JP2010220116A - Image processing apparatus, image processing method, image processing program, and computer readable storage medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To determine a mapping direction for each of pixels even while performing lightness conversion on image data. <P>SOLUTION: The present invention relates to an image processing apparatus for converting source image data including pixels out of a color gamut of an image output device into output image data within the color gamut of the image output device. The image processing apparatus comprises at least: a lightness converting section 104 for converting lightness of the source image data within a lightness range of the image output device based on at least lightness range that the source image data can represent and lightness range that the image output device can output, and outputting lightness converted image data; a mapping direction determining section 106 for determining a mapping direction of pixels that are the lightness converted image data and become pixels out of the color gamut of the image output device, based on at least the lightness converted image data and the color gamut that the image output device can output; and a color gamut converting section 107 for converting the lightness converted image data into image data within the color gamut of the image output device based on the mapping direction determined by the mapping direction determining section. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image processing apparatus, an image processing method, an image processing program, and a computer-readable storage medium.

  Conventionally, since the color gamut expressed by an image output device such as a color printer or display is narrower than the color gamut expressed by an image input device such as a color scanner or digital camera, the image data expressed by the image input device However, there is a problem that it cannot be expressed by the image output apparatus. Therefore, there is a technology of a color conversion method for converting a color gamut that can be expressed by the image input apparatus into a color gamut that can be expressed by the image output apparatus.

  For example, a method is known in which lightness is first corrected by lightness conversion and then saturation is corrected by saturation conversion (see Patent Document 1). In addition, for example, a technique for correcting an image by detecting a color distribution direction of image data, determining a mapping direction, and executing image conversion in the mapping direction is known (Patent Document 2, Patent Document 2). 3).

  However, the invention disclosed in Patent Document 1 has a problem that saturation and gradation loss are likely to occur because a mapping direction for correcting image data is predetermined.

  In addition, in the inventions disclosed in Patent Document 2 and Patent Document 3, since lightness conversion that is generally effective for image conversion is not executed, there is a problem that saturation reduction and gradation collapse are likely to occur. is there.

  The present invention has been made in view of the above, and an image processing apparatus and an image processing method capable of determining a mapping direction for each pixel while performing brightness conversion on image data. An object of the present invention is to provide an image processing program and a computer-readable storage medium.

  In order to solve the above-described problems and achieve the object, the present invention provides an image processing device that converts original image data including pixels outside the color gamut of the image output device into output image data within the color gamut of the image output device. The lightness of the original image data is converted into the lightness region of the image output device based on at least the lightness region that can be expressed by the original image data and the lightness region that can be output by the image output device. Lightness conversion means for outputting image data; and at least a lightness-converted image data and a pixel that is an out-of-gamut pixel of the image output device based on the lightness-converted image data and a color gamut that can be output by the image output device. Mapping direction determining means for determining a mapping direction as a conversion direction, and the lightness converted image data based on the mapping direction determined by the mapping direction determining means , Characterized in that it comprises at least a color gamut conversion means for converting the image data in the color gamut of the image output device.

  The present invention has been made in view of the above, and it is possible to determine the mapping direction for each pixel while performing lightness conversion on image data. There is an effect that it is possible to stably obtain a good image with reduced gradation.

FIG. 1 is a block diagram showing the configuration of the image processing apparatus according to this embodiment. FIG. 2 is an explanatory diagram illustrating an example of lightness conversion processing. FIG. 3 is a block diagram illustrating a configuration of the mapping direction determination unit. FIG. 4 is an explanatory diagram illustrating an example of processing performed by the color difference minimum direction determination unit. FIG. 5 is a cross-sectional view showing an example of the CIELAB color space cut along the brightness axis. FIG. 6 is a block diagram illustrating a configuration of the color distribution determination unit. FIG. 7 is an explanatory diagram illustrating an example of a color distribution of pixels outside the color gamut classified into a specific hue region. FIG. 8 is an explanatory diagram illustrating an example of processing of the high-lightness sticking determination unit. FIG. 9 is an explanatory diagram illustrating an example of processing of the high saturation side distribution determination unit. FIG. 10 is a flowchart showing the procedure of color gamut conversion processing of image data in the image processing apparatus according to the present embodiment. FIG. 11 is a flowchart showing a procedure of lightness conversion processing of original image data in the lightness conversion unit. FIG. 12 is a flowchart illustrating a processing procedure for determining the mapping direction of the mapping direction determination unit. FIG. 13 is a flowchart illustrating the procedure of the color gamut conversion process of the color gamut conversion unit. FIG. 14 is a flowchart illustrating a procedure of color distribution centroid detection processing of the color distribution centroid detection unit. FIG. 15 is a flowchart illustrating a processing procedure for selecting a mapping direction by the mapping direction selection unit. FIG. 16 is a block diagram of a hardware configuration of the image processing apparatus according to the first embodiment.

  Exemplary embodiments of an image processing apparatus, an image processing method and an image processing program, and a computer-readable storage medium according to the present invention are explained in detail below with reference to the accompanying drawings.

(First embodiment)
FIG. 1 is a block diagram illustrating a configuration of the image processing apparatus according to the first embodiment. The image input device sends an image to the image processing device, and the image processing device sends an output image to the image output device. The image processing apparatus mainly includes a brightness conversion unit, an image storage unit, a mapping direction determination unit, and a color gamut conversion unit.

  The image input device 101 outputs image data (hereinafter referred to as “original image data”) to the image processing device 102. The color format of the original image data is explicitly determined by an ICC profile embedded in the original image data, communication between the image input device 101 and the image processing device 102, or the like. Alternatively, a standard color specification format such as sRGB or AdobeRGB is implicitly determined as the color specification format. Then, the image input apparatus 101 outputs original image data whose color formats are clear to each other to the image processing apparatus 102.

  In the present embodiment, it is assumed that Adobe RGB is determined by communication as the color format of the original image data in the image input apparatus 101, but other color formats may be used.

  The image input device 101 is, for example, a digital still camera that captures a landscape or a person and stores it as image data, a color scanner that scans a document to generate image data, an SD memory or HDD that stores image data, and the like. The storage is composed of a storage medium and a control unit that controls reading and writing of the storage medium.

  The image output device 103 visualizes and outputs the image data output from the image processing device 102 (hereinafter referred to as “output image data”). The image output device 103 is, for example, an LCD display that displays image data on a screen, or a color printer that records image data on a recording medium such as paper. In this embodiment, as an example, the image output apparatus 103 will be described as a color printer.

  The lightness conversion unit 104 converts the lightness of the original image data into the lightness region of the image output device 103 based on the lightness region in which the original image data can be expressed and the lightness region in which the image output device 103 can output. It should be noted that the brightness range that can represent the original image data is determined by the color specification format described above. For example, in AdobeRGB, the lightness L * takes a value from 0 to 100.

  The brightness range that can be output by the image output device 103 is determined by the color gamut that the image output device 103 can output. For example, in a color printer, the upper limit of the brightness range is determined by the recording medium used in the color printer, and the lower limit of the brightness range is determined by the brightness when composite black or the like is recorded on the recording medium. In this embodiment, the color gamut that can be output by the image output apparatus 103 is notified from the image output apparatus 103 to the image processing apparatus 102 by communication, and the lightness conversion unit 104 can output colors that the image output apparatus 103 can output. The upper and lower limits of lightness that can be output are extracted from the range and used. Note that, for example, a method of notifying the image processing apparatus 102 of the color gamut that can be output by the image output apparatus 103 by using a method such as directly supplying the ICC profile of the image output apparatus 103 to the image processing apparatus 102 is used. May be.

  The brightness conversion performed by the brightness conversion unit 104 will be described in detail. FIG. 2 is an explanatory diagram illustrating an example of lightness conversion processing. FIG. 2A is a cross-sectional view showing an example of the CIELAB color space cut along the brightness axis. This shows an example of the relationship between the color gamut that can represent the original image data and the color gamut that the image output device 103 can output. As shown in FIG. 2A, the color gamut that can represent the original image data is larger than the color gamut that can be output by the image output apparatus 103. In particular, the brightness range that is the range in the brightness axis direction is In general, it is an inclusive relationship. Therefore, the lightness conversion unit 104 converts the lightness of the original image data within the lightness range of the image output device 103 and reproduces the lightness of the image data (hereinafter referred to as “lightness converted image data”) in the image output device. It can be so. FIG. 2B is an explanatory diagram showing an example of the brightness conversion characteristic. In this case, the brightness range that can represent the original image data is linearly converted to the brightness range that the image output apparatus 103 can output. FIG. 2C shows the relationship between a color gamut that can express lightness-converted image data, which is image data after the above-described conversion, and a color gamut that the image output device 103 can output. According to this, the brightness of the original image data is converted into the brightness range of the image output device 103. However, the saturation range of the brightness converted image data is wider than the saturation range of the image output device 103.

  Further, in the above, the brightness conversion is performed linearly, but when the upper and lower limits of the brightness range coincide and the middle part is simply increased, the processing performed in the present embodiment is not limited to the above, for example Nonlinear conversion represented by S-curve conversion or the like in FIG. 2B may be used.

  The image storage unit stores the lightness-converted image data output from the lightness conversion unit 104 and sends it to the mapping direction determination unit 106 and the color gamut conversion unit 107 as necessary.

  The mapping direction determination unit 106 refers to the lightness converted image data converted by the lightness conversion unit 104 and stored in the image storage unit 105, and the color gamut that can be output by the image output device 103, and the lightness converted image. The mapping direction of the data and the out-of-gamut pixels (hereinafter referred to as “out-of-gamut pixels”) of the image output apparatus 103 is determined. In the present embodiment, as described above, the color gamut of the image output apparatus 103 is notified from the image output apparatus 103 to the image processing apparatus 102 by communication.

  FIG. 3 is a block diagram illustrating a configuration of the mapping direction determination unit 106 according to the first embodiment. The mapping direction determination unit 106 mainly includes a color distribution centroid detection unit 301, a color difference minimum direction determination unit 302, a mapping direction generation unit 303, a color distribution determination unit 304, and a mapping direction selection unit 305.

  The color distribution centroid detection unit 401 detects the centroid of the pixels outside the color gamut for each hue region. For example, the hue indicated by the lightness-converted image data is divided into 12 equal parts, and the center of gravity is detected outside the color gamut for each area. That is, an outputable color gamut that is a color gamut that can be output by the image output device 103 is input, and it is determined whether or not the input brightness converted image data is out of the color gamut of the image output device 103. For example, aggregation is performed according to the hue area to which the brightness-converted image data belongs, and the center of gravity of the entire brightness-converted image data for each hue area is detected.

そして、色相領域別の集計値に基づいて、それぞれの重心を算出する。それぞれの重心は、以下の（２）式で表される。これにより、色相領域毎の明度変換画像データ全体の重心が検出される。

なお、色分布重心検出部４０１の処理手順の詳細は後述する。 The processing of the color distribution centroid detection unit 401 will be described. When the color gamut that can be output by the image output device 103 is acquired and the brightness conversion image data is acquired from the image storage unit 105, it is determined whether or not the acquired image data is out of the color gamut of the image output device 103. If so, the image data is totaled according to the hue region to which the image data belongs. Aggregation is expressed by the following equation (1), for example. Note that the number of pixels in the hue area is the sum of the totals.

Then, the center of gravity is calculated based on the total value for each hue region. Each center of gravity is expressed by the following equation (2). Thereby, the center of gravity of the entire brightness-converted image data for each hue region is detected.

Details of the processing procedure of the color distribution centroid detection unit 401 will be described later.

  The minimum color difference direction determination unit 402 determines, for each hue region, the direction in which the color difference is minimum with the same hue when the center of gravity of the pixels outside the color gamut detected by the color distribution center of gravity detection unit 401 is mapped in the color gamut of the image output device 103. judge. FIG. 4 is an explanatory diagram illustrating an example of processing performed by the color difference minimum direction determination unit 402. FIG. 4A is a cross-sectional view showing an example of the CIELAB color space cut along the brightness axis. Here, an example of the color gamut that can be output by the image output device 103 and the center of gravity of the pixels outside the color gamut are shown. As shown in FIG. 4A, the color gamut that can be output by the image output apparatus 103 does not represent an accurate quadrilateral. Therefore, when attention is paid to the equi-hue plane which is a cross section cut along the lightness axis, the direction when mapping out-of-gamut pixels to the minimum color difference direction with the same hue varies depending on the pixel position. Therefore, in the first embodiment, the determination of the minimum color difference direction is performed based on the center of gravity of the detected out-of-gamut pixels. Specifically, the determination of the Euclidean distance minimum direction, which is the minimum color difference direction, is performed in each of the points A, B, and C in FIG. Note that the minimum color difference direction is not limited to the minimum Euclidean distance direction, and determination may be made using an improved color difference formula such as CIE94 or CIEDE2000.

  Note that when the mapping direction is determined and the out-of-gamut pixels are mapped in the color gamut that can be output by the image output device 103, the brightness level of the highest saturation point that can be output by the image output device 103 is used as a boundary. It is necessary to handle it separately on the low brightness side. FIG. 4B is an explanatory diagram showing an example of mapping separately on the high brightness side and the low brightness side. As shown in FIG. 4B, the area outside the color gamut on the low lightness side is usually extremely narrow compared to the high lightness side. This is particularly noticeable when the output device is a color printer. Even if the mapping direction is changed on the low brightness side, the mapping destination is hardly changed. For this reason, in the first embodiment, the mapping direction on the low brightness side is fixed. In addition, if the center of gravity of the distribution detected without dividing the high brightness side and the low brightness side is located on the low brightness side, it is assumed that the center of gravity is on the brightness boundary between the high brightness side and the low brightness side, and the color difference is minimum. Determine the direction. Note that the process for determining the mapping direction performed in the present embodiment is not limited to the above, and the mapping direction may be determined by detecting the center of gravity of the pixels outside the color gamut on the low lightness side as with the high lightness side. .

  The mapping direction generation unit 403 generates a mapping direction of lightness priority, color difference priority, and saturation priority for each hue area based on the direction that minimizes the color difference determined by the minimum color difference direction determination unit 402. FIG. 5 is a cross-sectional view showing an example of the CIELAB color space cut along the brightness axis. As shown in FIG. 5, an example of the minimum color difference direction determined by the minimum color difference direction determination unit 402 and the mapping directions of the brightness priority, the color difference priority, and the saturation priority generated are shown. The color difference priority direction to be made coincides with the minimum color difference direction. The direction toward the lightness axis is the lightness preservation direction, and the direction parallel to the lightness axis is the saturation preservation direction. The generated brightness priority direction is set between the brightness storage direction and the minimum color difference direction, and the generated saturation priority direction is set between the saturation storage direction and the minimum color difference direction.

The generation of the lightness priority and saturation priority mapping directions is performed with reference to the minimum color difference direction as described above. Here, if the lightness preservation direction is defined as 0 degree, the lightness priority and saturation priority mapping directions are expressed by the following equation (3) with reference to, for example, the minimum color difference direction and the lightness preservation direction or the saturation preservation direction. Is done.

Further, the lightness and saturation priority mapping directions are not limited to the above-described methods and coefficients, and may be generated by, for example, the following equation (4) with reference to the minimum color difference direction.

  The color distribution determination unit 404 determines the characteristics of the color distribution of the pixels outside the color gamut for each hue area described above. An outputable color gamut that is a color gamut that can be output by the image output device 103 is input to the color distribution determination unit 404, and it is determined whether the input lightness-converted image data is outside the color gamut of the image output device 103. If it is out of the color gamut, it is added to the evaluation target of the hue region to which the lightness-converted image data belongs.

  FIG. 6 is a block diagram illustrating a configuration of the color distribution determination unit 404 according to the first embodiment. The color distribution determination unit 404 mainly includes a color distribution directionality determination unit 601, a low lightness sticking determination unit 602, a high lightness sticking determination unit 603, an occupation area ratio determination unit 604, and a high saturation side distribution determination unit 605.

The color distribution directionality determination unit 801 determines whether the directionality of the color distribution of the pixels outside the color gamut is small. The directionality determination is performed, for example, by performing principal component analysis on the out-of-gamut pixels added to the evaluation target for each hue region. FIG. 7 is an explanatory diagram illustrating an example of a color distribution of pixels outside the color gamut classified into a specific hue region. As shown in FIG. 7, by performing principal component analysis on the out-of-gamut pixels, it is possible to obtain a contribution rate indicating how much each of the three eigenvalue vectors and each eigenvector contributes to the dispersion of the color distribution. Accordingly, when the eigenvalue vectors are defined as V1, V2, and V3 in descending order of the contribution rate, if the difference between the contribution rates of the eigenvalue vector V1 and the eigenvalue vector V2 is small, it is determined that the directionality of the color distribution of the pixels outside the color gamut is small. it can. Therefore, for example, the predetermined threshold value α is set to 0.5, and the directionality of the color distribution of the pixels outside the color gamut is determined by the following equation (5).

  In the present embodiment, the difference in the contribution ratio between the eigenvalue vector V1 and the eigenvalue vector V2 is evaluated. This is because the unidirectional strength of the color distribution is evaluated. Therefore, when it is desired to evaluate the two-dimensional spread, the difference between the contribution rates of the eigenvalue vector V1 and the eigenvalue vector V3 may be evaluated.

  The low-lightness sticking determination unit 802 determines whether or not the pixels outside the color gamut are sticking to the outermost low-lightness side of the color gamut that can represent the image data.

  The high-lightness sticking determination unit 803 determines whether or not the pixels outside the color gamut are attached to the outermost high-lightness side of the color gamut that can represent the image data. Processing for determining whether or not the distribution is attached to the outermost shell is shown below.

  FIG. 8 is an explanatory diagram illustrating an example of processing of the high-lightness sticking determination unit 803. FIG. 8 shows a color gamut that can express the lightness-converted image data described above and a color gamut generated by reducing the color gamut toward a predetermined fixed point F on the lightness axis (hereinafter referred to as “reduced color gamut”). ). Specifically, for example, the reduced color gamut is generated by reducing the color gamut at a reduction ratio of 90% toward the fixed point F where L * is 50. An area corresponding to the difference between the two color gamuts (hereinafter referred to as “difference area”) can be regarded as the outermost neighborhood of the color gamut that can express the brightness converted image data. Therefore, referring to the lightness of A or B which is the highest hue saturation point of the color gamut that can be represented by the lightness-converted image data, and if the out-of-gamut pixels are distributed in the lower difference area, the outermost low-lightness side If pixels outside the color gamut are distributed in the upper difference area, it is determined that the pixel is stuck to the outermost high brightness side.

For this reason, the low-lightness sticking determination unit 802 and the high-lightness sticking determination unit 803 obtains a color gamut that can express the lightness-converted image data described above from, for example, the lightness conversion unit 104 described above, and the lower or upper difference region. Set. Then, it is determined whether or not the input brightness-converted image data is within the difference area, the number of pixels inside and outside the area is calculated, and if the ratio within the area is large, it is determined that the area is sticking. Therefore, the predetermined threshold value β is set to 1, and it is determined that it sticks to the outermost low brightness side or the outermost high brightness side according to the following equation (6).

The occupied area ratio determination unit 804 determines whether or not the pixels outside the color gamut have a small occupied area ratio. For example, the occupation area ratio is determined by calculating all pixels including out-gamut pixels and in-gamut pixels for each hue region, and evaluating the ratio. That is, the predetermined threshold γ is set to γ = 1/1000, for example, and it is determined whether or not the occupation area ratio is small according to the following equation (7).

  The high saturation side distribution determination unit 805 determines whether or not the main power of the pixels outside the color gamut is distributed on the high saturation side from the maximum saturation that can be output by the image output apparatus 103. FIG. 9 is an explanatory diagram illustrating an example of processing of the high saturation side distribution determination unit 805. Whether or not the image is distributed on the high saturation side is determined by, for example, the highest chroma that can be output by the image output device 103 as shown in FIG. The determination is made based on whether or not the pixel is located in a high saturation area on the higher saturation side than the degree point. Note that the determination performed by the high saturation side distribution determination unit 805 may be performed by the color distribution centroid detection unit 401.

  The mapping direction selection unit 405 selects the mapping direction of brightness priority, color difference priority, and saturation priority generated by the mapping direction generation unit 403 according to the determination result of the color distribution determination unit 404. Details of the color distribution determination process performed by the color distribution determination unit 404 will be described later.

  The color gamut conversion unit 107 converts lightness-converted image data, which is image data obtained by converting the lightness by the lightness conversion unit 104, based on the mapping direction determined by the mapping direction determination unit and the color gamut that can be output by the image output device 103. The image data is converted into image data in the color gamut of the image output device 103. Note that the color gamut of the image output apparatus 103 is notified from the image output apparatus 103 to the image processing apparatus 102 as described above. Details of the color distribution conversion processing performed by the color distribution conversion unit 107 will be described later.

  Next, the gamut conversion processing until the image data from the image input apparatus by the image processing apparatus 102 according to the first embodiment configured as described above is gamut converted into the gamut of the image output apparatus will be described. To do. FIG. 10 is a flowchart showing a procedure of color gamut conversion processing of image data in the image processing apparatus.

  First, the lightness conversion unit 104 converts the lightness of the original image data acquired from the image input device 101 into the lightness range of the image output device (step S1001). Details of the lightness conversion processing of the original image data in the lightness conversion unit 104 will be described later.

  Then, the image storage unit 105 stores the lightness conversion image data acquired from the lightness conversion unit 104 (step S1002).

  Next, the mapping direction determination unit 106 determines the mapping direction of the out-of-gamut pixels of the image output device in the brightness-converted image data acquired from the image storage unit 105 (step S1003). Details of the process of determining the mapping direction by the mapping direction determination unit 106 will be described later.

  Then, the color gamut conversion unit 107 converts the lightness converted image data in the mapping direction determined by the mapping direction determination unit 106 (step 1004). Details of the color gamut conversion processing of the color gamut conversion unit 107 will be described later.

  According to the processing procedure described above, the image data from the image input device can be color gamut converted into the color gamut of the image output device.

  Next, the lightness conversion processing of the original image data in the lightness conversion unit 104 will be described. FIG. 11 is a flowchart showing a procedure of lightness conversion processing of original image data in the lightness conversion unit 104 in the image processing apparatus according to the present embodiment.

  First, the lightness conversion unit 104 acquires a lightness region that can represent the original image data and a lightness region that can be output by the image output apparatus 103 (step S1101). This is executed with reference to the color specification format of the original image data and the color gamut notified from the image output apparatus 103.

  Next, the lightness conversion unit 104 refers to the acquired lightness range and determines a lightness conversion method (step S1102). Specifically, the linear transformation that is the lightness transformation characteristic shown in FIG.

  Next, the lightness conversion unit 104 starts outputting image data from the image input device 101, and acquires the output image data (step S1103). Note that the color specification format of the acquired image data is Adobe RGB in the present embodiment.

  Next, the lightness conversion unit 104 converts the acquired image data into CIELAB (step S1104).

  Next, the lightness conversion unit 104 converts the converted lightness L * of CIELAB according to the lightness conversion characteristics determined above (step S1105).

  Next, the lightness conversion unit 104 outputs CIELAB whose lightness L * has been converted to the image storage unit 105 (step S1106).

  Then, the lightness conversion unit 104 determines whether or not all the processing of the original image data has been completed (step S1107). If the lightness conversion unit 104 determines that the processing of all of the original image data has not been completed (step S1107: No), the process returns to step S1103.

  If the lightness conversion unit 104 determines that all the processing of the original image data has been completed (step S1107: Yes), the lightness conversion unit 104 ends the lightness conversion processing.

  The lightness conversion processing of the original image data in the lightness conversion unit 104 can be performed by the above-described processing procedure.

  Next, processing for determining the mapping direction of the mapping direction determination unit 106 will be described. FIG. 12 is a flowchart illustrating a procedure of processing for determining the mapping direction of the mapping direction determination unit 106 in the image processing apparatus according to the present embodiment.

  First, the color distribution centroid detection unit 301 detects the centroid of the color distribution from the brightness conversion image data (step S1201). Details of the processing of the color distribution centroid detection unit will be described later.

  Next, the color difference minimum direction determination unit 302 determines the color difference minimum direction (step S1202).

  Then, the mapping direction generation unit 303 generates a mapping direction (step S1203).

  Next, the color distribution determination unit 304 determines the color distribution from the lightness conversion image data (step S1204).

  Then, the mapping direction selection unit 305 selects a mapping direction (step S1205). Details of the mapping direction selection processing of the mapping direction selection unit 305 will be described later.

  With the processing procedure described above, the mapping direction determination unit 106 can perform the process of determining the mapping direction.

  Next, the color gamut conversion process of the color gamut conversion unit 107 will be described. FIG. 13 is a flowchart showing the procedure of the color gamut conversion process of the color gamut conversion unit 107 in the image processing apparatus according to the present embodiment.

  First, the color gamut conversion unit 107 acquires a color gamut that can be output by the image output apparatus 103 (step S1301). This is performed based on the color gamut notified from the image output device 103.

  Next, the color gamut conversion unit 107 creates a color conversion table based on the mapping direction determined by the mapping direction determination unit (step S1302). Here, the color conversion table is obtained for output image data corresponding to a representative value representing lightness-converted image data, and it is determined whether or not each representative value is out of the color gamut of the image output device 103. If it is out of the color gamut, the mapping destination is calculated based on the mapping direction of the corresponding hue region. If the color gamut is satisfied, the value as it is is made to correspond.

  Next, reading of lightness conversion image data from the image storage unit 105 is started, and the color gamut conversion unit 107 converts the read image data into output image data using the above-described color conversion table ( Step S1303).

  Then, the color gamut conversion unit 107 determines whether or not the processing of the lightness conversion image data has been completed (step S1304). If the color gamut conversion unit 107 determines that the processing of all the brightness converted image data has not been completed (step S1304: NO), the process proceeds to step S1303.

  When the color gamut conversion unit 107 determines that all of the lightness conversion image data processing has been completed (step S1304: Yes), the color gamut conversion processing of the color gamut conversion unit 107 ends.

  The color gamut conversion process of the color gamut conversion unit 107 can be performed by the processing procedure described above.

  Next, the color distribution centroid detection process of the color distribution centroid detection unit 301 will be described. FIG. 14 is a flowchart illustrating a procedure of color distribution centroid detection processing of the color distribution centroid detection unit 301 in the image processing apparatus according to the present embodiment.

  First, the color distribution centroid detection unit 301 acquires a color gamut that can be output by the image output apparatus 103 (step S1401). This is performed based on the color gamut notified from the image output device 103 described above.

  Next, the color distribution centroid detection unit 301 starts reading the brightness conversion image data from the image storage unit 105 and acquires the read image data (step S1402).

  Then, the color distribution center-of-gravity detection unit 301 determines whether the acquired image data is outside the color gamut of the image output device 103 (step S1403). When the color distribution centroid detection unit 301 determines that the acquired image data is outside the color gamut of the image output device 103 (step S1403: Yes), the color distribution centroid detection unit 301 responds to the hue region to which the image data belongs. The image data is totaled (step S1404). If the color distribution centroid detection unit 301 determines that the acquired image data is not out of the color gamut of the image output device 103 (step S1403: No), the process of step S1405 described below is performed.

  Next, the color distribution center-of-gravity detection unit 301 determines whether or not the processing of the brightness conversion image data has been completed (step S1405). If the color distribution center-of-gravity detection unit 301 determines that the processing of all the brightness-converted image data has not been completed (step S1405: No), the process of step S1402 is performed.

  Here, when the color distribution centroid detection unit 301 determines that all the processing of the lightness conversion image data has been completed (step S1405: Yes), the color distribution centroid detection unit 301 refers to the total value for each hue region, Each center of gravity is calculated (step S1406). Then, the process of the color distribution centroid detection unit 301 is terminated.

  The color distribution centroid detection process of the color distribution centroid detection unit 301 can be performed by the processing procedure described above.

  Next, processing for selecting a mapping direction by the mapping direction selection unit 305 will be described. FIG. 15 is a flowchart illustrating a processing procedure for selecting the mapping direction of the mapping direction selection unit 305 in the image processing apparatus according to the present embodiment.

  First, the mapping direction selection unit 305 sets a hue area (step S1501). As described above, the mapping direction generation unit 403 and the color distribution determination unit 404 generate the mapping direction of lightness priority, color difference priority, and saturation priority for each hue region, and determine the color distribution. Selection is also performed for each hue region.

  Then, the mapping direction selection unit 305 determines whether or not the directionality of the color distribution of the pixels outside the color gamut is small in each hue region (step S1502). Here, when the mapping direction selection unit 305 determines that the directionality of the color distribution of the out-of-gamut pixel is small in each hue region (step S1502: Yes), the mapping direction selection unit 305 selects the mapping direction with the color difference priority. Select (step S1507).

  If the mapping direction selection unit 305 determines that the directionality of the color distribution of the out-of-gamut pixel is not small in each hue region (step S1502: No), the mapping-direction selection unit 305 determines that the out-of-gamut pixel is the outermost contour. It is determined whether or not it is stuck to the low brightness side (step S1503).

  Here, when the mapping direction selection unit 305 determines that the out-of-gamut pixels are stuck on the outermost low brightness side (step S1503: Yes), the mapping direction selection unit 305 selects the brightness priority mapping direction. (Step S1508).

  When the mapping direction selection unit 305 determines that the out-of-gamut pixel is not attached to the outermost low brightness side (step S1503: No), the mapping direction selection unit 305 determines that the out-of-gamut pixel is the outermost high brightness side. It is determined whether or not it sticks to (step S1504).

  Here, when the mapping direction selection unit 305 determines that the out-of-gamut pixel is attached to the outermost high brightness side (step S1504: Yes), the mapping direction selection unit 305 selects the mapping direction with priority on saturation. (Step S1509).

  If the mapping direction selection unit 305 determines that the pixels outside the color gamut are not attached to the outermost high brightness side (step S1504: No), the mapping direction selection unit 305 has a small occupation area ratio of the pixels outside the color gamut. Whether or not (step S1505).

  If the mapping direction selection unit 305 determines that the occupied area ratio of the pixels outside the color gamut is small (step S1505: Yes), the mapping direction selection unit 305 selects a mapping direction with priority on saturation (step S1509). .

  If the mapping direction selection unit 305 determines that the occupied area ratio of the out-of-gamut pixels is not small (step S1505: No), the mapping-direction selection unit 305 determines whether the main power of the out-of-gamut pixels is distributed on the high saturation side. It is determined whether or not (step S1506).

  Here, when the mapping direction selection unit 305 determines that the main force of the out-of-gamut pixels is distributed on the high saturation side (step S1506: Yes), the mapping direction selection unit 305 selects a lightness priority mapping direction ( Step S1508).

  If the mapping direction selection unit 305 determines that the main color of the out-of-gamut pixels is not distributed on the high saturation side (step S1506: No), the mapping direction selection unit 305 selects a mapping direction with color difference priority (step S1506). S1507).

  Then, the mapping direction selection unit 305 determines whether selection of all hue regions has been completed (step S1510). When the mapping direction selection unit 305 determines that selection of all the hue regions is not completed (step S1510: No), the process of step S1501 is executed.

  Further, when the mapping direction selection unit 305 determines that selection of all the hue regions has been completed (step S1510: Yes), the processing of the mapping direction selection unit 305 is ended. As a result, the mapping direction prioritized in all the hue regions is determined, and the mapping direction is determined.

  With the processing procedure described above, the mapping direction selection unit 305 can select the mapping direction.

  As described above, in this embodiment, since the brightness conversion is performed on the image data and the mapping direction can be determined for each pixel when the saturation conversion is performed, the saturation reduction and the gradation are determined. A good image with reduced collapse can be stably obtained.

  FIG. 16 is a block diagram of a hardware configuration of the image processing apparatus according to the first embodiment. As shown in the figure, this image processing apparatus has a configuration in which a controller 10 and an engine unit (Engine) 60 are connected by a PCI (Peripheral Component Interface) bus. The controller 10 is a controller that controls the entire image processing apparatus and controls drawing, communication, and input from an operation unit (not shown). The engine unit 60 is a printer engine that can be connected to a PCI bus, and is, for example, a monochrome plotter, a one-drum color plotter, a four-drum color plotter, a scanner, or a fax unit. The engine unit 60 includes an image processing part such as error diffusion and gamma conversion in addition to a so-called engine part such as a plotter.

  The controller 10 includes a CPU 11, a north bridge (NB) 13, a system memory (MEM-P) 12, a south bridge (SB) 14, a local memory (MEM-C) 17, and an ASIC (Application Specific Integrated Circuit). 16 and a hard disk drive (HDD) 18, and the north bridge (NB) 13 and the ASIC 16 are connected by an AGP (Accelerated Graphics Port) bus 15. The MEM-P 12 further includes a ROM (Read Only Memory) 12a and a RAM (Random Access Memory) 12b.

  The CPU 11 performs overall control of the image processing apparatus. The CPU 11 includes a chip set including the NB 13, the MEM-P 12, and the SB 14, and is connected to other devices via the chip set.

  The NB 13 is a bridge for connecting the CPU 11 to the MEM-P 12, SB 14, and AGP 15, and includes a memory controller that controls reading and writing to the MEM-P 12, a PCI master, and an AGP target.

  The MEM-P 12 is a system memory used as a memory for storing programs and data, a memory for developing programs and data, a memory for drawing a printer, and the like, and includes a ROM 12a and a RAM 12b. The ROM 12a is a read-only memory used as a program / data storage memory, and the RAM 12b is a writable / readable memory used as a program / data development memory, a printer drawing memory, or the like.

  The SB 14 is a bridge for connecting the NB 13 to a PCI device and peripheral devices. The SB 14 is connected to the NB 13 via a PCI bus, and a network interface (I / F) unit and the like are also connected to the PCI bus.

  The ASIC 16 is an IC (Integrated Circuit) for image processing applications having hardware elements for image processing, and has a role of a bridge for connecting the AGP 15, PCI bus, HDD 18, and MEM-C 17. The ASIC 16 includes a PCI target and an AGP master, an arbiter (ARB) that forms the core of the ASIC 16, a memory controller that controls the MEM-C 17, and a plurality of DMACs (Direct Memory) that rotate image data using hardware logic. (Access Controller) and a PCI unit that performs data transfer between the engine unit 60 via the PCI bus. The ASIC 16 is connected to an FCU (Facsimile Control Unit) 30, a USB (Universal Serial Bus) 40, and an IEEE 1394 (the Institute of Electrical Engineering 50 interface) via a PCI bus. The operation display unit 20 is directly connected to the ASIC 16.

  The MEM-C 17 is a local memory used as a copy image buffer and a code buffer, and an HDD (Hard Disk Drive) 18 is a storage for storing image data, programs, font data, and forms. It is.

  The AGP 15 is a bus interface for a graphics accelerator card proposed for speeding up graphics processing. The AGP 15 speeds up the graphics accelerator card by directly accessing the MEM-P 12 with high throughput. .

  Further effects and modifications can be easily derived by those skilled in the art. The embodiments of the present invention are not limited to the specific embodiments as described above.

DESCRIPTION OF SYMBOLS 101 Image input device 102 Image processing device 103 Image output device 104 Lightness conversion part 105 Image storage part 106 Mapping direction determination part 107 Color gamut conversion part

Japanese Patent Laid-Open No. 04-196675 Japanese Patent Laid-Open No. 2002-027263 Japanese Patent No. 3502496

Claims (10)

An image processing device that converts original image data including pixels outside the color gamut of the image output device into output image data within the color gamut of the image output device,
Based on at least the lightness range that the original image data can represent and the lightness range that the image output device can output, the lightness of the original image data is converted into the lightness region of the image output device, and lightness converted image data is output. Brightness conversion means to
Mapping that determines a mapping direction that is a conversion direction of a pixel that is the lightness-converted image data and is a pixel outside the color gamut of the image output device, based on at least the lightness-converted image data and a color gamut that can be output by the image output device Direction determining means;
Image processing comprising at least color gamut conversion means for converting the lightness-converted image data into image data within the color gamut of the image output device based on the mapping direction determined by the mapping direction determination means. apparatus. The mapping direction determining means includes
Color distribution centroid detection means for detecting the centroid of pixels outside the color gamut of the image output device of the lightness conversion image data for each hue;
A color difference minimum direction determining means for determining a direction in which the color difference is minimum when mapping the center of gravity of the detected out-of-gamut pixels within the color gamut of the image output device;
Mapping direction generation means for generating a mapping direction of at least lightness / color difference / saturation priority based on the determined direction of minimum color difference;
Color distribution determination means for determining a color distribution of pixels outside the color gamut of the image output device of the lightness conversion image data for each hue;
The image processing apparatus according to claim 1, further comprising: a mapping direction selection unit that selects the generated mapping direction of at least brightness / color difference / saturation priority based on the determined color distribution. The color distribution determination means determines whether or not the directionality of the color distribution of the out-of-gamut pixels of the image output device of the lightness-converted image data is small;
The mapping direction selection unit selects the generated color difference priority mapping direction as the hue mapping direction when it is determined that the directionality of the color distribution of the out-of-gamut pixels is small. The image processing apparatus described. The color distribution determination means determines whether or not pixels outside the color gamut of the image output device of the lightness-converted image data are distributed on the outermost low brightness side of the color gamut that can be represented by the image data,
The mapping direction selection unit selects the generated lightness priority mapping direction as the hue mapping direction when it is determined that the mapping direction selection unit is attached to the low lightness side and is distributed. The image processing apparatus according to 3. The color distribution determining means determines whether or not pixels outside the color gamut of the image output device of the lightness-converted image data are distributed on the outermost high brightness side of the color gamut that can be represented by the image data,
The mapping direction selection unit selects the generated saturation priority mapping direction as the hue mapping direction when the high lightness sticking determination unit determines that the high lightness sticking is determined to be distributed on the high lightness side. The image processing apparatus according to any one of claims 2 to 4, wherein The color distribution determining means determines, for each hue, an occupation area ratio of pixels outside the color gamut of the image output device of the brightness converted image data,
The mapping direction selection unit selects the generated saturation priority mapping direction as the hue mapping direction when the occupied area rate unit determines that the occupied area rate is small. The image processing apparatus according to any one of? The color distribution determining means determines whether the main force of the out-of-gamut pixels of the image output device of the lightness-converted image data is distributed on the higher saturation side than the highest saturation of the printer gamut;
The mapping direction selection means selects the generated lightness-priority mapping direction as the hue mapping direction when the high saturation side distribution determination means determines that the distribution is on the higher saturation side than the highest saturation. The image processing apparatus according to any one of claims 2 to 6. An image processing method for converting original image data including pixels outside the color gamut of the image output device into output image data within the color gamut of the image output device,
Based on at least the lightness range that can be expressed by the original image data and the lightness range that can be output by the image output device, the lightness of the original image data is converted into the lightness range of the image output device, and lightness converted image data is output. A brightness conversion step to
A mapping direction determining step for determining a mapping direction of pixels outside the color gamut of the image output device of the lightness converted image data based on at least the lightness converted image data and a color gamut that can be output by the image output device;
A color gamut conversion step of converting the lightness-converted image data into image data within the color gamut of the image output device based on the mapping direction determined in the mapping direction determination step. Method.   An image processing program causing a computer to execute the image processing method according to claim 8.   A computer-readable recording medium storing the program according to claim 9.

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