Abstract:
In an image forming apparatus having storing means for storing image data to be composited with received image data, means for compositing the image data with the received image data, means for forming an image based on the resulting composite image data, and determining means for determining whether or not image formation is possible, the image formation based on the image data is executed or stopped according to the determination result of the determining means.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2004-41911 filed in Japan on Feb. 18, 2004, the entire contents of which are hereby incorporated by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to an image forming apparatus and an image forming system, capable of adding an image for restraining copying to printed material.  
         [0004]     2. Description of Related Art  
         [0005]     As one of techniques for preventing copying of printed material, a technique using a pantograph pattern in the background of a document which is prohibited from being copied has been known. A pantograph pattern consists of dots (foreground dots) in a size that remain even when a copy is made using a copying machine, and dots (background dots) which are so small and disappear when a copy is made. The background dots are provided around the foreground dots so that characters and patterns drawn by the foreground dots are not noticeable. When printed material on which a pantograph pattern is formed is copied, the background dots disappear and only the foreground dots remain, and consequently the characters and patterns drawn by the foreground dots appear. Therefore, by embedding characters such as “copy-prohibited” and “confidential document” drawn by the foreground dots in the pantograph pattern in advance, the printed material to be produced can have the effect of restricting copying by itself.  
         [0006]     The technique of preventing copying using a pantograph pattern is mainly classified into two types. One is a technique using a special paper on which a pantograph pattern is printed in advance, and the other is a technique in which a pantograph pattern and a document are printed together as to be described later. With the former technique, by setting the special paper with a pantograph pattern on a paper feed tray of a printing apparatus and printing a document, printed material having the copy preventing effect is obtained. However, since it is necessary to prepare the paper on which a pantograph pattern is printed in advance, such a technique has the problem of an increase in the printing cost. Moreover, since predetermined characters and patterns for restricting copying are used, it is difficult to change the pantograph pattern according to a document, and thus this technique also has the problem of lack of convenience.  
         [0007]     Therefore, in recent years, a technique was proposed to print a pantograph pattern on normal paper, etc. by providing a printer driver or a printing apparatus with the function of adding a pantograph pattern to an image of a document to be printed (see, for example, Japanese Patent Applications Laid Open No. 2001-324898 and No. 2003-224717). With a printer driver having the function of adding a pantograph pattern, by performing the process of compositing image data for a document and image data for a pantograph pattern together in an information processing apparatus in which the printer driver is installed and then transmitting to a printing apparatus a print job created based on the resulting composite image data, a document with the pantograph pattern in the background can be formed on normal paper. Similarly, in the case where a printing apparatus is provided with the function of adding a pantograph pattern, when addition of a pantograph pattern is instructed by a print job, it is possible to form a document with the pantograph pattern in the background on normal paper by compositing image data for the pantograph pattern with image data extracted from the print job and executing a print process based on the resulting composite image data. According to these techniques, by preparing a plurality of types of pantograph patterns in a printer driver or a printing apparatus, it is possible to select and use a pantograph pattern according to a document.  
         [0008]     Since a pantograph pattern as described above is composed of a pattern of finely adjusted gradations, in order to print the pantograph pattern on normal paper, a printing apparatus must be able to faithfully reproduce the gradations. By the way, in a printing apparatus that forms an image by electrophotographic processes, when consumable supplies such as a photosensitive drum and developer deteriorate and need to be replaced, or when the printing apparatus is in a period of adjustment, the printing apparatus may fail to faithfully reproduce the gradations of the pantograph pattern. If it is impossible to faithfully reproduce the gradations of the pantograph pattern, an image intended to appear when a copy is made will not appear, and consequently there arises a problem that the effect of the pantograph pattern that restrains copying may not be sufficiently exhibited.  
       BRIEF SUMMARY OF THE INVENTION  
       [0009]     The present invention has been made with the aim of solving the above problems, and it is an object of the present invention to provide an image forming apparatus and an image forming system capable of executing processes after finding the current status of the image forming apparatus by making a determination, when forming an image by compositing received image data and image data stored in storing means, as to whether or not image formation based on the resulting composite image data is possible and executing or stopping the image formation according to the determination result so as to provide printed material in a condition capable of exhibiting the effect of a pantograph pattern.  
         [0010]     An image forming apparatus according to the present invention is an image forming apparatus that receives image data and forms an image on a sheet based on the received image data, and characterized by comprising: storing means for storing image data to be composited with the received image data; means for compositing the image data with the received image data; means for forming an image based on the resulting composite image data; and determining means for determining whether or not image formation by the means is possible, wherein the image formation based on the image data is executed or stopped according to a determination result of the determining means.  
         [0011]     In the present invention, when forming an image by compositing received image data and image data stored in the storing means together, a determination is made as to whether or not image formation based on the resulting composite image data is possible, and then the image formation is executed or stopped according to the determination result. Therefore, when the determining means determines that it is impossible to form the resulting composite image due to deterioration of various parts and consumable supplies in the means for forming an image, it is possible to control the apparatus to stop the image formation. As a result, the quality of the image to be outputted can be maintained at a fixed level, and, for example, an image such as a pantograph pattern that requires fine gradation representation can be provided as printed material only when it is possible to faithfully reproduce the gradation representation.  
         [0012]     The image forming apparatus according to the present invention is characterized by comprising detecting means for detecting the quality of an image to be formed on a sheet, wherein the determining means determines, based on a detection result of the detecting means, whether or not image formation is possible.  
         [0013]     In the present invention, the quality of an image to be formed on a sheet is detected, and a determination as to whether image formation is possible or not is made based on the detection result. Therefore, when the determining means determines that it is impossible to form the composite image at a fixed level of quality due to deterioration of various parts, consumable supplies, etc., it is possible to control the apparatus to stop the image formation, and consequently the quality of the image to be outputted can be maintained at a fixed level.  
         [0014]     The image forming apparatus according to the present invention is characterized by comprising measuring means for measuring the density of an image, wherein the detecting means detects the quality of the image based on the density measured by the measuring means.  
         [0015]     In the present invention, the image quality is detected based on the result of measuring the density of the image. Therefore, for example, when it is impossible to faithfully reproduce the gradations of a pantograph pattern, it is possible to control the apparatus to stop the image formation.  
         [0016]     The image forming apparatus according to the present invention is characterized by comprising predicting means for predicting the quality of an image to be formed on a sheet, wherein the determining means determines, based on a prediction result of the predicting means, whether or not image formation is possible.  
         [0017]     In the present invention, the quality of an image to be formed on a sheet is predicted, and a determination as to whether image formation is possible or not is made based on the prediction result. Therefore, when it is possible to predict that it is impossible to form the composite image at a fixed level of quality due to deterioration of various parts, consumable supplies, etc., it is possible to control the apparatus to stop the image formation, and consequently the quality of the image to be outputted can be maintained at a fixed level.  
         [0018]     The image forming apparatus according to the present invention is characterized by comprising means for detecting the remaining amount of a consumable member used for image formation, wherein the predicting means predicts the quality of the image based on the detection result of the means.  
         [0019]     In the present invention, the remaining amount of a consumable member used for image formation is detected, and the quality of the image is predicted based on the detection result. Therefore, when it is possible to predict that it is impossible to form the composite image at a fixed level of quality due to deterioration of the consumable member, etc., it is possible to control the apparatus to stop the image formation, and consequently the quality of the image to be outputted is maintained at a fixed level.  
         [0020]     The image forming apparatus according to the present invention is characterized by comprising means for counting the number of times image formation was executed, wherein the predicting means predicts the quality of the image based on the number counted by the means.  
         [0021]     In the present invention, the number of times image formation was executed is counted, and the quality of the image is predicted based on the counted number. Therefore, when it is possible to predict degradation of image quality due to repetitions of image formation, it is possible to control the apparatus to stop the image formation, and consequently the quality of the image to be outputted can be maintained at a fixed level.  
         [0022]     The image forming apparatus according to the present invention is characterized by further comprising means for compensating for degradation of the image quality when the detection result or the prediction result shows degradation of the image quality.  
         [0023]     In the present invention, when the result of detecting the quality of an image, or the result of predicting the quality of an image shows degradation of the image quality, the degradation of the image quality is compensated. Therefore, the quality of the image to be outputted can be maintained at a fixed level, and, when it is impossible to compensate for the degradation of the image quality, the image formation can be stopped.  
         [0024]     The image forming apparatus according to the present invention is characterized by forming an image on a sheet by electrophotographic processes.  
         [0025]     In the present invention, since image formation is performed by electrophotographic processes, a determination as to whether or not it is possible to faithfully reproduce an image such as a pantograph pattern can be made after finding the condition of a photosensitive drum, developer, etc., and thus it is possible to provide printed material only when a faithful reproduction is possible.  
         [0026]     The image forming apparatus according to the present invention is characterized by further comprising means for giving information stating a determination result when the determining means determines that image formation based on the composite image data is impossible.  
         [0027]     In the present invention, when the determining means determines that image formation based on the composite image data is impossible, the information stating a determination result of the determining means is given, thereby warning the user that an image such as a pantograph pattern may not be added appropriately due to deterioration of the electrophotographic processes, etc.  
         [0028]     The image forming apparatus according to the present invention is characterized in that the image data stored in the storing means is image data for forming a pantograph pattern.  
         [0029]     In the present invention, since a pantograph pattern is stored as an image for composition, it is possible to provide printed material to which a pantograph pattern with faithfully reproduced gradation representation has been added.  
         [0030]     An image forming system according to the present invention is an image forming system including an image transmitting apparatus having means for transmitting image data, and an image forming apparatus for receiving image data transmitted from the image transmitting apparatus and forming an image on a sheet based on the received image data, and characterized in that the image forming apparatus comprises storing means for storing image data to be composited with the received image data; means for compositing the image data with the received image data; means for forming an image based on the resulting composite image data; determining means for determining whether or not image formation by the means is possible; and means for transmitting information regarding a determination result to the image transmitting apparatus, and the image transmitting apparatus comprises means for receiving the information transmitted from the image forming apparatus; and means for controlling, based on the received information, whether or not to transmit the image data.  
         [0031]     In the present invention, a determination as to whether or not to transmit the image data is made based on the information indicating whether or not image formation is possible. Therefore, when the image forming apparatus determines that it is impossible to form the resulting composite image due to deterioration of various parts and consumable supplies in the means for forming an image, it is possible to control the apparatus to stop the transmission of image data. As a result, the quality of the image to be outputted can be maintained at a fixed level, and, for example, an image such as a pantograph pattern that requires fine gradation representation can be provided as printed material only when it is possible to faithfully reproduce the gradation representation.  
         [0032]     The image forming system according to the present invention is characterized in that the image transmitting apparatus further comprises means for giving information stating that transmission of image data is stopped when the transmission of image data is stopped.  
         [0033]     In the present invention, when stopping the transmission of image data, since the information stating that the transmission of image data is stopped is given, it is possible to warn a user that an image such as a pantograph pattern may not be added appropriately due to deterioration of the electrophotographic processes, etc.  
         [0034]     The image forming system according to the present invention is characterized in that the image forming system comprises a plurality of the image forming apparatuses, and the image transmitting apparatus has means for selecting a destination to send image data, based on information transmitted from each image forming apparatus.  
         [0035]     In the present invention, since a destination to send image data is selected based on information transmitted from each image forming apparatus, it is possible, for example, to a select an image forming apparatus capable of faithfully reproducing a pantograph pattern and cause it to perform the processes.  
         [0036]     According to the present invention, when forming an image by compositing received image data and image data stored in the storing means, a determination is made as to whether or not image formation based on the resulting composite image data is possible, and the image formation is executed or stopped according to the determination result. Therefore, when the image forming apparatus determines that it is impossible to form the resulting composite image due to deterioration of various parts and consumable supplies in the means for forming an image, it is possible to control the apparatus to stop the image formation. As a result, the quality of the image to be outputted can be maintained at a fixed level, and, for example, an image such as a pantograph pattern that requires fine gradation representation can be provided as printed material only when it is possible to faithfully reproduce the gradation representation.  
         [0037]     According to the present invention, the quality of an image to be formed on a sheet is detected, and a determination as to whether image formation is possible or not is made based on the detection result. Therefore, when the image forming apparatus is determined to be unable to form the composite image at a fixed level of quality due to deterioration of various parts, consumable supplies, etc., it is possible to control the apparatus to stop the image formation, and consequently the quality of the image to be outputted can be maintained at a fixed level.  
         [0038]     According to the present invention, the quality of an image is detected based on the result of measuring the density of the image. Therefore, for example, if it is impossible to faithfully reproduce the gradations of a pantograph pattern, then it is possible to stop the image formation.  
         [0039]     According to the present invention, the quality of an image to be formed on a sheet is predicted, and a determination as to whether image formation is possible or not is made based on the prediction result. Therefore, when it is possible to predict that it is impossible to form the composite image at a fixed level of quality due to deterioration of various parts, consumable supplies, etc., it is possible to control the apparatus to stop the image formation, and consequently the quality of the image to be outputted can be maintained at a fixed level.  
         [0040]     According to the present invention, the remaining amount of a consumable member used for image formation is detected, and the quality of the image is predicted based on the detection result. Therefore, when it is possible to predict that it is impossible to form the composite image at a fixed level of quality due to deterioration of the consumable member, etc., it is possible to control the apparatus to stop the image formation, and consequently the quality of the image to be outputted can be maintained at a fixed level.  
         [0041]     According to the present invention, the number of times image formation was executed is counted, and the quality of the image is predicted based on the counted number. Therefore, when degradation of image quality is predicted from repetitions of image formation, it is possible to control the apparatus to stop the image formation, and consequently the quality of the image to be outputted can be maintained at a fixed level.  
         [0042]     According to the present invention, when the result of detecting the quality of an image, or the result of predicting the quality of an image shows degradation of the image quality, the degradation of the image quality is compensated. Therefore, the quality of the image to be outputted can be maintained at a fixed level, and, if it is impossible to compensate for the degradation of the image quality, the image formation can be stopped.  
         [0043]     According to the present invention, since image formation is performed by electrophotographic processes, a determination as to whether or not it is possible to faithfully reproduce an image such as a pantograph pattern can be made after finding the condition of a photosensitive drum, developer, etc., and thus it is possible to provide printed material only when a faithful reproduction is possible.  
         [0044]     According to the present invention, if image formation based on the composite image is determined to be impossible, the information stating a determined result is given, and thus it is possible to warn a user that an image such as a pantograph pattern may not be added appropriately due to deterioration of the electrophotographic processes, etc.  
         [0045]     According to the present invention, since a pantograph pattern is stored as an image for composition, it is possible to provide printed material to which a pantograph pattern with faithfully reproduced gradation representation has been added.  
         [0046]     According to the present invention, a determination as to whether or not to transmit image data is made based on the information indicating whether or not image formation is possible. Therefore, when the image forming apparatus determines that it is impossible to form the resulting composite image due to deterioration of various parts and consumable supplies in the means for forming an image, it is possible to control the apparatus to stop the transmission of image data. As a result, the quality of the image to be outputted can be maintained at a fixed level, and, for example, an image such as a pantograph pattern that requires fine gradation representation can be provided as printed material only when it is possible to faithfully reproduce the gradation representation.  
         [0047]     According to the present invention, when stopping the transmission of image data, since the information stating that the transmission of image data is stopped is given, it is possible to warn a user that an image such as a pantograph pattern may not be added appropriately due to deterioration of the electrophotographic processes, etc.  
         [0048]     According to the present invention, since a destination to send image data can be selected based on information transmitted from each image forming apparatus, it is possible, for example, to select an image forming apparatus capable of faithfully reproducing a pantograph pattern and cause it to perform the processes.  
         [0049]     The above and further object and features of the invention will more fully be apparent from the following detailed description with accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0050]      FIG. 1  is a schematic view showing the entire structure of an image forming system according to an embodiment;  
         [0051]      FIG. 2  is a block diagram for explaining the internal structure of a printing apparatus;  
         [0052]      FIG. 3  is a schematic cross sectional view for explaining the detail of an image forming section;  
         [0053]      FIG. 4  is a flowchart for explaining the processing steps to be executed when a printing apparatus receives a print job;  
         [0054]      FIG. 5  is a schematic view showing one example of a message screen displayed on an information processing apparatus if a reproduction of an additional image is impossible;  
         [0055]      FIG. 6  is a schematic view showing the entire structure of an image forming system according to an embodiment;  
         [0056]      FIG. 7  is a block diagram for explaining the internal structure of a print server;  
         [0057]      FIG. 8  is a concept view showing one example of an apparatus information management table;  
         [0058]      FIG. 9  is a flowchart for explaining the processing steps to be executed when the print server receives a print job; and  
         [0059]      FIG. 10  is a schematic view showing one example of a message screen to be displayed on an information processing apparatus if a reproduction of an additional image is impossible. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0060]     The following description will specifically explain the present invention, based on the drawings illustrating some embodiments thereof.  
       Embodiment 1  
       [0061]      FIG. 1  is a schematic view showing the entire structure of an image forming system according to this embodiment. In  FIG. 1, 100A ,  100 B and  100 C represent printing apparatuses for forming an image on a sheet of paper, OHP film, etc., and information processing apparatuses  300 ,  300 ,  300  such as personal computers and workstations are connected to these printing apparatuses  100 A,  100 B and  100 C through communication network N. In the information processing apparatus  300 , application programs for creating documents, graphics, etc. and a driver program (printer driver) for using the printing apparatus  100 A,  100 B or  100 C through the communication network N are installed in advance, and the information processing apparatus  300  can output prints of created documents, graphics, etc. by calling the printer driver from an arbitrary application program and transmitting print jobs created by the printer driver to a target printing apparatus  100 A (or printing apparatus  100 B or  100 C).  
         [0062]     It should be noted that the printing apparatuses  100 A,  100 B and  100 C will be hereinafter collectively referred to as the printing apparatuses  100  if it is not necessary to particularly distinguish them from each other.  
         [0063]     In this embodiment, when the printing apparatus  100  receives a print job giving an instruction to add a pantograph pattern, it confirms the condition of an image forming section  107  (see  FIG. 3 ) comprising a electrostatic charger, an exposure unit and a developing unit, and then determines whether or not it is possible to reproduce an image in a condition capable of exhibiting the effect of a pantograph pattern. Further, even when the electrostatic charger, exposure unit, developing unit, etc. were adjusted, if the image forming section  107  is not capable of compensating for a pantograph pattern, the printing apparatus  100  stops the print process and asks whether the user wants to continue the print process.  
         [0064]      FIG. 2  is a block diagram for explaining the internal structure of a printing apparatus  100 . The printing apparatus  100  comprises a controller  101 . When the controller  101  reads and executes a control program pre-stored in a ROM  103 , it controls various hardware devices connected through a bus  102  and causes them to operate as an apparatus for executing the above-mentioned processes as a whole. A management section  104  is composed of a semiconductor memory, and a part of its storage area is used as a management table  104   a  for managing the condition of the respective hardware devices, and an additional image storage area  104   b  for storing a pantograph pattern as image data. The controller  101  of the printing apparatus  100  obtains the information about the installed hardware by communicating with the respective hardware devices when power is supplied, and always confirms the hardware devices being in operation and updates the contents of the management table  104   a  if there is a change in the operation status.  
         [0065]     A communication section (a receiving section, a transmitting section)  105  has a communication interface according to the communication standards of communication network N, receives print jobs from the information processing apparatuses  300 ,  300 ,  300  connected to the communication network N, and transmits information to be given to the information processing apparatuses  300 ,  300 ,  300 . Further, the communication section  105  has a storage area for holding the information about the printing apparatus  100 , and manages the apparatus information such as the operation status, paper information, and the remaining toner amount in the form of a database called MIB (Management Information Base). Software (for example, SNMP manager, SNMP: Simple Network Management Protocol) for monitoring the apparatus information is installed in the information processing apparatus  300 . Upon a request from this software, the communication section  105  extracts necessary information from the MIB, and transmits the information to the information processing apparatus  300  which made the request. The communication section  105  controls the transmission and reception of the various types of information.  
         [0066]     An image processing section  106  comprises an image memory for temporarily holding image data extracted from a print job received by the communication section  105 , an IC (Integrated Circuit) for image processing and a DSP (Digital Signal Processor) to perform image processing on the image data held in the image memory. Image processing to be performed on the image data by the image processing section  106  includes an enlargement/reduction process, gradation adjustment process, pantograph pattern compositing process, etc. specified by print jobs.  
         [0067]     The image forming section  107  comprises a electrostatic charger for charging a photosensitive drum to a predetermined electric potential; an exposure unit for creating an electrostatic latent image on the photosensitive drum by emitting laser light according to image data received from an external device; a developing unit for visualizing the image by supplying toner to the electrostatic latent image formed on the photosensitive drum surface; and a transfer unit  15  (see  FIG. 3 ) for transferring the toner image formed on the photosensitive drum surface to a sheet of paper, OHP film, or the like. The image forming section  107  forms an image desired by the user on paper by using an electrophotographic technique.  
         [0068]      FIG. 3  is a schematic cross sectional view for explaining the detail of the image forming section  107 . This printing apparatus  100  comprises the image forming section  107  in which a electrostatic charger  12 , an exposure unit  13 , a developing unit  14 , a transfer unit  15  and a cleaning unit  16  are disposed around a photosensitive drum  11 . As the electrostatic charger  12 , a roller type electrostatic charger designed to come into contact with the photosensitive drum  11  is used, and the electrostatic charger  12  charges the surface of the photosensitive drum  11  uniformly to a predetermined electric potential by a voltage applied from a primary high voltage power supply  22 . Note that it may also be possible to use a brush type electrostatic charger or a charger type electrostatic charger instead of the roller type electrostatic charger. The exposure unit  13  is composed of a laser scanning unit (LSU) comprising a laser illuminating section, and a reflection mirror and a polygon mirror (not shown) are disposed so that the laser light emitted from the laser illuminating section strikes on the photosensitive drum  11 . Note that it may also be possible to use a write head composed of light emitting elements, such as EL (Electro luminescence) and LED (Light Emitting Diode), arranged in an array instead of the laser illuminating section. The developing unit  14  stores a black toner, and supplies the toner to the electrostatic latent image formed on the surface of the photosensitive drum  11  so as to visualize the image. In this case, a high voltage (developing bias) is applied to the toner by a development high voltage power supply  24 , and the electrostatic latent image is formed on the photosensitive drum  11  by supplying the toner charged to a predetermined polarity.  
         [0069]     The electrostatic latent image formed on the photosensitive drum  11  is transferred onto paper P by the transfer unit  15 . The transfer unit  15  has a transfer roller  15   a  disposed to face the photosensitive drum  11  in a region where it comes into contact with the paper P, and transfers the electrostatic latent image on the photosensitive drum  11  to the paper P by applying a high voltage (transfer bias) of the opposite polarity to the polarity of the charged toner to the transfer roller  15   a  by a transfer high voltage power supply  25 . Note that the paper P is separated and fed one sheet at a time from a paper feed cassette (not shown), and then temporarily held by resist rollers  31  located under the transfer unit  15 . The resist rollers  31  transport the paper P to a transfer region formed by the photosensitive drum  11  and the transfer roller  15   a  in a timing so that the top end of the electrostatic latent image on the photosensitive drum  11  is aligned with the top end of the image formation region of the paper P.  
         [0070]     The paper P with the transferred toner image is transported substantially perpendicularly and reaches a fixing unit  32 . The fixing unit  32  comprises a heat roller  32   a  and a pressure roller  32   b , and fixes the toner image onto the paper P by applying heat of the heat roller  32   a  to the paper P nipped between the two rollers  32   a  and  32   b . The paper P to which the toner image is fixed is discharged to a discharge tray (not shown).  
         [0071]     Moreover, in order to always keep the density of an image to be formed on the paper P at a uniform level in a stable manner, the adhesion amount of toner to be transferred to the surface of the photosensitive drum  11  needs to be kept uniform. In this embodiment, therefore, a photo sensor  20  is provided in the front stage of the cleaning unit  16  to detect the adhesion amount of toner on the photosensitive drum  11  and control the adhesion amount of toner based on the detection result. The photo sensor  20  comprises a light emitting diode for emitting light onto the photosensitive drum  11 , and a photodiode for receiving reflected light of the light emitted by the light emitting diode (not shown).  
         [0072]     When detecting the adhesion amount of toner, the exposure unit  13  performs an exposure process based on a patch image prepared for detection and the developing unit  14  executes a development process to form a toner image of the patch image for detection on the surface of the photosensitive drum  11 . Then, the photo sensor  20  detects the density of the patch image for detection, and transmits the detection result to the controller  101 . The controller  101  which received the detection result performs an arithmetic operation to calculate a toner adhesion amount on the photosensitive drum  11 . If the calculated toner adhesion amount does not fall within a predetermined range, the controller  101  optimizes the control values concerning the image density. Here, the control values concerning the image density are the charging voltage of the photosensitive drum  11  by the primary high voltage power supply  22 , the exposure value of the exposure unit  13 , and the developing bias applied by the development high voltage power supply  24 . The image density is adjusted by changing at least one of these control values. The values such as the output value of the photo sensor  20 , the charging voltage of the photosensitive drum  11 , the exposure value of the exposure unit  13  and the developing bias are recorded in the management table  104   a  and managed. Note that such an adjustment of the image density is made automatically or according to an instruction of the user, for example, when power is supplied to the printing apparatus  100  or when the printing apparatus  100  is waiting for a print job.  
         [0073]     In this embodiment, recommended ranges are set for both of an image density range capable of stably forming an image received as a print job and an image density range capable of faithfully reproducing the gradations of a pantograph pattern. Even when the above-mentioned control values were changed, if the image density falls outside the recommended ranges, a message stating that consumable supplies such as the photosensitive drum  11  and toner need to be replaced, or a message stating that the pantograph pattern can not be added appropriately, is given to the user.  
         [0074]     In this embodiment, although the printing apparatus  100  is explained as an image forming apparatus for forming a monochrome image, it is of course possible that the printing apparatus  100  may be an image forming apparatus which comprises a photosensitive drum  11 , a electrostatic charger  12 , an exposure unit  13 , a developing unit  14 , etc. for each of yellow, magenta, cyan and black colors, and forms a full-color image by transferring the toner images in the respective colors in a superimposed manner.  
         [0075]      FIG. 4  is a flowchart for explaining the processing steps to be executed when the printing apparatus  100  receives a print job. The controller  101  of the printing apparatus  100  always monitors the state of the communication section  105  so as to determine whether or not a print job has been received. As a result, when the controller  101  determines that a print job from an information processing apparatus  300  has been received (step S 11 ), it extracts print data from the print job. The print data contains the instruction content set by the printer driver in the information processing apparatus  300 , and image data for printing. Then, the controller  101  of the printing apparatus  100  refers to the instruction content set by the printer driver, and determines whether or not addition of an additional image (pantograph pattern) is requested (step S 12 ). If the controller  101  determines that the print job does not request addition of an additional image (S 12 : NO), then the controller  101  executes a print process based on the image data extracted from the print job (step S 15 ). On the other hand, if the controller  101  determines that the print job requests addition of an additional image (S 12 : YES), then it refers to the corresponding items registered in the management table  104   a  and confirms the condition of the image forming section  107  (step S 13 ).  
         [0076]     As a result of confirming the condition of the image forming section  107 , the controller  101  determines whether or not it is possible to reproduce the additional image, that is, whether or not the degradation of the pantograph pattern is in a range capable of being compensated by controlling the charging voltage of the photosensitive drum  11 , the amount of laser light emitted onto the photosensitive drum  11  by the exposure unit  13 , the developing bias applied to the developing unit  14  by the development high voltage power supply  24 , etc. (step S 14 ). If the controller  101  determines that it is possible to reproduce the additional image (S 14 : YES), then it reads the image data for the pantograph pattern stored in the additional image storage area  104   a  of the management section  104 , and executes a print process after performing the process of compositing the read image data and the image data extracted from the print job in the image processing section  106  (S 15 ).  
         [0077]     In step S 14 , if the controller  101  determines that it is impossible to reproduce the additional image (S 14 : NO), that is, if there is a possibility that the additional image may be printed in a condition incapable of exhibiting the effect of the pantograph pattern, then the controller  101  informs the user of this fact (step S 16 ). More specifically, the controller  101  informs the user of this fact by writing information stating that it is impossible to reproduce the additional image as the status of the apparatus into the above-mentioned MIB, and causing the SNMP manager of the information processing apparatus  300  to create and display a message screen on the display section (not shown) of the information processing apparatus  300  when the information is obtained.  FIG. 5  is a schematic view showing one example of a message screen to be displayed on the information processing apparatus  300  if a reproduction of an additional image is impossible. On a message screen  301  shown in  FIG. 5 , a message stating that there is a possibility that the pantograph pattern may not be printed appropriately is displayed, and select buttons  301   a  and  301   b  for asking whether the user wants to continue the print process are provided. When the select button  301   a  is pressed, the print process continues, whereas when the select button  301   b  is pressed, the print process is cancelled. The result of a selection made on this message screen  301  is given to the printing apparatus  100 .  
         [0078]     The controller  101  of the printing apparatus  100  determines, based on the selection result given from the information processing apparatus  300 , whether or not an instruction to continue the print process is given (step S 17 ). If the controller  101  determines that an instruction to continue the print process is given (S 17 : YES), then it executes the print process after compositing the image data extracted from the print job and the image data for the pantograph pattern (S 15 ). On the other hand, if the controller  101  determines that an instruction to continue the print process is not given (S 17 : NO), then it cancels the print job (step S 18 ), and finishes the processing of this flowchart.  
         [0079]     In this embodiment, the controller  101  confirms the condition of the image forming section  107  and determines whether or not it is possible to reproduce a pantograph pattern. However, it may also be possible to design the controller  101  so that the controller  101  counts the number of times the print process was executed after replacement of a consumable supply such as toner, and when the counted number exceeds a predetermined number, the controller  101  makes a determination that a faithful reproduction of a pantograph pattern is impossible and informs the user of this fact.  
       Embodiment 2  
       [0080]     In Embodiment 1, the printing apparatus  100  which received a print job confirms the condition of the image forming section  107  and determines whether or not it is possible to reproduce a pantograph pattern, and then gives information based on the determination result to the information processing apparatus  300  which sent this print job. However, if a network is constructed to send a print job through a print server, it may also be possible to manage the apparatus information about the respective printing apparatuses  100 A,  100 B and  100 C by the print server, and determine the reproducibility of a pantograph pattern when the print server receives a print job.  
         [0081]      FIG. 6  is a schematic view showing the entire structure of an image forming system according to this embodiment. A print server  200  is connected to information processing apparatuses  300 ,  300 ,  300  such as personal computers and workstations through communication network N, and a plurality of printing apparatuses  100 A,  100 B and  100 C are connected to the print server  200 . The information processing apparatus  300  can cause any printing apparatuses  100 A,  100 B and  100 C to execute outputting of prints via the print server  200 .  
         [0082]      FIG. 7  is a block diagram for explaining the internal structure of a print server  200 . The print server  200  comprises a controller  201 . When the controller  201  reads and executes a control program pre-stored in a ROM  203 , it controls various hardware devices connected through a bus  202 . A management section  204  is composed of a semiconductor memory, and a part of its storage area are used as an apparatus information management table  204   a  for managing the operation status of the connected printing apparatuses  100 A,  100 B and  100 C, and a job management table  204   b  for managing the information about print jobs received from the information processing apparatuses  300 . A communication section (a receiving section, a transmitting section)  205  has a communication interface according to the communication standards of communication network N, receives print jobs from the information processing apparatuses  300  connected to the communication network N, and transmits information to be given to the information processing apparatuses  300 . Moreover, software such as the SNMP manager for obtaining the apparatus information about the respective printing apparatuses  100 A,  100 B and  100 C is installed in the print server  200 , and the print server  200  periodically outputs to the respective printing apparatuses  100 A,  100 B and  100 C a request to transmit the apparatus information through the communication section  205 , and receives the apparatus information transmitted from the respective printing apparatuses  100 A,  100 B and  100 C. The received apparatus information is managed in the apparatus information management table  204   a  of the management section  204 . A storage section  206  is a semiconductor memory or a HDD device, and stores print jobs received through the communication section  205 . Further, the storage section  206  transmits a print job to a target printing apparatus  100 A (or printing apparatus  100 C or  100 C) in a timing instructed by the controller  201 .  
         [0083]     Note that since the internal structures of the printing apparatuses  100 A,  100 B and  100 C are the same as that of the printing apparatus  100  explained in Embodiment 1, the explanation thereof is omitted.  
         [0084]      FIG. 8  is a concept view showing one example of the apparatus information management table  204   a . In the apparatus information management table  204   a  shown in  FIG. 8 , the ON/OFF state of power supply, the operation status, and the condition of the image forming section  107  are stored in association with each other for each of the printing apparatuses  100 A,  100 B and  100 C. The ON/OFF state of power supply is indicated by “o” or “x”, “o” showing that the power supply is ON, and “x” showing that the power supply is OFF. As the operation status, whether the apparatus is “in operation” or “on standby” is shown. As the condition of the image forming section  107 , information indicating whether or not the image forming section  107  is in a condition capable of satisfactorily adding a pantograph pattern is registered. These pieces of information can be obtained by periodically requesting the printing apparatuses  100 A,  100 B and  100 C to transmit the apparatus information, and the apparatus information management table  204   a  is updated based on the obtained information as occasion arises.  
         [0085]      FIG. 9  is a flowchart for explaining the processing steps to be executed when the print server  200  receives a print job. The controller  201  of the print server  200  always monitors the state of the communication section  205  so as to determine whether or not a print job has been received. As a result, when the controller  201  determines that a print job from an information processing apparatus  300  has been received (step S 21 ), it extracts print data from the print job. The print data contains the instruction content set by the printer driver, and image data for printing. Then, the controller  201  of the print server  200  refers to the instruction content set by the printer driver, and determines whether or not the addition of an additional image (pantograph pattern) is requested (step S 22 ). If the controller  201  determines that the print job does not request the addition of an additional image (S 22 : NO), then the controller  201  transmits the print job to a target printing apparatus  100 A (or printing apparatus  100 B or  100 C) (step S 25 ). On the other hand, if the controller  201  determines that the print job requests the addition of an additional image (S 22 : YES), then it refers to the apparatus information management table  204   a  in the management section  204  and confirms the condition of the image forming section  107  of the specified printing apparatus  100 A (or printing apparatus  100 B or  100 C) (step S 23 ).  
         [0086]     As a result of confirming the condition of the image forming section  107  of the specified printing apparatus, the controller  201  determines whether or not it is possible to reproduce the additional image (step S 24 ). If the controller  201  determines that it is possible to reproduce the additional image (S 24 : YES), then it transmits the print job to the specified printing apparatus  100 A (or printing apparatus  100 B or  100 C) (S 25 ). The transmitted print job is processed by the printing apparatus  100 A (or printing apparatus  100 B or  100 C) to which the print job was sent, and the print process is performed after compositing the image data for printing and the image data for the pantograph pattern.  
         [0087]     In step S 24 , if the controller  201  determines that it is impossible to reproduce the additional image(S 24 : NO), that is, if there is a possibility that the additional image may be printed in a condition incapable of exhibiting the effect of the pantograph pattern, then the controller  201  informs the user of this fact (step S 26 ).  FIG. 10  is a schematic view showing one example of a message screen to be displayed on the information processing apparatus  300  if a reproduction of an additional image is impossible. On a message screen  302  shown in  FIG. 10 , a message stating that there is a possibility that the pantograph pattern may not be printed appropriately is displayed, and select buttons  302   a  and  302   b  for asking whether or not the user wants to change the destination are provided. When the select button  302   a  is pressed, the destination is changed, whereas when the select button  302   b  is pressed, the print job is transmitted to the originally set destination. The result of a selection made on this message screen  302  is given to the print server  200 .  
         [0088]     The controller  201  of the print server  200  determines, based on the selection result given from the information processing apparatus  300 , whether or not an instruction to change the destination is given (step S 27 ). If the controller  201  determines that an instruction to change the destination is given (S 27 : YES), then it changes the destination and transmits the print job to the new destination (step S 28 ). On the other hand, if the controller  201  determines that an instruction to change the destination is not given (S 27 : NO), then it transmits the print job to the originally set destination (S 25 ).  
         [0089]     As this invention may be embodied in several forms without departing from the spirit of essential characteristics thereof, the present embodiments are therefore illustrative and not restrictive, since the scope of the invention is defined by the appended claims rather than by the description preceding them, and all changes that fall within metes and bounds of the claims, or equivalence of such metes and bounds thereof are therefore intended to be embraced by the claims.