JP2006026936A - Image forming apparatus and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent density correction accuracy from deteriorating even in a case where density greatly varies and to perform image formation of a stable density. <P>SOLUTION: In a simple density measurement section 201, the image of a patch pattern of one density level is formed in a clearance between papers during printing for each color and a density is measured by using a sensor. It is determined in which density variation condition the image is by the density measured. In a density level set selection section 202, a density level set to be used in the density variation condition determined is selected. Subsequently, in a density measurement section 203 a patch pattern of a density level set consisting of a plurality of density levels selected by the density level set selection section 202 is formed, and a density value is measured by using the sensor. In a density characteristics computation section 204 density characteristics are computed from the density value measured. In a density correction table preparation section 205, a density correction table to correct an input density level is prepared to ensure that the density characteristics are target density characteristics. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus and method, and more particularly, to an image forming apparatus and method for performing density correction to maintain an appropriate image density and provide stable high image quality.

  Conventionally, adjustment of the printing density of a printing apparatus, which is an image forming apparatus, prints a test pattern at a predetermined density level, measures the density, and obtains density characteristics from the density level and the measured density value. Next, a density correction table is created so that the density characteristic thus obtained becomes the target density characteristic, and this is applied during printing. Here, the predetermined density level is generally set to an appropriate value in the middle assuming that the density changing due to density fluctuation is lowest and highest. Yes, this is known in the art.

  However, in the conventional method, when the density fluctuation is large, for example, when the density is extremely low, the density value is lower than the density value that can be accurately read by the sensor, or conversely, the density becomes extremely high. In such a case, the density of the low density area cannot be measured, so that the accuracy of density correction, particularly the correction precision of the low density area is deteriorated, and the quality of the printed image is deteriorated.

  The present invention has been made in view of such a problem, and is divided into a state of fluctuation in density, for example, a state in which the density is high, a state in which the density is low, and a standard state. Since a combination of density levels that are the density values necessary for density correction is retained and applied, it is possible to measure the density in the vicinity of the density value suitable for density correction, and the density even when the density fluctuation is large An object of the present invention is to provide an image forming apparatus and method capable of preventing a reduction in correction accuracy and performing printing with a stable density.

  In order to achieve such an object, the image forming apparatus of the present invention performs image formation at a predetermined input level, and acquires image formation density characteristics from the predetermined input level and the density of the image formed image. An image forming apparatus for measuring a first density by reading an image formed at a predetermined input level and measuring a first density, a predetermined input level, and a first measurement unit A simple density characteristic is calculated based on the first density, and a state determination unit that determines which density fluctuation state the image forming apparatus is in based on the calculated simple density characteristic, and a predetermined density fluctuation state are determined in advance. And a second measuring means for further reading an image formed at each input level of the set of the plurality of input levels and measuring a second density to obtain an image forming density characteristic. Features .

  The image forming method of the present invention is an image forming method for performing image formation at a predetermined input level and obtaining image formation density characteristics from the predetermined input level and the density of the image formed image, Simple density based on a first measurement step of reading an image formed at a predetermined input level and measuring a first density, a predetermined input level, and a first density measured in the first measurement step A state determination step for calculating the characteristics and determining in which density fluctuation state the image forming apparatus is in accordance with the calculated simple density characteristics, and a set of predetermined input levels in the determined density fluctuation state And a second measurement step of acquiring an image formation density characteristic by further reading the image formed at each input level and performing a second density measurement.

  By holding a combination of density levels that is a density value necessary for density correction for each density fluctuation state, selecting a density level combination suitable for the state, and measuring the density of the selected density level Therefore, it is possible to measure the density in the vicinity of the density value suitable for the density correction, and it is possible to prevent the density correction accuracy from being lowered even when the density fluctuation is large and to form an image with a stable density.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram for explaining a control configuration in an embodiment of a printing apparatus (hereinafter referred to as a printer) that is an image forming apparatus of the present invention. A host computer 101 is configured to display color information, characters, graphics, and images. Print information for performing print processing such as an image and the number of copies is sent to the printer 102. The printer 102 is roughly divided into an image processing unit 103 and a printer engine 114 that performs actual image formation based on the image signal transmitted from the image processing unit 103.

  Hereinafter, main configurations and operations of the image processing unit 103 will be described. In the image processing unit 103, the interface 104 controls transmission / reception of print information with the host computer 101. The reception buffer 105 holds input print information. In the object generation unit 106, information such as colors, characters, graphics, and image images, which are print information input from the host computer 101, is converted into intermediate information (hereinafter referred to as an object) and stored in the object buffer 107. . At this time, when the print information is color-related data such as gray level setting, color level setting, multi-value image, etc., a density correction table is created in the density correction processing unit 115 described later, and the density level correction processing unit 116 The density level is corrected using the correction table.

  Next, based on the object stored in the object buffer 107, the rendering unit 108 generates a bit image to be rendered. At this time, the dither processing unit 110 performs halftone processing and converts it into a bit image of output gradation for printing. The generated bit image is stored in the band buffer 109. In this way, the bit image stored in the band buffer 109 is sent to the printer engine 114 and formed on the recording medium.

  A central processing unit (CPU) 112 determines and controls various processes according to a control program 111a stored in the ROM 111. A ROM (read only memory) 111 stores various control programs 111a including the programs shown in the flowcharts of FIGS. 3, 7, and 9, and a measured density level 111b described later. A RAM (Random Access Memory) 113 stores data and status information for the CPU 112 to perform judgment control of each process according to a program stored in the ROM 111, a density correction table 113b, and is used as a work area 113a.

  FIG. 2 is a block diagram for explaining a control configuration in an embodiment of the density correction processing unit 115 of the present invention. In the simple density measurement unit 201 described later, a patch pattern of one density level for each color is printed. An image is formed in the gap between the two sheets, and the density is measured using a sensor. It is determined which density fluctuation state the printer is based on the measured density, and the density level set selection unit 202 selects a density level set to be used in the determined density fluctuation state. Next, a density level set patch pattern including a plurality of density levels selected by the density level set selection unit 202 described above is formed in the density measurement unit 203, and the density value is measured using a sensor. The density characteristic calculation unit 204 calculates density characteristics from the measured density value, and the density correction table creation unit 205 creates a density correction table for correcting the input density level so that the density characteristics become the target density characteristics. Further, the density level correction processing unit 116 performs density correction by correcting the input density data of the object generation unit 106 using the density correction table.

  Hereinafter, the printing process in the present embodiment will be described with reference to the flowchart shown in FIG. Note that the control program for realizing the processing shown in the flowchart of FIG. 3 is stored in the ROM 111 as described above, and is executed by the CPU 112. In FIG. 3, first, print data is received from the host computer 101 (S301) and held in the reception buffer 105 (S302). Data for one processing unit is extracted from the reception buffer 105 (S303), and it is determined whether or not all data extraction has been completed (S304). If it is determined that the processing has not been completed, it is determined whether or not the data processing for one page has been completed (S305).

  If it is determined that the print data has not been completed, it is determined whether the print data is color-related data such as color information or a color image (S306). If it is determined that the data is color-related data, the density level correction processing unit 116 corrects the density level (S307). After the object is created (S308) and stored in the object buffer 109 (S309), the process returns to step S303 to retrieve the next data.

  On the other hand, if it is determined in step S306 that the data is not color-related data, it is determined whether the data is mask data for characters, figures, etc. (S310). When it is determined that the data is mask data, an object of mask data is created (S308), and the process returns to step S309. On the other hand, when it is determined that the data is not mask data, print data processing corresponding to the type of data is performed (S311), and the process returns to step S303.

  If it is determined in step S305 that one page of data has been completed, rendering processing is performed based on the object held in the object buffer 107 (S312), and the bit image is transmitted to the printer engine 114. A printing process for printing on the paper is performed (S313). If it is determined in step S304 that the data is complete, the process ends.

  Next, density correction processing in the present embodiment will be described with reference to FIGS. The density correction process is performed for each color (C, M, Y, K). FIG. 4 is a diagram illustrating an example of the simple concentration measurement unit 201 in FIG. In the printer 102, between the step of transferring the print data image-formed on the intermediate transfer body 402 of the normal printing process to the printing paper and the step of transferring the printing data of the next page to the printing paper, so-called inter-page A patch pattern having a predetermined density level is formed in the gap, and the density is measured by the sensor 401. This is a simple density measurement, which is performed for each color (C, M, Y, K).

  FIG. 5 is a diagram illustrating an example of the concentration measurement unit 203 in FIG. In the printer 102, Y, M, C, and K color patterns are formed on the intermediate transfer member 402 in the density level held in a later-described measurement density level set, and the density is measured by the sensor 401.

  FIG. 6 is a diagram for explaining the measured density level set 111b of the present embodiment. A measured density level set, which is a set of input levels, is a combination of input density levels for calculating density characteristics. When actually measuring density, each input density level included in the measured density level set A patch pattern is formed. In this embodiment, there are a plurality of types of measurement density level sets, and a plurality of sets are prepared according to the state of the printer. From these, an appropriate set is selected by the simple density measurement which is the first measurement means described above. Apply.

  For example, the density fluctuation state at that time of the printer is classified into three states: (a) a low density state, (b) a high density state, and (c) a density standard state and three states. On the other hand, each has a density level set. The density level is a ratio in which the maximum density level value 255 is 100% with respect to the density level value 0 to 255, and the density value is 100% with respect to the actual density value 0 to 1.6. The description will be made using the ratio of%, that is, the concentration rate. By performing statistical processing in this way, it becomes easy to adjust density characteristics described later.

  In order to calculate the density characteristics of the whole (density level of 0 to 100%), the low density area, medium density area, and high density area are generally measured. In this embodiment, four measurement points are used. That is, the entire density characteristics are calculated by measuring the density value around 10% as the low density area, the density values around 30% and 50% as the medium density area, and the density value around 70% as the high density area. . Note that the measurement points are not limited to four points.

  In order to calculate density characteristics, when the density measurement unit measures four density levels in the vicinity of 10%, 30%, 50%, and 70%, the density shown in FIG. Even if a patch pattern is formed at an input density level of, the input density level corresponding to the density values of 10%, 30%, 50%, and 70% can be obtained from the density characteristics if an image with a density lower than normal is obtained. The concentration levels are 25%, 55%, 75%, 90%, and the combination of concentration levels 25%, 55%, 75%, 90% as a measured concentration level set (measurement concentration level set 1) with low concentration Hold. Similarly, in the state where the density of FIG. 6B is high, the input density levels corresponding to the density values of 10%, 30% .50%, and 70% are the density levels of 5%, 15%, 30%, and 50%. As the measurement density level set 2, the combinations of density levels 5%, 15%, 30%, and 50% are retained, and in the state where the density in FIG. 6 (c) is high, the density values are 10%, 30% .50%, The input density level corresponding to 70% is the density level 10%, 30%, 50%, 70%, and the combination of the density level 10%, 30%, 50%, 70% is held as the measured density level set 3. .

  The measured density level set in each density fluctuation state is selected according to the density fluctuation state by the above-described simple density measurement, and is measured by the density measurement unit using the measurement density level set corresponding to the selected density fluctuation state.

  FIG. 7 is a flowchart showing an example of the density level set selection process in the density correction processing unit (FIG. 2), and FIG. 8 is a diagram for explaining the relationship between the measured density value and the density fluctuation state of the present embodiment. It is. In FIG. 7, first, a patch pattern of one density level for each color is measured by the simple density measurement process (FIG. 4) (S701), and the density variation state is determined from the measured density value (S702).

  For example, when a patch pattern with an input density level of 40% is measured in the simple density measurement process, and the measured density value is within ± 10% of the density value of 40% (variation state level 3 in FIG. 8) as shown in FIG. Is determined to be the standard concentration fluctuation state of FIG. 6 (c), and when the measured concentration value is 10% or more lower than the concentration of 40% (fluctuation state level 1 of FIG. 8), (a) of FIG. ) Is in a low density fluctuation state, and when the measured density value is 10% or more higher than the density value 40% (fluctuation state level 2 in FIG. 8), the density in FIG. 6 (b) is high. Judged as a fluctuating state. The measured density level set shown in FIG. 6 is selected from the density fluctuation state determined as described above (S703). That is, (1) measured density level set 1 when the density is low, (2) measured density level set 2 when the density is high, and (3) measured density level set 3 when the density is in the standard state. Select.

  In the present embodiment, the measurement density level of the above simple density measurement process is easily affected by the density fluctuation when the normal density fluctuation occurs, and can be read by the sensor even when the density greatly fluctuates. The density level in the density region is 40%, but the density level is not limited to 40%, and any density level can be used as long as the density fluctuation state can be determined.

  FIG. 9 is a flowchart showing an example of processing for creating a density correction table by density measurement in the density correction processing unit (FIG. 2). In FIG. 9, first, the measurement density level set selected by the density level set selection processing unit 202 is acquired (S901), and the patch pattern of the density level of the acquired measurement density level set is measured by the density measurement process (FIG. 5). The current density characteristic is calculated from the measured density value (S903), and a density correction table for converting the input density level so that the current density characteristic becomes the target density characteristic is created (S904). .

  FIG. 10 is a diagram showing actual density characteristics of the present embodiment. Since the concentration fluctuation state is determined to be a high concentration state as shown in FIG. 6B by simple concentration measurement, the concentration measurement processing sets the concentration levels 5%, 15%, 30% and 50% of the measured concentration level set 2 to Applied to measure concentration. Each measured density value is indicated by a black dot on the solid line in the figure, and its density characteristic is as shown by a solid line.

  However, if density correction is performed using a curve indicated by a solid line, accurate correction cannot be performed. Therefore, a more linear density characteristic than that indicated by a broken line is required. Here, the broken line indicates the target density characteristic (linear characteristic). When the input density level indicating the density characteristic (solid line in FIG. 10) obtained by the density measurement is corrected to the target density characteristic (broken line in FIG. 10), the correction is performed as shown by the solid line in FIG. A correction density level characteristic is obtained, and the correction density level characteristic is tabulated to generate a one-dimensional density correction table shown in FIG. Using this density correction table, the density level correction processing unit 116 corrects the density level.

  By converting the color data input from the host computer into YMCK data and correcting the density level by using the density correction table (FIG. 12), it is possible to suppress variations in color.

FIG. 3 is a block diagram for explaining a control configuration in an embodiment of a printing apparatus that is an image forming apparatus of the present invention. It is a block diagram for demonstrating the control structure in one Embodiment of the density | concentration correction process part of this invention. It is a flowchart for demonstrating one Embodiment of this invention. It is a figure which shows an example of the simple density | concentration measurement part of FIG. FIG. 3 is a diagram illustrating an example of a concentration measurement unit 203 in FIG. 2. It is a figure for demonstrating the measurement density level set of this embodiment. (A) shows a state where the concentration is low, (b) shows a state where the concentration is high, and (c) shows a state where the concentration is standard. It is a flowchart which shows an example of the density level set selection process in a density correction process part (FIG. 2). It is a figure for demonstrating the relationship between the measured density value of this embodiment, and a density fluctuation state. It is a flowchart which shows an example of the process which produces the density | concentration correction table by density | concentration measurement in a density | concentration correction process part (FIG. 2). It is a figure which shows the actual density | concentration characteristic of this embodiment. It is a figure which shows the density | concentration characteristic after correction | amendment linearly of this embodiment. It is a figure which shows the density | concentration correction table of this embodiment.

Explanation of symbols

101 Host computer 102 Printer 103 Image processing unit 104 Interface 105 Reception buffer 106 Object generation unit 107 Object buffer 108 Rendering unit 109 Band buffer 110 Dither processing unit 111 ROM
111a Control program 111b Measurement density level 112 CPU
113 RAM
113a Work area 113b Density correction table area 114 Printer engine 115 Density correction processing unit 116 Density level correction processing unit 201 Simple density measurement unit 202 Measurement density level set 203 Density measurement unit 204 Density characteristic calculation unit 205 Density correction table creation unit 401 Sensor 402 Intermediate transfer member

Claims (6)

An image forming apparatus that performs image formation at a predetermined input level and acquires image formation density characteristics from the predetermined input level and the density of the image formed.
First measuring means for reading the image formed at the predetermined input level and measuring a first density;
A simple density characteristic is calculated from the predetermined input level and the first density measured by the first measuring means, and the image forming apparatus is in any density fluctuation state based on the calculated simple density characteristic. State determination means for determining whether or not
In the determined density fluctuation state, an image formed at each input level of a plurality of predetermined input level sets is further read, and a second density measurement is performed to obtain the image formation density characteristics. An image forming apparatus comprising: a second measuring unit.   The image forming apparatus according to claim 1, further comprising a correction acquisition unit configured to correct the measured second density based on the determined density fluctuation state to acquire an image formation density characteristic. .   The image formed at the predetermined input level is obtained by forming a test pattern of a halftone pattern having several density levels at the predetermined input level. The image forming apparatus according to claim 1, wherein the second density is measured by reading the density of the test pattern using a sensor.   The image formed at the predetermined input level is obtained by forming a test pattern of a halftone pattern having a small number of density levels in the idle time at the time of image formation at the predetermined input level. 3. The image forming apparatus according to claim 1, wherein the first density is measured by reading a density of the image-formed test pattern using a sensor. 4.   The image forming apparatus according to claim 1, further comprising a changing unit that changes an image forming condition based on the acquired image forming density characteristic. An image forming method for performing image formation at a predetermined input level and acquiring an image formation density characteristic from the predetermined input level and the density of the image formed image,
A first measuring step of reading an image formed at the predetermined input level and measuring a first density;
A simple density characteristic is calculated based on the predetermined input level and the first density measured in the first measurement step, and the image forming apparatus is in any density fluctuation state based on the calculated simple density characteristic. A state determination step for determining whether or not
In the determined density fluctuation state, an image formed at each input level of a plurality of predetermined input level sets is further read, and a second density measurement is performed to obtain the image formation density characteristics. An image forming method comprising: a second measuring step.

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