KR101828180B1 - Tone mapping method and apparatus for digital images - Google Patents

Abstract

Provided are a method and an apparatus for mapping a tone of a digital image which can consistently obtain a tone mapping image with the high recognition image quality without intervention of a user. According to an embodiment of the present invention, the apparatus for mapping a tone of a high dynamic range (HDR) image comprises: a global tone mapping unit for performing global compression on an HDR image, performing normalization on the global compressed image, and performing a global contrast improved technique on the normalized image so as to generate a global tone mapping image; a local tone mapping unit for compressing a difference between each pixel value and an adaptive reference value of the global compressed image, and applying an algorithm to strengthen contrast so as to generate a local tone mapping image; and a tone mapping image combining unit for combining the generated global tone mapping image and the local tone mapping image so as to generate a final tone mapping image.

Description

TECHNICAL FIELD [0001] The present invention relates to a tone mapping method and apparatus for digital images,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for mapping a digital image, and more particularly, to a technique for consistently acquiring a natural and detailally reproduced image in tone mapping for a high dynamic range (HDR) will be.

The dynamic range of a digital image is defined as the ratio of the brightest pixel value to the darkest pixel value in the image.

A human visual perception system (HVS) recognizes a dynamic area of 3.73 order magnitude while a dynamic area appearing in the real world has a magnitude of 8 order magnitude Respectively.

Therefore, an existing display device can not capture or display an image perceived by a human being as it is.

Accordingly, a 'tone mapping algorithm' for effectively representing a high dynamic range (HDR) image in a display device having a low dynamic range (LDR) It is essential to maintain compatibility between the image and the existing LDR display device.

However, since the conventional tone mapping method uses a plurality of parameters and the performance depends on the parameter values, appropriate intervention (parameter selection) of the user is required according to the image, and the naturalness and detail reproduction There is a problem that acquisition of the tone mapping image is difficult.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems of the conventional art, and it is an object of the present invention to provide a tone mapping method and a tone mapping method, which can adaptively emphasize naturalness and detail reproduction according to image characteristics, And to provide a method for acquiring images consistently.

In order to achieve the above object, a high dynamic range (HDR) image tone mapping apparatus according to an embodiment of the present invention performs global compression of an HDR image, A global tone mapping unit for performing normalization on the normalized image and performing a global contrast enhancement technique on the normalized image to generate a global tone mapping image, A local tone mapping unit for compressing a difference between adaptive reference values and applying an algorithm for enhancing contrast to generate a local tone mapping image, And a tone mapping image combining unit for combining the local tone mapping images to generate a final tone mapping image.

According to an aspect of the present invention, there is provided a method for tone mapping a high dynamic range (HDR) image in a tone mapping apparatus, comprising: (a) performing global compression on an HDR image; (B) performing normalization on the globally compressed image, performing a global contrast enhancement technique on the normalized image to generate a global tone mapping image, Generating a local tone mapping image by compressing a difference between each pixel value of the compressed image and an adaptive reference value and applying an algorithm for contrast enhancement; and (c) And generating a final tone mapping image by combining the generated global tone mapping image and the local tone mapping image.

According to an embodiment of the present invention, naturalness and detailed reproduction power can be adaptively emphasized according to image characteristics.

Also, it is possible to consistently acquire a tone-mapped image of high cognitive image quality without user intervention.

It should be understood that the effects of the present invention are not limited to the above effects and include all effects that can be deduced from the detailed description of the present invention or the configuration of the invention described in the claims.

FIG. 1A is a diagram illustrating a configuration of a tone mapping system according to an embodiment of the present invention.
1B is a block diagram illustrating a configuration of a tone mapping apparatus according to an embodiment of the present invention.
2 is a flowchart illustrating an HDR tone mapping process according to an embodiment of the present invention.
3 is a flowchart illustrating a process of calculating an adaptive reference value R according to an embodiment of the present invention.
4 is a diagram illustrating a tone mapping process together with an image according to an embodiment of the present invention.
5A and 5B are views illustrating an image generated in the tone mapping process according to an exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification.

Throughout the specification, when a part is referred to as being "connected" to another part, it includes not only "directly connected" but also "indirectly connected" .

Also, when an element is referred to as "comprising ", it means that it can include other elements, not excluding other elements unless specifically stated otherwise.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1A is a diagram illustrating a configuration of a tone mapping system according to an embodiment of the present invention.

The tone mapping system according to an embodiment of the present invention may include an image acquisition device 10, a tone mapping device 100, and an image display device 20.

Although the tone mapping apparatus 100 is shown separately from the image capturing apparatus 10 and the image display apparatus 20 in FIG. 1A for the sake of understanding, according to the embodiment, May be included in the acquiring device 10 or may be included in the image display device 20.

The scene of the real world is converted into an HDR photographed image by the image acquisition device 10 and the HDR photographed image is converted into an LDR image through the tone mapping device 100 and displayed by the image display device 20 of the LDR .

In other words, the user views the LDR image displayed on the image display device 20 instead of the real-world scene, and determines how closely the LDR image displayed on the image display device 20 is similar to the scene viewed by the user in the real world ) Is important.

As described above, implementing the image similar to the real-world scene in the image display apparatus 20 depends on how accurate tone mapping is performed, apart from improving the hardware performance of the image display apparatus 20 have.

This tone mapping can be divided into a global tone mapping method and a local tone mapping method. Since the conventional tone mapping method uses a plurality of parameters and performance depends on parameter values, And it is difficult to effectively store the detail parts which are likely to be lost in the excessive light amount and the excessive light amount area.

Accordingly, the present invention proposes a method of adaptively emphasizing naturalness and detail reproduction according to the characteristics of an image, and consistently acquiring a tone-mapped image of high cognitive quality without user intervention.

1B is a block diagram illustrating a configuration of a tone mapping apparatus according to an embodiment of the present invention.

The tone mapping apparatus 100 according to an exemplary embodiment of the present invention includes a global tone mapping unit 110, a local tone mapping unit 120, a tone mapping image combining unit 130, a control unit 140, and a storage unit 150, . ≪ / RTI >

The global tone mapping unit 110 may perform initial global compression of the HDR image using the log function.

This is in accordance with the Weber-Fechner law, in which the sensory intensity (corresponding to the perceived brightness of the HDR image) is proportional to the log of the stimulus intensity (corresponding to the luminance of the HDR image).

Global compression using the logarithm function of the global tone mapping unit 110 can use the following equation (1).

Where i and j are the pixel coordinates of the image and L (i, j) is the HDR luminance of the pixel.

And C is a threshold value used for preventing a singularity problem in which a pixel value is 0, and 10 ^-6 is used in the embodiment of the present invention.

In addition, the global tone mapping unit 110 the Equation 1 a may generate an image (I _log) image (I _{log _norm)} qualified to perform regularization (normalization) to produce through, and normalized output The image can be expressed by the following equation (2).

here. max (output) and min (ouput) represent the maximum and minimum values of the output image.

In addition, the global tone mapping unit 110 performs the global contrast (contrast) enhancement techniques in the normalized image (I _{log _norm)} may generate a global tone mapping image (O _GTMO), this contrast can be enhanced by have.

Here, histogram equalization may be used as an example of the global contrast enhancement technique. The histogram equalization may be expressed by the following equation (3).

Conventional global compression methods using linear, gamma, and logarithmic functions compress the dynamic range based on the minimum value or 0 of the image. The global compression methods are dependent on the mapping function, There is a problem of generating loss.

In order to compress the dynamic range without loss of the detail information, an adaptive reference value is set instead of the minimum value or 0 of the image, and the difference between the pixel value and the adaptive reference value is set as a nonlinearity Difference Compression (hereinafter referred to as " difference compression ") can maintain details in both dark and light areas.

Difference Compression with a Constant Reference Value (DCCR) using the fixed reference value R can be defined by Equation (4) below.

Here, f (x) is a nonlinear mapping function (including a logarithmic function and an exponential function), and the exponential function f (x) in the embodiment of the present invention can be defined as the following equation (5).

Where the parameter? Represents the level of differential compression and may have a value in the range 0??? 1.

Equation (4) can be derived from an existing global compression method that compresses a dynamic range based on a minimum value of an image or a constant value such as 0 using a linear function, a gamma function, and a log function.

The local tone mapping unit 120 may generate the image O _DCAR through differential compression using the adaptive reference value instead of the fixed reference value, which can be defined by Equation (6) below.

Where sgn (x) is a sign function and R is the adaptive reference value.

For example, the contrast around the adaptive reference value R can be further enhanced when? Is close to zero, and 0.9 as a preferred embodiment of the? Value can be used.

Since? is an exponent? smaller than 1, the pixel value close to the adaptive reference value R can be strengthened. That is, β is emphasized as the pixel value is closer to the adaptive reference value R, which means that the pixels around the adaptive reference value R after the normalization are applied show a larger difference value between the pixels.

The local tone mapping unit 120 may use an edge preserving smoothing filter and a low pass filter to calculate the adaptive reference value R of Equation (6).

Specifically, the local tone mapping unit 120 _applies a first edge preserving smoothing filter to the normalized image I _{log_norm} through Equation (2) to generate a first smoothed image I _{init -} smooth, Can be generated.

Here, the halo artifact can be minimized by applying an edge preserving filter.

Thereafter, local tone mapping unit 120, a first smoothed image (I _{init _smooth)} generating a second smoothed image by applying a low-pass filter is a Gaussian low-pass filter (hereinafter Gaussian Low Pass Filter, hereinafter 'GLPF' hereinafter) to can do.

The first smoothed image (I _{init _smooth)} may be in a smoother image than the second smoothing the first smoothed image (I _{init_smooth)} obtained by applying the GLPF.

Thereafter, local tone mapping part 120 by applying a second smoothed image, and a first second edge preserving smoothing filter for smoothing the image (I _{init _smooth)} by the first edge preserving smoothing filter applied GLPF, final smoothing image (I _{final_smoothed} ).

Here, the local tone mapping unit 120 may generate the final smoothed image I _{final_smoothed} using the following Equation (7).

Here, GLPF () denotes a function of GLPF, and Guided (p, q) denotes a guide filter corresponding to an edge preserving smoothing filter, and denotes an input image p and a guide image q for filtering, respectively.

The local tone mapping unit 120 may calculate the adaptive reference value R using the above result, and use the following equation (8).

Here, alpha is a reference value variation index for selectively retaining details of the bright region or the dark region, and can be used to enhance the overall contrast of the region.

The reference value strain index a may be defined as any constant value smaller than 1, and may preferably be set to a = 0.1 in one embodiment.

If? Is less than 1, the bright region is enhanced and if it is greater than 1, the dark region can be enhanced. That is, the brightness can be adjusted by using?.

For reference, reinforcing a dark region has no significant meaning, so the case where? Is less than 1 is considered in the present invention.

Then, the local tone mapping unit 120 generates a local tone mapping unit 120, such as 'Contrast Limited Adaptive Histogram Equalization (CLAHE)', to the image O _DCAR generated through differential compression using the adaptive reference value R A local tone enhancement technique can be applied to generate a local tone mapping image (O _LTMO ) that faithfully utilizes a given dynamic range.

The local tone mapping unit 120 can generate a local tone mapping image (O _LTMO ) using the following Equation (9), whereby the contrast can be enhanced.

Meanwhile, the tone mapping image combining unit 130 may _{blend the} local tone mapping image O _LTMO and the global tone mapping image O _GTMO .

For this, the tone mapping image combining unit 130 may use the following Equation (10) as an embodiment.

Where gamma is a blending factor and can be used to balance local detail and global luminance, ranging from 0 to 1.

In one embodiment, if γ is greater than 0.5, the local detail may be more emphasized, and if γ is less than 0.5, the global luminance may be kept more natural.

It is important to adaptively set the γ value according to the characteristics of the image, and γ can be determined using an objective image quality evaluation method.

In addition, the tone mapping image combination unit 130 may combine the visual attention (visual saliency) modeling, local tone mapping image (O _LTMO) and global tone mapping image (O _GTMO) using an alternative embodiment.

Where the visual attention can be predicted by determining a detailed image area having a high visual attention that affects the overall quality.

The tone mapping image combining unit 130 can generate a locally adaptive blending image OTMO_L that adaptively reflects a detailed image area having a high visual attention using the following Equation (11) have.

은 관심 영역 지도(saliency map)로서 HDR 톤 맵핑을 위한 가중치 함수(saliency aware weighting function)로 사용될 수 있다.here

Can be used as a saliency aware weighting function for HDR tone mapping as a saliency map.

In other words, the tone mapping image combining unit 130 _extracts a combination ratio of the local tone mapping image (O _LTMO ) and the global tone mapping image (O _GTMO ) according to the visual attention map based on the ROI map reflecting the visual attention map in contrast to it it is possible to generate a local adaptive combination image (O _{TMO _L).}

The control unit 140 controls the components of the tone mapping system 100 such as the global tone mapping unit 110, the local tone mapping unit 120 and the tone mapping image combining unit 130, And may control the storage unit 150, which will be described later.

Meanwhile, the storage unit 150 may store an algorithm for controlling the components of the tone mapping system 100 to perform the respective operations described above and various data derived therefrom.

2 is a flowchart illustrating an HDR tone mapping process according to an embodiment of the present invention.

The flowchart shown in FIG. 2 can be performed by the tone mapping apparatus 100 of FIG. 1. Hereinafter, the flowchart of FIG. 2 will be described with the tone mapping apparatus 100 as an execution subject.

The tone mapping apparatus 100 generates an initial compressed image I _log by initial global compression of the HDR image (S201).

Here, global compression can be performed using a log function.

After S201, the tone mapping apparatus 100 normalizes the initial compressed image I _log to generate a normalized image I _{log_norm} (S202).

S202 generates then, the tone mapping unit 100 is a normalized image (I _{log _norm)} histogram (histogram equalization) and a global tone mapping image (O _GTMO) to perform the global contrast enhancement technique, such a (S203).

On the other hand, the tone mapping apparatus 100 calculates the adaptive reference value R after S201 (S204).

To this end, the tone mapping apparatus 100 may use an edge preserving smoothing filter and a low pass filter.

A method of calculating the adaptive reference value R will be described later with reference to Fig.

After S204, the tone mapping apparatus 100 generates an image (O _DCAR ) by performing differential compression using the adaptive reference value R (S205).

After S205, the tone mapping apparatus 100 applies a local contrast enhancement technique such as adaptive histogram smoothing (CLAHE) to the generated image (O _DCAR ) to adjust the local tone mapping image O _LTMO ) (S206).

Tone mapping apparatus 100 may combine the local tone mapping image (O _LTMO) and global tone mapping image (O _GTMO) generated in S203 and S206, respectively produce the final tone mapping image (O _TMO) (S207).

Here, the tone mapping apparatus 100 determines the combination ratio of the local tone mapping image (O _LTMO ) and the global tone mapping image (O _GTMO ) on a pixel-by-pixel basis according to the visual attention map based on the ROI map reflecting the visual attention map, an adaptive combination image (O _{_L TMO)} can be generated.

2 can be applied after the pixel level is converted to the luminance level. When the process of FIG. 2 is finished, the luminance level is converted back to the pixel level.

3 is a flowchart illustrating a process of calculating an adaptive reference value R according to an embodiment of the present invention.

The tone mapping apparatus 100 performs initial global compression of the HDR image to generate an initial compressed image I _log (S301).

After S301, the tone mapping apparatus 100 normalizes the initial compressed image I _log to generate a normalized image I _{log_norm} (S302).

S302 generates a first smoothed image (I _{init_smooth)} Then, the tone mapping unit 100 may apply a first edge preserving smoothing filter to the normalized image (I _{log _norm)} (S303).

After S303, the tone mapping unit 100 generates a first smoothed image a second smoothed image of claim 1 further smooth the smoothed image by applying a low-pass filter (GLPF) to (I _{init _smooth)} (S304).

After S304, the tone mapping unit 100 may apply the second edge preserving smoothing filter in the first smoothed image by the second smoothed image and the first edge preserving smoothing filter applied GLPF (I _{init _smooth),} final smoothing image ( I _{final_smoothed} ) (S305).

After S305, the tone mapping unit 100 calculates an adaptive reference value R using the last smoothed image (I _{final _smoothed)} the generated (S306)

For reference, the adaptive reference value R can be calculated using Equation (8), and the overall contrast of the region can be enhanced by applying a reference value deformation index to selectively maintain the detail of the bright region or the dark region have.

4 is a diagram illustrating a tone mapping process together with an image according to an embodiment of the present invention.

The tone mapping apparatus 100 generates an image (O _DCAR ) by performing differential compression using the adaptive reference value R (S401).

Thereafter, the tone mapping apparatus 100 applies a local contrast enhancement technique such as adaptive histogram smoothing (CLAHE) to the image (O _DCAR ) of S401 to adjust the local tone mapping image (O _LTMO ) (S402).

On the other hand, the tone mapping apparatus 100 is initially compressed image (I _log) the normalized image (I _{log _norm)} histogram (histogram equalization) and a global tone mapping image (O _GTMO) to perform the global contrast enhancement techniques such as in the (S403).

For convenience of explanation, _although the step of generating the global tone mapping image O _GTMO is described after the step of generating the local tone mapping image O _LTMO , the two steps may be performed in parallel.

Then, the tone mapping unit 100 generates the final image tone mapping (O _{TMO, TMO _L} O) a combination of a global tone mapping image (O _GTMO) and the local tone mapping image _(LTMO O) (S404).

The tone mapping unit 100 may generate the last tone mapping image (O _TMO, O _{TMO _L)} by using the equation 10 or equation (11)], where γ is used for an objective image quality evaluation method ≪ / RTI >

5A and 5B are views illustrating an image generated in the tone mapping process according to an exemplary embodiment of the present invention.

(a) is an image (O _DCAR ) generated by differential compression using an adaptive reference value R, which is generated by Equation (6).

(b) is a local tone mapping image (O _LTMO ) generated by (9). (B) is the result of performing the adaptive histogram smoothing (CLAHE) of the contrast limitation on the image (O _DCAR ) of (a).

(c) is a global tone mapping image (O _GTMO ) generated by Equation (3).

(d) is a final tone mapping image ( _TMO ) obtained by combining the global tone mapping image O _GTMO and the local tone mapping image O _LTMO according to _Equation ( ₁₀ ). For reference, in (d), γ in (10) is set to 0.5.

(e) is an image based on a saliency map VS, and it is possible to identify a part to be visually noted, that is, a stained glass part.

)이다.(f) is an image obtained by applying an edge preserving smoothing filter to the map of interest area (e)

)to be.

(g) can be obtained by _{combining the} global tone mapping image O _GTMO and the local tone mapping image O _LTMO according to _Equation ( ₁₁ ), and the final tone mapping image O _{TMO_L} ).

(h) is a final tone mapping image ( _TMO ) obtained by combining the global tone mapping image O _GTMO and the local tone mapping image O _LTMO according to _Equation ( ₁₀ ).

For reference, γ in Equation (10) in (h) is the optimal value (γ = 0.8) set by the objective image quality evaluation method.

For reference, in (g) and (h), detail preservation or naturalness can be selectively emphasized according to the parameter? Value corresponding to the combination ratio of two images (O _GTMO , O _LTMO ) Is necessary.

For this purpose, the optimal γ can be determined using the objective quality model of the tone mapping image.

It will be understood by those skilled in the art that the foregoing description of the present invention is for illustrative purposes only and that those of ordinary skill in the art can readily understand that various changes and modifications may be made without departing from the spirit or essential characteristics of the present invention. will be.

It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

For example, each component described as a single entity may be distributed and implemented, and components described as being distributed may also be implemented in a combined form.

The scope of the present invention is defined by the appended claims, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included within the scope of the present invention.

100: tone mapping device
110: Global tone mapping unit
120: Local tone mapping unit
130: tone mapping image combining unit
140:
150:

Claims (18)

1. A tone mapping apparatus for a high dynamic range (HDR) image,
Global compression of the HDR image, normalization of the global compressed image, and global contrast enhancement of the normalized image to generate a global tone mapping image A global tone mapping unit generating;
A local tone mapping unit generating a local tone mapping image by compressing a difference between each pixel value of the global compressed image and an adaptive reference value and applying an algorithm for contrast enhancement; And
A tone mapping image combining unit for combining the generated global tone mapping image and the local tone mapping image to generate a final tone mapping image,
, ≪ / RTI &
The local tone mapping unit
Calculating the adaptive reference value,
Applying a first edge preserving smoothing filter to the normalized image to generate a first smoothed image, applying a low pass filter to the first smoothed image to generate a second smoothed image, A second edge preserving smoothing filter is applied to the smoothing image and the second smoothing image to generate a final smoothing image,
And calculates the adaptive reference value using the final smoothed image, the global compressed image, and the adaptive reference value deformation index.
delete The method according to claim 1,
The adaptive reference value change index
Is an arbitrary constant value that is less than one, and is used to selectively maintain details of a bright region or a dark region.
The method of claim 3,
The local tone mapping image portion
And calculates the adaptive reference value R using the following equation.
[Mathematical Expression]

Here, i and j are pixel coordinates, I _log is the global compression image, I _{final smoothed} is the final smoothing image, and a is the adaptive reference value deformation index.
5. The method of claim 4,
The local tone mapping unit
And generates an image ODCAR obtained by compressing a difference between each pixel value of the global compressed image and an adaptive reference value using the following equation.
[Mathematical Expression]

Here, i and j are pixel coordinates, I _log is the global compression image, R is the adaptive reference value,? Is the exponent of the nonlinear compression function, and sgn () is the sign function.
6. The method of claim 5,
The nonlinear compression function index < RTI ID = 0.0 >
Wherein the enhancement unit enhances the contrast of a pixel value located in the periphery of the adaptive reference value with a value of 0?
6. The method of claim 5,
The local tone mapping unit
_Wherein the local tone enhancement technique, which is an algorithm for enhancing the contrast, is applied to the O _DCAR to generate the local tone mapping image O _LTMO , using the following equation.
[Mathematical Expression]

Here, i and j are pixel coordinates, and CLAHE () is a Contrast Limited Adaptive Histogram Equalization (CLAHE) function of the contrast limitation included in the local contrast enhancement technique.
The method according to claim 1,
The tone mapping image combining unit
And generates the final tone mapping image O _TMO using the following equation.
[Mathematical Expression]

Here, i and j are pixel coordinates, O _GTMO is a global tone mapping image, O _LTMO is a local tone mapping image, and γ is a blending factor.
The method according to claim 1,
The tone mapping image combining unit
Visual attention (visual saliency) a detailed tone mapping unit to reflect the image region is adaptively, characterized in that using the last tone mapping image O _TMO but generate _{_L,} the following equation has.
[Mathematical Expression]

Here, i and j are pixel coordinates, O _GTMO is a global tone mapping image, O _LTMO is a local tone mapping image, γ is a blending factor,

Is a saliency aware weighting function for HDR tone mapping as a saliency map of interest.
10. The method according to claim 8 or 9,
Wherein the blending factor gamma is for balance between local detail and global luminance, and has a range from 0 to 1, and is determined by an objective image quality evaluation method.
A method for tone mapping a high dynamic range (HDR) image in a tone mapping apparatus,
(a) globally compressing an HDR image;
(b) performing normalization on the global compressed image, performing a global contrast enhancement technique on the normalized image, and generating a global tone mapping image,
Generating a local tone mapping image by compressing a difference between each pixel value of the global compressed image and an adaptive reference value and applying an algorithm for contrast enhancement; And
(c) generating a final tone mapping image by combining the generated global tone mapping image and a local tone mapping image
, ≪ / RTI &
The step (b)
Calculating the adaptive reference value
, ≪ / RTI &
The step of calculating the adaptive reference value
Generating a first smoothed image by applying a first edge preserving smoothing filter to the normalized image;
Generating a second smoothed image by applying a low pass filter to the first smoothed image;
Generating a final smoothing image by applying a second edge preserving smoothing filter to the first smoothing image and the second smoothing image; And
Calculating the adaptive reference value using the final smoothed image, the global compressed image, and the adaptive reference value modification index
Gt; a < / RTI > tone mapping method.
delete 12. The method of claim 11,
Wherein the adaptive reference value change index
Is a constant value that is less than one and is used to selectively maintain details of the bright or dark areas.
14. The method of claim 13,
The step (b)
Generating an image O _{DCAR in} which a difference between each pixel value of the global compressed image and an adaptive reference value is compressed,
Wherein the non-linear compression function index has a value in a range of 0?? 1, and the non-linear compression function index that enhances the contrast of a pixel value located in the periphery of the adaptive reference value closer to 0 is generated.
15. The method of claim 14,
The step (b)
And the local tone mapping image O _LTMO is generated by applying a local contrast enhancement technique to the O _DCAR , which is an algorithm for enhancing the contrast.
Wherein the local contrast enhancement technique comprises Contrast Limited Adaptive Histogram Equalization (CLAHE) of contrast constraint.
12. The method of claim 11,
The step (c)
Generates a final tone mapping image O _TMO by applying a blending factor,
Wherein the blending factor is for balance of local detail and global luminance, and has a range from 0 to 1, and is determined by an objective image quality evaluation method.
12. The method of claim 11,
The step (c)
A final tone mapping image O _{TMO_L} is generated by adaptively reflecting a detailed image area having a blending factor and a visual _saliency ,
The blending factor is for balance between local detail and global luminance, ranging from 0 to 1, and is determined by an objective image quality evaluation method. The visual attention score is a saliency map, aware weighting function. < / RTI >
A computer program stored in a recording medium comprising a series of instructions for performing the method according to claim 11.

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