Abstract:
A method of printing a subject on a medium by use of a printing device including a printhead assembly, wherein the printhead assembly has at least one printhead having an array of marking elements, is accomplished by scanning the printhead assembly along a medium by a succession of passes, the passes being offset from each other in a direction transverse to a scanning movement of the printhead assembly relative to the medium. The subject consists of textual and non-textual material, and pixels of the subject are loaded into the printing device. The method provides for separating pixels of the textual material from pixels of the non-textual material, and printing pixels of at least a portion of the subject by passing the printhead along the medium in a plurality of the passes. In an offsetting of successive ones of the passes, a translation of the printhead in the transverse direction accumulated over the succession of the plurality of passes does not exceed a transverse dimension of the printhead. Non-textual material of the subject is printed in more than one of the plurality of the passes, and textual material of the subject is printed during only one of the plurality of the passes. Examination of print command signals may be made to alter printing protocol based on the presence or absence of color or black.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates to printing of both text and non-text (graphics) material in printing apparatus employing an array of sources of media marking elements, such as ink jets, and particularly to the activation of the marking elements to optimize the quality of printed text and printed non-text material.  
           [0002]    Various types of printing devices are known for printing markings on a print medium. Of particular interest herein is a printing device employing a linear array of printing elements constituting a printhead which moves along the medium in a direction perpendicular to the linear array. In one well-known form of such printing device, two printheads are joined together in a unitary print-head assembly wherein one of the linear arrays comprises color marking elements, such as inkjets, while the second linear array comprises black marking elements, such as inkjets. For example, the first printhead may comprise a linear array of inkjets wherein some of the inkjets employ yellow ink, some of the inkjets employ magenta ink, and the remainder of the inkjets employ cyan ink. In the second printhead, all of the inkjets employ black ink. In a typical printing task, both of the printheads may be employed in presenting a graphic subject such as scenery having multiple colors and black, while only the second printhead is employed for printing black text within the subject imprinted on the medium.  
           [0003]    In one typical form of construction of the color printhead, the inkjets are grouped together by color. For example, the inkjets may be arranged in a yellow band, a magenta band, and a cyan band. In order to provide an interleaving of the swaths of color laid down on the medium during successive passes of the printhead assembly across the medium, it is common practice to advance the medium, transversely to the direction of head movement, by a distance of one-half the width of a color swath for improved print quality. This has been found to minimize the effect of possible variations in the spraying patterns of successive ones of the color inkjets. Also, it has also been the practice, in the operation of a printhead, to employ some form of randomizing in the activation of the various ones of the inkjets during successive ones of the passes of the printhead assembly so as to obtain improved uniformity in the printing of regions of the subject matter.  
           [0004]    In the foregoing technique for interleaving the swaths of color laid down by the inkjets in a printhead, a problem arises in that this technique introduces a lack of clarity in lettering or text wherein the edge lines of each printed character are not as sharply defined as is desirable.  
         SUMMARY OF THE INVENTION  
         [0005]    The aforementioned problem is overcome and other advantages are provided, in accordance with the practice of the invention, by implementation of a printing mode wherein the printing of text is separated from the printing of non-text material. To facilitate description of the invention, in accordance with a first embodiment of the invention, it is presumed that the text is printed with black ink by a single print head (the black printhead) while the non-textual material may include both color and black, wherein the color is printed by use of a separate printhead (the color printhead) having inkjets operative with magenta, yellow and cyan inks. A single printhead assembly carries both printheads. The black text, in a region of the medium, is printed solely within a single pass of a printhead laying down solely black ink across the region of the medium while more than one pass is provided for the color printhead to lay down colored inks in the same region of the medium. The printing of the black text is accomplished independently of the interleaving and randomizing of the various colors and black components of the non-textual subject matter.  
           [0006]    As a matter of convenience in the implementation of the invention, the black textual material may be imprinted simultaneously with the printing of black non-textual material subject to the proviso that while a plurality of passes of the printhead assembly may be employed for printing black markings over a band of subject matter equal in width to the length of the black inkjet array, only one pass of the plurality of passes of the printhead assembly is employed for the printing of the textual material. Thereby, the printing of the textual material is free from the foregoing interleaving and randomizing procedures for the printing of non-textual subject matter such as scenery on the medium. As a result, the textual material is provided with clearly shaped characters, such as alphanumeric characters, these characters being superposed upon the graphical, non-textual, portions of the subject matter.  
           [0007]    If the text were to be printed in a color such as magenta, by way of example, rather than in black, then, in accordance with the first embodiment of the invention, a separate printhead would be used for the magenta rather than for the black. Alternatively, in accordance with a second embodiment of the invention, the principle of printing the text in a single pass of the printhead is applied to the color printhead such that, in the foregoing example of magenta, non-textual or graphic material would be printed in more than one pass of the color printhead across a region of the medium while the textual material would be printed solely within a single pass of the color printhead across that region of the medium.  
           [0008]    In a further feature of the invention, there is examination of binary digital pixel signals that are fed to the inkjets to produce the image on the medium. These pixel signals are one bit signals that serve as print command signals for directing the respective inkjets to print a mark or to leave a blank space on the medium. As a result of the examination of the pixel signals, the printing protocol may be altered, based on the presence or absence of color or black. This is accomplished efficiently by concurrent examination of print command signals of individual ones of a plurality of color and black signals by use of an OR function to search for a color or black print command signal. Such information may be used to speed up the printing process by deleting extra passes of the printhead assembly employed for the foregoing interleaving in the situation, wherein only one of the foregoing colors is to be employed.  
           [0009]    In the ensuing description, the principles of the invention will be described first with respect to the first embodiment of the invention, with a printing of text in black ink. 
       
    
    
     BREF DESCRIPTION OF THE DRAWING  
       [0010]    The aforementioned aspects and other features of the invention are explained in the following description, taken in connection with the accompanying drawing figures wherein:  
         [0011]    [0011]FIG. 1 shows a stylized fragmentary view of a printer, partially in diagrammatic form, operative in accordance with the method of the invention;  
         [0012]    [0012]FIG. 2 shows a path of travel of a printhead of the printer of FIG. 1 traveling across the medium for receiving printing;  
         [0013]    [0013]FIG. 3 shows an imprinting of subject matter on the medium by a printhead assembly of the printer of FIG. 1 wherein the subject matter includes regions of different color with black text superposed upon the color;  
         [0014]    [0014]FIG. 4 is a block diagram showing a portion of the host computer of FIG. 1 providing for the separation of the colored, black and textual portions of pixels of the subject being imprinted on the medium, in accordance with a first embodiment of the invention;  
         [0015]    [0015]FIG. 4A shows a portion of FIG. 4 modified in accordance with a second embodiment of the invention:  
         [0016]    [0016]FIG. 5 comprises FIGS. 5A and 5B presenting timing diagrams showing operation of the circuitry of FIG. 4 in accordance with the first and second embodiments, respectively, of the invention; and  
         [0017]    [0017]FIG. 6 is a block diagram of a black/color analyzer of FIG. 4. 
     
    
       [0018]    Identically labeled elements appearing in different ones of the figures refer to the same element but may not be referenced in the description for all figures.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0019]    [0019]FIG. 1 shows a printer  20  having a medium  22  for receiving marks imprinted thereon by a printhead assembly  24 , the medium  22  being in the form of a sheet carried by a plurality of rolls  26 , only one of the rolls  26  being shown to simplify the drawing. The printhead assembly  24  travels along a guide  28  which supports the printhead assembly  24  during subsequent passes of the printhead assembly  24  in a transverse direction across the medium  22  for imprinting successive lines of a subject on the medium  22 . Transverse movement of the printhead assembly  24  is controlled by a cable  30  which is moved by a rotatable pulley about which the cable  30  is wrapped. The pulley  32  is rotated by a motor  34  operative under control of electric signals applied thereto by a controller  36 . The controller  36  also applies electric signals to a further motor  38  which rotates the roll  26  for transporting the medium  22  in a longitudinal direction, perpendicular to the transverse direction of passage of the printhead assembly  24 . The controller  36  is controlled, in turn, by electric signals applied thereto by a system computer  40 .  
         [0020]    The invention is applicable to printhead assemblies having various arrangements of printheads. In a preferred embodiment of printer employed for carrying out of the method of the invention, the printhead assembly  24  has two printheads  42  and  44 . The printhead  42  includes a linear array of inkjets  46  oriented perpendicularly to the direction of movement of the printhead assembly  24 , wherein differing ones of the inkjets  46  carry different colors of ink. The printhead  44  also includes a linear array of inkjets  46  disposed parallel to the color array of inkjets of the printhead  42 , and being offset from the printhead  42  in the longitudinal direction of travel of the medium  22 . The inkjets  46  of the black printhead  44  carry black ink for printing black portions of subject matter, and also for printing black text within the subject matter. Electric signals for operating the inkjets  46  of both of the printheads  42  and  44  are provided by the controller  36  via an electric cable  48  interconnecting the controller  36  with the printhead assembly  24 . The offsetting of the black printhead  44  relative to the color printhead  42  provides for improved interleaving of markings imprinted via respective ones of the printheads  42  and  44  for improved rendition of the printing of the subject matter.  
         [0021]    With reference to FIG. 2, there are shown details in the construction and operation of the color printhead  42 . The printhead  44  is not shown in FIG. 2 to simplify the drawing, it being understood that, apart from the use of black ink instead of colored ink, the operation of the printhead  44  is the same as that of the printhead  42 . By way of example in the construction of the color printhead  42 , there are approximately 320 of the inkjets  46  arranged in a linear array of which approximately the first 100 inkjets at the top of the printhead carry yellow ink, approximately 100 inkjets in the middle of the printhead carry magenta ink, and approximately 100 inkjets at the bottom of the printhead carry cyan ink. Between the group, or sub-array, of yellow inkjets and the group of the magenta inkjets, there are a few inkjets which are unused and, also, between the group of magenta inkjets and the group of cyan inkjets, there are a few inkjets which are unused. Thus, the inkjets may be viewed as being arranged in three sub-arrays of equal width and differing color. The width of each color band is approximately equal to one third of the length of the array of the inkjets of the color printhead  42 . The unused inkjets provide improved separation of the colors to be imprinted on the medium  22 . Arrows in the figure show the transverse movement of the printhead  42  towards the left during a printing operation, and the downward movement of the medium  22  between the successive passes of the printhead  42 . The present pass traversed by the printhead  42 , a previous pass, and the pass before the previous pass are shown at  50 ,  52  and  54 . The bottom edges of the passes are indicated at  50 A,  52 A and  54 A, while the top edges of these passes are indicated at  50 B,  52 B and  54 B, respectively. The offsets between successive ones of the passes  50 ,  52  and  54  are equal to each other, and are equal to one-sixth the total length of the array of the inkjets  46  of the printhead  42 , and also of the printhead  44  (not shown in FIG. 2). Thus, the width of the offset is equal to one-half the width of one of the foregoing color bands.  
         [0022]    [0022]FIG. 3 provides an example of a subject  56  being printed on the medium  22  by the printhead assembly  24 . The subject  56  is a graphical representation of the production of produce showing a yellow region imprinted with text, namely, the word “CORN”, and blue, green and red regions imprinted respectively with the words RYE, BARLEY and WHEAT. In each printing pass of the printhead assembly  24 , various ones of the inkjets  46  (FIG. 2) are activated to provide for coloring various ones of the pixels of the subject  56 , with specific ones of the passes in the sequence of passes being designated for imprinting the text in accordance with the practice of the invention. This is accomplished by separating the colors to be imprinted at the sites of various ones of the pixels along with a separation of black non-textual material and a separation of the black textual material from the colors.  
         [0023]    [0023]FIG. 4 shows details in the construction of the system computer  40  to accomplish the foregoing separation of the colors and the black material to be imprinted at the sites of various ones of the pixels. The system computer  40  includes a memory  58 , and a buffer store  60  which receives signals read out of the memory  58  under control of an address generator  62 . The buffer store  60  includes registers  64 ,  66 ,  68 ,  70  and  72  operative in response to clocking and address signals from the address generator  62 . The register  64  receives information regarding the imprinting of yellow at the sites of various ones of the pixels, with the registers  66  and  68  receiving corresponding information with respect to the imprinting of magenta and cyan at the sites of respective ones of the pixels. Black non-textual information for respective ones of the pixels is read out of the memory  58  to the registers  70 , with textual black material being read out of the memory  58  to the register  72 . The address generator  62  is responsive to timing signals from a timing unit  74 , the timing unit  74  providing signals also for synchronizing operation of the controller  36  with the address generator  62 . A black/color analyzer  76  may also be connected with the output on the memory  58 , an output of the address generator  62 , and an input of the controller  36  for operation of the controller  36  in accordance with the detection of colored and black regions of the subject  56  (FIG. 3) in accordance with a further feature of the invention.  
         [0024]    Output ports of the registers  64 ,  66  and  68  apply control signals to various ones of the inkjets  46  of the color printhead  42  such that the signals of the register  64  are coupled to those inkjets carrying yellow ink, the signals of the register  66  are coupled to those inkjets carrying magenta ink, and the signals of the register  68  are coupled to those inkjets carrying cyan ink. The signals outputted by the registers  70  and  72  are applied via an OR circuit  78  to the printhead  44  for control of the inkjets  46  carrying the black ink. With the arrangement of the circuitry shown in FIG. 4, the address generator  62  has individual control of the times of imprinting the various colors and black at each of the sites of the various pixels of the subject  56  to be printed, which printing can take place in a pseudo-random fashion, or other manner as may be desirable for blending the printing of successive ones of the passes of the printhead assembly  24  and for reducing the effect of any misalignment in the locations of the various inkjets  46  of the printhead  42  and  44 . Such improvement in rendition of the printed subject is accomplished in accordance with the invention by a sequencing of the printing stages of the various passes of the printhead assembly  24  as is described with reference to the timing diagram of FIG. 5.  
         [0025]    With respect to the timing diagram FIG. 5, it is noted that the printhead assembly  24  makes a sequence of six passes across the printer medium  22 . During this sequence of six passes, the medium  22  advances a distance equal to the length of the array of the inkjets  46  of the printhead  42  which, in turn, is equal to the length of the array of the inkjets  46  of the printhead  44 . As shown in the first graph of the timing diagram, color is imprinted at only 50 percent of the maximum amount of color which can be applied in a region to be colored. However, all of the requisite color for any one of the color bands can be printed within two passes of the printhead assembly  24  because the offset between successive passes of the printhead assembly  24  is equal to half the width of the band of color, as has been described above. Accordingly, an imprinting of all three of the colors, in all three of the color bands, is accomplished in a total of six passes of the printhead assembly  24 . This is shown in the first graph of the timing diagram wherein the color is laid down on the medium at a rate of 50 percent of capacity during each of the six successive passes of a printing cycle. Therefore, in the printing process, the printhead assembly  24  cycles through a set of six passes across the medium  22 , after which a new cycle begins, the cyclical procedure continuing until all of the subject matter has been printed.  
         [0026]    The second graph of the timing diagram shows the procedure for printing black non-textual material by use of the inkjets  46  of the black printhead  44 . All of the inkjets  46  of the black printhead  44  are employed for the printing of the black non-textual material. Since there are six passes of the printhead assembly  24  during each of the printing cycles, the black material may be imprinted at a rate of one third of total capacity, as shown in the second graph, wherein the printing occurs on alternate ones of the passes, such as pass No.  1 , pass No.  3  and pass No.  5  depicted in the timing diagram. Alternatively, in accordance with the practice of the invention, the printing can be done at a rate of one sixth of capacity with printing in every pass of the printing cycle. By printing in either alternate passes or in every pass of the printing cycle, there is good interleaving of a printing of the successive passes for a high quality rendition of the subject.  
         [0027]    The third graph of the timing diagram depicts a feature of the invention wherein all of the text is printed with the black ink by the inkjets  46  of the black printhead  44  in a single pass of the printing cycle. Thus, 100 percent of the textual material is printed in a single pass, shown as pass No.  1 , of the printing cycle. Here, no attempt is made to interleave text among successive passes of the printing cycle but, in accordance with the practice of the invention, the completed printing in a single pass with availability of all of the black inkjets produces more clearly defined and precisely configured printed characters on the print medium  22 . In particular, the edge lines of the alphanumeric characters are more sharply defined by imprinting all of the textual material at 100 percent of capacity within a single pass of the printing cycle.  
         [0028]    By way of alternative embodiments of the invention, it is noted that text could be printed in a color, such as magenta, yellow or cyan, by way of example, instead of in black. In such case, if desired, the printhead  44  (FIG. 1) could carry inkjets filled with ink of the desired color for imprinting the text, and the printhead  42  could carry inkjets filled with inks having the remaining colors and black. The foregoing description of the operation of the printer  20  would still apply, except that the ink of the selected color would be interchanged with the black ink.  
         [0029]    However, preferably, the printing of text in color would be accomplished by use of the color printhead  42 , in accordance with a further embodiment of the invention, without replacing the black inkjets  46  of the black printhead  44  with color inkjets  46  from the color printhead  42 . This further embodiment of the invention enables the printing of the text in color to be accomplished by use of color inkjets  46  of the color printhead  42  in a manner which enhances the print quality similarly to the enhancement of the print quality by the first embodiment of the invention.  
         [0030]    In order to understand the theory of the second embodiment of the invention, if is useful to recall that, in the first embodiment of the invention, the printhead assembly  24  makes a sequence of six passes across the printer medium  22  and that, during this sequence of six passes, textual material is printed during only one of the passes. Furthermore, during the cyclical sequence of the six passes, the medium  22  advances a distance equal to the length of the array of the inkjets  46  of the black printhead  44  which prints the textual material.  
         [0031]    In analogous fashion, printing of colored text, in accordance with the second embodiment of the invention, is accomplished by use of the array of color inkjets comprising the individual smaller arrays of the respective yellow, magenta and cyan inkjets. As has been described above, each of the individual arrays of color inkjets is approximately one-third the length of the array of the black inkjets of the black printhead  44 . Thus, in the foregoing cyclical sequence of six passes, a region of the medium  22  would be passed over by the array of yellow inkjets (or other ones of the colored inkjets) in only two passes for the imprinting of yellow marks in graphical subject matter. Only one of these two passes is to be employed for the imprinting of yellow textual material.  
         [0032]    The next two passes would be available for imprinting further color marks into the graphical subject matter such as magenta marks. If the textual material is to have a magenta component, then one of these two passes would be employed for the imprinting of the magenta textual material. Similarly, in the final two passes of the cyclical sequence of passes, cyan marks would be printed in the same region the medium  22  in the event that there is to be a cyan component in the graphical subject material. However, only one of these two passes would be employed for printing cyan in the textual subject matter.  
         [0033]    The foregoing operation of the second embodiment of the invention is depicted in the first two graphs of FIG. 5B, wherein the first graph shows that, in each of the passes in the cyclical sequence of six passes, there is an imprinting of color marks by actuation of the inkjets  46  of the color printhead  42 . Since two passes are employed for laying down all of the cyan, or other color, for the graphical subject matter in a region of the medium  22 , the colors are laid down at a rate of 50 percent of a maximum rate in any one pass. This provides a full amount of any one color component of the graphical subject matter in two successive passes of the color printhead  42 . On the other hand, as shown in the second graph of FIG. 5B, since the textual material is imprinted for any one of the colors in only one of the two passes, the coloring is applied at the full rate of 100 percent. In the event that black ink is to be laid down on the medium, along with color ink, for the printing of the graphic and/or textual material, the procedure for such usage of black ink remains the same as has been described above for the printing of black text and graphic material, such printing being depicted in the bottom two graphs of both FIGS. 5A and 5B.  
         [0034]    The first graph of FIG. 5B also identifies the color of ink to be printed during the respective passes in the cyclic sequence of the six passes of a color printhead  42 . In the event that one of these colors is not required, such as the yellow of pass No.  2  or the magenta of pass No.  4  by way of example, then the controller  36  (FIGS. 1 and 4) is able to speed up the printing process by deleting this pass of the printhead assembly  24 , and by advancing the medium  22  by an extra increment of the width of one pass before directing the printhead assembly  24  to do any printing.  
         [0035]    The second embodiment of the invention is readily accomplished by modifying the system computer  40 , as depicted in FIG. 4, by enlarging the number of registers of the buffer store  60 , and the inclusion of additional OR circuits as shown in FIG. 4A. The additional registers are identified as registers  64 A,  66 A and  68 A for storing, respectively, the yellow text pixels, the magenta text pixels, and the cyan text pixels. The additional OR circuits comprise the OR circuit  78 A for the yellow pixels, the OR circuit  78 B for the magenta pixels, and the OR circuit  78 C for the cyan pixels.  
         [0036]    The operation of the circuitry in FIG. 4A follows that described above with reference to the circuitry of FIG. 4. Thus, data is read out of the memory  58 , in response to signals of the address generator  62 , to be stored in respective ones of the registers of the buffer store  60 , and to be read out from these registers in response to signals applied to the registers from the address generator  62 . The signals read out of the registers are applied to the respective ones of the inkjets  46  in the respective arrays of the inkjets in accordance with a procedure analogous to the procedure described above for the reading out of the data of black graphic pixels of the register  70  and the black text pixels of the register  72  via the OR circuit  78  to the black inkjets  46 .  
         [0037]    In accordance with the timing of the operation of the colored-ink inkjets, as set forth in FIG. 5B, the address generator  62  is responsive to the timing unit  74  for directing the register  64  to read out yellow graphic pixels via the OR circuit  78 A to the yellow inkjets  46  at times designated in the first graph of FIG. 5B, and also for directing the register  64 A to read out yellow text pixels via the OR circuit  78 A to the yellow inkjets  46  at times designated in the second graph of FIG. 5B. Similar comments apply to the reading out of the magenta graphic pixels and the magenta text pixels respectively from the registers  66  and  66 A via the OR circuit  78 B for activating the magenta inkjets, and to the reading out of the cyan graphic pixels and the cyan text pixels respectively from the registers  68  and  68 A via the OR circuit  78 C for activating the cyan inkjets.  
         [0038]    With reference to FIG. 6, and in accordance with a further feature of the invention, the analyzer  76 , shown also in FIG. 4, comprises four registers  80 ,  82 ,  84  and  86  for storing information with respect to, respectively, the cyan, the magenta, the yellow, and the black to be imprinted on the medium  22  in the printing of the subject  56  (FIG. 3). The registers  80 ,  82 ,  84  and  86  are addressed by signals from the address generator  62  and receive information from the memory  58  with respect to the pixels of the subject. The address generator  62  and the memory  58  are shown also in FIG. 4. For the printing of any one of the colors, such as cyan, at the site of a pixel, it is necessary to provide only a one-bit signal to indicate the presence or absence of a dot of cyan to be printed on the medium  22 . Thus, the register  80  stores a lengthy series of digits, one for each pixel in a line of pixels to be printed, wherein the presence of a logic 1 or a logic 0 indicates the presence or absence of the color cyan at the respective pixels and serves as a command signal for an inkjet. In similar fashion, each of the registers  82 ,  84  and  86  stores a series of digits wherein a logic 1 or a logic 0 indicates the presence or absence of the magenta, the yellow, or the black to be imprinted at the respective pixels.  
         [0039]    In the operation of the analyzer  76 , the presence of color in the subject is indicated by the detection of a logic-1 signal in any one of the registers  80 ,  82  and  84 . To determine whether color is to be present at a specific portion of the subject, the invention provides for a gathering of logic-1 signals of the three colors in the three registers  80 ,  82  and  84  prior to a detecting of the presence of a logic-1 signal. This is accomplished by performing an OR operation on the digital signals stored in the registers  80 ,  82  and  84 . Instead of performing the OR operation on a digit by digit basis, which is costly in terms of time, the OR operation is performed on segments or bytes, such as 32 bits, of the data to provide for a much faster determination of the presence of color. The bits in each of the registers  80 ,  82  and  84  are addressed by the address generator  62 . An OR circuit  88  operates on signals, such as the foregoing example of a segment of 32 bits, outputted by the registers  80  and  82  and stores the result of the OR operation in a register  90 . A further OR circuit  92  operates on the contents of the register  90  and the register  84  and outputs the results of the OR operation in a register  94 . The presence of a logic 1 in either of the registers  80  and  82  appears also in the register  90  and, similarly, the presence of a logic 1 in either of the registers  90  and  84  appears in the register  94 . Thereby, the register  94  has gathered the logic-1 signals of all of the color registers  80 ,  82  and  84 . The presence of the logic-1 signal and, hence, the presence of color, is detected at the register  94  by a detector  96 .  
         [0040]    A further OR circuit  98  operates upon the contents of the register  94  and the register  86  and outputs the results of the OR operation in a register  100 . The contents of the register  100  indicate the presence of both color and/or black in the subject being printed. Also included in the analyzer  76  are two more detectors  102  and  104 , and a control logic unit  106 . The detector  102  detects the presence of a logic-1 signal in the bits of the byte addressed by the generator  62  in the register  86 . The presence of the logic-1 signal indicates that there is black in the subject matter while the absence of the logic-1 signal indicates the absence of black in the portion of the subject matter represented by the bits of the byte addressed by the generator  62 . The detector  104  detects the presence of a logic-1 signal in the register  100 , this representing the presence of either color or black or both color and black at the locations of the pixels of the 32-bit set of addresses applied by the generator  62  to the registers  80 ,  82 ,  84  and  86 . The absence of the logic-1 signal is an indication that the field of the subject matter represented by the foregoing set of addresses is empty in terms of an absence of color and an absence of black.  
         [0041]    The results of the detections of the detectors  96 ,  102  and  104  are applied to the control logic unit  106  which is operative, in response to a user mode selection at  108 , to direct the address generator  62  to provide addresses for examining for the presence of color or black or color and black at a smaller region of the subject matter, or to continue looking at some other region of the subject matter for this information. By way of example in the use of the control unit  106 , in the absence of color, the unit  106  may direct the controller  36  (shown also in FIG. 4) to print text during one pass of the printing cycle, and then to advance the medium  22  by a displacement equivalent to the displacement of a complete printing cycle. Further information in the construction and utilization of a printer operable in plural modes involving color with black, and black only, is disclosed in copending application (Ser. No.: 09/349,025, Inventor: Bloomberg, S., Filing date: Jul. 7, 1999), the contents of which are incorporated herein by reference. As has been explained above, such displacement is equal to the length of the array of inkjets  46  of the black printhead  44 . Thereby, by altering the printing protocol in terms of the number of printing passes in the cycle of printing passes to be employed for printing a portion of the subject, this feature of the invention provides for a much more rapid printing of the subject matter and eliminates the interleaving of bands of color when no color is to the printed.  
         [0042]    The functions of the circuitry of the analyzer  76  can be implemented by use of a computer, and the benefits of the analyzer  76  are available for other purposes in addition to the foregoing purpose of selecting an operating mode of the printer  20 . For example, the analyzer  76  may be used to identify regions of an image having only color but no black, or the absence of either color or black, by way of example. Thus, the analyzer  76  is operative generally as a tool in image analysis.  
         [0043]    It is to be understood that the above described embodiments of the invention are illustrative only, and that modifications thereof may occur to those skilled in the art. Accordingly, this invention is not to be regarded as limited to the embodiments disclosed herein, but is to be limited only as defined by the appended claims.