JP2005064801A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which solves a hue problem based on vision which may occur even after LUT adjustment using a test chart image. <P>SOLUTION: The image forming apparatus is provided with a first calibrating arithmetic part 41 and a second calibrating arithmetic part 42. The first calibrating arithmetic part 41 adjusts an image data conversion function by comparing measured pixel colorant values of the test chart image outputted by using prescribed test chart image data with their target pixel colorant values. The second calibrating arithmetic part 42 calculates the amount of correction of the image data conversion function in accordance with pixel colorant values of test image data corresponding to a test image determined to be most suitable, out of a plurality of test images which are formed on a recording material with a prescribed layout on the basis of a plurality kinds of test image data obtained by changing pixel colorant values of fundamental test image data converted by the adjusted image data conversion function. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus that forms and outputs an image on a recording material based on image data.

  As a typical example of such an image forming apparatus, image data is obtained from an image source such as a photographic film forming an image taken by an optical camera or a semiconductor memory storing an image taken by a digital camera, and this image data is used. There are devices that output color photographic prints. For example, to create a color photographic print from a negative film, a scanner is used as an image input device, and a photographed image based on the obtained image data is loaded on a photographic photosensitive material such as photographic paper with a digital exposure head as an image output device. It is used for printing exposure and subjected to development processing and the like. At that time, the exposure head and the developing tank as the image input device and the image output device have unique characteristics. Therefore, in order to realize appropriate color reproduction, the image data input through the image input device is used. Pixel value (gradation) conversion function that adjusts the pixel dye value of the image data between the image input device and the image output device so that the target dye value of the image and the dye value of the image output by the image output device match as much as possible Will intervene.

Such a conversion function is generally performed using a look-up table (hereinafter simply referred to as an LUT) that functions as a conversion function. Such an LUT is created or adjusted in the following steps. ;
First, a test chart is output using the test chart image data. The created color chart includes a plurality of patches having different pixel dye values (density values for each dye such as RBG and CMY), and measures the density of each of the patches. The measured density value is compared with the target density value set for each patch, and a conversion function, that is, an LUT for each dye is created to compensate for these differences. By applying this conversion to the input pixel data, appropriate color reproduction is possible (for example, see Patent Document 1).

  As described above, many techniques for creating / adjusting an LUT using a test chart are known. For example, a gray-based hue in which each patch value is set to be approximately equal to each color value of cyan, magenta, and yellow. These patches were obtained by measuring the density of each patch, that is, the density of each of the cyan, magenta, and yellow dyes constituting the gray hue using a test chart in which the gray densities of the patches were different from each other. There is also a technique for adjusting the LUT using the density measurement value (see, for example, Patent Document 2).

  In addition, in order to obtain an optimal image output by changing image processing parameters for each shot image frame, a predetermined area in a photographic image represented by digital image data is set as a test print area and a test print A plurality of image processing parameters to be changed in the image processing conditions and their shake amounts are set, and the set image processing parameters are changed according to the set shake amounts for the digital image data in the test print area. The image processing is performed under the image processing conditions to create a plurality of test print image data, and the test print image data is recorded on a predetermined recording medium with a predetermined layout to create a test print. There is also a technology that uses the image processing parameters of a test print image that is considered to be used during actual printing. (E.g., see Patent Document 3.).

Japanese Patent Laid-Open No. 2003-116017 (paragraph numbers 0002-0005, FIG. 7)

JP 2003-094732 A (paragraph number 0033-0034, FIG. 1, FIG. 5)

JP 2002-209090 A (paragraph numbers 0037-0042, FIGS. 4 and 6)

The image forming apparatus has been calibrated by adjusting the LUT using the test chart image in order to solve the problem of color reproducibility due to the unique characteristics of the image input device and the image output device, but it is used for such calibration work. However, depending on the color meter or densitometer error or the same measured pixel dye value depending on the type of recording material, there is a problem of giving a different impression to the human eye.
In view of the above circumstances, an object of the present invention is to provide an image forming apparatus that solves a visual color tone problem that may occur even after adjustment of an LUT using a test chart image.

  One of the image forming apparatuses according to the present invention for solving the above-mentioned problems is to compare the measured pixel dye value of a test chart image output using predetermined test chart image data with its target pixel dye value. A first calibration calculation unit that adjusts the data conversion function, and a plurality of types of test image data obtained by changing pixel dye values of the basic test image data converted by the adjusted image data conversion function A correction amount for the image data conversion function is calculated from a pixel dye value of test image data corresponding to a test image regarded as optimal among a plurality of test images formed on a recording material with a predetermined layout based on 2 calibration calculation unit.

  In this image forming apparatus, the calibration operation of the apparatus is not completed by adjusting the image data conversion function based on the measured pixel dye value and the target pixel dye value of the test chart image in the conventional manner by the first calibration calculation unit. After the adjustment of the data conversion function, a plurality of test images obtained by changing the pixel dye value of the basic test image data having a predetermined pixel dye value using the adjusted image data conversion function The data is created, the pixel dye value of each test image data is converted by the adjusted image data conversion function, and a plurality of test images formed on the recording material in a predetermined layout are output. The most suitable image is selected by human vision. Next, the second calibration calculation unit calculates a correction amount for the image data conversion function from the pixel pigment value of the test image data corresponding to the test image regarded as optimal. By combining this correction amount and the adjusted image data conversion function, a print output having color reproducibility that is satisfactory even for human eyes is realized. Note that the image data conversion function here is generally implemented on a computer in the form of a look-up table (= LUT), and the implementation is not limited in the present invention. A pixel value conversion means implemented in software and / or hardware for converting image data defined in the input three-dimensional color space into image data defined in the output three-dimensional color space; Should be understood.

  Another one of the image forming apparatuses according to the present invention for solving the above problems is to compare a measured pixel dye value of a test chart image output using predetermined test chart image data with its target pixel dye value. A first calibration calculation unit that adjusts the image data conversion function by a parameter change unit that generates a plurality of auxiliary image data conversion functions by assigning a plurality of different values to the parameters of the adjusted image data conversion function; A plurality of test images formed on a recording material in a predetermined layout based on a plurality of test image data obtained by applying each of the auxiliary image data conversion functions to basic test image data having a predetermined pixel dye value From the parameter values of the auxiliary image data conversion function corresponding to the test image deemed optimal among the test images of And a second calibration calculation unit for calculating a correction amount for the image data conversion function.

  Also in this image forming apparatus, the calibration work of the apparatus is not completed by adjusting the image data conversion function based on the measured pixel dye value and the target pixel dye value of the test chart image as in the conventional case by the first calibration calculation unit. After the adjustment of the data conversion function, the parameter changing unit further generates a plurality of auxiliary image data conversion functions by assigning a plurality of different values to the parameters of the adjusted image data conversion function, and a predetermined pixel pigment value A plurality of test images formed on a recording material in a predetermined layout based on a plurality of test image data obtained by applying each of the auxiliary image data conversion functions to basic test image data having The optimum one of the plurality of test images is selected by human vision. Next, the second calibration calculation unit calculates a correction amount for the image data conversion function from the parameter value of the image data conversion function corresponding to the test image regarded as optimal. By combining this correction amount and the adjusted image data conversion function, this image forming apparatus can also realize a print output with color reproducibility that is satisfactory for human eyes.

  In a preferred embodiment of the present invention, the basic test image data is a gray system in which the respective pigment values of cyan, magenta and yellow (or R: red, G: green, B: blue), which are pixel components, are substantially the same. Is set to This is because, in many recording materials, especially photosensitive materials such as photographic paper, the difference in gray balance among the types is most conspicuous. Therefore, using gray, especially neutral gray, as a basic test image provides significant advantages. is there.

Further, in order to facilitate the determination of the optimum image by human eyes, in a preferred embodiment of the present invention, the plurality of test images are laid out on a single recording medium so as to be adjacent to each other in a strip shape and output. Is adopted.
Other features and advantages of the present invention will become apparent from the following description of embodiments using the drawings.

  FIG. 1 is an external view showing a photographic printing apparatus as an example of an image forming apparatus according to the present invention. This photographic printing apparatus is a printing station 1B as a photographic printer that performs exposure processing and development processing on photographic paper P. FIG. And an operation station 1A that processes photographed image data captured from an image input device such as a developed photographic film 2a or a digital camera memory card 2b to generate and transfer print data used in the print station 1B. It is configured.

  This photo printing apparatus is also called a digital minilab. As can be understood from FIG. 2, the printing station 1B pulls out the roll-shaped printing paper P stored in the two printing paper magazines 11 and prints it with the sheet cutter 12. The back print unit 13 prints print processing information such as color correction information and frame number on the back side of the photographic paper P, and the print exposure unit 14 cuts the print paper P into the size. A photographed image is exposed on the surface of the photographic paper P, and the exposed photographic paper P is sent to a processing tank unit 15 having a plurality of development processing tanks for development processing. After drying, the photographic paper P, that is, the photographic prints P, sent to the sorter 17 from the transverse feed conveyor 16 at the upper part of the apparatus is collected in a plurality of trays 17a of the sorter 17 in a state of being sorted in order units (FIG. 1). reference). Note that the test print TP, which will be described in detail later, is also developed in the post-processing tank unit 15 after being exposed to the appropriately cut photographic paper P by the print exposure unit 14 in the same manner as the photographic print P. 16 is output.

  A photographic paper transport mechanism 18 is laid to transport the photographic paper P at a transport speed in accordance with various processes for the photographic paper P described above. The photographic paper transport mechanism 18 is composed of a plurality of nipping and transporting roller pairs including a chucker type photographic paper transport unit 18a disposed before and after the print exposure unit 14 in the photographic paper transport direction.

  The print exposure unit 14 applies R (red), G (green), and B (blue) to the printing paper P conveyed in the sub-scanning direction based on print data from the operation station 1A along the main scanning direction. A line exposure head for irradiating laser beams of the three primary colors (1) is provided. The processing tank unit 15 includes a color developing tank 15a for storing a color developing processing liquid, a bleach-fixing tank 15b for storing a bleach-fixing processing liquid, and a stabilizing tank 15c for storing a stable processing liquid.

  A film scanner 20 for acquiring photographed image data from photographed image frames of the photographic film 2a is disposed at the upper position of the desk-like console of the operation station 1A, and is used as an image recording medium 2b mounted on a digital camera or the like. A media reader 21 that acquires photographed image data from various semiconductor memories, CD-Rs, and the like is incorporated in a general-purpose personal computer that functions as the controller 3 of the photographic printing apparatus. The general-purpose personal computer further includes a monitor 23 for displaying various information, a keyboard 24 and a mouse 25 used as an operation input unit used for various settings and adjustments, and various colors of the test chart image formed on the test print TP. A colorimeter that reads density or side color values is also connected.

  The controller 3 includes a CPU as a core member, and a functional unit for performing various processes on input data is implemented by hardware and / or software. The functional unit particularly related to the present invention. As shown in FIG. 3, working for temporarily storing raw image data of a shot frame image transferred from a film scanner 20 or a media reader 21 as an image input device for various processes. A memory 30, an operation screen generating unit 31 for generating various operation screens, various image data constituting the operation screen and image data of other display items are taken into a video memory, and images developed in the video memory are video-converted by a video controller. The video control unit 32 that converts the signal and sends it to the monitor 23 and the working memory 30 are displayed. To optimize the image data, such as color correction, filtering (blurring, sharpness, etc.) and trimming, and the characteristics of the image input device and image output device used in this photo printing device An image processing unit 33 that performs image data conversion processing for converting image data, and an LUT that stores conversion functions used in the image data conversion processing performed by the image processing unit 33 in the form of a conversion function or a matrix table Unit 34, a LUT calibration unit 40 that adjusts and manages the contents of the LUT unit 34, and final image data processed by the image processing unit 33 is transferred as print image data to the print exposure unit 14 of the print station 1B. An example of the management unit 35 is given.

  In the present invention, the LUT unit 34 is conventionally performed in a photographic printing apparatus (see, for example, Japanese Patent Application Laid-Open Nos. 2002-209090 and 2003-94732), and a test print output using predetermined test chart image data. The first LUT 34a adjusted by comparing the measured pixel dye value (density value or colorimetric value of RGB or CMY color dye) detected by the colorimeter 26 of the test chart image in the TP with its target pixel dye value. A test image that is regarded as optimal among a plurality of output test images of a plurality of types of test image data obtained by further converting the test image data converted using the first LUT 34a with a plurality of types of auxiliary conversion patterns. Additional conversion functions (or conversion tables) from auxiliary conversion patterns corresponding to Directing, a first 2LUT34b is a feature of the present invention.

  The LUT calibration unit 40 includes a first calibration calculation unit 41 that performs adjustment management of the first LUT 34a by a conventional calibration operation, a second calibration calculation unit 42 that performs adjustment management of the second LUT 34b by an added calibration operation, and a conventional method. A calibration data storage unit 43 for storing test chart image data used for calibration work and test image data used for additional calibration work, and a plurality of types of test image data used as a reference in the additional calibration work A ring-around data generation unit 44 that converts and outputs a plurality of test image data based on the auxiliary conversion pattern is provided.

  Preferably, these test images are strip-shaped so that the operator can easily and accurately visually determine from the test images printed by a plurality of test image data converted and output by a plurality of types of auxiliary conversion patterns. The print management unit 35 lays out a plurality of test image data so as to be formed on one photographic paper P so as to be adjacent to each other, and transfers the test image data to the exposure print unit 14 as print data. The test print TP printed out in this way is called ring-around print.

Next, the setup using the test print TP in this photographic printing apparatus will be described with reference to FIG. 4 showing the function of the calibration work and FIG. 5 showing the flow of the calibration work.
Test chart image data is read from the calibration data storage unit 43 into the working memory 30 (# 11). The image processing unit 33 converts the pixel dye value of the test chart image data based on the conversion function defined by the first LUT 34a set as a reference value in consideration of the characteristics of the exposure print unit 14 as an image output device ( # 12). The converted test chart image data is transferred as print data to the print station 1B, and the exposure print unit 14 is driven to output a test chart print TP (# 13). Here, since an 18-step gray chart is used as the test chart image, an 18-step gray gradation (including white and black) is formed on the test chart print TP.

  The output test chart print TP is input to the colorimeter (density meter) 26, and the gray pixel dye value of each step, that is, the density value of each of R, G, and B colors is measured (# 14). When the measured density values are input to the controller 3 via the input interface, the target pixel dye value assigned to the test chart image data used by the first calibration calculation unit 41, that is, the target density value of each color, and The difference value is obtained by comparison (# 15). If the difference value is within the predetermined range, it is considered that the used first LUT 34a is accurately adjusted, and the calibration work (first calibration work) for the first LUT 34a is ended (# 16). If the difference value does not fall within the predetermined range, the first LUT 34a is readjusted using the difference value (# 17), and this first calibration operation is repeated until the difference value falls within the predetermined range. . Since the readjustment of the first LUT 34a is disclosed in detail in the above-mentioned publicly-known documents, detailed description thereof is omitted here.

  When the first calibration work is completed, the calibration work (second calibration work) for the second LUT 34b, which is a feature of the present invention, is performed. First, basic test image data stored in advance in the calibration data storage unit 43 is read into the working memory 30 (# 21). In this embodiment, the basic test image data is an intermediate gray in the 8-bit color image data, and the pixel pigment values are R value = 100, G value = 100, and B value = 100. A CMY color system may be used as the pixel value, and the pixel pigment value is a generic term for them. Gray is adopted as the basic test image data because the difference in gray balance is conspicuous as the color difference between the types of photographic paper P. The purpose of the second calibration work is to optimize this gray balance visually. It is because.

  The basic test image data having the pixel values described above is converted into image data suitable for the characteristics of the exposure print section 14 using the first LUT 34a (# 22). The ring-around data generation unit 44 generates a plurality of types of test image data as ring-around data from the converted basic test image data (# 23). As shown in FIG. 6, the ring-around data is generated by changing the pixel dye value with a predetermined swing amount on the basis of the basic test image data converted using the first LUT 34a. For example, the first ring-around data increases the R value only by 5 points, and the second ring-around data decreases the R value only by 5 points. Thereafter, a plurality of types of test image data are generated by similarly increasing / decreasing the G value and B value, or changing the combination of the increased R value, G value, and B value. Such pixel pigment value swing amounts and combinations of the changed R, G, and B values are set so that the difference in gray balance is most easily visually determined.

  Based on the generated plurality of test image data (ring-around data), each test image is formed on the photographic paper P in a layout that is strip-shaped and adjacent to each other, and is output as a ring-around print TP (# 24). ). When the operator determines an optimum test image among a plurality of test images belonging to the output ring-around print TP, the number of ring-around data corresponding to the test image is input through the keyboard 24. (# 25). Next, the second calibration calculation unit 42 determines the value of the second LUT 34b, that is, the first LUT 34a from the pixel pigment value of the test image data (ring around data) corresponding to the test image determined to be optimal or the amount of swing from the reference value. The correction amount (or correction function) for the image data conversion function is set or adjusted (# 26). This completes the second calibration operation.

  When the second calibration operation is completed, the photo printing apparatus is also optimally adjusted for gray balance based on visual judgment, so the printer profile creation routine is subsequently entered, and it consists of several hundred color patches. A color chart is printed out and color management adjustment of this photographic printing apparatus is performed (# 30). Since color management adjustment itself is a well-known technique, a detailed description thereof is omitted here.

Next, another embodiment of the second calibration operation described above will be described.
In this alternative embodiment, as described above, the ring-around data generation unit 44 changes the pixel dye value with a predetermined swing amount with reference to the basic test image data converted using the first LUT 34a. Instead of generating ring-around data, a parameter changing unit that generates a plurality of auxiliary image data conversion functions by changing a plurality of parameters of the image data conversion function as the first LUT 34a to a plurality of different values is provided. A schematic diagram for explaining such a plurality of auxiliary image data conversion functions is shown in FIG. For example, assuming that the image data conversion function is expressed by a cubic expression, different image data conversion functions, that is, a plurality of auxiliary image data conversion functions: f1 are obtained by changing the selected coefficient of the cubic expression. , F2, f3... Are created. When the auxiliary image data conversion function is created, a plurality of test image data (ring-around data) is obtained by applying each of the auxiliary image data conversion functions to the basic test image data, and based on this ring-around data Each test image is formed on the photographic printing paper P in a strip-like layout so as to be adjacent to each other, and is output as a ring around print TP. Even in this case, when the operator determines an optimum test image among the plurality of test images belonging to the output ring-around print TP, the number of the ring-around data corresponding to the test image is obtained through the keyboard 24. Instruction is input. Next, the second calibration calculation unit 42 calculates the correction amount (or correction function) for the value of the second LUT 34b from the parameter value of the auxiliary image data conversion function corresponding to the test image determined to be optimal, that is, the image data conversion function in the first LUT 34a. Is set or adjusted.

  Image forming devices that realize this characteristic color calibration function can be applied to color image forming devices that require accurate color management, such as color printing devices that reproduce color images and color copies, in addition to photographic printing devices. It is.

1 is an external view of a photographic printing apparatus as an example of an image forming apparatus of the present invention. Functional explanatory diagram of photo printing device Functional block diagram of controller Functional block diagram for calibration work Calibration work flow chart Explanatory drawing explaining image data for ring-around printing Schematic diagram explaining auxiliary image data conversion function

Explanation of symbols

3 Controller 14 Print exposure unit 24 Keyboard 26 Colorimeter (Density meter)
34a First LUT unit 34b Second LUT unit 33 Image processing unit 35 Print management unit 41 First calibration calculation unit 42 Second calibration calculation unit 43 Calibration data storage unit 44 Ring around generation unit TP Test print (test chart print, ring around print)

Claims (4)

An image forming apparatus that forms and outputs an image on a recording material based on image data,
A first calibration calculator that adjusts an image data conversion function by comparing a measured pixel dye value of a test chart image output using predetermined test chart image data with its target pixel dye value;
The basic test image data converted by the adjusted image data conversion function was formed on a recording material with a predetermined layout based on a plurality of types of test image data obtained by changing the pixel dye value. And a second calibration calculation unit that calculates a correction amount for the image data conversion function from a pixel dye value of test image data corresponding to a test image regarded as optimal among the plurality of test images. Image forming apparatus. An image forming apparatus that forms and outputs an image on a recording material based on image data,
A first calibration calculator that adjusts an image data conversion function by comparing a measured pixel dye value of a test chart image output using predetermined test chart image data with its target pixel dye value;
A parameter changing unit that generates a plurality of auxiliary image data conversion functions by assigning a plurality of different values to the parameters of the adjusted image data conversion function;
A plurality of test image data obtained by applying each of the auxiliary image data conversion functions to basic test image data having a predetermined pixel dye value, and a plurality of test images formed on a recording material in a predetermined layout An image comprising: a second calibration calculation unit that calculates a correction amount for the image data conversion function from a parameter value of the auxiliary image data conversion function corresponding to the test image regarded as optimum among the test images. Forming equipment.   The image forming apparatus according to claim 1, wherein the basic test image data is a gray system.   The image forming apparatus according to claim 1, wherein the plurality of test images are strip-shaped and are laid out and output on a single recording medium so as to be adjacent to each other.

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