JP2007159029A - Image processing apparatus and image processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily create a look-up table for image processing suitable for a user's preference.
A look-up table is created for image data acquired by a digital camera from the gradation characteristics of the digital camera used, the gradation characteristics of the printer that prints the image data, and the target input / output overall gradation characteristics. An image processing apparatus comprising: means for performing gradation conversion processing on the image data using the lookup table; and storage means for storing information for creating the overall gradation characteristics; The apparatus includes a creating unit that creates the look-up table based on information stored in the storage unit, and an editing unit that edits information that creates the overall gradation characteristics.
[Selection] FIG.

Description

  The present invention relates to creation of a lookup table for image processing.

With the increase in image quality of digital cameras and printers, the number of users who print photographs at home is increasing. In addition, a new demand for camera direct that prints more easily by directly connecting a digital camera and a printer without using a PC is also attracting attention. Against this background, with the aim of further improving image quality, development of technology that makes the overall image quality combined with digital cameras and printers or color reproduction more user-friendly (for example, patents) is progressing. Reference 1).
Japanese Patent Laid-Open No. 11-136504

  However, since the invention described in Document 1 uses many RGB or CMY complex 3D look-up tables, the amount of memory used increases, and it is very difficult for users to customize complex look-up tables themselves. There is a problem that it is difficult. In addition, since the brightness range that can be output by the printer depends greatly on the paper to be printed, a complex look-up table is required to print a photo with color reproduction that suits the user's preference on any paper. There is a problem that it must be customized for each paper.

  Therefore, an object of the present invention is to easily create a look-up table for image processing that meets user preferences.

  In order to achieve the above-described object, the present invention provides a digital camera with gradation characteristics of a digital camera used, gradation characteristics of a printer that prints the image data, and a target input / output total scale for image data acquired by a digital camera. An information processing apparatus comprising: means for creating a look-up table from tone characteristics; and means for performing tone conversion processing on the image data using the look-up table; storing information for creating the overall tone characteristics Storage means for creating, a creation means for creating the lookup table based on information stored in the storage means, and an editing means for editing information for creating the overall gradation characteristics by a user. And

  According to the present invention, it is possible to easily create a look-up table for image processing that meets user preferences.

  Next, details of the present invention will be described in accordance with the description of the embodiments.

  The present embodiment will be described below with reference to the drawings.

  FIG. 1 is a block diagram showing the present embodiment. As shown in FIG. 1, the system configuration according to the present embodiment includes an image input unit 101 for inputting image data to a system from a recording medium storing an image acquired by photographing a subject with a digital camera, The tone conversion unit 102 that converts the tone characteristics of image data so as to optimize the overall tone reproducibility combined with the output, the table creation unit 104 that creates a lookup table used for tone conversion, and the table Table creation information storage unit 105 that stores information for creation, print information input unit 108 for selecting the model of the digital camera used for shooting or the model of the printer that prints image data, and the types of a plurality of digital cameras Camera gradation table storage unit 106 for storing each gradation characteristic for each of the plurality of printer types A printer gradation table storage unit 107 that stores each gradation characteristic, an image output unit 103 that outputs image data to a storage medium, and a table editing unit that edits the table created by the table creation unit 104 Part 111 is provided.

  Image data taken with a digital camera is recorded on a storage medium such as a hard disk of a PC, and is usually compressed in a predetermined format such as JPEG. In the image input unit 101, image data is acquired from a file of image data recorded on this recording medium. At this time, the image data is expanded by a predetermined algorithm corresponding to the compression method, and is expanded into image data S0 composed of a two-dimensional pixel array of RGB 3 channels.

  Next, the user selects the type of digital camera used to acquire the image data S0, the printer model and paper used for printing, and inputs the selection details using the keyboard of the PC, etc. In the unit 108, a digital camera model, a printer model, paper, and the like are selected. The selection of the type of the digital camera and the shooting mode in the print information input unit 108 may be a method that allows the user to select from the menu shown in FIG. 13, for example. Here, a menu 1301 is a menu for selecting a digital camera model. A menu 1302 is a menu for selecting a shooting mode for the digital camera type selected in the menu 1301, and the items differ depending on the digital camera type. However, when these pieces of information can be read from the tag information of the image data, a method of automatically obtaining from the tag information or the like can be used.

  The camera gradation table storage unit 106 stores in advance gradation characteristics for each type of digital camera or each shooting mode of the digital camera. For example, in the case of the digital camera C shown in FIG. 13, the gradation characteristics differ in advance according to the strobe ON / OFF, ISO sensitivity setting, and shooting mode setting, and conversion is performed based on these settings. In order to absorb the difference in the gradation characteristics of the image data, a plurality of gradation characteristics are stored in advance for each flash ON / OFF, ISO sensitivity setting, and shooting mode setting.

  Here, the gradation characteristics of the digital camera are recorded in the format shown in FIG. 8, for example. The brightness of the subject photographed by the digital camera and the digital camera when the subject is photographed by the digital camera. This represents the relationship with the output value of. In the present embodiment, a table indicating the correspondence between the brightness of a subject and Y obtained by converting the image data of RGB 3 channels obtained by photographing the subject with a digital camera using equation (1) is a gradation of the digital camera. Characteristic.

  In this embodiment, a YCC color base is used as a method for extracting brightness from RGB format image data. Formula (1) is a conversion formula from RGB to YCC color base, which calculates a value based on the YCC color base of the image data, and uses that Y to convert the gradation characteristics.

  This characteristic can be obtained, for example, by photographing an achromatic gray chart with a digital camera and acquiring image data, and simultaneously measuring the brightness of each patch of the gray chart using a measuring instrument. Note that the gradation characteristics of a digital camera are not limited to those described above, and represent the relationship between the brightness of a subject photographed by the digital camera and the output value of the digital camera when the subject is photographed by the digital camera. Any amount can be used. Also, for example, a measured value obtained by measuring the amount of light received by the CCD sensor or the illuminance on the CCD sensor surface of the digital camera by some means, and an output value of the digital camera when an input corresponding to the measured value is given to the digital camera (for example, It may be a correspondence with the average value of RGB values).

  Similar to the gradation characteristics of the digital camera, the print information input unit 108 selects the type of printer used when printing the image data S0 or the print mode of the printer. Selection of the printer type and the print mode in the print information input unit 108 is performed by, for example, a menu shown in FIG. Here, a menu 1401 is a menu for selecting a printer type. A menu 1402 is a menu for selecting a print mode for the printer type selected in the menu 1401, and the items differ depending on the printer type.

  The printer gradation table storage unit 107 stores a plurality of printer types or gradation characteristics for each printer printing mode in advance. For example, in the case of the printer C shown in FIG. 14, the gradation characteristics differ depending on the setting of the printing paper and the halftone setting, and the difference in the gradation characteristics of the print printed according to each of these settings is absorbed. Therefore, a plurality of gradation characteristics are stored in advance according to the setting of the printing paper and the setting of the halftone. Of these gradation characteristics, the printer type selected by the print information input unit 108 or the gradation characteristics of the printer printing mode is stored.

  Here, the gradation characteristics of the printer are recorded in the format shown in FIG. 9, for example, and the relationship between the input value of the printer and the output value (print brightness) of the printer corresponding to the input value. Is expressed. In the present embodiment, a table indicating the correspondence between Y obtained by converting the image data composed of RGB three channels input to the printer by Expression (1) and the brightness corresponding to the output of the printer corresponding to the input is displayed on the printer. The gradation characteristics are used. This characteristic is, for example, known gray chart image data composed of RGB 3 channels (digital data obtained by allocating values from 0 to 255 having the same RGB value in each patch ((0,0,0), (1, 1,1), ... (255,255,255)), printed by a printer, and measured by using a colorimeter to measure the brightness of each patch.In this case, each patch in the created gray chart image data is obtained. The correspondence between the Y obtained by converting the RGB value by the equation (1) and the brightness of each patch obtained by measuring what is printed by the printer is the gradation characteristic of the printer. The gradation characteristics are not limited to those described above, and any gradation characteristic may be used as long as it represents the relationship between the input value of the printer and the output of the printer corresponding to the input value. The value corresponding to the output of It can also be a reflection rate.

  Next, the table creation unit 104 creates a look-up table for converting the image data S0 in order to obtain a photograph having preferable gradation reproducibility that does not depend on the digital camera used for photographing or the printer used for printing. At this time, in the table creation information storage unit 105, for example, as shown in FIG. 3, from photographing of a subject to output for an outputable brightness range (hereinafter referred to as an output range) depending on the printer model and paper type. The gradient of the halftone (γ value) of the input / output overall tone characteristics, which is the overall tone characteristics throughout, is recorded as a look-up table or function, and the table creation unit 104 stores this table creation information. Based on the information stored in the unit 105, a lookup table is created. Hereinafter, the processing in the table creation unit 104 will be described in detail with reference to FIG.

  FIG. 2 is a diagram showing the flow of processing in the table creation unit 104. First, in step 101, the slope of the input / output total gradation characteristics corresponding to the output range is obtained according to the information stored in the table creation information storage unit and stored in the memory 109. Here, the output range means a range of brightness that can be output in the printer gradation characteristics corresponding to the printer type selected by the print information input unit 108 or the paper type. In step 101, the gradient of the halftone in the corresponding input / output overall gradation characteristic is obtained according to the characteristic stored in the table creation information storage unit 106 using this output range as an input. Here, as shown in FIG. 3, the table creation information storage unit 105 can store a plurality of different characteristics (look-up tables or functions) for each category such as glossy paper and matte paper, and the print information input unit 108. The characteristics of an appropriate category are selected based on the information input in.

  Next, in step 102, the input / output overall gradation characteristics are automatically designed and stored in the memory 109. The input / output overall tone characteristics are the overall tone characteristics throughout the entire process from shooting to output of the subject. What is the brightness after an object with a certain brightness is shot and printed? It represents whether it should be reproduced on the print. In the present embodiment, as shown in FIG. 7, the input / output total gradation characteristics are expressed by a table representing the correspondence between the brightness of the subject and the output value (brightness) of the printer corresponding to the brightness. In step 102, the input / output overall gradation characteristics are designed so as to have the halftone gradient obtained in step 101. The method will be described later. Note that the input / output overall gradation characteristics are not limited to this, and any input can be used as long as it represents the relationship between the brightness of the subject or the illuminance of the CCD sensor surface of the digital camera and the output value of the printer. good. However, the amount corresponding to the brightness of the subject must be an input value of the digital camera in the gradation characteristics of the digital camera, or an amount that can be easily converted from the input value. Also, the amount corresponding to the output value of the printer must be capable of mutual conversion into the output value of the printer in the gradation characteristics of the printer, or easily into the output value.

  In step 103, in order to realize the input / output total gradation characteristics designed in step 102, a lookup table for conversion applied to the image data S0 is created. The lookup table created in step 103 is shown in FIG. FIG. 12 is a diagram illustrating a flowchart for explaining the creation of the lookup table, and FIG. 11 is a diagram illustrating how the lookup table is created from the values of each table. Hereinafter, a method for creating a lookup table will be described with reference to FIGS. Here, the table 1101 represents the input / output overall gradation characteristics shown in FIG. 7, the table 1102 represents the gradation characteristics of the digital camera shown in FIG. 8, and the table 1103 represents the gradation characteristics of the printer shown in FIG. Table 1104 is the look-up table shown in FIG. However, the gradation characteristics of the digital camera in the table 1102 are interpolated by linear interpolation or a spline curve so that the output (D column) of the digital camera takes all values (256 points) from 0 to 255. And

  First, in each value recorded in the A column of the input / output total gradation table 1101, the value closest to the respective value is searched from the C column in the digital camera gradation table 1102, and the D column that is paired with that value is searched. Is recorded in the G column of the lookup table 1104 (step 1201). Next, for each value recorded in the B column of the target gradation table 1101, a value closest to the respective value is searched from the F column in the printer gradation table 1103, and the value of the E column that is a pair with the value is searched. The value is recorded in the H column of the lookup table 1104 (step 1202). Finally, interpolation processing is performed by linear interpolation or a spline curve so that the input (G column) in the lookup table 1104 takes all values (256 points) from 0 to 255, and the lookup table 1104 is created. (Step 1203).

  Next, in the gradation conversion unit 102, the image data S0 composed of RGB 3 channels input from the image input unit 101 is also image data S1 composed of RGB 3 channels for realizing a print having a gradation desired by the user. Tone conversion is performed. In the present embodiment, the RGB data in the image data S0 is converted into data composed of luminance Y, Cb, and Cr using equation (1), and only the luminance Y is created in the lookup table 1104 created by the table creation unit 104. Convert table using. After that, RGB image data of the image data S1 is obtained from the table-converted luminance Y, Cb, and Cr by Expression (2).

  Finally, the converted image data S1 is sent to a predetermined printer by the image output unit 109 and printed in the print mode input by the print information input unit. Alternatively, the image data S1 can be recorded on a storage medium such as a hard disk of a PC in a predetermined format such as JPEG.

  FIG. 15 is a diagram showing a user interface in the table editing unit 111. The user interface shown in FIG. 15 includes an image data display unit 1801 that displays the image data S1, a table creation information display unit 1802 that indicates the characteristics stored in the table creation information storage unit 105, and a look created by the table creation unit 104. A table editing slider 1805 for the user to adjust the uptable, a table editing knob 1806, a table creation information update button 1807 for instructing an update of the characteristics stored in the table creation information storage unit 105, and an image data display unit 1801 An OK button 1808 for sending the displayed image data S1 to the image output unit 103 and ending the process, and a cancel button 1809 for stopping the process are provided. Further, in the table creation information display unit 1802, the table creation characteristic 1803 is, for example, information stored in the table creation information storage unit 105 shown in FIG. 3 or the table creation information itself adjusted by the user. A point 1804 represents a point on the table creation characteristic 1803 that is arbitrarily designated by the user to edit the table creation characteristic 1803.

  While viewing the image data S1 displayed on the image data display unit 1801, the user adjusts the table editing knob 1806 or the table creation characteristic control point 1804 using an input device such as a mouse. The table edit knob 1806 can be moved on the table edit slider 1805, and when the user moves the table edit knob 1806, the input / output total gradation characteristics are determined by the positional relationship of the table edit knob 1806 within the table edit slider 1805. The gradient of the halftone is determined. When the user moves the table creation characteristic control point 1804, the table creation characteristic 1803 is automatically changed to pass through the table creation characteristic control point 1804, and the input / output overall gradation characteristics are according to the table creation characteristic 1803. The gradient of the halftone is determined. When the gradient of the halftone of the input / output total gradation characteristics is determined, the input / output total gradation characteristics are automatically designed (step 102 in FIG. 2), and a lookup table is created (as in the first embodiment). FIG. 2 step 103). Then, based on the created lookup table, the image data S1 converted by the gradation conversion unit 102 is displayed on the image display unit 1801.

  When the user selects the table creation information update button 1807 with an input device such as a mouse, the table creation information 1803 is stored in the table creation information storage unit 105. If the user selects the OK button, the image data S1 displayed on the image data display unit 1801 is sent to the image output unit 103, and after printing or saving in a storage medium, all processing is performed. finish. A cancel button 1809 is a button for the user to cancel processing. When the user selects the cancel button 1809, processing such as updating of the table creation characteristics 1803 and transmission of the image data S1 to the image output unit 103 is not performed. finish.

<Description of Design Step 102 for Input / Output Total Tone Characteristics>
FIG. 4 is a diagram showing the flow of processing in step 102 for designing the input / output overall gradation characteristics. FIG. 5 shows basic characteristics for designing the input / output total gradation characteristics in step 102, and is recorded in advance in the table creation unit 104. This basic characteristic is normalized so that the range of the lightness of the subject (corresponding to the horizontal axis) and the lightness of the print (corresponding to the vertical axis) is 0 to 1, and the minimum point (0,0) And a set of points including the maximum point (1,1). In the example of FIG. 5, the basic characteristics are defined by a total of 10 points P1 to P10, where P1 corresponds to the maximum point and P10 corresponds to the minimum point. Hereinafter, the i-th point is denoted by Pi and its coordinates are denoted by (xi, yi). Here, xi is the normalized subject brightness at the point Pi, and yi is the normalized print brightness at the point Pi. Hereinafter, the processing flow of step 102 will be described with reference to FIG.

  First, in step 201, the horizontal axis and the vertical axis in the basic characteristics are linearly expanded by Equation (3) so as to correspond to the subject brightness and the print brightness, respectively.

  Here, x'max and x'min are the maximum and minimum values of the subject brightness corresponding to the input of the gradation characteristics of the digital camera, respectively, and y'max and y'min are the output of the gradation characteristics of the printer, respectively. It means the maximum and minimum values of the corresponding print brightness. Further, x′i and y′i represent the x coordinate and y coordinate at the i-th point P′i in the set of points defining the input / output overall gradation characteristics, respectively.

  Next, in step 202, a straight line L that determines the halftone characteristic of the input / output total gradation characteristic is defined by equation (4).

  In equation (4), γ is the gradient of the halftone determined in step 101, and x′hc and y′hc are the values of the x coordinate at all points of the input / output overall gradation characteristics, ie, highlight and halftone. It means the x-coordinate and y-coordinate of the point Phc closest to the value x′mh predetermined as the boundary.

  In step 203, a shadow correction coefficient S for correcting the shadow part in the input / output overall gradation characteristics is calculated by the equation (5).

  In equation (5), x'sc and y'sc are points where the value of the x coordinate is closest to the value x'sm predetermined as the boundary between the halftone and the shadow at all points of the input / output overall gradation characteristics It means the x coordinate and y coordinate of Psc, respectively.

  Finally, in step 204, the input / output total tone characteristics are corrected so that the halftone gradient becomes γ. FIG. 6 is a diagram for explaining the processing in step 204. The characteristic shown as uncorrected in FIG. 6 is the input / output total gradation characteristic P′i obtained in step 201. The characteristic before correction is changed so that the halftone is along the straight line L defined in step 202, and the characteristic after correction is obtained. At this time, the shadow is corrected by applying a shadow correction coefficient S in accordance with the change of the halftone. Expression (6) shows an expression for correcting the input / output overall gradation characteristics.

  Each point P′i of the input / output total gradation characteristics obtained as described above is stored in the memory 109 as a table shown in FIG. Further, the method for obtaining the input / output total gradation characteristics is not limited to the method described above, and when the gradient of the halftone is defined as in the present embodiment, the input / output is uniquely input to the gradient of the halftone. Any method may be used as long as the overall gradation characteristic is determined.

(Other examples)
This embodiment can be applied to a system for displaying and converting image data by processing image data captured and recorded with a digital camera with an application program operating on a personal computer (PC). Here, the PC generally includes a CPU and a RAM for operating programs such as an OS and applications, an input interface such as a memory card or USB for inputting image data, and for outputting processed image data. A data output interface to a display or printer and a user interface such as a keyboard for a user to instruct an application are provided.

  In the above embodiment, the image processing system that outputs the image data acquired by the digital camera with the printer is described. However, the present invention is not limited to this. For example, the silver halide photographic film is digitized with a scanner or the like and displayed on the monitor. The present invention can also be applied to an image processing system. At this time, the table stored in the camera gradation table in the first to third embodiments is a table that represents the correspondence between the brightness of the subject that combines the characteristics of the silver halide photographic film and the scanner and the digital data after scanning. The table stored in the printer gradation table is a table representing the correspondence between the digital data output to the monitor and the brightness actually displayed on the monitor.

  Furthermore, in the above-described embodiment, the image processing system that adjusts the appearance of the image data using the gradient of the halftone in the input / output overall gradation characteristics as a parameter has been described. However, the present invention is not limited thereto. It is also possible to adjust the input / output overall gradation characteristics as parameters.

It is a block diagram which shows the process of a present Example. It is a figure explaining the flow of processing in a table creation part. It is a figure explaining table creation information. It is a figure which shows the flow of the process which designs an input-output total gradation characteristic. It is a figure explaining a basic characteristic. It is a figure explaining the process which designs an input-output total gradation characteristic. It is a figure which shows the input / output total gradation table. It is a figure which shows a camera gradation table. It is a figure which shows a printer gradation table. It is a figure which shows the look-up table used for gradation conversion. It is a figure which shows a mode that a look-up table is produced from the value of each table. It is a flowchart for demonstrating creation of a lookup table. It is a figure which shows the example of the menu which selects a digital camera classification and imaging | photography mode. FIG. 4 is a diagram illustrating an example of a menu for selecting a printer type and a print mode. It is a figure explaining the user interface in a table edit part.

Claims (4)

Means for creating a look-up table for the image data acquired by the digital camera from the gradation characteristics of the used digital camera, the gradation characteristics of the printer that prints the image data, and the target input / output overall gradation characteristics;
Means for performing a gradation conversion process on the image data using the lookup table;
Storage means for storing information for creating the overall gradation characteristics;
Creating means for creating the lookup table based on information stored in the storage means;
An image processing apparatus comprising: editing means for a user to edit information for creating the overall gradation characteristic. The image processing apparatus according to claim 1.
The image processing apparatus, wherein the storage unit includes at least information on paper used for printing as a parameter, and stores information for determining a halftone inclination in the overall gradation characteristics from the parameter. For the image data acquired by the digital camera, a step of creating a lookup table from the gradation characteristics of the digital camera used, the gradation characteristics of the printer that prints the image data, and the target input / output total gradation characteristics;
A step of performing a gradation conversion process on the image data using the lookup table,
A storage step of storing information for creating the overall gradation characteristics;
A creation step of creating the lookup table based on the information stored in the storage step;
An image processing method comprising: an editing step in which a user edits information for creating the overall gradation characteristic.
  A program for causing a computer to execute the image processing method according to claim 3.

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