KR101389932B1 - Apparatus and method for performing tone mapping for image - Google Patents

Abstract

The present invention relates to an image tone mapping apparatus and method. According to the present invention, a more natural and finely rendered image can be obtained compared to the conventional tone mapping algorithm. Furthermore, according to the present invention, the representation of the dark region of the image can be preserved better than the conventional tone mapping algorithm, thereby improving the subjective image quality felt by the user.

Description

Image tone mapping device and method {APPARATUS AND METHOD FOR PERFORMING TONE MAPPING FOR IMAGE}

The present invention relates to an apparatus and method for performing tone mapping on an image.

The dynamic range of brightness that the human eye can feel ranges from hundreds of thousands to billions. On the other hand, a display device for reproducing a general video has a dynamic range of 256 because hundreds of dynamic ranges are enough to display most of the image information. However, in the case of a medical image that needs to generate an image similar to an actual natural image through a large amount of calculation or a more detailed information, the image must be represented with a dynamic range larger than 256. Such an image is called an image having a wide dynamic range. In order to reproduce an image having a wide dynamic range on a general display device or a printing device, it is necessary to convert the image having a limited dynamic range supported by each device. Tone mapping refers to a process of converting an image having a wide dynamic range, that is, a high dynamic range (HDR) image into a low dynamic range (LDR) image, which has a limited dynamic range that can be reproduced on a display device or a printing device. do.

The present invention provides an image tone mapping apparatus and method for adaptively determining a parameter used for tone mapping according to the contrast ratio of an image, and tone mapping the image to match the contrast ratio of the display device using the parameter. For the purpose of

An image tone mapping apparatus according to an embodiment of the present invention includes: a parameter determining unit configured to acquire a contrast ratio of an image and determine a parameter regarding a distribution of illumination irradiated to a subject of the image according to the contrast ratio; A color value calculator configured to calculate an original color value of the subject from the color value of the image using the parameter; A luminance value calculator for calculating a luminance value from the original color value; A luminance value adjusting unit that adjusts the luminance value to match the contrast ratio of the display device; And a color value adjusting unit for adjusting the original color value based on a relationship between the luminance value before the adjustment and the luminance value after the adjustment.

The image tone mapping method according to an embodiment of the present invention determines a parameter relating to the distribution of illumination irradiated to a subject of the image according to the contrast ratio of the image, and uses the parameter to match the contrast ratio of the display device. Tone can be mapped. According to an embodiment of the present invention, the image tone mapping method includes: obtaining a contrast ratio of the image; Determining the parameter according to the contrast ratio; Calculating the original color value of the subject from the color value of the image using the parameter; Calculating a luminance value from the original color value; Adjusting the luminance value to match the contrast ratio of the display device; And adjusting the original color value based on a relationship between the luminance value before the adjustment and the luminance value after the adjustment.

An image processing apparatus according to an embodiment of the present invention includes: a receiving unit for receiving an image; A tone mapping unit for tone mapping the received image; And an output unit configured to output the tone-mapped image, wherein the tone mapping unit comprises: a parameter for acquiring a contrast ratio of the image and determining a parameter regarding a distribution of illumination irradiated to a subject of the image according to the contrast ratio Decision unit; A color value calculator configured to calculate an original color value of the subject from the color value of the image using the parameter; A luminance value calculator for calculating a luminance value from the original color value; A luminance value adjusting unit that adjusts the luminance value to match the contrast ratio of the display device; And a color value adjusting unit for adjusting the original color value based on a relationship between the luminance value before the adjustment and the luminance value after the adjustment.

The image tone mapping method according to an embodiment of the present invention described above may be implemented as a computer executable program and recorded on a computer readable recording medium.

According to the present invention, it is possible to provide a more naturally rendered image than the conventional tone mapping algorithm. As a result, the subjective quality felt by the user for the tone-mapped image may be improved, and artifacts in the image may be reduced.

In addition, according to the present invention, it is possible to obtain an effect that can more precisely express the dark region of the image than the conventional tone mapping algorithm.

1 is a block diagram of an image tone mapping apparatus according to an embodiment of the present invention.
2 is a graph illustrating a relationship between a contrast ratio of an image and a parameter k value of a Retinex algorithm according to an embodiment of the present invention.
3 illustrates a graph of luminance values of an image after tone mapping with respect to luminance values of an image before tone mapping according to an embodiment of the present invention.
4 is a flowchart of an image tone mapping method according to an embodiment of the present invention.
5 is a block diagram of an image processing apparatus according to an embodiment of the present invention.
6 to 10 are diagrams comparing a tone mapped image with a tone mapped image in a conventional manner according to an embodiment of the present invention.

Other advantages and features of the present invention and methods of achieving them will become apparent with reference to the embodiments described below in detail with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art. Is provided to fully convey the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims.

Unless defined otherwise, all terms (including technical or scientific terms) used herein have the same meaning as commonly accepted by the generic art in the prior art to which this invention belongs. Terms defined by generic dictionaries may be interpreted to have the same meaning as in the related art and / or in the text of this application, and may be conceptualized or overly formalized, even if not expressly defined herein I will not.

The terminology used herein is for the purpose of illustrating embodiments and is not intended to be limiting of the present invention. In the present specification, the singular form includes plural forms unless otherwise specified in the specification. As used herein, the terms' comprise 'and / or various forms of use of the verb include, for example,' including, '' including, '' including, '' including, Steps, operations, and / or elements do not preclude the presence or addition of one or more other compositions, components, components, steps, operations, and / or components. The term 'and / or' as used herein refers to each of the listed configurations or various combinations thereof.

It should be noted that the terms such as '~', '~ period', '~ block', 'module', etc. used in the entire specification may mean a unit for processing at least one function or operation. For example, a hardware component, such as a software, FPGA, or ASIC. However, '~ part', '~ period', '~ block', '~ module' are not meant to be limited to software or hardware. Modules may be configured to be addressable storage media and may be configured to play one or more processors. ≪ RTI ID = 0.0 >

Thus, by way of example, the terms 'to', 'to', 'to block', 'to module' refer to components such as software components, object oriented software components, class components and task components Microcode, circuitry, data, databases, data structures, tables, arrays, and the like, as well as components, Variables. The functions provided in the components and in the sections ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ' , '~', '~', '~', '~', And '~' modules with additional components.

1 is a block diagram illustrating an image tone mapping apparatus 100 according to an embodiment of the present invention. The image tone mapping apparatus 100 according to an embodiment of the present invention determines a parameter related to the distribution of illumination irradiated to a subject of an image according to the contrast ratio of the image to be tone mapped, and uses the parameter to display an image of the display apparatus. Tone mapping can be made to match the contrast ratio.

Image tone mapping apparatus 100 according to an embodiment of the present invention is a parameter determination unit 101, the color value calculation unit 102, the luminance value calculation unit 103, the luminance value adjustment unit 104 and the color value adjustment unit ( 105). The parameter determiner 101 may acquire a contrast ratio of an image and determine a parameter regarding a distribution of illumination emitted to a subject of the image according to the contrast ratio. The color value calculator 102 may calculate the original color value of the subject from the color value of the image using the parameter. The luminance value calculator 103 may calculate a luminance value from the original color value. The luminance value adjusting unit 104 may adjust the luminance value to match the contrast ratio of the display device. The color value adjusting unit 105 may adjust the original color value based on the relationship between the luminance value before the adjustment and the luminance value after the adjustment.

The parameter determiner 101 may calculate the contrast ratio, that is, the dynamic range, of the image to be tone mapped by the following equation:

Here, D is the contrast ratio of the image, I _max is the maximum luminance value of the pixels constituting the image, I _min is the minimum luminance value of the pixels constituting the image.

Then, the parameter determiner 101 may determine a parameter relating to the distribution of illumination irradiated to the subject of the image, according to the calculated contrast ratio. The parameter is a parameter used in a tone mapping algorithm, and according to an embodiment of the present invention, the parameter may correspond to a parameter k of a Retinex algorithm as shown in the following equation:

Here, R _SSR is a reflection component of the subject shown in the image, and represents a color value of light reflected from the subject regardless of the distribution of illumination applied to the subject. The color value may include an R color value, a G color value, and a B color value in which light forms three primary colors. I (x, y) is the color value of the pixels constituting the image. I _m is a ^blur convolution values the I (x, y) with the Gaussian filter (Gaussian Filter).

The color of an object recognized by a human may be expressed as a product of a distribution of a light source and a reflection component that is light reflected from the object. If we estimate the distribution of the light source from the color perceived by humans, we can find the reflection component representing the original color value of the object. The light irradiated from the light source has a non-uniform distribution, and the Retinex algorithm estimates the distribution of the light source using a Gaussian filter. As such, the Retinex algorithm can compensate for blurring that may occur in the image generation process based on human visual characteristics, maintain the constant color of the image even when the lighting environment changes, and contrast ratio of the HDR image. Can be used to generate the LDR image by compressing.

According to one embodiment of the present invention, the parameter determiner 101, according to the contrast ratio of the image to be tone-mapped, the distribution of the illumination irradiated to the subject in the equation (2) representing the Retinex algorithm log (I _m ^blur ( It is possible to adaptively determine the parameter k, which is a weight for x, y)).

Referring to Equation 2, since the larger the value of the parameter k divides the reflection value in the image more, the contrast ratio of the image can be compressed more. However, if the reflection component is divided more than necessary in the image, the information of the original image is excessively removed, and thus many artifacts such as color fading may occur in the image. In other words, the larger the value of k, the larger the compression ratio of the contrast ratio of the image, but the artifacts increase. Conversely, the smaller the value of k, the smaller the compression ratio of the contrast ratio of the image, but the artifacts decrease. Since the image tone mapping apparatus 100 according to an embodiment of the present invention performs tone mapping by adaptively determining the k value according to the contrast ratio of the image, the tone mapping efficiency considering the contrast ratio compression factor and the artifact of the image may be improved. have.

2 is a graph illustrating a relationship between contrast ratio of an image and a parameter k value of a Retinex algorithm according to an exemplary embodiment of the present invention.

As shown in FIG. 2, according to an embodiment of the present invention, the parameter determiner 101 may determine the parameter k to be proportional to the contrast ratio. Further, when the contrast ratio is less than or equal to the preset minimum contrast ratio, the parameter determiner 101 may determine the parameter k as the preset minimum parameter value. In addition, when the contrast ratio is greater than the preset maximum contrast ratio, the parameter determiner 101 may determine the parameter k as a preset maximum parameter value.

According to an embodiment of the present invention, the minimum contrast ratio may be 0.25 and the minimum parameter value may be 0.2. According to an embodiment of the present invention, the maximum contrast ratio may be 5.5, and the maximum parameter value may be 0.5. According to an embodiment of the present invention, the slope of the graph of the parameter k value with respect to the contrast ratio may be 0.1. As a result, the parameter determiner 101 may determine the parameter k value from the contrast ratio D according to the following equation:

The aforementioned minimum and maximum contrast ratios, minimum and maximum parameter values, and slopes may be set differently according to embodiments. Furthermore, Equation 3 expresses the relationship between the contrast ratio and the parameter k value in the form of a linear function graph for the contrast ratio section of 0.25 to 5.5, but the parameter determiner 101 has a nonlinearity such as a quadratic function and a tertiary function in the interval. You can map the contrast and parameter k values in the form of a graph. In addition, the section in which the parameter k value increases in proportion to the contrast ratio may be changed according to an embodiment. For example, in one embodiment the interval may be wider or narrower than the interval of 2.5 to 5.5.

According to an embodiment of the present invention, the color value calculating unit 102 uses a retinex algorithm as shown in Equation 3 above (ie, the color value R _SSR of the light reflected from the object). Can be calculated.

The luminance value calculator 103 may calculate a luminance value from the original color value of the subject. According to an embodiment of the present invention, the luminance value calculator 103 may calculate the luminance value L from the original color values R, G, and B of the subject by the following equation:

L = 0.299R + 0.587G + 0.114B

The luminance value adjusting unit 104 may adjust the calculated luminance value to match the contrast ratio of the display device. In other words, the luminance value adjusting unit 104 may adjust the luminance value of each pixel constituting the HDR image to be suitable for a display device for an LDR image having a low contrast ratio. As a result, the contrast ratio of the HDR image can be compressed to a smaller value and converted into an LDR image.

According to an embodiment of the present invention, the luminance value adjusting unit 104 may adjust the luminance value of the image at different ratios according to the luminance period. 3 illustrates a graph of luminance values of an image after tone mapping with respect to luminance values of an image before tone mapping according to an embodiment of the present invention.

As shown in FIG. 3, the luminance value I _in of the image may be largely divided into a first luminance period 31 and a second luminance period 32, and the first luminance The luminance value of the section 31 is smaller than the luminance value of the second luminance section 32. Curve slope of said adjusted first brightness section 31, before the luminance value adjusted after the luminance value of the I _in I _out is the adjustment in the second brightness section 32, before the luminance value I after adjustment to the _in luminance value I _out Can be greater than the graph slope of. In other words, the third luminance period 33 corresponding to the first luminance period 31 of I _in among the entire luminance intervals of I _out is the fourth luminance interval (ie, the second luminance interval 32 of I _in ). May be wider than 34). As a result, the dark areas of the image can be expressed in more detail and detail, and the bright areas can be expressed by compressing the luminance section as compared to before tone mapping.

According to an embodiment of the present invention, the luminance value may be adjusted by the following equation:

Here, I _out is the luminance value after adjustment, I is the luminance value before adjustment, I _max is the maximum luminance value of the pixel which comprises an image, and a is a parameter regarding the adjustment ratio of a luminance value. A is a parameter related to the curvature of the graph shown in FIG. 3, and as the a is larger, the curvature of the graph becomes larger and the fourth luminance section 34 becomes narrower, and as the a is smaller, the curvature becomes smaller and thus the fourth luminance section 34 becomes smaller. This widens. According to an embodiment of the present invention, the a may be set to 4, but is not limited thereto and may be set to various values according to the embodiment.

Algorithm such as the above equation (5) reflects the characteristic that the human visual system is more sensitive to changes in the dark part than the bright part. When the luminance value adjusting unit 104 adjusts the luminance value of the image as shown in Equation 5, since the luminance level section representing the dark region is wider than the bright region, the dark region of the tone-mapped image may be better preserved. have.

According to another embodiment of the present invention, the luminance value I _in before adjustment may be divided into three or more sections. In this case, the graph inclination of the luminance value after the adjustment with respect to the luminance value before the adjustment may be set differently for each section.

The color value adjusting unit 105 may adjust the original color value of the subject based on the relationship between the luminance value before the adjustment and the luminance value after the adjustment. According to one embodiment of the invention, the color value adjusting unit 105, the ratio of the luminance value I _out after the adjustment to the luminance value I _in before the adjustment, the ratio of the original color value after the adjustment to the original color value before adjustment The original color value of the subject may be adjusted to be the same. For example, the color value adjusting unit 105 may adjust the color value of the subject by the following equation:

Where R _out , G _out, and B _out are the original color values of the subject after adjustment, R _in , G _in, and B _in are the original color values of the subject before adjustment, L 'is the luminance value of the image after adjustment, and L _in is the luminance value of the image before adjustment, and s is the gamma correction coefficient. According to an embodiment of the present invention, the s may be selected to a value of 0 to 1, for example, may be set to 0.75.

4 is a flowchart illustrating an image tone mapping method according to an embodiment of the present invention. As shown in FIG. 4, the image tone mapping method 40 according to an exemplary embodiment of the present invention may include obtaining a contrast ratio of an image (S41), and a distribution of illumination irradiated onto a subject of the image according to the contrast ratio. Determining a related parameter (S42), calculating an original color value of the subject from the color value of the image using the parameter (S43), calculating a luminance value from the original color value (S44), and the luminance Adjusting the value to match the contrast ratio of the display device (S45), and adjusting the original color value based on the relationship between the luminance value before the adjustment and the luminance value after the adjustment (S46).

Obtaining the contrast ratio of the image (S41) may include calculating the contrast ratio of the input image by using Equation 1 described above.

Determining a parameter relating to a distribution of illumination irradiated onto a subject of an image according to the contrast ratio may include determining the parameter to be proportional to the contrast ratio; If the contrast ratio is less than or equal to a preset minimum contrast ratio, determining the parameter as a preset minimum parameter value; If the contrast ratio is greater than a preset maximum contrast ratio, the method may include determining the parameter as a preset maximum parameter value. According to an embodiment of the present invention, the determining of the parameter according to the contrast ratio (S42) may include determining the parameter using Equation 3 described above.

Computing the original color value of the subject from the color value of the image using the parameter (S43), calculating the original color value of the subject using a Retinex algorithm implemented by Equation 2 described above. It may include.

The calculating of the luminance value from the original color value (S44) may include calculating the luminance value from the original color values R, G, and B values of the subject using Equation 4 described above.

The adjusting of the luminance value to match the contrast ratio of the display apparatus (S45) may include adjusting the luminance value at a different ratio according to the luminance period. According to an exemplary embodiment of the present disclosure, in the adjusting of the luminance value (S45), the slope of the graph of the luminance value after the adjustment with respect to the luminance value before the adjustment in the first luminance period 31 may include a second luminance interval ( And adjusting the luminance value to be greater than the slope of the graph of the luminance value after the adjustment with respect to the luminance value before the adjustment. The luminance value of the first luminance period 31 may be lower than the luminance value of the second luminance period 32. According to an embodiment of the present disclosure, the adjusting of the luminance value (S45) may include adjusting the luminance value according to Equation 5 described above.

Adjusting the original color value based on the relationship between the luminance value before the adjustment and the luminance value after the adjustment (S46), the ratio of the luminance value after the adjustment to the luminance value before the adjustment And adjusting the original color value to be equal to the ratio of values. According to an embodiment of the present disclosure, the adjusting of the original color value (S46) may include adjusting the original color value by Equation 6 described above.

5 is a block diagram illustrating an image processing apparatus 50 according to an embodiment of the present invention. As shown in FIG. 5, the image processing apparatus 50 according to an exemplary embodiment of the present invention includes a receiver 51 that receives an image, a tone mapper 52 that tone-tones the received image, and a tone mapping. It may include an output unit 53 for outputting the image. The tone mapping unit 52 may include a parameter determiner 521, a color value calculator 522, a luminance value calculator 523, a luminance value adjuster 524, and a color value adjuster 525. The parameter determiner 521, the color value calculator 522, the luminance value calculator 523, the luminance value adjuster 524, and the color value adjuster 525 included in the tone mapping unit 52 are shown in FIG. 1. The parameter determiner 101, the color value calculator 102, the luminance value calculator 103, the luminance value adjuster 104, and the color value adjuster 105 included in the image tone mapping apparatus 100 described with reference to the image tone mapping apparatus 100 described above. Same as the configuration.

The image processing apparatus 50 may further include a storage 53. The storage unit 53 may store information required to perform tone mapping on the image. The storage unit 53 may store at least one of an image to be tone mapped and a tone mapped image.

According to an embodiment of the present invention, the tone mapping unit 52 may adjust the luminance value level of the received image according to the contrast ratio of the display device so as to convert the HDR image into an LDR image.

The image tone mapping method 40 according to an embodiment of the present invention described above may be produced as a program for execution in a computer and stored in a computer-readable recording medium. The computer-readable recording medium includes all kinds of storage devices in which data that can be read by a computer system is stored. Examples of the computer-readable recording medium include ROM, RAM, CD-ROM, magnetic tape, floppy disk, optical data storage, and the like.

6 to 10 are diagrams comparing a tone mapped image with a tone mapped image in a conventional manner according to an embodiment of the present invention. (A) of FIG. 6 to FIG. 10 are tone mapped images using a logarithmic tone mapping algorithm, which is a representative wide tone mapping algorithm, and (b) is a gradient tone mapping algorithm for performing tone mapping in the frequency domain. (C) is a tone-mapped image by a Retinex algorithm using a fixed k value, and (d) is a tone-mapped image by a tone mapping method according to an embodiment of the present invention. Tone mapping for the images of FIGS. 6-10 was performed on a computer equipped with a 2.40 GHz CPU and 3 GB of RAM. The contrast ratios and corresponding parameter k values for each of the images of FIGS. 6 to 10 are as follows:

image Contrast ratio (log) Parameter k 6 1.96 0.20 7 3.94 0.34 8 4.61 0.41 9 5.52 0.50 10 5.59 0.50

When comparing the tone-mapped output images of (a) to (d) in each of FIGS. 6 to 10, according to an embodiment of the present invention, the tone-mapped images (a) to (c) by conventional algorithms are compared. You can see that the tone-mapped image (d) is rendered more naturally and the artifacts are reduced. Furthermore, in the case of tone mapping according to an embodiment of the present invention, it can be seen that the representation of the dark area of the image is more sophisticated.

The image tone mapping apparatus and method according to an embodiment of the present invention for adaptively determining a parameter relating to the distribution of illumination irradiated to the subject of the image according to the contrast ratio of the image and tone mapping the image using the parameter Explained. According to the present invention, a more natural and finely rendered image can be obtained compared to the conventional tone mapping algorithm. Furthermore, according to the present invention, the representation of the dark region of the image can be preserved better than the conventional tone mapping algorithm, thereby improving the subjective image quality felt by the user.

100: image tone mapping device 101: parameter determination unit
102: color value calculator 103: luminance value calculator
104: luminance value adjusting unit 105: color value adjusting unit

Claims (21)

A parameter determining unit obtaining a contrast ratio of an image and determining a parameter regarding a distribution of illumination irradiated to a subject of the image according to the contrast ratio;
A color value calculator configured to calculate an original color value of the subject from the color value of the image using the parameter;
A luminance value calculator for calculating a luminance value from the original color value;
A luminance value adjusting unit that adjusts the luminance value to match the contrast ratio of the display device; And
A color value adjusting unit for adjusting the original color value based on a relationship between the luminance value before the adjustment and the luminance value after the adjustment;
Image tone mapping device comprising a. The method of claim 1,
And the parameter determiner determines the parameter to be proportional to the contrast ratio. The method of claim 1,
And the parameter determining unit determines the parameter as a predetermined minimum parameter value when the contrast ratio is less than or equal to a predetermined minimum contrast ratio. The method of claim 1,
And the parameter determining unit determines the parameter as a preset maximum parameter value when the contrast ratio is greater than a preset maximum contrast ratio. The method of claim 1,
The color value calculator calculates an original color value of the subject using a Retinex algorithm. The method of claim 1,
The image tone mapping apparatus of claim 1, wherein the distribution of illumination irradiated onto the subject is obtained by convolving a color value of the image and a Gaussian filter. The method of claim 1,
The luminance value calculating section is a luminance value by a formula of L = 0.299 R + 0.587 G + 0.114 B (where L is luminance value, R is R color value, G is G color value and B is B color value). Image tone mapping device to yield. The method of claim 1,
And the luminance value adjusting unit adjusts the luminance value at different ratios according to luminance intervals. The method of claim 8,
The luminance value adjusting unit may be configured such that the slope of the graph of the luminance value after adjustment with respect to the luminance value before adjustment in the first luminance period is greater than the slope of the graph of the luminance value after adjustment with respect to the luminance value before adjustment in the second luminance period. And an image tone mapping device for adjusting the luminance value. The method of claim 9,
And a luminance value of the first luminance interval is lower than a luminance value of the second luminance interval. The method of claim 1,
And the color value adjusting unit adjusts the original color value such that the ratio of the brightness value after the adjustment to the brightness value before the adjustment is equal to the ratio of the original color value after the adjustment to the original color value before the adjustment. And determining a parameter relating to a distribution of illumination irradiated to a subject of the image according to the contrast ratio of the image, and tone mapping the image to match the contrast ratio of the display device using the parameter. 13. The method of claim 12,
The image tone mapping method is:
Obtaining a contrast ratio of the image;
Determining the parameter according to the contrast ratio;
Calculating the original color value of the subject from the color value of the image using the parameter;
Calculating a luminance value from the original color value;
Adjusting the luminance value to match the contrast ratio of the display device; And
Adjusting the original color value based on a relationship between the luminance value before adjustment and the luminance value after adjustment;
Image tone mapping method comprising a. 14. The method of claim 13,
Obtaining the contrast ratio of the image is:

Obtaining a contrast ratio by a formula wherein D is a contrast ratio, I _max is a maximum luminance value of the image, and I _min is a minimum luminance value of the image. 14. The method of claim 13,
Determining the parameter according to the contrast ratio:

Determining a parameter by a formula of k where a parameter is a parameter and D is a contrast ratio. 14. The method of claim 13,
The step of calculating the original color value is:

(Where I (x, y) is the R, G, and B color values of the image, k is the parameter, and I _m ^blur is the convolution of I (x, y) and a Gaussian filter) And calculating a value. 14. The method of claim 13,
Adjusting the luminance value is:

Where I _out is the adjusted luminance value, I is the luminance value before adjustment, I _max is the maximum luminance value of the image, and a is a parameter relating to the adjustment ratio of the luminance value. Include image tone mapping method. 14. The method of claim 13,
Adjusting the original color value is:

(Where R _out , G _out, and B _out are the adjusted original color values, R _in , G _in, and B _in are the adjusted original color values, L 'is the luminance value after adjustment, L _in is the luminance value before adjustment, s And adjusting the original color value by the equation of gamma correction coefficient. A receiving unit for receiving an image;
A tone mapping unit for tone mapping the received image; And
An output unit for outputting the tone-mapped image,
The tone mapping unit:
A parameter determining unit obtaining a contrast ratio of the image and determining a parameter regarding a distribution of illumination irradiated to a subject of the image according to the contrast ratio;
A color value calculator configured to calculate an original color value of the subject from the color value of the image using the parameter;
A luminance value calculator for calculating a luminance value from the original color value;
A luminance value adjusting unit that adjusts the luminance value to match the contrast ratio of the display device; And
A color value adjusting unit for adjusting the original color value based on a relationship between the luminance value before the adjustment and the luminance value after the adjustment;
And the image processing apparatus. The method of claim 19,
The tone mapping unit converts a high dynamic range (HDR) image into a low dynamic range (LDR) image. A computer-readable recording medium,
Obtaining a contrast ratio of the image;
Determining a parameter relating to a distribution of illumination irradiated to a subject of the image according to the contrast ratio;
Calculating the original color value of the subject from the color value of the image using the parameter;
Calculating a luminance value from the original color value;
Adjusting the luminance value to match the contrast ratio of the display device; And
Adjusting the original color value based on a relationship between the luminance value before adjustment and the luminance value after adjustment;
A recording medium on which a program for implementing an image tone mapping process is recorded.

Images