensity value calculating means. The image edge intensity value and the negative image edge intensity value calculated by the negative image edge intensity value calculating means are added to each other to obtain an edge intensity value dk of the pixel.
And (n) normalizing the edge strength value dk (v) of each pixel calculated by the edge strength calculating means to be within the range of the output range. v) edge intensity normalizing means for calculating;
[O] An edge intensity calculation device comprising: an edge intensity image output unit configured to output an entire image based on the normalized conversion value dV (v) of each pixel calculated by the edge intensity normalization unit. is there.

(Operation) Therefore, the inventions corresponding to the first and fourth aspects have the following features.
By determining the overall average value v _mean of the input image without assuming in advance the distribution characteristics of the luminance value of the input image, the contrast is adapted to the distribution of the local luminance values v1 to vi. Since the degree of emphasis can be adjusted only by processing in the vicinity of each pixel, the image quality can be improved by a simple calculation without requiring the user's judgment.

According to the second and fifth aspects of the present invention, in addition to the action of the first aspect, the overall average value v
_{Since the mean} correction value k (v _mean ) is normalized by associating it with the intermediate value V _mid with good sensitivity of the output range, the local contrast and the global contrast can be enhanced simultaneously.

Further, according to the inventions corresponding to claims 3 and 6, since the edge strength is calculated after the contrast enhancement similar to the claims 1 and 4, fine objects or objects can be obtained in both the bright and dark portions. For most of the images including the structure, accurate calculation of edge strength and edge detection can be executed by simple calculation without user's judgment, and an excellent edge-enhanced image can be output. .

[0036]

Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) FIG. 1 shows a first embodiment of the present invention.
It is a block diagram showing the composition of the picture quality improvement device concerning an embodiment. This image quality improvement device includes an image input unit 1, an overall average calculation unit 2, a neighborhood image extraction unit 3, a neighborhood average calculation unit 4, a coefficient calculation unit 5, a positive image pixel value variation determination unit 6, and a negative image pixel value variation determination unit. 7, pixel value correction unit 8, pixel value correction control unit 9, pixel correction value storage unit 10, pixel correction value maximum / minimum value calculation unit 11, pixel value normalization unit 12, pixel value normalization control unit 13, pixel value normalization A conversion conversion value storage unit 14 and an image output unit 15 are provided. The data obtained by the components at the preceding stage can be used by the components at the subsequent stage.

Here, the image input section 1 is for inputting and storing an image, and is readable from the overall average calculation section 2 and the neighborhood average calculation section 3 and the like. A camera or a digital camera can be used as appropriate.

The overall average calculator 2 calculates the overall average v _mean by averaging the luminance values (pixel values) of all the pixels of the image input by the image input unit, and calculates the overall average v _mean by a coefficient. It has a function to be given to the calculation unit 5.

The neighboring image extracting unit 3 extracts, for each pixel of the image input by the image input unit 1, the luminance value v of the pixel and the luminance values v1 to vi of i pixels in the vicinity thereof. It has a function to be provided to the neighborhood average calculation unit 4.

The neighborhood average calculation section 4 calculates the neighborhood average value v _ave by averaging the luminance values v1 to vi of the neighborhood pixels extracted by the neighborhood image extraction section 3, and calculates the neighborhood average value v _ave by the coefficient calculation section. 5. It has a function of giving to the positive image pixel value variable determining unit 6 and the negative image pixel value variable determining unit 7.

The coefficient calculator 5 calculates the coefficient α of the positive image corresponding to the ratio between the overall average value v _mean received from the overall average calculator 2 and the neighborhood average value v _ave received from the neighborhood average calculator.
It is for calculating the coefficient alpha _nega of _posi and negative images, positive image pixel value coefficient alpha _posi variable determining unit 6
, And a function of providing the coefficient α _nega to the negative image pixel value variation determining unit 7.

The positive image pixel value variation determining unit 6 determines the luminance value v of the pixel extracted by the neighboring image extracting unit 5,
The overall average value v _mean calculated by the overall average calculation unit 2,
The neighborhood average value v _ave calculated by the neighborhood average calculation unit 4,
The pixel value variation δ _posi of the positive image is determined based on the coefficient α _posi calculated by the coefficient calculation unit 5 and has a function of giving the pixel value variation δ _posi to the pixel value correction unit 8.

The negative image pixel value variable determining unit 7 determines the luminance value v of the pixel extracted by the neighborhood image extracting unit 3,
The overall average value v _mean calculated by the overall average calculation unit 2,
The neighborhood average value v _ave calculated by the neighborhood average calculation unit 4,
The pixel value variation δ _nega of the negative image is determined based on the coefficient α _nega calculated by the coefficient calculation unit 5 and has a function of giving the pixel value variation δ _nega to the pixel value correction unit 8.

The pixel value correction unit 8 _calculates the pixel value variation δ _posi determined by the positive image pixel value variation determination unit 6 and the pixel value variation δ _nega determined by the negative image pixel value variation determination unit 7. The luminance value v of the pixel
To calculate the pixel correction value k (v) by calculating the logarithm of the ratio of the respective correction results.
(V) to the pixel value correction controller 9.

The pixel value correction control unit 9 has a function of providing the pixel correction value k (v) received from the pixel value correction unit 8 to the pixel correction value storage unit 10 and a pixel correction value k (v) for all the pixels.
Is calculated so that the neighboring image extracting unit 3 to the pixel value correcting unit 8 calculate
It has a function to control

The pixel correction value storage unit 10 stores each pixel correction value k (v) received from the pixel value correction control unit 9 in a memory or the like. The pixel correction value maximum / minimum value calculation unit 11 and the pixel value normal It can be read from the conversion means.

The pixel correction value maximum / minimum value calculator 11 calculates all the pixel correction values k stored in the pixel correction value storage 10.
(V) has a function of calculating the maximum value k _max and the minimum value _kmin and providing the calculated value to the pixel value normalization unit 12.

The pixel value normalizing section 12 receives the maximum value k _max and the minimum value k received from the pixel correction value maximum / minimum value calculating section 11.
Based on the _min , the pixel correction value k (v) of each pixel calculated by the pixel value correction unit 8 is normalized within the range of the output range to calculate a normalized conversion value V (v), respectively. It has a function of giving the converted value V (v) to the pixel value normalization control unit 13.

The pixel value normalization control section 13 has a function of giving the normalized conversion value V (v) received from the pixel value normalization section 12 to the pixel value normalization conversion value storage section 14 and a normalization conversion for all pixels. It has a function of controlling the pixel value normalization unit 12 to calculate the value V (v).

The pixel value normalized conversion value storage section 14 stores each normalized conversion value V (v) received from the pixel value normalization control section 13 in a memory or the like, and is readable from the image output section 15. Has become.

The image output unit 15 stores the normalized conversion value V (v) of each pixel stored in the pixel value normalized conversion value storage unit 14.
Has the function of composing and outputting the entire image based on the

Next, an image quality improving method by the image quality improving apparatus configured as described above will be described with reference to the flowchart of FIG.

First, an image is input by an image input unit 1 such as an image sensor, a monitor camera, or a digital camera. At this time, the lower limit of the domain that each pixel value of the input image can take is represented by v _L , and the upper limit is represented by v _U.

The overall average calculating unit 2 calculates the overall average value v _mean of the input image by adding up all the pixel values of the input image and dividing the addition result by the total number of pixels (ST1).

The neighborhood image extraction unit 3 receives the image from the input unit 1, extracts a neighborhood area having a given or appropriately determined number of pixels, and sets it as a neighborhood image (ST2).

The simplest example of the neighborhood is the pixel 8 of interest.
In the neighborhood, as shown in FIG.
It is assumed that the eight pixel values in the vicinity of the pixel of interest are represented by any of the signs v1 to v8. Also,
FIG. 4 is a schematic diagram showing the relationship between the entire image, the pixel of interest, and its neighboring pixels. Hereinafter, an example in which the number of neighboring pixels is eight will be described.

The neighborhood average calculation unit 4 receives the neighborhood image from the neighborhood image extraction unit 3 and calculates the neighborhood average value v _ave by averaging the pixel values of the neighborhood image as shown in the following equation (1). ST3).

[0059]

(Equation 1)

The coefficient calculating section 5 receives the overall average value v _mean from the overall average calculating section 2, receives the neighborhood average value v _ave from the neighborhood average calculating section 4, and obtains the following equations (2) and (3). As described above, the ratio is calculated (ST4), and is set as the positive pixel value correction coefficient α _posi and the negative pixel value correction coefficient α _nega .

[0061]

(Equation 2)

The positive image pixel value variable determining unit 6 receives the neighboring pixel value average value v _ave from the neighboring average calculating unit 4, receives the pixel value correction coefficient _αposi from the coefficient calculating unit 5, and is _expressed by the following equation (4). As described above, the difference between the input image pixel value lower limit value v _L and the calculated value is multiplied by the pixel value correction coefficient α _posi and an appropriate constant β _posi is added to obtain a positive image pixel value variable δ _posi (ST5).

Δ _posi = α _posi (v _ave −v _L ) + β _posi (4) The negative image pixel value variation determining unit 7 receives the neighboring pixel value average value v _ave from the neighboring average calculating unit 4, and receiving a pixel value correction coefficient alpha _nega than 5, as shown in the following equation (5), suitable by multiplying the pixel value correction coefficient alpha _nega to that calculates a difference between the pixel value limit v _U of the input image The constant β _nega is added to _obtain a negative image pixel value variable δ _nega (ST6).

Δ _nega = α _nega (v _U −v _ave ) + β _nega (5) The pixel value correction unit 8 is a positive image pixel value variable determination unit 6
The positive image pixel value variable δ _posi is received from the negative image pixel value variable determining unit 7 and the negative image pixel value variable δ _nega is received from the negative image pixel value variable determining unit 7 as shown in the following equation (6).
The positive image pixel value variable δ _posi is added to the value obtained by subtracting the lower limit value v _{L of the} image from the pixel value v of the _target pixel to obtain a positive image pixel value correction value, and the pixel value of the _target pixel is obtained from the upper limit value v _{U of the} image. The negative image pixel variable δ _nega is added to the value obtained by subtracting v to obtain a negative image pixel value correction value. The positive image pixel value correction value is divided by the negative image pixel value correction value to obtain a ratio. (Natural logarithm) is calculated as a pixel correction value k (v) (ST
7).

[0065]

(Equation 3)

The pixel value correction control section 9 controls the pixel value correction section 8 and the like so as to calculate the pixel correction value k for all the pixels of the input image.

The pixel correction value storage section 10 receives the pixel correction values k of all the pixels from the pixel value correction control section 9 for all the pixels, and stores them in a memory or the like.

The pixel correction value maximum / minimum value calculation unit 11 reads out the pixel correction values of all the pixels from the pixel value correction storage unit 10, and calculates the maximum values of the pixels as shown in the following equations (7) to (8). A value k _max and a minimum value _kmin are calculated.

K _max = max (k (v ₀ ), k (v ₁ ), k (v ₂ ),..., K (v _n )) (7) _kmin = min (k (v ₀ ), k (V ₁ ), k (v ₂ ),..., K (v _n )) (8) where n is the total number of pixels.

The pixel value normalizing section 12 reads the pixel correction value from the pixel correction value storage section 10 and outputs the maximum value V of the output range.
_max, for the minimum value V _min, normalized conversion as shown pixel correction value k to (v) in the following equation (9) (ST7).

[0071]

(Equation 4)

The pixel value conversion control unit 13 calculates a pixel value conversion value V (v) by the pixel value normalization unit 12 for all pixels of the input image.

The pixel value normalized conversion value storage unit 14 receives and stores the pixel value conversion values V (v) of all pixels from the pixel value normalization control unit 13 for all pixels.

The image output unit 15 receives the pixel value conversion value V (v) of each pixel from the pixel value normalized conversion value storage unit 14 and forms and outputs the entire image.

(Evaluation) Next, how the image contrast and sharpness are improved by such an image quality improving method will be described.

FIG. 5 is a view showing an original image before image quality improvement in a model that resembles a scenery image of a gas station having a bright portion, an intermediate portion, and a dark portion, and is entirely blurred. The visibility of the dark part located in the upper half is low.

On the other hand, the image after the image quality improvement according to the present embodiment becomes sharp as a whole as shown in FIG. 6, and, unlike the original image in particular, the inside of the store in the dark part can be visually recognized well and the car washer and the stand The visibility of bright parts such as the parts is also improved.

As described above, according to the first embodiment, the overall average value v _mean of the input image is obtained without assuming in advance the distribution characteristics of the luminance values of the input image. The degree of enhancing the contrast by adapting to the distribution of the local luminance values v1 to vi can be adjusted only by processing in the vicinity of each pixel, so that a simple calculation can be performed without the user's judgment. , Image quality can be improved.

More specifically, a sharp image with improved contrast near each pixel can be obtained from the input original image. For example, it is possible to correct the luminance signal from the image sensor with high precision and high resolution, and to improve the image quality of image data with low contrast.

(Second Embodiment) Next, a second embodiment of the present invention will be described.
An image quality improving device according to the embodiment will be described.

FIG. 7 is a block diagram showing the structure of the image quality improving apparatus. The same parts as those in FIG. 1 are denoted by the same reference numerals, detailed description thereof will be omitted, and only different parts will be described here.

That is, in the present embodiment, in addition to the processing of the first embodiment, the contrast of the entire image is improved by normalizing the average luminance and the luminance center of the display system in association with each other. Specifically, as shown in FIG. 7, instead of the pixel value normalizing unit 12 to the image output unit 15,
Overall average correction value calculation unit 20, pixel correction value conversion unit 21, pixel correction value conversion control unit 22, pixel correction value conversion value storage unit 23
And a normalized image output unit 24.

Here, the overall average correction value calculating section 20 includes an overall average value v _mean calculated by the overall average calculating section 2, a neighborhood average value v _ave calculated by the neighborhood average calculating section 4, and a coefficient calculating section 5. The correction value k (v _mean ) of the overall average value v _mean is calculated based on the coefficients α _posi and α _nega calculated by the above equation, and this correction value k (v _mean ) is calculated by the pixel correction value conversion unit 21.
It has a function to give to.

The pixel correction value conversion unit 21 includes the pixel value correction unit 8
And the correction value k calculated by the overall average correction value calculation unit 20.
(V _mean ), and when k (v) <k (v _mean ), the pixel correction value k (v) is set to the intermediate value V within the output range.
linearly converted to an output range section smaller than _mid , k (v)
= K (v _mean ), the pixel correction value k (v) is linearly converted to an intermediate value V _mid within the output range, and k (v)> k
When (v _mean ), the pixel correction value k (v) is linearly converted into an output range section larger than the intermediate value V _{mid in the} output range, so that each pixel correction value k (v) falls within the output range. The normalization conversion value V (v) is calculated by normalization, and has a function of giving the normalization conversion value V (v) to the pixel correction value conversion control unit 22.

The pixel correction value conversion control unit 22 has a function of giving the normalized conversion value V (v) received from the pixel correction value conversion unit 21 to the pixel correction value conversion value storage unit 23, It has a function of controlling the pixel correction value conversion unit 21 to calculate V (v).

The pixel correction value conversion value storage unit 23 stores each normalized conversion value V (v) received from the pixel correction value conversion control unit 22 in a memory or the like.
Can be read from.

The normalized image output unit 24 calculates the normalized conversion value V for each pixel stored in the pixel correction value conversion value storage unit 23.
It has a function of composing and outputting the entire image based on (v).

Next, an image quality improving method by the image quality improving apparatus thus configured will be described with reference to the flowchart of FIG.

Assume that the processes from the image input unit 1 to the pixel correction value maximum / minimum value calculation unit 11 have been completed (ST1 to ST7) as described above.

[0090] Overall average correction value calculation unit 20, based on such overall average value v _mean calculated by the overall average calculation unit 2, using the aforementioned equation (6), the correction value k of the overall mean value v _mean ( v _mean ) is calculated and given to the pixel correction value conversion unit 21.

The pixel correction value converter 21 calculates the correction value k
(V _mean ), and reads the pixel correction value k (v) from the pixel correction value storage unit 20. Further, as shown in the following equation (10), the maximum value V _max of the output range, for the minimum value V _min, and calculates the intermediate value V _min (ST20).

[0092]

(Equation 5)

Next, the overall average value v _mean is changed to the intermediate value v _mid
The pixel correction value k (v) is changed to the following (11) so as to correspond to
Linear conversion is performed as shown in Expressions (12) (ST21).

[0094]

(Equation 6)

The pixel correction value conversion control unit 23 controls the pixel correction value conversion unit 21 so as to calculate the pixel correction value conversion value V (v) for all the pixels of the input image.

The pixel correction value conversion value storage unit 85 receives the pixel correction value conversion values V (v) of all pixels from the pixel correction value conversion control unit 23 for all pixels, and stores them in a memory or the like.

The normalized image output unit 24 reads the pixel correction value conversion value V (v) of each pixel from the pixel correction value conversion value storage unit 23, and constructs and outputs the entire image.

(Evaluation) Next, according to this image quality improving method,
The following describes how the contrast and sharpness of an image can be improved.

FIG. 9 is a diagram showing an original image before image quality improvement similar to FIG.

On the other hand, as shown in FIG. 10, in the image after the image quality improvement according to the present embodiment, in addition to the improvement of the sharpness and the visibility of the bright and dark parts as described above, the good local contrast is maintained. However, the overall sense of contrast is increased, and natural global contrast enhancement is realized.

As described above, according to the second embodiment, in addition to the effects of the first embodiment, the overall average value v _mean
Is normalized by associating the correction value k (v _mean ) with the intermediate value V _mid with good sensitivity of the output range, so that the local contrast and the global contrast can be enhanced simultaneously.

More specifically, from the input original image, the contrast in the vicinity of each pixel is improved, and the contrast of the entire image is also improved, so that a sharp and highly visible image can be obtained. . For example, it is possible to correct the luminance signal from the image sensor with high precision and high resolution, and to improve the image quality of image data with low contrast.

(Third Embodiment) Next, a third embodiment of the present invention will be described.
The edge strength calculation device according to the embodiment will be described. FIG. 11 is a block diagram showing the configuration of the edge strength calculation apparatus. The same parts as those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof will be omitted. Only different parts will be described here.

That is, in the present embodiment, an edge intensity image is output by a modification of the first embodiment. Specifically, as shown in FIG. 11, the pixel value correction unit 8 to the image output unit 15, the neighborhood image pixel value maximum gradient value calculation unit 30, the edge strength calculation unit 31, the edge strength calculation control unit 32, the edge strength value storage unit 33, the edge strength value maximum / minimum value calculation unit 34, and the edge strength value normal A normalizing unit 35, an edge intensity value normalization control unit 36, an edge intensity value normalized conversion value storage unit 37, and an edge intensity image output unit 38.

Here, the neighborhood image pixel value maximum gradient value calculation unit 30 calculates the absolute value of each gradient along a plurality of predetermined directions between the luminance values v1 to vi of the neighborhood pixels extracted by the neighborhood image extraction unit 3. The maximum gradient value dv (v) indicating the maximum
And gives the maximum gradient value dv (v) to the edge strength calculation unit 31.

The edge strength calculator 31 has a function of calculating a positive image edge strength value, a function of calculating a negative image edge strength value, and an edge strength calculating function of calculating an edge strength value dk (v) of a pixel.

The function of calculating the positive image edge intensity value is as follows.
The pixel value variation δ _posi determined by the positive image pixel value variation determining unit 6 is added to the relative value of the luminance value v of the pixel in the positive image to correct the relative value, and the maximum gradient value calculating unit 30 for the neighboring pixels is used. Maximum gradient value dv received from
This is a process of calculating the positive image edge intensity value by dividing (v) by the correction result.

The function of calculating the negative image edge intensity value is as follows.
The pixel value variation δ _nega determined by the negative image pixel value variation determining unit 7 is added to the relative value of the luminance value v of the pixel in the negative image to correct the relative value, and the maximum gradient value calculating unit 30 for the neighboring pixels is used. Maximum gradient value dv received from
This is a process of calculating the negative image edge intensity value by dividing (v) by the correction result.

The edge strength calculation function calculates the edge strength value dk (v) of the pixel by adding the positive image edge strength value and the negative image edge strength value calculated by these two functions to each other. dk (v)
Is given to the edge strength calculation control unit 32.

The edge strength calculation control unit 32 provides the edge strength value dk (v) received from the edge strength calculation unit 31 to the edge strength value storage unit 33, and calculates the edge strength values dk (v) for all the pixels. To control the neighboring image extraction unit 3 to the edge strength calculation unit 31 so as to perform the operation.

The edge strength value storage section 33 stores each edge strength value dk (v) received from the edge strength calculation control section 32 in a memory or the like, and is readable from the edge strength value maximum / minimum value calculation section. Has become.

The edge intensity value maximum / minimum value calculation unit 34 calculates the maximum value dk _max and the minimum value dk _{min of} all the edge intensity values dk (v) stored in the edge intensity value storage unit 33.
Is calculated and given to the edge intensity value normalizing unit 35.

[0113] edge intensity value normalization unit 35, based on the maximum value dk _max and the minimum value dk _min received from the edge strength value maximum-minimum value calculation unit 34, for each pixel stored in the edge intensity value storage unit 33 The edge strength value dk (v) is normalized within the range of the output range, and the respective normalized converted values dV (v) are obtained.
Is calculated, and these normalized conversion values dV (v) are provided to the edge intensity value normalization control unit 36.

The edge intensity value normalization control unit 36 receives the normalized conversion value dV (v) received from the edge intensity value normalization unit 35.
To the edge intensity value normalized conversion value storage unit 37, and the function of controlling the edge intensity value normalization unit 35 to calculate the normalized conversion value dV (v) for all pixels.

The edge intensity value normalized conversion value storage unit 37 stores
Each normalized conversion value dV (v) received from the edge intensity value normalization control unit 36 is stored in a memory or the like, and can be read from the edge intensity image output unit 38.

The edge intensity image output section 38 constructs and outputs the entire image based on the normalized conversion value dV (v) of each pixel stored in the edge intensity value normalized conversion value storage section 37. Have.

Next, an edge strength calculation method by the above-described edge strength calculation apparatus will be described with reference to the flowchart of FIG.

Assume that the processing from the image input unit 1 to the negative image pixel value variable determination unit 7 has been completed (ST1 to ST6), as described above.

The neighborhood image pixel value maximum gradient value calculating section 30 calculates
The absolute value of the pixel value change amount of the target pixel in the four directions of up, down, left, right, diagonally left, and diagonally right is obtained, and the maximum value is set as the maximum gradient value dv of the neighboring pixel value.

The edge intensity calculating section 31 sends the positive image pixel value variable δ from the positive image pixel value variable determining section 6.
_Posi is received, the negative image pixel value variation δ _nega is received from the negative image pixel value variation determination unit 7, and the maximum neighboring image pixel value gradient value dv is received from the maximum neighboring image pixel value gradient value calculation unit 30.

[0121] Then, the edge strength calculating unit 31, as shown in the following equation (13), a positive image pixel value variable from the pixel value v of the target pixel to a value obtained by subtracting the lower limit value v _L of the image [delta] _{po si} the seek positive image pixel values in addition, also added negative image pixel value variable [delta] _nega the upper limit value v value obtained by subtracting the pixel value v of the target pixel from the _U of the image sought negative image pixel value, the positive image pixel value Then, the quotient is obtained by dividing the neighboring image pixel value maximum gradient value dv to obtain a positive image edge intensity value, and the quotient is obtained by dividing the neighboring pixel pixel value maximum gradient value dv by the negative image pixel value to obtain the negative image edge intensity. , And a linear sum of the positive image edge intensity value and the negative image edge intensity value is calculated, and is set as the edge intensity value dk (v) of the pixel (ST3).
0).

[0122]

(Equation 7)

The edge strength calculation controller 32 controls the edge strength calculator 31 so as to calculate the edge strength value of all the pixels of the input image.

The edge intensity value storage unit 33 receives the edge intensity values dk (v) of all the pixels from the edge intensity calculation control 32 and stores them in a memory or the like.

The edge intensity maximum / minimum value calculator 34 calculates
From the edge intensity value storage 33, the edge intensity values dk of all pixels
(V) is read out, and the maximum value dk _max and the minimum value dk _min are calculated as shown in the following equations (14) to (15).

Dk _max = max (dk (v ₀ ), dk (v ₁ ), dk (v ₂ ),..., Dk (v _n )) (14) dk _min = min (dk (v ₀ ), dk (V ₁ ), dk (v ₂ ),..., Dk (v _n )) (15) where n is the total number of pixels.

The edge intensity value normalizing section 35 receives the edge intensity value dk (v) for the pixel value v of the target pixel,
The maximum edge value dk _max and the minimum edge value dk _min are received from the edge intensity maximum / minimum value calculation unit 34, and as shown in the following equation (16), the edge intensity value dk (v) is set to each pixel value. Normalization is performed within the domain [v _L , v _U ] of the variable that can be taken to obtain an edge intensity value normalized conversion value dV (v) (ST31).

[0128]

(Equation 8)

The edge-intensity-value-normalized conversion control unit 36 controls the edge-intensity-value-normalized conversion value d for all the pixels of the input image.
The edge intensity value normalizing unit 35 is controlled so as to calculate V (v).

The edge intensity value normalized conversion value storage unit 37
The edge intensity value normalized conversion value dV (v) of all pixels is received from the edge intensity value normalization conversion control unit 36 for all pixels, and stored.

The edge strength image output section 38 reads out the edge strength value normalized conversion value dV (v) of each pixel from the edge strength value normalized conversion value storage section 37 and forms the entire edge strength image (differential image). Output.

(Evaluation) Next, how the edge strength of an image is represented by such an edge strength calculation method will be described.

FIG. 13 is a diagram showing an original image similar to FIG.

On the other hand, as shown in FIG. 14, the edge intensity image according to the present embodiment has
In particular, the in-store structure that cannot be confirmed in the original image often appears. In addition, from the light part to the middle part, in particular, detailed structures such as a car wash machine and a stand part are clarified. That is, an output result with a high edge emphasis effect is obtained in both the bright part and the dark part.

As described above, according to the third embodiment, the edge intensity is calculated after the contrast enhancement similar to that of the first embodiment, so that both bright and dark parts include fine objects and structures. For most of the images, accurate calculation of edge strength and edge detection can be performed by simple calculations without requiring user judgment, and an excellent edge-emphasized image can be output.

In other words, since the edge intensity is calculated from the input original image while greatly improving the contrast in the vicinity of each pixel, unlike the related art, even a fine edge in a bright portion or a dark portion can be detected. can do. For example, edge detection with high accuracy and high resolution of the luminance signal from the image sensor,
It becomes possible to detect the structure and the like of image data with low visibility such as a bright portion and a dark portion with high accuracy.

(Other Embodiments) In the first to third embodiments, the size of the neighboring area may be fixed to an appropriate value or may be appropriately given as a parameter. Regarding the size of the neighboring region, for example, in a substantially concentric region, it is preferable that the radius is 3 to 4 pixels, and the area is 20 to 40 pixels.

In the first to third embodiments, the values of β _posi and β _nega may be fixed to appropriate values, or may be appropriately given as parameters.

The method described in the above embodiment can be executed by a computer as a program such as a magnetic disk (floppy disk, hard disk, etc.), an optical disk (CD-ROM, DVD, etc.),
It can also be stored in a storage medium such as a semiconductor memory and distributed.

In addition, the present invention can be variously modified and implemented without departing from the gist thereof.

[0141]

As described above, according to the image quality improving method and apparatus of the present invention, the local sharpness of an image input from a monitor camera, a digital camera or the like is increased, and the local contrast and the global contrast are improved. Can be greatly improved.

Further, according to the edge strength calculation method and apparatus of the present invention, a fine gradation change in a bright portion and a dark portion, which cannot be detected by the conventional edge strength calculation method, can be detected, and a good edge can be obtained over the entire brightness range. Detection can be realized.

[Brief description of the drawings]

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

FIG. 2 is a flowchart for explaining an operation in the embodiment;

FIG. 3 is a schematic diagram for explaining a pixel of interest and pixels in the vicinity thereof according to the embodiment;

FIG. 4 is a schematic diagram showing the relationship between the entire image, a pixel of interest, and its neighboring pixels according to the embodiment;

FIG. 5 is a diagram showing a photo-printed original image before image quality improvement in the embodiment.

FIG. 6 is a diagram showing a photo-printed image after the image quality is improved in the embodiment.

FIG. 7 is a block diagram showing a configuration of an image quality improving device according to a second embodiment of the present invention.

FIG. 8 is a flowchart for explaining the operation in the embodiment.

FIG. 9 is a view showing an original image before image quality improvement in the embodiment by photo printing;

FIG. 10 is a diagram showing a photo-printed image after the image quality is improved in the embodiment.

FIG. 11 is a block diagram showing a configuration of an edge strength calculation device according to a third embodiment of the present invention.

FIG. 12 is a flowchart for explaining the operation in the embodiment;

FIG. 13 is a diagram showing an original image before the calculation of the edge strength in the same embodiment by photo printing.

FIG. 14 is a view showing an edge strength image after edge strength calculation in the embodiment by photo printing;

FIG. 15 is a diagram for explaining a conventional image quality improving method by linear conversion.

FIG. 16 is a view for explaining a conventional image quality improving method by logarithmic conversion or exponential conversion.

FIG. 17 is a view for explaining a conventional image quality improving method by exponential conversion.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Image input part 2 ... Whole average calculation part 3 ... Neighborhood image extraction part 4 ... Neighborhood average calculation part 5 ... Coefficient calculation part 6 ... Positive image pixel value variation determination part 7 ... Negative image pixel value variation determination part 8 ... Pixel value Correction unit 9 Pixel value correction control unit 10 Pixel correction value storage unit 11 Pixel correction value maximum / minimum value calculation unit 12 Pixel value normalization unit 13 Pixel value normalization control unit 14 Pixel value normalization conversion value storage Unit 15: Image output unit 20: Overall average correction value calculation means 21: Pixel correction value conversion unit 22: Pixel correction value conversion control unit 23: Pixel correction value conversion value storage unit 24: Normalized image output unit 30: Neighboring image pixels Value maximum gradient value calculation unit 31 ... edge intensity calculation unit 32 ... edge intensity calculation control unit 33 ... edge intensity value storage unit 34 ... edge intensity value maximum / minimum value calculation unit 35 ... edge intensity value normalization unit 36 ... edge intensity value normalization Conversion Conversion control unit 37 ... edge intensity value normalized conversion value storage unit 38 ... edge strength image output unit

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Yuichi Kobayashi Inside Toppan Printing Co., Ltd., 1-1-1, Taito, Taito-ku, Tokyo

Claims (6)

[Claims] 1. An average value v _mean of luminance values v of pixels in an entire image is determined, and an average value v _ave of i luminance values v1 to vi in the vicinity of the pixel is determined for each pixel of the image. , The mean value v _{mean of the} whole and the mean value v of the neighborhood
A coefficient corresponding to the ratio with _ave , the coefficient is multiplied by the relative value of the average value v _ave of the neighborhood in a positive image to determine a positive pixel variable δ _posi, and the coefficient is the neighborhood of the neighborhood in a negative image. The negative pixel variable δ _nega is obtained by multiplying the relative value of the average value v _ave to correct the relative value by adding the positive pixel variable δ _posi to the relative value of the luminance value of the pixel in the positive image, and correcting the negative value. The pixel variable δ _nega is added to the relative value of the luminance value of the pixel in the negative image to correct the relative value, and the luminance value v of the pixel is calculated by the logarithm of the ratio of the corrected relative values.
, And normalizing the correction result k (v) within the range of the output range. 2. The image quality improving method according to claim 1, wherein the normalization is performed by correcting a correction result k of the overall average value v _mean.
(V _mean ) corresponding to the intermediate value V _mid of the output range. 3. An average value v of luminance values v of all pixels of an image.
seek _mean, for each pixel of the image, the average value v _{av e} of i pieces of luminance values v1~vi in the vicinity of the pixel,
A coefficient corresponding to a ratio between the overall average value v _mean and the neighborhood average value v _ave is obtained, and the coefficient is multiplied by a relative value of the neighborhood average value v _{ave in} a positive image to obtain a positive pixel variable δ _posi And the coefficient is multiplied by the relative value of the average value v _ave of the neighborhood in the negative image to obtain a negative pixel variable δ _nega , and the positive pixel variable δ _posi is _calculated as the luminance value v of the pixel in the positive image. In addition to correcting this relative value in addition to the relative value, correcting the relative value by adding the negative pixel variable δ _nega to the relative value of the luminance value v of the pixel in the negative image, and further correcting each of the neighboring luminance values The maximum gradient value dv (v) indicating the maximum among the absolute values of the gradients along the four directions of up and down, left and right, left diagonal, and right diagonal between the values v1 to vi is obtained, and this maximum gradient value dv (v) is calculated. Said positive The edge intensity value of the positive image is obtained by dividing by the correction result of the relative value in the image, and the edge intensity of the negative image is obtained by dividing the maximum gradient value dv (v) by the correction result of the relative value in the negative image. An edge strength calculation method comprising: calculating a value, adding the two edge strength values to each other, calculating the edge strength of the pixel, and normalizing the calculation result dk (v) within the range of the output range. 4. An image input means for inputting an image, and [b] an overall average value v _mean is calculated by averaging luminance values of all pixels of the image input by the image input means. Average calculating means; and [c] neighboring image extracting means for extracting, for each pixel of the image input by the image inputting means, a luminance value v of the pixel and luminance values v1 to vi of i pixels in the vicinity thereof. [D] a neighborhood average calculation means for calculating a neighborhood average value v _ave by averaging the luminance values v1 to vi of the neighborhood pixels extracted by the neighborhood image extraction means, and [e].
The overall average value v calculated by the overall average calculation means
a coefficient calculating means for calculating a coefficient corresponding to the ratio between the neighboring average value v _ave calculated by _mean and the neighboring average calculation means, [f] the luminance value v of the pixel extracted by the neighborhood image extracting unit, Based on the overall average value v _mean calculated by the overall average calculation means, the neighborhood average value v _ave calculated by the neighborhood average calculation means, and the coefficient calculated by the coefficient calculation means, the pixel value variation of the positive image is calculated. a positive image pixel value variable determining means for determining δ _posi , [g] a luminance value v of the pixel extracted by the neighboring image extracting means, a global average value v _mean calculated by the global average calculating means, and the neighborhood near the average value v _ave calculated by the average calculating means, and based on the coefficient calculated by the coefficient calculation means, negative for determining a pixel value variable [delta] _nega negative image And I Bed image pixel value variable determining means, [h] the positive image pixel value pixel value variable determined by the variable determining means [delta] _{po si} and the pixel value variables determined by the negative image pixel value variable determining means [delta] _{ne ga}
Pixel value correction means for correcting the luminance value v of the pixel based on each of the above, calculating the logarithm of the ratio of the respective correction results to calculate the pixel correction value k (v), and [j] the pixel correction means. Correction value maximum / minimum value calculation means for calculating a maximum value _kmax and a minimum value _{kmin of} all the pixel correction values k (v) calculated by [1], and [1] the correction value maximum / minimum value calculation means The pixel correction value k calculated by the pixel value correction means based on the calculated maximum value k _max and minimum value _kmin
Pixel value normalization means for normalizing (v) within the range of the output range to calculate a normalized conversion value V (v); [m] normalization conversion of each pixel calculated by the pixel value normalization means An image quality improving apparatus comprising: an image output unit configured to output an entire image based on the value V (v). 5. The image quality improving device according to claim 4, wherein said pixel value normalizing means and said image output means are replaced by:
[A] The overall average is calculated based on the overall average value v _mean calculated by the overall average calculation means, the neighborhood average value v _ave calculated by the neighborhood average calculation means, and the coefficient calculated by the coefficient calculation means. correction value k (v value v _mean
mean ), and [b] a pixel correction value k (v) of each pixel calculated by the pixel value correction means and a correction value k calculated by the total average correction value calculation means. (V _mean ), and k (v) <k (v
_mean ), the pixel correction value k (v) is linearly converted to an output range section smaller than the intermediate value V _{mid in the} output range, and when k (v) = k (v _mean ), the pixel correction value k (v) is converted.
(V) is converted to an intermediate value V _mid of the output range, and k (v)
When> k (v _mean ), each pixel correction value k (v) is linearly converted into an output range section larger than the intermediate value V _{mid in the} output range, thereby converting each pixel correction value k (v) into the output range. A pixel correction value conversion means for calculating a normalized conversion value V (v) by normalizing the values in [c], and a normalized conversion value V (v) of each pixel calculated by the pixel correction value conversion means.
And a normalized image output means for constructing and outputting the entire image based on the image quality improvement device. 6. An image input means for inputting an image, and [b] an overall average value v _mean is calculated by averaging luminance values of all pixels of the image input by the image input means. Average calculating means; and [c] neighboring image extracting means for extracting, for each pixel of the image input by the image inputting means, a luminance value v of the pixel and luminance values v1 to vi of i pixels in the vicinity thereof. [D] a neighborhood average calculation means for calculating a neighborhood average value v _ave by averaging the luminance values v1 to vi of the neighborhood pixels extracted by the neighborhood image extraction means, and [e].
The overall average value v calculated by the overall average calculation means
a coefficient calculating means for calculating a coefficient corresponding to the ratio between the neighboring average value v _ave calculated by _mean and the neighboring average calculation means, [f] the luminance value v of the pixel extracted by the neighborhood image extracting unit, Based on the overall average value v _mean calculated by the overall average calculation means, the neighborhood average value v _ave calculated by the neighborhood average calculation means, and the coefficient calculated by the coefficient calculation means, the pixel value variation of the positive image is calculated. a positive image pixel value variable determining means for determining δ _posi , [g] a luminance value v of the pixel extracted by the neighboring image extracting means, a global average value v _mean calculated by the global average calculating means, and the neighborhood near the average value v _ave calculated by the average calculating means, and based on the coefficient calculated by the coefficient calculation means, negative for determining a pixel value variable [delta] _nega negative image And (h) gradients along the four directions of up, down, left, right, diagonally left, and diagonally right between the luminance values v1 to vi of the neighboring pixels extracted by the neighborhood image extracting means. And [j] the pixel value variable δ _{po si} determined by the positive image pixel value variable determining means, which calculates the maximum gradient value dv (v) indicating the maximum value among the absolute values of This relative value is corrected in addition to the relative value of the luminance value v of the pixel in the image, and the maximum gradient value dv (v) calculated by the neighboring pixel maximum gradient value calculating means is divided by the correction result. a positive image edge intensity value calculating means for calculating a positive image edge strength value, [l] bright of the pixel of the pixel value variable [delta] _{ne ga} decided by the negative image pixel value variable determining means negative image In addition to the relative value of the value v as well as fix the relative value, the maximum slope value dv calculated by the neighboring pixel maximum gradient value calculating means
Negative image edge intensity value calculating means for calculating a negative image edge intensity value by dividing (v) by the correction result; [m] the positive image edge intensity value calculated by the positive image edge intensity value calculating means; Edge strength calculating means for calculating the edge strength value dk (v) of the pixel by adding together the negative image edge strength values calculated by the negative image edge strength calculating means, and [n] calculating by the edge strength calculating means Edge intensity normalizing means for normalizing the obtained edge intensity value dk (v) of each pixel within the range of the output range to calculate a normalized conversion value dV (v); [o] the edge intensity normalizing means Edge strength image output means for constructing and outputting the entire image based on the calculated normalized conversion value dV (v) of each pixel. The edge intensity computing device.