JP2008271096A - Method and device for correcting gray balance of image data, and storage medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a correcting method in which color charts for correcting gray balance are easily set and the gray balance of each gradation from a bright part to a dark part is precisely corrected while keeping brightness. <P>SOLUTION: The gradations from the bright part to the dark part are extracted from image data which is obtained by photographing objects (the color charts) to be reference of the gray balance, such as a gray color chart. The gray balance correction coefficient of each gradation is calculated based on the extracted gradations. An image is converted in accordance with the calculated gray balance correction coefficients. A user interface with an operation lug for a user input arranged therein is positioned in each one of a plurality of brightness regions. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention makes it easy to detect the gray balance of each gradation when operating the operation screen of a personal computer to correct the gray balance of image data taken with a digital camera using a color chart such as a gray chart. The present invention relates to a gray balance correction method and a correction apparatus in which color charts can be easily set.

For example, photos used in product catalogs for clothing, etc. must be accurately recorded in color so that the buyer who viewed the catalog does not have a complaint due to the color difference between the catalog and the product actually purchased. is required.
However, the color of the subject is often influenced by photographing equipment such as a photographing light source and a digital camera.
For this reason, even if the same subject is photographed, if the photographing light source and the photographing device are different, printing using the stored image data as it is often differs from the actual subject color.

Therefore, when shooting a subject, under the same shooting conditions as the shooting conditions of the subject, for example, a color card such as a gray card with an achromatic color and a reflectance of 18%, or a gray scale in which the brightness of the achromatic color is divided into several stages. Take a color chart.
Then, after shooting, from the color chart position of the image, one point is extracted for the gray color chart and one point for each gradation in the case of the gray scale, and the gray scale is calculated from the RGB pixel values of the extracted pixels. In general, a tone correction table is created, and the correction data is used to correct image data obtained by photographing the subject so that the actual subject and the gray balance of the product catalog match.

The gray balance correction of image data handled by a conventional image processing program will be described with reference to FIG.
FIG. 12 is a diagram showing a schematic configuration of a gray balance correction apparatus to which a conventional gray balance correction method is applied.
This apparatus is composed of external devices such as a personal computer 1201, a digital camera 1202, and a display 1203.
The personal computer 1201 includes a CPU 1204 that operates a program, a memory 1205 that temporarily stores data and programs, and a hard disk 1206 that stores image data.
Assume that the hard disk 1206 stores in advance an operating system for executing a program and an image processing program equipped with a conventional gray balance correction method. The digital camera 1202 does not need to be connected to the personal computer 1201 at all times. If the digital camera 1202 is connected when the image data captured by the digital camera 1202 is taken into the personal computer 1201, it is disconnected at other times. May be.

FIG. 13 is a schematic diagram showing an example of an operation screen of an image processing program equipped with a conventional gray balance correction method.
The operation screen 1321 includes an image window 1322 for displaying a color image reproducing the image data, a black designation button 1323a for designating an achromatic / low brightness part of the image data, and a gray for designating the gray / medium brightness part of the image data. A designation button 1323b and a white designation button 1323c for designating the white / high brightness portion of the image data are arranged.
In addition, a tone curve operation panel 1328 for manipulating the tone curves of each color of RGB, an “open” button 1324 for reading image data from the hard disk 1206 into the memory 1205 and displaying it on the image window 1322, and an “execute” button 1325 for executing gray balance correction processing. A “save” button 1326 for saving the image data subjected to gray balance correction to the hard disk 1206 is arranged.
In addition, an “end” button 1327 for instructing the end of the gray balance correction operation is provided.

FIG. 14 is a schematic diagram of the tone curve operation panel 1328 of FIG.
In the tone curve operation panel details 1401 (that is, the image of the tone curve operation panel 1328), a tone curve display unit 1402 for displaying one of RGB tone curves and an RGB selection for selecting RGB to be displayed on the tone curve display unit 1402 A menu 1403, a black adjustment knob 1404 for operating the black portion of the tone curve, a gray adjustment knob 1405 for operating the gray portion of the tone curve, and a black adjustment knob 1406 for operating the white portion of the tone curve are arranged.

A schematic operation of a conventional image processing program (that is, a gray balance correction program) will be described with reference to a flowchart of FIG.
Although not shown in the schematic diagram of FIG. 12, the gray balance correction program stored in the hard disk 1206 is activated via an operating system by an input device such as a keyboard or a mouse.
After starting the gray balance correction program, the gray balance correction program displays the operation screen 1321 shown in FIG. 13 on the display 1203 in step 1501.
The gray balance correction program determines an end instruction when the end button 1327 is pressed by the keyboard or the mouse in step 1502 or a black designation button 1323a, a gray designation button 1323b, a white designation button 1323c, an open button 1324, and an execution button 1325. In step 1503, the system waits for input until an operation instruction by pressing the save button 1326 or an operation instruction by operating the tone curve operation panel 1328 is determined in step 1503.

If the operator (user) gives an end instruction using the end button 1327, the end determination is made in step 1502, and the gray balance correction program ends.
When any one of the black designation button 1323a, the gray designation button 1323b, the white designation button 1323c, the open button 1324, the execution button 1325, and the save button 1326 is pressed, processing corresponding to the type of the pressed button is performed. .
In the case of the open button 1324, the opening process in step 1504, in the case of the black designation button 1323a, in the black designation process in step 1505, in the case of the gray designation button 1323b, in the gray designation process in step 1506, in the case of the white designation button 1323c, in step 1507. In the case of the white color specification process, the tone curve operation panel 1328, the tone curve process in step 1508 is performed, in the case of the execution button 1325, the execution process of step 1509 is performed, and in the case of the save button 1326, the storage process of step 1510 is performed.
When each processing is finished, the end button 1327, the black designation button 1323a, the gray designation button 1323b, the white designation button 1323c, the open button 1324, the execution button 1325, and the save button 1326 are pressed again, or the tone curve operation is performed. A standby state is entered in which it is determined whether there is an operation instruction from panel 1328.
The gray balance correction program repeats the above operation until an end instruction is given by the end button 1327.

Next, the opening process in step 1504 of FIG. 15 will be described using the flowchart of FIG.
When the open button 1324 is pressed, the gray balance correction program is captured by the operator with the digital camera 1202, and is stored in the hard disk 1206 of the personal computer 1201 in advance as a file by the function of the operating system. In order to select an image data file to be opened, a file selection screen is displayed in step 1601.
Since the file name on the hard disk is displayed on the file selection screen, the operator selects a file for gray balance correction with a mouse or the like.
The gray balance correction program acquires the file name selected in step 1602 and closes the file selection screen. The gray balance correction program controls the CPU 1204 in step 1603 to open the selected file from the hard disk 1206 to the memory 1205 by the function of the operating system, reads the image data, and further selects the image window 1322 on the operation screen 1321 in step 1604. The image data of the file is displayed as a color image.
Thus, the opening process ends, and the process returns to step 1502 in FIG.

Next, the black designation process in step 1505 of FIG. 15 will be described using the flowchart of FIG.
When the black designation button 1323a is pressed, the gray balance correction program enters a black designation waiting state in step 1701.
The operator looks at the color image reproducing the image data displayed in the image window 1322, clicks on the black part of the gray scale photographed with the subject with the mouse, and designates the position of the black part on the image data.
In step 1702, black data of the designated portion is acquired.
Thus, the black designation process ends, and the process returns to step 1502 in FIG.

Next, the gray designation process in step 1506 of FIG. 15 will be described using the flowchart of FIG.
When the gray designation button 1323b is pressed, the gray balance correction program enters a gray designation waiting state in step 1801. The operator looks at the color image that reproduces the image data displayed in the image window 1322, clicks the gray portion of the gray scale photographed with the subject with the mouse, and designates the position of the gray portion on the image data. In step 1802, gray data of the designated portion is acquired.
Thus, the gray designation process ends, and the process returns to step 1502 in FIG.

Next, the white color designation process in step 1507 of FIG. 15 will be described using the flowchart of FIG.
When the white designation button 1323c is pressed, the gray balance correction program enters a white designation waiting state in step 1901.
The operator looks at the color image that reproduces the image data displayed in the image window 1322, clicks the white portion of the gray scale photographed with the subject with the mouse, and designates the position of the white portion on the image data.
In step 1902, white data of the designated portion is acquired.
Thus, the white designation process ends, and the process returns to step 1502 in FIG.

Next, the tone curve process in step 1508 of FIG. 15 will be described.
The tone curve operation panel 1328 displays a tone curve of any of RGB selected by the RGB selection menu 1403.
At this time, the horizontal position of the black adjustment knob 1404 is the corresponding color component of the black data acquired by the black designation process in step 1505, and the horizontal position of the gray adjustment knob 1405 is the corresponding of the gray data acquired in the gray designation process of step 1506. The horizontal position of the color component and white adjustment knob 1406 is the corresponding color component of the white data acquired in the white designation process in step 1507. The vertical position of the black adjustment knob 1404 is the corresponding color component of the black target value, the vertical position of the gray adjustment knob 1405 is the corresponding color component of the gray target value, and the vertical position of the white adjustment knob 1406 is the corresponding color component of the white target value. Become. At this time, each target value is a value in which a gray balance with a color component ratio of 1: 1: 1 is maintained.
The user changes the color data of black data, gray data, and white data and their target values by moving the positions of the black adjustment knob 1404, the gray adjustment knob 1405, and the white adjustment knob 1406, respectively, as necessary. be able to.

Next, the execution process of step 1509 in FIG. 15 will be described using the flowchart in FIG.
In step 2001, R correction LUT creation processing is performed from the R component of the black data, gray data, and white data.
In step 2002, G correction LUT creation processing is similarly performed from the G component.
In step 2003, B correction LUT creation processing is similarly performed from the B component.
In step 2004, gray balance correction of the image data is performed using the R correction LUT, G correction LUT, and B correction LUT.
In step 2005, the corrected image data is displayed as a corrected color image in the image window 1322 of the operation screen 1321 displayed on the display, and the execution process is terminated.
The user repeats the tone curve processing in step 1508 and the execution processing in step 1509 to adjust the gray balance until desired image data is obtained.
The desired image data is image data having an arbitrary gray balance required by the user.

Next, the storing process in step 1510 of FIG. 15 will be described using the flowchart of FIG.
The gray balance correction program displays a file saving screen in step 2101 after starting the saving process. Although not shown, the file storage screen is equivalent to general application software that designates a file name of a file to be stored and a directory to be stored in the hard disk.
The file name input by the user in step 2102 and the storage location input by the user in step 2103 are acquired, the image data is read from the memory 1205 in step 2104, and the file name input by the user is stored in the directory of the hard disk 1206 input by the user. Write and save as a file using the functions of the operation system.

Next, the R correction LUT creation processing in step 2001 of FIG. 20 will be described with reference to FIG.
Note that “LUT” refers to a lookup table (LOOK UP TABLE).
As shown in FIG. 22, the black data, gray data, and white data acquired by the black designation process in step 1505, the gray designation process in step 1506, and the white designation process in step 1507, and changed in the tone curve process in step 1508. The R component of each target value of black, gray and white is taken on the vertical axis.
An LUT is created in which the points of each color are connected by a fitted curve, the horizontal axis is an address, and the vertical axis is a conversion value.
In FIG. 22, black circles are black data changed by the tone curve processing in step 1508, gray circles (hatched circles) are gray data changed by the tone curve processing in step 1508, and white is step 1508. The white data changed by the tone curve processing is shown.
Also in the G correction LUT creation process in Step 2002 of FIG. 20, the G component is processed to create a G correction LUT in the same manner as the R correction LUT creation process.
Also in the B correction LUT creation processing in step 2003 of FIG. 20, the B component is processed to create a B correction LUT in the same manner as the R correction LUT creation processing.

Next, the gray balance correction process in step 2004 of FIG. 20 will be described using the flowchart of FIG.
After starting the gray balance correction process, the gray balance correction program controls the CPU 1204 in step 2301 to read out RGB format image data for one pixel from the memory 1205. In Step 2302, the R component of the image data is given as the address of the R correction LUT, the corresponding table value is taken out, and used as the R component conversion value.
In step 2303, the G component is converted by the G correction LUT as in the R correction. In step 2304, the B component is converted by the B correction LUT as in the R correction.
In step 2305, RGB format image data is written back to the memory 1205 again.
In step 2306, it is determined whether the processing from step 2301 to step 2305 has been performed on all the pixels. If all the pixels have not been completed, the processing returns to step 2301 and continues. When all the pixels are finished, the gray balance correction process is finished.
The above description is an example of gray balance correction using three points of black, gray, and white using a gray scale. When a gray card is used, the gray balance correction is similarly performed at one gray point.
Perfect color matching for digital cameras (p94) [Publisher: Graphic Co., Ltd., First Edition: March 25, 2000, Author: Soji Koyama et al.]

Since the conventional gray balance correction method is configured as described above, when photographing using a gray scale, it is necessary to uniformly illuminate each gradation from the bright part to the dark part without unevenness.
However, the illumination optimized for the subject to be originally photographed is often not evenly applied to the gray scale. In addition, it is necessary to search for an installation position with uniform illumination, and it takes a very long time to install a gray scale.
On the other hand, in the case of a gray card, since the entire color chart is uniform compared to the gray scale, it is not necessary to take into account uneven illumination, so installation is easy.
However, since there is no gradation, it is necessary to match the gray balance of all gradations with one gradation, and there is a problem that the accuracy of the gray balance deteriorates.
Further, in the user interface using the RGB tone curve, not only the gray balance but also the brightness is changed by the operation, and therefore there is a problem that an operation for adjusting only the gray balance while maintaining the brightness cannot be performed intuitively.

  The present invention has been made to solve the above-described problems, and it is easy to install an object (for example, a color chart) as a reference for correcting the gray balance, and from the bright part to the dark part. A gray balance correction method for an image, a gray balance correction device for an image, and a gray balance correction for an image with a user interface that can accurately correct the gray balance of each gradation and can easily operate only the gray balance while maintaining the brightness. It is an object of the present invention to provide a storage medium storing a processing program of a method.

  The gray balance correction method for image data according to the present invention includes an achromatic data input step for acquiring achromatic data of a portion corresponding to the object from image data obtained by photographing an object which is a gray balance reference together with the subject, and the achromatic color Based on the brightness of the achromatic color data acquired in the data input step, a conversion table calculation step for calculating a gray balance conversion table for correcting the gray balance of the image data for each brightness, and a calculation in the conversion table calculation step. An image data calculation step for calculating the converted image data using the gray balance conversion table, and a gray balance of the converted image data via a user interface in which operation knobs for user input are arranged in each of the plurality of brightness areas. Gray for setting Those having a balance setting step.

  Further, the gray balance correction device for image data according to the present invention comprises an achromatic color data input means for acquiring achromatic color data of a portion corresponding to the object from image data obtained by photographing an object which is a reference for gray balance together with the subject, Based on the lightness of the achromatic color data acquired by the achromatic color data input means, conversion table calculating means for calculating a gray balance conversion table for correcting the gray balance of the image data for each lightness, and the gray balance conversion table Gray for setting the gray balance of the converted image data via an image data calculating means for calculating the converted image data and a user interface in which operation knobs for user input are arranged in each of the plurality of brightness areas. And a balance setting means.

  The storage medium according to the present invention stores the program of “the gray balance correction method for image data” according to the present invention so that it can be read by a computer.

According to the present invention, gradation is generated in pixels of an object part (for example, a color chart portion) that is a reference for gray balance of captured image data from a light / dark difference due to illumination when a uniform color chart is captured, Since the coefficient for correcting the gray balance is calculated from the gradation, there is an effect that it is easy to install a gray scale and the accuracy of the gray balance of each gradation is good.
Further, since only the gray balance can be operated while maintaining the brightness, there is an effect that the operation can be performed more intuitively.
Further, by using the storage medium of the present invention, the “image data gray balance correction method” or the “image data gray balance correction apparatus” according to the present invention can be easily realized.

Embodiment 1 FIG.
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of a gray balance correction apparatus for image data to which a gray balance correction method according to the present invention is applied.
This gray balance correction device is composed of, for example, an external device such as a personal computer 1, a digital camera 2, and a display 3.
The personal computer 1 includes a CPU 4 that operates a program, a memory 5 that temporarily stores data and programs, and a hard disk 6 that stores image data.
It is assumed that the hard disk 6 stores in advance an operating system for executing the program and a color conversion program equipped with the color conversion method according to the present invention.
The digital camera 2 does not need to be connected to the personal computer 1 at all times, and may be connected when the image data captured by the digital camera 2 is taken into the personal computer 1, and is disconnected at other times. It may be.

FIG. 2 is a schematic diagram showing an example of an operation screen of a gray balance correction program equipped with the gray balance correction method according to the present invention.
On the operation screen 21, an image window 22 for displaying a color image reproducing the image data, an achromatic color designation button 23 for designating an achromatic portion of the image data, and an operation knob for user input in each of a plurality of lightness areas. The gray balance operation panel 28, an “open” button 24 for reading image data from the hard disk 6 into the memory 5 and displaying it in the image window 22, an “execute” button 25 for executing gray balance correction processing, and the image data subjected to gray balance correction. A “save” button 26 for saving to the hard disk 6 is arranged. Further, an “end” button 27 for instructing the end of the gray balance correction operation is provided.

An outline of the gray balance correction operation will be described with reference to the flowchart of FIG.
Although not shown in the schematic diagram of FIG. 1, the gray balance correction program stored in the hard disk 6 is activated via an operating system by an input device such as a keyboard or a mouse.
After starting the gray balance correction program, the gray balance correction program displays the operation screen 21 shown in FIG.
In the gray balance correction program, until an end instruction due to pressing of the end button 27 by the keyboard or the mouse is determined in step 402, or the achromatic color designation button 23, the open button 24, the execution button 25, and the save button 26 are displayed. Until the operation instruction by pressing and the operation instruction by which the gray balance operation panel 28 is operated are determined in step 403, the apparatus waits for input.
If the operator gives an end instruction using the end button 27, the end determination is made in step 402, and the gray balance correction program ends.

When any one of the achromatic color designation button 23, the open button 24, the execution button 25, and the save button 26 is pressed, processing corresponding to the type of the pressed button is performed.
When the open button 24 is pressed, the opening process of step 404, when the achromatic color designation button 23 is pressed, the achromatic color designation process of step 405, when the execute button 25 is pressed, the execution process of step 407, and storage When the button 26 is pressed, the storage process in step 408 is performed.
When each processing is completed, it is determined again whether any one of the end button 27, the achromatic color designation button 23, the open button 24, the execution button 25, and the save button 26 is pressed, or there is an operation instruction on the gray balance operation panel 28. Enter the standby state.
The gray balance correction program repeats the above operation until an end instruction is given by the end button 27.

Next, the opening process in step 404 of FIG. 4 will be described using the flowchart of FIG.
In the gray balance correction program, when the open button 24 is pressed, the operator takes a picture with the digital camera 2 and is stored in advance on the hard disk 6 of the personal computer 1 as a file by the function of the operating system. In order to select a file of image data to be opened, a file selection screen is displayed in step 501.
Since the file name on the hard disk is displayed on the file selection screen, the operator selects a file for gray balance correction with a mouse or the like.
The gray balance correction program acquires the file name selected in step 502 and closes the file selection screen.
The gray balance correction program controls the CPU 4 in step 503 to open the selected file from the hard disk 6 to the memory 5 by the function of the operating system, read the image data, and further selects the image window 22 on the operation screen 21 in step 504. The image data of the file is displayed as a color image.
Thus, the opening process ends, and the process returns to step 402 in FIG.

Next, the achromatic color designation process in step 405 of FIG. 4 will be described using the flowchart of FIG.
When the achromatic color designation button 23 is pressed, the gray balance correction program enters an achromatic color designation waiting state at step 601.
The operator looks at the color image that reproduces the image data displayed in the image window 22, selects a region of an object serving as a gray balance reference such as a gray color chart photographed together with the subject with the mouse, Specifies the position of the achromatic part of.
In step 602, achromatic color data in the RGB format of the designated area (that is, the area of the object serving as a reference for gray balance) is acquired.
In step 603, the achromatic color data is converted from the RGB format to the XYZ format using a 3 × 3 conversion matrix.

Further, in step 604, conversion is performed from the XYZ format defined in JIS 8701 using a conversion formula in the Yxy format.
In step 605, the data in the Yxy format is classified for each brightness (Y value) area.
In step 606, for each lightness region, the most frequently occurring value among the chromaticity point x values in the lightness region is determined as a representative value.
In step 607, for each lightness area, the most frequently occurring value is determined as a representative value among the chromaticity point y values that are the components of the color balance in the lightness area.
This completes the achromatic color designation process and returns to step 402 in FIG.

Next, the gray balance changing process in step 406 of FIG. 4 will be described with reference to FIG. FIG. 3 is a schematic diagram of the gray balance operation panel 28 of FIG.
Note that FIG. 3 is an example in which the brightness area is classified into five, but it may be increased or decreased if necessary.
The gray balance operation panel 28 includes an x value operation unit 301 that operates an x value among chromaticity points of gray balance, and a y value operation unit 309 that operates a y value among chromaticity points of gray balance.
In the present embodiment, the x value operation unit 301 includes five knobs 302 to 306 corresponding to five brightness areas. A connection line 307 connects the knobs 302 to 306.
The vertical direction 317 corresponds to the lightness Y value, and the horizontal direction 308 corresponds to the chromaticity point x value.

The knobs 302 to 306 can be moved in the horizontal direction by a mouse drag operation by a user operation, and can change the x value of each brightness area.
Further, each of the knobs 302 to 306 corresponds to the median value of the brightness of each brightness area.
The y value operation unit 309 includes five knobs 310 to 314 corresponding to the brightness area in this example. A connection line 315 connects the knobs 310 to 314. The vertical direction 317 corresponds to the lightness Y value, and the horizontal direction 316 corresponds to the chromaticity point y value.
The knobs 310 to 314 can be moved in the horizontal direction by a mouse drag operation by a user operation, and the y value of each brightness area can be changed.
The knobs 310 to 314 each correspond to the median brightness value of each brightness area.
That is, the knobs arranged next to the knobs 302 to 306 and the knobs 310 to 314 indicate chromaticity points in the same brightness region.

In the gray balance changing process in step 406, the representative values of the x value and the y value for each lightness area obtained in the achromatic color specifying process in step 405 are given as horizontal position information of the knobs 302 to 306 and the knobs 310 to 314, respectively. Show gray balance status to the user.
If necessary, the user operates the knobs 302 to 306 and the knobs 310 to 314 to change the gray balance state for each brightness area.
Although FIG. 3 shows an example in which the Y value is arranged in the vertical direction and the x value and the y value are arranged in the horizontal direction, the x value and the y value are arranged in the vertical direction and the Y value is arranged in the horizontal direction, contrary to FIG. May be.

Next, the execution process of step 407 of FIG. 4 will be described using the flowchart of FIG.
In step 701, an X-value correction LUT is created from the Yxy value for each lightness area and the target gray balance chromaticity.
In step 702, a Z value correction LUT is created from the Yxy value for each lightness region and the target gray balance chromaticity.
In step 703, gray balance correction of the image data is performed using the X value correction LUT and the Z value correction LUT.
In step 704, the corrected image data is displayed as a color image with the corrected image data on the image window 22 of the operation screen 21 displayed on the display, and the execution process ends.
The user repeats the gray balance changing process in step 406 and the execution process in step 407, and adjusts the gray balance until desired image data (that is, image data of an arbitrary gray balance desired by the user) is obtained.

Next, the storing process in step 408 of FIG. 4 will be described using the flowchart of FIG.
The gray balance correction program displays a file saving screen in step 801 after starting the saving process.
Although not shown, the file storage screen is equivalent to general application software that designates a file name of a file to be stored and a directory to be stored in the hard disk.
The file name input by the user in step 802 and the storage location input by the user in step 803 are acquired, the image data is read from the memory 5 in step 804, and the directory of the hard disk 6 input by the user with the file name input by the user is obtained. Write and save as a file using the functions of the operation system.

Next, the X value correction LUT creation processing in step 701 of FIG. 7 will be described using the flowchart of FIG.
Here, after step 406 gray balance change processing in FIG. 4, an X value correction LUT is created from the operation results of the x value operation unit 301 and the y value operation unit 309 in FIG.
In step 901, among the Yxy values, the chromaticity point xy is obtained from the position of the knob arranged next to FIG. 3, and the Y value is obtained from the correspondence with the vertical position of the knob.
For example, in FIG. 3, 302 and 310 are the knobs with the highest Y value (for example, Y = 90), 303 and 311 are the knobs with the next highest Y value (for example, Y = 70), and 304 and 312. Is the knob with the next highest lightness Y value (for example, Y = 50), 305 and 313 are the knobs with the next highest lightness Y value (for example, Y = 30), and 306 and 314 are the Y values with the next highest lightness. (For example, Y = 10).

When the knob 302 is moved in the + direction (right direction), the x value of the data having the Y value 90 is increased, and when the knob 302 is moved in the − direction (left direction), the x value of the data having the Y value 90 is increased. Will decrease the value. Further, when the knob 310 is moved in the + direction (right direction), the y value of the data having the Y value 90 is increased, and when the knob 310 is moved in the − direction (left direction), the data having the Y value 90 is increased. The y value of is reduced.
Assuming that the horizontal dotted line range of the x value operation unit 301 and the y value operation unit 309 is ± 0.1, FIG. 3 shows the x and y values of the data having a Y value of 90 by the knobs 302 and 310, respectively. +0.2 and ± 0.0.
In addition, the knobs 306 and 314 indicate that the x and y values of data having a Y value of 10 are approximately −0.2 and ± 0.0, respectively.

In step 902, the Yxy value is converted from the Yxy format defined in JIS8701 by a conversion formula in the XYZ format.
In step 903 , the xy chromaticity value of the gray balance as the correction target and the Yxy value by the brightness Y value corresponding to the vertical position of the knob are converted in the same manner as described above to obtain the XYZ value of the correction target.
In step 904, the X value correction coefficient in the brightness Y value is calculated from the ratio of the X value (Xc) obtained in step 902 and the X value (Xr) obtained in step 903 as in the following equation (1). obtain.
X value correction coefficient = Xr / Xc (1)
In step 905, it is determined whether or not the processing of all brightness knobs has been completed, and the processing from steps 901 to 904 is repeatedly performed until the processing is completed.
In step 906, an X value correction LUT having the Y value as an address and the X value correction coefficient as a table value is created by interpolation processing.

Next, the Z value correction LUT creation processing in step 702 of FIG. 7 will be described using the flowchart of FIG.
Here, after step 406 gray balance change processing in FIG. 4, a Z value correction LUT is created from the operation results of the x value operation unit 301 and the y value operation unit 309 in FIG.
In step 1001, among the Yxy values, the chromaticity point xy is obtained from the position of the knob arranged next to FIG. 3, and the Y value is obtained from the correspondence with the vertical position of the knob.
In step 1002, the Yxy value is converted from the Yxy format defined in JIS8701 by a conversion formula in the XYZ format.
In step 1003, the xy chromaticity value of the gray balance as the correction target and the Yxy value by the brightness Y value corresponding to the vertical position of the knob are similarly converted to obtain the XYZ value of the correction target.
In Step 1004, the Z value correction coefficient in the brightness Y value is calculated from the ratio of the Z value (Zc) obtained in Step 1002 and the Z value (Zr) obtained in Step 1003 as shown in the following equation (2). obtain.
Z value correction coefficient = Zr / Zc (2)

In step 1005, it is determined whether or not the processing of all brightness knobs has been completed, and the processing from steps 1001 to 1004 is repeated until the processing is completed.
In step 1006, a Z value correction LUT having a Y value as an address and a Z value correction coefficient as a table value is created by interpolation processing.
Next, the gray balance correction process in step 703 of FIG. 7 will be described using the flowchart of FIG.
After starting the gray balance correction process, the gray balance correction program controls the CPU 4 in step 1101 to read out one pixel of RGB format image data from the memory 5.
In step 1102, conversion from the RGB format to the XYZ format is performed using a 3 × 3 conversion matrix.
In step 1103, the X value correction coefficient is acquired from the X value correction LUT using the Y value of the XYZ format pixel as an address.

In step 1104, correction is performed by multiplying the X value of the XYZ format pixel by the X value correction coefficient.
In step 1105, the Z value correction coefficient is acquired from the Z value correction LUT using the Y value of the XYZ format pixel as an address.
In step 1106, correction is performed by multiplying the Z value of the XYZ format pixel by the Z value correction coefficient.
In step 1107, the image data is converted from the XYZ format to the RGB format image by the inverse matrix of the 3-by-3 conversion matrix from the RGB format to the XYZ format.
In step 1108, RGB format image data is written back to the memory 5 again.
In step 1109, it is determined whether the processing from step 1101 to step 1108 has been performed on all pixels. If all the pixels have not been completed, the processing returns to step 1101 and continues. When all the pixels are finished, the gray balance correction process is finished.
As described above, the user (operator) can easily and accurately correct the gray balance of the image data.

  As described above, the gray balance correction apparatus for image data according to the present embodiment acquires achromatic data for a portion corresponding to an object from image data obtained by photographing an object that is a reference for gray balance together with a subject. An input means; a conversion table calculating means for calculating a gray balance conversion table for correcting the gray balance of the image data for each brightness based on the brightness of the achromatic color data acquired by the achromatic color data input means; and a gray balance conversion For setting the gray balance of the converted image data via an image data calculating means for calculating the converted image data using a table and a user interface in which a user input operation knob is arranged in each of the plurality of brightness areas. Gray balance setting means.

  Further, the gray balance correction method of the image data according to the present embodiment includes an achromatic color data input step of acquiring achromatic color data of a portion corresponding to the object from image data obtained by photographing an object which is a gray balance reference together with the subject; A conversion table calculation step for calculating a gray balance conversion table for correcting the gray balance of the image data for each lightness based on the lightness of the achromatic color data acquired in the achromatic color data input step; and The image data calculation step for calculating the converted image data using the calculated gray balance conversion table, and the gray of the converted image data via a user interface in which a user input operation knob is arranged in each of the plurality of brightness areas. Gray for balance setting And a lance setting step.

Therefore, according to the present embodiment, a gradation is generated in the pixels of the color chart portion of the captured image data from the difference in brightness due to illumination when a uniform color chart is photographed, and the gray balance is corrected from the gradation. In order to calculate the coefficient for this purpose, it is easy to install a gray scale, and the gray balance accuracy of each gradation is good.
Further, according to the present embodiment, the gray balance is corrected by changing the X value and the Z value, which are the other two elements, for each lightness without changing the lightness Y value.
Therefore, only the gray balance can be operated while maintaining the brightness, and there is an effect that the operation can be performed more intuitively.

Embodiment 2. FIG.
In addition, even if the knobs 302 to 306 and the knobs 310 to 314 of the gray balance operation panel 28 according to the first embodiment are associated with the corrected target chromaticity value xy, the display of the user interface that can operate only the gray balance while maintaining the brightness. A screen display part can be realized.
That is, according to the present embodiment, when setting the gray balance, it is possible to set (correct) the gray balance of the image data while maintaining the lightness using the gray balance target value data.

Embodiment 3 FIG.
Further, even if both the gray balance operation panel in the first embodiment and the display screen display portion of the gray balance operation panel in the second embodiment are provided, the gray balance is maintained while maintaining the lightness even if it corresponds to the corrected target chromaticity value xy. It is possible to realize the display screen display portion of the user interface in the present invention that can be operated only.
That is, according to the present embodiment, when setting the gray balance, it is possible to set (correct) the gray balance of the image data using the gray balance target value data and the converted image data. .

Embodiment 4 FIG.
In general image data, it is rare that all brightness values are included equally, and as in the first and second embodiments, it is not necessary to correspond one-to-one to the brightness regions in which the operation knobs are equally divided. On the other hand, for a lightness area having a high appearance frequency, the lightness area is further divided and made to correspond to the operation knob, so that a more accurate gray balance can be achieved.
In other words, according to the present embodiment, it is possible to achieve a higher-accuracy gray balance by further dividing a lightness region having a high appearance frequency among a plurality of lightness regions and arranging an operation knob in the divided lightness region. It becomes.

In the first to fourth embodiments described above, it is easy to install an object (for example, a color chart) as a reference for correcting the gray balance, and the gray balance of each gradation from the bright part to the dark part is accurately corrected. An image gray balance correction method having a user interface capable of easily operating only gray balance while maintaining brightness has been described.
The software (program) of the image gray balance correction method according to the present invention can be stored in a storage medium so as to be readable by a computer.
By using a storage medium storing software (program) of the image gray balance correction method according to the present invention, the present invention can be easily realized anytime, anywhere.

  The present invention is most suitable for the purpose of easily correcting the gray balance of an image photographed by a digital camera or the like, but is not only a photographed image of a digital camera but also a bitmap obtained from any source such as an image obtained by a scanner. It can be used for gray balance correction of images, and can also be applied to color correction of file data for printing images and web images.

1 is a schematic configuration diagram of a gray balance correction apparatus according to Embodiment 1. FIG. 6 is an operation screen of a gray balance correction program according to the first embodiment. FIG. 6 is a diagram showing a gray balance operation panel according to the first embodiment. 6 is a flowchart illustrating an operation of a gray balance correction program according to the first embodiment. 5 is a flowchart showing an operation of opening a gray balance correction program according to the first embodiment. 6 is a flowchart showing an operation of an achromatic color designation process of the gray balance correction program according to the first embodiment. 6 is a flowchart illustrating an operation of a gray balance correction program execution process according to the first embodiment. 6 is a flowchart illustrating an operation of a gray balance correction program storing process according to the first embodiment. 6 is a flowchart illustrating an operation of X value correction LUT creation processing of the gray balance correction program according to the first embodiment. 6 is a flowchart showing an operation of a Y value correction LUT creation process of the gray balance correction program according to the first embodiment. 6 is a flowchart illustrating an operation of a gray balance correction process of the gray balance correction program according to the first embodiment. It is a schematic block diagram of the conventional gray balance correction apparatus. It is an operation screen of the gray balance correction program in the conventional apparatus. It is a figure which shows the gray balance operation panel in a conventional apparatus. It is a flowchart which shows operation | movement of the gray balance correction program in a conventional apparatus. It is a flowchart which shows the operation | movement of the process which opens the gray balance correction program in a conventional apparatus. It is a flowchart which shows the operation | movement of the black designation | designated process of the ray balance correction program in a conventional apparatus. It is a flowchart which shows the operation | movement of the gray designation | designated process of the gray balance correction program in a conventional apparatus. It is a flowchart which shows the operation | movement of the white designation | designated process of the gray balance correction program in a conventional apparatus. It is a flowchart which shows the operation | movement of the execution process of the gray balance correction program in a conventional apparatus. It is a flowchart which shows the operation | movement of the preservation | save process of the gray balance correction program in a conventional apparatus. It is explanatory drawing of correction | amendment LUT creation processing of the gray balance correction program in a conventional apparatus. It is a flowchart which shows the operation | movement of the gray balance correction process of the gray balance correction program in a conventional apparatus.

Explanation of symbols

1 Personal computer 2 Digital camera 3 Display 4 CPU
5 memory 6 hard disk 21 operation screen 22 image window 23 achromatic color designation button 24 open button 25 execute button 26 save button 27 end button 28 gray balance operation panel 301 x value operation unit 302 to 306 x value operation knob 307 x value operation knob connection Line 308 x value operation direction
309 y value operation unit 310 to 314 y value operation knob 315 y value operation knob connecting line 316 y value operation direction 317 Y value direction 401 to 408 Steps showing processing procedure of gray balance correction program 501 to 504 showing procedure of opening process Steps 601 to 607 Steps showing the procedure of achromatic color designation processing 701 to 704 Steps showing the procedure of execution processing 801 to 804 Steps showing the procedure of storage processing 901 to 906 Steps showing the procedure of X value correction LUT creation processing 1001 to 1006 Steps showing the procedure of the Z value correction LUT creation process 1101-1109 Steps showing the procedure of the gray balance correction process

Claims (11)

An achromatic color data input step of acquiring achromatic data of a portion corresponding to the object from image data obtained by photographing an object which is a gray balance reference together with the subject;
A conversion table calculating step for calculating a gray balance conversion table for correcting the gray balance of the image data for each lightness based on the lightness of the achromatic color data acquired in the achromatic color data input step;
An image data calculation step of calculating image data after conversion by the gray balance conversion table calculated in the conversion table calculation step;
And a gray balance setting step for setting a gray balance of the converted image data via a user interface in which operation knobs for user input are arranged in each of a plurality of brightness areas. Gray balance correction method.   2. The gray balance correction method for image data according to claim 1, wherein in the gray balance setting step, gray balance setting of the image data is performed using gray balance target value data.   2. The gray balance correction method for image data according to claim 1, wherein in the gray balance setting step, the gray balance setting of the image data is performed using the achromatic color data acquired in the achromatic color data input step.   4. The image according to claim 1, wherein among the plurality of lightness areas, a lightness area having a high appearance frequency is further divided, and the operation knob is arranged in the divided lightness areas. Data gray balance correction method.   The gray balance correction method according to claim 1, wherein the object is a color chart. Achromatic color data input means for acquiring achromatic color data of a portion corresponding to the object from image data obtained by photographing an object serving as a gray balance reference together with the subject;
Conversion table calculating means for calculating a gray balance conversion table for correcting the gray balance of the image data for each lightness based on the lightness of the achromatic color data acquired by the achromatic color data input means;
Image data calculation means for calculating image data after conversion by the gray balance conversion table;
Image data comprising: gray balance setting means for setting gray balance of the converted image data via a user interface in which operation knobs for user input are arranged in each of a plurality of brightness areas Gray balance correction device.   7. The gray balance correction apparatus for image data according to claim 6, wherein the gray balance setting means sets gray balance of image data using gray balance target value data.   7. The gray balance correction apparatus for image data according to claim 6, wherein the gray balance setting means sets the gray balance of the image data using the achromatic color data acquired by the achromatic color data input means.   9. The lightness region having a high appearance frequency among the plurality of lightness regions is further divided, and the operation knob is arranged also in the divided lightness region. Gray balance correction device for image data.   The gray balance correction apparatus according to claim 6, wherein the object is a color chart.   6. A storage medium in which a program of a gray balance correction method for image data according to claim 1 is stored so as to be readable by a computer.

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