JP2015035755A - Luminosity adjusting device, luminosity adjusting method, and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a luminosity adjusting device and the like which can adjust brightness of an image while retaining visual saturation for a user.SOLUTION: A feature amount acquisition part 25 acquires as a feature amount A a luminance value that averages all pixels by a moving average filter with respect to an input image, an image in an RGB color space of adjusted luminance, and an image in a YCbCr color space respectively. The feature amount acquisition part 25 acquires as a feature amount B a ratio of a luminance value of an attention pixel to the feature amount A of a peripheral pixel with respect to the input image, the image in the RGB color space of adjusted luminance, and the image in the YCbCr color space respectively. A luminosity adjustment part 26 determines an output pixel value of each pixel by using a first determination condition to adopt a pixel value of an image in a color space of small feature amount difference from the feature amount B of the input image, a second determination condition to adopt a pixel value of an image in a color space of large feature amount difference from the feature amount A of the input image, and a third determination condition to adopt a pixel value of an image in the color space that is not adopted in the second determination condition.

Description

  The present invention relates to image processing such as image editing and correction, and more particularly to a brightness adjusting device for adjusting the brightness of an image.

  When editing or correcting an image, a process is performed in which a dark image is bright and a bright image is dark. In general image processing software, the brightness of an image is controlled by manipulating a tone curve using the RGB value of the image as luminance or a tone curve only for L (brightness) in the Lab color space (L * a * b * color space). Adjust the height. However, in the case of a tone curve with RGB values as luminance, the saturation is lowered when the image is brightened, and the saturation is increased when the image is darkened. Also, not only the lightness and darkness of the image changes, but also the user does not intend. The image may end up.

  In the case of a tone curve having only L (brightness) in the Lab color space, the brightness can be adjusted without affecting the saturation. For example, Patent Document 1 describes an image processing apparatus that adjusts L (brightness) and then performs color balance adjustment on the ab plane with the L value fixed.

JP 2007-228322 A

  However, the technique described in Patent Document 1 has a problem that a desired saturation is partially obtained by adjusting L (brightness), but a region with insufficient brightness is generated.

  In addition, when adjusting the brightness of an image by operating a tone curve with RGB values as luminance, there is a problem that a desired brightness can be partially obtained but a region with insufficient saturation is generated. .

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a brightness adjustment device and the like that can adjust the brightness of an image while maintaining the saturation of the appearance of the user. That is.

A first invention for achieving the above-described object is a lightness adjusting device for adjusting the lightness of an input image represented in a predetermined color space, wherein the amount of change in the lightness of the output image with respect to the input image is subjected to image processing. Image processing intensity determining means for determining the intensity, color space converting means for converting the image represented in the predetermined color space into an image of another color space including luminance information, and the determined image processing intensity. In response to the input image and the other color space image obtained by converting the input image by the color space conversion unit, a luminance adjustment unit that performs luminance adjustment, and the input that is not luminance-adjusted For each of the image, the brightness-adjusted input image, and the brightness-adjusted image in the other color space, a feature amount acquisition unit that acquires a feature amount, and based on the acquired feature amount, The input , And brightness adjusting means for performing brightness adjustment of the image is the brightness adjusting device, characterized in that it comprises a.
Here, the “predetermined color space” is, for example, an RGB color space. “Another color space including luminance information” is, for example, a YCbCr color space or a Lab color space.
According to the first invention, it is possible to adjust the brightness of the image while maintaining the apparent saturation of the user.

The feature amount acquisition unit acquires luminance information for each image by the color space conversion unit, and for all pixels, a feature amount indicating brightness in the vicinity of the target pixel and brightness in the vicinity of the target pixel. It is desirable to acquire a feature amount indicating a ratio to
Thereby, the brightness of the neighboring pixels in the target pixel with respect to each of the input image that has not been brightness adjusted, the input image that has been brightness adjusted, and the image of the other color space that has been brightness adjusted. It is possible to acquire a feature quantity related to.

The feature amount acquisition unit acquires luminance information for each image by the color space conversion unit, calculates an average luminance value from the target pixel and peripheral pixels for all pixels, and calculates the position of the target pixel. The feature value A (referred to as feature values AA, AB, and AC for each image) is acquired and the ratio between the brightness value of the target pixel and the brightness value at the position of the target pixel of the feature amount A is acquired. It is desirable to acquire a feature amount B (referred to as feature amounts BA, BB, and BC for each image) as a pixel value at the position of the target pixel.
Accordingly, the luminance value of the pixel in the vicinity of the target pixel with respect to each of the input image that has not been adjusted in luminance, the input image that has been adjusted in luminance, and the image in the other color space that has been adjusted in luminance. It is possible to acquire a feature quantity related to.

The brightness adjustment unit employs, for all the pixels of the input image, a pixel value of an image related to a feature quantity having a small difference from the feature quantity BA among the feature quantity BB or the feature quantity BC. A second condition that employs a pixel value of an image relating to a feature quantity having a large difference from the feature quantity AA among the condition, the feature quantity AB or the feature quantity AC, and the feature quantity AB or the feature quantity AC Among them, it is desirable to calculate the output pixel value for each pixel using the third condition that employs the pixel value of the image relating to the feature amount having a small difference from the feature amount AA.
Thus, natural brightness adjustment can be realized based on the feature quantities of a plurality of color spaces.

It is desirable that the lightness adjusting means calculates K, α, and β as constants satisfying K + α + β = 1, and calculates an output pixel value by the equation (1).
Accordingly, the pixel values adopted based on the feature amounts of the plurality of color spaces can be used after being adjusted according to the target image quality.

It is desirable that the brightness adjustment unit adopts a pixel value of the input image that has not been subjected to luminance adjustment when the difference in the feature amount is larger than an allowable range in the first determination condition.
This makes it possible to realize natural brightness adjustment.

The image processing intensity is preferably a tone curve representing a correspondence relationship between the brightness of the input image and the brightness of the output image.
This makes it possible to adjust the brightness with a tone curve that is easy to understand visually.

It is desirable to further include output means for outputting the input image whose brightness has been adjusted by the brightness adjustment means as an output image.
As a result, an image whose brightness has been adjusted can be output to the outside or displayed on the display unit.

A second invention is a lightness adjustment method for adjusting the lightness of an input image represented in a predetermined color space, and determining an image processing intensity that determines an amount of change in lightness of an output image with respect to the input image as an image processing intensity. A color space conversion step of converting the image represented in the predetermined color space into an image of another color space including luminance information, the input image according to the determined image processing intensity, and A luminance adjustment step for performing luminance adjustment on each of the images of the other color spaces obtained by converting the input image by the color space conversion step; the input image that has not been subjected to luminance adjustment; and the input that has undergone luminance adjustment A feature amount acquisition step of acquiring a feature amount for each of the image and the image of the other color space whose brightness has been adjusted, and the input image based on the acquired feature amount. And brightness adjusting step of adjusting a brightness adjusting method characterized in that it comprises a.
According to the second invention, it is possible to adjust the brightness of the image while maintaining the apparent saturation of the user.

A third invention is a program for causing a computer to function as a brightness adjustment device for adjusting the brightness of an input image represented in a predetermined color space, the computer controlling the brightness of an output image with respect to the input image. Image processing intensity determining means for determining the amount of change as image processing intensity, color space converting means for converting an image represented in the predetermined color space into an image of another color space including luminance information, and the determined image In accordance with the processing intensity, a luminance adjustment unit that performs luminance adjustment for each of the input image and the image of the other color space obtained by converting the input image by the color space conversion unit, the luminance is not adjusted Feature quantity acquisition means for acquiring a feature quantity for each of the input image, the brightness-adjusted input image, and the brightness-adjusted image of the other color space, Based on the feature quantity, a program for causing the brightness adjusting means for performing brightness adjustment of the input image function as a.
By installing the program of the third invention in a general-purpose computer, the brightness adjustment device of the first invention can be obtained and the brightness adjustment method of the second invention can be executed.

  According to the present invention, it is possible to adjust the brightness of an image while maintaining the apparent saturation for the user.

It is a figure which shows the structural example of the hardware of the brightness adjustment apparatus which concerns on embodiment of this invention. It is a block diagram which shows the function structural example of a brightness adjustment apparatus. It is a figure explaining the example of a tone curve. It is a flowchart explaining a brightness adjustment process. It is a figure which shows an example of an input image. It is a figure which shows an example of the brightness adjustment image by RGB color space using a prior art. It is a figure which shows an example of the brightness adjustment image by the Y (luminance) channel of YCbCr color space. It is a figure which shows an example of the brightness adjustment image by this Embodiment.

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

[Embodiments of the present invention]
FIG. 1 is a diagram illustrating a hardware configuration example of a brightness adjustment apparatus 1 according to an embodiment of the present invention. Note that the hardware configuration in FIG. 1 is an example, and various configurations can be adopted depending on the application and purpose.

  In the brightness adjustment device 1, a control unit 11, a storage unit 12, a media input / output unit 13, a communication control unit 14, an input unit 15, a display unit 16, a peripheral device I / F unit 17 and the like are connected via a bus 18. The

  The control unit 11 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like. The CPU calls and executes a program stored in the storage unit 12, ROM, recording medium, etc. to a work memory area on the RAM, drives and controls each device connected via the bus 18, and the brightness adjustment device 1 The process to be described later is realized. The ROM is a non-volatile memory, and permanently stores programs such as a boot program of the brightness adjustment device 1, a BIOS (Basic Input / Output System), data, and the like. The RAM is a volatile memory, and temporarily stores a program, data, and the like loaded from the storage unit 12, ROM, recording medium, and the like, and includes a work area used by the control unit 11 to perform various processes.

  The storage unit 12 is an HDD (hard disk drive) or the like, and stores a program executed by the control unit 11, data necessary for program execution, an OS (operating system), and the like. As for the program, a control program corresponding to the OS and an application program for causing the brightness adjusting apparatus 1 to execute processing described later are stored. Each of these program codes is read by the control unit 11 as necessary, transferred to the RAM, read by the CPU, and executed as various means.

  The media input / output unit 13 (drive device) inputs / outputs data, for example, media such as a CD drive (-ROM, -R, -RW, etc.), DVD drive (-ROM, -R, -RW, etc.) Has input / output devices.

  The communication control unit 14 includes a communication control device, a communication port, and the like, and is a communication interface that mediates communication between the brightness adjustment device 1 and the network, and performs communication control between other devices via the network. The network may be wired or wireless.

  The input unit 15 inputs data and includes, for example, a keyboard, a pointing device such as a mouse, and an input device such as a numeric keypad. An operation instruction, an operation instruction, data input, and the like can be performed on the brightness adjustment device 1 via the input unit 15.

  The display unit 16 includes a display device such as a CRT monitor and a liquid crystal panel, and a logic circuit (such as a video adapter) for realizing the video function of the brightness adjustment device 1 in cooperation with the display device.

The peripheral device I / F (interface) unit 17 is a port for connecting a peripheral device to the brightness adjustment device 1. The brightness adjustment device 1 transmits and receives data to and from the peripheral device via the peripheral device I / F unit 17. I do. The peripheral device I / F unit 17 is a USB (Universal Serial Bus) or IEEE (The Institute of Electrical and
Electronics Engineers) 1394, RS-235C, etc., and usually has a plurality of peripheral devices I / F. The connection form with the peripheral device may be wired or wireless.

  The bus 18 is a path that mediates transmission / reception of control signals, data signals, and the like between the devices.

FIG. 2 is a block diagram illustrating a functional configuration example of the brightness adjustment apparatus 1.
The function of the brightness adjustment device 1 includes an image input unit 21, an image processing intensity determination unit 22, a color space conversion unit 23, a brightness adjustment unit 24, a feature amount acquisition unit 25, a brightness adjustment unit 26, and an image display unit 27. The At least a part of the functional units shown in FIG. 2 is realized by executing a brightness adjustment processing program by the control unit 11 of FIG.

  The image input unit 21 inputs an RGB image from a recording medium or a peripheral device via the media input / output unit 13, the communication control unit 14, or the peripheral device I / F (interface) unit 17, or stores in advance a storage unit The image stored in 12 is acquired. The image input unit 21 outputs the input (acquired) RGB image to the image processing intensity determination unit 22, the luminance adjustment unit 24, and the image display unit 27. The image input unit 21 stores an RGB image input from the outside in the storage unit 12.

  The image processing intensity determination unit 22 analyzes the input image from the image input unit 21, extracts the feature amount of the image, and determines the image processing intensity (for example, the shape of the tone curve) according to the feature amount.

  The image processing intensity determination unit 22 displays the input image and tone curve from the image input unit 21 on the display unit 16, and determines the image processing intensity by operating the tone curve from the input unit 15 by the user. You may do it.

  The tone curve is a graph showing the correspondence between the pixel value of the input image and the pixel value of the output image used when adjusting the overall brightness and contrast of the image. As shown in FIG. 3, the value to be changed is represented by a line graph (solid line in the figure), and the tone curve is a straight line (broken line in the figure) showing a direct proportion in the initial state. For example, assume that brightness adjustment is performed for a certain pixel of the input image. Let the amount of increase or decrease in the brightness of this pixel be ΔL. ΔL is the amount of change in L (brightness) of the output image with respect to the input image when the brightness of the image is adjusted by tone curve adjustment of general image processing software (display on the tone curve is “+ ΔL” or “−ΔL”) )).

The color space conversion unit 23 converts the input image from the RGB color space to the YCbCr color space or the Lab color space. Hereinafter, in the present embodiment, an image obtained by converting the RGB color space to the YCbCr color space is used for the brightness adjustment processing.
Note that the color space of the conversion destination converted by the color space conversion unit 23 may be any color space as long as the luminance signal (luminance channel) representing the luminance value is separated from other signals, and the YCbCr color space. And the Lab color space.

The conversion from the RGB color space to the YCbCr color space and its reverse conversion, and the conversion from the RGB color space to the Lab color space and its reverse conversion may be performed using a general color space conversion method.
For example, the conversion from the RGB color space to the YCbCr color space and the reverse conversion from the YCbCr color space to the RGB color space are performed by the following equations (2) and (3), respectively. However, the range of R, G, B, and Y is 0 to 255, and the range of Cb and Cr is 0 to 255 with 128 as the center.

The YCbCr color space is the luminance signal (Y), the difference between the luminance signal Y and the blue component B (U: BY = Cb), and the difference between the luminance signal Y and the red component R (V: R−Y = Cr). It is a color model that expresses color with three pieces of information.
The Lab color space is a type of complementary color space, “L” representing lightness (brightness), “a” representing chromaticity from red (R) to green (G), and blue (B) to yellow (Y 3) “b” representing the chromaticity of), and the amount of change in this three-dimensional space is corrected to be proportional to the impression of the visual color change caused by the change, all that can be perceived by humans It is a color model that represents the color of.

The luminance adjustment unit 24 performs luminance adjustment on the image channel using the tone curve determined by the image processing intensity determination unit 22.
Specifically, the luminance adjustment unit 24 adjusts the luminance of each of the RGB channels with respect to the input image RGB from the image input unit 21 using a tone curve.
Further, the luminance adjustment unit 24 outputs the input image RGB from the image input unit 21 to the color space conversion unit 23, acquires the image converted into the YCbCr color space by the color space conversion unit 23, and Y of the acquired image (Luminance) Adjust the brightness of only the channel using the tone curve.
Then, the luminance adjustment unit 24 outputs to the feature amount acquisition unit 25 an image in the RGB color space in which the luminance of each RGB channel is adjusted, and an image in the YCbCr color space in which only the Y (luminance) channel is adjusted in luminance. To do.

The feature amount acquisition unit 25 acquires two feature amounts from the Y (luminance) channel of each image.
Specifically, first, the feature amount acquisition unit 25 is an RGB image in which the input image from the image input unit 21 (hereinafter referred to as the original image A) and the RGB channels from the luminance adjustment unit 24 are adjusted in luminance. A space image (hereinafter referred to as a brightness adjustment image B) and a YCbCr color space image (hereinafter referred to as a brightness adjustment image C) in which only the Y (luminance) channel has been adjusted in brightness are input.

  Then, the feature amount acquisition unit 25 outputs the original image A to the color space conversion unit 23, and acquires the Y (luminance) channel of the image converted into the YCbCr color space by the color space conversion unit 23 (this process is performed once). Therefore, the converted Y (luminance) channel may be acquired from the color space conversion unit 23 or the luminance adjustment unit 24). Then, the feature amount acquisition unit 25 calculates the average of the target pixel and the surrounding pixels with respect to all pixels of the Y (luminance) channel related to the original image A by using an N × N (for example, 3 × 3) moving average filter. The feature value AA is obtained as the brightness value at the position of the target pixel. That is, the feature amount AA is an image having an average value of luminance values in the vicinity of the target pixel for all pixels.

  Similarly, the feature amount acquisition unit 25 outputs the brightness adjustment image B to the color space conversion unit 23, and acquires the Y (luminance) channel of the image converted into the YCbCr color space by the color space conversion unit 23. Then, the feature amount acquisition unit 25 calculates an average luminance value from the target pixel and the surrounding pixels by using an N × N moving average filter for all pixels of the Y (luminance) channel related to the luminance adjustment image B. Thus, the feature amount AB as the luminance value at the position of the target pixel is acquired.

  Also, the feature amount acquisition unit 25 calculates an average luminance value from the target pixel and the surrounding pixels by using an N × N moving average filter for all pixels of the Y (luminance) channel related to the luminance adjustment image C. Thus, the feature amount AC is acquired as the luminance value at the position of the target pixel.

  Next, the feature amount acquisition unit 25 calculates the ratio between the luminance value of the target pixel and the luminance value of the position of the target pixel of the feature amount AA for all pixels of the Y (luminance) channel related to the original image A. A feature amount BA is obtained as a pixel value at the position of the target pixel. That is, the feature amount BA is an image having a ratio between the luminance value of the target pixel and the average value of the luminance values in the vicinity thereof for all pixels.

  Similarly, the feature amount acquisition unit 25 compares the luminance value of the target pixel and the luminance value of the position of the target pixel of the feature amount AB with respect to all pixels of the Y (luminance) channel related to the luminance value adjusted image B. Is obtained as a pixel value at the position of the target pixel.

  Further, the feature amount acquisition unit 25 calculates the ratio between the luminance value of the target pixel and the luminance value at the position of the target pixel of the feature amount AC for all the pixels of the Y (luminance) channel related to the luminance value adjusted image C. Then, the feature value BC is acquired as the pixel value at the position of the target pixel.

  Then, the feature amount acquisition unit 25 outputs the feature amount AA, the feature amount AB, the feature amount AC, the feature amount BA, the feature amount BB, and the feature amount BC to the brightness adjustment unit 26.

  The brightness adjustment unit 26 includes a feature amount AA, a feature amount AB, a feature amount AC (hereinafter also referred to as a feature amount A), a feature amount BA, a feature amount BB, and a feature amount BC (and above) from the feature amount acquisition unit 25. Based on the feature amount B), the following three determination conditions are applied to each pixel of the image to generate an image with the brightness adjusted.

(First judgment condition)
In the first determination condition, the feature amount BA, the feature amount BB, and the feature amount BC are compared, and the color space in which the brightness correction is performed with less visual discomfort is determined. Note that the allowable range of the feature amount B is determined in advance so as to obtain a color space close to the luminance of the original image A.

(1-1) When the difference between the feature value BA of the original image A and the feature value BB of the brightness adjustment image B <the difference between the feature value BA of the original image A and the feature value BC of the brightness adjustment image C, Adopt a color space.
(1-2) If the difference between the feature amount BA of the original image A and the feature amount BB of the brightness adjustment image B> the difference between the feature amount BA of the original image A and the feature amount BC of the brightness adjustment image C, the brightness adjustment image C Adopt a color space.

(1-3) Allowable range of feature quantity B <difference between feature quantity BA of original image A and feature quantity BB of brightness adjusted image B <difference between feature quantity BA of original image A and feature quantity BC of brightness adjusted image C In this case, the color space of the original image A is adopted.
(1-4) Allowable range of feature quantity B <difference between feature quantity BA of original image A and feature quantity BC of brightness adjusted image C <difference between feature quantity BA of original image A and feature quantity BB of brightness adjusted image B In this case, the color space of the original image A is adopted.

(Second determination condition)
Under the second determination condition, the feature amount AA, the feature amount AB, and the feature amount AC are compared to determine a color space having a large luminance feature amount.
(2-1) When the difference between the feature amount AA of the original image A and the feature amount AB of the brightness adjustment image B <the difference between the feature amount AA of the original image A and the feature amount AC of the brightness adjustment image C, the brightness adjustment image C Adopt a color space.
(2-2) The difference between the feature amount AA of the original image A and the feature amount AB of the brightness adjustment image B> the difference between the feature amount AA of the original image A and the feature amount AC of the brightness adjustment image C, the brightness adjustment image B Adopt a color space.

(Third determination condition)
In the third determination condition, a color space that is not adopted in the second determination condition, that is, a color space with a small luminance feature amount is determined.
(3-1) When the difference between the feature amount AA of the original image A and the feature amount AB of the brightness adjustment image B <the difference between the feature amount AA of the original image A and the feature amount AC of the brightness adjustment image C, the brightness adjustment image B Adopt a color space.
(3-2) If the difference between the feature amount AA of the original image A and the feature amount AB of the brightness adjustment image B> the difference between the feature amount AA of the original image A and the feature amount AC of the brightness adjustment image C, the brightness adjustment image C Adopt a color space.

The brightness adjustment unit 26 determines the output pixel value of each pixel according to the following equation (4) using the above-described three determination conditions, and generates an image with the brightness adjusted. The coefficients K, α, and β are arbitrarily set such that K + α + β = 1 (for example, K = 0.5, α = 0.25, β = 0.25), and their values are It is appropriately changed according to the image quality. For example, if the change in the entire image is to be reduced, K is increased, and if the change in luminance is important, α is increased.

  The brightness adjustment unit 26 outputs the image whose brightness has been adjusted to the image display unit 27. Further, the lightness adjusting unit 26 may output the lightness-adjusted image to the storage unit 12 or to the outside (not shown).

  The image display unit 27 displays the input image from the image input unit 21 on the display unit 14. The image display unit 27 causes the display unit 14 to display the image whose brightness has been adjusted by the brightness adjustment unit 26 as an output image.

(Brightness adjustment processing)
FIG. 4 is a flowchart showing the flow of brightness adjustment processing executed by the brightness adjustment apparatus 1.

  In step S1, the control unit 11 (image input unit 21) of the brightness adjustment apparatus 1 outputs an input image to be subjected to brightness adjustment as a media input / output unit 13, a communication control unit 14, or a peripheral device I / F (interface). An image is input from a recording medium or a peripheral device via the unit 17 or an image stored in advance in the storage unit 12 is acquired.

  In step S2, the control unit 11 (image processing intensity determination unit 22) of the brightness adjustment apparatus 1 analyzes the image input in the process of step S1, and determines the shape of the tone curve according to the feature amount of the image. The shape of the tone curve is determined by adjustment by the user, or automatically determined according to the image feature amount obtained from the image analysis result.

  In step S3, the control unit 11 (color space conversion unit 23) of the brightness adjustment device 1 changes the color space of the image input in the process of step S1 from the RGB color space to the YCbCr color space (Lab color space or other color space). However, in the following, it is converted to YCbCr). The color space conversion is performed using a general color space conversion method.

  In step S4, the control unit 11 (brightness adjustment unit 24) of the brightness adjustment device 1 uses the tone curve determined in step S3 to adjust the luminance of each RGB channel of the image input in step S1. At the same time, only the Y (luminance) channel in the image converted into the YCbCr color space in the process of step S3 is adjusted in luminance.

  In step S5, the control unit 11 (feature amount acquisition unit 25) of the brightness adjustment device 1 applies to all pixels of the Y (luminance) channel converted into the YCbCr color space for the original image A input in the process of step S1. Then, an average luminance value is calculated from the target pixel and the surrounding pixels by the N × N moving average filter, and the feature amount AA is obtained using the calculated luminance value as the luminance value at the position of the target pixel. In addition, the control unit 11 (feature amount acquisition unit 25) of the brightness adjustment apparatus 1 has only the luminance adjustment image B in the RGB color space whose luminance is adjusted in the process of step S4 and the Y (luminance) channel in the process of step S4. Similarly, the feature amount AB and the feature amount AC are acquired for the brightness adjusted image C in the YCbCr color space after the brightness adjustment (the feature amount AA, the feature amount AB, and the feature amount AC are collectively referred to as the feature amount A). .

  In step S <b> 6, the control unit 11 (feature amount acquisition unit 25) of the brightness adjustment device 1 determines the luminance value of the target pixel for all pixels of the Y (luminance) channel converted into the YCbCr color space for the original image A. Then, the feature amount BA is obtained by using the ratio of the feature amount AA to the luminance value at the position of the target pixel as the pixel value at the position of the target pixel. In addition, the control unit 11 (feature amount acquisition unit 25) of the brightness adjustment apparatus 1 similarly uses the feature amount AB and the feature amount AC for the brightness adjustment image B and the brightness adjustment image C, respectively, and the feature amount. BB and feature quantity BC are acquired (feature quantity BA, feature quantity BB, and feature quantity BC are collectively referred to as feature quantity B).

  In step S <b> 7, the control unit 11 (brightness adjustment unit 26) of the brightness adjustment apparatus 1 selects a processing target pixel for performing brightness adjustment. Generally, the control unit 11 (brightness adjustment unit 26) of the brightness adjustment apparatus 1 sequentially selects from the upper left pixel to the lower right pixel in the input image.

  In step S8, the control unit 11 (brightness adjustment unit 26) of the brightness adjustment device 1 has the feature amount BA, the feature amount BB, and the feature amount acquired in the process of step S6 in the processing target pixel selected in the process of step S7. The BCs are compared, and based on the first determination condition described above, the pixel value of the color space in which the brightness is corrected with less visual discomfort is adopted. As a result, the pixel value of the color space of the brightness adjusted image having the feature amount with a small difference from the feature amount BA of the original image A is employed. Further, when the difference between the feature amount of the original image A and the feature amount of the selected brightness adjustment image is larger than the allowable range, the pixel value of the color space of the original image A is adopted.

  In step S9, the control unit 11 (brightness adjustment unit 26) of the brightness adjustment apparatus 1 has the feature amount AA, feature amount AB, and feature amount acquired in the process of step S5 in the processing target pixel selected in the process of step S7. AC is compared, and a pixel value in a color space having a large luminance feature amount is adopted based on the second determination condition described above. Thereby, the pixel value of the color space of the brightness adjustment image having a feature amount having a large difference from the feature amount AA of the original image A is adopted.

  In step S10, the control unit 11 (brightness adjustment unit 26) of the brightness adjustment device 1 is employed in the process of step S9 in the processing target pixel selected in the process of step S7 based on the above-described third determination condition. The pixel value of the color space that did not exist is adopted.

  In step S11, the control unit 11 (brightness adjustment unit 26) of the brightness adjustment apparatus 1 uses the above-described equation (4) to output pixel values from the pixel values in the color space adopted in the processes in steps S8 to S10. Determine the value.

  In step S12, the brightness adjustment unit 26 determines whether or not the brightness adjustment processing for all the pixels has been completed. If it is determined that there is a pixel that has not been adjusted, the process returns to step S7, and the next pixel to be processed is determined. Select and repeat the process described above. In step S <b> 11, if the lightness adjustment unit 26 determines that the lightness adjustment process for all pixels has been completed, the process ends.

(Result display example)
5 to 8 are diagrams illustrating an example of an input image and an image on which brightness adjustment has been performed.

  FIG. 5 shows an example of the input image, FIG. 6 shows an example of the brightness adjustment image in the RGB color space using the conventional technique, and FIG. 7 shows the brightness adjustment image in the Y (luminance) channel of the YCbCr color space. An example is shown, and FIG. 8 shows an example of a brightness adjustment image according to the present embodiment.

  The brightness-adjusted image according to the present embodiment shown in FIG. 8 is a natural image in which the brightness is adjusted overall brighter than the input image shown in FIG. 5, and the apparent saturation is also maintained. . In addition, the brightness adjustment image shown in FIG. 8 retains the vividness of the sky and plants as compared to the brightness adjustment images shown in FIGS. 6 and 7, and the natural brightness adjustment is performed visually.

[Effects of the embodiment of the present invention]
1. As described above, according to the present embodiment, it is possible to perform adjustment to achieve desired brightness based on the change in appearance from the processing results in a plurality of color spaces, compared with the conventional case. It is possible to achieve natural brightness adjustment.
2. In the present embodiment, feature amounts are obtained from the original image A of the input image, the luminance adjustment image B obtained by adjusting the luminance of the RGB channel of the RGB color space, and the luminance adjustment image C obtained by adjusting the luminance of only the Y (luminance) channel of the YCbCr color space. The feature values are acquired and used for the brightness adjustment processing. However, the present invention is not limited to this, and the feature values are acquired from the brightness adjustment image obtained by adjusting the brightness of the L (brightness) channel of the Lab color space. You may make it use for a brightness adjustment process.

  The preferred embodiments of the brightness adjustment device and the like according to the present invention have been described above with reference to the accompanying drawings, but the present invention is not limited to such examples. It will be apparent to those skilled in the art that various changes or modifications can be conceived within the scope of the technical idea disclosed in the present application, and these naturally belong to the technical scope of the present invention. Understood.

DESCRIPTION OF SYMBOLS 1 ..... Lightness adjustment device 21 .......... Image input part 22 ....... Image processing intensity determination part 23 ........ Color space conversion part 24 ........ Luminance adjustment part 25 ........ Feature amount acquisition part 26 .......... Lightness adjustment section 27 ... …… Image display section

Claims (10)

A brightness adjustment device for adjusting the brightness of an input image represented in a predetermined color space,
Image processing intensity determination means for determining the amount of change in brightness of the output image with respect to the input image as image processing intensity;
Color space conversion means for converting an image represented in the predetermined color space into an image of another color space including luminance information;
In accordance with the determined image processing intensity, a luminance adjustment unit that performs luminance adjustment on each of the input image and an image in the other color space obtained by converting the input image by the color space conversion unit; ,
A feature amount acquisition means for acquiring a feature amount for each of the input image that has not been subjected to brightness adjustment, the input image that has been subjected to brightness adjustment, and an image in the other color space that has undergone brightness adjustment;
Brightness adjustment means for adjusting the brightness of the input image based on the acquired feature quantity;
A brightness adjustment device comprising: The feature amount acquisition unit acquires luminance information for each image by the color space conversion unit, and for all pixels, a feature amount indicating brightness in the vicinity of the target pixel and brightness in the vicinity of the target pixel. The brightness adjustment apparatus according to claim 1, wherein a feature amount indicating a ratio to is acquired. The feature amount acquisition unit acquires luminance information for each image by the color space conversion unit, calculates an average luminance value from the target pixel and peripheral pixels for all pixels, and calculates the position of the target pixel. The feature value A (referred to as feature values AA, AB, and AC for each image) is acquired and the ratio between the brightness value of the target pixel and the brightness value at the position of the target pixel of the feature amount A is acquired. The feature amount B (referred to as feature amounts BA, BB, and BC for each image) is acquired as a pixel value at the position of the pixel of interest. The brightness adjustment unit employs, for all the pixels of the input image, a pixel value of an image related to a feature quantity having a small difference from the feature quantity BA among the feature quantity BB or the feature quantity BC. A second condition that employs a pixel value of an image relating to a feature quantity having a large difference from the feature quantity AA among the condition, the feature quantity AB or the feature quantity AC, and the feature quantity AB or the feature quantity AC The output pixel value for each pixel is calculated using a third condition that employs a pixel value of an image related to a feature amount having a small difference from the feature amount AA. Brightness adjustment device. The brightness adjustment means calculates K, α, and β as constants satisfying K + α + β = 1, and calculates an output pixel value by Expression (1).
The brightness adjustment apparatus according to claim 4, wherein 5. The brightness adjustment unit employs a pixel value of the input image that has not been subjected to luminance adjustment when the difference in the feature amount is larger than an allowable range in the first determination condition. Item 6. The brightness adjustment device according to item 5. The brightness adjustment apparatus according to any one of claims 1 to 6, wherein the image processing intensity is a tone curve representing a correspondence relationship between the brightness of the input image and the brightness of the output image. The lightness adjusting apparatus according to any one of claims 1 to 7, further comprising output means for outputting the input image whose lightness has been adjusted by the lightness adjusting means as an output image. A brightness adjustment method for adjusting the brightness of an input image represented in a predetermined color space,
An image processing intensity determination step for determining an amount of change in brightness of the output image with respect to the input image as an image processing intensity;
A color space conversion step of converting the image represented in the predetermined color space into an image of another color space including luminance information;
In accordance with the determined image processing intensity, a luminance adjustment step for performing luminance adjustment on each of the input image and the image of the other color space obtained by converting the input image by the color space conversion step; ,
A feature amount acquisition step of acquiring a feature amount for each of the input image that has not been brightness adjusted, the input image that has been brightness adjusted, and the image of the other color space that has been brightness adjusted;
A brightness adjustment step for adjusting the brightness of the input image based on the acquired feature quantity;
A brightness adjustment method comprising: A program for causing a computer to function as a brightness adjustment device for adjusting the brightness of an input image represented in a predetermined color space,
The computer,
Image processing intensity determining means for determining the amount of change in brightness of the output image with respect to the input image as image processing intensity;
Color space conversion means for converting the image represented in the predetermined color space into an image of another color space including luminance information;
In accordance with the determined image processing intensity, a luminance adjustment unit that performs luminance adjustment on each of the input image and the image of the other color space obtained by converting the input image by the color space conversion unit,
Feature amount acquisition means for acquiring a feature amount for each of the input image that has not been subjected to luminance adjustment, the input image that has been subjected to luminance adjustment, and an image in the other color space that has undergone luminance adjustment;
Brightness adjustment means for adjusting the brightness of the input image based on the acquired feature quantity;
Program to function as.