JP2005182232A - Luminance correcting device and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a luminance correcting device for smoothing the luminance of an original image in a dynamic range, and for suppressing the blur of the image, and for correcting it to an image suitable for even recognition processing or the like. <P>SOLUTION: This luminance correcting device 1 is provided with an image acquiring part 12 for acquiring an original image, a single-scale retinex processing part 13 for applying luminance smoothing processing to an original image acquired by the image acquiring part 12, and for generating a luminance smoothing processing image and an emphasis image generating part 14 for generating an emphasis image for defining an image by using the luminance smoothing processing image. The luminance smoothing processing image and the emphasis image are compounded by an image compounding part 15 so that the luminance correction image can be generated. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  In the present invention, when an original image obtained by a camera or the like is an extremely dark image, an extremely bright image, or an image having a partial shadow, the luminance for correcting the original image to be easily viewable It relates to correction technology.

  When a subject is photographed with a camera, an extremely dark image or an extremely bright image may be generated depending on the brightness of the subject. In addition, an image that is partially shaded may be generated. In these images, pixel values are biased to a specific level within the dynamic range, and the images are difficult to see.

  Conventionally, luminance correction processing including luminance smoothing processing for smoothing luminance within a dynamic range is known. Examples of the luminance smoothing process include a single scale Retinex method (see, for example, Non-Patent Document 1) and a multiscale Retinex method (see, for example, Non-Patent Document 2).

In these brightness correction processes, an image is made easy to view by increasing the brightness value of a dark part with a low brightness value and decreasing the brightness value of a bright part with a high brightness value.
Daniel J. Jobson, two others, “Properties and Performance of a Center / Surround Retinex”, (USA), IEEE Transactions on Image Processing ( IEEE Transactions On Image Processing), March 1997, Vol. 6, no. 3, p. 451-462 Daniel J. Jobson and two others, “A Multiscale Retinex for Bridging the Gap Between Color Images and the Human Observation of Scenes), (USA), IEEE Transactions On Image Processing, July 1997, Vol. 6, no. 7, p. 965-976

  However, when luminance smoothing processing such as Retinex processing is performed on the original image, the luminance value is increased in the low luminance portion and the luminance value is decreased in the high luminance portion. For this reason, the dynamic range of the brightness smoothed image obtained by the brightness smoothing process is narrower than that of the original image. When the dynamic range becomes narrow, features such as line segments and edges in the image become small. For this reason, the luminance smoothing processed image is less sharp than the original image and becomes a blurred image. In such a blurred image, it is difficult to perform recognition processing using features in the image.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a brightness correction apparatus that makes an image easier to see and can suppress blurring of the image.

  The luminance correction apparatus of the present invention includes an image acquisition unit that acquires an original image, a luminance smoothing unit that generates a luminance smoothed image from the original image acquired by the image acquisition unit, and the luminance smoothed image. An enhanced image generating means for generating an enhanced image for image sharpening using the blurred image generated in the generation process, and an image for generating a combined image by combining the brightness smoothed image and the enhanced image Synthesizing means.

  With this configuration, even if a brightness smoothed image without sharpness is generated from the original image by the brightness smoothing process, the brightness smoothed image and the enhanced image for image sharpening are combined, so that the recognition process A sharp brightness-corrected image suitable for the above is obtained. In addition, since the enhanced image is generated using the blurred image generated in the process of generating the luminance smoothed image, there is no need to perform the process of generating the blurred image for generating the enhanced image. The processing burden is reduced.

  In addition, the luminance correction apparatus of the present invention includes a separating unit that separates the original image acquired by the image acquiring unit into a color image and a luminance image, and a color combining unit that combines the combined image and the color image. I have. The luminance smoothing means smoothes the luminance of the luminance image to generate the luminance smoothed image.

  With this configuration, a sharp brightness-corrected image suitable for recognition processing or the like can be obtained for a color original image.

  In the luminance correction apparatus of the present invention, the luminance smoothing means generates the luminance smoothed image by single scale Retinex processing or multiscale Retinex processing.

  With this configuration, it is possible to suitably reduce the influence of blur associated with single-scale Retinex processing or multi-scale Retinex processing.

  The luminance correction method of the present invention includes an image acquisition step for acquiring an original image, a luminance smoothing step for generating a luminance smoothed image from the original image acquired in the image acquisition step, and the luminance smoothed image. Using the blurred image generated in the generation process, an enhanced image generation step for generating an enhanced image for image sharpening, and the brightness smoothed image and the enhanced image are combined to generate a combined image. Image synthesis step.

  With this configuration, even if a brightness smoothed image without sharpness is generated from the original image by the brightness smoothing process, the brightness smoothed image and the enhanced image for image sharpening are combined, so that the recognition process A sharp brightness-corrected image suitable for the above is obtained. In addition, since the enhanced image is generated using the blurred image generated in the process of generating the luminance smoothed image, there is no need to perform the process of generating the blurred image for generating the enhanced image. The processing burden is reduced.

  The luminance correction method of the present invention includes a separation step of separating the original image acquired in the image acquisition step into a color image and a luminance image, and a color combination step of combining the combined image and the color image. Contains. In the brightness smoothing step, the brightness of the brightness image is smoothed to generate the brightness smoothed image.

  With this configuration, a sharp brightness-corrected image suitable for recognition processing or the like can be obtained for a color original image.

  Further, the present invention is not limited to the aspect of the luminance correction apparatus and the luminance correction method. Another aspect of the present invention is, for example, a program for causing a computer to execute the above luminance correction method, and for example, a recording medium on which the program is recorded.

  The present invention generates an enhanced image for image sharpening using luminance smoothing means for generating a luminance smoothed image from an original image and a blurred image generated in the process of generating the luminance smoothed image. Since the brightness smoothed image and the enhanced image are combined with the enhanced image generating means, the brightness is smoothed within the dynamic range for the original image obtained by imaging with the camera. At the same time, it is possible to provide a luminance correction apparatus having an effect of suppressing blurring of an image and correcting the image to an image suitable for recognition processing.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.
In FIG. 1, the luminance correction apparatus 1 according to the first embodiment of the present invention includes an image acquisition unit 12, a single scale Retinex processing unit 13, an enhanced image generation unit 14, and an image synthesis unit 15. A camera 11 and an image output device 16 are connected to the brightness correction device 1.

  The brightness correction apparatus 1 is configured by a computer. When the brightness correction apparatus 1 executes a brightness correction program, an image acquisition unit 12, a single scale Retinex processing unit 13, an enhanced image generation unit 14, and an image composition unit 15 are configured, and brightness correction processing described below is performed. Is executed. In the luminance correction apparatus 1, the image acquisition unit 12, the single scale Retinex processing unit 13, the enhanced image generation unit 14, and the image synthesis unit 15 may be configured by hardware.

  The camera 11 includes a fixed image sensor such as a charge coupled device (CCD) or a complementary metal-oxide-silicon (CMOS). The camera 11 captures a subject image using a fixed image sensor, generates an image signal, and outputs the image signal to the image acquisition unit 12. The camera 11 includes a pan mechanism, a tilt mechanism, and a zoom mechanism (not shown). For example, the camera 11 is installed outdoors as a monitoring camera or installed in an automobile.

  When the camera 11 is a camera that captures a monochrome image, the image acquisition unit 12 of the brightness correction apparatus 1 uses the original image signal input from the camera 11 as a monochrome image signal as a single-scale Retinex processing unit 13. And output to the enhanced image generation unit 14. When the camera 11 includes an RGB filter and captures a color image, the image acquisition unit 12 outputs an image signal of the original image input from the camera 11 as an image signal of an RGB full-color image. .

ここで、「＊」は畳み込み積分を表している。また、Ｇは、式（２）で表されるガウシアン関数である。

式（２）に含まれるＫは正規化のための定数である。また、δはガウス周辺関数の標準偏差であり、平滑化処理を行う際に用いる周辺領域の面積の大きさの度合いを表す。式（１）で示されるレチネックス処理画像は、本発明の輝度平滑化画像に相当する。 The single scale retinex processing unit 13 performs single scale retinex processing on the original image input from the image acquisition unit 12. Assuming that the pixel value of the target pixel (x, y) in the original image is Ii (x, y), the pixel value Ri (x, y) of the Retinex processed image is expressed by Expression (1). Note that i represents the luminance component of the image.

Here, “*” represents a convolution integral. G is a Gaussian function expressed by Equation (2).

K included in Equation (2) is a constant for normalization. Further, δ is a standard deviation of the Gaussian peripheral function, and represents the degree of the size of the peripheral region used when performing the smoothing process. The Retinex processed image represented by Expression (1) corresponds to the luminance smoothed image of the present invention.

式（３）に示されるように、強調画像はＧ（ｘ，ｙ）＊Ｉｉ（ｘ，ｙ）（以下、ボケ画像という）と原画像Ｉｉ（ｘ，ｙ）の差分の絶対値を定数倍したものである。 The enhanced image generation unit 14 generates an enhanced image for image sharpening. The emphasized image is an image in which the edge portion of the original image acquired by the image acquisition unit 12 is emphasized. Assuming that the pixel value of the target pixel (x, y) in the original image is Ii (x, y), the pixel value I′i (x, y) of the emphasized image generated by the emphasized image generation unit 14 is expressed by Equation (3). ).

As shown in Expression (3), the emphasized image is obtained by multiplying the absolute value of the difference between G (x, y) * Ii (x, y) (hereinafter referred to as a blurred image) and the original image Ii (x, y) by a constant. It is a thing.

  Here, the blurred image G (x, y) * Ii (x, y) used to generate the enhanced image in Expression (3) has already been generated in the course of the single-scale Retinex process represented by Expression (1). Has been. Therefore, as illustrated in FIG. 1, the enhanced image generation unit 14 generates the blurred image G that has already been generated by the single scale Retinex processing unit 13 according to the equation (1) when generating the enhanced image according to the equation (3). (X, y) * Ii (x, y) is used. In addition, the constant B of Formula (3) is a value obtained by experiment and it is desirable to set to about 0.1-0.5.

ここで、Ｏｉ（ｘ，ｙ）は、合成画像の画素値であり、本実施の形態の輝度補正装置１における輝度補正の結果である。なお、式（４）の計算結果が値の上限を超えた場合には、クリッピング処理が施される。例えば、Ｏｉ（ｘ，ｙ）の取り得る範囲が、０〜２５５である場合に、ある画素についての式（４）の計算結果が２５５を超えたときは、その画素値は２５５とされる。 The image synthesis unit 15 synthesizes the output of the single scale Retinex processing unit 13 and the output of the enhanced image generation unit 14, that is, the Retinex processed image and the enhanced image. This synthesis process is expressed by equation (4).

Here, Oi (x, y) is a pixel value of the composite image, and is a result of the brightness correction in the brightness correction apparatus 1 of the present embodiment. When the calculation result of Expression (4) exceeds the upper limit of the value, clipping processing is performed. For example, when the range that Oi (x, y) can take is 0 to 255 and the calculation result of Expression (4) for a certain pixel exceeds 255, the pixel value is set to 255.

  The image output device 16 outputs the composite image generated by the image composition unit 15 to a monitor or a subsequent processing device.

The operation of the brightness correction apparatus 1 configured as described above will be described with reference to FIG.
First, the single scale Retinex processing unit 13 performs a single scale Retinex process on the original image acquired by the image acquisition unit 12 (Step S31). Next, the enhanced image generation unit 14 generates an enhanced image with enhanced edges using the blurred image generated in the course of the single scale Retinex process and the original image acquired by the image acquisition unit 12 ( Step S32). Then, the image synthesizing unit 15 synthesizes the enhanced image and the Retinex processed image to generate a synthesized image (step S33).

  In the first embodiment described above, since the enhanced image generated by the enhanced image generation unit 14 is an image in which the edge portion in the original image is enhanced as described above, the Retinex processed image is blurred. Even in the case where the image is closed, the edge image is emphasized and sharpened by combining the enhanced image with the retinex processed image. Therefore, according to the luminance correction apparatus 1 of the first embodiment, the luminance of the input original image can be smoothed within the dynamic range, and can be corrected to a sharp image suitable for recognition processing and the like.

  Further, in the luminance correction apparatus 1 of the first embodiment, the blurred image already generated in the course of the Retinex process as a blurred image used for generating an enhanced image for image sharpening in the enhanced image generation unit 14. Use images. Accordingly, it is not necessary to generate a blurred image for generating an emphasized image, and the processing load for generating the emphasized image can be reduced.

(Second Embodiment)
Next, an image correction apparatus 2 according to a second embodiment of the present invention is shown in FIG.
In addition to the configuration of the luminance correction apparatus 1 of the first embodiment, the luminance correction apparatus 2 of the present embodiment includes a color information separation unit 23 and a color information synthesis unit 27.

  The camera 21 includes RGB filters. The image acquisition unit 22 acquires an image signal of an original image generated by photographing with the camera 11 and outputs the image signal as an RGB full-color image signal to the color information separation unit.

  The color information separation unit 23 extracts color information from the input original image to generate a color image, and extracts luminance information from the original image to generate a luminance image. As the technique for separating the original image, which is a full-color image, into the color image and the luminance image in the color information separation unit 23, various known techniques can be employed. In the present embodiment, the color information separation unit 23 converts the original image into HSV data using the HSV space. Then, the color information separation unit 23 generates a color image and a luminance image using (H, S) as the color information and V as the luminance information. Conversion from RGB data to HSV data is performed using the following conversion formula.

H = tan ⁻¹ {(GB) / (2R−GB)}
S = {(BR) ² + (RG) ² + (GB) ² } / 3
V = R + G + B
However, R, G, and B are normalized from 0 to 1, respectively, V is normalized from 0 to 3, H is normalized from 0 to 2π, and S is normalized from 0 to 2/3. The conversion from RGB data to HSV data is described, for example, by Mikio Takagi et al., “Image Analysis Handbook”, University of Tokyo Press, p. 485-491 (1991).

色画像は、色情報合成部２７に出力され、輝度画像は、シングルスケールレチネックス処理部２４および強調画像生成部２５に出力される。 As another method of image separation, in addition to the HSV space, another color space in which color information and luminance information can be separated can be used. For example, a YIQ space represented by Formula (5) or a YCrCv space represented by Formula (6) may be used.

The color image is output to the color information synthesis unit 27, and the luminance image is output to the single scale Retinex processing unit 24 and the enhanced image generation unit 25.

  The single scale retinex processing unit 24 performs the single scale retinex processing on the luminance image input from the color information separation unit 23 in the same manner as in the first embodiment. The enhanced image generation unit 25 uses the luminance image generated by the color information separation unit 23 and the blurred image generated by the single-scale retinex processing unit 24 to perform edge processing in the same manner as in the first embodiment. An enhanced image in which a portion is enhanced is generated. The image composition unit 26 also composes the retinex processed image and the enhanced image in the same manner as in the first embodiment to generate a composite image.

  The color information synthesizing unit 27 takes in the color image generated by the color information separating unit 23 and synthesizes the color image and the synthesized image generated by the image synthesizing unit 26 to generate a color synthesized image. Here, the synthesized image generated by the image synthesizing unit 26 is an image representing only luminance information, while the color image output from the color information separating unit 23 is the original image output from the image acquiring unit 22. It is an image representing only the color information of the image. Therefore, the color composite image generated by combining both images is a color image with the luminance component corrected.

  The image output device 28 captures the color composite image generated by the color information composition unit 27 and outputs it to a monitor or a subsequent processing device.

The operation of the brightness correction apparatus 2 configured as described above will be described with reference to FIG.
First, the color information separation unit 23 separates the original image acquired by the image acquisition unit 22 into a color image and a luminance image (step S41). Then, the single scale retinex processing unit 24 performs single scale retinex processing on the luminance image separated by the color information separation unit 23 (step S42). Next, the enhanced image generation unit 25 generates an enhanced image with an edge enhanced using the blurred image generated in the course of the single scale Retinex process and the luminance image separated by the color information separation unit 23. (Step S43). Next, the image synthesizing unit 26 synthesizes the enhanced image and the retinex processed image to generate a synthesized image (step S44). Finally, the color information combining unit 27 combines the color image separated by the color information separating unit 23 and the combined image generated by the image combining unit 26 to generate a color combined image (step S45). .

  According to the brightness correction apparatus 2 of the second embodiment as described above, the single scale Retinex process, the enhanced image generation process, and the synthesis process are performed using only the brightness component of the input color original image. The color image is also corrected to an easy-to-view image in which pixel values are preferably smoothed within the dynamic range, and a sharp brightness-corrected image suitable for recognition processing and the like is obtained.

  In the first and second embodiments described above, the single scale Retinex processing unit 13 is provided to perform the single scale Retinex processing on the original image or the luminance image separated from the original image. The process for smoothing the brightness may be a multi-scale Retinex process or another brightness smoothing process.

  As described above, the brightness correction apparatus according to the present invention uses the brightness smoothing unit that generates the brightness smoothed image from the original image and the blurred image generated in the process of generating the brightness smoothed image. It includes an enhanced image generating means for generating an enhanced image for sharpening, and is configured to synthesize the brightness smoothed image and the enhanced image, so that the original image obtained by taking a picture with a camera, etc. , Smoothing the brightness within the dynamic range, reducing blurring of the image, and correcting it to an image suitable for recognition processing. The original image obtained with a camera is extremely dark. In the case of an image, an extremely bright image, or an image with a partial shadow, it is useful as a luminance correction device for correcting the original image into an easily viewable image.

The block diagram of the brightness correction apparatus in the 1st Embodiment of this invention The flowchart for operation | movement description of the brightness correction apparatus in the 1st Embodiment of this invention The block diagram of the brightness correction apparatus in the 2nd Embodiment of this invention Flow chart for explaining the operation of the brightness correction apparatus in the second embodiment of the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 2 Brightness correction apparatus 12, 22 Image acquisition part 13, 24 Single scale Retinex processing part 14, 25 Enhanced image generation part 15, 26 Image composition part 23 Color information separation part 27 Color information composition part

Claims (8)

Image acquisition means for acquiring an original image;
Brightness smoothing means for generating a brightness smoothed image from the original image acquired by the image acquisition means;
Emphasized image generating means for generating an emphasized image for image sharpening using the blurred image generated in the generation process of the luminance smoothing processed image;
A luminance correction apparatus comprising: an image synthesis unit that synthesizes the luminance smoothed image and the enhanced image to generate a synthesized image. Separating means for separating the original image obtained by the image obtaining means into a color image and a luminance image;
Color synthesis means for synthesizing the synthesized image and the color image;
The brightness correction apparatus according to claim 1, wherein the brightness smoothing unit generates the brightness smoothed image by smoothing brightness of the brightness image. The brightness correction apparatus according to claim 1, wherein the brightness smoothing unit generates the brightness smoothed image by single scale Retinex processing or multiscale Retinex processing. An image acquisition step of acquiring an original image;
A luminance smoothing step for generating a luminance smoothing processed image from the original image acquired in the image acquisition step;
Using the blurred image generated in the process of generating the luminance smoothed image, an enhanced image generating step for generating an enhanced image for image sharpening,
A luminance correction method comprising: an image synthesis step of generating a synthesized image by synthesizing the luminance smoothed image and the enhanced image. A separation step of separating the original image acquired in the image acquisition step into a color image and a luminance image;
A color synthesis step of synthesizing the synthesized image and the color image;
The brightness correction method according to claim 4, wherein, in the brightness smoothing step, the brightness smoothed image is generated by smoothing brightness of the brightness image. An image acquisition step of acquiring an original image;
A luminance smoothing step for generating a luminance smoothing processed image from the original image acquired in the image acquisition step;
Using the blurred image generated in the process of generating the luminance smoothed image, an enhanced image generating step for generating an enhanced image for image sharpening,
The program for making a computer perform the brightness correction method characterized by including the image synthetic | combination step which synthesize | combines the said brightness | luminance smoothing process image and the said emphasis image, and produces | generates a synthesized image. A separation step of separating the original image acquired in the image acquisition step into a color image and a luminance image;
A color synthesis step of synthesizing the synthesized image and the color image;
The program for causing a computer to execute the brightness correction method according to claim 6, wherein, in the brightness smoothing step, the brightness smoothed image is generated by smoothing brightness of the brightness image. A computer-readable recording medium on which the program according to claim 6 or 7 is recorded.

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