JP2008060855A - Image processor, image processing program, and image processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processor capable of outputting a naturally seen image, to provide an image processing program, and to provide an image processing method. <P>SOLUTION: The image processor generates a gradation-corrected image by a gradation correcting process. It comprises a means for acquiring a plurality of images; a means for setting the gradation converting characteristics in the gradation correcting process; a means for selecting one or a plurality of selective images used in the gradation correcting process among the plurality of images, based on the contrast amplification factor conformed with the gradation converting characteristics; a means for selecting at least one image as a reference image among the plurality of images; and a gradation converting processing means for conforming the output gradation of the gradation corrected image with the input gradation of the reference image in the gradation correcting process, based on gradation information of the one or the plurality of selected images. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image processing apparatus, an image processing program, and an image processing method, and in particular, an image processing apparatus capable of performing gradation correction processing, which is processing for associating an output gradation with an input gradation, and an image The present invention relates to a processing program and an image processing method.

  The dynamic range is the luminance ratio between the brightest portion of an image or scene that can be recorded and the darkest portion of the image or scene. In general, for example, an indoor scene has a narrow dynamic range, while an outdoor scene ranging from bright sunlight to a dark shadow has a wide dynamic range.

In particular, when a scene having a wide dynamic range is captured by, for example, an electronic camera and digitized as image data, the range may be narrowed and output as an image with an unnatural appearance. Then, for example, by performing processing such as gradation conversion on the unnaturally-appearing image, the narrowed dynamic range is visually expanded, and an image with a natural-looking appearance can be output. As a method for expanding the apparent dynamic range by gradation conversion and improving the image quality of an image, for example, there is an image quality improvement method proposed in Patent Document 1 and an apparatus therefor.
JP-T-2004-530368

  However, the method described in Patent Document 1 has a low quantization value, for example, because the quantization width becomes coarse when gradation conversion is performed on a portion having a low luminance value in one image. This may cause a phenomenon in which noise existing in a portion is emphasized or a gradation in a portion having a low luminance value is skipped. As a result, in the method described in Patent Document 1, the one image after gradation conversion may be output as an image that looks unnatural.

  The present invention has been made in view of the above-described points, and an image processing apparatus and image processing capable of outputting an image with a natural appearance by suppressing coarsening of a quantization width at the time of gradation conversion It is an object to provide a program and an image processing method.

  A first image processing apparatus according to the present invention is a process for generating a gradation correction image by performing gradation correction processing, which is processing for associating an output gradation with an input gradation. Based on the contrast amplification factor corresponding to the gradation conversion characteristics, the gradation characteristic setting means for setting the gradation conversion characteristics in the gradation correction processing, Used image selecting means for selecting one or a plurality of selected images, which are images used in the tone correction processing, reference image selecting means for selecting at least one of the plurality of images as a reference image, and As the gradation correction process, a gradation change process is performed in which the output gradation of the gradation correction image is associated with the input gradation of the reference image based on the gradation information of the one or more selected images. Processing means, characterized by having a.

  According to a second image processing device of the present invention, in the first image processing device, the use image selecting unit is configured to use the singular or plural images based on the input tone of the reference image based on the contrast amplification factor. The selected image is selected from the plurality of images so that either the average luminance in the selected image or the total value of the average luminance in the one or more selected images is different.

  According to a third image processing apparatus of the present invention, in the first image processing apparatus, the use image selecting unit is configured to use the singular or plural images based on the input tone of the reference image based on the contrast amplification factor. The selected image is selected from the plurality of images so that either the variance value of the luminance in the selected image or the average value of the variance values of the luminance in the one or more selected images is different.

  According to a fourth image processing apparatus of the present invention, in the first image processing apparatus, the use image selecting unit is configured to select the number of selected images according to the input gradation of the reference image based on the contrast amplification factor. The selected images are selected from the plurality of images so that the two are different from each other.

  According to a fifth image processing apparatus of the present invention, in the first image processing apparatus, the gradation characteristic setting unit includes the gradation according to at least one of position information and luminance information of the reference image. The conversion characteristic is set.

  According to a sixth image processing apparatus of the present invention, in the first image processing apparatus, the used image selecting unit includes a contrast amplification factor and a predetermined constant among total values of average luminances of the plurality of images. The minimum value exceeding the multiplication value is set as a total value of average luminance of the single or plural selection images, and a selection image is selected from the plurality of images based on the setting, and the gradation conversion processing means Then, a correction coefficient is calculated based on the contrast amplification factor and the total value of the average luminance of each selected image selected by the used image selection means, and the input gradation of each selected image is multiplied by the correction coefficient, respectively. In addition, a process for associating the output gradation of the gradation corrected image with the input gradation of the reference image based on the sum of the multiplication values is performed as the gradation correction process.

  According to a seventh image processing apparatus of the present invention, in the first image processing apparatus, the used image selection unit calculates a maximum integer value equal to or less than a value obtained by dividing the contrast amplification factor by a predetermined first constant. Then, a value obtained by multiplying a value obtained by adding 1 to the integer value and a predetermined second constant is set as the number of selected images used in the gradation correction processing, and the plurality of images are set based on the setting. The gradation conversion processing means calculates a correction coefficient based on the contrast amplification factor and the number of images set by the used image selection means, and each of the images for the number of images is selected. A process of multiplying the input gradation of the selected image by the correction coefficient and associating the output gradation of the gradation corrected image with the input gradation of the reference image based on the sum of the multiplication values. Key And performing a correction process.

  According to an eighth image processing apparatus of the present invention, in the first image processing apparatus, the gradation conversion processing unit calculates a correction coefficient according to a luminance value of a pixel existing at one position on the reference image. And multiplying the luminance value of each pixel present at the same position as the one position on each selected image selected by the use image selecting means by the correction coefficient, and summing the sum of the multiplied values. The process of setting the luminance value of the pixel existing at the same position as the one position on the gradation correction image is performed as the gradation correction process.

  The first image processing program according to the present invention acquires a plurality of images in a computer that generates a gradation correction image by performing gradation correction processing, which is processing for associating an output gradation with an input gradation. The tone correction is performed from the plurality of images based on the image acquisition procedure to be performed, the tone characteristic setting procedure for setting the tone conversion characteristic in the tone correction process, and the contrast amplification factor corresponding to the tone conversion characteristic. A used image selection procedure for selecting one or a plurality of selected images, which are images used in the processing, a reference image selection procedure for selecting at least one of the plurality of images as a reference image, and the gradation As a correction process, a gradation for performing a process of associating an input gradation of the reference image with an output gradation of the gradation-corrected image based on gradation information of the one or more selected images Characterized in that to execute a conversion processing procedure, the.

  According to a second image processing program of the present invention, in the first image processing program, the used image selection procedure is based on the contrast amplification factor, and the singular or plural number is selected according to the input gradation of the reference image. The selected image is selected from the plurality of images so that either the average luminance in the selected image or the total value of the average luminance in the one or more selected images is different.

  According to a third image processing program of the present invention, in the first image processing program, the used image selection procedure is based on the contrast amplification factor, and the singular or plural number is selected according to the input gradation of the reference image. The selected image is selected from the plurality of images so that either the variance value of the luminance in the selected image or the average value of the variance values of the luminance in the one or more selected images is different.

  According to a fourth image processing program of the present invention, in the first image processing program, the used image selection procedure is based on the contrast amplification factor and the number of images of the selected image according to the input gradation of the reference image. The selected images are selected from the plurality of images so that the two are different from each other.

  According to a fifth image processing program of the present invention, in the first image processing program, the gradation characteristic setting procedure includes the gradation according to at least one of position information and luminance information of the reference image. The conversion characteristic is set.

  According to a sixth image processing program of the present invention, in the first image processing program, the used image selection procedure includes: the contrast amplification factor and a predetermined constant among a total value of average luminances of the plurality of images. A minimum value exceeding a multiplication value is set as a total value of average luminance of the single or plural selection images, and a selection image is selected from the plurality of images based on the setting. Then, a correction coefficient is calculated based on the contrast amplification factor and the total value of the average luminance of each selected image selected by the used image selection procedure, and the input gradation of each selected image is multiplied by the correction coefficient, respectively. In addition, a process for associating the output gradation of the gradation-corrected image with the input gradation of the reference image based on the sum of the multiplication values is performed as the gradation correction process. To.

  According to a seventh image processing program of the present invention, in the first image processing program, the used image selection procedure calculates a maximum integer value equal to or less than a value obtained by dividing the contrast amplification factor by a predetermined first constant. Then, a value obtained by multiplying a value obtained by adding 1 to the integer value and a predetermined second constant is set as the number of selected images used in the gradation correction processing, and the plurality of images are set based on the setting. The gradation conversion processing procedure calculates a correction coefficient based on the contrast amplification factor and the number of images set by the use image selection procedure, and the number of images corresponding to the number of images is selected. A process of multiplying the input gradation of the selected image by the correction coefficient and associating the output gradation of the gradation corrected image with the input gradation of the reference image based on the sum of the multiplication values. A and performs as the tone correction processing.

  An eighth image processing program according to the present invention is the first image processing program, wherein the gradation conversion processing procedure calculates a correction coefficient according to a luminance value of a pixel existing at one position on the reference image. And multiplying each luminance value of a pixel existing at the same position as the one position on each selected image selected by the used image selection procedure by the correction coefficient, and summing each of the multiplied values. The process of setting the luminance value of the pixel existing at the same position as the one position on the gradation correction image is performed as the gradation correction process.

  A first image processing method according to the present invention is a process for generating a gradation correction image by performing gradation correction processing, which is processing for associating an output gradation with an input gradation. An image acquisition step for acquiring the image, a gradation characteristic setting step for setting a gradation conversion characteristic in the gradation correction process, and a contrast amplification factor corresponding to the gradation conversion characteristic, from the plurality of images, A used image selecting step for selecting one or a plurality of selected images, which is an image used in the tone correction processing, a reference image selecting step for selecting at least one of the plurality of images as a reference image, and As gradation correction processing, the output gradation of the gradation correction image is made to correspond to the input gradation of the reference image based on gradation information of the one or more selected images. A gradation conversion processing step of performing processing, characterized by having a.

  According to a second image processing method of the present invention, in the first image processing method, the used image selection step is based on the contrast amplification factor, and the singular or plural images are selected according to the input gradation of the reference image. The selected image is selected from the plurality of images so that either the average luminance in the selected image or the total value of the average luminance in the one or more selected images is different.

  According to a third image processing method of the present invention, in the first image processing method, the use image selecting step is based on the contrast amplification factor, and the singular or plural images are selected according to an input gradation of the reference image. The selected image is selected from the plurality of images so that either the variance value of the luminance in the selected image or the average value of the variance values of the luminance in the one or more selected images is different.

  According to a fourth image processing method of the present invention, in the first image processing method, the used image selection step is configured such that, based on the contrast amplification factor, the number of selected images according to the input gradation of the reference image The selected images are selected from the plurality of images so that the two are different from each other.

  According to a fifth image processing method of the present invention, in the first image processing method, the gradation characteristic setting step includes the gradation according to at least one of position information and luminance information of the reference image. The conversion characteristic is set.

  According to a sixth image processing method of the present invention, in the first image processing method, the used image selecting step includes: the contrast amplification factor and a predetermined constant among total values of average luminances of the plurality of images. A minimum value exceeding the multiplication value is set as a total value of average luminance of the single or plural selection images, and a selection image is selected from the plurality of images based on the setting, and the gradation conversion processing step includes Then, a correction coefficient is calculated based on the contrast amplification factor and the total value of the average luminance of each selected image selected in the used image selection step, and the input gradation of each selected image is multiplied by the correction coefficient, respectively. In addition, a process for associating the output gradation of the gradation-corrected image with the input gradation of the reference image based on the sum of the multiplication values is performed as the gradation correction process. To.

  According to a seventh image processing method of the present invention, in the first image processing method, the used image selection step calculates a maximum integer value equal to or less than a value obtained by dividing the contrast amplification factor by a predetermined first constant. Then, a value obtained by multiplying a value obtained by adding 1 to the integer value and a predetermined second constant is set as the number of selected images used in the gradation correction processing, and the plurality of images are set based on the setting. The gradation conversion processing step calculates a correction coefficient based on the contrast amplification factor and the number of images set by the use image selection step, and the number of images corresponding to the number of images is selected. A process of multiplying the input gradation of the selected image by the correction coefficient and associating the output gradation of the gradation-corrected image with the input gradation of the reference image based on the sum of the multiplication values. , And performs as the tone correction processing.

  According to an eighth image processing method of the present invention, in the first image processing method, the gradation conversion processing step calculates a correction coefficient according to a luminance value of a pixel existing at one position on the reference image. And multiplying each luminance value of a pixel present at the same position as the one position on each selected image selected by the used image selection step by the correction coefficient, and summing each of the multiplied values. The process of setting the luminance value of the pixel existing at the same position as the one position on the gradation correction image is performed as the gradation correction process.

  According to the image processing apparatus, the image processing program, and the image processing method of the present invention, it is possible to output an image that looks natural by suppressing the coarsening of the quantization width at the time of gradation conversion.

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

(First embodiment)
1 to 15 relate to a first embodiment of the present invention.

  FIG. 1 is a diagram illustrating an example of a configuration of an image processing apparatus according to the first embodiment of the present invention. FIG. 2 is a diagram showing an example of gradation conversion characteristics for each input luminance gradation set in the gradation characteristic setting means of FIG. FIG. 3 is a diagram showing the contrast amplification factor for each input luminance gradation calculated from the gradation conversion characteristics of FIG. FIG. 4 is a diagram showing the total value of the average luminance of the selected image for each input luminance gradation according to the contrast amplification factor of FIG. FIG. 5 is a diagram showing correction coefficients for each input luminance gradation calculated from the contrast amplification factor shown in FIG. 3 and the total value of the average luminances of the selected images shown in FIG. FIG. 6 is a diagram schematically illustrating the gradation correction process performed in the first embodiment. FIG. 7 is a diagram showing an example of the number of selected images for each input luminance gradation in accordance with the contrast amplification factor of FIG. FIG. 8 is a diagram showing an example different from FIG. 7 of the number of selected images for each input luminance gradation in accordance with the contrast amplification factor of FIG. FIG. 9 is a diagram showing correction coefficients for each input luminance gradation calculated from the contrast amplification factor shown in FIG. 3 and the number of selected images shown in FIG. FIG. 10 is a diagram showing correction coefficients for each input luminance gradation calculated from the contrast amplification factor shown in FIG. 3 and the number of selected images shown in FIG.

  FIG. 11 is a diagram showing an example of the gradation conversion characteristic for each input luminance gradation set by the gradation characteristic setting means in FIG. 1 that is different from FIG. FIG. 12 is a diagram showing the contrast amplification factor for each input luminance gradation calculated from the gradation conversion characteristics of FIG. 11 and the number of selected images for each input luminance gradation according to the contrast amplification factor. is there. FIG. 13 is a diagram showing an example of the configuration of the image processing apparatus according to the first embodiment of the present invention, which is different from FIG. FIG. 14 is a flowchart showing an outline of processing performed by the image processing apparatus shown in FIG. FIG. 15 is a diagram illustrating an example of the configuration of the image processing apparatus according to the first embodiment of the present invention, which is different from FIGS. 1 and 13.

  As shown in FIG. 1, the image processing apparatus 1A according to the present embodiment includes an input image acquisition unit 10 that acquires a plurality of images, a gradation characteristic setting unit 13 that sets gradation conversion characteristics, and the gradation conversion. A contrast amplification factor setting unit 14 for acquiring a contrast amplification factor according to characteristics; a reference image selection unit 15 for generating at least one image as a reference image from the plurality of images; and the gradation from the plurality of images. Use image selection means 16 for selecting a selection image, which is an image used in the correction process, in accordance with the contrast amplification factor; and gradation conversion processing means 17 for performing the gradation correction process on the reference image. Have.

  The gradation characteristic setting means 13 performs processing so that the gradation conversion characteristic Q (I) with respect to the input luminance gradation I is set as shown in FIG.

  The contrast amplification factor setting means 14 is based on the gradation conversion characteristic Q (I) set by the gradation characteristic setting means 13, and the contrast amplification factor R (I), which is a differential value of the gradation conversion characteristic Q (I). To get. It is assumed that the input gradation I and the contrast amplification factor R (I) are shown as having a correlation as shown in FIG. 3, for example.

  The used image selection means 16 first uses the following formula (1) shown as a function of R (I) as the process for setting the number of the selected images, and uses the total value T ( I) is calculated.

なお、上記数式（１）において、Ｐは定数を示すものとする。また、上記数式（１）の右辺は、Ｔｎ＞Ｐ×Ｒ（Ｉ）を満たす最小のＴｎの値を示す。さらに、選択画像の平均輝度の合計値Ｔ（Ｉ）を定めるための方法は、入力輝度階調Ｉの関数に基づいて定めるものであれば、例えば、Ｔ（Ｉ）＝Ｌ×Ｒ（Ｉ）＋Ｍ（Ｌ及びＭは所定の定数）として算出されるものであっても良く、また、コントラスト増幅率Ｒ（Ｉ）を用いて定めるものでなくとも良い。一般的に、電子カメラ等により、露光時間が各々異なる状態として被写体の像が撮像された場合に得られる、複数の画像の平均輝度の合計値のデータは、Ｔｎ＝Ｔ１，Ｔ２，Ｔ３，…（Ｔ１＜Ｔ２＜Ｔ３＜…）という、無次元化された数列として示される。そして、数式（１）の右辺におけるＴｎは、前述した数列に含まれる各値を示すものである。

In the above formula (1), P represents a constant. The right side of the above formula (1) indicates the minimum value of Tn that satisfies Tn> P × R (I). Furthermore, if the method for determining the total value T (I) of the average luminance of the selected image is determined based on the function of the input luminance gradation I, for example, T (I) = L × R (I) It may be calculated as + M (L and M are predetermined constants), and may not be determined using the contrast amplification factor R (I). Generally, the data of the total value of the average luminance of a plurality of images obtained when an image of a subject is captured with an electronic camera or the like with different exposure times is Tn = T1, T2, T3,. It is shown as a dimensionless number sequence (T1 <T2 <T3 <...). And Tn in the right side of Formula (1) shows each value contained in the numerical sequence mentioned above.

  For example, when Tn = 1, 1.5, 2.7, 3.7,..., And the constant P = 1, and the contrast amplification factor R (I) is as shown in FIG. The total value T (I) of the average luminance of the selected image for each gradation I is calculated as shown in FIG. That is, each value of Tn corresponds to the number of selected images.

  Then, the used image selection means 16 uses the total number T (I) of the average brightness of the selected images calculated by the above formula (1), and the number of selected images F (I) used in the gradation correction processing. Is set (one or more).

  As described above, the used image selection unit 16 determines the average luminance of each selected image used in the gradation correction process or the average of each selected image used in the gradation correction process according to the input luminance gradation I. The selected image is selected from the plurality of images acquired by the input image acquisition unit 10 so that any one of the total luminance values is different. In other words, since the difference in average luminance of each selected image corresponds to the variance value of luminance, the used image selecting unit 16 determines the selection image used in the gradation correction processing according to the input luminance gradation I. The selected image is selected from the plurality of images acquired by the input image acquisition means 10 so that either the luminance variance value or the average value of the luminance variance values of the selected images used in the gradation correction process is different. Make a selection.

  Thereafter, the gradation conversion processing means 17 calculates a correction coefficient G (I) used in the gradation correction process based on the total average value T (I) of the average luminance of the selected image calculated by the above formula (1). It calculates using the following numerical formula (2).

なお、上記数式（２）により算出される、入力輝度階調Ｉ各々に対するＧ（Ｉ）の値は、図５に示すようなものになる。

Note that the value of G (I) for each input luminance gradation I calculated by the above equation (2) is as shown in FIG.

  The gradation conversion processing means 17 corresponds to the number of images F (I) calculated by the used image selection means 16, the correction coefficient G (I) calculated by the above equation (2), and the number of images F (I). Then, gradation correction processing is performed on the reference image output from the reference image selection unit 15 using the following formula (3) determined based on the luminance value of each selection image output from the input image acquisition unit 10. In the following mathematical formula (3), the luminance value of the pixel existing at one position (i, j) of the reference image is indicated as I (i, j), and the k-th image (1 ≦ 1) at the one position. Assume that the luminance value of the selected image with k ≦ F (I)) is indicated as Ik (i, j).

すなわち、階調変換処理手段１７は、上記数式（３）に基づく階調補正処理を行うことにより、基準画像の一の位置（ｉ，ｊ）に存在する画素の輝度値Ｉ（ｉ，ｊ）を、Ｆ（Ｉ（ｉ，ｊ））枚の画像内の一の位置（ｉ，ｊ）における輝度値及び補正係数Ｇ（Ｉ）を用い、Ｑａ（Ｉ（ｉ，ｊ））に変換する。

In other words, the gradation conversion processing unit 17 performs the gradation correction processing based on the above formula (3), whereby the luminance value I (i, j) of the pixel existing at one position (i, j) of the reference image. Is converted into Qa (I (i, j)) using the luminance value and the correction coefficient G (I) at one position (i, j) in the F (I (i, j)) images.

  More specifically, as shown in FIG. 6, the gradation conversion processing unit 17 amplifies the luminance value for a pixel existing at a position A having a low luminance value among the positions on the reference image, for example. The gradation correction processing is performed using a relatively large number of images so that the rate is relatively high. Further, as shown in FIG. 6, the gradation conversion processing unit 17 has, for example, the relative amplification factor of the luminance value with respect to the pixel existing at the position B where the luminance value is high among the positions on the reference image. The gradation correction processing is performed using a relatively small number of images so that the image becomes lower.

  In the above-described processing, the used image selection unit 16 selects the number F of selected images to be used in the gradation correction processing based on the total value T (I) of the average luminance of the selected image for each input luminance gradation I. For example, when the exposure time of each image acquired by the input image acquisition unit 10 is constant, the following equation (4) is used to calculate the contrast amplification factor R (I). It is also possible to directly calculate the number of images F (I).

なお、上記数式（４）におけるＮ_１及びＮ_２は、各々所定の定数であるとする。また、上記数式（４）においてＮ_１＝Ｎ_２＝１とした場合、入力輝度階調Ｉ各々に対するＦ（Ｉ）の値は、図７に示すようなものになる。さらに、上記数式（４）においてＮ_１＝２及びＮ_２＝３とした場合、Ｆ（Ｉ）の値は、図８に示すようなものになる。

Note that N ₁ and N ₂ in Equation (4) are each a predetermined constant. When N ₁ = N ₂ = 1 in the above equation (4), the value of F (I) for each input luminance gradation I is as shown in FIG. Further, when N ₁ = 2 and N ₂ = 3 in the above formula (4), the value of F (I) is as shown in FIG.

  Then, the used image selection unit 16 calculates the correction coefficient G () used in the gradation correction process based on the number of selected images F (I) used in the gradation correction process calculated by the above mathematical expression (4). I) is calculated using the following mathematical formula (5).

なお、上記数式（４）においてＮ_１＝Ｎ_２＝１とした場合のＦ（Ｉ）の値に応じて算出される、入力輝度階調Ｉ各々に対するＧ（Ｉ）の値は、図９に示すようなものになる。また、上記数式（４）においてＮ_１＝２及びＮ_２＝３とした場合のＦ（Ｉ）の値に応じて算出される、入力輝度階調Ｉ各々に対するＧ（Ｉ）の値は、図１０に示すようなものになる。

Note that the value of G (I) for each input luminance gradation I calculated according to the value of F (I) when N ₁ = N ₂ = 1 in Equation (4) is shown in FIG. It will be as shown. In addition, the value of G (I) for each input luminance gradation I calculated according to the value of F (I) when N ₁ = 2 and N ₂ = 3 in the above equation (4) is shown in FIG. As shown in FIG.

  Further, when the gradation characteristic setting unit 13 performs processing so that the gradation conversion characteristic Q (I) with respect to the input luminance gradation I is set as shown in FIG. 11, for example, the input luminance gradation The value of the contrast amplification factor R (I) for each I is as shown in FIG. At this time, if the exposure time of each image acquired by the input image acquisition means 10 is constant, the value of F (I) for each of the input luminance gradations I is shown in FIG. Calculated as shown.

  Based on the gradation conversion characteristic Q (I) shown in FIG. 11, the value of F (I) shown in FIG. 12 is calculated, so that the gradation conversion processing means 17 has, for example, a luminance value on the reference image. The gradation separation performance in the case of performing gradation correction processing on a medium pixel can be improved, and an image with a more natural appearance can be output.

  As a first modification, the image processing apparatus 1A according to the present embodiment acquires the image information of the reference image generated by the reference image selection unit 15 in addition to the configuration described above as the configuration illustrated in FIG. The image processing apparatus 1 </ b> B shown in FIG. 13 may further include an image information acquisition unit 12 that outputs the acquired image information to the gradation characteristic setting unit 13.

  Here, an outline of processing performed by the image processing apparatus 1B will be described with reference to FIG.

  First, as described above, the reference image selection unit 15 generates at least one image as a reference image from the plurality of images acquired by the input image acquisition unit 10. The image information acquisition unit 12 acquires, for example, at least one of position information and luminance information as the image information of the reference image, and outputs the acquired image information to the gradation characteristic setting unit 13. To do.

  The gradation characteristic setting unit 13 is, for example, an appropriate gradation conversion characteristic Q (in accordance with the image information output from the image information acquisition unit 12 among the gradation conversion characteristics shown in FIGS. 2 and 11. I) is set (step S001 in FIG. 14).

  Thereafter, the contrast amplification factor setting unit 14 calculates the differential value of the gradation conversion characteristic Q (I) set by the gradation characteristic setting unit 13 as the contrast amplification factor R (I) (step S002 in FIG. 14).

  The used image selection unit 16 calculates the value of the number of images F (I) based on the contrast amplification factor R (I) calculated by the contrast amplification factor setting unit 14 and the above equation (4) (FIG. 14). Along with step S003), the selected image corresponding to the number of images F (I) is output from the input image acquisition means 10 to the gradation conversion processing means 17.

  The gradation conversion processing means 17 outputs the output gradation based on the number of images F (I) and the correction coefficient G (I) calculated from the number of images F (I) using the above equation (5). After calculating the conversion characteristic Qa (I) (step S004 in FIG. 14), gradation conversion processing is performed on the reference image output from the reference image selection means 15 based on the output gradation conversion characteristic Qa (I) ( Step S005 in FIG. 14).

  Further, as a second modification, the image processing apparatus 1A of the present embodiment records a plurality of images acquired by the input image acquisition unit 10 in addition to the configuration of the image processing apparatus 1B described above as the configuration illustrated in FIG. It may be configured as an image processing apparatus 1C shown in FIG. As a result, the reference image selection means 15 generates a reference image from the image recorded in the image recording means 18. The used image selection unit 16 causes the gradation conversion processing unit 17 to output a selected image corresponding to the number of images F (I) from the images recorded in the image recording unit 18.

  In addition to the processing described above, the processing performed by each unit of the image processing device 1C is substantially the same as the processing performed by each unit of the image processing device 1B, and thus will not be described in detail here.

  As described above, each of the image processing apparatuses 1A, 1B, and 1C according to the present embodiment can suppress the coarsening of the quantization width at the time of gradation conversion, and as a result, the natural appearance can be reduced. An image can be output.

(Second Embodiment)
16 to 20 relate to the second embodiment of the present invention.

  FIG. 16 is a diagram illustrating an external appearance of an imaging apparatus configured as an embodiment of an image processing apparatus according to the second embodiment of the present invention. 17 is a diagram illustrating an internal configuration of the imaging apparatus illustrated in FIG. FIG. 18 is a flowchart of processing related to the blur correction processing performed by each unit illustrated in FIG. FIG. 19 is a diagram illustrating an example of gradation conversion characteristics that can be set by operating a mode selection dial included in the imaging apparatus of FIG. FIG. 20 is a diagram illustrating an example of gradation conversion characteristics that can be set by operating the mode selection dial included in the imaging apparatus in FIG. 17, which is different from that in FIG. 19.

  Note that detailed description of portions having the same configuration as in the first embodiment is omitted. Moreover, about the component similar to 1st Embodiment, description is abbreviate | omitted using the same code | symbol.

  For example, an imaging apparatus 101 configured as a digital camera as one form of an image processing apparatus can set a release switch 3001 that captures an image of a subject and content that matches a determined position, as illustrated in FIG. A mode selection dial 3004 is provided on the exterior surface. As shown in FIG. 17 (not shown in FIG. 16), the imaging apparatus 101 includes a display element 2001, a menu switch 3002 capable of displaying a menu screen of the imaging apparatus 101 on the display element 2001, An operation key 3003 that can be operated on the menu screen is provided.

  In addition, as shown in FIG. 17, the imaging apparatus 101 is arranged at a system controller 1000 that controls each part of the imaging apparatus 101, a lens 1001 that collects and forms an image of a subject, and an imaging position of the lens 1001. Then, after passing through the solid-state image sensor 1002 that captures the image of the subject, the aperture / shutter 1003 that changes the exposure amount and exposure time of the solid-state image sensor 1002, and the aperture / shutter 1003, the solid-state image sensor 1002 forms an image An imaging circuit 1004 configured by an analog front-end processor or the like that outputs an imaging signal corresponding to a subject image to be captured, and an analog imaging signal output from the imaging circuit 1004 are converted into digital image data and output. A / D conversion circuit 1005 and image data output from A / D conversion circuit 1005 are detected. , On the basis of the detection result, and a shake detection / correction circuit 1007 for performing blur correction processing, the on the image data.

  Furthermore, the imaging apparatus 101 is based on the memory 1008 that stores the image data after the blur correction process, which is output from the blur detection / correction circuit 1007, and the image data in the memory 1008 that is read according to the control of the system controller 1000. A signal processing circuit 1009 that performs gradation correction processing on image data output from the shake detection / correction circuit 1007, a memory 1010 that stores image data after gradation correction processing, and image data stored in the memory 1010 A compression circuit 1011 that performs image compression processing on the image data and outputs the image data after the image compression processing to a portable recording medium 2002.

  Here, the processing performed by each unit of the imaging apparatus 101 after the subject is imaged and before the blur correction process is performed by the blur detection / correction circuit 1007 will be described with reference to the flowchart of FIG.

  First, the system controller 1000 determines whether or not (Bv + Sv)> Ev (max) (step S201 in FIG. 18).

  Here, Bv (Brightness value) is represented by an index based on the APEX (Additive System of Photographic Exposure) method (hereinafter referred to as “apex value”), and Sv (Sensitive). ISO sensitivity as the apex value, Ev (Exposure Value) is the exposure value as the apex value, and Ev (max) is the maximum value of the exposure value as the apex value that can be controlled by the digital camera. Further, when the exposure time as the apex value is Tv (Time Value) and the aperture value (F number) as the apex value is Av (Aperture Value), the following formula (6) is established.

Ev = Tv + Av = Bv + Sv (6)

Therefore, if the brightness (Bv) of the subject obtained by photometry and the ISO sensitivity (Sv) set on the menu screen of the imaging apparatus 101 are known, the exposure value (Ev) is determined by the above equation (6). Tv and Av can be calculated.

  When the system controller 1000 detects that (Bv + Sv)> Ev (max) by performing the process of step S201 in FIG. 18, the system controller 1000 issues an overexposure warning (step S202 in FIG. 18). Note that the overexposure warning is performed by, for example, displaying a warning on the display element 2001 or generating a warning sound through a speaker (not shown) together with the warning display. Then, the system controller 1000 continues the process of step S205 of FIG. 18 described later after performing the process of step S202 of FIG.

  If the system controller 1000 detects that Bv + Sv> Ev (max) by performing the process of step S201 of FIG. 18, then the system controller 1000 determines whether Bv + Sv <Ev (min). Determination is made (step S203 in FIG. 18). The Ev (min) indicates the minimum exposure value as an apex value that can be controlled by the digital camera.

  When the system controller 1000 detects that Bv + Sv <Ev (min) by performing the process of step S203 in FIG. 18, the system controller 1000 issues an underexposure warning (step S204 in FIG. 18). The under-exposure warning is also performed by displaying a warning on the display element 2001, or by emitting a warning sound through a speaker (not shown) together with the warning display, as with the above-described over-exposure warning. Then, the system controller 1000 continues the process of step S205 of FIG. 18 described later after performing the process of step S204 of FIG.

  When it is detected in step S203 in FIG. 18 that Bv + Sv <Ev (min) is not satisfied, or when the processing in step S202 or step S204 in FIG. 18 described above is completed, the system controller 1000 displays the menu of the imaging apparatus 101. It is determined whether or not the mode setting state on the screen is set to the shutter priority shooting mode (step S205 in FIG. 18).

  Here, when the system controller 1000 determines that the imaging apparatus 101 is set to the shutter priority shooting mode, the system controller 1000 calculates the aperture value (Av) by Av = Bv + Sv−Tv (step S206 in FIG. 18).

On the other hand, if the system controller 1000 determines in step S205 of FIG. 18 that the imaging apparatus 101 is not set to the shutter priority shooting mode, the imaging apparatus 101 is further set to the aperture priority mode. It is determined whether or not (step S207 in FIG. 18). Here, when the system controller 1000 detects that the aperture priority shooting mode is set, the system controller 1000 calculates the exposure time T _EXP (step S208 in FIG. 18). Note that the exposure time T _EXP corresponds to Tv, and is obtained by obtaining the apex value Tv of the exposure time from Tv = Bv + Sv−Av and converting the apex value into the actual exposure time T _EXP .

When the system controller 1000 detects in step S207 in FIG. 18 that the aperture priority shooting mode is not set, the system controller 1000 determines that the program shooting mode has been set, and determines, for example, the focus according to the focal length of the lens 1001. The exposure time T _EXP and the aperture value (Av) are set so that the longer the distance, the shorter the exposure time T _EXP and the smaller the aperture value (the aperture aperture becomes larger) (step S209 and step S210 in FIG. 18). .

The system controller 1000 calculates the divided shooting count m after completing any one of steps S206, S208, and S210 in FIG. 18 (step S211 in FIG. 18). Specifically, the system controller 1000 calculates T _EXP / T _Limit , and calculates a value equal to the calculation result, or a value larger than this and the closest value (an integer value of 1 to 10) as the divided imaging count m. To do. For example, when the value of T _EXP / T _Limit is 2.5, the value of m is set to 3, and when the value of T _EXP / T _Limit is 4, the value of m is 4 Set to It is assumed that the exposure time T _EXP in the shutter priority shooting mode described above is a value set by the user. Further, the value of T _Limit indicates a limit time during which camera shake does not occur. When the diagonal length of the image frame of the lens 1001 is d (mm) and the focal length of the lens 1001 is f (mm), It is expressed as the following mathematical formula (7).

その後、システムコントローラ１０００は、Ｔ_Limitの値を、上記数式（７）により算出される値から、Ｔ_ＥＸＰ ／ｍにより算出される値に更新（図１８のステップＳ２１２）するとともに、前述した処理において算出した絞り値に応じた絞り開口になるように、絞り／シャッタ１００３を制御して絞りを設定する（図１８のステップＳ２１３）。なお、前述した絞り優先撮影モードの場合の絞り値は、ユーザにより設定される値であるとする。

Thereafter, the system controller 1000 updates the value of T _{Limit from} the value calculated by Equation (7) to the value calculated by T _EXP / m (step S212 in FIG. 18), and in the above-described processing. The aperture is set by controlling the aperture / shutter 1003 so that the aperture opening according to the calculated aperture value is obtained (step S213 in FIG. 18). It is assumed that the aperture value in the above-described aperture priority shooting mode is a value set by the user.

  Then, the system controller 1000 controls the shake detection / correction circuit 1007 according to each process of FIG. 18 described above, and performs, for example, a process such as alignment based on a motion vector between frames in input image data. A blur correction process is performed (step S214 in FIG. 18).

  The image data in which the blur is corrected is output from the blur detection / correction circuit 1007 by the above-described processes shown in FIG.

  When the mode selection dial 3004 is operated by the user, for example, when the first mode is set, a gradation conversion characteristic Q (I) capable of enhancing the gradation of a bright subject as shown in FIG. Selected. Further, when the mode selection dial 3004 is operated by the user, for example, when the second mode is set, as shown in FIG. 20, a gradation conversion characteristic Q (I ) Is selected.

  The system controller 1000 calculates and outputs the contrast amplification factor R (I) from the differential value of the gradation conversion characteristic Q (I) selected by operating the mode selection dial 3004, and further uses the above equation (4). The number of images F (I) corresponding to the contrast amplification factor R (I) is calculated and output.

  The signal processing circuit 1009 calculates the correction coefficient G (I) from the contrast amplification factor R (I) and the number of images F (I) output from the system controller 1000 using the above equation (5). Then, the signal processing circuit 1009 reads the image number F (I) of images from the memory 1008, and applies the correction coefficient G (I) and the image to the image data output from the shake detection / correction circuit 1007. The tone correction processing is performed using the above equation (3) regarding the number of sheets F (I).

  Accordingly, each image output to the display element 2001 and the recording medium 2002 is an image in which blurring is corrected and is output as an image that looks natural. That is, the imaging device 101 can output an image that looks natural.

  Note that the present invention is not limited to the above-described embodiments, and various modifications and applications can be made without departing from the spirit of the invention.

1 is a diagram illustrating an example of a configuration of an image processing apparatus according to a first embodiment of the present invention. FIG. 2 is a diagram illustrating an example of gradation conversion characteristics for each input luminance gradation set by the gradation characteristic setting unit in FIG. 1. The figure which shows the contrast amplification factor with respect to each input luminance gradation calculated from the gradation conversion characteristic of FIG. The figure which shows the total value of the average brightness | luminance of the selection image with respect to each input brightness | luminance gradation according to the contrast amplification factor of FIG. The figure which shows the correction coefficient with respect to each input brightness | luminance gradation calculated from the contrast amplification factor shown in FIG. 3, and the total value of the average brightness | luminance of the selection image shown in FIG. The figure which shows typically the gradation correction process performed in 1st Embodiment. FIG. 4 is a diagram illustrating an example of the number of selected images for each input luminance gradation in accordance with the contrast amplification factor of FIG. 3. The figure which shows the example different from FIG. 7 of the number of the selection images with respect to each input luminance gradation according to the contrast amplification factor of FIG. FIG. 8 is a diagram showing a correction coefficient for each input luminance gradation calculated from the contrast amplification factor shown in FIG. 3 and the number of selected images shown in FIG. 7. The figure which shows the correction coefficient with respect to each input brightness | luminance gradation calculated from the contrast amplification factor shown in FIG. 3, and the number of the selection images shown in FIG. The figure which shows the example different from FIG. 2 of the gradation conversion characteristic with respect to each input luminance gradation set in the gradation characteristic setting means of FIG. FIG. 12 is a diagram showing a contrast amplification factor for each input luminance gradation calculated from the gradation conversion characteristics of FIG. 11 and the number of selected images for each input luminance gradation according to the contrast amplification factor. FIG. 2 is a diagram showing an example different from FIG. 1 of the configuration of the image processing apparatus according to the first embodiment of the present invention. 14 is a flowchart showing an outline of processing performed by the image processing apparatus shown in FIG. 13. The figure which shows the example different from FIG.1 and FIG.13 of the structure of the image processing apparatus which concerns on the 1st Embodiment of this invention. The figure which shows the external appearance of the imaging device comprised as one form of the image processing apparatus based on the 2nd Embodiment of this invention. The figure which shows the internal structure of the imaging device shown in FIG. The flowchart of the process regarding the blurring correction process which each part shown in FIG. 17 performs. FIG. 18 is a diagram illustrating an example of gradation conversion characteristics that can be set by operating a mode selection dial included in the imaging apparatus of FIG. 17. FIG. 20 is a diagram illustrating an example different from FIG. 19 of gradation conversion characteristics that can be set by operating a mode selection dial included in the imaging apparatus of FIG. 17.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1A, 1B, 1C ... Image processing apparatus, 10 ... Input image acquisition means, 12 ... Image information acquisition means, 13 ... Gradation characteristic setting means, 14 ... Contrast gain setting means, DESCRIPTION OF SYMBOLS 15 ... Standard image selection means, 16 ... Use image selection means, 17 ... Gradation conversion processing means, 18 ... Image recording means, 101 ... Imaging device, 1000 ... System controller, DESCRIPTION OF SYMBOLS 1001 ... Lens, 1002 ... Solid-state image sensor, 1003 ... Aperture / shutter, 1004 ... Imaging circuit, 1005 ... A / D conversion circuit, 1007 ... Blur detection / correction circuit 1008, DESCRIPTION OF SYMBOLS 1010 ... Memory, 1009 ... Signal processing circuit, 1011 ... Compression circuit, 2001 ... Display element, 2002 ... Recording medium, 3001 ... Release switch, 3002 ... Menu switch, 3003 ... operation key, 3004 ... mode selection dial

Claims (24)

In an image processing apparatus that generates a gradation correction image by performing gradation correction processing, which is processing for associating an output gradation with an input gradation,
Image acquisition means for acquiring a plurality of images;
Gradation characteristic setting means for setting gradation conversion characteristics in the gradation correction processing;
Use image selection means for selecting one or a plurality of selected images that are images used in the gradation correction processing from the plurality of images based on the contrast amplification factor according to the gradation conversion characteristics;
Reference image selection means for selecting at least one of the plurality of images as a reference image;
Gradation conversion processing means for performing a process of associating an output gradation of the gradation corrected image with an input gradation of the reference image based on gradation information of the one or more selected images as the gradation correction processing; ,
An image processing apparatus comprising:   The used image selection means is based on the contrast amplification factor, and depending on the input gradation of the reference image, the average brightness of the single or multiple selection images, or the sum of the average brightness of the single or multiple selection images The image processing apparatus according to claim 1, wherein a selected image is selected from the plurality of images so that any one of the values is different.   The use image selection unit is configured to, based on the contrast amplification factor, depending on an input gradation of the reference image, a luminance dispersion value in the one or more selected images, or a luminance value in the one or more selected images. The image processing apparatus according to claim 1, wherein a selected image is selected from the plurality of images so that any one of the average values of the variance values is different.   The used image selection unit selects a selected image from the plurality of images based on the contrast amplification factor so that the number of images of the selected image differs according to an input gradation of the reference image. The image processing apparatus according to claim 1.   The image processing apparatus according to claim 1, wherein the gradation characteristic setting unit sets the gradation conversion characteristic according to at least one of position information and luminance information of the reference image. The used image selection means is configured to calculate a minimum value exceeding a multiplication value of the contrast amplification factor and a predetermined constant among total values of average brightness of the plurality of images as an average brightness of the selected image or the plurality of selected images. Set as a total value, and select a selected image from the plurality of images based on the setting,
The gradation conversion processing unit calculates a correction coefficient based on the contrast amplification factor and a total value of average luminances of the selected images selected by the used image selecting unit, and calculates an input gradation of each selected image. A process of multiplying each of the correction coefficients and associating the output gradation of the gradation correction image with the input gradation of the reference image based on the sum of the multiplication values is performed as the gradation correction process. The image processing apparatus according to claim 1, wherein: The use image selection unit calculates a maximum integer value equal to or smaller than a value obtained by dividing the contrast amplification factor by a predetermined first constant, and multiplies the value obtained by adding 1 to the integer value by a predetermined second constant. The selected value is set as the number of selected images used in the gradation correction process, and a selected image is selected from the plurality of images based on the setting,
The gradation conversion processing means calculates a correction coefficient based on the contrast amplification factor and the number of images set by the used image selection means, and corrects the correction to the input gradation of each selected image for the number of images. A process of multiplying each coefficient and associating the output gradation of the gradation correction image with the input gradation of the reference image based on the sum of the multiplication values is performed as the gradation correction process. The image processing apparatus according to claim 1.   The gradation conversion processing unit calculates a correction coefficient according to a luminance value of a pixel existing at one position on the reference image, and the one position on each selected image selected by the use image selecting unit. A pixel existing in the same position as the one position on the gradation-corrected image, and multiplying each of the luminance values of the pixels existing in the same position by the correction coefficient. The image processing apparatus according to claim 1, wherein the process of setting the luminance value is performed as the gradation correction process. To a computer that generates a gradation-corrected image by performing gradation correction processing, which is processing for associating output gradation with input gradation,
An image acquisition procedure for acquiring multiple images;
A gradation characteristic setting procedure for setting gradation conversion characteristics in the gradation correction process;
A use image selection procedure for selecting one or a plurality of selected images, which are images used in the tone correction processing, from the plurality of images based on the contrast amplification factor according to the tone conversion characteristics;
A reference image selection procedure for selecting at least one of the plurality of images as a reference image;
As the gradation correction processing, a gradation conversion processing procedure for performing processing for associating the output gradation of the gradation correction image with the input gradation of the reference image based on gradation information of the one or more selected images When,
An image processing program for executing   The used image selection procedure is based on the contrast amplification factor, and depending on the input gradation of the reference image, the average luminance in the single or plural selected images, or the sum of the average luminance in the single or plural selected images The image processing program according to claim 9, wherein a selected image is selected from the plurality of images so that any one of the values is different.   The use image selection procedure is based on the contrast amplification factor, and in accordance with an input gradation of the reference image, a luminance dispersion value in the one or more selected images, or a luminance value in the one or more selected images. The image processing program according to claim 9, wherein a selected image is selected from the plurality of images so that any one of the average values of the variance values is different.   The used image selection procedure selects a selected image from the plurality of images based on the contrast amplification factor so that the number of images of the selected image differs according to an input gradation of the reference image. The image processing program according to claim 9.   The image processing program according to claim 9, wherein the gradation characteristic setting procedure sets the gradation conversion characteristic according to at least one of position information and luminance information of the reference image. The used image selection procedure includes calculating a minimum value exceeding a multiplication value of the contrast amplification factor and a predetermined constant among the average values of the average brightness of the plurality of images as the average brightness of the single or plurality of selected images. Set as a total value, and select a selected image from the plurality of images based on the setting,
The gradation conversion processing procedure calculates a correction coefficient based on the contrast amplification factor and a total value of average luminances of the selected images selected by the used image selection procedure, and sets the input gradation of each selected image. A process of multiplying each of the correction coefficients and associating the output gradation of the gradation correction image with the input gradation of the reference image based on the sum of the multiplication values is performed as the gradation correction process. The image processing program according to claim 9, wherein: The used image selection procedure calculates a maximum integer value equal to or less than a value obtained by dividing the contrast amplification factor by a predetermined first constant, and multiplies the integer value by 1 to a predetermined second constant. The selected value is set as the number of selected images used in the gradation correction process, and a selected image is selected from the plurality of images based on the setting,
The gradation conversion processing procedure calculates a correction coefficient based on the contrast amplification factor and the number of images set by the use image selection procedure, and corrects the correction to the input gradation of each selected image for the number of images. A process of multiplying each coefficient and associating the output gradation of the gradation correction image with the input gradation of the reference image based on the sum of the multiplication values is performed as the gradation correction process. The image processing program according to claim 9.   The gradation conversion processing procedure calculates a correction coefficient according to a luminance value of a pixel existing at one position on the reference image, and the one position on each selected image selected by the use image selection procedure. A pixel existing in the same position as the one position on the gradation-corrected image, and multiplying each of the luminance values of the pixels existing in the same position by the correction coefficient. The image processing program according to claim 9, wherein the process of setting the luminance value is performed as the gradation correction process. In an image processing method for generating a gradation correction image by performing gradation correction processing, which is processing for associating an output gradation with an input gradation,
An image acquisition step of acquiring a plurality of images;
A gradation characteristic setting step for setting gradation conversion characteristics in the gradation correction processing;
A use image selection step of selecting one or a plurality of selection images, which are images used in the gradation correction process, from the plurality of images based on the contrast amplification factor according to the gradation conversion characteristics;
A reference image selection step of selecting at least one of the plurality of images as a reference image;
As the gradation correction process, a gradation conversion processing step of performing a process of associating an output gradation of the gradation correction image with an input gradation of the reference image based on gradation information of the one or more selected images When,
An image processing method comprising:   In the use image selection step, based on the contrast amplification factor, depending on an input gradation of the reference image, the average luminance in the single or plural selection images, or the sum of average luminance in the single or plural selection images The image processing method according to claim 17, wherein a selected image is selected from the plurality of images so that any one of the values is different.   In the use image selection step, based on the contrast amplification factor, in accordance with an input gradation of the reference image, a luminance dispersion value in the one or more selected images, or a luminance value in the one or more selected images. The image processing method according to claim 17, wherein a selected image is selected from the plurality of images so that any one of the average values of the variance values is different.   In the use image selection step, a selection image is selected from the plurality of images based on the contrast amplification factor so that the number of images of the selection image differs according to an input gradation of the reference image. The image processing method according to claim 17.   The image processing method according to claim 17, wherein the gradation characteristic setting step sets the gradation conversion characteristic according to at least one of position information and luminance information of the reference image. In the use image selection step, a minimum value exceeding a multiplication value of the contrast amplification factor and a predetermined constant among total values of the average brightness of the plurality of images is determined as an average brightness of the single or plurality of selected images. Set as a total value, and select a selected image from the plurality of images based on the setting,
The gradation conversion processing step calculates a correction coefficient based on the contrast amplification factor and a total value of average luminances of the selected images selected in the used image selection step, and sets the input gradation of the selected images. A process of multiplying each of the correction coefficients and associating the output gradation of the gradation correction image with the input gradation of the reference image based on the sum of the multiplication values is performed as the gradation correction process. The image processing method according to claim 17, wherein: In the use image selection step, a maximum integer value equal to or less than a value obtained by dividing the contrast amplification factor by a predetermined first constant is calculated, and a value obtained by adding 1 to the integer value is multiplied by a predetermined second constant. The selected value is set as the number of selected images used in the gradation correction process, and a selected image is selected from the plurality of images based on the setting,
The gradation conversion processing step calculates a correction coefficient based on the contrast amplification factor and the number of images set by the use image selection step, and corrects the correction to the input gradation of each selected image for the number of images. A process of multiplying each coefficient and associating the output gradation of the gradation correction image with the input gradation of the reference image based on the sum of the multiplication values is performed as the gradation correction process. The image processing method according to claim 17.   The gradation conversion processing step calculates a correction coefficient according to a luminance value of a pixel existing at one position on the reference image, and the one position on each selected image selected by the use image selecting step. A pixel existing in the same position as the one position on the gradation-corrected image, and multiplying each of the luminance values of the pixels existing in the same position by the correction coefficient. The image processing method according to claim 17, wherein the process of setting the luminance value is performed as the gradation correction process.

Images