Abstract:
Printers selectively connected to a computer terminal device is identified. By controlling the printer using a dedicated correction data, a quality of the printing image is improved. As an identification data of the printer connected to the computer terminal device, a printer ID is checked. By reading the correction data corresponding to the printer ID, the head shading process is performed for the printer connected to the computer terminal device using the correction data.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a printing method and a printing system for printing an image on a printing medium under control by a control unit. 
     2. Description of the Related Art 
     In general, in a printer employing a printing head ejecting an ink from ink passages forming a plurality of nozzles, it is possible to cause density fleck in a printed image due to adverse effect of fine fluctuation of shapes of the ink passage forming the nozzles or to variation of ejection amount of the ink as printing material. One of the correction methods to make such density fleck not perceptible is called as head shading (HS). 
     FIG. 8 is a general block diagram showing a system actually performing head shading. Hereinafter, at first, the conventional head shading technology in the case where three systems of reading, image processing and printing are constructed in a single apparatus. 
     In FIG. 8, an original exposure system  801  is a portion performing reading of an original, forms a portion of reading a result of printing necessary for performing head shading. An image processing portion  802  serves as a portion performing arithmetic operation and the like with respect to the image read by the original exposure system  801 . The arithmetic operation performed in the image processing portion  802  includes color processing, binarizing process, head shaping and so on. An image forming portion  803  is a portion for printing an image read by the original exposure system  801  and processed by the image processing portion  802 . The image forming portion  803  includes printing heads  804  to  807  for printing the images. In the shown example,  804  denotes a head for ejecting a black ink,  805  denotes a head for ejecting a cyan ink,  806  denotes a head for ejecting a magenta ink and  807  denotes a head for ejecting a yellow ink. 
     In the printer constructed as set forth above, in order to check output characteristics of respective of the printing heads  804  to  807  in the image forming portion  803 , printing of the predetermined test pattern is performed so that an image of the predetermined density is formed by respective of the printing heads  804  to  807 . Then, the resultant print is read by the original exposure system  801 . A read data read by the original exposure system  801  is used for forming a HS data  808  in the image processing portion  802 . The HS data is data for correcting output density of ink per ink passage forming a plurality of nozzles in respective of the printing heads  804  to  807 . The HS data  808  is used as a correction data for the image data input from the original exposure system  801  so as to make the density fleck not perceptible. As a result, an image avoided the density fleck is printed by the image forming portion  803 . 
     In the printer constructed as set forth above, the original exposure system  801 , the image processing portion  802  and the image forming portion  803  will never been separated individually. Therefore, a discrepancy such as that explained later, will never be caused between the characteristics of the printing heads  804  to  807  in the image forming portion  803  and the HS data  808 . 
     On the other hand, in a printing system, in which a reader device  3 , a computer terminal device  2  which can perform image processing and transmission, and a printer  1  are mutually independent, and connected through connection cable  5 , as shown in FIG. 1, it is possible that the printer  1  is replaced with other printer. 
     In the system construction as illustrated in FIG. 1, when the printer  1  connected to the computer terminal device  2  is replaced, a discrepancy is inherently arisen between the characteristics of the printer and the HS data managed by the computer terminal device  2  to make it impossible to perform appropriate data correction. Therefore, in the prior art, head shading cannot be performed in the system shown in FIG.  1 . 
     On the other hand, in the system construction set forth above, if condition of formation of the density fleck is varied due to secular change, it is possible that the HS data cannot be adapted to the secular change of the head to make it difficult to effect appropriate data correction. Particularly, where the printer is changed, appropriate data correction cannot be performed unless the HS data corresponding to the printer and the timing where the HS data is generated, are properly managed. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a printing method and a printing system which can identify printers which are selectively connected to a control unit, and can control the selected printer with a dedicated data therefor to improve a printing image quality. 
     Another object of the present invention is to provide a printing method and a printing system which can avoid a problem to be caused by control of the printer with a correction data which has been obtained long ago exceeding a predetermined period, and whereby can improve a printing image quality. 
     In a first aspect of the present invention, there is provided a printing method for selectively connecting a plurality of printers, each having a plurality of printing elements, to a control unit, and performing printing of an image on a printing medium by controlling the connected printer by the control unit, comprising the steps of: 
     storing correction data relative to control per each printer available for connection with the control unit, in a storage device; 
     identifying the printer connected to the control unit to be controlled by the control unit, on the basis of an identification code corresponding to the printer; 
     reading out the correction data corresponding to the printer identified as the object for control, from the storage device; and 
     controlling the printer to be controlled using the read out correction data. 
     In a second aspect of the present invention, there is provided a printing system for selectively connecting a plurality of printers, each having a plurality of printing elements, to a control unit, and performing printing of an image on a printing medium by controlling the connected printer by the control unit, comprising the steps of: 
     a storage device storing correction data relative to control per each printer available for connection with the control unit; 
     identifying means for identifying the printer connected to the control unit to be controlled by the control unit, on the basis of an identification code corresponding to the printer; 
     retrieving means for retrieving the correction data corresponding to the printer identified as the object for control, from the storage device; and 
     correction means for controlling the printer to be controlled using the read out correction data. 
     In a third aspect of the present invention, there is provided a printing method for printing an image on a printing medium with controlling a printer by a control unit, comprising the steps of: 
     storing a correction data relating to control of the printer and a storage time and date, on which the correction data is stored, in a storage device; 
     reading out the correction data and the storage time and date upon controlling the printer, from the storage device; 
     controlling the printer using the correction data when an elapsed time from the storage time and date is not more than or equal to a predetermined period; and 
     interrupting control of the printer when an elapsed time from the storage time and date is more than or equal to a predetermined period. 
     In a fourth aspect of the present invention, there is provided a printing method for printing an image on a printing medium with controlling a printer by a control unit, comprising the steps of: 
     storing a correction data relating to control of the printer and storage time and date, on which the correction data is stored, in a storage device; 
     reading out the correction and the storage time and date upon controlling the printer, from the storage device; 
     controlling the printer using the correction data when an elapsed time from the storage time and date is not more than or equal to a predetermined period; and 
     continuing control of the printer without using the correction data when an elapsed time from the storage time and data than or equal to a predetermined period. 
     In a fifth aspect of the present invention, there is provided a printing system for printing an image on a printing medium with controlling a printer by a control unit, comprising: 
     storage device for storing a correction data relating to control of the printer and a storage time and date, on which the correction data is stored; 
     reading means for reading out the correction data and the storage time and date from the storage device upon controlling the printer; 
     means for controlling the printer using the correction data when an elapsed time from the storage time and date is not more than or equal to a predetermined period; 
     means for demanding resetting the correction data when an elapsed time from the storage time and date is more than equal to a predetermined period; and 
     means for interrupting control for the printer when an elapsed time from the storage time and date is more than equal to a predetermined period. 
     In a sixth aspect of the present invention, there is provided a printing system for printing an image on a printing medium with controlling a printer by a control unit, comprising: 
     storage device for storing a correction data relating to control of the printer and a storage time and date, on which the correction data is stored; 
     reading means for reading out the correction data and the storage time and date from the storage device upon controlling the printer; 
     means for controlling the printer using the correction data when an elapsed time from the storage time and date is not more than or equal to a predetermined period; and 
     means for continuing control of the printer without using the correction data when an elapsed time from the storage time and date is more than equal to a predetermined period. 
     Since the present invention identifies printers selectively connected to the control unit to read out the dedicated correction data for control the selected printer, and controls the printer with using the dedicated correction data, therefor, the selected printer can be appropriately controlled with the dedicated correction data to permit printing of high quality image with no density fleck. 
     Also, the present invention identifies printers selectively connected to the control unit to read out the dedicated correction data for control the selected printer, and controls the printer with using the dedicated correction data and a setting data concerning the printing condition set per the printer, therefor, the selected printer can be appropriately controlled with the dedicated correction data to permit printing of high quality image with no density fleck. 
     On the other hand, by recording a time and date, at which the correction data is derived, it becomes possible to avoid a potential problem which may be caused in control using the correction data, about which a period longer than or equal to the predetermined period has past. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be understood more fully from the detailed description given hereinafter and from the accompanying drawings of the preferred embodiment of the present invention, which, however, should not be taken to be limitative to be present invention, but are for explanation and understanding only. 
     In the drawings: 
     FIG. 1 is a general perspective view of a printing system, to which the present invention is applicable; 
     FIG. 2A is an illustration showing a general construction of the first embodiment of the present invention; 
     FIG. 2B is an explanatory illustration of a HS table shown in FIG. 2A; 
     FIG. 3 is a flowchart for explaining operation for generating a HS data in the first embodiment of the present invention; 
     FIG. 4 is a flowchart for explaining a generating operation of a HS table in the first embodiment of the present invention; 
     FIG. 5 is a flowchart for explaining a printing operation in the first embodiment of the present invention; 
     FIG. 6 is a flowchart for explaining a printing operation in the second embodiment of the present invention; 
     FIG. 7A is a side elevation of a printer, to which the present invention is applicable; 
     FIG. 7B is an enlarged perspective view of the printing head is shown in FIG. 7A; 
     FIG. 8 is an illustration showing general construction for explaining the conventional printing system; 
     FIG. 9A is an illustration showing a general construction of the third embodiment of the present invention; 
     FIG. 9B is an explanatory illustration of the HS table is shown in FIG. 9A; 
     FIG. 10 is a flowchart for explaining operation for generating a HS table in the third embodiment of the present invention; 
     FIG. 11 is a flowchart for explaining a printing operation in the third embodiment of the present invention; 
     FIG. 12 is a flowchart for explaining a printing operation in the fourth embodiment of the present invention; 
     FIG. 13 is a flowchart for explaining a printing operation in the fifth embodiment of the present invention; 
     FIG. 14 is a flowchart for explaining a printing operation in the sixth embodiment of the present invention; 
     FIG. 15 is an explanatory illustration for a printing set value shown in FIG. 9A; 
     FIG. 16A is an illustration showing a general construction of the seventh embodiment of the present invention; 
     FIG. 16B is an explanatory illustration of the HS table is shown in FIG. 16A; 
     FIG. 17 is a flowchart for explaining a printing operation in the seventh embodiment of the present invention; 
     FIG. 18 is a flowchart for explaining a printing operation in the eighth embodiment of the present invention; 
     FIG. 19 is a flowchart for explaining a printing operation in the ninth embodiment of the present invention; 
     FIG. 20 is a flowchart for explaining a printing operation in the tenth embodiment of the present invention; 
     FIG. 21A is an illustration showing general construction of the eleventh embodiment of the present invention; 
     FIG. 21B is an explanatory illustration of the HS table is shown in FIG. 21A; 
     FIG. 22 is a flowchart for explaining a generating operation of a HS table in the eleventh embodiment of the present invention; 
     FIG. 23 is a flowchart for explaining a printing operation in the eleventh embodiment of the present invention; and 
     FIG. 24 is a flowchart for explaining a printing operation in the twelfth embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention will be discussed hereinafter in detail in terms of the preferred embodiment of the present invention with reference to the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be obvious, however, to those skilled in the art that the present invention may be practiced without these specific details. In other instance, well-known structures are not shown in detail in order to avoid unnecessary obscure the present invention. 
     First Embodiment 
     FIG. 1 is a general perspective view of a printing system, to which the present invention is applicable. A color bar code printer  1  as a printer using the system according to the present invention, employs a printing head having an ink passage forming a plurality of nozzles. The construction of the printing head is shown in FIGS. 7A and 7B. As printing heads, a head  704  for ejecting black ink, a head  703  for ejecting cyan ink, a head  702  for ejecting magenta ink and a head  701  for ejecting yellow ink are provided. FIG. 7B shows a perspective view of the head  701 , as representative. In FIG. 7B, the reference numeral  706  denote a plurality of ejection openings for ejecting the ink. 
     In FIG. 1, the bar code printer  1  as the printer, a computer terminal device  2  which can perform image processing and transmission, an image scanner  3  as a reading device, and a storage device  4  storing foregoing HS data for correcting an output image are connected by connection cables  5 . 
     FIG. 3 is a flowchart for explaining operation from measuring output characteristics of the printing heads of the bar code printer  1  to generation HS data for performing image correction. At first, for detecting density fleck of the printing image, predetermined density measuring pattern is printed by respective printing heads  701  to  704  (step S 301 ). 
     The density measuring pattern is a printing pattern, in which each printing heads  701  to  704  forms images of predetermined densities per unit area. In this embodiment, a pattern, in which density of printing images by respective printing heads  701  to  704  are 50%, was used. Subsequently, the result of printing of the density measuring pattern is read by the reading device  3  connected to the computer terminal device  2  (step S 302 ) for detecting density fleck of the image printed by respective printing heads  701  to  704 . Then, the HS data is generated on the basis of the detecting data of density block (step S 303 ). 
     FIGS. 2A and 2B are explanatory illustrations showing a relationship between the printer and the storage content of the storage device  4 . Here, as the printer  1 , various types of printers other than the bar code printer can be connected. In FIG. 2A, those printers are identified as printers  1 ,  2 , . . . , n, and the printing heads for respective of cyan, magenta, yellow and black inks in each printer are identified as HC, HM, HY, HB. 
     In the storage device  4 , a HS data portion  204  and a printer identifying portion  206  are provided. The HS data portion  204  stores HS data  207 ,  208 ,  209  and  210  for the printing heads HC, HM, HY and HB of per each printers  1 ,  2 , . . . n, connected to the computer terminal device  2 . The printer identifying portion  206  stores information consisted of symbol, figure or so forth for identifying the printers  1 ,  2 , . . . , n connected to the computer terminal device  2 . In the printer identifying portion  206 , printer IDs corresponding to printer IDs registered in respective printers  1 ,  2 , . . . , n are stored. By checking these printer IDs, the printers  1 ,  2 , . . . , n connected to the computer terminal device  2  is identified. By storage data in the data portion  204  and the printer identifying portion  206 , the HS table is formed. On the other hand, FIG. 2B show one of the printer identifying portions  206  and the data portions  204  as representative. 
     As set forth above, each of the printing heads HC, HM, HY and HB is provided with ink passages forming a plurality of nozzles. Therefore, it becomes necessary to know degree of printing density corresponding to each nozzle. For this purpose, read data obtained from the reading device  3 , namely, the read data as a result of printing of the density measuring pattern, performs analysis. With respect to the density of the predetermined density measuring pattern to be printed at the predetermined density, variation of the actual printing density is detected. 
     Next, using flow chart of FIG. 4, generating operation of the HS data and HS table will be discussed. 
     At first, in order to establish correspondence between read data obtained from the reading device  3 , namely the read density data as a result of printing of the density measuring pattern, and the nozzle of respective head, it becomes necessary to make the resolution of the read density data comparable with the resolution of the printer. Therefore, the resolution of the read density data is converted into the resolution of the printer. Here, the read density data for one line of the reading device  3  are corresponded to respective nozzles of each printing head. 
     In order to establish correspondence between the printing density corresponding to the nozzle of each printing head and the read density data of the reading device  3 , sampling process of the nozzle positions (step S 401 ) is performed. Here, the reading density data obtained from the reading device  3  becomes moderate at rising and falling edges of variation at the boundary between printing region and non-printing region. Therefore, it is difficult to assign the interval from the first nozzle to the final nozzle to the read density data. Thus, paying attention for the portion of rising and falling of data variation, the first nozzle is statistically detected from the read density data, and then with reference to this, other nozzles are corresponded in the sequential order. 
     Next, per each printing head, an average value of the read density data corresponding to each nozzle is derived (step S 402 ). Then it is used in the later stage for calculation of the correction value. A data shifting process in the next step (step S 403 ) is a process corresponding to variation of the read density data from the reading device  3  depending upon kinds of inks ejected from respective printing head. If where is a large difference is between the average values of the read density data in each printing head, effect of correction which will be described later, should vary significantly per printing head. Thus, the average value of the read density data of each printing head is modified into the same value. For this purpose, the average value per each printing head is further averaged to derive an average value of the read density data common to respective head. 
     Then, a weighting process (step S 404 ) is the process for improving reliability of the value of the data, for which the sampling process is performed (step S 401 ), namely for the read density data corresponded to each nozzle. Namely, by performing weighting for the peripheral data before and after the data in question, accurate process of the data value corresponding to each nozzle is enabled. Thus obtained read density data per each nozzle is compared with the average value of the read density data per printing head derived in preceding process to calculate a difference therebetween. Then, on the basis of the result of calculation, the HS data per each head is generated (step S 406 ). 
     Also, the printer ID is added to the HS data so as to identify the corresponding printer (step S 407 ) to establish a HS table (step S 408 ). This HS table is stored in the storage device  4  connected to the computer terminal device  2 . With making reference to or retrieving the HS table, head shading is performed. 
     One example of operation of head shaping process employing the HS table will be explained with reference to FIG.  5 . 
     At first, the image data for which an output demand is issued from the computer terminal device  2  is converted into the image data in a form adapted for execution of the head shading (step S 501 ). Then, the printer ID of the printer currently connected to the computer terminal device  2  is checked (step S 502 ). Then, the printer ID is retrieved from all of HS tables registered in the storage device  4  (step S 503 ). Then, if the printer ID is retrieved, it represents that the information of HS data and so on relating to the printer currently connected to the computer terminal device  2  is present. Thus, head shading is implemented using the retrieved HS data (step S 505 ). On the other hand, if the printer ID cannot be retrieved, retrieving process is repeated (steps S 503  and S 504 ). If the printer ID cannot be retrieved even after checking all of the HS tables stored in the storage device  4 , judgment is made that the information, such as the HS data relating to the currently connected to the computer terminal device  2  is not present. Then, the fact is displayed by way of alarm or the like for error processing (step S 506 ). A series of process is interrupted (step S 507 ). 
     Upon implementation of the head shading process (step S 505 ), with respect to the image data divided per each printing head, arithmetic process for making the corresponding printing density of the image uniform. Namely, a difference between the average value of the common density data common to respective printing head in the HS data, and the density data of respective nozzle is derived. On the basis of the difference, head shading is performed. In the head shading, when the density data of the nozzle in question is lower than the average value, the printing density of the nozzle in question is increased. On the other hand, when the density data of the nozzle is higher than the average value, the printing density of the nozzle in question is reduced. 
     After the head shading process (step S 505 ), various color processes of output γ correction, masking process, gray processing and so on is performed (step S 509 ). Also, when the currently connected printer is a binary printer, after binarizing process, typically dither method, error diffusion method, is performed (step S 510 ), and then the data is transferred to the printer (step S 511 ) to perform printing (step S 512 ). 
     Second Embodiment 
     FIG. 6 is flowchart for explaining another embodiment of head shading process employing the HS table similar to the first embodiment as set forth above. In FIG. 6, a point different from the first embodiment illustrated in FIG. 5 is that, when the printer ID is not retrieved at steps S 503  and S 504 , the head shading process is skipped to advance the process to the color processing (step S 509 ). 
     It should be noted that the printers  1 ,  2 , . . . , n which can be connected as shown in FIG. 2, it is not specified to the color bar code printer, but can be various printer having the printing heads each formed with a plurality of nozzles. On the other hand, the present invention is widely applicable for printing systems having the computer terminal device  2  which can edit the printing data to be transferred to the printer. The printer, the computer terminal device  2  and the reading device are not specified. 
     On the other hand, a method for determining the HS data, the color process (steps S 509 , S 608 ) and the other steps, the binarizing process (steps S 510 , S 609 ) in the process, the conventional processed can be used and thus no further explanation will be given. While the detailed discussion is neglected, concerning these processes, the method and procedure will not be limited. 
     Third Embodiment 
     FIGS. 9A,  9 B,  10  and  11  are illustration for explaining the third embodiment of the present invention. In the following description, like elements to those in the former embodiment will be identified by the same reference numeral, and the detailed description therefor will be neglected. 
     In case of the shown embodiment, for the printer identifying portion  206  of the storage device  4  shown in FIG. 9B, the date and time, at which the HS data is obtained, they are stored as the time and date data  211 . On the other hand, as shown in FIG. 9A, for the printers  1 ,  2 , . . . , n, specific print setting value  212  is set with respect to printing medium. The print setting value  212  may be a printing arrange or a set value of margin of the printing medium. FIG. 9B shows one of the printer identifying portions  206  and the data portions  204  as representative. 
     FIG. 10 is a flowchart for explaining HS data and HS table generating operation. In FIG. 10, a point different from the embodiment of FIG. 4 is that, the time and date, at which the HS date is obtained, they are registered in the identifying portion  206  (step S 407 A) as the time and date data  211 . Accordingly, by adding the printing ID and the time and date data  211  to the HS data, the HS table can be established. FIG. 11 is a flowchart of explaining head shading process employing such HS table. In this FIG. 11, the point different from the embodiment of FIG. 5A is that steps S 504 A, S 504 B, S 504 C, S 504 D and S 504 E are added. The following is the description for the additional steps. 
     When the printer ID can be retrieved at step S 504 , reference is made to the time and date data  211  registered in the printer identifying portion  206  (step S 504 A). Then, if a period longer than a predetermined elapsed period has been elapsed after obtaining HS data corresponding to the currently retrieved printer ID, re-setting of the HS data is demanded (steps S 504 B, S 504 C). Then, process goes end (step S 504 D). Accordingly, a problem which can be caused when the head shading is performed using the HS data obtained long before, i.e. more than or equal to a predetermined period has been elapsed from obtaining the HS data in question, can be avoided. Namely, when the position of the density fleck is differentiated due to secular change of the printing head, correction using the old HS data should affect adversely. 
     If the predetermined period is not yet elapsed from obtaining the HS data, with reference to the printer setting value  212  registered in the currently connected printer (step S 504 E), head shading is performed (step S 505 ). When the head shading is performed, certain type of printing heads requires to consider the printer setting value  212 , such as printing range or margin set, for example. In such case, process will be performed with reference to the printer setting value  212 . 
     Here, the print setting value  212  will be described. 
     When the printer  1  is a so-called full line type printer, it has a printing head H extending in the width direction of the printing medium S. Then, printing is performed for printing the image on the printing medium by ejecting the ink from respective nozzles N of the printing head H with transporting the printing medium S in the longitudinal direction as indicated by arrow. In case of such printer, depending on the set values of the printing ranges L 1 -A, L 2 -A for the printing medium S and set values of the margin L 1 -B, L 2 -B, the nozzles to be used are differentiated. Therefore, such set values are preliminarily set as the print setting value  212 . By using such setting value  212 , accurate head shading can be performed with assigning the corresponding HS data for the nozzles to be used. 
     Fourth Embodiment 
     FIG. 12 is a flowchart showing another embodiment of the head shading processing operation using the same HS data as that in the third embodiment set forth above. In FIG. 12, the point different from the third embodiment of FIG. 11 is that, when the printer ID is not retrieved at steps S 503  and S 504 , the head shading process is skipped to advance the process to the color processing (step S 509 ). 
     Fifth Embodiment 
     FIG. 13 is a flowchart for explaining a further embodiment of the head shading processing operation using the same HS data as that in the third embodiment set forth above. In FIG. 13, a point different from the foregoing third embodiment of FIG. 11 is that, when a period longer than or equal to the predetermined elapsed period has been elapsed after obtaining the HS data, the process is advanced from the step S 504 B to the color processing (step S 509 ). Accordingly, in this case, the head shading process (step S 505 ) is skipped to avoid problem which can be caused by implementation with the old HS data. 
     Sixth Embodiment 
     FIG. 14 is a flowchart for explaining a still further embodiment of the head shading processing operation using the same HS data as that in the third embodiment set forth above. In FIG. 14, a point different from the former fifth embodiment of FIG. 13 is that, when the printer ID is not retrieved at steps S 503  and S 504 , the head shading process is skipped and the process is advanced to the color processing (step S 509 ). 
     Seventh Embodiment 
     FIGS. 16A and 16B are explanatory illustration of the seventh embodiment of the present invention. In the following description, like elements to those in the former embodiment will be identified by same reference numeral, and the detailed description therefor will be neglected. 
     In the shown embodiment, as shown in FIG. 9B, the time and date data  211  is stored in the printer identifying portion  206  of the storage device  4  of the first embodiment shown in FIGS. 2A and 2B. FIG. 9B illustrates one of the printer identifying portions  206  and one of the data portion  204  as representative. The generating operation of the HS data and the HS table are the same as those in the third embodiment as explained with respect to FIG.  10 . 
     FIG. 17 is an explanatory illustration of the head shading processing operation using the HS table. In FIG. 17, the point different from the foregoing first embodiment of FIG. 5 is that, the steps S 504 A, S 504 B, S 504 C and S 504 D are added. The additional steps will be described hereinafter. 
     When the printer ID can be retrieved at step S 504 , reference is made to the time and date data  211  registered in the printer identifying portion  206  (step S 504 A). Then, if a period longer than a predetermined elapsed period has been elapsed after obtaining HS data corresponding to the currently retrieved printer ID, re-setting of the HS data is demanded (steps S 504 B, S 504 C). Then, process goes end (step S 504 D). Accordingly, a problem which can be caused when the head shading is performed using the HS data obtained long before, i.e. more than or equal to a predetermined period has been elapsed from obtaining the HS data in question, can be avoided. Namely, when the position of the density fleck is differentiated due to secular change of the printing head, correction using the old HS data should affect adversely. 
     If the predetermined period is not yet elapsed from obtaining the HS data, head shading is performed (step S 505 ). 
     Eighth Embodiment 
     FIG. 18 is a flowchart for explaining a yet further embodiment of the head shading processing operation using the same HS table as that in the seventh embodiment set forth above. In FIG. 18, a point different from the seventh embodiment of FIG. 17 is that when the printer ID is not retrieved at steps S 503  and S 504 , the head shading process is skipped and the process is directly advanced to the color processing (step S 509 ). 
     Ninth Embodiment 
     FIG. 19 is a flowchart for explaining a still further embodiment of the head shading processing operation using the same HS data as that in the seventh embodiment set forth above. In FIG. 19, a point different from the foregoing seventh embodiment of FIG. 17 is that, when a period longer than or equal to the predetermined elapsed period has been elapsed after obtaining the HS data, the process is advanced from the step S 504 B to the color processing (step S 509 ). Accordingly, in this case, the head shading process (step S 505 ) is skipped to avoid problem which can be caused by implementation with the old HS data. 
     Tenth Embodiment 
     FIG. 20 is a flowchart for explaining a still further embodiment of the head shading processing operation using the same HS data as that in the seventh embodiment set forth above. In FIG. 20, a point different from the former ninth embodiment of FIG. 19 is that, when the printer ID is not retrieved at steps S 503  and S 504 , the head shading process is skipped and the process is advanced to the color processing (step S 509 ). 
     Eleventh Embodiment 
     FIGS. 21A,  21 B,  22  and  23  are illustration for explaining the eleventh embodiment of the present invention. In the following description, like elements to those in the former embodiment will be identified by the same reference numeral, and the detailed description therefor will be neglected. 
     In the storage device  4 , the HS data portion  204  and data attribute portion  215  are provided. The HS data portions  204  stores the HS data  207 ,  208 ,  209  and  210  of respective printing heads HC, HM, HY and HB of the printer  1  connected to the computer terminal device  2 . The data attribute portion  215  stores the time and date data  211  indicative of time and date, at which the corresponding HS data is obtained. By the stored data in the HS data portion  204  and the data attribute portion  215 , the HS table is established. In the printer  1 , specific print setting value  212  for printing is set. The setting value  212  is the printing range or printing margin on the printing medium to be printed, for example. 
     FIG. 22 is a flowchart for explaining operation for generating the HS data and HS table. In FIG. 22, a point different from the foregoing third embodiment illustrated in FIG. 10 is that the operation for adding the printer ID in FIG. 10 is neglected. In the shown embodiment, a specific printer  1  is connected to the computer terminal device  2 , it is not necessary to identify the printer connected to the computer terminal device  2  among a plurality of the printers. 
     FIG. 23 is an explanatory illustration of the operation of head shading process using the HS table. In FIG. 23, a point different from the third embodiment in FIG. 11 is that, the steps S 502 , S 503 , S 504 , S 506  and S 507  are neglected. 
     Twelfth Embodiment 
     FIG. 24 is a flowchart for explaining a yet further embodiment of the head shading processing operation using the same HS table as that in the eleventh embodiment. In FIG. 24, a point different from the eleventh embodiment of FIG. 22 is that, when a period more than or equal to a predetermined elapsed period has been elapsed after obtaining the HS data, the process is advanced from step S 504 B to the color processing (step  509 ). Accordingly, in this case, the head shading process (step S 505 ) is skipped to avoid problem which can be caused by implementation with the old HS data. 
     The present invention achieves distinct effect when applied to a recording head or a recording apparatus which has means for generating thermal energy such as electrothermal transducers or laser light, and which causes changes in ink by the thermal energy so as to eject ink. This is because such a system can achieve a high density and high resolution recording. 
     A typical structure and operational principle thereof is disclosed in U.S. pat. Nos. 4,723,129 and 4,740,796, and it is preferable to use this basic principle to implement such a system. Although this system can be applied either to on-demand type or continuous type ink jet recording systems, it is particularly suitable for the on-demand type apparatus. This is because the on-demand type apparatus has electrothermal transducers, each disposed on a sheet or liquid passage that retains liquid (ink), and operates as follows: first, one or more drive signals are applied to the electrothermal transducers to cause thermal energy corresponding to recording information; second, the thermal energy induces sudden temperature rise that exceeds the nucleate boiling so as to cause the film boiling on heating portions of the recording head; and third, bubbles are grown in the liquid (ink) corresponding to the drive signals. By using the growth and collapse of the bubbles, the ink is expelled from at least one of the ink ejection orifices of the head to form one or more ink drops. The drive signal in the form of a pulse is preferable because the growth and collapse of the bubbles can be achieved instantaneously and suitably by this form of drive signal. As a drive signal in the form of a pulse, those described in U.S. pat. Nos. 4,463,359 and 4,345,262 are preferable. In addition, it is preferable that the rate of temperature rise of the heating portions described in U.S. pat. No. 4,313,124 be adopted to achieve better recording. 
     U.S. pat. Nos. 4,558,333 and 4,459,600 disclose the following structure of a recording head, which is incorporated to the present invention: this structure includes heating portions disposed on bent portions in addition to a combination of the ejection orifices, liquid passages and the electrothermal transducers disclosed in the above patents. Moreover, the present invention can be applied to structures disclosed in Japanese Patent Application Laying-open Nos. 123670/1984 and 138461/1984 in order to achieve similar effects. The former discloses a structure in which a slit common to all the electrothermal transducers is used as ejection orifices of the electrothermal transducers, and the latter discloses a structure in which openings for absorbing pressure waves caused by thermal energy are formed corresponding to the ejection orifices. Thus, irrespective of the type of the recording head, the present invention can achieve recording positively and effectively. 
     The present invention can be also applied to a so-called full-line type recording head whose length equals the maximum length across a recording medium. Such a recording head may consists of a plurality of recording heads combined together, or one integrally arranged recording head. 
     In addition, the present invention can be applied to various serial type recording heads: a recording head fixed to the main assembly of a recording apparatus; a conveniently replaceable chip type recording head which, when loaded on the main assembly of a recording apparatus, is electrically connected to the main assembly, and is supplied with ink therefrom; and a cartridge type recording head integrally including an ink reservoir. 
     It is further preferable to add a recovery system, or a preliminary auxiliary system for a recording head as a constituent of the recording apparatus because they serve to make the effect of the present invention more reliable. As examples of the recovery system, are a capping means and a cleaning means for the recording head, and a pressure or suction means for the recording head. As examples of the preliminary auxiliary system, are a preliminary heating means utilizing electrothermal transducers or a combination of other heater elements and the electrothermal transducers, and a means for carrying out preliminary ejection of ink independently of the ejection for recording. These systems are effective for reliable recording. 
     The number and type of recording heads to be mounted on a recording apparatus can be also changed. For example, only one recording head corresponding to a single color ink, or a plurality of recording heads corresponding to a plurality of inks different in color or concentration can be used. In other words, the present invention can be effectively applied to an apparatus having at least one of the monochromatic, multi-color and full-color modes. Here, the monochromatic mode performs recording by using only one major color such as black. The multi-color mode carries out recording by using different color inks, and the full-color mode performs recording by color mixing. 
     Furthermore, although the above-described embodiments use liquid ink, inks that are liquid when the recording signal is applied can be used: for example, inks can be employed that solidify at a temperature lower than the room temperature and are softened or liquefied in the room temperature. This is because in the ink jet system, the ink is generally temperature adjusted in a range of 30° C.-70° C. so that the viscosity of the ink is maintained at such a value that the ink can be ejected reliably. 
     In addition, the present invention can be applied to such apparatus where the ink is liquefied just before the ejection by the thermal energy as follows so that the ink is expelled from the orifices in the liquid state, and then begins to solidify on hitting the recording medium, thereby preventing the ink evaporation: the ink is transformed from solid to liquid state by positively utilizing the thermal energy which would otherwise cause the temperature rise; or the ink, which is dry when left in air, is liquefied in response to the thermal energy of the recording signal. In such cases, the ink may be retained in recesses or through holes formed in a porous sheet as liquid or solid substances so that the ink faces the electrothermal transducers as described in Japanese Patent Application Laying-open Nos. 56847/1979 or 71260/1985. The present invention is most effective when it uses the film boiling phenomenon to expel the ink. 
     Furthermore, the ink jet recording apparatus of the present invention can be employed not only as an image output terminal of an information processing device such as a computer, but also as an output device of a copying machine including a reader, and as an output device of a facsimile apparatus having a transmission and receiving function. 
     The present invention has been described in detail with respect to various embodiments, and it will now be apparent from the foregoing to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and it is the intention, therefore, in the appended claims to cover all such changes and modifications as fall within the true spirit of the invention.