JP2011109256A - Image processing apparatus and image processing program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To express the density of an image in as preferable manner as possible, even if the maximum density is deteriorated. <P>SOLUTION: When a decision is made that the background color of an image has a density higher than a decision threshold density Ix, i.e., when a decision is made that the input density of the background color has a target density which is higher than the current maximum density Dmax (where a possibility of reduced density, as compared with normal density) (S107:YES), or when a decision is made that two or more colors having a density higher than the density Ix exist in the image, i.e., when a decision is made that two kinds or more of input density, having a target density which is higher than the current maximum density Dmax are contained in the image (S108:YES), the correspondence between the input density and the target density is changed to a correspondence where the target density is decreased with reference to the current (decreased) maximum density Dmax (S109), and gamma correction of the print data is carried out, in accordance with the changed correspondence (S111). <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

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

  Conventionally, an image forming apparatus that forms an image using an image forming material such as toner is known. In this type of image forming apparatus, the density of the printed result varies due to various factors such as environmental changes, temporal changes, toner changes, and so on. Processing is required. For example, as shown in FIG. 8, although the target density characteristic (correspondence between input density and target density) is a linear relationship indicated by a solid line, the correspondence between actual input density and output density is When the relationship is a curve indicated by a broken line, the image data can be corrected by a gamma correction so that the relationship is a straight line indicated by a solid line.

  Here, the target density characteristic is generally set based on the maximum density Dmax that can be expressed by the image forming apparatus. This is because the contrast of the formed image can be maximized by setting the target density characteristics so that the target density corresponding to the maximum value of the input density is the maximum density Dmax.

JP-A-7-20669

  However, with the density characteristics set in this way, when the maximum density Dmax is reduced for some reason, such as a change over time, toner shortage, or use other than recommended toner (genuine product), the density is higher than the reduced maximum density Dmax. There is a problem that the target output density cannot be obtained for the input density having the target density.

  The present invention has been made in view of these problems, and an object of the present invention is to provide an image processing apparatus capable of expressing the image density as preferably as possible even when the maximum density is lowered.

  In order to achieve the above object, an image processing apparatus according to claim 1 of the present invention is based on a correspondence relationship between an input density and a target density set in advance based on a maximum density that can be expressed by an image forming unit. A correction unit that corrects image data representing an image to be formed by the image forming unit, and an input density having a target density that is higher than the reduced maximum density due to a decrease in the maximum density that can be expressed by the image forming unit. Is included in the image data, and the correction unit includes the input density in which the target density is higher than the maximum density reduced by the image determination unit. The image data is corrected in accordance with the correspondence relationship in which the target density is changed to be low with reference to the reduced maximum density.

  According to such an image processing apparatus, even when the maximum density is lowered, the density of the image can be expressed as preferably as possible according to the content of the image represented by the image data. In other words, when the maximum density that can be expressed by the image forming means is reduced for some reason, the input density having a higher density than the reduced maximum density as the target density is formed as an image having the same density. It becomes impossible to express. However, if the target density is simply changed based on the reduced maximum density, the gradation can be expressed, but the density of the formed image becomes light overall and the contrast is lowered. In this regard, in the image processing apparatus of the present invention, the target density is changed to be low on condition that the image data includes an input density whose target density is higher than the reduced maximum density. For example, it is possible to maintain a high contrast without changing the target density for an image with an overall low input density, and the density of the image can be expressed as preferably as possible according to the content of the image.

Here, the determination that the input density having the target density higher than the reduced maximum density is included in the image data can be performed, for example, as described in claim 2.
That is, the image processing apparatus according to the second aspect measures the density of the patch corresponding to the input density in a plurality of stages formed in the image forming unit. Then, the image determination means uses the input density at which the measured density reaches a peak value as a determination threshold value, and if the input density higher than the determination threshold value is included in the image data, the image determination means It is determined that the input density having a higher density as the target density is included in the image data.

According to such an image processing apparatus, it is possible to accurately determine that the input density having the density higher than the reduced maximum density as the target density is included in the image data.
By the way, as image data that is preferably corrected according to a correspondence relationship in which the target density is changed to a low value instead of the correspondence relationship between the preset input density and the target density, for example, a density higher than the reduced maximum density is set as the target. Examples include image data in which the input density as the density occupies most of the image.

  Therefore, in the image processing apparatus according to claim 3, when the image data is command data having the background color of the image as a parameter, the image determination unit has a density higher than the reduced maximum density. Is determined to be an input density having a target density higher than the maximum density at which the background color is reduced. The image data is corrected in accordance with the correspondence relationship in which the target density is changed to be low with reference to the reduced maximum density.

  According to such an image processing apparatus, when the input density has a target density that is higher than the maximum density at which the background color of the image is reduced, in other words, the density that is higher than the reduced maximum density is set as the target density. When the input density is likely to occupy most of the image, the gradation of the background color can be appropriately expressed by correcting the image data according to the correspondence relationship in which the target density is changed to be low. In particular, in this image processing apparatus, since the density of the background color of the image is determined based on the parameters of the command data, the processing can be simplified.

  Here, as described in claim 4, for example, when the image data is not command data having the background color of the image as a parameter, the correcting means follows a correspondence relationship between a preset input density and a target density. The image data may be corrected. In this way, it is not necessary to analyze the image represented by the image data even for image data that does not have the background color of the image as a parameter, so that the processing can be further simplified.

  For example, in the image processing apparatus according to claim 5, the correction unit includes that the image data includes two or more types of input densities having a target density higher than the maximum density reduced by the image determination unit. When the determination is made, the image data is corrected according to the correspondence relationship in which the target density is changed to be low with reference to the reduced maximum density.

  According to such an image processing apparatus, an image corresponding to two or more types of input densities having a higher density than the reduced maximum density as a target density can be expressed so that gradation can be distinguished.

  For example, in the image processing apparatus according to claim 6, the image determination unit has an input density in which a color that occupies a predetermined ratio or more in an image represented by image data has a higher density than the reduced maximum density as a target density. If it is determined that the input density has a density higher than the maximum density at which the color occupying a predetermined ratio or more is reduced by the image determination means, the correction means decreases the color density. The image data is corrected according to a correspondence relationship in which the target density is changed to be lower with the maximum density as a reference.

  According to such an image processing apparatus, when the input density having a higher density than the reduced maximum density as a target density occupies a predetermined ratio or more of the image, the image data is corrected according to the correspondence relationship in which the target density is changed to be lower. Thus, the gradation of the density can be appropriately expressed.

  According to the image processing program recited in claim 7, the computer can function as the image processing apparatus recited in claim 1, thereby obtaining the above-described effects.

1 is a block diagram illustrating a schematic configuration of a printing system according to an embodiment. It is a graph which shows the correspondence of input density and target density. It is explanatory drawing for demonstrating the method of calculating | requiring the threshold value for determination. It is a flowchart of the image correction process of 1st Embodiment. It is explanatory drawing which shows the specific example of the image which print data represents. It is a flowchart of the image correction process of 2nd Embodiment. It is a flowchart of the image correction process of 3rd Embodiment. It is a graph for demonstrating gamma correction.

Embodiments to which the present invention is applied will be described below with reference to the drawings.
[1. First Embodiment]
First, the printing system of the first embodiment will be described.

[1-1. overall structure]
FIG. 1 is a block diagram illustrating a schematic configuration of a printing system according to a first embodiment in which a personal computer (PC) 1 and a printer 2 are configured to be capable of data communication.

The personal computer 1 is a general-purpose information processing apparatus and includes a control unit 11, a storage unit 12, a communication unit 13, an operation unit 14, and a display unit 15.
The control unit 11 performs overall control of each unit of the personal computer 1 and includes a CPU 111, a ROM 112, and a RAM 113.

  The storage unit 12 is a nonvolatile storage device capable of rewriting stored data, and a hard disk device is used in this embodiment. The storage unit 12 is installed with an operating system (OS) 121, an application program 122 such as a word processor, and a printer driver 123 that is software (program) for making the printer 2 available from the personal computer 1. .

The communication unit 13 is an interface for performing data communication with the printer 2.
The operation unit 14 is an input device for inputting a command by an external operation from a user. In the present embodiment, a keyboard and a pointing device (such as a mouse or a touch pad) are used.

The display unit 15 is an output device for displaying various types of information as images that can be visually recognized by the user. In the present embodiment, a liquid crystal display is used.
On the other hand, the printer 2 is an electrophotographic image forming apparatus (printing apparatus), and includes a control unit 21, a storage unit 22, a communication unit 23, an operation unit 24, a display unit 25, and an image forming unit 26.

  The control unit 21 performs overall control of each unit of the printer 2 and includes a CPU 211, a ROM 212, and a RAM 213. The ROM 212 stores a program for causing the CPU 211 to execute an image correction process (FIG. 4) described later.

The storage unit 22 is a non-volatile storage device capable of rewriting stored data, and a flash memory is used in this embodiment.
The communication unit 23 is an interface for performing data communication with the personal computer 1.

The operation unit 24 is an input device for inputting a command by an external operation from a user, and includes various operation buttons.
The display unit 25 is an output device for displaying various information as an image that can be visually recognized by the user, and a small liquid crystal display is used.

  The image forming unit 26 forms a monochrome image by fixing toner as an image forming material onto a sheet as a recording medium. Specifically, an electrostatic latent image is formed by exposing the surface of a uniformly charged photoconductor based on binary image data, and a toner image is formed by attaching toner to the electrostatic latent image. To do. Then, the toner image is transferred to a sheet conveyed by the conveying belt, and further heat-fixed by a fixing device, whereby an image is formed (printed) on the sheet. The image forming unit 26 includes a density sensor for detecting the density of a patch for density measurement described later when the patch is formed on the conveyance belt.

[1-2. processing]
Next, processing executed in the printing system according to the first embodiment will be described.
In the printing system of the present embodiment, the printer 2 executes processing for expressing the image density as preferably as possible even when the maximum density Dmax decreases.

  Specifically, the printer 2 is configured to realize the target density characteristic by gamma correction. As shown by a broken line in FIG. 2, the printer 2 has a normal maximum density Dmax (for example, 1.4) as a reference. The input density and the target density are set in a linear relationship (a part of the wavy line overlaps with the solid line) so that the target density corresponding to the maximum value of the input density becomes the maximum density Dmax. Therefore, in a state where the maximum density Dmax is not lowered (normal state), the characteristics of the output density according to the input density have a linear relationship indicated by a broken line by gamma correction.

  However, if the maximum density Dmax decreases for some reason (for example, 1.4 → 1.0), an output density higher than the maximum density Dmax after the decrease cannot be expressed. As shown by a solid line in FIG. 2, the relationship reaches a peak at the maximum density Dmax after the decrease. Therefore, the gradation of an image with a high input density cannot be expressed.

  Here, as shown by a dotted line in FIG. 2, a straight line such that the target density corresponding to the maximum value of the input density becomes the maximum density Dmax after the decrease is set with reference to the maximum density Dmax (1.0) after the decrease. Although it is conceivable to change the relationship, the density of the formed image is entirely reduced and the contrast is lowered.

  Therefore, in the printer 2 of the present embodiment, whether or not to change (decrease) the target density is selected according to image data representing an image to be printed on paper (hereinafter referred to as “print data”). Yes.

  Specifically, the printer 2 has a plurality of levels of input density as shown in FIG. 3A at a predetermined timing (for example, when the printer 2 is turned on and every predetermined number of sheets (for example, 100 sheets) is printed). An image (patch) for density measurement corresponding to (for example, a density level in increments of 10% of 0 to 100%) is formed on the conveyance belt in the image forming unit 26. Then, the density of the formed patch is detected by the density sensor, and as shown in FIG. 3B, the input density of the portion where the measured density reaches the peak as the input density rises from the relationship between the input density and the measured density. (Density Ix) is determined. That is, the input density at which the output density reaches the maximum density Dmax is determined. The density Ix determined here is used as a determination threshold value for determining the density of print data in a process described later. If the maximum density Dmax is not lower than that in the normal state, the density Ix is the maximum value of the input density.

  On the other hand, in the personal computer 1, when a print start operation is performed during execution of the application program 122 such as a word processor, the printer driver 123 is activated and print data representing an image to be printed is transferred from the application program 122 to the printer driver 123. It is. Then, the personal computer 1 transmits the print data to the printer 2 as processing of the printer driver 123. The print data created by the application program 122 and transmitted to the printer 2 is configured in units of print commands such as a text drawing command, a raster image command, a line drawing command, and a graphic drawing command. The text drawing command includes information on the background color (density), information on the character color (density), and the like.

When the printer 2 receives print data from the personal computer 1, the printer 2 executes an image correction process described below.
FIG. 4 is a flowchart of image correction processing executed by the control unit 21 (specifically, the CPU 211) of the printer 2.

  When the image correction process is started, the control unit 21 first selects one unprocessed print command (that has not been subjected to the process of S102 described later) from among the print commands constituting the print data as a processing target in S101. Select and check the contents of the print command.

Subsequently, in S102, the print command is developed into raster data of 256 gradations for each RGB in accordance with the contents of the print command checked in S101.
Subsequently, in S103, it is determined whether all print commands constituting the print data have been checked. If it is determined that there is an unchecked print command, the process returns to S101. That is, the processes of S101 to S103 are repeated for the number of print commands constituting the print data.

  On the other hand, if it is determined in S103 that all the print commands have been checked, the process proceeds to S104, and raster data of 256 tones for each RGB (image represented by the print data) created in the processes of S101 to S103 is displayed on the 256th floor in monochrome. Convert to key raster data. The reason why the color image is converted into the monochrome image is because the printer 2 of the present embodiment is a monochrome printer.

  Subsequently, in S105, a color (density) that occupies 50% or more in the image represented by the monochrome 256-tone raster data obtained in S104 is specified as the background color. Specifically, for example, the number of pixels is counted for each gradation to identify the gradation having the largest number of pixels, and when the number of pixels is 50% or more of the total number of pixels, that gradation is used as the background color. What is necessary is just to specify. If there is no color that occupies 50% or more of the image, the background color is not specified.

Subsequently, in S106, it is determined whether or not a background color is specified in S105.
If it is determined in S106 that the background color has been specified, the process proceeds to S107, and it is determined whether or not the background color is higher than the density Ix (the input density at which the above-mentioned measured density reaches the peak). That is, it is determined whether or not the background color is an input density having a target density that is higher than the current maximum density Dmax (which may be lower than normal). If it is determined in S107 that the background color is higher than the density Ix (in other words, if the target density corresponding to the background color is determined to be higher than the current maximum density Dmax), the process proceeds to S109.

  On the other hand, if it is determined in S106 that the background color is not specified, or if it is determined in S107 that the background color is less than the density Ix (in other words, the target density corresponding to the background color is less than the current maximum density Dmax). If it is determined that there is, the process proceeds to S108. Note that if the current maximum density Dmax is not lower than that in the normal state, the density Ix is the maximum value of the input density, and therefore the background color is determined to be less than or equal to the density Ix in S107.

  In S108, it is determined whether or not two or more colors (density) higher than the density Ix exist in the image represented by the monochrome 256-tone raster data obtained in S104. That is, it is determined whether or not the image includes two or more types of input densities whose target density is higher than the current maximum density Dmax. When it is determined in S108 that there are two or more colors higher than the density Ix (in other words, when it is determined that there are two or more colors corresponding to the target density higher than the current maximum density Dmax), The process proceeds to S109. Note that in the processing of S108, only colors that occupy a predetermined ratio (5% in the present embodiment) or more in the image are targeted, and colors that are less than the predetermined ratio are not targeted.

  In S109, the correspondence relationship between the input density and the target density is temporarily changed to a correspondence relation (straight line indicated by a dotted line in FIG. 2) obtained by changing the target density to a lower level based on the current (reduced) maximum density Dmax. Change only for this print data). Thereafter, the process proceeds to S111.

  On the other hand, if it is determined in S108 that there are not two or more colors higher than the density Ix (in other words, there is only one color corresponding to the target density higher than the current maximum density Dmax, or there is also one color). If it is determined not to), the process proceeds to S110. If the current maximum density Dmax is not lower than that at normal time, the density Ix is the maximum value of the input density. Therefore, in S108, there is one color corresponding to the target density higher than the current maximum density Dmax. It will be determined not to.

  In S110, the correspondence relationship between the input density and the target density remains the preset correspondence relation (straight line indicated by a broken line in FIG. 2) regardless of the current maximum density Dmax. Thereafter, the process proceeds to S111.

  In S111, the monochrome 256-gradation raster data obtained in S104 is converted into the correspondence relationship between the input density and the target density (the correspondence relation in which the target density is changed to be low when the process in S109 is performed, the process in S110 is performed). In such a case, gamma correction is performed according to a correspondence relationship set in advance).

  Subsequently, in S112, binarization processing (halftone processing) is performed on the monochrome 256-gradation raster data after gamma correction using a dither matrix. Thereby, monochrome binary image data is generated. Thereafter, the image correction process is terminated. As described above, the image forming unit 26 prints the image represented by the binary image data on a sheet.

[1-3. effect]
As described above, in the printing system of the first embodiment, the printer 2 uses the correspondence between the input density set in advance and the target density based on the normal maximum density Dmax that can be expressed by the image forming unit 26. In accordance with (the relationship of straight lines indicated by broken lines in FIG. 2), print data representing an image to be formed by the image forming unit 26 is gamma-corrected (S110, S111). However, it is a necessary condition that it is determined that the print data includes an input density whose target density is higher than the reduced maximum density Dmax due to a decrease in the maximum density Dmax that can be expressed by the image forming unit 26. (S107, S108), the print data is gamma-corrected according to the correspondence (relationship of straight lines indicated by dotted lines in FIG. 2) in which the target density is changed low with reference to the reduced maximum density Dmax (S109, S111).

  In this way, the target density is changed to be low on condition that the print data includes an input density having a density higher than the reduced maximum density Dmax as a target density. An optimum target density can be selected. Note that, for example, even when the maximum density Dmax is formed by forming a patch having the maximum density Dmax and the image forming conditions such as the developing bias are adjusted based on the measured density, the maximum density Dmax is kept constant. Since there is a limit to the adjustment of the conditions, there may be a situation where the reduction in the maximum density Dmax cannot be prevented even if the image forming conditions are adjusted to the maximum. Accordingly, even in such a situation, it is required to express the image density as preferably as possible.

  For example, in the case of an image composed entirely of low-density graphics (FIG. 5A), or a white background text image with few high-density character types (FIG. 5B), the target density is Since the density is not changed, it is possible to prevent the images having different densities from becoming difficult to distinguish due to the further decrease in density as a whole. On the other hand, for example, in the image (FIG. 5 (c)) or the text image with the black background (FIG. 5 (d)) consisting of a figure having a high density as a whole, the target density is changed to a low value. It is possible to prevent all images from being expressed at the same density. As described above, even when the maximum density Dmax is lowered, the density of the image can be expressed as preferably as possible according to the content of the image represented by the print data.

  Specifically, when it is determined that the color occupying a predetermined ratio (50%) or more in the image represented by the print data is the input density with the density higher than the reduced maximum density Dmax as the target density (S107). Then, the print data is gamma-corrected according to the correspondence relationship in which the target density is changed to be low with reference to the reduced maximum density Dmax. For this reason, when the input density whose target density is higher than the reduced maximum density Dmax occupies most of the image, the gradation of that density can be appropriately expressed.

  Also, when it is determined that the print data includes two or more types of input densities whose target density is higher than the reduced maximum density Dmax (S108), the target is based on the reduced maximum density Dmax. The print data is gamma-corrected according to the correspondence relationship in which the density is changed low. For this reason, when two or more types of input densities whose target density is higher than the reduced maximum density Dmax are included, these densities can be expressed so that the gradations can be distinguished.

  In addition, in this printer 2, the density of the patch corresponding to the input density at a plurality of stages formed in the image forming unit 26 is measured, and the input density at which the measured density reaches the peak is set as a determination threshold value (density Ix). When the input density higher than the density Ix is included in the print data, it is determined that the print data includes an input density whose target density is higher than the reduced maximum density Dmax. For this reason, it can be accurately determined that the print data includes an input density whose target density is higher than the reduced maximum density Dmax.

[1-4. Correspondence with Claims]
In the first embodiment, the printer 2 corresponds to an image processing apparatus, the image forming unit 26 corresponds to an image forming unit, the control unit 21 that executes the processes of S101 to S108 corresponds to an image determining unit, and S109. The control unit 21 that executes the processes of S111 corresponds to a correction unit.

[2. Second Embodiment]
Next, a printing system according to the second embodiment will be described. Since the basic configuration of the printing system of the second embodiment is the same as that of the first embodiment, common parts are denoted by the same reference numerals and description thereof is omitted.

In the printing system of the second embodiment, the printer 2 executes an image correction process (FIG. 6) described below instead of the image correction process (FIG. 4) described in the first embodiment.
When the control unit 21 starts this image correction process, first, in S201, an unprocessed print command (the processes of S202 to S211 to be described later have not been performed yet) among the print commands constituting the print data is processed. Select one and check the contents of the print command.

Subsequently, in S202, based on the contents of the print command checked in S201, it is determined whether or not the print command is a text drawing command.
If it is determined in step S202 that the print command is a text drawing command, the color (background color and character color) in the print command is converted to monochrome in step S203, and the process proceeds to step S204. Based on the contents of the command, it is determined whether or not the background density is higher than the density Ix. That is, it is determined whether or not the background density is an input density whose target density is a density higher than the current maximum density Dmax (which may be lower than normal). If it is determined in S204 that the background density is higher than the density Ix (in other words, if the target density corresponding to the background density is determined to be higher than the current maximum density Dmax), the process proceeds to S207. .

  On the other hand, if it is determined in S204 that the background density is lower than the density Ix (in other words, if the target density corresponding to the background density is determined to be lower than the current maximum density Dmax), the process proceeds to S205. To do. Note that if the current maximum density Dmax is not lower than that at the normal time, the density Ix is the maximum value of the input density, so in S204, it is determined that the background density is less than the density Ix.

  In S205, based on the content of the text drawing command, it is determined whether or not there are two or more colors (two types) of characters having a density higher than the density Ix. That is, it is determined whether or not the image includes two or more types of input density characters whose target density is higher than the current maximum density Dmax. When it is determined in S205 that there are two or more characters having a density higher than the density Ix (in other words, it is determined that two or more kinds of characters having a density corresponding to the target density higher than the current maximum density Dmax exist) ), The process proceeds to S207.

In S207, the correspondence relationship between the input density and the target density is temporarily changed to a correspondence relation in which the target density is changed to be low with reference to the current maximum density Dmax. Thereafter, the process proceeds to S209.
On the other hand, if it is determined in S205 that there are no two or more characters having a density higher than the density Ix (in other words, only one type of character having a density corresponding to the target density higher than the current maximum density Dmax exists) If it is determined that there is no type, the process proceeds to S208. Note that if the current maximum density Dmax is not lower than that at the normal time, the density Ix is the maximum value of the input density. Therefore, in S205, there is one type of character having a density corresponding to the target density higher than the current maximum density Dmax. Is determined not to exist.

  If it is determined in S202 that the print command is not a text drawing command, the color (background color and character color) in the print command is converted to monochrome in S206, and the process proceeds to S208.

In S208, the correspondence relationship between the input density and the target density is maintained as the correspondence relation set in advance regardless of the current maximum density Dmax. Thereafter, the process proceeds to S209.
In step S209, the print command is expanded into monochrome 256-gradation raster data.

Subsequently, in S210, the monochrome 256-tone raster data obtained in S209 is gamma-corrected according to the correspondence between the input density and the target density.
Subsequently, in S211, binarization processing (halftone processing) is performed on the raster data of monochrome 256 gradation after gamma correction using a dither matrix. Thereafter, the image correction process is terminated.

  As described above, in the printer 2 of the second embodiment, when the print command to be processed is a text drawing command having the background color of the image as a parameter, the background density or characters of two or more colors are If it is determined that the input density has a density higher than the reduced maximum density Dmax as a target density (S204, S205), the print data is obtained according to the correspondence relationship in which the target density is changed to be low with reference to the reduced maximum density Dmax. Gamma correction is performed (S207, S210). If the print command to be processed is not a text drawing command, the print data is gamma-corrected according to the correspondence relationship between the preset input density and the target density regardless of the content of the image (S208, S210). As described above, the background color density of the image is determined based on the parameters of the print command, and the image is not analyzed for the print command other than the text drawing command, so that the processing can be simplified.

[3. Third Embodiment]
Next, a printing system according to the third embodiment will be described. Since the basic configuration of the printing system of the third embodiment is the same as that of the first embodiment, common parts are denoted by the same reference numerals and description thereof is omitted.

  In the printing system of the third embodiment, the printer 2 executes an image correction process (FIG. 7) described below instead of the image correction process (FIG. 4) described in the first embodiment. 7 are the same as those of S201 to S205, S207, S208, S104 to S108, S206, S109, S110, and S209 to S212 described above. Therefore, detailed description is omitted.

  When the control unit 21 starts the image correction process, first, in S301, an unprocessed print command (that has not been subjected to the processes of S302 to S319 described later) is selected as a processing target from among the print commands constituting the print data. Select one and check the contents of the print command.

Subsequently, in S302, based on the contents of the print command checked in S301, it is determined whether or not the print command is a text drawing command.
If it is determined in S302 that the print command is a text drawing command, the processes of S303 to S307 and S317 to S320 (the same processes as S202 to S205 and S207 to S212) are executed. That is, as in the second embodiment, when the background density or the density of characters of two or more colors is higher than the density Ix, the target density is changed to be low and gamma correction is performed.

On the other hand, if it is determined in S302 that the print command is not a text drawing command, the process proceeds to S308 to determine whether or not the print command is a raster image command.
If it is determined in S308 that the print command is a raster image command, the processes of S309 to S313 and S315 to S320 (the same processes as S104 to S110 and S209 to S212) are executed. That is, as in the first embodiment, when the density of the color occupying 50% or more of the image or the density of two or more colors is higher than the density Ix, the target density is changed to be low and gamma correction is performed.

  On the other hand, if it is determined in S308 that the print command is not a raster image command (a line drawing command or a graphic drawing command), the processing in S314, S316, S317 to S320 (the same processing as S206, S110, and S209 to S212) ). That is, the target density is not changed regardless of the content of the image.

  As described above, in the printer 2 of the third embodiment, as in the second embodiment, when the print command to be processed is a text drawing command having the background color of the image as a parameter, the background density or When it is determined that a character of two or more colors has an input density whose target density is higher than the reduced maximum density Dmax (S304, S305), the target density is changed to be lower with reference to the reduced maximum density Dmax. The print data is gamma-corrected according to the corresponding relationship (S306, S318).

  On the other hand, when the print command to be processed is not a text drawing command, the color occupying a predetermined ratio (50%) or more in the image represented by the print data is higher than the reduced maximum density Dmax, as in the first embodiment. When it is determined that the input density has the density as the target density (S312), it is determined that the print data includes two or more types of input densities whose target density is higher than the reduced maximum density Dmax. In this case (S313), the print data is gamma-corrected according to the correspondence relationship in which the target density is changed low with reference to the reduced maximum density Dmax (S315, S318).

  For this reason, according to the printer 2 of the third embodiment, it is possible to express the image density as preferably as possible according to the contents of the image other than the text drawing command while simplifying the processing for the text drawing command.

[4. Other forms]
As mentioned above, although embodiment of this invention was described, it cannot be overemphasized that this invention can take a various form, without being limited to the said embodiment.

  For example, in the above embodiment, the color occupying a predetermined ratio or more of the image is specified as the background color (S105, S310). However, the color here is not limited to the exact same color, and the color within a predetermined range. In this way, it is possible to cope with a background color with gradation. In this case, the color specified as the background color may be, for example, a maximum value, a minimum value, an intermediate value, an average value, or the like of a predetermined range of colors.

  In the above-described embodiment, an input density that is higher than the density Ix is included in the print data, with the input density at which the measured density of the patch formed in the image forming unit 26 reaches a peak value as a determination threshold (density Ix). In this case, it is determined that the print data includes an input density whose target density is higher than the reduced maximum density Dmax. However, the present invention is not limited to this. For example, when the maximum density Dmax is reduced (or estimated to have been reduced), the print data includes an input density that is higher than a preset density (fixed determination threshold). In addition, it may be determined that the print data includes an input density whose target density is higher than the reduced maximum density Dmax.

  Furthermore, in the above-described embodiment, the configuration in which the density measurement patch is formed on the conveyance belt and detected by the density sensor is exemplified. However, the present invention is not limited to this. For example, the density measurement patch is formed on the intermediate transfer belt or the photoconductor. The patch may be detected by a density sensor, or the patch may be printed on a recording medium such as paper.

  On the other hand, the criterion for determining whether or not to change the target density to a low level is not limited to the one exemplified in the above embodiment, and it is determined that the print data includes an input density whose target density is higher than the maximum density Dmax. What is necessary is just to change the target density to a low level as a necessary condition. For example, the background color (density) may be required to be higher than the density Ix (for example, S108, S205, S305, and S313 are deleted). Conversely, two or more colors (density) higher than the density Ix are available. It may be necessary to exist (for example, S105 to S107, S204, S304, S310 to S312 are deleted). Further, if the image includes an input density whose target density is higher than the reduced maximum density Dmax, the input density is not the background density, and there is only one type of such input density. Even if not, the target density may be changed to a lower value.

  On the other hand, in the above embodiment, the printer 2 which is an electrophotographic image forming apparatus that forms a monochrome image by fixing toner on a sheet is exemplified, but the present invention is not limited to this, and a color image is formed. The present invention can also be applied to an image forming apparatus and an image forming apparatus that forms an image with an image forming material (for example, ink) other than toner.

  In the above-described embodiment, the configuration in which the printer 2 functions as the image processing apparatus of the present invention among the personal computer 1 and the printer 2 configuring the printing system is illustrated, but the present invention is not limited to this. That is, the above-described image correction processing can be executed on the personal computer 1 side (for example, as processing of the printer driver 123). In this case, the personal computer 1 functions as the image processing apparatus of the present invention.

  DESCRIPTION OF SYMBOLS 1 ... Personal computer, 2 ... Printer, 11 ... Control part, 12 ... Memory | storage part, 13 ... Communication part, 14 ... Operation part, 15 ... Display part, 21 ... Control part, 22 ... Storage part, 23 ... Communication part, 24 ... Operation unit, 25 ... Display unit, 26 ... Image forming unit

Claims (7)

A correction unit that corrects image data representing an image to be formed on the image forming unit according to a correspondence relationship between a preset input density and a target density based on the maximum density that can be expressed by the image forming unit;
An image determination unit that determines that an input density having a higher density than the reduced maximum density as a target density is included in the image data due to a decrease in the maximum density that can be expressed by the image forming unit;
With
The correction unit determines the reduced maximum density on condition that the image data includes an input density having a density higher than the reduced maximum density as a target density. An image processing apparatus, wherein the image data is corrected in accordance with a correspondence relationship in which the target density is changed to be low as a reference. The density of the patch corresponding to the multi-stage input density formed on the image forming means is measured, and the image judging means uses the input density at which the measured density reaches the peak as a judgment threshold, and the judgment threshold. When an input density higher than a value is included in the image data, it is determined that the image data includes an input density having a density higher than the reduced maximum density as a target density. The image processing apparatus according to claim 1. When the image data is command data having the background color of the image as a parameter, the image determination means determines that the background color is an input density having a density higher than the reduced maximum density as a target density. Judgment,
When the image determining unit determines that the background color is an input density having a higher density than the reduced maximum density as a target density, the correction unit determines the target based on the reduced maximum density. The image processing apparatus according to claim 1, wherein the image data is corrected according to a correspondence relationship in which the density is changed to be low. If the image data is not command data having the background color of the image as a parameter, the correction means corrects the image data according to a correspondence relationship between a preset input density and a target density. The image processing apparatus according to claim 3. The correction means, when it is determined by the image determination means that the image data includes two or more types of input densities whose target density is higher than the reduced maximum density, the reduced The image processing apparatus according to any one of claims 1 to 4, wherein the image data is corrected according to a correspondence relationship in which the target density is changed to be low with reference to the maximum density. The image determination means determines that a color occupying a predetermined ratio or more in an image represented by the image data is an input density having a target density that is higher than the reduced maximum density,
When the image determining unit determines that the color occupying the predetermined ratio or more is an input density having a higher density than the reduced maximum density as a target density, the correcting unit determines the reduced maximum density The image processing apparatus according to any one of claims 1 to 5, wherein the image data is corrected in accordance with a correspondence relationship in which the target density is changed to be low with reference to the above. A correction unit that corrects image data representing an image to be formed on the image forming unit according to a correspondence relationship between a preset input density and a target density based on the maximum density that can be expressed by the image forming unit;
The computer functions as an image determination unit that determines that the image data includes an input density whose target density is higher than the reduced maximum density due to a decrease in the maximum density that can be expressed by the image forming unit. An image processing program for causing
The correction unit determines the reduced maximum density on condition that the image data includes an input density having a density higher than the reduced maximum density as a target density. An image processing program, wherein the image data is corrected in accordance with a correspondence relationship in which the target density is changed to be low as a reference.