Image printing method, and apparatus thereof

Abstract: Provided are an image printing method and apparatus in which printing is made possible in a multiscanning mode for printing the same line using a plurality of printing elements of a printing head (2a) in order that uneven density caused by a variance in the printing elements may be rendered inconspicuous. When the multiscanning mode is designated, a plurality of nozzles of the printing head (2a) are divided into a plurality of blocks (A,B,C,D), the nozzle blocks used are changed over every scan of the printing head (2a), and the image of the printing width (band) printed using all of the nozzles is printed by causing the printing head (2a) to perform scanning a plurality of times.

Description: BACKGROUND OF THE INVENTION [Field of the Invention] This invention relates to an image printing method and apparatus, as well as to a copying apparatus, in which an image is printed on the basis of entered image information by scanning a printing head having a plurality of printing elements (nozzles or heating elements) arranged in a direction substantially perpendicular to the scanning direction of the printing head. [Description of the Related Art] In an ink-jet printer known in the art, an ink-jet head having a plurality of nozzles arranged in a subscan direction is mounted on a carriage and the carriage is made to scan in a main-scan direction to perform printing. When printing is performed using an ink-jet head, images on a plurality of lines are capable of being printed simultaneously on a recording medium such as recording paper by a single scan of the carriage. The width of the image thus printed generally is referred to as a "band". With an ink-jet head of this kind, however, 128 nozzles, for example, are arranged at intervals of about 60 µm, and inevitably a variance develops in the accuracy with which ink is jetted from each of the nozzles. This variance in the jetting accuracy appears as unevenness in the printing density of the printed image. Such uneven density gives rise to a decline in the image quality of the printed image. The present invention is directed to alleviating this problem. US Patent Specification No. US-A-4521123 discloses a printing apparatus for preventing deterioration of the legibility of characters in which the character line is greater than the height of the printing elements. In accordance with a first aspect of the present invention there is provided image recording apparatus as set out in claim 1. In accordance with a second aspect there is provided an image recording method as set out in claim 21. In order that the present invention may be more readily understood, embodiments thereof will now be described by way of example and with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a structural sectional view illustrating the internal structure of a copying apparatus embodying the present invention; Fig. 2 is a schematic view illustrating the manner in which ink is jetted by an ink-jet head; Fig. 3 is a diagram showing an example in which an image is printed using an ink-jet head having the characteristic illustrated in Fig. 2; Fig. 4 is a diagram showing an example in which an image is printed by sequential multiscanning using an ink-jet head having the characteristic illustrated in Fig. 2; Fig. 5 is a schematic view showing a process through which printing is performed by sequential multiscanning in a copying apparatus of the present invention; Fig. 6 is a block diagram schematically showing the construction of a full-color copying apparatus in this embodiment; Fig. 7 is a flowchart illustrating copy processing in a copying apparatus according to a first embodiment of this invention; and Fig. 8 is a flowchart illustrating copy processing in a copying apparatus according to another embodiment of this invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings. Fig. 1 is a structural sectional view illustrating the internal structure of a full-color copying apparatus using an ink-jet printer according to an embodiment of the present invention. The full-color copying apparatus of this embodiment comprises a reader 20 (hereinafter referred to as a scanner) for reading an original, and a printing unit 1 for printing the image of the original on a recording medium such as recording paper. In the scanner 20, the original placed upon a glass platen 21 is illuminated by an illuminating lamp 23, and light reflected from the original is imaged upon an photoelectric transducer (a reading sensor) 25 via a lens 24. The photoelectric transducer 25 generates an electric signal based upon the image of the original incident thereon, and information indicative of the original image can be obtained based upon this electric signal. The photoelectric transducer 25 is caused to scan below the original from right to left in the drawing (the main-scan direction) owing to rotation of a main-scan motor 416 (see Fig. 6) and is moved in the sub-scan direction owing to rotation of a sub-scan motor 417, whereby the image of the original is scanned in successive fashion. Furthermore, the photoelectric transducer 25 is composed of a row of microelements to respective ones of which R, G and B filters are attached. Thus, an image signal representing one pixel is generated by three elements. The density of these elements is 400 elements per inch, and the total number of elements is that for 144 pixels (144 x 3 = 432). After making one round trip in the left-right direction as seen in the drawing, the photoelectric transducer 25 is moved by the width of one read (printed) pixel inward in Fig. 1 so that the next line of the original image is read. An image signal for the entire original is obtained by repeating this operation a number of times conforming to the size of the original. The image signal obtained by the photoelectric transducer 25 is subjected to image processing such as a color correction, a luminance-density conversion and then a density correction, after which the signal is sent to the printing (recording) head of the printing unit 1 as a four-value signal for each of the colors cyan (C), magenta (M), yellow (Y) and black (K), which are the colors of the inks used in the printer. In the printing unit 1, recording paper P is fed from a paper cassette 3 by a paper-feed roller 5 and reaches conveyor rollers 8, 9 through a paper-feed sensor 19 and paper-feed guides 6, 7. The recording paper conveyed by the conveyor rollers 8, 9 reaches the platen 15. On the basis of the image information from the scanning unit 20, ink within an ink tank 2 is discharged (jetted) from nozzles onto the recording paper, which has been conveyed to the platen 15, by means of the printing head 2a, whereby an image conforming to the image of the original is printed. The printing head 2a has a row of 128 nozzles arranged in a direction (sub-scan direction) substantially perpendicular to the scanning direction of the printing head 2a and is capable of printing an image by a single scan of the printing head 2a. That is, the printing head 2a performs printing, while being made to scan inward in Fig. 1, in synchronism with the reading operation of the photoelectric transducer 25 of the scanning unit 1. One band (a width of about 8 mm) of an image thus is printed on the recording paper. When the printing of one band of the image ends, the recording paper is conveyed by an amount equivalent to one band by conveyor rollers 8, 9, 10, 13 in order to prepare for printing of the next band. When the printing of one page of the original ends, the recording paper on which printing has been completed is discharged into a paper-discharge tray 12 through a conveyance path 11. Numeral 16 denotes a paper-discharge sensor for sensing whether or not the recording paper is in the conveyance path 11. Figs. 2 through 4 are diagrams for describing uneven printing in an ink-jet head (multinozzle head) having a plurality of nozzles. Fig. 2 is a diagram illustrating the manner in which ink is discharged by such an ink-jet head. As shown in Fig. 2, the output of the multinozzle head develops a variance in the size of the discharged ink droplets, as shown at 201 in Fig. 2, owing to the manufacturing precision of the ink-jet head, the quality of the material or a change in the ink with the passage of time. Another problem is that since the ink is not discharged at right angles to the head surface, dots may overlap each other, as indicated at 202 in Fig. 2. When one band is printed using an ink-jet head of this kind, locations develop at which the ink droplets are too small and at which the dots are spaced too far apart because the ink is not discharged at right angles to the head. These locations produce strips (banding) that are too faint or strips (banding) where the ink droplets are too large. In addition, portions at which ink dots overlap produce image strips that are too dark. These strip-like portions (banding) appear as an unevenness in the density of the image. (In this embodiment, this conventional method of scanning is referred to as single scanning.) Accordingly, if, when one band is to be printed, the print head 2a is scanned a plurality of times and the nozzle used is changed each time one pixel is printed, portions where the ink is too dark or too light are dispersed, as shown in Fig. 4, as a result of which the aforementioned uneven density is rendered inconspicuous. In this embodiment, this novel method of printing shall be referred to as "sequential multiscanning". The unevenness in the density is conspicuously shown in the half-tone print mode in which an ink dot is alternately discharged, but the unevenness becomes less noticeable in a case where a dense image is printed because of spreading ink on a paper. Fig. 5 is a diagram schematically illustrating sequential multiscanning according to this embodiment. Here the plurality of nozzles of the printing head 2a are divided into four blocks A through D. As shown in Fig. 5, a dot printed by a nozzle in the block A of nozzles is represented by "X", a dot printed by a nozzle in the block B of nozzles is represented by "□", a dot printed by a nozzle in the block C of nozzles is represented by "▵", and a dot printed by a nozzle in the block D of nozzles is represented by "○". First, printing is performed every four pixels in the main-scan direction using the nozzles of block D in the first scan. Printing by this first scan is indicated at 501 in Fig. 5. Next, the recording paper is conveyed 32 pixels in the sub-scan direction (since the printing head 2a in this embodiment prints 128 pixels, the recording paper is conveyed by one-fourth of the total number of pixels, namely 32 pixels) and the nozzles of block C are used in the second scan to print dots every four pixels in the main-scan direction at locations offset by one pixel in the main-scan direction with respect to the dots printed by the nozzles of block D (the image thus printed is indicated at 502 in Fig. 5). Next, in the third scan, printing is performed in the same manner as in the second scan using the nozzles of block B (see 503 in Fig. 5). In the fourth scan, printing is performed in the same manner using the nozzles of block A (see 504). This ends the printing of one band by four scans of the printing head 2a. Fig. 6 is a block diagram schematically showing the construction of a full-color copying apparatus in this embodiment. A CPU 401 executes various control operations based upon a control program stored in a ROM 402 and illustrated in the flowchart of Fig. 7. A RAM 403 stores various working data that accompanies the operation of the CPU 401. A control panel 406 has a copy starting key 601 for commanding the start of copying, various keys for setting a variety of functions, such as a selection key (referred to as a "high-quality mode key") 602 for deciding whether printing is to be performed by sequential scanning, and a display for presenting a variety of messages to be viewed by the operator. Input/output circuits I/O 404, I/O 405 control respective drive sections. The illumination lamp 23 of the scanning unit 20 and the main-scan and sub-scan motors 416, 417 for moving the reading sensor 25 are connected to the I/O port 404. These input/output circuits are controlled by the CPU 401. A main-scan motor 418 for moving the printing head 2a of the printing unit 20, a sub-scan motor 419 for moving the recording paper, and various sensors 420 such as the paper-discharge sensor 16 and a paper-feed sensor 19 are connected to the I/O port 405. Motor-drive signals from the CPU 401 are outputted to the corresponding motors, and signals from the various sensors are outputted to the bus of the CPU 401. The bus is further connected to an image processing circuit 301, which executes various processing such as a density-luminance conversion and undercolor removal, as well as to a binarizing circuit 306 for converting a multivalued image signal into a binary image signal. The circuits also operated under the control of the CPU 401. The reading sensor 25 outputs RGB signals each composed of eight bits. This image signal is applied to the image processing circuit 301, which subjects the signal to a logarithmic conversion, namely the luminance-density conversion, masking processing for a color correction, black generation for producing a distinct black color and processing for zooming, etc. As a result of these processing operations, the signals are converted into eight-bit CMYK signals for the colors C (cyan), M (magenta), Y (yellow) and K (black), respectively. The CMYK signals are converted into binary data by the binarizing circuit 306, after which the resulting signals are outputted to respective ones of ink-jet heads 310 ∼ 313 corresponding to these four colors via a head driving circuit 307. Each ink-jet head discharges ink conforming to the image signal, thereby performing printing. It should be noted that the head driving circuit 307 is capable of being set by the CPU 401 so that all nozzles of the ink-jet head are used to discharge ink for all of the pixels, so that dots are printed every several pixels or so that no ink is discharged at all. Fig. 7 is a flowchart illustrating a copying operation in a copying apparatus according to this embodiment. The control program for executing this processing is stored in the ROM 402. First, at step S1, it is determined whether the copy starting key 601 on the control panel 406 has been pressed to command the starting of the copying operation. If the key 601 has been pressed, the program proceeds to step S2, at which the recording paper P is fed into the apparatus from the paper cassette 3. Thus, when the sensor 19 senses that the recording paper has reached the position of the platen 15 owing to rotation of the conveyor rollers 8, 9, the program proceeds to step S3. Here it is determined whether the sequential multiscanning mode has been set, namely whether the high-quality mode switch 602 has been pressed on the control panel 406. The pixel printing mode [printing every four pixels (sequential scanning) or printing all pixels] of the head driving circuit 307 is set depending upon the status of the high-quality mode key 602. More specifically, when the sequential multiscanning mode has been set (when the high-quality mode key has been pressed), the program proceeds to step S4. Here the nozzles of each head of the ink-jet heads 310 ∼ 313 are divided into four blocks, as shown in Fig. 5, and the mode for printing every four pixels in the main-scan direction is set. If the sequential multiscanning mode is not set, the program proceeds to step S5, at which the ordinary printing mode is set, namely the mode in which all nozzles of each ink-jet head are driven simultaneously and one band is printed by a single scan. Thus, the program proceeds to step S6, where the image of the original is read and printing of the image is performed in synchronism with the reading operation. Here, since image processing such as shading of the original-image signal is completed in the scanning unit 20 when recording paper has been fed to the printing unit 1, the reading of the image of the original and the printing processing by the ink-jet heads 310 ∼ 313 are capable of being performed while synchronization is achieved between the scanning unit 20 and the printing unit 1. Thus, copy processing comprising the reading of one band of the original and printing processing can be carried out. When copy processing for one band is thus concluded, the program proceeds to step S7. Here, in a manner similar to that of step S3, it is determined whether the sequential multiscanning mode is in effect or not, and the amount by which the recording paper is conveyed is controlled based upon the result of the determination. More specifically, when the sequential multiscanning mode is in effect, the program proceeds to step S8. Here the recording paper and the reading sensor 25 are each conveyed by 32 pixels in the sub-scan direction. When the sequential multiscanning mode is not in effect, the program proceeds to step S9. Here the recording paper and the reading sensor 25 are each moved by 128 pixels (the printing width of the ink-jet head 2a). Next, the program proceeds to step S10, at which it is determined, based upon sensing of the trailing edge of the recording paper and the size of the reading area of the scanning unit 20, whether the copy processing for one page of the original has been concluded. If the copy processing for one page has not been concluded, the program returns to step S3, where reading of the original and the printing operation by the printing unit 1 are repeated until copying ends. When the copying of one page ends at step S10, the program proceeds to step S11, at which the recording paper that has been printed on is discharged from the copying apparatus. Then, at step S12, the reading sensor 25 and the ink-jet head 2a (heads 310 ∼ 313) are returned to their home positions and copy processing is terminated. In accordance with this embodiment, as described above, the arrangement is such that it is possible to select the single scanning mode, in which all of the pixels on one line are printed using specific nozzles, and the sequential multiscanning mode, in which pixels on the same line are printing using a plurality of nozzles. As a result, a full-color image having conspicuous unevenness is printed in the sequential multiscanning mode whereas a dense image or an image such as a manuscript of characters is printed in the single scanning mode. This makes it possible to raise printing speed. Fig. 8 is a flowchart illustrating copying processing in a full-color copying apparatus according to another embodiment of the invention. The control program for executing this processing is stored in the ROM 402. The construction of the copying apparatus according to this embodiment is similar to that shown in Figs. 1 and 6 and need not be described again. First, at step S21, it is determined whether the copy starting key 601 on the control panel 406 has been pressed to command the starting of the copying operation. If the key 601 has been pressed, the program proceeds to step S22, at which the recording paper P starts to be fed into the apparatus from the paper cassette 3. When the recording paper P has reached the position of the platen 15, the program proceeds to step S23, where one band of the image of the original is read by causing the reading sensor 25 to perform scanning. The program then proceeds to step S24, at which it is determined whether the density of the image to be printed is high or not. This is done by determining whether pixels for which the density is greater than 160 make up more than half the length of the band in the image data of any of the colors C, M, Y, K. In the case of a dense image, image unevenness caused by uneven discharging of the ink from the nozzles is not conspicuous. Accordingly, the head driving circuit 307 is set to the single scanning mode, in which printing of the image is performed by all of the nozzles of the ink-jet head. On the other hand, if the image is faint, the program proceeds to step S25, at which a multiscanning flag (provided in the RAM 403) is turned on, and then to step S26, at which the head driving circuit 307 is set to the sequential multiscanning mode so that printing is performed every four pixels in the main-scan direction, as illustrated in Fig. 5. Specifically, in the case of an image having a low density, a decline in image quality due to uneven discharging of the ink from the nozzles is conspicuous. Therefore, in order to print an image of higher quality, the nozzles of each of the ink-jet heads 310 ∼ 313 are divided into four blocks and the mode for printing every four pixels in the main-scan direction is set, as shown in Fig. 5. Thus, the program proceeds to step S28, where the image of the original is read and printing of the image is performed in synchronism with the reading operation. Here, since image processing such as shading of the original-image signal is completed in the scanning unit 20 when recording paper has been fed to the printing unit 1, the reading of the image of the original and the printing processing by the ink-jet heads 310 ∼ 313 are capable of being performed while synchronization is achieved between the scanning unit 20 and the printing unit 1. Thus, copy processing comprising the reading of one band of the original and printing processing can be carried out. When copy processing for one band is thus concluded, the program proceeds to step S29. Here the status of the multiscanning flag is checked to determine whether the multiscanning mode is in effect, and the amount by which the recording paper is conveyed is controlled based upon the result of the determination. More specifically, when the sequential multiscanning mode is in effect, the program proceeds to step S30. Here the recording paper and the reading sensor 25 are each conveyed by 32 pixels in the sub-scan direction. Next, it is determined at step S32 whether the printing of 128 pixels and conveyance of the recording paper has ended, i.e., whether the copy processing of one band has been concluded. If the decision rendered is NO, then the program returns to step S28, where reading of the original conveyed by 32 pixels is performed and printing processing is executed. If it is determined at step S29 that the sequential multiscanning mode is not in effect, then the program proceeds to step S31, at which the recording paper and the reading sensor 25 are each moved by 128 pixels (the printing width of the ink-jet head 2a). The program then proceeds to step S34. Thus, when printing by the 128 nozzles (one band) and the reading of the original end at step S32, the program proceeds to step S33, at which the multiscanning flag is turned off, and then to step S34, at which it is determined, based upon sensing of the trailing edge of the recording paper and the size of the reading area of the scanning unit 20, whether the copy processing for one page of the original has been concluded. If the copy processing for one page has not been concluded, the program returns to step S24, where reading of the original and the printing operation by the printing unit 1 are repeated until copying ends. In this embodiment, scanning (which corresponds to the prescanning of step S23) for judging density from the second band onward is carried out at the time of back-scanning when the reading sensor returns to the starting position after reading the image. When the copying of one page ends at step S34, the program proceeds to step S35, at which the recording paper that has been printed on is discharged from the copying apparatus. Then, at step S35, the reading sensor 25 and the ink-jet head 2a (heads 310 ∼ 313) are returned to their home positions and copy processing is terminated. In this embodiment, it is so arranged that a changeover is made between the single scanning mode in which one band is copied by a single scan and the sequential multiscanning mode in which one band is copied by sequential multiscanning, with the changeover being performed in dependence upon the image density of the original from one band to the next. However, an arrangement may be adopted in which the operator designates the mode area by area using an area-designating function or the like. Further, in this embodiment, the scanning method is changed over in conformity with the density of the image. However, an arrangement may be adopted in which character information is judged and the printing mode is changed over based upon the results of judgment. Furthermore, an arrangement may be adopted in which the entire original is prescanned by a low-resolution reading sensor and copying is carried out after the particular mode is decided. Though the image density is judged at the time of back-scanning in the above-described embodiment, an arrangement may be adopted in which density is judged by performing prescanning at a speed higher than usual. Though this embodiment has been described in connection with a copying apparatus, it goes without saying that the present invention is applicable also to a printing apparatus in which the printing mode is designated by a host or the like and the method of printing an image from the host is controlled in accordance with the designation, as well as to various other printing apparatus such as facsimile machine having a communication function. Furthermore, though sequential multiscanning is employed as multiscanning in the above-described embodiment, the present invention is not limited to such an arrangement. An arrangement may be adopted in which a predetermined area (e.g. one band) is formed in complementary fashion by a plurality of scans using different nozzle positions. The present invention provides excellent effects especially in a printing apparatus having an ink jet printing head of the type in which printing is performed by forming flying droplets utilizing thermal energy. With regard to a typical configuration and operating principle, it is preferred that the foregoing be achieved using the basic techniques disclosed in the specifications of USP 4,723,129 and 4,740,796. This scheme is applicable to both so-called on-demand-type and continuous-type apparatus. In particular, in the case of the on-demand type, at least one drive signal, which provides a sudden temperature rise that exceeds that for film boiling, is applied, in accordance with print information, to an electrothermal transducer arranged to correspond to a sheet or fluid passageway holding a fluid (ink). As a result, thermal energy is produced in the electrothermal transducer to bring about film boiling on the thermal working surface of the printing head. Accordingly, air bubbles can be formed in the fluid (ink) in one-to-one correspondence with the drive signals. A discharging port is made to discharge the fluid (ink) by growth and contraction of the air bubbles so as to form at least one droplet. If the drive signal has the form of a pulse, growth and contraction of the air bubbles can be made to take place rapidly and in appropriate fashion. This is preferred since it will be possible to achieve fluid (ink) discharging having excellent response. Signals described in the specifications of USP 4,463,359 and 4,345,262 are suitable as drive pulses having this pulse shape. It should be noted that even better printing can be performed by employing the conditions described in the specification of USP 4,313,124, which discloses an invention relating to the rate of increase in the temperature of the above-mentioned thermal working surface. In addition to the combination of the discharging port, fluid passageway and electrothermal transducer (in which the fluid passageway is linear or right-angled) disclosed as the construction of the recording head in each of the above-mentioned specifications, the present invention covers also an arrangement using the art described in the specifications of USP 4,558,333 and 4,459,600, which disclose elements disposed in an area in which the thermal working portion is curved. Further, it is permissible to adopt an arrangement based upon Japanese Patent Application Laid-Open No. 59-123670, which discloses a configuration having a common slot for the discharging portions of a plurality of electrothermal transducers, or Japanese Patent Application Laid-Open No. 59-138461, which discloses a configuration having openings made to correspond to the discharging portions, wherein the openings absorb pressure waves of thermal energy. It is permissible to use a freely exchangeable tip-type printing head attached to the main body of the apparatus and capable of being electrically connected to the main body of the apparatus and of supplying ink from the main body, or a cartridge-type recording head in which an ink tank is integrally provided on the printing head itself. The addition of recovery means for the printing head and spare auxiliary means provided as components of the printing apparatus of the invention is desirable since these stabilize the effects of the invention greatly. Specific examples of these means that can be mentioned are capping means for capping the printing head, cleaning means, pressurizing or suction means, and preheating means such as an electrothermal transducer or another heating element or a combination thereof. Implementing a preliminary discharging mode for performing discharging separately of recording also is effective in order to perform stabilized printing. The printing mode of the printing apparatus is not limited merely to a printing mode for a mainstream color only, such as the color black. The printing head can have a unitary construction or a plurality of printing heads can be combined. The apparatus can be one having at least one recording mode for a plurality of different colors or for full-color recording using mixed colors. Further, ink is described as being the fluid in the embodiments of the invention set forth above. The ink used may be one which solidifies at room temperature or lower, or one which softens of liquefies at room temperature. Alternatively, in an ink-jet arrangement, generally the ink is temperature-controlled by regulating the temperature of the ink itself within a temperature range of between 30°C and 70°C so that the viscosity of the ink will reside in a region that allows stable discharging of the ink. Therefore, it is permissible to use an ink liquefied when the printing signal is applied. In order to positively prevent elevated temperature due to thermal energy when this is used as the energy for converting the ink from the solid state to the liquid state, or in order to prevent evaporation of the ink, it is permissible to use an ink which solidifies when left standing. In any case, the present invention is applicable also in a case where use is made of an ink which solidifies in response to application of thermal energy, such as an ink solidified by application of thermal energy conforming to a printing signal or ink which has already begun to solidify at the moment it reaches the recording medium. Such inks may be used in a form in which they oppose the electrothermal transducer in a state in which they are held as a liquid or solid in the recesses or through-holes of a porous sheet, as described in Japanese Patent Application Laid-Open Nos. 54-56847 and 60-71260. In the present invention, the most effective method of dealing with these inks is the above-described method of film boiling. Furthermore, as to the form of the printing apparatus according to the present invention, use is not limited to an image output terminal of an image processing apparatus such as a word processor or computer described above. Other configurations, which may be provided as a separate or integral part, include a copying machine in combination with a reader or the like, a facsimile machine having a transmitting/receiving function, etc. In accordance with the other embodiment of the invention as described above, the density of one band of an image is judged and a changeover is made between the single scanning mode in which the entire image of one line is printed by a specific nozzle and the sequential multiscanning mode in which ink is discharged using a plurality of nozzles, whereby a full-color image in which unevenness is conspicuous even in one page of the original is printed in the sequential multiscanning mode. When a portion having high density, such as a character portion, is printed, unevenness in the density of the printed image is rendered inconspicuous, even when the image is printed in the single scanning mode. Printing speed is not slowed that much, the copying apparatus is easy to use and the copying apparatus employs a multinozzle head. The present invention can be applied to a system constituted by a plurality of devices or to an apparatus comprising a single device. Furthermore, it goes without saying that the invention is applicable also to a case where the object of the invention is attained by supplying a program to a system or apparatus. Thus, an effect obtained in accordance with the present invention, as described above, is that an image is printed upon selecting between a method of printing the same line using a plurality of printing elements and a method of printing the same line using a specific printing element, thereby making it possible to print an image without conspicuous unevenness in the density of the printed image. Another advantage of the present invention is that an image can be printed by changing over between printing methods, i.e., by printing the same line using a specific printing element in a case where an image having inconspicuous density unevenness is printed, and printing the same line using a plurality of printing elements in a case where an image having conspicuous density unevenness is printed. As many apparently widely different embodiments of the present invention can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims. Thus the embodiments described provide an image printing method and apparatus, as well as a copying apparatus, in which the printing speed is improved and printing can be performed without a conspicuous unevenness in density caused by such a printing head. The described embodiments also provide an image printing method and apparatus, as well as a copying apparatus, in which an image is printed upon selecting between a method of printing the same line using a plurality of printing elements and a method of printing the same line using a specific printing element, thereby making it possible to perform printing without conspicuous unevenness in the density of the printed image. An advantage of the described embodiments is that they provide an image printing method and apparatus, as well as a copying apparatus, in which an image can be printed by changing over between methods, i.e., by printing the same line using a specific printing element in a case where an image having inconspicuous density unevenness is printed, and printing the same line using a plurality of printing elements in a case where an image having conspicuous density unevenness is printed. Yet another advantage of the described embodiments is that they provide an image printing method and apparatus, as well as a copying apparatus, in which an image whose image data has a high density and whose density unevenness is inconspicuous is printed by the usual single scan, whereas an image having a low density and a conspicuous density unevenness is printed by multiple scans.

Claims: An image recording apparatus for recording an image in response to image data and using a recording portion comprising a printing head (2a) having an array of printing elements each capable of printing a dot on a recording medium, characterised by comprising: image forming means (2a, 401, 408) for forming an image of a prescribed area by causing said recording portion to perform main scanning in a direction different from the direction in which said recording elements are arrayed, said image forming means having a first scanning mode for forming the image of said prescribed area by a single scan of said recording portion, and a second scanning mode for forming the image of an area corresponding to said prescribed area by a plurality of complementary scans of different ones of the recording elements of said recording portion; selecting means (S3) for selecting between said first and second scanning mode; and control means for dividing the printing elements in the printing head into a plurality of blocks when the apparatus prints in said second scanning mode, and for controlling the operation of the printing elements during said second scanning mode so that during each scan of said plurality of scans a different block of printing elements is operated to print until every block has performed scanning over the corresponding area as printed during a single scan in said first scanning mode; and so that printed dots have adjoining dots in the main scan direction, from a printing element of a different block. Apparatus according to claim 1, wherein the dots printed in the main scanning direction in said second mode are interlaced with a modulus equal to the number of blocks. Apparatus according to Claim 2 and further comprising conveyance means (419) for conveying the printing medium in a sub-scan direction by a length corresponding to the width of each block for every scan of said printing head when printing is performed in said second scanning mode. Apparatus according to any one of Claims 1 to 3 and further comprising judging means for judging characteristics of an image to be printed by the apparatus. Apparatus according to Claim 4, wherein said selecting means selects between said first and second scanning modes in dependence upon the output of said judging means. Apparatus according to Claim 5, wherein said judging means judges whether said image is character information or not. Apparatus according to Claim 6, wherein said selecting means selects said first scanning mode when said judging means judges that the image data represents a character image. Apparatus according to any one of Claims 1 to 4, wherein said judging means judges whether or not said image data has a density that is less than a predetermined value. Apparatus according to Claim 8, wherein said selecting means selects said second scanning mode when said judging means judges that the image density is less than said predetermined value. Apparatus according to claim 9, further comprising reading means (23, 24, 25) for reading an image to be recorded by said recording elements, wherein said judging means judges the characteristics of the image read by said reading means. Apparatus according to claim 10, wherein reading speed of said reading means is higher when reading is performed for a judgement to be rendered by said judging means than when reading is performed for the recording by said printing elements. Apparatus according to either one of claims 10 or 11, wherein said judging means judges the characteristics of the image in a unit equivalent to said prescribed area before said reading means reads the image for printing the image. Apparatus according to either of claims 10 or 11, wherein said judging means judges the characteristics of the image in a unit of one screen before said reading means reads the image. Apparatus according to any preceding claim, wherein said image recording apparatus is applied to a printer connected to a host computer. Apparatus according to claim 14, wherein said selecting means selects said modes in response to a command from the host computer. Apparatus according to any one of claims 1 to 13, wherein said image recording apparatus is applied to a facsimile apparatus having a communication function. Apparatus according to any one of the preceding claims wherein the recording portion or printing head is an ink jet head, and said plurality of printing elements include a plurality of ink discharging nozzles. Apparatus according to claim 17, wherein each printing element includes a thermal energy transducer for ejecting ink through its associated nozzle. Apparatus according to any one of the preceding claims and further comprising reading means (23,24,25) including a photoelectric scanner for scanning and reading an original image to generate an electrical signal corresponding to the scanned image; and signal processing means (301,306) for creating image data from the signal generated by said reading means. A method of recording an image in response to image data using a recording portion comprising a printing head (2a) having an array of printing elements each capable of printing a dot on a recording medium, characterised by: forming (2a, 401, 408) an image of a prescribed area by causing said recording portion to perform main scanning in a direction different from the direction in which said recording elements are arrayed, said image forming means having a first scanning mode for forming the image of said prescribed area by a single scan of said recording portion, and a second scanning mode for forming the image of an area corresponding to said prescribed area by a plurality of complementary scans of different ones of the recording elements of said recording portion; selecting (S3) between said first and second scanning modes; dividing the printing elements in the printing head into a plurality of blocks when the apparatus prints in said second scanning mode; and controlling the operation of the printing elements during said second scanning mode so that during each scan of said plurality of scans a different block of printing elements is operated to print until every block has performed scanning over the corresponding area as printed during a single scan in said first scanning mode; and so that printed dots have, in the main scan direction, adjoining dots from a printing element of a different block. A method according to claim 20, wherein in the second scanning mode the printed dots in the main scan direction from the different blocks are interlaced in accordance with the modulus of the blocks. A method according to claim 20 or claim 21 and further comprising conveying (419) the printing medium in a sub-scan direction by a length corresponding to the width of each block for every scan of said printing head when printing is performed in said second scanning mode. A method according to any one of claims 20 to 22 and further comprising judging characteristics of an image to be printed by the apparatus, and selecting between said first and second scanning modes in dependence upon the output of said judging means. A method according to claim 23, wherein said judging means judges whether said image is character information or not, and said selecting means selects said first scanning mode when said judging means judges that the image data represents a character image. A method according to any one of claims 20 to 23, wherein said judging means judges whether or not said image data has a density that is less than a predetermined value. A method according to claim 25, wherein said selecting means selects said second scanning mode when said judging means judges that the image density is less than said predetermined value. A method according to any one of claims 20 to 26, wherein each printing element ejects ink to generate a dot using thermal energy.

Inventors: SUGISHIMA KIYOHISA, SUGISHIMA, KIYOHISA, Sugishima, Kiyohisa, c/o Canon Kabushiki Kaisha
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1993
Main classification: B41J2
IPC codes: B41J2