JP2009177426A - Image processor and image processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device and a method for applying image processing to a printed matter, formed by copying an original image, to have the same colors even under an observation light source different from that for the original image. <P>SOLUTION: The following processing is executed when printing an image onto a recording medium by an output device on the basis of image data obtained by reading an original image by an input device. Device color information shown by the image data and depending on the input device is converted into device-independent color information showing the color when the original image is observed by a first observation light source. The device-independent color information obtained by the conversion is subjected to metamerism correction such that printed matter obtained by printing the image onto a recording medium has the same colors as that for the original image when the printed matter is observed by a second observation light source different from the first observation light source. The corrected device-independent color information is converted into device color information dependent on the output device. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image processing apparatus that reads a document image, performs image processing, and outputs a copy, and an image processing method used in the apparatus.

  In recent years, digital image input / output devices such as a color image scanner (hereinafter referred to as a scanner) and a color printer (hereinafter referred to as a printer) have become widespread and can easily handle digital images. Also, as a device combining these devices, a multi-function printer (hereinafter referred to as MFP) that provides multi-functions such as scanning, printing, and copying combining the devices is becoming widespread due to its convenience.

  Now, the document reading performance of the scanner and the output color gamut representation performance of the printer are improving year by year. As a result, for example, by scanning and printing a silver halide photograph or the like as a document in the MFP, it is possible to obtain a color copy image having a color gamut equivalent to that of the document.

  Here, in order to faithfully reproduce the color of an original, it is important that color reproduction information is correctly transmitted between these devices, in addition to the performance of the scanner and printer as described above. .

  A color management system (hereinafter referred to as CMS) is widely known as a technique (color matching technique) for reproducing the same color between devices having different color gamuts.

  FIG. 11 is a block diagram showing an outline of the configuration of CMS, and shows CMS using a device-independent (device-independent) color space.

  As shown in FIG. 11, in the CMS, an input device (camera, scanner, etc.) and an output device (printer, monitor, etc.) are connected. In this case, the conversion from the color signal of the input device to the color signal of the output device is realized by interposing a color space (device-independent color space, also referred to as PCS) independent of each profile and device. PCS includes, for example, CIEXYZ, CIELab, and the like. The profile is provided as a conversion expression that links each device-dependent color space (hereinafter referred to as device color) and PCS, or as a lookup table (LUT) that is a conversion table in which the relationship between device color and PCS is described in advance.

  In order to reproduce colors that can be reproduced by the input device by the output device or to obtain colors that can be reproduced by the output device when the color is reproduced by each device of the CMS, different colors between the input and output devices A gamut compression technique that absorbs the effects of the area is used.

  Here, the profile of the input device and the profile of the output device are generally created using CIELab colorimetric values under a D50 light source, which is a standard evaluation light source for printed matter.

  However, in the copy output by the input / output profile created in this way, the color of the original and the output product match under the D50 light source, but the other light sources (for example, the F10 light source used everyday in the office, etc.) Wavelength fluorescent light sources, etc.) may show different colors. This is caused by the difference in spectral reflection characteristics between the color material of the original (for example, silver salt photograph) and the output material (for example, printing by an inkjet recording apparatus).

  Even under the D50 light source, the spectral reflection characteristics may be different even for colors that are the same to the human eye (in other words, colors with the same tristimulus values XYZ). In such a case, when the light source is changed, it looks different to human eyes (in other words, when the light source is changed, the tristimulus values XYZ are different). Such a phenomenon is called metamerism (conditional color etc.) and is widely known as a precaution when performing color matching.

  On the other hand, since the original and copy output of a color copying machine are assumed to be used under an unspecified light source depending on the user's application, many countermeasures against such a phenomenon have been proposed.

For example, Patent Document 1 discloses an invention that selects how to use ink so that the influence of metamerism is reduced by controlling the UCR amount and color adjustment at the time of output. Patent Document 2 discloses an invention that uses CMS based on the perceived amount of color appearance by specifying an observation environment. Further, Patent Document 3 discloses an invention in which characteristics of an original, a color material, a scanner device, and ambient light are stored in advance and are combined automatically or manually during hard copy processing. Further, Patent Document 4 obtains the center of gravity of colorimetric values under a plurality of light sources (hereinafter, colorimetric values under a plurality of light sources Fx, or simply colorimetric values under a Fx light source), and the colorimetric values thereof. An invention that utilizes CMS using the above is disclosed.
Japanese Patent Laid-Open No. 2002-247397 Japanese Patent No. 3416538 Japanese Patent Laying-Open No. 2005-311446 Japanese Patent No. 3968565

  However, since Patent Document 1 uses color separation of ink, it affects not only metamerism but also color granularity, stability against disturbance, and the like, and adjustment in a state where image quality is kept good. There is a problem that it is difficult.

  Further, in Patent Document 2, since the user designates the observation environment, the difference in appearance still exists in the observation environment that is not designated by the user.

  Furthermore, according to Patent Document 3, it is necessary to store all possible characteristic values. This can be achieved with a PC system or business copier equipped with a large-capacity memory, but is practically realized when a consumer device with a small memory capacity is used alone (without connecting to a PC). Impossible.

  Patent Document 4 is an invention related to a printer, but the same idea can be applied to a scanner. Further, it can be easily estimated that metamerism in hard copy can be reduced by performing color matching on the scanner and the printer with the colorimetric values under the Fx light source. However, in the technique disclosed in Patent Document 4, the color measurement value in the work color space (PCS) is different from the color measurement value under a standard light source.

  If the image read by the scanner is printed out without any changes, the colorimetric values in the image are consistent with the expected meaning of the printer. If this is the case, color matching is achieved and there is no problem. However, in practice, various types of image processing such as brightness and color change and contour enhancement are often performed on the read image.

  In addition, as a working color space for various image processing handled in such a case, a D50 light source is often used as a standard in the past, and a Lab value under the D50 light source or Adobe (registered trademark) RGB based on the Lab value. In many cases, values are used. Therefore, there is no guarantee that the same effect can be obtained with colorimetric values under an Fx light source that is a light source other than D50 for image processing for the D50 light source. Therefore, if the colorimetric values under the Fx light source are adopted as the work color space, it is necessary to verify and correct each of the above whether or not these conventional image processing can be reused.

  In addition, there are many devices equipped with a color facsimile function in current MFPs. These devices transmit and receive images to and from an unspecified device through a telephone line and realize hard copy at the transmission source and the reception destination. As a facsimile communication standard, for example, Super G3 (compliant with ITU-T, V.34) is generally used. In this standard, Lab colorimetric values under a D50 light source are used as a standard work color space for transmission and reception. Therefore, in order to correctly perform color matching with a facsimile, it is necessary that the D50 can be used as a work color space between devices that transmit and receive.

  The present invention has been made in view of the above-described conventional example, and an image processing apparatus and an image processing method capable of performing image processing so that even if a printed matter obtained by copying an original image is viewed with an observation light source different from that of the original image, the same color is obtained. The purpose is to provide.

  In order to achieve the above object, an image processing apparatus of the present invention has the following configuration.

  That is, an image processing apparatus that prints an image on a recording medium by an output device based on image data obtained by reading an original image by an input device, the device color information depending on the input device represented by the image data Is converted into device-independent color information representing the color when the original image is observed with the first observation light source, and the device non-obtained by the first conversion unit The printed matter obtained by printing the image on the recording medium with the dependent color information has the same color as the original image when observed with a second observation light source different from the first observation light source. Correction means for performing metamerism correction processing on the device, and device-independent color information corrected by the correction means as device color information dependent on the output device And having a second conversion means for conversion, and output means for outputting a device color information that depends on the output device in order to obtain the printed matter on the output device.

  According to another invention, there is provided an image processing method of an image processing apparatus for printing an image on a recording medium by an output device based on image data obtained by reading an original image by an input device, which is represented by the image data. A first conversion step of converting device color information dependent on the input device into device-independent color information representing a color when the original image is observed with a first observation light source; When the printed matter obtained by printing the image on the recording medium is observed with a second observation light source different from the first observation light source, on the device-independent color information obtained in the conversion step 1 A correction step for performing metamerism correction processing so as to have the same color as the original image, and device-independent color information corrected in the correction step, And a second conversion step for converting the device color information depending on a device, and an output step for outputting the device color information depending on the output device to the output device to obtain the printed matter. A processing method is provided.

  According to still another invention, a program for causing a computer to execute each step of the above method is provided.

  Therefore, according to the present invention, for example, image processing with reduced metamerism is performed so that even if the original image is viewed with the second observation light source, for example, the printed material obtained by copying the original image, and the original image. be able to.

  For example, when a photograph is a document image, the photograph observed with a light source different from D50 such as F10 and a printed material that is a copy of the document image can have the same color.

  Hereinafter, preferred embodiments of the present invention will be described more specifically and in detail with reference to the accompanying drawings. In addition, the same code | symbol is attached | subjected to the already demonstrated part and duplication description is abbreviate | omitted.

  In this specification, “recording” (sometimes referred to as “printing”) is not limited to the case of forming significant information such as characters and graphics, but may be significant. Furthermore, it also represents a case where an image, a pattern, a pattern, or the like is widely formed on a recording medium or a medium is processed regardless of whether or not it is manifested so that a human can perceive it visually.

  “Recording medium” refers not only to paper used in general recording apparatuses but also widely to cloth, plastic film, metal plate, glass, ceramics, wood, leather, and the like that can accept ink. Shall.

  Further, “ink” (sometimes referred to as “liquid”) should be interpreted widely as in the definition of “recording (printing)”. Therefore, by being applied on the recording medium, it is used for formation of images, patterns, patterns, etc., processing of the recording medium, or ink processing (for example, solidification or insolubilization of the colorant in the ink applied to the recording medium). It shall represent a liquid that can be made.

  FIG. 1 is a schematic perspective view of a multi-function printer apparatus (hereinafter referred to as MFP apparatus) that is a typical embodiment of the present invention.

  The MFP apparatus 1 has a function as a printer that receives and prints data from a host computer (PC), and a function as a scanner that outputs image data obtained by reading a document to the PC. Further, the MFP apparatus 1 has a copy function for printing an image read by a scanner with a printer, and image data stored in a storage medium such as a memory card or image data from a digital camera as functions that operate alone. It has a function to input and print.

  As shown in FIG. 1, the MFP apparatus 1 includes a reading unit 34 such as a flat bed scanner, a recording unit 33 using a printer engine according to an inkjet recording method, an operation panel unit 35 including a display panel 39, various key switches 35, and the like. Has been. The recording unit 33 may be a printer engine that conforms to an electrophotographic system.

  Further, a USB port (not shown) for communicating with the PC is provided on the back of the MFP apparatus 1. In addition, a card slot (card interface) 42 into which various memory cards are inserted and a camera port (camera interface) 43 for data communication with the digital camera are provided on the front surface of the MFP apparatus 1. On the other hand, an auto document feeder (hereinafter referred to as ADF) 31 for automatically setting a document on the document table is provided on the upper surface of the MFP apparatus 1.

  1A shows a state where the ADF 31 is closed, and FIG. 1B shows a state where the ADF is lifted and the reading unit 34 can be seen.

  FIG. 2 is a block diagram showing a control configuration of the MFP apparatus 1.

  In FIG. 2, the same components as those shown in FIG. 1 are denoted by the same reference numerals.

  In FIG. 2, the CPU 11 controls various functions provided in the MFP apparatus 1 and executes an image processing program stored in the ROM 16 in accordance with user operations and instructions on the operation panel unit 35.

  A reading unit 34 including a CCD reads an original image and outputs analog luminance data of red (R), green (G), and blue (B) colors. Note that the reading unit 14 may include a contact image sensor (CIS) instead of the CCD. In addition, a plurality of sheet-like document images can be read continuously using the ADF 31 shown in FIG.

  Also, image data captured by, for example, a digital still camera (hereinafter referred to as DSC) via the card interface 42 and recorded on a memory card or the like is read according to a predetermined operation on the operation panel unit 35. The color space of the image data read via the card interface 42 is changed from the DSC color space (for example, YCbCr) to the standard RGB color space (for example, NTSC-RGB) by the image processing unit 12 if necessary. Or sRGB). Also, based on the header information of the image data, the read image data is subjected to various processes necessary for the application, such as resolution conversion to the effective number of pixels, as necessary.

  Further, the camera interface 43 is used for directly connecting to the DSC via a predetermined cable or the like to read image data.

  The image processing unit 12 performs image processing such as image analysis, calculation of conversion characteristics, conversion from a luminance signal (RGB) to a density signal (CMYK), image processing such as scaling, gamma conversion, and error diffusion described below, Data obtained thereby is stored in the RAM 17. When the correction data stored in the RAM 17 reaches a predetermined amount necessary for recording by the recording unit 33, the recording operation by the recording unit 13 is executed.

  The NVRAM 18 is a non-volatile memory composed of battery-backed SRAM, EEPROM, FeRAM, or the like, and stores data unique to the image processing apparatus.

  The operation panel unit 35 is provided with keys for performing various instructions. Keys include image data stored in the storage medium, a photo direct print start key for starting recording, a key for printing a document image, a document image reading key, and copying during monochrome / color copying A start key is included. Furthermore, a mode key for designating a mode such as copy resolution and image quality, a stop key for stopping a copy operation, a numeric keypad for entering the number of copies, a registration key, and the like are also included.

  The CPU 11 detects the pressed state of these keys and controls each part according to the state.

  The display panel 39 includes a dot matrix type LCD and an LCD driver, and displays various types of information based on the control of the CPU 11. In addition, thumbnails of the image data recorded on the storage medium are displayed.

  The recording unit 33 is configured by an inkjet recording head, a general-purpose IC, a head scanning mechanism, and the like, and reads the recording data stored in the RAM 17 under the control of the CPU 11 and prints it out as a hard copy.

  The drive unit 21 controls a stepping motor such as a stepping motor for driving the paper supply / discharge roller, a gear for transmitting the driving force of the stepping motor, and the stepping motor in the operations of the reading unit 34 and the recording unit 33 described above. It consists of a driver circuit.

  The sensor unit 20 includes a recording sheet width sensor, a recording sheet presence sensor, a document width sensor, a document presence sensor, a recording medium detection sensor, and the like. The CPU 11 detects the state of the original and the recording paper based on information obtained from these sensors.

  The PC interface 24 is an interface between the PC and the MFP apparatus 1. The MFP apparatus 1 performs a printing operation based on image data transmitted from the PC via the PC interface 24, a scan of a document image according to an instruction from the PC, and a transfer operation of the read image data to the PC.

  During the copying operation, the image data obtained by reading the document image by the reading unit 34 is processed inside the MFP apparatus 1 and printed out by the recording unit 33. When the user instructs the operation panel unit 35 to perform a copying operation, the reading unit 14 reads a document placed on the document table. The read data is sent to the image processing unit 12, subjected to image processing to be described later, and then sent to the recording unit 33 for print output.

  The image processing unit is realized by a dedicated processor such as an ASIC, a DSP (digital signal processor), or a processor that executes an image processing program.

  Next, image processing executed during the copying operation in the MFP apparatus 1 having the above configuration will be described.

  FIG. 3 is a flowchart showing image processing executed at the time of copying.

  Hereinafter, description will be given for each step, but details of processing not directly related to the present invention will be omitted.

  In step S501, the image data obtained by reading the document image by the reading unit 34 and subjected to A / D conversion is subjected to shading correction for correcting variations in the image sensor.

  Next, in step S502, color conversion of the input device is executed (first conversion). As a result, device-specific image data (device color information) is converted into standard color space regions such as sRGB defined by IEC and Adobe (registered trademark) RGB proposed by Adobe Systems. Is done. Note that IEC is an abbreviation for International Electrotechnical Commission. Examples of the conversion method include a calculation method using a 3 × 3 or 3 × 9 matrix, a lookup table method in which a table describing conversion rules is referenced and determined based on the table. In this embodiment, description will be made using Adobe (registered trademark) RGB as a standard color space.

  In step S503, correction / processing is performed on the color-converted image data. The processing includes edge enhancement processing for correcting blur caused by reading a document image, character processing processing for improving character readability, and processing for removing show-through caused by reading by light irradiation. The processing that characterizes the present invention is desirably executed at the end of step S503 or after step S504 described below.

  In step S504, enlargement / reduction processing is executed, and conversion to a desired magnification is performed, for example, when zooming is designated by the user, or by allocation copying in which two originals are assigned to one sheet of paper. As a conversion method, methods such as bicubic and nearest neighbor are common.

  In step S505, output device conversion for converting data in the standard color space into image data unique to the output device is executed (second conversion). This conversion will be described later.

  In step S506, color separation processing is performed from image data unique to the output device to color component data corresponding to ink used in the recording unit 33 using a printer engine such as cyan, magenta, yellow, black, or the like that uses an ink jet method. . In this conversion, the same processing method as in step S502 is used.

  Finally, in step S507, quantization processing for converting each color component data subjected to color separation into the number of recordable levels is performed. For example, if data is expressed by binary values of whether or not ink is ejected to dots, binarization processing may be executed in a quantization method such as error diffusion. As a result, the image data has a data format that can be recorded by the printer engine, and a recording operation is executed based on the data format to form an image.

  Next, the color conversion in step S505 will be described in detail.

  In this embodiment, the output profile is defined in a look-up table format, and its name is called an output color conversion table.

  The output color conversion table associates image data in the printer color gamut with color signals in the Adobe (registered trademark) RGB color space in the standard color space. Specifically, the Adobe (registered trademark) RGB color space is discretely divided by grid points, and a color signal in the printer color gamut is associated with each grid point.

  FIG. 4 is a diagram showing the Adobe (registered trademark) RGB color space, which is a standard color space, and the color gamut of the printer engine according to the ink jet system in the CIE-L * a * b * color system. Hereinafter, it is assumed that all the color spaces mentioned in this embodiment are handled in the CIE-L * a * b * color system.

  In FIG. 4, reference numeral 601 represents an Adobe (registered trademark) RGB color space, and reference numeral 606 represents a color gamut of a printer engine according to an ink jet system.

  The present invention is not particularly limited to the CIE-L * a * b * color system, and the present invention can be realized if the color space is similar to the L * u * v * color space. It goes without saying that it can be done.

  As can be seen from FIG. 4, the Adobe® RGB color space and the printer color gamut are different. Therefore, when creating the color conversion table, a “gamut compression” technique for compressing the color gamut of the standard color space into the printer color gamut is used.

  The gamut compression method described here provides a non-compressed area in the printer color gamut for color reproduction that matches the color of the standard color space colorimetrically, and other colors in the standard color space are displayed in the non-compressed area. Compresses to an external printer color gamut. When this gamut compression method is used, color reproduction that matches the color of the standard color space in the non-compressed area can be realized, and gradation can be held outside the non-compressed area. For example, even when the printing media at the time of copying differ in color gamut shape, such as photographic paper and matte paper, the same color reproduction can be realized between the two.

  FIG. 5 is a diagram for explaining an example of the gamut compression method according to this embodiment.

  In FIG. 5, a color space 701 and a color space 702 are obtained by projecting an Adobe (registered trademark) RGB color space and a printer color gamut onto the L * a * plane. A color space 703 represents an uncompressed region in which color reproduction in which colors in the Adobe (registered trademark) RGB color space are colorimetrically matched is performed. The non-compressed area has a shape similar to the printer color gamut and a size of 80%. Point O represents a compression convergence point. Points 704 and 708 represent grid points in the Adobe (registered trademark) RGB color space.

  The gamut compression process is executed as follows.

  First, it is determined whether or not a grid point in the Adobe (registered trademark) RGB color space is located in an uncompressed region. The color gamut inside / outside determination process is performed as follows.

  First, the length of a vector (hereinafter referred to as a source vector) connecting a point to be determined whether or not to belong to a certain color gamut and a compression convergence point set inside the color gamut is calculated.

  Further, the distance from the compression convergence point to the intersection of the vector (hereinafter referred to as the color gamut vector) from the compression convergence point to the determination target point is obtained, and the lengths of the source vector and the color gamut vector are compared.

  Here, when the length of the source vector is larger than the length of the color gamut vector, it is determined that the determination target point is out of the color gamut, and when it is small, it is within the color gamut.

  As a result of such color gamut inside / outside determination processing, it is determined that the point 708 shown in FIG. 5 is located in the non-compressed region. In that case, the compression process is not performed, and the same value as the Adobe (registered trademark) RGB value is held.

  On the other hand, the point 704 shown in FIG. 5 is determined not to be a color in the uncompressed region.

  Therefore, the gamut compression process is performed as follows.

  Since the point 704 is a color outside the non-compressed area, it is gamut-compressed into the printer color gamut outside the non-compressed area. First, the distance X between the point 704 and the point O (compression convergence point) is calculated. Further, a point 705 where the straight line connecting the point O and the point 704 intersects the outline of the Adobe (registered trademark) RGB color space, a point 706 where the outermost outline of the printer color gamut intersects, and a point 707 where the outline of the uncompressed area intersects are searched for, The distance is calculated. The distances from the point O are denoted as T, D, and F, respectively.

Next, based on the relationship between the compression convergence point O and the above-described distance, the point 704 is compressed into the printer color gamut. The point after compression is linearly compressed to a distance that can be calculated by the following compression function (1) on a straight line connecting point O and point 704.
X ′ = {(D−F) (X−F) / (T−F)} + F (1)
Note that the compression function does not need to be linear, and a multi-order function that collapses the gradation as it is located outside the color gamut or a similar function may be used.

  In this embodiment, the size of the uncompressed area is about 80% of the printer color gamut, but the present invention is not limited to this. For example, when the size is set to 100%, it is possible to implement a gamut compression method that emphasizes colorimetric consistency in the printer color gamut and crushes colors outside the color gamut.

  In this embodiment, the Adobe (registered trademark) RGB color space is used as the standard color space, but other color space definitions may be used.

  Further, in this embodiment, F10, which is a three-wavelength fluorescent lamp light source, is used as a correction light source for which D50 is actually color-matched as a standard light source used in existing image processing, FAX transmission / reception, and the like. A combination of light sources may be used.

  In addition, the light source that is actually desired to be color-matched may not be a single light source. For example, a virtual correction light source that is the middle of the appearance of the F10 and D50 light sources may be assumed. At this time, as a method for obtaining the colorimetric value of the virtual correction light source, for example, the colorimetric value obtained by simulating the state in which the light sources of the plurality of light sources are summed and the light sources are irradiating simultaneously can be obtained. It ’s fine.

  Moreover, what obtained the colorimetric value in the emission spectrum of each light source, and took the average of them, and took the middle of the situation where each of the plurality of light sources is used alone may be used. At this time, if an average of the characteristics of the light wavelength itself is taken, for example, a colorimetric value (directly connected to the wavelength characteristics) such as XYZ may be used. On the other hand, if an average of perceptual characteristics of light is taken, for example, a colorimetric value (considering perceptual characteristics) such as Lab or CIECAM02 may be used.

  In addition to simply obtaining the average of a plurality of light sources, it may be obtained by weighting according to the arrangement status and usage frequency of the light sources used.

  Furthermore, when the color temperature of the white point differs between these light sources, the average of the colorimetric values obtained as a result of adaptation to an arbitrary white point using a known chromatic adaptation method (such as Bradford transformation) may be taken. . Alternatively, an average of colorimetric values in which white adaptation is considered in advance, such as JCh colorimetric values defined in CIECAM02, may be used.

  In the above description, a silver halide photograph is used as an input original, and a printed matter (hereinafter referred to as an inkjet printed matter) by an ink jet printer engine is assumed as an output printed matter. However, the present invention is not limited thereto. For example, a halftone dot photo or an ink-jet print may be used as the input original. Similarly, an electrophotographic or printed matter by a sublimation printer may be used as the output printed matter.

<Light source metamerism correction table creation part>
Here, a procedure for creating a correction table used in this embodiment will be described with reference to a flowchart.

  FIG. 6 is a flowchart showing correction table creation processing.

  First, in step S101, pair information of a colorimetric value and a spectral reflection distribution (Spectrum 1, Spectrum 2,...) With a D50 light source of an arbitrary representative color of a silver salt photograph is obtained. When obtaining, a spectrocolorimeter or the like may be used.

  FIG. 7 is a diagram showing the pair information to be created.

  Next, in step S102, based on the pair information obtained in step S101, when an arbitrary colorimetric value is given by the D50 light source as an input document, what spectral reflection distribution it has is determined. Create a table to predict. Any colorimetric value may be used, but in this embodiment, Adobe (registered trademark) RGB is used as the work color space, so that the colorimetric value at 17 × 17 × 17 grid points of Adobe (registered trademark) RGB is used.

  For the creation of the prediction table, a matrix obtained by using the least square method based on the pair information may be used, or a plurality of pair information in the vicinity of the lattice point may be searched and subjected to an interpolation calculation. Also, depending on the area, these may be used together with arbitrary weighting, and in areas where interpolation is possible (pair information around the grid points exists), the interpolation calculation result is emphasized and extrapolation is required (pair information around the grid points) In the area where there is no), the matrix calculation result may be used with emphasis.

  FIG. 8 is a diagram illustrating a prediction table to be created.

  In step S103, colorimetric values under the F10 light source are calculated from the spectral reflection distribution (Spectrum 1, Spectrum 2,...) At each point of the prediction table obtained in step S102. As a result, a correction table (color rendering prediction table) is generated that indicates what colorimetric value the color on the document having an arbitrary colorimetric value under the D50 light source will render under the F10 light source.

  FIG. 9 is a diagram showing a created color rendering prediction table.

  In step S104, as in step S101, pair information of a colorimetric value and a spectral reflection distribution with an F10 light source of an arbitrary representative color of a printed matter by a printer engine according to the ink jet method is obtained.

  Further, in step S105, an output color prediction table is created based on the pair information in step S104 as in step S102. In other words, when outputting colorimetric values of 17 × 17 × 17 grid points of Adobe (registered trademark) RGB under an F10 light source as an output product, a table for predicting what spectral reflection distribution it has is created. To do.

  In step S106, the colorimetric values under the D50 light source are calculated from the spectral reflection distribution (Spectrum A ′, Spectrum B ′,...) At each point in the table obtained in step S105, as in step S103.

  Finally, in step S107, the light source metamerism correction table is created by combining the tables created in steps S103 and S106.

  Here, the color rendering prediction table created in step S103 represents “how color rendering of a silver halide photograph having an arbitrary colorimetric value under a D50 light source performs under a F10 light source”. Further, the color rendering prediction table created in step S106 represents “how the color of the ink-jet printed matter having an arbitrary colorimetric value under the F10 light source is rendered under the D50 light source”.

  Therefore, when these tables are combined, the color of the printed material is selected when the color of the silver halide photograph having an arbitrary colorimetric value under the D50 light source is the same color under the F10 light source. Can create a table indicating what kind of colorimetric value will be under the D50 light source. Here, the same color means the same color.

  This table is used as a “light source metamerism correction table” in image processing described later.

<Using light source metamerism correction table>
Next, processing for applying image processing to the “light source metamerism correction table” created as described above will be described. This process is executed in step S503 in FIG.

  FIG. 10 is a flowchart in which detailed processing in step S503 is expanded. Note that the various image processes performed in steps S110 to S112 function effectively for the D50 colorimetric value of the original image.

  First, in step S110, the color of the background region is brought close to white with image data obtained by reading a document image and converted into data in a standard color space. For the determination of the background area, for example, a combination of lightness and saturation of the colorimetric values may be used. It should be noted that the background removal processing may be suppressed depending on the situation, and whether to execute the background removal may be determined by an instruction from the user, or may be determined in advance based on the feature amount of the document image.

  Next, in step S111, the color of the skin color area is corrected with the image data of the original image converted into the data in the standard color space. For example, a combination of brightness, hue, and saturation of colorimetric values may be used to determine the skin color area. Examples of the correction method include processing to a color preferable as a skin color, or correcting the brightness only in a locally darkened area, for example. The flesh color correction process may be inhibited depending on the situation, and whether or not to execute the flesh color correction process may be determined by an instruction from the user, or may be determined in advance from a feature amount of the document image.

  In step S112, the color fading occurring in the original image is corrected. For the fading determination / correction, for example, a known technique such as detecting / correcting a difference in dynamic range in each of the RGB channels may be used. The execution of this process may be suppressed depending on the situation, and whether or not to execute the process may be determined by an instruction from the user, or may be determined in advance based on the feature amount of the document image.

  Finally, in step S113, correction processing is performed by applying the “light source metamerism correction table” created by the above-described procedure to the image data of the original image converted into data in the standard color space. The execution of this process may be suppressed depending on the situation, and whether to execute the process depends on an instruction from the user. For example, when “office mode” which is an environment under the F10 light source is selected, the process is executed (ON), and “print standard environment mode” which is an environment under the D50 light source is selected. At that time, the execution of the processing may be suppressed (OFF). Alternatively, it may be set to ON during a normal copy operation, and set to OFF when image data is transmitted to another apparatus by FAX transmission.

  Therefore, according to this embodiment, by performing the image processing as described above, a silver halide photographic original that has been subjected to skin color correction and fading correction under the D50 light source is rendered the same color as the silver salt photographic original under the F10 light source. An ink-jet printed material is obtained. Thereby, the color of the printed material seen in the user environment becomes more plausible.

  In the embodiment described above, the following example is taken for an original image of a silver salt photograph after correction in which skin color correction and fading correction are performed on the silver salt photograph under a D50 light source (first observation light source). It was. That is, when an F10 light source is viewed as an observation light source (second observation light source) assuming that an inkjet printed material obtained by copying the original image and a corrected silver halide photograph actually exist, It is an example which compares. However, the present invention is not limited to these light sources as observation light sources. For example, a light source other than F10 may be used as the second observation light source, and a D65 light source may be used as the first observation light source.

  Specifically, the second observation light source includes ordinary fluorescent light sources such as F2 and F6, high color rendering fluorescent light sources such as F7 and F8, and three-wavelength fluorescent light sources such as F11. In addition, among these light sources, an observation light source in which a plurality of light sources are mixed may be used. Further, when mixing a plurality of light sources, the spectral distribution characteristics of the plurality of light sources may be mixed, or device-independent color information obtained by each of the plurality of light sources may be mixed. . Further, as the second observation light source, an observation light source obtained by mixing any of the plurality of light sources and the D50 or D65 light source may be used. Furthermore, as the second observation light source, a mixed light source of a plurality of light sources selected from among an F-series light source, a D-series light source, and another standard light source, which are standard light sources, may be used.

  As described above, when an environment in which an average value of colorimetric values of a plurality of light sources is used as a colorimetric value, even when a copy is observed as described above using any one of the plurality of light sources as an observation light source, the plurality of light sources. A printed copy with no significant difference in color observed under each of the above is obtained.

  In addition, it is possible to easily provide a printed matter by a copying operation under a standard light source such as D50, and it can be used for, for example, FAX transmission / reception.

  Furthermore, it is not always necessary to assume a FAX operation. For example, if the existing image processing is performed in the sRGB color space (the work color space is sRGB), the white point of sRGB is 6500K, so D65 may be used as the standard light source.

  Further, the control program for the recording apparatus according to the present invention includes a host apparatus (PC) and a recording apparatus connected to the apparatus from a storage medium such as a CD-ROM or a flexible disk, or via a network such as e-mail or personal computer communication. Etc. and may be executed. For example, this program can be stored in the memory of a recording device or the HDD of a PC. The present invention is realized by the CPU of the recording apparatus or the CPU of the host apparatus executing the program.

  In addition, as an embodiment of the ink jet recording apparatus of the present invention, in addition to those used as an image output apparatus of information processing equipment such as a computer, a copying apparatus combined with a reader or the like, and further a facsimile apparatus having a transmission / reception function. It may be one taken.

1 is a schematic perspective view of a multifunction printer apparatus (MFP apparatus) that is a typical embodiment of the present invention. 2 is a block diagram showing a control configuration of the MFP apparatus 1. FIG. It is a flowchart which shows the image processing performed at the time of copying. FIG. 4 is a diagram illustrating an Adobe (registered trademark) RGB color space that is a standard color space and a color gamut of a printer engine that conforms to an inkjet method in a CIE-L * a * b * color system. It is a figure explaining the example of the gamut compression method. It is a flowchart which shows the preparation process of a correction table. It is a figure showing the pair information created. It is a figure showing the prediction table produced. It is a figure showing the color rendering prediction table produced. It is the flowchart which expanded the detailed process of step S503. It is a block diagram which shows the structure outline | summary of a color management system (CMS).

Explanation of symbols

1 MFP device 11 CPU
12 Image processor 16 ROM
17 RAM
18 NVRAM
20 Sensor unit 21 Drive unit 24 PC interface 31 Auto document feeder (ADF)
33 Recording unit 34 Reading unit 35 Operation panel unit 39 Display panel 42 Card slot (card interface)
43 Camera port (camera interface)

Claims (12)

An image processing apparatus for printing an image on a recording medium by an output device based on image data obtained by reading a document image by an input device,
A device color information which is represented by the image data and which is dependent on the input device is converted into device-independent color information which represents a color when the original image is observed with a first observation light source. Conversion means;
The printed matter obtained by printing the image on the recording medium with the device-independent color information obtained by the first conversion means was observed with a second observation light source different from the first observation light source. Correction means for performing metamerism correction processing so that the same color as the original image at the time,
Second conversion means for converting device-independent color information corrected by the correction means into device color information dependent on the output device;
An image processing apparatus comprising: output means for outputting device color information dependent on the output device to the output device in order to obtain the printed matter.   The image processing apparatus according to claim 1, wherein the first observation light source and the second observation light source have different spectral distribution characteristics. The first observation light source and the second observation light source are standard light sources,
The image processing apparatus according to claim 2, wherein the first observation light source is D50 or D65. The first observation light source and the second observation light source are standard light sources,
The second observation light source is one of F10 and F11 which are three-wavelength fluorescent lamp light sources, F2 and F6 which are ordinary fluorescent lamp light sources, and F7 and F8 which are high color rendering fluorescent lamp light sources. The image processing apparatus according to claim 2. The first observation light source and the second observation light source are standard light sources,
The image processing apparatus according to claim 2, wherein the second observation light source is a light source obtained by mixing a plurality of standard light sources.   The image processing apparatus according to claim 1, wherein the second observation light source is one light source or a mixture of a plurality of light sources.   The image processing apparatus according to claim 1, further comprising instruction means for instructing whether to execute the correction process. The input device is a scanner;
The output device is a printer according to an inkjet method;
The image processing apparatus according to claim 1, wherein the image processing apparatus is a multi-function printer apparatus. The original image includes a silver halide photograph,
The image processing apparatus according to claim 8, wherein the printed material is an inkjet printed material.   The correction processing is a relationship between a color obtained when the original image is observed with the first observation light source and a color obtained when the printed matter is observed with the second observation light source. 2. The image processing apparatus according to claim 1, wherein the device-independent color information converted by the first conversion unit is corrected with reference to a table indicating the color difference. An image processing method of an image processing apparatus for printing an image on a recording medium by an output device based on image data obtained by reading a document image by an input device,
A device color information which is represented by the image data and which is dependent on the input device is converted into device-independent color information which represents a color when the original image is observed with a first observation light source. Conversion process;
The printed matter obtained by printing the image on the recording medium with the device-independent color information obtained in the first conversion step was observed with a second observation light source different from the first observation light source. A correction step of performing metamerism correction processing so that the original image has the same color as the original image,
A second conversion step of converting the device-independent color information corrected in the correction step into device color information dependent on the output device;
And an output step of outputting device color information depending on the output device to the output device in order to obtain the printed matter.   The program which makes a computer perform each process of the image processing method of Claim 11.

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