JPH11355586A - Device and method for processing image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device and a method for processing image with which exact color conversion characteristics can be easily provided for image input equipment such as digital still camera or digital video camera. SOLUTION: The image data of a color target photographed on the condition corresponding to the photographic condition of a color image are selected (S301), the signal value of gray scale contained in these image data and the color specification value of gray scale are acquired (S303-S205) and the signal value and color specification value of a color having lightness higher than that of a white color patch contained in the color target are predicted (S306). Then, color conversion characteristics are provided by adding the predicted signal value and color specification value to the signal value and color specification value of each color chart acquired from the selected image data (S307-S310).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image processing apparatus and method, and more particularly to an image processing apparatus and method for performing color matching processing on an input image captured by a digital still camera or digital video camera.

[0002]

2. Description of the Related Art In a multimedia system mainly including a host computer, a color matching system (CMS) for performing color matching processing of image data between an input device and an output device has been actively developed.

[0003] Apple's ColorS, a typical CMS framework
ync (TM) is a color space (Device Depende
(nt Color Space) image signal to a device-independent color space (Device Independent Color Space), and further, image signal in a device-independent color space to an output device-dependent color space. , Common on the system
CMS is realized.

[0004] The conversion characteristics for this conversion process are based on the Inter Color Profile format (Inter Color Profile).
le Format) is stored in data called a profile. The profile is prepared in the host computer for each device, and is automatically or manually selected at the time of conversion, and the color space of the image signal is converted according to the conversion characteristics of the selected profile.

In an image input device represented by a flatbed scanner, a profile can be created by the following method. A color target having a plurality of color patches is scanned or photographed by an image input device for which a profile is to be created, and a signal value of a color space that is obtained in advance and is independent of a device corresponding to the color patches and a color target is obtained. By calculating the relationship between the color charts obtained by scanning or photographing and the signal values of the color space dependent on the image input device, the color space independent of the image input device is calculated from the color space independent of the device. A color conversion characteristic for converting a color signal into a color, that is, a profile is derived.

The above-described method of deriving the color conversion characteristics by scanning or photographing a color target has a great merit for the user because the color target is inexpensive and the operation can be performed easily by the user. .

In the following description, a signal value in a color space that does not depend on a device may be described as a “color value”, and a signal value in a color space that depends on a device may be simply described as a “signal value”.

[0008]

However, the above technique has the following problems.

That is, the above-described method for deriving the color conversion characteristic is based on the premise that a color lighter than the brightest white color of the color target does not exist in the document. Devices that scan paper documents and save or duplicate document images, such as flatbed scanners, were originally designed to read “white paper” as the color with the highest brightness. Therefore, the above assumption is also practical in the color reproduction range of a medium such as paper.

[0010] Clouds and the like included in the scenery may have a higher brightness than the brightest white of the color target. Therefore, image input devices such as a digital still camera and a digital video camera are more suitable than "paper white". Is designed to read a color having a fairly high brightness as a color having the highest luminance.

However, even if a color target is photographed by a digital still camera or a digital video camera, a color signal having a luminance value equal to or higher than a certain value cannot be obtained as a sample. Therefore, even if the color conversion characteristic is derived from the color specification value of the color chart of the color target and the signal value obtained by photographing the color chart, for a cloud-like object including a color having high luminance, It is not possible to obtain accurate color conversion characteristics.

An object of the present invention is to solve the above-mentioned problem, and an image processing apparatus capable of easily obtaining accurate color conversion characteristics for an image input device such as a digital still camera or a digital video camera. And a method thereof. It is another object of the present invention to provide an image processing apparatus and a method for performing a color matching process based on the color conversion characteristics obtained for the image input apparatus.

[0013]

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

[0014] An image processing apparatus according to the present invention comprises a storage means for storing reference image data obtained by photographing a reference image composed of a plurality of color patches, and color data of the color patches in a device-independent color space. Selecting means for selecting reference image data corresponding to a shooting condition of a color image; shooting data of each color chart obtained from the selected reference image data; and color data of the color charts, converting the shooting data into the color data. And an operation means for obtaining a conversion characteristic for conversion into.

Preferably, the photographing data of a color having a higher brightness than a white color chart contained in the reference image is obtained from the photographing data of the gray scale included in the selected reference image data and the color data of the gray scale. And predicting means for predicting color data, wherein the calculating means calculates the conversion characteristic by adding the predicted photographing data and color data to the photographing data and color data of each color chart. .

More preferably, input means for inputting a color image and photographing conditions of the color image, and processing means for performing a color matching process on the input color image based on the conversion characteristics obtained by the arithmetic means are provided. It is characterized by having.

According to the image processing method of the present invention, the reference image data obtained by photographing the reference image composed of a plurality of color patches and the storage means storing the color data of the color patches in a device-independent color space are stored. Selecting the reference image data corresponding to the shooting condition of the color image, obtaining the shooting data of each color chart from the selected reference image data, obtaining the color data of each color chart from the storage unit, and obtaining the obtained shooting data And a conversion characteristic for converting the photographing data into the color data from the color data.

Preferably, grayscale photographing data included in the selected reference image data is obtained, the grayscale color data is obtained from the storage unit, and the grayscale color data is obtained from the white color chart included in the reference image. It is characterized in that photographing data and color data of a color having a high brightness are predicted, and the predicted photographing data and color data are added to the photographing data and color data of each color chart for calculating the conversion characteristic.

Further, reference image data obtained by photographing a plurality of color patches with an image pickup device and reference values of the color patches are input, and extrapolation is performed based on the reference data and the standard values. The color correction data for the imaging device is created based on the result of (1).

[0020]

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

[Configuration] FIG. 1 is a block diagram showing a system configuration of the present embodiment.

The present system uses a camera 11 as an input device.
And a host computer 10 that performs image processing including color matching processing and editing processing on image data, and a monitor 12 and a printer 13 that are output devices. Note that the host computer 10 may be a personal computer that executes software having the functions described below, or dedicated hardware having the same functions.

The camera 11 is an image and video input device such as a digital still camera or a digital video camera, and has various environmental conditions and adjustment states (color of illumination light, white balance, exposure amount, etc. at the time of shooting). It is. Therefore, each shooting has various shooting conditions (input characteristics),
Its input characteristics cannot be specified. Also the camera
11 can handle both moving and still images.

The monitor 12 is composed of a display such as a CRT or a liquid crystal panel, and is an image display device which displays images, displays information necessary for a user to make an input to the system, and confirms the operation of the system. is there. Also a printer
Reference numeral 13 denotes a printing machine, which is an image output device that forms a visible image on a recording medium such as recording paper using a recording material such as ink or toner.

The external storage device 14 includes a storage medium such as a hard disk, a magneto-optical disk or a floppy disk,
And a drive which is a device for reading and writing these recording media. The host computer 10 stores the image data supplied from the camera 11 in the external storage device 14, performs image processing on the stored image data, and further stores the stored unprocessed or processed image data. By supplying the image data to the monitor 12 or the printer 13, an image corresponding to the image data can be displayed and printed.

Further, the photographing conditions supplied from the camera 11 or input by the user can be stored in the external storage device 14 in association with the target image data. Then, the host computer 10 stores the external storage device 14
, The photographing conditions and the like corresponding to the image data can be read together with the image data.

The external storage device 14 also stores profiles required for color matching processing. The host computer 10 reads the profile stored in the external storage device 14 as necessary, and performs a color matching process.

Further, in order to calculate the conversion characteristics based on the color values and the signal values of each color patch of the color target, the color values of each color patch of the color target and an image of the color target are stored in the external storage device 14. Have been.

Normally, the image processing program and the control program for the apparatus according to the present invention are
However, these programs can be stored in the external storage device 14. That is, the host computer 10 can read the program stored in the external storage device 14 and execute the image processing and the control of the device according to the present embodiment in accordance with the user's instruction.

The keyboard 15 and the mouse 16 are operated by the user as needed, and are used to input instructions, data, and the like to the host computer 10.

[Host Computer] FIG. 2 is a block diagram showing a configuration example of the host computer 10. The figure
2, a console 21 including a keyboard 15, a mouse 16, a monitor 12, and the like includes an input / output interface 22 and
It is connected to the CPU 17 via the CPU bus 25. Further, the external storage device 14 includes an external storage device interface 26 and a CPU.
It is connected to the CPU 17 via the bus 25.

The CPU 17 has a system control section 171 for controlling the entire system, an arithmetic processing section 172 for executing various arithmetic operations, and a working memory 173 for storing necessary data at the time of arithmetic operations. The CPU 17 executes the host computer 10 based on a program stored in the ROM 18 or the RAM 19.
Then, the image data stored in the RAM 19 is subjected to image processing such as color matching processing and output to an output device.

The video RAM 23 stores a screen to be displayed on the monitor 12.

[Color Matching Processing] In this system,
The following combinations are available as combinations of input devices and output devices. Note that the combination (4) is a combination for performing a so-called “preview”, and is used for displaying an image output from the printer 13 on the monitor 12 and confirming the image. (1) Camera 11 → Monitor 12 (2) Camera 11 → Printer 13 (3) Monitor 12 → Printer 13 (4) Printer 13 → Monitor 12

When performing the color matching process corresponding to the above combination, the CPU 17 reads the input profile corresponding to the input device and the output profile corresponding to the output device from the external storage device 14. The profile contains
Data indicating a relationship between a device-dependent color space and a device-independent color space is stored. Therefore, in the input profile, the image signal of the color space depending on the input device,
Data for converting into an image signal of a color space independent of the device is stored. On the other hand, the output profile
Data for converting an image signal in a device-independent color space into an image signal in a color space that depends on an output device is stored. Further, the output profile data may include not only color space conversion but also color space compression for compressing input image data into the color reproduction range of the output device.

That is, the CPU 17 first reads out an input profile from the external storage device 14 based on the combination of the input device and the output device, and uses the input profile to generate an image signal depending on the color space of the input device. Into an image signal in a color space that does not depend on

Next, the CPU 17 reads an output profile corresponding to the output device from the external storage device 14 and uses the output profile to convert an image signal in a color space independent of the device into a color space independent of the output device. Convert to image signal.

As described above, the profile used in the color matching processing is data based on the characteristics of the device.

[Method of Deriving Color Conversion Characteristics] Next, a method of deriving the conversion characteristics from the color values (standard values) of each color chart of the color target and the signal values obtained by photographing the color target will be described. I do. Note that the color values of the color patches stored in the external storage device 14 in advance are expressed in the XYZ color system and the signal values are expressed in the RGB color system, and the signal values are converted into the color values by the equation (1). be able to.

Determining the optimum color conversion characteristic is performed by optimizing the matrix M in equation (1), that is, by substituting the signal value of each color chart obtained by photographing a color target into equation (1). A matrix M for minimizing the error between the color values of each color chart and the color values of each color chart stored in the external storage device 14.
Is to determine the elements of In other words, such a matrix M represents a color conversion characteristic that is a relationship between a signal value and a color specification value.

Since equation (1) can handle colors not present in the color target, it is also possible to convert a color having a higher lightness as a color specification value than the brightest white color of the color target. However, digital still cameras use a gray scale (achromatic group) with a color target color value Y.
Are the constants αr, αg, αb, β
Using r, βg, βb, γr, γg, and γb, it is designed so that the relationship represented by the equation (2) is obtained. R = αr ・ {Y / βr} ^ γr G = αg ・ {Y / βg} ^ γg… (2) B = αb ・ {Y / βb} ^ γb where a ^ b represents a raised to the power of b

On the other hand, since the gray scale is a set of achromatic colors, the color values X and Z with respect to the color value Y have a relationship represented by the equation (3) using constants αx and αz. X = αx ・ YZ = αz ・ Y… (3)

Therefore, if the constant groups of the equations (2) and (3) are calculated from the gray scale color values of the color target and the signal values obtained by photographing the gray scale, the gray scale color With regard to, it is possible to obtain a conversion coefficient with higher accuracy than using equation (1). Further, by using the obtained conversion coefficient, it is possible to predict, from the gray scale of the color target, a white color value having a higher brightness as a color value than the white color included in the color target. Then, by predicting the signal value that would be obtained by photographing the predicted white by extrapolation or the like, and including the predicted white color value and the signal value in the calculation process of the color correction coefficient, In addition, it is possible to reduce the error of the color correction coefficient for such a high brightness color. Therefore, it is possible to obtain a profile with more accurate color conversion characteristics for high brightness colors that are not included in the color target, especially for white, and apply that profile to the CMS to obtain digital still cameras and digital video cameras. High-precision color matching can be performed on images and videos shot by the image input device.

[Processing Procedure] FIG. 3 is a flowchart showing an example of a color conversion characteristic deriving process according to the present embodiment.
This is the process executed by U17.

First, in step S301, image data of a color target photographed under the same photographing condition as that of the subject in the image data to be color-matched or regarded as the same as the photographing condition is stored in the external storage device 14.
Read from In step S302, a signal value of each color patch is extracted from the read image data of the color target, and in step S303, a grayscale signal value is extracted from the extracted signal value of each color patch.

Next, in step S304, the color values of the respective color patches of the color target are read from the external storage device 14. In step S305, the gray scale color values are extracted from the read color values of the respective color patches. I do.

Next, in step S306, based on the extracted grayscale signal value and color specification value, a color specification value of a color having a higher brightness than a white color chart included in the color target and a color specification value of the color having a higher brightness are obtained. Estimate the signal value that would be obtained when capturing a color. Then, in step S307, the predicted signal value is added to the extracted signal value of each color chart, and in step S308, the predicted color value is added to the read color chart value of each color chart.

Next, in step S309, the relationship between the signal value and the color value is calculated from the signal value and the color value of each color chart, and in step S310, the relationship between the obtained color value and the signal value is calculated. Create a profile from The obtained profile is stored in the external storage device 14 or the RAM 19.

The designation of the photographing conditions or the selection of the image data of the color target in step S301 is performed by the user or added to data indicating the photographing conditions of the profile to be created, for example, to the image data to be subjected to the color matching processing. This is selected based on the data indicating the shooting conditions. For image data of a color target in each shooting condition, or for image data of a color target shot under typical shooting conditions of a group by grouping almost the same shooting conditions,
By performing the processing shown in FIG. 3, profiles under these shooting conditions can be created in advance and stored in the external storage device 14.

FIG. 4 is a flowchart showing an example of the procedure of the color matching process in this embodiment, which is a process executed by the CPU 17.

First, in step S321, image data to be subjected to color matching processing is input from, for example, the camera 11 to the host computer 10, and in step S322, the external storage device 14
The input profile is selected from the profiles stored in. This selection is made by the user based on the shooting conditions of the input image data, or based on data indicating the shooting conditions added to the input image data.

Next, in step S323, from the profiles stored in the external storage device 14, the output device (for example, the monitor 12 or the printer 13) desired by the user as the output destination of the image data matches the setting state thereof. The profile is selected as the output profile.

Subsequently, in step S324, color matching processing based on the selected input profile and output profile is performed on the input image data. In step S325, the image data on which the color matching processing has been performed is output to its output destination. Sent to an output device.

As described above, according to this embodiment, an accurate profile is created for an image input device such as a digital still camera or a digital video camera by using the same equipment and operation as in the method of creating a profile in a flatbed scanner. be able to. Therefore, it is possible to perform a high-precision color conversion process on an image and a video, such as a landscape, photographed by the image input device, and obtain a good color matching result.

Although the process of deriving a color conversion characteristic for creating a profile and the process of color matching have been described separately with reference to FIGS. 3 and 4, it goes without saying that these processes can be executed as a series of processes.

In the above-described embodiment, Colo
Assuming that a CMS framework such as rSync (TM) is used,
Although the example in which the relationship between the color specification value and the signal value, that is, the color conversion characteristic is profiled has been described, a case where the color conversion processing is performed without performing the profile conversion is also included in the present invention. In other words, based on the color conversion characteristics obtained by the processing shown in FIG. 3, even if the color matching operation is performed on each pixel of the image data,
The same effects as in the above embodiment can be obtained.

Further, the profile obtained by the procedure shown in FIG. 3 is used for the image data photographed in the normal photographing mode, and in the case of the image data photographed in the macro photographing mode, the profile shown in FIG. Whether or not to perform a prediction process for a color having a higher lightness than the white color chart of the included color target may be made selectable according to a user setting. When the prediction process is not performed, the processes of steps S303 and S305 to S308 in FIG. 3 may be passed through.

[0058]

[Other Embodiments] Even if the present invention is applied to a system including a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.), an apparatus (for example, a copying machine) Machine, facsimile machine, etc.).

Another object of the present invention is to provide a storage medium storing a program code of software for realizing the functions of the above-described embodiments to a system or an apparatus, and to provide a computer (or a CPU or MPU) of the system or the apparatus.
Needless to say, this can also be achieved by the PU) reading and executing the program code stored in the storage medium. In this case, the program code itself read from the storage medium implements the functions of the above-described embodiment, and the storage medium storing the program code constitutes the present invention. When the computer executes the readout program code, not only the functions of the above-described embodiments are realized, but also the OS running on the computer based on the instructions of the program code.
It goes without saying that an (operating system) performs a part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.

Further, 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, based on the instruction of the program code, It goes without saying that the CPU included in the function expansion card or the function expansion unit performs part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.

[0061]

As described above, according to the present invention,
It is possible to provide an image processing apparatus and method capable of easily obtaining accurate color conversion characteristics for an image input device such as a digital still camera or a digital video camera. Further, it is possible to provide an image processing apparatus and method for performing a color matching process based on the color conversion characteristics obtained for the image input apparatus.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a system configuration of an embodiment;

FIG. 2 is a block diagram showing a configuration example of a host computer;

FIG. 3 is a flowchart illustrating an example of a color conversion characteristic deriving process according to the embodiment;

FIG. 4 is a flowchart illustrating an example of a procedure of a color matching process according to the embodiment.

Claims (14)

[Claims] 1. A storage means for storing reference image data obtained by shooting a reference image composed of a plurality of color patches, and color data of the color patches in a device-independent color space. Selecting means for selecting the reference image data to be converted; photographing data of each color chart obtained from the selected reference image data; and conversion characteristics for converting the photographing data into the color data from the color data of the color charts. An image processing apparatus comprising: an arithmetic unit that obtains the following. 2. A method for photographing a color having a higher brightness than a white color chart included in the reference image, based on grayscale photographing data included in the selected reference image data and the grayscale color data. A predicting unit for predicting data and color data, wherein the calculating unit calculates the conversion characteristic by adding the predicted photographing data and color data to the photographing data and color data of each color chart. 2. The image processing device according to claim 1, wherein: 3. An input unit for inputting a color image and a photographing condition of the color image, and a processing unit for performing a color matching process on the input color image based on the conversion characteristics obtained by the calculation unit. 3. The image processing device according to claim 1, wherein: 4. The image processing apparatus according to claim 1, wherein the conversion characteristic obtained by the calculation unit is stored in the storage unit. 5. An input unit for inputting a color image and a shooting condition of the color image; an obtaining unit for obtaining a conversion characteristic according to the shooting condition from a plurality of conversion characteristics stored in the storage unit; 3. The image processing apparatus according to claim 1, further comprising a processing unit configured to perform a color matching process on the input color image based on the acquired conversion characteristics. 6. The acquisition unit further acquires a conversion characteristic corresponding to a device that outputs the input color image, and the processing unit acquires a conversion characteristic corresponding to the device and the conversion characteristic acquired according to the photographing condition. 6. The image processing apparatus according to claim 5, wherein the color matching processing is performed based on a conversion characteristic to be performed. 7. The conversion characteristic according to claim 1, wherein the conversion characteristic is managed as data having a structure conforming to or conforming to an Inter Color Profile Format. Image processing device. 8. A storage unit storing reference image data obtained by capturing a reference image including a plurality of color patches and color data of the color patches in a device-independent color space. Selecting the reference image data to be acquired, acquiring the photographing data of each color chart from the selected reference image data, acquiring the color data of each color chart from the storage unit, and acquiring the photographing data from the acquired photographing data and color data. An image processing method comprising calculating conversion characteristics for converting data into the color data. 9. Acquiring grayscale photographing data included in the selected reference image data, acquiring the grayscale color data from the storage unit, and acquiring the grayscale color data from the white color chart included in the reference image. The photographing data and color data of a color having high brightness are also predicted, and the predicted photographing data and color data are added to the photographing data and color data of each color chart for calculating the conversion characteristic. Item 7. The image processing method according to Item 7. 10. A recording medium on which a program code for image processing is recorded, wherein reference image data obtained by photographing a reference image composed of a plurality of color patches, and color data of the color patches in a device-independent color space. A code of a step of selecting reference image data corresponding to a shooting condition of a color image from a storage unit in which is stored a code of a step of obtaining shooting data of each color chart from the selected reference image data; and And code for a step of calculating a conversion characteristic for converting the photographing data into the color data from the acquired photographing data and color data. Characteristic recording medium. 11. A code for acquiring grayscale photographing data included in the selected reference image data, a code for acquiring the grayscale color data from the storage unit, and the reference image. A code of a step of predicting photographing data and color data of a color having a higher brightness than the white color patch included in the photographing; and a photographing data predicted for the photographing data and color data of each color patch for calculating the conversion characteristic. 11. The recording medium according to claim 10, further comprising a code for adding data and color data. 12. A recording medium on which data of color conversion characteristics for performing color matching processing on image data is recorded,
The color conversion characteristics are obtained by the following image processing. From a storage unit storing reference image data obtained by photographing a reference image composed of a plurality of color patches and color data of the color patches in a device-independent color space. Selecting the reference image data corresponding to the shooting condition of the color image, obtaining the shooting data of each color chart from the selected reference image data, obtaining the color data of each color chart from the storage means, A recording medium characterized by being calculated from data and color data. 13. The image processing further obtains grayscale photographing data included in the selected reference image data, obtains the grayscale color data from the storage unit, and includes the grayscale color data in the reference image. Predict photographing data and color data of a color having a higher lightness than a white color patch, and add the predicted photographing data and color data to the photographing data and color data of each color patch for calculating the conversion characteristic. 13. The recording medium according to claim 12, wherein: 14. Inputting reference image data obtained by photographing a plurality of color patches with an imaging device and reference values of the color patches, performing extrapolation based on the reference data and the standard values, An image processing method for generating color correction data for the imaging device based on the result of (1).