WO2010084560A1 - 画像処理方法、画像処理装置および記録媒体 - Google Patents
画像処理方法、画像処理装置および記録媒体 Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
- H04N1/46—Colour picture communication systems
- H04N1/56—Processing of colour picture signals
- H04N1/60—Colour correction or control
- H04N1/603—Colour correction or control controlled by characteristics of the picture signal generator or the picture reproducer
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- H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
- H04N1/46—Colour picture communication systems
- H04N1/56—Processing of colour picture signals
- H04N1/60—Colour correction or control
- H04N1/6027—Correction or control of colour gradation or colour contrast
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- the present invention relates to an image processing method, an image processing apparatus, and a recording medium for a color image reproducing apparatus, and more particularly to an image processing technique for realizing a desired color reproduction with a color image brighter in the color image reproducing apparatus.
- the color reproduction method disclosed in Annex D of Non-Patent Document 1 is a profile connection using a color device value of a color image reproducing device and a CIE standard light D50 defined by ICC (International Color Consortium) as a reference white.
- the correspondence with the space (PCS) is obtained.
- the color device value of the input source color image reproduction device is converted to the color device value of the output destination color image reproduction device.
- the color device value of the input color image reproduction device is converted to PCS, and the PCS is converted to the color device value of the output destination color image reproduction device.
- the color reproduction is color conversion in which the color device value corresponding to the white color of the input source color image reproduction device is converted to the color device value corresponding to the white color of the output destination color image reproduction device.
- This color conversion method that takes into account human complete color adaptation is based on the von Kries model.
- the three types of spectral sensitivity ( ⁇ ) in human vision perform color adaptation by changing the sensitivity balance so that white matches without changing the shape. .
- the ⁇ sensory amount of the illumination 1 is ( ⁇ 0, ⁇ 0, ⁇ 0)
- the ⁇ sensory amount of the object under the illumination 1 is ( ⁇ , ⁇ , ⁇ )
- the ⁇ sensory amount of the illumination 2 is ( ⁇ 0 ′, ⁇ 0 ′, ⁇ 0 ′).
- the ⁇ sensory amount under illumination 2 of the same object is ( ⁇ ′, ⁇ ′, ⁇ ′)
- the ⁇ sensory amount of the object color visual system is ⁇ / ⁇ 0, ⁇ / ⁇ 0, ⁇ / ⁇ 0, ⁇ '/ ⁇ 0', ⁇ '/ ⁇ 0', ⁇ '/ ⁇ 0'.
- the above ⁇ sensory amounts may be matched as shown in the equations (1) and (2).
- the ⁇ sensory amount is obtained from the tristimulus values XYZ by the linear transformation shown in Equation (3).
- Equation (3) By substituting the tristimulus values (X0, Y0, Z0) and (X0 ′, Y0 ′, Z0 ′) of illumination 1 and illumination 2 into equation (3), ⁇ 0, ⁇ 0, ⁇ 0, ⁇ 0 ′, ⁇ 0 ′, and ⁇ 0 ′ are obtained.
- transformation matrix M in Equation (3) a Pitt matrix, an Estevez matrix, a Bradford matrix, or the like is used.
- Equation (3) by substituting Equation (3) into Equation (2), the von Kries chromatic adaptation prediction equation shown in Equation (4) can be obtained.
- D in Formula (4) is shown by Formula (5).
- the correspondence between the color device values RGB and the tristimulus values XYZ is as shown in Equation (6).
- the color device value RGB is obtained by performing inverse gamma correction in advance and linearly converting the input characteristics in consideration of the gamma characteristics of the color image reproduction apparatus.
- Equation (6) Q is a 3 ⁇ 3 matrix, and is hereinafter referred to as an RGB-XYZ conversion matrix.
- the RGB-XYZ conversion matrix Q varies depending on the color characteristics of the color image reproducing apparatus. In consideration of black tristimulus values (Xk, Yk, Zk), equation (6) becomes equation (7).
- the RGB of the color image reproducing device whose RGB-XYZ conversion matrix Q is “A” is changed from the RGB of the color image reproducing device whose RGB-XYZ conversion matrix Q is “B”.
- the color conversion to R′G′B ′ is as shown in Equation (8) when the above color conversion method taking into account human complete color adaptation is used.
- the matrix D in the equation (8) can be calculated using the white tristimulus values in the two color image reproduction apparatuses and the equations (3) and (5).
- Patent Document 1 proposes a color reproduction method that takes into account incomplete color adaptation in color reproduction between color image reproduction apparatuses having different white colors.
- This method uses the correlated white color temperature of the source and destination color image playback devices to restore the white surface reflectance at the source and destination, and restores the two white surface reflections that have been restored. From the rate, the white adapted white surface reflectance in the incomplete chromatic adaptation state is calculated.
- the white surface reflectance of the conversion source and the white adaptive white surface reflectance in the incomplete color adaptation state is calculated.
- Japanese Patent Application Laid-Open No. 2004-228561 uses a color correction table that varies the amount of change in white point according to the brightness of white output from a color image reproduction device, and performs color image reproduction by performing desired image processing on an input signal.
- An image processing apparatus that outputs to an apparatus is disclosed. This image processing apparatus utilizes the characteristic that the human eye is easily adapted to light that is brighter than dark light. As the white brightness output from the color image reproduction apparatus increases, the converted target white Processing is performed so that the point is close to the white point of the color image reproduction apparatus.
- Patent Document 2 discloses an image including a color correction priority color correction table for performing color correction capable of faithful color reproduction and a brightness priority color correction table for performing brightness priority color correction.
- a color correction priority color correction table for performing color correction capable of faithful color reproduction
- a brightness priority color correction table for performing brightness priority color correction.
- color that gives priority to brightness according to input signals such as natural images and presentation data
- a method of switching between a correction table and a color correction table with priority on color reproduction is also disclosed. With regard to switching according to the input signal, it is assumed that switching is made to a color conversion table with priority on color reproduction in the case of natural image data, and to a color correction table with priority on brightness in the case of data for presentation.
- Patent Document 3 discloses a method in which processing for changing the amount of change of the white point according to the elapsed time after the start of color correction is added to the method of Patent Document 2.
- the chromaticity of the adaptive white reproduced by the color image reproducing device is taken into account by considering the (incomplete) color adaptation in human color perception by corresponding color reproduction or equivalent color reproduction. It can be said that the color reproduction method is set to a desired chromaticity and applies color conversion based on adaptive white for colors other than white.
- the color display realizes color reproduction relatively easily in a specific color space (for example, CIE standard light D65 for sRGB and AdobeRGB) in which the color to be reproduced is specified by colorimetric color reproduction. it can. Furthermore, as the corresponding color reproduction or equivalent color reproduction, considering the (incomplete) color adaptation in human color perception, the adaptive white chromaticity reproduced by the color image reproduction device is set to a desired chromaticity, For the colors other than white, a color reproduction method that applies color correction (color conversion) obtained on the basis of the adaptive white color is shown in the conventional methods of Patent Document 1 to Patent Document 3 described above.
- a color image reproduction device may be required to reproduce a color image brighter while matching the color appearance.
- a color image reproduction device may be required to reproduce a color image brighter while matching the color appearance.
- the chromaticity of the color having the maximum luminance that can be output by the color image reproduction device is the white chromaticity in the specified color space.
- the luminance of white falls below the maximum luminance that can be output by a color image reproduction device.
- the brightness of the color image becomes dark during reproduction.
- each of the above methods applies color conversion based on white to all colors. If the white color of the color image playback device is set to the maximum luminance color that can be output by the color image playback device in order to maintain the brightness during playback, color conversion is not performed or the color conversion effect Is known to weaken. Therefore, with these methods, a color image can be reproduced brightly, but there is a possibility that the color appearances cannot be matched.
- Patent Document 2 and Patent Document 3 there is no description about a method for creating a brightness-priority color correction table. For this reason, the appearance of color when color correction is performed using the brightness-priority color correction table is unknown.
- One aspect of the present invention is an image processing method for generating an output image that is an image in the target color space from an input image that is an image in the original color space.
- a feature amount acquisition process a difference calculation process, a first color conversion, and an output image generation process are performed.
- the feature amount acquisition processing acquires, for each color represented by each color device value of the input image, a feature amount that can indicate the brightness of the color and a white feature amount in the original color space.
- the difference calculation process is a difference between a feature amount that can indicate the brightness of white in the original color space and the feature amount of the color represented by the color device value for each color represented by each color device value of the input image. A first difference is calculated.
- the color device value of the color is converted into a first color device value that is a color device value in the target color space by colorimetric color reproduction. Convert.
- the output image generation processing outputs the second color device value obtained by the second color conversion as the color device value of the output image.
- the second color conversion for each color represented by each color device value of the input image, when the first difference is 0, the color device value (color device value in the original color space) is obtained, and the first color conversion is performed.
- the difference is greater than 0, a value obtained by multiplying the second difference, which is the difference between the first color device value and the color device value, by a coefficient less than or equal to 1 and greater than 0;
- the second color device value is calculated so as to be the sum of.
- the second color conversion can be expressed by the following equation (9).
- the function f outputs 0 when the first difference is 0, and outputs a value less than or equal to 1 and greater than 0 when the first difference is other than 0.
- P2 P0 + f (DI) (P1-P0) (9)
- P0 color device value in the original color space DI: first difference
- the image processing method of the above aspect is expressed by replacing the image processing apparatus or system with a program that causes a computer to execute the processing according to the image processing method, a recording medium that records the program, or the like. It is effective as
- a color image can be reproduced more brightly while matching the color appearance.
- FIG. 1 is a diagram illustrating an image processing apparatus according to a first embodiment of the present invention. It is a flowchart which shows the process in the image processing apparatus shown in FIG. It is a figure which shows the image processing apparatus concerning the 2nd Embodiment of this invention.
- the storage medium includes, for example, a flexible disk, a hard disk, a magnetic disk, a magneto-optical disk, a CD-ROM, a DVD, a ROM cartridge, a battery-backed RAM memory cartridge, a flash memory cartridge, and a nonvolatile RAM cartridge.
- the communication medium includes a wired communication medium such as a telephone line, a wireless communication medium such as a microwave line, and the like.
- FIG. 1 shows an image processing apparatus 100 according to the first embodiment of the present invention.
- the image processing apparatus 100 generates an image (output image) corresponding to the input image in the target color space from the image (input image) in the original color space. Two color spaces having different characteristics.
- the image processing apparatus 100 includes a feature amount acquisition unit 102, a difference calculation unit 104, a first color conversion unit 106, and an output image generation unit 110.
- the output image generation unit 110 includes a second color conversion unit 108.
- the color system of the input image and the output image is the RGB color system. That is, the color device values of the input image and the output image are a combination of the R value, the G value, and the B value.
- the correspondence between RGB values and tristimulus values is known for both the original color space and the target color space.
- the RGB-XYZ conversion matrix Q is known in Equation (6) or Equation (7) described above for both the original color space and the target color space.
- the RGB-XYZ conversion matrix of the original color space is A and the RGB-XYZ conversion matrix of the target color space is B.
- the feature amount acquisition unit 102 acquires a white feature amount in the original color space and a feature amount of each pixel of the input image.
- This feature amount can indicate brightness, and for example, luminance can be used.
- the feature amount acquisition unit 102 first calculates the white luminance Yw in the original color space according to the following equation (10) or equation (11).
- A is an RGB ⁇ XYZ conversion matrix of the color space as the conversion source, and “X bk , Y bk , Z bk ” are black tristimulus values XYZ in the original color space.
- the feature quantity acquisition unit 102 calculates the luminance Y of each pixel in the input image in the original color space according to the following equation (12) or (13).
- the feature quantity acquisition unit 102 needs to calculate the luminance Y from the color device value P0 (RGB) of the input image.
- the feature amount acquisition unit 102 may acquire the luminance Y directly from the color device value of the input image.
- the white luminance Yw in the original color space is not necessarily acquired by calculation. For example, when it is set in advance, it may be acquired by reading the set value.
- the difference calculation unit 104 calculates a difference DI between the luminance Y of the pixel and the white luminance Yw in the original color space.
- This difference DI is, for example, as shown in Expression (14).
- DI In the case of a white pixel, since Y and Yw are the same, DI becomes 0. In the case of a black pixel, DI is 1 because Y is 0. That is, the difference DI is a real number from 0 to 1.
- the first color conversion unit 106 performs the first color conversion by colorimetric color reproduction, and converts the color device value P0 (RGB) of each pixel in the input image into a color device value in the target color space.
- the color device value obtained by the first color conversion unit 106 is hereinafter referred to as “first color device value” and expressed as “P1” or “R′G′B ′”.
- the tristimulus value XYZ of each pixel of the input image is calculated, and the first color device value P1 (described above) is calculated from the color device value P0 (RGB) of each pixel in the input image according to Expression (15). R′G′B ′) is calculated.
- B ⁇ 1 is an inverse matrix of the RGB-XYZ conversion matrix B in the target color space.
- the second color conversion unit 108 converts the color device value P0 in the original color space into the color device value in the target color space for each pixel of the input image.
- the color device value obtained by the second color conversion unit 108 is referred to as a second device value, and “P2” or “R It is expressed as “G” B ”.
- the difference DI is 0.
- the second color of each pixel of the input image according to equation (16) using a function f that outputs 0 at some time and a value greater than 0 and less than or equal to 1 when the difference DI is non-zero.
- the device value P2 is obtained.
- the second color conversion unit 108 measures, for each pixel of the input image, a coefficient that is 0 when the difference DI is 0, and is greater than 0 and 1 or less when the difference DI is other than 0.
- the second color device value P2 is obtained. obtain.
- the output image generation unit 110 outputs the second color device value obtained by the second color conversion unit 108 as the color device value of the output image. Thereby, an output image in the target color space is generated.
- FIG. 2 is a flowchart showing processing of the image processing apparatus 100 shown in FIG. As illustrated, first, the feature amount acquisition unit 102 acquires the white luminance Yw in the original color space and the luminance Y of each pixel of the input image (S12, S14). Then, the difference calculation unit 104 calculates a difference DI between the luminance Yw of white in the original color space and the luminance Y for each pixel of the input image (S16).
- the first color conversion unit 106 performs first color conversion by colorimetric color reproduction, and for each pixel of the input image, the color device value P0 (RGB) in the original color space is the first color in the target color space.
- the color device value P1 (R′G′B ′) is converted (S18).
- the second color conversion unit 108 obtains a second color device value P2 for each pixel of the input image according to Expression (16) (S20).
- the output image generation unit 110 outputs each second color device value P2 obtained by the second color conversion unit 108. Thereby, an output image is obtained. (S22).
- the color device value in the white original color space is maintained.
- the color device values (R, G, B) in the white original color space are (255, 255, 255)
- '', B '') is also (255, 255, 255).
- the white brightness of the input image is maintained.
- the color device value (second color device value P2) of the output image is the color device value P0 in the original color space and the original color space.
- Expression (16) becomes the following Expression (17).
- luminance is used as a feature quantity that can indicate brightness, but brightness may also be used.
- the feature amount may include a color component, and for example, a color difference Eab in which the color component is added to the brightness may be used.
- the color device value itself (for example, RGB value) may be used.
- the feature amount difference is the Euclidean distance of the color device value. For example, when the white color device value in the original space is (255, 255, 255), the difference DI is calculated as shown in Expression (18).
- FIG. 3 shows an image processing apparatus 200 according to the second embodiment of the present invention.
- the image processing apparatus 200 generates an image (output image) corresponding to the input image in the target color space from the image (input image) in the original color space, and includes the color space information storage unit 210 and the representative color.
- LUT Has a look-up table
- the color system of the input image and the output image is the RGB color system. That is, the color device values of the input image and the output image are a combination of the R value, the G value, and the B value.
- the color space information storage unit 210 stores color space information of the original color space and the target color space.
- various conventionally known methods can be used.
- the image editing software PhotoShop (registered trademark) has a GUI capable of setting an ICC profile in order to obtain color information of the original color space and the target color space.
- the color space information storage unit 210 may store color space information of the original color space and the target color space set via the GUI (not shown).
- the color space information is information that defines the color space, and includes, for example, the chromaticity of the RGB phosphor, the chromaticity and luminance of white, and the gamma characteristic of each color signal.
- the representative color generation unit 220 generates a plurality of representative colors and obtains RGB values of the representative colors.
- the plurality of representative colors are preferably generated so as to cover as wide a range of colors as possible.
- the feature amount acquisition unit 232, the first color conversion unit 236, and the second color conversion unit 238 are different from the feature amount acquisition unit 102 in the image processing apparatus 100 shown in FIG.
- the difference calculation unit 104 and the second color conversion unit 108 perform the same processing.
- luminance is used as a feature amount indicating brightness.
- the feature amount acquisition unit 232 calculates white luminance Yw in the original color space and luminance Ys of each representative color.
- the feature amount acquisition unit 232 reads out the white luminance Yw in the original color space from the color space information storage unit 210, and the chromaticity and whiteness of the RGB phosphors in the original color space stored in the color space information storage unit 210.
- the RGB-XYZ conversion matrix Q of the original color space is calculated from the chromaticity (see Non-Patent Document 2). Assume that the RGB-XYZ conversion matrix Q of the original color space is A.
- the feature amount acquisition unit 232 calculates the luminance Ys from the color device value Ps (RGB) of each representative color according to the equation (6) or the equation (7).
- the feature amount acquisition unit 232 outputs the white luminance Yw in the original color space and the luminance Ys in the original color space of each representative color to the difference calculation unit 234, and the RGB-XYZ conversion matrix A of the original color space is output to the first color space.
- the data is output to the color conversion unit 236.
- the difference calculation unit 234 calculates, for each representative color, a difference DI between the luminance Ys of the representative color and the white luminance Yw in the original color space.
- This difference DI is, for example, as shown in Expression (19).
- the first color conversion unit 236 performs, for each representative color, first color conversion by colorimetric color reproduction to obtain the color device value Ps (RGB) of the representative color in the original color space of each representative color.
- Ps RGB
- an RGB-XYZ conversion matrix B of the target color space is calculated from the chromaticity of the RGB phosphor and the white chromaticity of the target color space stored in the color space information storage unit 210, and RGB-XYZ conversion is performed.
- the first color device value Ps (RGB) of each representative color is The color device value P1s (R′G′B ′) is calculated.
- the second color conversion unit 238 obtains the second color device value P2s (R ′′ G ′′ B ′′) of each representative color according to Expression (16) and outputs it to the LUT 240 for each representative color. To do.
- the LUT 240 stores the color device value P0 in the original color space and the second color device value P2s from the second color conversion unit 108 in association with each representative color.
- the output image generation unit 250 uses the color device value P0w in the original color space for the white pixels of the input image, and refers to the LUT 240 for the pixels other than white, and corresponds to the color device value P0 of the pixel.
- Each color device value of the output image is obtained by calculating the color device value P2 (R ′′ G ′′ B ′′) of 2 by interpolation. For example, an 8-point interpolation method can be used as the interpolation method.
- the image processing apparatus 100 shown in FIG. 1 performs a second color that becomes a color device value of an output image through feature amount acquisition, difference calculation, first color conversion, and second color conversion for each pixel of the input image.
- a device value P2 is obtained.
- the image processing apparatus 200 performs feature amount acquisition, difference calculation, first color conversion, and second color conversion only for a plurality of representative colors, and the second color device values of the plurality of representative colors. Get P2s.
- the color device value P0 in the original color space of the plurality of representative colors and the second color device value P2s are associated with each other and registered in the LUT 240, and the registered contents of the LUT 240 are referred to, so A second color device value P2 is calculated. Except for this point, it can be said that the image processing apparatus 100 and the image processing apparatus 200 perform the same processing.
- each effect obtained by the image processing apparatus 100 can be obtained.
- the feature amount acquisition, difference calculation, first color conversion, and second color conversion are performed only for a plurality of representative colors, the amount of calculation is small and an output image can be generated at high speed.
- an image such as the use of a feature quantity other than luminance, such as brightness, color difference Eab, and color device value, and the type of function f used when second color conversion is performed to calculate the second color device value P2s.
- a feature quantity other than luminance such as brightness, color difference Eab, and color device value
- the type of function f used when second color conversion is performed to calculate the second color device value P2s may be made to the image processing device 200.
- the technique according to the present invention can be used, for example, for color reproduction between color image reproducing apparatuses having different color characteristics.
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Abstract
Description
また、式(3)を式(2)に代入することによって、式(4)に示すvon Kriesの色順応予測式を得ることができる。なお、式(4)におけるDは、式(5)に示されている。
P2=P0+f(DI)(P1-P0) (9)
但し,P2:第2のカラーデバイス値
P1:第1のカラーデバイス値
P0:元色空間におけるカラーデバイス値
DI:第1の差分
こうすることにより、色の見えを一致させながら、カラー画像をより明るく再生できる。
それに対して、画像処理装置200は、複数の代表色についてのみ、特徴量取得、差分算出、第1の色変換、第2の色変換を行い、該複数の代表色の第2のカラーデバイス値P2sを得る。そして、該複数の代表色の元色空間におけるカラーデバイス値P0と、第2のカラーデバイス値P2sとを対応付けてLUT240に登録し、LUT240の登録内容を参照して、白色以外の各画素の第2のカラーデバイス値P2を算出する。この点を除いて、画像処理装置100と画像処理装置200が同一の処理を行っているといえる。
102 特徴量取得部
104 差分算出部
106 第1の色変換部
108 第2の色変換部
110 出力画像生成部
200 画像処理装置
210 色空間情報記憶部
220 代表色生成部
232 特徴量取得部
234 差分算出部
236 第1の色変換部
238 第2の色変換部
240 LUT
250 出力画像生成部
Claims (18)
- 元色空間における画像である入力画像から、目的色空間における画像である出力画像を生成する画像処理方法において、
前記入力画像の各カラーデバイス値が表す夫々の色について、前記元色空間における白色の明るさを示し得る特徴量と、前記カラーデバイス値が表す色の前記特徴量との差分である第1の差分を算出する差分算出処理をし、
前記入力画像の各カラーデバイス値が表す夫々の色について、測色的色再現により該色の前記カラーデバイス値を前記目的色空間におけるカラーデバイス値である第1のカラーデバイス値に変換する第1の色変換を行い、
前記入力画像の各カラーデバイス値が表す夫々の色について、前記第1の差分が0であるときに前記カラーデバイス値になり、前記第1の差分が0より大きいときに、前記第1のカラーデバイス値と前記カラーデバイス値との差分である第2の差分に、1以下0より大きい係数を乗算して得た値と、前記カラーデバイス値との和になる第2のカラーデバイス値を算出する第2の色変換を行い、該第2のカラーデバイス値を前記出力画像のカラーデバイス値として出力する出力画像生成処理を行うことを特徴とする画像処理方法。 - 前記係数は、前記第1の差分が大きいほど大きくなるものであることを特徴とする請求項1に記載の画像処理方法。
- 前記差分算出処理と、前記第1の色変換は、複数の代表色についてのみ行われるものであり、
前記出力画像生成処理は、
前記複数の代表色に対してのみ前記第2の色変換を行い、
該複数の代表色について、前記元色空間におけるカラーデバイス値と、前記第2の色変換により得られた前記第2のカラーデバイス値とを対応付けてルックアップテーブルに登録し、
前記入力画像の各カラーデバイス値が表す夫々の色のうちの白色以外の色については、前記ルックアップテーブルを参照して該色のカラーデバイス値に対応する前記第2のカラーデバイス値を算出し、白色については、元色空間における白色のカラーデバイス値を用いるようにして、前記出力画像のカラーデバイス値を得ることを特徴とする請求項1または2に記載の画像処理方法。 - 前記特徴量は、輝度または明度であることを特徴とする請求項1から3のいずれか1項に記載の画像処理方法。
- 前記特徴量は、色成分が含まれることを特徴とする請求項1から3のいずれか1項に記載の画像処理方法。
- 前記特徴量は、色差Eabであることを特徴とする請求項5に記載の画像処理方法。
- 前記特徴量は、カラーデバイス値であり、
前記差分は、カラーデバイス値のユークリッド距離であることを特徴とする請求項5に記載の画像処理方法。 - 元色空間における画像である入力画像から、目的色空間における画像である出力画像を生成する画像処理装置であって、
前記入力画像の各カラーデバイス値が表す夫々の色について、前記元色空間における白色の明るさを示し得る特徴量と、前記カラーデバイス値が表す色の前記特徴量との差分である第1の差分を算出する差分算出処理手段と、
前記入力画像の各カラーデバイス値が表す夫々の色について、測色的色再現により該色の前記カラーデバイス値を前記目的色空間におけるカラーデバイス値である第1のカラーデバイス値に変換する第1の色変換手段と、
前記入力画像の各カラーデバイス値が表す夫々の色について、前記第1の差分が0であるときに前記カラーデバイス値になり、前記第1の差分が0より大きいときに、前記第1のカラーデバイス値と前記カラーデバイス値との差分である第2の差分に、1以下0より大きい係数を乗算して得た値と、前記カラーデバイス値との和になる第2のカラーデバイス値を算出する第2の色変換を行い、該第2のカラーデバイス値を前記出力画像のカラーデバイス値として出力する出力画像生成処理手段とを備えることを特徴とする画像処理装置。 - 前記係数は、前記第1の差分が大きいほど大きくなるものであることを特徴とする請求項8に記載の画像処理装置。
- 前記差分算出処理手段と、前記第1の色変換手段は、複数の代表色についてのみ処理を行うものであり、
前記出力画像生成処理手段は、
ルックアップテーブルをさらに備え、
前記複数の代表色に対してのみ前記第2の色変換を行い、
該複数の代表色について、前記元色空間におけるカラーデバイス値と、前記第2の色変換により得られた前記第2のカラーデバイス値とを対応付けて前記ルックアップテーブルに登録し、
前記入力画像の各カラーデバイス値が表す夫々の色のうちの白色以外の色については、前記ルックアップテーブルを参照して該色のカラーデバイス値に対応する前記第2のカラーデバイス値を算出し、白色については、元色空間における白色のカラーデバイス値を用いるようにして、前記出力画像のカラーデバイス値を得ることを特徴とする請求項8または9に記載の画像処理装置。 - 前記特徴量は、輝度または明度であることを特徴とする請求項8から10のいずれか1項に記載の画像処理装置。
- 前記特徴量は、色成分が含まれることを特徴とする請求項8から9のいずれか1項に記載の画像処理装置。
- 前記特徴量は、色差Eabであることを特徴とする請求項12に記載の画像処理装置。
- 前記特徴量は、カラーデバイス値であり、
前記差分は、カラーデバイス値のユークリッド距離であることを特徴とする請求項13に記載の画像処理装置。 - 前記複数の代表色を生成する代表色生成手段をさらに備えることを特徴とする請求項8から14のいずれか1項に記載の画像処理装置。
- 元色空間における画像である入力画像から、目的色空間における画像である出力画像を生成する際に、
前記入力画像の各カラーデバイス値が表す夫々の色について、前記元色空間における白色の明るさを示し得る特徴量と、前記カラーデバイス値が表す色の前記特徴量との差分である第1の差分を算出する差分算出処理と、
前記入力画像の各カラーデバイス値が表す夫々の色について、測色的色再現により該色の前記カラーデバイス値を前記目的色空間におけるカラーデバイス値である第1のカラーデバイス値に変換する第1の色変換と、
前記入力画像の各カラーデバイス値が表す夫々の色について、前記第1の差分が0であるときに前記カラーデバイス値になり、前記第1の差分が0より大きいときに、前記第1のカラーデバイス値と前記カラーデバイス値との差分である第2の差分に、1以下0より大きい係数を乗算して得た値と、前記カラーデバイス値との和になる第2のカラーデバイス値を算出する第2の色変換を行い、該第2のカラーデバイス値を前記出力画像のカラーデバイス値として出力する出力画像生成処理とをコンピュータに実行させるプログラムを記録した記録媒体。 - 前記係数は、前記第1の差分が大きいほど大きくなるものであることを特徴とする請求項16に記載の記録媒体。
- 前記差分算出処理と、前記第1の色変換は、複数の代表色についてのみ行われるものであり、
前記出力画像生成処理は、
前記複数の代表色に対してのみ前記第2の色変換を行い、
該複数の代表色について、前記元色空間におけるカラーデバイス値と、前記第2の色変換により得られた前記第2のカラーデバイス値とを対応付けてルックアップテーブルに登録し、
前記入力画像の各カラーデバイス値が表す夫々の色のうちの白色以外の色については、前記ルックアップテーブルを参照して該色のカラーデバイス値に対応する前記第2のカラーデバイス値を算出し、白色については、元色空間における白色のカラーデバイス値を用いるようにして、前記出力画像のカラーデバイス値を得ることを特徴とする請求項16または17に記載の記録媒体。
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CN106780648B (zh) * | 2016-12-15 | 2018-11-13 | 北京金山软件有限公司 | 一种图像颜色的动态变换方法及装置 |
US10733487B2 (en) * | 2017-10-17 | 2020-08-04 | Canon Kabushiki Kaisha | Information processing apparatus that generates color conversion table to be set in image forming apparatus, information processing method, and storage medium |
CN110113590A (zh) * | 2019-05-13 | 2019-08-09 | 北京海辰亿华科技有限公司 | 一种图像色彩空间的转换方法及装置 |
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