JP2008147937A - Image processor and image processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a recording system capable of optimumly recording on recording media under different environments without degrading recording quality while maintaining a wide color reproduction range. <P>SOLUTION: Image processing is performed by selecting a table in which the amount of ink is set in accordance with environment in which recording is performed, according to a recording medium. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image processing apparatus and an image processing method.

  Recent recording apparatuses capable of color recording have a wide variety of uses, and recording on various types of recording media is possible. In addition to recording business documents on plain paper, recording natural images such as photographs on glossy paper, drawing documents on CAD with tracing paper, POP / flyers on coated paper, etc., CG / monochrome on art paper Art works such as photographs are also recorded.

  As described above, since the recording apparatus has various uses, it is expected to be used in various environments, and high-quality recording in a wide color reproduction range is required for various recording media under various environments. ing.

  On the other hand, various ideas have been conventionally made to keep the quality of an image output in a recording apparatus at a certain level. For example, in order to prevent the image from being affected by the environment at the time of recording as much as possible, the image forming apparatus is provided with means for detecting the environmental parameter, and the image is calculated by using the environmental parameter detected thereby. A method for setting formation conditions has been proposed (Patent Document 1). In addition, the optimum recording operation is performed according to the ambient temperature, humidity, etc. of the recording device, and when the recording operation is requested, the ambient environment conditions such as temperature and humidity are measured by the sensor in the recording device, and based on the result. There is a configuration in which recording is performed by selecting an optimum recording operation subroutine (Patent Document 2).

Japanese Patent Laid-Open No. 5-80626 JP-A-7-256876

  The amount of ink that can be received by the recording medium varies depending on the environmental conditions of the recording location. If the amount of ink applied to the recording medium is large, the color reproduction range can be widened.However, if the amount of ink applied exceeds the capacity of the recording medium, bleeding occurs and the recording quality is impaired, or the recording medium is wavy. The recording head may be rubbed with the recording head and damaged. Although it is possible to prevent bleeding and waviness of the recording medium by reducing the amount of ink used for recording, in that case, the color reproduction range becomes narrow.

  The above problems can be dealt with by changing the image processing parameter when creating the recording data. However, if there is no association between a series of image processing executed when creating recording data, there arises a problem that a color reproduction range in actual recording cannot be sufficiently realized. For example, even if an attempt is made to widen the color reproduction range by increasing the amount of ink applied in the color separation process, if the process for obtaining a sufficiently wide color reproduction area is not performed by the color matching process in the preceding stage, it is actually recorded. The color gamut of the image will not be as wide as intended.

  The present invention has been made from such a viewpoint, and image processing that enables optimum recording in various recording media in various environments while maintaining a wide color reproduction range without deteriorating recording quality. An object is to provide an apparatus and an image processing method.

  Therefore, the image processing apparatus of the present invention has an image signal output unit for recording on a recording medium, environment acquisition means for acquiring surrounding environment information for recording, and a signal that can be processed in a later process. An image for setting a table used in the color matching processing unit, color separation processing unit, output gamma correction unit, color matching processing unit, color separation processing unit, and output gamma correction unit for converting each input image signal In the recording system comprising: a processing unit, the image processing unit includes, based on a type of the recording medium and the environment information acquired by the environment acquisition unit, the color matching processing unit, the color separation processing unit, The gamma correction unit selects each table and performs recording.

  The image processing method of the present invention is a color matching processing unit, a color separation processing unit, and an output gamma correction unit in an image processing method for creating recording data used in a recording unit that performs recording by ejecting ink onto a recording medium. In addition to setting the conversion parameters used in each of the process of processing the image signals input in the above, the color matching processing unit, the color separation processing unit, and the output gamma correction unit for each type of recording medium used for recording, Further, a parameter setting step for setting a conversion parameter used in the color separation processing unit corresponding to the environmental information of the recording unit, the type of the recording medium and the environmental information are acquired, and the type of the acquired recording medium Depending on the environment information, the color matching processing unit, the color separation processing unit, and the gamma correction unit use the respective tables. Select Le, to the color matching unit, a color separation processing unit, and a processing execution step of executing the process by the gamma correction unit, characterized in that comprises a.

  According to the present invention, it is possible to select a table in which the ink ejection amount for each recording medium is set based on environmental information automatically acquired by a sensor and perform image processing, thereby maintaining a wide recording quality while maintaining high recording quality. A recording system that enables recording in the color reproduction range can be realized.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(overall structure)
The present embodiment is a recording system in which RGB image data is input and separated into color material colors that can be used in the recording apparatus and recorded in a recording apparatus that performs recording by discharging ink. Color matching processing that matches the color reproduction characteristics of input image data RGB and the color of the recording apparatus, and input multi-value R′G′B ′ image data is an N-dimensional lookup table (hereinafter referred to as LUT). Recording is performed by the recording unit by applying the color separation processing using the processing and the processing for correcting the gradation characteristics via the one-dimensional LUT for each color material according to the color reproduction characteristics of the recording apparatus.

  Further, a color matching parameter, a color separation N-dimensional LUT, and a gradation correction one-dimensional LUT are prepared for each type of recording medium, and the color separation N-dimensional LUT includes a plurality of types for each type of recording medium. LUTs with different maximum ink amounts are prepared. The recording apparatus includes a temperature / humidity sensor, and an optimum color separation N-dimensional LUT can be selected according to the surrounding environment.

  FIG. 1 is a diagram illustrating an example of a hardware configuration of an image forming system according to the present embodiment. The image processing apparatus 100 is a personal computer or the like. The CPU 101 is a central processing unit that integrally controls each unit of the image processing apparatus 100 by executing an operating system, application programs, device drivers, and the like. The RAM 102 is a memory that provides a work area for the CPU 100. The ROM 103 is a memory that stores a boot program such as BIOS. The HDD 104 is a fixed storage device such as a hard disk drive, and stores image data such as test pattern images in addition to computer programs such as application programs, operating systems, and various driver programs. The communication IF 105 is an interface for performing data communication with an external device such as USB, IEEE 1394, wired LAN, or wireless LAN. The display IF 106 is a control unit for controlling display of image information and the like on a display device 109 connected to the outside or the inside. The operation unit 107 is an input device such as a pointing device or a key input device. The recording apparatus 108 is an image forming apparatus that forms an image on a recording medium by an inkjet method or a laser beam method. The display device 109 is a liquid crystal display for displaying image data and the like. The temperature / humidity sensor 110 is a sensor that measures the temperature and humidity of the surrounding environment.

  FIG. 2 is a diagram illustrating an example of a software configuration of the image processing apparatus 100. The flow at the time of recording will be described using FIG. 1 and FIG. As the recording apparatus 108 that performs recording, an ink jet recording apparatus or the like that has been widely used can be used. When recording the output image data, the application 202 issues an output request to the operating system (hereinafter also simply referred to as OS) 201. For example, the graphics data part is composed of a graphics rendering command, and the image image data part issues a rendering command group indicating an output image composed of an image rendering command to the OS 201.

  In response to an application output request, the OS 201 issues a drawing command group to the printer driver 208 corresponding to the recording apparatus that outputs the application. The printer driver 208 processes the recording request and drawing command group input from the OS 201, creates recording data that can be recorded by the recording device 108, and transfers it to the recording device 108. When the recording device 108 is a so-called raster printer, the printer driver 208 sequentially executes image correction processing in response to a drawing command from the OS 201. Then, the rendering commands are sequentially rasterized in the RGB 24-bit page memory, and after all rendering commands are rasterized, the contents of the RGB 24-bit page memory are converted into a data format that can be recorded by the recording device 108, for example, CMYK data. Forward to.

  Next, processing performed by the printer driver 208 will be described with reference to FIG. The image correction processing unit 301 performs image correction processing on color information included in the drawing command group input from the OS 201. As the image correction processing, for example, RGB color information is converted into luminance / color difference signals, exposure correction processing is performed on the luminance signals, and the corrected luminance / color difference signals are inversely converted into RGB color information.

  First, the recording device correction processing unit 302 rasterizes a rendering command based on the RGB color information subjected to the image correction process, and generates a raster image on the RGB 24-bit page memory. Then, color matching processing for performing color reproduction space mapping, color separation processing for color material color data, gamma correction processing, and halftone processing are performed. As a result, color material color data (CMYK, CMYKcm, or CMYKcmRGB) depending on the color reproducibility of the recording apparatus is generated for each pixel, and the printable image data is transferred to the recording apparatus 108.

(Correction processing for recording device)
FIG. 3 is a diagram schematically showing the internal processing configuration of the printer driver 208. The processing in the recording apparatus correction processing unit 302 will be described in detail. FIG. 4 is a diagram illustrating an example of a detailed block configuration of the recording apparatus correction processing unit 302. FIG. 5 is a diagram schematically representing the color space in two dimensions. This is a two-dimensional representation of a color space that is usually represented in three dimensions for the sake of simplicity.

  First, RGB 8-bit image data whose brightness, contrast, and color tone are adjusted by the image correction processing unit 301 is input to the image signal input unit 401 in the correction processing unit 302 for the recording apparatus. The RGB 8-bit image data input to the image signal input unit 401 corresponds to the color reproduced on the display device 109. For example, in the coordinate values of the CIE L * a * b * color system which is a uniform color space, the image data represents a color (L_Monitor, a_Monitor, b_Monitor).

  However, as can be seen from FIG. 5, the color reproduction space of the display device 109 and the color reproduction space of the recording device 108 do not coincide with each other in a uniform color space such as an L * a * b * space. This is because the recording apparatus cannot form an image outside the color reproduction space of the recording apparatus shown in FIG. 5 and an area (shaded portion) in the color reproduction space of the display apparatus. More specifically, the subsequent color separation processing unit 403 performs conversion from RGB to color material color data on the image data expressed on the display device 109, and the output γ correction processing unit 404 performs gradation. Even if correction processing is performed and binarization processing is executed by the halftone processing unit 405 and then output to the image output unit 406, an area where image formation is impossible, that is, a color space that cannot be expressed by the recording device 108. Area (shaded area) occurs.

  Therefore, on the recording device 108 side, a pseudo color (L * a * b * value) for an area (shaded portion) on the color space that can be reproduced by the display device 109 but cannot be reproduced by the recording device 108, That is, it is necessary to generate and record a pseudo color different from the color of the display device 109.

Hereinafter, the L * a * b * space is copied to the cylindrical coordinates H (= atan (b / a)), S (= sqrt (a * ² + b * ² )), V (= L *) as a uniform color space. A case where color space compression is performed on the entire space will be described. Here, atan (x) is a function for obtaining the arc tangent of x. Further, sqrt (x) is a function for obtaining √x.

(Color matching processing part)
In the color matching processing unit 402 in the correction processing unit 302 for the recording device, the color of the recording device 108 is compressed by compressing an area that cannot be reproduced by the recording device 108 in the color reproduction space (monitor gamut) of the display device 109. Corresponds to a point in the reproduction space (printer gamut). That is, the RGB 8-bit data processed by the color matching processing unit 402 is converted into R′G′B ′ 8-bit data corresponding to points on the color reproduction space.

  Specifically, the color matching processing unit 402 performs conversion from the RGB color signal space of the display device 109 to the R′G′B ′ color signal space of the recording device 108 according to the following procedure.

In the color matching processing unit 402 shown in FIG. 4, the saturation S is maintained while maintaining the lightness L * so that the gamut based on the monitor RGB enters the inside of the printer R′G′B ′ gamut in the L * a * b * space. Compression is performed by performing processing such as lowering (= sqrt (a * ² + b * ² )). An example of this compression processing is shown in FIG.

FIG. 6 is a diagram conceptually showing gamut compression in the saturation (S) direction on the SV plane. That is, the set of L * a * b * values in the printer gamut corresponding to the monitor RGB values is obtained. When the compressed monitor gamut fits in the printer gamut, the color difference ΔE (= sqrt ((L * ′ − L *) ² + (a * ′ − a *) ² + (b * ′ − b *) ² )) A set of monitor (R, G, B) and printer (R ′, G ′, B ′) is determined using the minimum L * a * b * value as a key. Thereby, the printer R′G′B ′ value corresponding to the monitor RGB value can be obtained. Of course, the color matching processing unit 402 can be realized by using a LUT (Look Up Table).

  In the present embodiment, since the size of the printer gamut varies depending on the type of recording medium, a plurality of matching tables are held in the matching table unit 407 as LUTs for each recording medium in a 3D-LUT format by interpolation calculation.

(Color separation processing part)
Next, processing in the color separation processing unit 403 in the recording apparatus correction processing unit 302 will be described.

The color separation processing unit 403 converts the 8-bit signal of each color converted into R′G′B ′ for the recording apparatus by the color matching processing unit 402 into color material color data (CMYK, (CMYKcm or CMYKcmRGB) each is converted into a signal value of 8 bits. As an example of color separation processing, as a method for converting a color signal from R′G′B ′ to CMYK, for example, a method by color masking is known. The color conversion method by this color masking is shown in the following formula. The optical densities D _r , D _g , and D _b can be expressed as follows.
Dr = -log (R / 255)
Dg = -log (G / 255)
Db = -log (B / 255)
The main concentration can be expressed as follows.

  By calculating these mathematical formulas, CMY values can be obtained. There are various methods for determining the K (black) signal value. The rightmost side in the determinant is replaced with a vector [Dr-KDg-KDb-K] t obtained by subtracting the K value from the vector element, and the condition that each color signal value CMY corresponding to the ink amount is always positive or 0 is used. While constraining the K value, the masking matrix is obtained erroneously by trial chain. In this way, the K value can be determined. Of course, the color separation processing unit 403 can be realized by using an LUT.

  The color separation table of CMYKcm or CMYKcmRGB can be created by replacing colors based on the RGB-CMYK conversion table. For example, the value of (C, M, Y, K) = (0, 255, 255, 0) is changed to (C, M, Y, K, c, m, R, G, B) = (0, 0, 0, (0, 0, 0, 255, 0, 0).

  In the present embodiment, the color separation table unit 408 holds a plurality of color separation tables having different maximum ink amounts for each type of recording medium in a 3D-LUT format by interpolation calculation.

(Output gamma correction processing section)
Next, processing in the output gamma correction processing unit 404 in the recording apparatus correction processing unit 302 will be described.

  The output gamma correction processing unit 404 sequentially converts and outputs the color signal of the input image by the color matching processing unit 402 and the color separation processing unit 403. Each 8-bit data of the output N color material color data (CMYK, CMYKcm, or CMYKcmRGB) is converted into data that can be processed by the subsequent halftone processing unit 405. Then, 8-bit data for each N ′ color material color data is output. The output gamma correction processing unit 404 performs adjustment using a one-dimensional LUT for each ink in order to compensate for nonlinear characteristics with respect to lightness.

  In this embodiment, since the non-linear characteristic of brightness varies depending on the type of recording medium, a plurality of gamma correction tables are held in the gamma correction table unit 409 as LUTs for each recording medium in a one-dimensional LUT format for each color.

(Halftone processing part)
Next, processing in the halftone processing unit 405 in the recording correction processing unit 302 will be described.

  In the halftone processing unit 405, the 8-bit data of each N ′ color material color data and the color signal of the input image are sequentially converted by the color matching processing unit 402, the color separation processing unit 403, and the output gamma correction processing unit 404 and output. The 8-bit data for each N ′ color material color data is converted into 1-bit data for each N ″ color material color data that can be recorded by the recording device 108.

  In this halftone processing method, for example, a Bayer type 16 × 16 dither matrix is used for the input N ′ color material color data image. This is realized by setting 1 when the pixel value on the corresponding image is larger than the threshold value in this matrix, and 0 when the pixel value is equal to or smaller than the threshold value. In addition, an error diffusion method or the like can be used as another halftone processing method.

  Each 1-bit data of N ″ color material color data that can be recorded by the recording apparatus thus obtained is sent to the recording apparatus 108 and an image is formed on the recording medium.

(Characteristic configuration)
(Table by recording medium and ink amount)
A matching table unit 407, a color separation table unit 408, and a gamma correction table unit (gamma correction unit) 409 store a plurality of tables for each type of recording medium. Specifically, the matching table unit 407 is prepared with a table having a different color reproduction space (gamut) size and shape for each type of recording medium. The color separation table unit 408 also stores and prepares a plurality of tables in which the amount of applied ink differs depending on the environmental temperature and humidity for each type of recording medium. The gamma correction table unit 409 stores a table for each correction characteristic corresponding to the type of recording medium.

  In this way, each process of color matching, color separation, and gamma correction can be set uniformly for each type of recording medium. For example, when the color separation process uses a table that increases the amount of applied ink, the color reproduction range of the printer obtained by the color matching process is widened in association therewith. As a result, a sufficiently wide color gamut can be recorded in actual recording.

  FIG. 7 is a diagram showing a color separation table prepared for each recording medium and for each environmental temperature and humidity in the present embodiment, and specifically shows the amount of applied ink. As shown in the figure, when a table of “100%” (“plain paper”, “low temperature”, “high humidity”) is used as the basic application amount table, for example, the table of 220% is the basic for the same input signal. A color separation signal corresponding to an ink amount 2.2 times the table is output. As described above, color separation (determination of applied ink amount) suitable for color matching processing or the like can be performed by changing the applied ink amount for each recording medium and for each temperature and humidity. Accordingly, it is possible to perform recording with no ink bleeding and sufficiently exhibiting the color reproduction range.

  FIG. 8 is a flowchart of color separation table selection processing in the present embodiment. When the color separation table selection process is executed, first, in step S701, the type of the recording medium used for recording is set by the information from the recording medium type input unit 410. Next, the process proceeds to step S <b> 702, and ambient temperature / humidity data is acquired from the temperature / humidity sensor 110. Next, the process proceeds to step S703, and the process is switched according to the type of the recording medium set in step S701.

  If plain paper is set as the recording medium in step S701, the process proceeds from step S703 to step S704. In step S704, the ink amount of the color separation table for plain paper is selected according to the temperature / humidity data acquired in step S702. Thereafter, the process proceeds to step S707, and a table corresponding to plain paper is set in the color matching processing unit 402, the color separation processing unit 403, and the output gamma correction processing unit 404 by the image processing parameter setting unit 411.

  When coated paper is set in step S701, the process proceeds from step S703 to step S705. In step S705, the ink amount of the color separation table of the coated paper is selected according to the temperature / humidity data acquired in step S702. Thereafter, the process proceeds to step S708, and a table corresponding to the coated paper is set in the color matching processing unit 402, the color separation processing unit 403, and the output gamma correction processing unit 404 by the image processing parameter setting unit 411.

  When glossy paper is set in step S701, the process proceeds from step S703 to step S706. In step S706, the ink amount in the color separation table for glossy paper is selected according to the temperature and humidity data acquired in step S702. Thereafter, the process proceeds to step S709, and a table corresponding to glossy paper is set in the color matching processing unit 402, the color separation processing unit 403, and the output gamma correction processing unit 404 by the image processing parameter setting unit 411.

  After setting the table corresponding to each recording medium in step S707, step S708, and step S709, the process proceeds to step S710 and the image signal output unit 406 performs recording on the recording medium.

  In this way, according to the recording medium, environmental information is acquired in accordance with the surrounding environment where recording is performed, and each processing execution unit selects a table in which the amount of ink applied according to the environment is selected to perform image processing. Do it. As a result, it was possible to realize a recording system that enables recording in a wide color reproduction range while maintaining high recording quality.

  In this embodiment, a table for plain paper, coated paper, and glossy paper (the amount of ink in the color separation table corresponding to temperature and humidity) is prepared as a recording medium. However, the present invention is not limited to this, and tracing paper is used. Or a table of a recording medium such as an OHP sheet may be prepared.

1 is a diagram illustrating an example of a hardware configuration of an image forming system. It is a figure which shows an example of the software configuration of an image processing apparatus. FIG. 3 is a diagram schematically illustrating an internal processing configuration of a printer driver. It is a figure which shows an example of the detailed block structure of the correction process part for recording devices. It is the figure which expressed color space typically in two dimensions. It is a figure which shows notionally the gamut compression to a saturation (S) direction in SV plane. FIG. 6 is a table showing acceptable ink amounts of a color separation table with respect to temperature and humidity for each recording medium. It is a flowchart of a color separation table selection process.

Explanation of symbols

1000 Host device (computer)
DESCRIPTION OF SYMBOLS 100 Image processing apparatus 101 Central processing unit 102 RAM
103 ROM
104 Fixed Storage Device 105 Communication Interface 106 Display Interface 107 Input Device 108 Image Forming Device 109 Display Device 110 Temperature Humidity Sensor

Claims (5)

In an image processing apparatus for creating recording data used in a recording unit that performs recording by discharging ink to a recording medium,
A color matching processing unit, a color separation processing unit, and an output gamma correction unit for processing each input image signal;
A conversion parameter used in each of the color matching processing unit, the color separation processing unit, and the output gamma correction unit is set for each type of recording medium used for recording, and a conversion parameter used in the color separation processing unit is further set. Parameter setting means for setting corresponding to the environmental information of the recording unit;
The type of the recording medium and the environment information are acquired, and according to the acquired type of the recording medium and the environment information, the respective tables used in the color matching processing unit, the color separation processing unit, and the gamma correction unit are selected, An image processing apparatus comprising: processing execution means for executing processing by the color matching unit, color separation processing unit, and gamma correction unit.   The image processing apparatus according to claim 1, wherein the maximum amount of ink used for recording varies according to the table.   The image processing apparatus according to claim 1, wherein the environmental information includes temperature and humidity.   The image according to any one of claims 1 to 3, wherein among the input image signals, the color matching processing unit includes color signals of three elements of RGB. Processing equipment. In an image processing method for creating recording data used in a recording unit that performs recording by discharging ink to a recording medium,
Processing each of the image signals input by the color matching processing unit, the color separation processing unit, and the output gamma correction unit;
A conversion parameter used in each of the color matching processing unit, the color separation processing unit, and the output gamma correction unit is set for each type of recording medium used for recording, and a conversion parameter used in the color separation processing unit is further set. A parameter setting step for setting corresponding to the environmental information of the recording unit;
The type of the recording medium and the environment information are acquired, and according to the acquired type of the recording medium and the environment information, the respective tables used in the color matching processing unit, the color separation processing unit, and the gamma correction unit are selected, An image processing method comprising: a process execution step of executing processing by the color matching unit, the color separation processing unit, and the gamma correction unit.

Images