JP4401853B2 - Image processing apparatus and method - Google Patents

Description

The present invention relates to image processing for calculating color conversion parameters for an image capturing apparatus that converts image data of an image capturing apparatus such as a digital camera into data in an optimized color space corresponding to output data of the image capturing apparatus.

  An imaging apparatus such as a digital camera converts the output signal of an image sensor such as a CCD into a desired color signal, and performs color conversion processing to realize a target color. A typical color conversion data used for this color conversion process is a color profile. A color profile is composed of data indicating device characteristics such as gradation characteristics and color characteristics, and colors between image capturing devices such as digital cameras, image display devices such as displays and projectors, and image output devices such as color printers. Used for management (color management).

  For creating a color profile, a predetermined color chart (IT8, Macbeth chart, etc.) is photographed with a digital camera for which a profile is to be created, for example, and the photographed signal value is converted into a color space signal using a color conversion parameter. Then, by comparing the colorimetric value obtained by measuring the color chart in advance with the color space signal obtained from the photographing signal value, a color conversion parameter that minimizes the color difference between the two signals is calculated, and the color conversion parameter Use to create a digital camera profile. Of course, the method of creating the profile is not limited to the digital camera, and the same applies to an image input device such as a color scanner or an image input unit of a color copying machine.

  Imaging devices such as digital cameras have expanded the range and dynamic range of color areas that can be imaged and processed by increasing the sensitivity and noise of image sensors and increasing the number of bits in signal processing. On the other hand, conventionally used color charts are composed of colors with relatively low saturation. For this reason, as a profile creation chart for an imaging apparatus with an expanded color gamut and dynamic range, the color reproduction range of the constituent color charts and the interval between the color values of the constituent color charts are insufficient. The color chart has a problem that it is not possible to create a profile that realizes a high color gamut, a high dynamic range, and a high accuracy.

  As techniques for solving such problems of color charts, there are techniques disclosed in JP-A-11-355586 and JP-A-2002-77654.

  The technique disclosed in Japanese Patent Application Laid-Open No. 11-355586 discloses color values of color charts of a color target in order to obtain accurate color conversion characteristics for an object such as a cloud including a color having high brightness, In addition to deriving the color conversion characteristics from the signal value obtained by photographing it, it also obtains the photographed gray scale signal value and gray scale color value from the white color chart included in the color target. Predict signal values and color values of light colors. Then, the predicted signal value and color value are added to the signal value and color value of each photographed color chart to obtain color conversion characteristics. However, the predicted color is only a prediction, and the reproduction accuracy is not sufficient.

  On the other hand, the technology disclosed in Japanese Patent Laid-Open No. 2002-77654 is defined by a color perception model that does not depend on the viewing environment instead, because IT8 of the color chart does not have complete equality with respect to the perceptual metric amount. A color chart having a uniform color arrangement on the color space is used. However, it is not always possible to create a highly accurate profile even with an even color arrangement.

Japanese Patent Laid-Open No. 11-355586 JP 2002-77654 JP

An object of the present invention is to enable generation of color conversion parameters for an image pickup apparatus that reproduces shooting data of the image pickup apparatus with high color gamut, high dynamic range, and high accuracy.

  The present invention has the following configuration as one means for achieving the above object.

The image processing according to the present invention is performed when calculating color conversion parameters for the image pickup device that converts the shooting data of the image pickup device into data of an optimized color space corresponding to the output data of the image pickup device. The data of the optimized color space of the image capturing device is set according to the user's instruction, and the color chart colorimetric data and the color chart photographed by the image capturing device are set according to the user's instruction. Add the imaging data to the data of the color chart, colorimetric data and the imaging data of a color chart color chart containing the added color chart, as well as the imaging data by using the data of the optimum color space, corresponding Calculating the color conversion parameter to be converted into the data of the optimized color space corresponding to the colorimetric data of the color chart to be calculated, and the color gamut indicated by the data of the optimized color space It was and displaying the chromaticity diagram of the chromaticity of the color chart of the color chart, including a color chart.

According to the present invention, the high color gamut of the picture imaging apparatus, a high dynamic range, reproduced with high accuracy, generation of the color conversion parameters for imaging apparatus capable ing.

  Hereinafter, an image processing apparatus according to an embodiment of the present invention will be described in detail with reference to the drawings.

[Overview]
Below, in order to create color profiles for image input devices such as digital cameras, color scanners, and film scanners with high accuracy, it contributes to the reproduction of high color gamut, high dynamic range, and high accuracy from among the additional color chart candidates. A description will be given of image processing for selecting a color chart to be created, adding it as a color chart for a color chart for profile creation, and creating a profile easily while checking accuracy.

  With this image processing, when creating a color profile for an image input device, the user refers to the user interface, sets the basic color chart used to create the profile, sets the target color space for the profile, It is possible to set the measurement data of the color chart, and set the shooting or reading data obtained by shooting or reading the color chart of the basic color chart by the image input device to be profiled. In addition, the user refers to the user interface, selects a color chart that contributes to high color gamut, high dynamic range, and high precision reproduction from the additional color chart candidates, and adds it as a color chart for the basic color chart. The profile can be easily created while checking the accuracy.

[Constitution]
FIG. 1 is a block diagram illustrating a configuration example of the image processing apparatus 1 according to the embodiment.

  The image processing apparatus 1 is connected to a colorimeter 2 that measures a color chart for profile creation and an image input apparatus 3 that is a profile creation target. FIG. 1 shows, as an example, a digital camera as a profile creation target device and photographing data obtained by photographing a color chart of a color chart with the digital camera. In the case of a scanner, read data obtained by reading a color chart of a color chart with a scanner may be used instead of shooting data.

The image processing apparatus 1 is a computer, measurement devices, digital cameras and color other devices interface for exchanging data and commands, such as a scanner (I / F) 4, measuring and names of the color chart for creating profiles basic chart data storage unit 5, optimized color space data storage unit 6 for storing data such as names and definitions of the target color space of the output signal values of the digital camera 3 for storing data such as color values, the measurement unit 2 measurement data storage unit 7 for storing the colorimetric data of the profile used, imaging data storage unit 8 for storing the imaging data of the profile using the digital camera 3, optimizing converts the output signal value of the digital camera 3 in the target color space Optimization processing unit 9 to add, candidate color data that stores the names, colorimetric data, shooting data, etc. of candidate colors that may be added for profile creation Data storage unit 10, user interface (UI) unit 11 that provides a user interface for the user to perform processing operations such as selecting additional colors and creating profiles, profiles that create profiles using the calculated color conversion parameters creation unit 12, the color coordinate conversion unit 13 performs color coordinate conversion inside the image processing apparatus 1, the color difference calculating unit 14 for calculating a color difference, the data buffer 15 for temporarily storing image data and color measurement data for the image data processing Etc.

  The candidate colors stored in the additional candidate color data storage unit 10 are set in advance with a color that may be added when a profile is created, and an additional color chart composed of color charts of the colors is created. Then, corresponding to the name (or identification number) of the color chart of the additional color chart, its colorimetric data and its photographing data are created and stored in advance in the additional candidate color data storage unit together with the color chart data. Keep it.

  The various data storage units described above are assigned to a predetermined area such as a hard disk, and a program for realizing processing of the image processing apparatus 1 described later is also stored in the predetermined area such as the hard disk. The data buffer 15 uses a memory such as a RAM. Furthermore, the UI unit 11 displays a user interface (to be described later) on a monitor (not shown), and based on the user interface, the user operates an input device (not shown) such as a keyboard or a mouse on the image processing apparatus 1. Enter instructions and data.

[processing]
2 and FIG. 3 are flowcharts for explaining image processing executed by the image processing apparatus 1. FIG. 4 is a diagram showing an example of a user interface provided by the image processing apparatus 1. Hereinafter, with reference to FIG. 2 to FIG. 4, details of processing such as additional color selection and profile creation by the image processing apparatus 1 will be described.

  First, the image processing apparatus 1 displays the user interface shown in FIG. 4, and reads the basic chart data selected by the user from the basic chart menu 301 from the basic chart data storage unit 5 to the data buffer 15 (S201). Data of color space (hereinafter referred to as “optimized color space data”) for optimization conversion of the output signal value of the digital camera 3 selected by the optimized color space menu 302 from the optimized color space data storage unit 6 Read out to the data buffer 15 (S202), read the color measurement data of the profile creation chart using the measuring instrument 2 selected by the user from the measurement data menu 303 from the measurement data storage unit 7 to the data buffer 15 (S203), Shoots the shooting data of the profile creation chart using the digital camera 3 selected by the shooting data menu 304 Reading out the data buffer 15 from over data storage unit 8 (S204).

  The data selected by the user using the basic chart menu 301, the measurement data menu 303, and the shooting data menu 304 is the same color chart chart data, the color measurement data obtained by measuring the color chart with the colorimeter 2, Also, image data obtained by photographing or inputting the color chart with a device such as the digital camera 3. Therefore, the data of each color chart included in each data can be associated one-to-one with the color chart number, name, or position on the image.

Then, when the user presses the optimization button 308, performed, the optimization process so that the color difference is minimum between the colorimetric data captured data using optimized color space data, the colorimetric data and the imaging data, the The processing result is displayed on the optimum parameter display unit 305 and the color difference display unit 306 (S205). Subsequently, it is determined whether or not the user has instructed detailed display (S206). When the user presses the detail button 307, the optimization result is displayed in detail (S207).

  Figure 5 shows an example of a window that displays the details of the optimization results. The colorimetric values X, Y, and Z for the color chart names that make up the selected basic chart, and the color difference after optimization The values are displayed individually. When the user presses the button 402, this window is closed.

  Next, it is determined whether or not the user has instructed to add a color to the basic chart (S208), and when the user presses the color addition button 310, the user interface for color addition shown in FIG. 6 is displayed. Display (S209) and allow the user to select a color to be added for profile creation (S210).

  The addition candidate color list 501 of the color addition window displays a list of color candidate names and colorimetric data xy of the addition candidates stored in the addition candidate color data storage unit 10 (note that the shooting data is also an additional candidate color data storage unit) 10 but not shown in this example). In the additional color list 502, color charts selected by the user from the additional candidate color list 501 and instructed to be added are displayed in a list.

  The user operates the add / delete button 503 to instruct the addition of the color chart selected from the addition candidate color list 501 or the deletion of the color chart selected from the additional color list 502. That is, when the add button is pressed, the selected color chart in the additional candidate color list 501 moves to the additional color list 502, and when the delete button is pressed, the selected color chart in the additional color list 502 is added to the additional candidate color window 501. Move to (return).

  The basic color list 504 displays the names and colorimetric values of the color charts constituting the basic chart, that is, the current optimization processing target chart. The color distribution display 505 is an xy chromaticity diagram plotted based on the colorimetric values of the color chart. The color distribution display 505 includes a color gamut display 506 of the color space to be optimized, a color chart data plot 507 of the basic chart indicated by a cross, and a color chart data plot 508 additionally indicated by a black mark. Is displayed.

  The user selects a color to be added to the current optimization processing target chart displayed in the basic color list 504 from the additional candidate color list 501 while referring to the xy chromaticity diagram of the color distribution display 505. The selection result can be confirmed by the additional color list 502 and the color distribution display 505. The color distribution display 505 allows the user to visually recognize the position of the added color chart on the xy chromaticity diagram and the relationship between the distribution of the added color chart and the color chart of the basic chart. An appropriate color chart can be easily and appropriately selected.

When it is detected that the user has pressed the save button 509 (S211), the name and colorimetric value of the color chart instructed to be added are added to the basic chart stored in the data buffer 15 (S212). If it is detected that the user has pressed the button 510 (S213), it is determined that the color addition is completed, the color addition window is closed, and the basic chart data stored in the data buffer 15 is given a new name and the basic chart data. Save the storage unit 5, the added color chart data (name, colorimetric data, photographic data) was added to the colorimetric data and the imaging data stored in the data buffer 15 (S214), then step S205 the process Return to.

  Then, the optimization process, the color difference display and detailed display, and the color addition determination in steps S205 to S208 described above are repeated until the user determines that the color addition is unnecessary and presses the result storage button 309.

  When the user presses the result save button 309 (S215), the optimization process result displayed on the optimum parameter display unit 305 and the color difference display unit 306 and the chart data used for the optimization process are saved in the basic chart data storage unit 5. (S216). Further, when the user presses the profile creation button 311 (S217), profile data (ICC format) is created using the conversion parameter displayed on the optimum parameter display unit 305 (S218), and the process is terminated.

  If the optimization is not successful or the created profile is not as expected, the user can cancel part or all of the processing in the middle of the processing by pressing the cancel button 313. For example, when the cancel button 313 is pressed in step S215, the process of step S216 is canceled, and when the cancel button 313 is pressed in step S217, the process of step S218 is canceled, and the process ends.

[Optimization processing]
FIG. 7 is a flowchart for explaining the details of the optimization processing (S205) executed by the optimization processing unit 9.

First, the R′G′B ′ value is calculated by correcting the gradation of the shooting data (for example, RGB value) (S801). Note that the gradation correction processing may be gradation conversion using a lookup table (LUT). Next, a predetermined color conversion matrix coefficient is set in equation (1) (S802), and the R'G'B 'value after gradation correction is color-converted using the optimization matrix calculation equation (1). The R "G" B "value is calculated (S803).
┌ ┐ ┌ ┐┌ ┐
│R''│ │a11 a12 a13││R'│
│G "│ = │a21 a22 a23││G'│… (1)
│B''│ │a31 a32 a33││B'│
└ ┘ └ ┘└ ┘

Next, the R "G" B "value is converted into tristimulus values XYZ by equation (2) (S804), and the definition coefficient of the color space to be optimized is used as the matrix coefficient in equation (2). The expression is stored in advance in the optimized color space data storage unit 6 for each color space to be optimized.
┌ ┐ ┌ ┐┌ ┐
│XP│ │b11 b12 b13││ R '' │
│YP│ = │b21 b22 b23││ G " │… (2)
│ZP│ │b31 b32 b33││ B '' │
└ ┘ └ ┘└ ┘

Next, XP, YP, and ZP values are converted into Lab values in a uniform color space by substituting X, Y, and Z in Equation (3) (S805). The Xn, Yn, and Zn values of Equation (3) are stored in advance in the optimized color space data storage unit 6 for each color space to be optimized.
When Y / Yn> 0.008856 L * = 116 (Y / Yn) ¹ /3-16
When Y / Yn ≦ 0.008856 L * = 903.29 ・ Y / Yn
a * = 500 {f (X / Xn)-f (Y / Yn)}… (3)
b * = 200 {f (Y / Yn)-f (Z / Zn)}
Here, when X / Xn> 0.008856, f (X / Xn) = (X / Xn) ^1/3
When X / Xn≤0.008856 f (X / Xn) = 7.78 ・ X / Xn + 16/116
When Y / Yn> 0.008856 f (Y / Yn) = (Y / Yn) ^1/3
When Y / Yn ≦ 0.008856 f (Y / Yn) = 7.78 ・ Y / Yn + 16/116
When Z / Zn> 0.008856, f (Z / Zn) = (Z / Zn) ^1/3
When Z / Zn ≦ 0.008856, f (Z / Zn) = 7.78 ・ Z / Zn + 16/116

Then converted XM calorimetric data, YM, the ZM value X of the formula (3), Y, into Lab values by substituting the Z (S806). The Xn, Yn, and Zn values are the same as those in step S805. Subsequently, the color difference between the Lab value (LP, ap, bp) calculated in Step S805 and the Lab value (LM, am, bm) calculated in Step S806 is obtained by the calculation of Equation (4) by the color difference calculation unit 14. Then, the color conversion matrix coefficient and color difference set in step S802 are stored as a set in the data buffer 15 (S807).
ΔE * ab = √ {(ΔL *) ² + (Δa *) ² + (Δb *) ² } … (4)
Where ΔL * = LP-LM
Δa * = ap-am
Δb * = bp-bm

Next, it is determined whether or not the calculated color difference is equal to or smaller than a predetermined value (S808). If not smaller than the predetermined value, the process returns to step S802, and the color conversion matrix coefficient is changed so that the color difference becomes smaller. If the color difference is equal to or smaller than the predetermined value, it is determined whether or not the number of loops in steps S802 to S808 has reached a preset number (S809). If not, the process returns to step S802. The color conversion matrix coefficient is changed. Further, when the loop reaches the specified number of times, as a result of the optimization process, among the color conversion matrix coefficients for the specified number of times stored in the data buffer 15, the color conversion matrix coefficient with the smallest color difference is selected as the optimum parameter display unit 305. The color difference is displayed on the color difference display unit 306 (S810).

  As described above, according to the first embodiment, when creating a high-accuracy color profile of the image input device, the user selects a color chart from among color chart candidates with reference to the user interface shown in FIG. Add the color chart data to the chart data for profile creation, and visually add the position of the added color chart on the chromaticity diagram, the distribution of the other color charts on the chromaticity diagram, and the color gamut of the color space. It is possible to easily select and add color charts that contribute to high color gamut, high dynamic range, and high precision reproduction. Of course, if the user determines that the color chart to be selected and added does not contribute to high color gamut, high dynamic range, and high-precision reproduction, the user interface shown in FIG. 6 makes it easy to add the color chart. You can also cancel.

  The image processing apparatus according to the second embodiment of the present invention will be described below. Note that in the present embodiment, the same reference numerals are given to substantially the same configurations as those in the first embodiment, and detailed description thereof will be omitted.

  The second embodiment differs from the first embodiment in the detailed display of the optimization result in step S207 and the configuration of the user interface for color addition displayed in step S209.

[Detail View]
FIG. 8 is a diagram showing an example of a window that displays the details of the optimization result of the second embodiment. Each of the colorimetric values L, C, and h for the color chart name constituting the selected basic chart, the optimum The color difference values after the conversion processing are individually displayed.

[User interface for color addition]
FIG. 9 is a diagram illustrating an example of a user interface for adding colors according to the second embodiment. The display of color values in the additional candidate color list 501, the additional color list 502, and the basic color list 504 is all Lab.

  The color distribution display 705 includes a Lab space two-dimensional display diagram (ab plan view) and an LCh space two-dimensional display diagram (LC plan view) plotted based on the colorimetric values of the color chart. The color distribution display 705 includes a color gamut display 706 of the color space to be optimized, a color chart data plot 707 of the basic chart indicated by a cross, and a color chart data plot 708 additionally indicated by a black mark. Is displayed.

  The user selects a color to be added to the current optimization target chart displayed in the basic color list 504 from the additional candidate color list 501 while referring to the two-dimensional display diagram of the color distribution display 705. The selection result can be confirmed by the additional color list 502 and the color distribution display 705. Using the ab plan view and LC plan view of Example 2, the user can more intuitively understand the color distribution (color difference distribution, luminance and saturation distribution) of the color chart than the xy chromaticity diagram of Example 1. The color chart to be added can be selected more appropriately.

[Modification]
Optimization Process The optimization process in step S205 is not limited to the process shown in FIG. For example, as long as the optimization is such that the color difference between the LP, ap, and bp values calculated in step S805 and the LM, am, and bm values calculated in step S806 is small, the method is not limited. In addition, as shown in Equation (1), a 3 × 3 matrix has been described as an example of a color conversion matrix, but it is not limited to a 3 × 3 conversion matrix, and 3 × 9 or 3 × 20 including a nonlinear term is included. A conversion matrix may be used. Furthermore, a configuration may be used in which color conversion is performed using an LUT that uses lattice point data measured in advance.

● Selection of additional color An example of using the user interface shown in FIG. 5 or FIG. 9 has been described for selecting an additional color in step S210, but the present invention is not limited to this. That is, the display of each list is not limited to the xy value, the Lab value, and the LCh value, and may be, for example, an RGB value of shooting data when a color chart is shot.

  In addition, although it has been described that the user selects a color to be added from the color chart displayed in the additional candidate color list 501, the user can specify a color value indicating xy value, XYZ value, RGB value, or hue / lightness / saturation. It is also possible to directly enter a numerical value such as and select a color chart having a value closest to the input value as a color to be added. Of course, a configuration in which a color name is input and a color chart having a color name closest to the color name is selected as a color to be added may be used. In other words, the selection method is not limited as long as the user can select the color desired to be added from the color chart of the additional candidate colors.

  Further, although the color distribution displays 505 and 705 have been described as two-dimensional displays, the display method of the color distribution is not limited, and three-dimensional displays such as XYZ and Lab may be used.

● Profile format The profile format created in step S218 has been described as the ICC format, but any format that is suitable for data exchange with other devices may be used.

● The color difference calculation in color difference calculation step S807 was explained using equation (4), but the space used for calculating the color difference is not limited to Lab space, and the color difference of YCC, Luv, CIECAM97s, CIECAM02, etc. space is calculated May be.

[Other embodiments]
Note that the present invention can be applied to a system including a plurality of devices (for example, a host computer, an interface device, a reader, and a printer), and a device (for example, a copying machine and a facsimile device) including a single device. You may apply to.

  Also, an object of the present invention is to supply a storage medium (or recording medium) on which a program code of software that realizes the functions of the above-described embodiments is recorded to a system or apparatus, and the computer (or CPU or CPU) of the system or apparatus. Needless to say, this can also be achieved by the MPU) reading and executing the program code stored in the storage medium. In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the storage medium storing the program code constitutes the present invention. Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also an operating system (OS) running on the computer based on the instruction of the program code. It goes without saying that a case where the function of the above-described embodiment is realized by performing part or all of the actual processing and the processing is included.

  Furthermore, after the program code read from the storage medium is written into a memory provided in a function expansion card inserted into the computer or a function expansion unit connected to the computer, the function is determined based on the instruction of the program code. Needless to say, the CPU of the expansion card or the function expansion unit performs part or all of the actual processing and the functions of the above-described embodiments are realized by the processing.

  When the present invention is applied to the storage medium, the storage medium stores program codes corresponding to the flowcharts described above.

Block diagram showing a configuration example of the image processing apparatus 1 of the embodiment, A flowchart illustrating image processing executed by the image processing apparatus; A flowchart illustrating image processing executed by the image processing apparatus; The figure which shows an example of the user interface which an image processing apparatus provides, Figure showing an example of a window displaying details of optimization results. The figure which shows an example of the user interface for a color addition, A flowchart for explaining the details of the optimization processing executed by the optimization processing unit; The figure which shows the example of the window which displays the details of the optimization result of execution example 2, FIG. 10 is a diagram illustrating an example of a user interface for adding colors according to the second embodiment.

Claims (5)

An image processing method for calculating color conversion parameters for the image pickup device, which converts image data of the image pickup device into data in an optimized color space corresponding to output data of the image pickup device,
In accordance with a user instruction, set the data of the optimized color space of the imaging device,
In accordance with the user's instruction, color chart colorimetric data and the color chart photographing data photographed by the image capturing device are added to color chart data ,
Corresponding to the colorimetric data of the color chart of the color chart including the added color chart and the colorimetric data of the corresponding color chart, the shooting data using the data of the optimized color space Calculating the color conversion parameter to be converted into the data of the optimized color space;
An image processing method, wherein a color gamut indicated by data in the optimized color space and a chromaticity of a color chart of a color chart including the added color chart are displayed on a chromaticity diagram. An image processing device for calculating color conversion parameters for the image pickup device, which converts image data of the image pickup device into data in an optimized color space corresponding to output data of the image pickup device,
Setting means for setting data of the optimized color space of the image pickup device according to a user instruction;
In accordance with an instruction from the user, an adding means for adding color chart colorimetric data and color chart shooting data shot by the image pickup device to color chart data ;
Corresponding to the colorimetric data of the color chart of the color chart including the added color chart and the colorimetric data of the corresponding color chart, the shooting data using the data of the optimized color space Calculating means for calculating the color conversion parameter to be converted into the data of the optimized color space;
An image processing apparatus comprising: a display unit configured to display a color gamut indicated by data in the optimized color space and a chromaticity of a color chart of a color chart including the added color chart on a chromaticity diagram.   The color chart including the added color chart includes the color chart of the basic color chart and the added color chart, and the display unit includes the chromaticity diagram and the chromaticity of the color chart of the basic color chart. 3. The image processing apparatus according to claim 2, wherein chromaticity of the added color chart is divided and displayed.   The calculation means includes means for setting a color conversion matrix coefficient, means for color-converting the photographic data using the color conversion matrix, and means for calculating a color difference between the color-converted photographic data and the colorimetric data. 4. The color conversion matrix coefficient change, the color conversion, and the calculation of the color difference are repeated so that the color difference is equal to or less than a predetermined value. Image processing device.   5. A program for controlling a computer to function as each unit of the image processing apparatus according to claim 2.

Images