JP2005057702A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus provided with a highly accurate image correction function in which an image output characteristic is not erroneously determined by the show-through effects of an original. <P>SOLUTION: This image forming apparatus is provided with an image forming means for forming an image by using an image reading means for optically scanning an original and converting the original into an image signal and an image correcting means for correcting the image signal read by the image reading means. The reading means reads a test pattern, the image signal correcting means forms a correction value of the image signal on the basis of a read result, and the image forming means forms an image on the basis of the correction value. In this image forming apparatus, when a prescribed set-off detecting means for detecting set-off of an image detects set-off, the prescribed set-off detecting means emits an alarm when forming the correction value. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer apparatus, a facsimile machine, and a multifunction machine having an image correction function.

  It is known that the hue and the like differ depending on the characteristics of the image forming apparatus between the original and the original read and printed by a copying machine. Various methods are used as a method for correcting the output characteristics of the image forming apparatus.

  For example, after a specific gradation test pattern is formed on a transfer sheet in an image forming apparatus, the density of the gradation test pattern on the formed transfer sheet is read by an image reading unit, and a correction value is calculated based on the image information. However, there is a method of setting γ (gamma) correction means or the like. By this method, it is possible to stabilize the image quality by correcting the variation in the image output characteristics of the image forming apparatus due to the variation in environmental conditions and the change with time. A method for increasing the correction accuracy using a plurality of test patterns (for example, Patent Document 1) has also been proposed.

In addition, image forming apparatuses such as printers, facsimiles, and copiers are equipped with lenses, mirrors, LED arrays, and other mounting accuracy, laser or ink head scanning in the main scanning direction, transfer paper skew during pattern creation, In some cases, the correction value is influenced by the positional deviation of the document. For these error factors, there has been proposed a method for easily correcting the inclination of an image or the like (for example, Patent Document 2).
JP 2002-59626 A JP 2000-101801 A

  However, the following points are not considered in the conventional method as described above. For example, when printing is already performed on the paper used as the transfer paper, that is, when the gradation pattern is output using the backing paper, a gradation pattern is formed on the front surface and an unspecified image is formed on the back surface. Will be.

When the gradation pattern formed on such a sheet is read by the image reading unit, the image on the back surface may pass through the sheet and overlap with the gradation pattern on the front surface. Therefore, there is a problem that the read value differs from the actual gradation pattern, and when the correction value is calculated based on the image information, an apologized correction value may be set.
SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus having a highly accurate image correction function without correcting image output characteristics due to the influence of show-through of a document.

  In order to solve the above problems, the invention described in claim 1 is an image reading unit that optically scans a document to convert it into an image signal, and an image that corrects the image signal read by the image reading unit. And an image forming unit that forms an image based on an image read by the image reading unit, the reading unit reads a test pattern, and the image signal correcting unit reads the test pattern. A correction value of an image signal is formed based on a result, and the image forming unit includes a predetermined show-through detection unit for detecting a show-through of the image in the image forming apparatus that forms an image based on the correction value. When detected, a warning is issued when the correction value is formed.

According to the first aspect of the present invention, it is possible to provide an image forming apparatus having a highly accurate image correction function without correcting image output characteristics due to the influence of show-through of a document.
According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the show-through detecting unit detects a show-through portion based on edge intensity detection and color threshold processing.

  According to the invention described in claim 2, since the show-through detection is performed based on the edge intensity detection and the color threshold value processing, the show-through detection can be performed more accurately.

  According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the show-through detection unit displays an area of the show-through portion and determines whether to perform correction based on the area. It has the selection means to select, It is characterized by the above-mentioned.

  According to the third aspect of the present invention, since the area of the show-through is displayed and it is possible to select whether or not to correct the image signal according to the display result, it is possible to set the allowance for show-through according to the judgment of the user. .

  According to a fourth aspect of the present invention, the image forming apparatus according to any one of the first to third aspects has a function of selecting presence / absence of a show-through detection unit.

  According to the invention described in claim 4, since the show-through detection means does not perform the show-through determination process, the user has knowledge about whether or not the document is show-through depending on the paper quality, thickness, and type of the document. Based on the above, it is possible to select whether or not the show-through document determination process is performed.

  According to the present invention, it is possible to provide an image forming apparatus having an image correction function with high accuracy without correcting image output characteristics due to the influence of show-through of a document.

  Embodiments of the present invention will be described with reference to the drawings.

[First embodiment]
FIG. 1 is a diagram illustrating an example of an image used in the present embodiment. 1A shows a test pattern formed on the front side of the paper 105, FIG. 1B shows an example of an image already printed on the back side of the paper 105, and FIG. 1C shows the test pattern shown in FIG. ) Is read from the front side, an example of recognition in which the image on the back side is seen through and superimposed on the test pattern is recognized by the image forming apparatus. In the present embodiment, as shown in FIG. 6C, the fact that the image on the back surface is read or copied while being superimposed on the image on the front surface is expressed as “show-through”. In addition, the figure (c) is exaggerated for clarity. In addition, as shown in FIG. 5C, a part where an image that is not originally on the surface is recognized is called a show-through part.

  Conventionally, as shown in FIG. 2C, the correction value is sometimes calculated based on an image in which the printed content of the back surface is superimposed on the test pattern.

  FIG. 2 is a configuration diagram illustrating a configuration of the copying machine 100 as an example of the image forming apparatus. The copying machine 100 includes an image reading unit 111, an image correcting unit 112, an image forming unit 113, a show-through detection unit 114, and a correction value storage unit 115. The image reading unit 111 optically scans the original and converts it into an image signal, and the image forming unit 113 adsorbs toner to an image latent imaged on a photosensitive drum, for example, and fixes it on a sheet or the like. The correction value storage unit 115 is a storage area for storing a correction value for calibrating an image signal obtained by converting the image into a read signal by the image reading unit 111 and a conversion table for correction. The image correction unit 112 calculates a correction value based on the image signal data obtained by reading the test pattern, and the show-through detection unit 114 detects a show-through part based on the read image. The image correction unit 112 and the show-through detection unit 114 will be described in detail later.

  The outline of this embodiment will be described with reference to FIGS. First, using the paper 105 printed on the back surface as shown in FIG. 1B, the image forming unit 113 prints a test pattern and outputs an image as shown in FIG. When the image reading unit 111 reads the paper 105 in FIG. 1A, if the show-through is not recognized, it is recognized by the image forming apparatus 100 as shown in FIG. 1A. If the show-through is shown, FIG. It is recognized as (c).

  The show-through detection unit 114 detects whether or not the recognized image is show-through as an output image of the test pattern. The image correction unit 112 is controlled based on the detection result of the show-through detection unit 114. The image correction unit 112 does not function when the show-through is performed, and calculates a correction value of a predetermined image signal when the show-through is not performed and stores the correction value in the correction value storage unit 115.

  Next, the present embodiment will be described in detail based on the flowchart of FIG. FIG. 3 is a diagram showing a flowchart of the operation of the present embodiment.

  First, the user selects an automatic image correction function in the copying machine 100 (S401). The automatic image correction function is a function for automatically correcting output characteristics of the image forming apparatus based on a test pattern. If this function is not selected prior to operation, it will provide normal functions as a copier, such as discharging copied images. Therefore, when correcting output characteristics using a test pattern, this function should be used first. select.

  Subsequently, based on the image forming means of the copying machine 100, a test pattern is printed on the transfer paper and output (S402). This operation may be performed again following step 401, or a test pattern may be automatically output using the selection in step 401 as a trigger.

  This embodiment is effective when outputting the test pattern paper shown in FIG. 1B on which some image characters or the like are printed on the back surface.

  The test pattern data is already stored in the storage device of the copying machine 100. Therefore, as a result of executing step 402, an image is formed based on the test pattern data and a test pattern is output.

  An example of the test pattern is shown in FIG. The test pattern in FIG. 1A is obtained by changing the density stepwise in each color patch of CMYK. CMYK means C is cyan, M is magenta, Y is yellow, and K is black. The test pattern is not limited to that shown in the figure, and any pattern that can correct the output characteristics of the image forming apparatus may be used. For example, an IT8.7 image standardized by ANSI (American Standards Association) may be used.

  Next, the sheet 105 printed with the test pattern output by the copying machine 100 is placed on the document table or ADF (automatic document feeder) of the copying machine 100 (S403). The surface shown in FIG. 1A is set toward the image reading unit of the copying machine 100. Now that the test pattern is ready to be read, the test pattern is read using the image reading means of the copying machine 100 (S404).

  When the reading of the test pattern is completed, it is subsequently determined whether or not the sheet 105 is a show-through document. An example of the determination method will be described in detail.

(Back-through determination processing)
FIG. 4 is a flowchart illustrating a method for determining whether or not the read document is show-through. The show-through determination process uses an existing method (Japanese Patent Laid-Open No. 2001-169080 “Color image processing method, color image processing apparatus, and recording medium therefor”).

  First, when a test pattern image is input in step 404 (S1), the image is reduced (S2). By processing an image created by reducing the original image, the processing speed is increased, the amount of working memory is saved, and the implementation is simplified. Next, the color coordinate system is converted (S3). In this embodiment, a CMYK color patch is used as a test pattern. However, in the case of an RGB color patch, since the RGB space has low independence between components, the edge detection accuracy and noise robustness are improved. Since there may be no, the coordinate system is converted to an appropriate one to improve edge detection accuracy and noise robustness.

  Subsequently, edge strength calculation is performed (S4). By performing the edge strength calculation, as a result, a foreground portion of a color document such as text or a line drawing, or a background portion having a higher brightness (lighter color) than the show-through portion can be retained. Next, binarization processing is performed to detect edges (S5), and color threshold processing is executed for regions other than the edges (S6). As a result, the show-through portion can be corrected without inputting and accumulating the back side image. By color threshold processing, the surface and the show-through portion can be separated and the color can be specifically estimated. The size of the show-through part to be removed can be explicitly specified according to the size of the window to be set. By doing so, the processing becomes a local operation, which leads to saving of working memory and simplification of implementation.

  Next, the show-through removed image is synthesized based on the background color image estimated by the color threshold processing (S7).

  Subsequently, the edge strength of the show-through removed image is calculated (S8), and an edge difference image is generated for the original image and the show-through removed image (S9). By comparing the image created as a result of processing with the original image, it is possible to detect a portion where the image has deteriorated due to inappropriate processing by a simple operation. By executing the process again around that part, it is possible to prevent image degradation and improve the processing result. Next, the edge intensity difference is binarized (S10), the processing scale (window size) is reduced, the color threshold processing is performed in the same manner as in Step 6 to estimate the background color image (S11), and the show-through removal is performed. The images are synthesized (S12).

  Subsequently, the show-through part is identified by calculating the difference between the show-through removed image and the reduced original image (S13). If there are many parts estimated as the show-through part, it is determined that the document is a show-through document, If there is little or no show-through part, it is determined that the document is not a show-through document (S14).

  The above is the show-through determination process (S405).

  If it is determined that the document is a show-through document based on the determination in step 405, the process in step 407 is performed. In this case, since the test pattern output to the paper 105 read by the image reading means is shown through as shown in FIG. 1C, the paper 105 is shown through in the image forming apparatus. Warning to that effect. As a result, even if a show-through with a large area is detected in the read image of the test pattern, an image forming apparatus having a high-accuracy image correction function without erroneously determining image output characteristics due to the effect of show-through of the document Can be provided.

  If it is determined that the document is not a show-through document based on the determination in step 405, the process proceeds to step 406, and image correction processing such as calculation and setting of a gradation correction curve is performed.

(Image signal correction processing)
The image forming signal data A obtained by reading the output test pattern and converting it into image forming signal data is equal to the image forming signal data B originally stored in the storage device. However, strictly speaking, the image formation signal data A and the original image formation signal data B are different. For example, when expressed in terms of image quality, the hue, brightness, brightness, etc. of the output test pattern differ from the hue, brightness, brightness, etc. of the original image forming signal data.

  The image signal correcting means corrects the image forming signal data A read from the output test pattern so as to approach the original image forming signal data B.

As for image output characteristic correction processing, a conventional method (Japanese Patent Laid-Open No. 2002-59626)
The method described in “Image forming apparatus”) is used.

  The image forming signal data A read and converted by the image reading means is compared with the image forming signal data B of the test pattern originally stored in the storage device, and the unevenness of the image sensor, the uneven illumination of the light source, the input system Correction values such as degradation of MTF (modulation transfer) characteristics, differences in color separation characteristics of the input system and spectral characteristics of the color material of the output system, and the like are formed.

  The gradation correction curve can be realized by a method equivalent to the method described in Japanese Patent Laid-Open No. 9-107477, for example. This gradation correction method is performed as follows.

The test pattern output by the image forming unit 113 is read by the image reading unit 111. At this time, an image signal conversion table (hereinafter referred to as LUT) is used to correct the output characteristics of the image forming means and to emphasize a specific density region. Since the image density of the image output by the image forming means is not proportional to the input image signal and deviates from the image density of the original, it is necessary to convert the image signal by the LUT in order to reduce this input / output image density difference. It is known that there is. The LUT is stored in the image correction unit, converts an input image signal input from the image reading unit, and outputs the converted image signal to the image forming unit.

  If the output characteristics of the image forming means 113 have not changed from the state at the time of LUT creation, the image forming signal data A and the image forming signal data B of the test pattern originally stored in the storage device should be equal. However, if the image formation signal data A and the image formation signal data B are different from each other due to deterioration of characteristics of the image forming unit 113, the correction for correcting the image signal is performed in the same manner as when creating the LUT. A table is created and corrected so as to correspond to the characteristics of the copier when the test pattern is read.

  These correction values are set in the gradation correction table of the correction value storage means 115 or the like. The above is the processing performed by the image signal correction unit.

  When the image signal correction in step 406 or the warning display in step 407 is performed, the processing of the automatic image correction function ends. The copying machine 100 may display an end message to the user. In order to improve the accuracy of image signal correction, not only one original but also a plurality of test patterns may be used as a test pattern.

  According to the present embodiment, since a warning is issued when the show-through area is large, it is possible to use a sheet with some printing on the back surface even in the automatic image correction function. In other words, it is possible to try image correction of the image forming apparatus using a sheet of paper that is printed on one side generated in an office or the like, and the effective use of the sheet is promoted, which can be used for environmentally friendly corporate activities.

[Second Embodiment]
Next, a second embodiment will be described. FIG. 5 is a flowchart of the operation of the second embodiment. 5, the same processes as those in FIG. 3 are denoted by the same reference numerals, and the description thereof is omitted. The flowchart of FIG. 5 includes a step 411 that is a process for displaying the area of the show-through part after step 404 and a process for determining whether or not to continue the correction process after step 411. 3 is different from the flowchart of FIG. 3 in that step 412 is included.

  In this embodiment, the area of the show-through portion is displayed on, for example, the operation screen of the copying machine 100 by using the show-through determination process in step 405 of the first embodiment (S411). In the show-through determination process in step 405, as shown in FIG. 4, the show-through portion is identified by calculating the difference between the show-through removed image and the reduced original image (S13), and the portion estimated as the show-through portion is determined. If so, it is determined that the document is a show-through document, and if there is little or no show-through portion, it is determined that the document is not a show-through document (S14).

  Therefore, the area of the show-through portion can be displayed based on the processing results of these steps 13 and 14. As for the area of the show-through part, the area estimated to be the show-through part may be displayed by some method. For example, the size of the area of the show-through part may be displayed in 10 steps, or the back of the document The area of the reflected portion may be displayed as a percentage.

  When the area of the show-through portion is displayed, the user looks at the displayed area and selects whether to form and set a correction value for correcting the output characteristics of the image forming apparatus. This means that the user can choose whether to make the show-through judgment stricter or sweeter, and change the judgment strength according to how much show-through is acceptable according to the user's judgment criteria. Make it possible.

  That is, in this embodiment, the test pattern can be output using paper already printed on the back side, which is the same as in the first embodiment, but the user can make a more detailed show-through determination according to the area of the show-through portion. There is an advantage that can be done.

[Third embodiment]
Subsequently, a third embodiment will be described. FIG. 6 is a flowchart of the operation of the third embodiment. In FIG. 6, the same processes as those in FIG. 3 are denoted by the same reference numerals, and the description thereof is omitted. The flowchart in FIG. 6 is different from the flowchart in FIG. 3 in that step 421 that is a process of setting the show-through determination process to OFF is included after step 401. Further, since there is a process for setting the show-through determination process to OFF (S421), step 405 is a process for determining whether the document is a show-through document, and step 407 is a process for issuing a warning that the document is a show-through document. Are different from the flowchart of FIG.

  Therefore, in this embodiment, since the process relating to the show-through determination performed in the first and second embodiments is not performed, the gradation correction is always performed regardless of whether the paper on which the test pattern is output is show-through. Image correction processing such as curve calculation and setting is performed (S406).

  According to this embodiment, the user can utilize knowledge about whether or not a document to show through by recognizing the paper quality, thickness, type, etc. of the document to be used, and perform the show-through document determination process based on that knowledge. You can choose whether or not to do it. Further, the user can select so that automatic gradation processing can be performed even when there is a show-through.

  Although the above embodiment has been described based on the copying machine 100, the present invention may be applied to other image forming apparatuses such as a printer apparatus, a facsimile machine, and a multifunction machine having an image correction function.

FIG. 3 is a diagram illustrating an example of an image output or recognized by the image forming apparatus. 1 is a diagram illustrating an example of a configuration of a copying machine. It is a flowchart figure which shows operation | movement of 1st Example. It is a flowchart figure which shows operation | movement of show-through determination processing. It is a flowchart figure which shows operation | movement of 2nd Example. It is a flowchart figure which shows operation | movement of 3rd Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Image forming apparatus 105 Paper 106 Example of recognized image 111 Image reading means 112 Image correction means 113 Image forming means 114 Show-through detection means 115 Correction value storage means

Claims (4)

Based on the image read by the image reading means using an image reading means for optically scanning the document and converting it into an image signal, and an image signal correcting means for correcting the image signal read by the image reading means. Image forming means for forming an image
In the image forming apparatus, the reading unit reads a test pattern, the image signal correcting unit forms a correction value of an image signal based on the reading result of the test pattern, and the image forming unit forms an image based on the correction value. ,
An image forming apparatus comprising: a predetermined show-through detection unit that detects show-through of an image, and issues a warning when the show-through is detected when the show-through is detected. The show-through detection means detects the show-through portion based on edge intensity detection and color threshold processing,
The image forming apparatus according to claim 1. The show-through detection means has a selection means for displaying the area of the show-through part and selecting whether or not to perform correction based on the area.
The image forming apparatus according to claim 1.   The image forming apparatus according to claim 1, further comprising a selection unit that selects whether or not the show-through detection unit functions.

Images