Patent Publication Number: US-2004051902-A1

Title: Image formation device

Description:
TECHNICAL FIELD  
       [0001] The present invention relates to an image formation device that can achieve optimal dot reproduction and improve reproducibility of highlights.  
       BACKGROUND ART  
       [0002] Conventionally, to reproduce halftones corresponding to image information of vector type, an image formation device converts the image information into image data (bitmap data), reads out the image data at a certain timing to subject the image data to γ-correction (density correction) dot by dot, and then subjects the γ-corrected image data to pseudo halftone processing such as dither processing.  
       [0003] Japanese Patent Application Laid-Open No. 3-80768 exemplifies an image formation device that performs density correction on image data using a multilevel dither method to obtain a halftone image in image processing. This type of image formation device comprises a first correcting unit that corrects a density characteristic of multivalue image data based on a dither processing, a dither-processing unit that performs a multilevel dither processing on the multivalue image data corrected by the first correcting unit, and a second correcting unit that corrects a density characteristic of the multilevel dither data obtained by the dither-processing unit based on a printer output characteristic. Thus, the image formation device can easily respond to various combinations of printer output characteristics. In addition, the image formation device performs the γ-correction based on a single γ-characteristic.  
       [0004] However, in the conventional art, it is not possible to respond to a variety of pseudo halftone processing because the γ-correction is performed based on the single γ-characteristic. Therefore, in the conventional art, it is not possible to reproduce halftones of image information with fidelity, resulting in a difficulty to achieve optimal dot reproduction and a lower reproducibility of highlights.  
       [0005] The present invention has been achieved in consideration of the above and accordingly has an object to provide an image formation device that can achieve optimal dot reproduction and improve reproducibility of a highlight.  
       DISCLOSURE OF THE INVENTION  
       [0006] The image formation device according to the present invention for forming a dot image on a recording medium based on image data, comprises: a peripheral dot detecting unit that detects whether there is a peripheral dot located at an arbitrary distance from a target dot at least in a main scanning direction and in a subscanning direction in the dot image; a space dot detecting unit that detects whether space dots surround the target dot based on a result of detection by the peripheral dot detecting unit; and a data amount control unit that increases data corresponding to the target dot based on a result of detection by the space dot detecting unit.  
       [0007] According to the image formation device, the data corresponding to the target dot is increased based on the result of detection by the peripheral dot detecting unit and the result of detection by the space dot detecting unit. Therefore, it is possible to achieve optimal dot reproduction based on the surrounding situation around the target dot and improve reproducibility of a highlight.  
       [0008] In the image formation device according to the present invention, the data amount control unit adds an arbitrary amount of additional data to the data corresponding to the target dot.  
       [0009] According to the image formation device, the arbitrary amount of additional data is added to the data corresponding to the target dot. Therefore, it is possible to achieve further optimal dot reproduction because the additional data can be varied.  
       [0010] In the image formation device according to the present invention, the peripheral dot detecting unit detects whether there is a peripheral dot located at a minimal distance from the target dot.  
       [0011] According to the image formation device, the presence or absence of a peripheral dot located at the minimal distance from the target dot is detected and the data corresponding to the target dot is increased based on the detected result. Therefore, it is possible to achieve optimal dot reproduction based on the surrounding situation around the target dot and improve reproducibility of a highlight.  
       [0012] The image formation device according to the present invention further comprises a phase control unit that shifts a phase of the target dot based on an empty state of the peripheral dot in the main scanning direction and an empty state of the peripheral dot in the subscanning direction.  
       [0013] According to the image formation device, the phase of the target dot is shifted based on empty states of the peripheral dots in the main and subscanning directions. Therefore, it is possible to achieve optimal dot reproduction in consideration of the empty states of the peripheral dots.  
       [0014] The image formation device according to the present invention further comprises a both-adjacent-dots detecting unit that detects whether there are dots adjacent to both sides of the target dot at least in the main scanning direction; and a phase control unit that, if either of the dots is determined a space dot based on a result of detection by the both-adjacent-dots detecting unit, shifts a phase of the target dot to the opposite side to the space dot when the target dot is formed on the recording medium.  
       [0015] According to the image formation device, the phase of the target dot is shifted to the opposite side to the space dot. Therefore, it is possible to achieve further optimal dot reproduction because the target dot can be emphasized while remaining the space dot.  
       [0016] The image formation device according to the present invention for forming a dot image on a recording medium based on image data, comprises: a number-of-areas detecting unit that detects a number of detection areas each in which presence of at least one peripheral dot is detected, among a plurality of detection areas around a target dot in the dot image, each of the plurality of detection areas containing a plurality of peripheral dots; and a converting unit that subjects the target dot to level conversion based on a result of detection by the number-of-areas detecting unit.  
       [0017] According to the image formation device, the target dot is subjected to level conversion based on the result of detection by the number-of-areas detecting unit. Therefore, it is possible to achieve optimal dot reproduction even for a high-resolution dot based on the surrounding situation around the target dot.  
       [0018] In the image formation device according to the present invention, one of the detection areas is an area spreading in a main scanning direction and a subscanning direction.  
       [0019] According to the image formation device, the detection area is spread in the main and subscanning directions. Therefore, it is possible to allow influence of the surrounding (wide range) over the target dot to be reflected to the data conversion of the target dot.  
       [0020] In the image formation device according to the present invention, the detection areas are distributed among areas each spreading in the main and subscanning directions.  
       [0021] According to the image formation device, the detection areas are distributed among areas each spreading in the main and subscanning directions. Therefore, it is possible to allow a degree of the influence of the peripheral dot over the target dot to be reflected to the data conversion of the target dot.  
       [0022] The image formation device according to the present invention further comprises a storage unit that stores a conversion table indicating a correlation between the result of detection and degrees of the level conversion. The converting unit switches between the degrees of the level conversion based on the result of detection by referring to the conversion table.  
       [0023] According to the image formation device, the conversion table is employed to switch the degree of the level conversion based on the detected result. Therefore, it is possible to perform optimal data conversion automatically.  
       [0024] The image formation device according to the present invention for forming a dot image on a recording medium based on image data, comprises: a detecting unit that detects whether there is a set of peripheral dots in detection areas around a target dot in the dot image, each of the detection areas containing a plurality of peripheral dots as a set; and a converting unit that subjects the target dot to level conversion based on a result of detection by the detecting unit.  
       [0025] According to the image formation device, the target dot is subjected to level conversion based on the result of detection by the detecting unit. Therefore, it is possible to achieve optimal dot reproduction even for a high-resolution dot based on the surrounding situation around the target dot.  
       [0026] In the image formation device according to the present invention, the set of peripheral dots has the same resolution in main and subscanning directions.  
       [0027] According to the image formation device, the set of peripheral dots are designed to have the same resolution in the main and subscanning directions. Therefore, it is possible to achieve optimal dot reproduction in the main and subscanning directions based on the surrounding situation around the target dot.  
       [0028] In the image formation device according to the present invention, the target dot includes a plurality of dots as a set and has the same resolution in main and subscanning directions.  
       [0029] According to the image formation device, the target dot is designed to have the same resolution in the main and subscanning directions. Therefore, it is possible to achieve optimal dot reproduction in the main and subscanning directions based on the surrounding situation around the target dot.  
       [0030] The image formation device according to the present invention for forming a dot image on a recording medium based on image data, comprises: a detecting unit that detects each state of peripheral dots in an adjacent area adjacent to a target dot and in a plurality of areas adjacent to the adjacent area in the dot image; and a converting unit that subjects the target dot to level conversion based on a result of detection by the detecting unit.  
       [0031] According to the image formation device, the target dot is subjected to level conversion based on the state of the peripheral dots in the adjacent area and the plural areas with respect to the target dot. Therefore, it is possible to achieve optimal dot reproduction even for a high-resolution dot based on the surrounding situation.  
       [0032] In the image formation device according to the present invention, the detecting unit detects a level state of the peripheral dot in the adjacent area, and the converting unit selects one of level conversion tables for level conversion based on the level state.  
       [0033] According to the image formation device, one of the level conversion tables is selected based on the level state of the peripheral dot in the adjacent area. Therefore, it is possible to achieve optimal dot reproduction corresponding to a halftone processing.  
       [0034] In the image formation device according to the present invention, the detecting unit detects a number of peripheral dots that are present in the adjacent area, and the converting unit executes separately at least a level conversion for the number that is zero from a level conversion for the number that is any other than zero.  
       [0035] According to the image formation device, the level conversion when the number of peripheral dots that are present is zero is executed separately from the level conversion for the number other than zero. Therefore, it is possible to reduce a memory area required for management as compared to that for integrally managing both cases.  
       [0036] In the image formation device according to the present invention, the converting unit generates an arbitrary dot based on a result of detection by the detecting unit even if the target dot has a level of zero.  
       [0037] According to the image formation device, an arbitrary dot is generated based on the result of detection by the detecting unit even if the target dot has a level of zero. Therefore, it is possible to improve dropout of a single dot and failure of reproducibility.  
       [0038] In the image formation device according to the present invention, there is a case where the dot image is to be written into the medium with multiple beams. The image formation device further comprises a layout unit that lays out positions of the target dot in a subscanning direction corresponding to the respective multiple beams on positions corresponding to an integral multiple of a number of the multiple beams.  
       [0039] According to the image formation device, when the dot image is to be written into the medium with multiple beams, positions of the target dot in the subscanning direction corresponding to the respective multiple beams are laid out on positions corresponding to the integral multiple of the number of the multiple beams. Therefore, it is possible to minimize the use of line buffers because the target dot can be converted per plural lines. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0040]FIG. 1 shows a mechanical structure of a color image formation device according to a first embodiment of the present invention;  
     [0041]FIG. 2 is a partially enlarged view of the color image formation device shown in FIG. 1;  
     [0042]FIG. 3 is a block diagram that shows the configuration of a processing section applied to the color image formation device shown in FIG. 1;  
     [0043]FIG. 4 shows diagrams of operation of the first embodiment;  
     [0044]FIG. 5 is a block diagram that shows the configuration of a processing section applied to a color image formation device according to a second embodiment of the present invention;  
     [0045]FIG. 6 shows diagrams of operation of the second embodiment;  
     [0046]FIG. 7 is a block diagram that shows a configuration of a processing section applied to a color image formation device according to a third embodiment of the present invention;  
     [0047]FIG. 8 shows a conversion table T 1  and an associated graph G 1  applied to the color image formation device according to the third embodiment;  
     [0048]FIG. 9 shows diagrams of operation of the third embodiment;  
     [0049]FIG. 10 shows diagrams of operation of the third embodiment;  
     [0050]FIG. 11 is a block diagram that shows a configuration of a processing section applied to a color image formation device according to a fourth embodiment of the present invention;  
     [0051]FIG. 12 shows a conversion table T 2  and an associated graph G 2  applied to the color image formation device according to the fourth embodiment;  
     [0052]FIG. 13 is a block diagram that shows a configuration of a printer controller  1010  applied to a color image formation device according to a fifth embodiment of the present invention;  
     [0053]FIG. 14 is a block diagram that shows a configuration of a processing section applied to the color image formation device according to the fifth embodiment;  
     [0054]FIG. 15 shows diagrams of operation of the fifth embodiment;  
     [0055]FIG. 16 is a schematic diagram that shows a positional relation in the subscanning direction between an EVEN processing section  1070  and an ODD processing section  1080  shown in FIG. 14;  
     [0056]FIG. 17 shows a conversion table TT 1  and an associated graph GG 1  applied to the color image formation device according to the fifth embodiment;  
     [0057]FIG. 18 shows a conversion table TT 2  and an associated graph GG 2  applied to the color image formation device according to the fifth embodiment;  
     [0058]FIG. 19 shows a conversion table TT 3  and an associated graph GG 3  applied to the color image formation device according to the fifth embodiment;  
     [0059]FIG. 20 is a flowchart that explains operation of the fifth embodiment;  
     [0060]FIG. 21 shows a first dither threshold matrix for thin lines  1300 , a second dither threshold matrix for thin lines  1310 , and a third dither threshold matrix for thin lines  1320  applied to the color image formation device according to the fifth embodiment;  
     [0061]FIG. 22 shows a first dither threshold matrix for images  1400 , a second dither threshold matrix for images  1410 , and a third dither threshold matrix for images  1420  applied to the color image formation device according to the fifth embodiment;  
     [0062]FIG. 23 is a block diagram that shows an embodiment of the image formation device according to the present invention;  
     [0063]FIG. 24 is an explanatory view that shows a bit conversion table shown in FIG. 23;  
     [0064]FIG. 25 is an explanatory view that details the bit conversion table shown in FIG. 24;  
     [0065]FIG. 26 is an explanatory view that shows a conversion characteristic of the bit conversion table shown in FIG. 24 and FIG. 25;  
     [0066]FIG. 27 is an explanatory view that shows a correction table shown in FIG. 24;  
     [0067]FIG. 28 is a block diagram that shows an embodiment of the image formation device according to the present invention;  
     [0068]FIG. 29 is a block diagram that shows a system configuration of the image formation device according to the present invention;  
     [0069]FIG. 30 is a block diagram that shows a schematic configuration of a printer controller shown in FIG. 29;  
     [0070]FIG. 31 is a flowchart that shows a processing procedure for the printer controller shown in FIG. 30;  
     [0071]FIG. 32 shows dither tables that indicate dither thresholds for pseudo halftone processing for thin lines and dither thresholds for images;  
     [0072]FIG. 33 is a block diagram that shows a schematic configuration of the major part of a printer engine shown in FIG. 29; and  
     [0073]FIG. 34 is an explanatory view that shows the contents stored in the correction table. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION  
     [0074] The image formation device of the present invention, applied to a color image formation device, will be explained below with reference to the drawings.  
     [0075] First Embodiment:  
     [0076]FIG. 1 shows a mechanical structure of a color image formation device according to a first embodiment of the present invention. In this figure, the reference numeral  1  denotes a flexible belt-like photoreceptor as an image carrier (recording medium). The belt-like photoreceptor  1  is suspended around rotating rollers  2  and  3  and is rotated clockwise when the rotating rollers  2  and  3  drive it. The reference numeral  4  denotes a charger as a charging unit, and  5  denotes a laser writing unit as an image exposing unit. The reference numerals  6  to  9  denote developing devices as developing units that contain different specific color toners therein.  
     [0077] The laser writing unit  5  is housed in a support cabinet having a slit-like aperture for exposure formed on the upper surface of the support cabinet to be incorporated in the device body. The laser writing unit  5  may include a light emission section and a convergent optical transmission medium integrally. The charger  4  and a cleaning unit  15  are arranged opposite to the rotating roller  2  of the two rotating rollers  2  and  3  that allow the belt-like photoreceptor  1  to be suspended around them.  
     [0078] The developing devices  6  to  9  contain toners of yellow, magenta, cyan, and black, respectively, for example. These devices include development sleeves that are close to or contact with the belt-like photoreceptor  1  at certain positions, and also have functions of developing a latent image on the belt-like photoreceptor  1  by a non-contact development method or a contact development method. The reference numeral  10  denotes an intermediate transfer belt as a transferred image carrier (recording medium). The intermediate transfer belt  10  is suspended around rotating rollers  11  and  12  and is rotated counterclockwise when a bias roller  13  is driven.  
     [0079] The belt-like photoreceptor  1  and the intermediate transfer belt  10  contact the rotating roller  3 . Thus, a first developed image on the belt-like photoreceptor  1  is transferred onto the intermediate transfer belt  10  by the bias roller  13  disposed inside the intermediate transfer belt  10 . By repeating similar processes, second, third, and fourth developed images are superimposed on one another on the intermediate transfer belt  10  so that the images are transferred without any positional deviation.  
     [0080] A transfer roller  14  is disposed so as to come in contact with and separate from the intermediate transfer belt  10 . The reference numeral  15  denotes a cleaner for the belt-like photoreceptor  1 , and  16  denotes a cleaner for the intermediate transfer belt  10 . The cleaning unit  16  has a blade  16 A, kept at a position separated from the surface of the intermediate transfer belt  10  during image formation, and at a position press-contacted with the surface of the intermediate transfer belt  10  as shown only during cleaning after the image formation.  
     [0081] The image formation device operates, for example, in the following process for color image formation. A multi-colored image formation according to the first embodiment is achieved in accordance with the following image formation system. An image reader, not shown, includes a color image data input section (scanner) that can obtain data when an image pickup device scans an original draft. The data is operationally processed in an image data processor to create image data (multivalue bitmap data), which is stored once in an image memory.  
     [0082] The image data stored in the image memory is then read out for image formation and fed to the color image formation device shown in FIG. 1. Image data (color signal) is output from the image reader different from the color image formation device (printer). When the output image data is input to the laser writing unit  5  through a γ-correcting section and a writing section for a printer controller and engine as explained later, the laser writing unit  5  operates in the following manner.  
     [0083] A not-shown semiconductor laser generates a laser beam modulated in response to image data. The laser beam is polarized and scanned by a polygon mirror  5 B that is rotated by a drive motor  5 A. After passing through an fθ lens  5 C, the laser beam is bent at a mirror  5 D, and then exposed onto the circumference of the belt-like photoreceptor  1  which has been erased by an erasing lamp  21  and charged uniformly by the charger  4  in advance, to form an electrostatic latent image thereon.  
     [0084] The image pattern to be exposed is one of image patterns having respective monochromatic colors obtained when a desired full-color image is decomposed into the colors of yellow, magenta, cyan, and black. Electrostatic latent images formed on the belt-like photoreceptor  1  are sequentially developed by the developing devices  6  to  9  of yellow, magenta, cyan, and black constituting a rotary developing unit to form monochromatic images (dot images), respectively. The monochromatic images are then transferred to and superimposed on each other on the intermediate transfer belt  10  that rotates counterclockwise while being in contact with the belt-like photoreceptor  1 .  
     [0085] The images of yellow, magenta, cyan, and black superimposed on the intermediate transfer belt  10  are transferred by the transfer roller  14  to a transfer paper conveyed from a paper feed tray  17  to a transfer portion through a paper feed roller  18  and regist rollers  19 . After completion of the transfer, the transfer paper is subjected to fixing by a fixing device  20  to finish a full-color image. The intermediate transfer belt  10  and the belt-like photoreceptor  1  are seamless.  
     [0086]FIG. 2 is an enlarged view that shows a part of the color image formation device shown in FIG. 1. The intermediate transfer belt  10  has the six marks  41 A to  41 F on the edge thereof. When a mark detecting sensor  40  senses an arbitrary mark (for example,  41 A), a first color writing is started, and when the mark detecting sensor  40  senses the mark  41 A again after one rotation, a second color writing is started.  
     [0087] At this point in time, the number of marks is managed so as to prevent the marks  41 B to  41 F from being used as write timings and also to mask the corresponding signals from the mark detecting sensor  40 . At a location slightly upstream from the contact portion of the belt-like photoreceptor  1  with the intermediate transfer belt  10 , a P sensor  22  as an optical sensor is arranged for detecting an amount of toner (image density) on the belt-like photoreceptor  1 . The P sensor  22  may be disposed at a location suitable for detecting the image density on the intermediate transfer belt  10 .  
     [0088]FIG. 3 is a block diagram that shows a configuration of the processing section applied to the color image formation device shown in FIG. 1. In FIG. 3, image data D is such data that has a weight of four bits and is subjected to multilevel dither processing. A 1-line buffer L 0  is a buffer that temporarily holds the image data D for one line. A 1-line buffer L 1  is a buffer that temporarily holds the image data D delayed by one line from the 1-line buffer L 0 .  
     [0089] A 4-bit/1-bit converter  100  is interposed between the 1-line buffer L 1  and a 1-line buffer L 2  to convert the 4-bit weighed image data D held in the 1-line buffer L 1  into data with a weight of one bit. Specifically, if all bits in the 4-bit weighed image data D are “0”, the 4-bit/1-bit converter  100  converts the image data D into 1-bit data of “0”. If any one of bits in the image data D is “1”, it converts the image data D into 1-bit data of “1”. In other words, the data from the 4-bit/1-bit converter  100  is data that indicates the presence or absence of written image data.  
     [0090] The 1-line buffer L 2  is a buffer that temporarily holds the 1-bit weighed image data converted by the 4-bit/1-bit converter  100 . A 1-line buffer L 3  is a buffer that temporarily holds the image data held in the 1-line buffer L 2 . Latch circuitries D 04  to D 44  are arranged corresponding to the 1-line buffers L 3  to L 0  and the input line to latch the output data of the 1-line buffers L 3  to L 0  and the image data D on the input line in synchronization with a synchronizing signal.  
     [0091] Latch circuitries D 00  to D 40  are arranged corresponding to the latch circuitries D 04  to D 44  to latch the output data of the latch circuitries D 04  to D 44  in synchronization with the synchronizing signal, respectively. Latch circuitries D 01 , D 11 , a target dot latch circuitry x, and latch circuitries D 31  and D 41  are arranged corresponding to the latch circuitries D 00  to D 40  to latch the output data of the latch circuitries D 00  to D 40  in synchronization with the synchronizing signal, respectively.  
     [0092] The target dot latch circuitry x holds image data associated with a target dot. Latch circuitries D 02  to D 42  are arranged corresponding to the latch circuitries D 01 , D 11 , the target dot latch circuitry x, and the latch circuitries D 31  and D 41  to latch the output data of the latch circuitries D 01 , D 11 , the target dot latch circuitry x, and the latch circuitries D 31  and D 41  in synchronization with the synchronizing signal, respectively. Latch circuitries D 03  to D 43  are arranged corresponding to the latch circuitries D 02  to D 42  to latch the output data of the latch circuitries D 02  to D 42 .  
     [0093] A determination section  200  determines a situation of the surrounding around the target dot (such as the presence or absence of a dot) by referring to the image data in each of the latch circuitries (a dot on the surrounding around the target dot in the main scanning direction and the subscanning direction). The determination section  200  outputs the determined result as an additional-on/off signal b, or an emphasis signal c. The additional-on/off signal b is a signal for instructing an adder  400 , explained later, to or not to add an additional value m (an arbitrary value), to target dot image data d from the target dot latch circuitry x. If the value is added, then the additional-on/off signal b becomes “1”, and if not, the additional-on/off signal b becomes “0”.  
     [0094] Further, the determination section  200  determines the presence or absence of and the number of all output data from the latch circuitries D 40 , D 30 , D 20 , D 10 , D 00 , D 43 , D 33 , D 23 , D 13 , D 03 , D 00 , D 01 , D 02 , D 40 , D 41 , and D 42 , and outputs the emphasis signal c of “1” if all the output data are “0”. In cases other than this case, the determination section  200  outputs the emphasis signal c of “0”. An adder  400  adds the additional value m (an arbitrary value) stored in a storage  300  to the target dot image data d of the target dot latch circuitry x under the following condition. Detailed operation of the adder  400  will be explained later.  
     [0095] Operation of the first embodiment is explained next. The multilevel dither-processed 4-bit image data D shown in FIG. 3 is sequentially latched line by line in the latch circuitry D 44  in synchronization with the synchronizing signal and also sequentially held in the 1-line buffer L 0 . At the next synchronized timing, the output data of the 1-line buffer L 0  is latched in the latch circuitry D 34  and is also held in the 1-line buffer L 1 .  
     [0096] At the next synchronized timing, the output data of the 1-line buffer L 1  is latched in the latch circuitry D 24 , and also converted from 4 bits into 1 bit at the 4-bit/1-bit converter  100 , then held in the 1-line buffer L 2  as 1-bit data. If the dot corresponding to the output data from the 1-line buffer L 1  is a space dot, the data from the 4-bit/1-bit converter  100  is “0”. In contrast, if the dot corresponding to the output data from the 1-line buffer L 1  is not a space dot, then the data from the 4-bit/1-bit converter  100  is “1”.  
     [0097] At the next synchronized timing, the output data of the 1-line buffer L 2  is latched in the latch circuitry D 14  and is also held in the 1-line buffer L 3 . At the next synchronized timing, the output data of the 1-line buffer L 3  is latched in the latch circuitry D 04 . Thereafter, in synchronization with the synchronizing signal, the data latched in the latch circuitries D 04  to D 44  are sequentially shifted from the latch circuitries D 00  to D 40 , through the latch circuitries D 01 , D 11 , the target dot latch circuitry x, and the latch circuitries D 31  and D 41 , and through the latch circuitries D 02  to D 42 , to the latch circuitries D 03  to D 43 , respectively.  
     [0098] In the series of shift operations, respective pieces of the output data from the latch circuitries D 04  to D 44 , D 00  to D 40 , D 01 , D 11 , D 31 , D 41 , D 02  to D 42 , and D 03  to D 43  are fed to the determination section  200 . The output data from the target dot latch circuitry x is fed to the adder  400 .  
     [0099] The determination section  200  outputs the additional-on/off signal b of “1” if the target dot image data d in the target dot latch circuitry x is “0” and also satisfies the following &lt;Condition 1&gt; or &lt;Condition 2&gt;.  
     [0100] &lt;Condition 1&gt; 
     [0101] The output data of the latch circuitry D 22  is not “0”.  
     [0102] All pieces of the output data of the latch circuitries D 10  to D 13 , D 30  to D 33 , D 20  and D 23  surrounding around the target dot latch circuitry x are “0”.  
     [0103] &lt;Condition 2&gt; 
     [0104] &lt;Condition 1&gt; is not satisfied.  
     [0105] The latch circuitry D 11  is not “0”.  
     [0106] All pieces of the output data from the latch circuitries D 00  to D 02 , D 10 , D 12 , D 20 , D 22 , and D 30  to D 32  surrounding around the target dot latch circuitry x are “0”.  
     [0107] The &lt;Condition 1&gt; and &lt;Condition 2&gt; can be satisfied if the target dot is a dot that is solely present at least in the main scanning direction and the subscanning direction. If the &lt;Condition 1&gt; or &lt;Condition 2&gt; is satisfied, the determination section  200  outputs the additional-on/off signal b of “1” to the adder  400 . The determination section  200  also outputs a phase signal S 2  of “0” to a writing section (not shown). Thus, the adder  400  adds the additional value m (“32” in this case) stored in the storage  300  to the target dot image data d latched in the target dot latch circuitry x. As a result, the density of the target dot image data d is corrected by the additional value m (=“32”). The density-corrected target dot is written into a recording medium.  
     [0108] If the phase signal S 2  is “0”, as shown in FIG. 4( a ) (Mode “0”, Right mode), the dot width of the target dot grows from the center to the left, and two dots are linked with each other at the center. Therefore, the target dot is dot-emphasized with natural touch.  
     [0109] If the &lt;Condition 1&gt; and &lt;Condition 2&gt; are not be satisfied, the additional-on/off signal b is determined “0” and the phase signal S 2  is determined “1” so that the density correction with the additional value m is not executed. In this case, the determination section  200  outputs the target dot image data d to the writing section (not shown) as 8-bit write data S 1  without correcting the density of the target dot image data d from the target dot latch circuitry x. Thus, the density-uncorrected target dot is written into a recording medium.  
     [0110] If the phase signal S 2  is “1”, as shown in FIG. 4( b ) (Mode “1”, Left mode), the dot width of the target dot grows from the center to the right, and two dots are linked with each other at the center. Therefore, the target dot is dot-emphasized with natural touch. If the &lt;Condition 1&gt; is satisfied, a dot is formed as shown in FIG. 4( c ). In this formation, the additional value m is added to the target dot image data d corresponding to a single dot (target dot).  
     [0111] If all pieces of the output data from the latch circuitries D 40 , D 30 , D 20 , D 10 , D 00 , D 43 , D 33 , D 23 , D 13 , D 03 , D 00 , D 01 , D 02 , D 40 , D 41 , D 42  are “0”, or if a space dot is present at either of dots adjacent to both sides of the target dot at least in the main scanning direction, the determination section  200  outputs the emphasis signal c of “1” to the adder  400 . The determination section  200  also outputs the phase signal S 2  of “0” to the writing section (not shown). Thus, as shown in FIG. 4( d ), the phase of dot formation is shifted in the opposite direction to the side of the space dot adjacent to the target dot. Therefore, it is possible to optimize dot reproduction based on the situation of the surrounding around the target dot.  
     [0112] If the data is output from the target dot latch circuitry x (the presence of a dot), and if the data is output from the latch circuitries D 20  and D 22  adjacent to the target dot latch circuitry x (the presence of dots), or if the data is output from the latch circuitry D 22  (the presence of a dot), the dot or dots are written in the left mode. If the data is output from the latch circuitry D 20  (the presence of a dot), the dot is written in the right mode. Thus, two dots are linked with each other to form dots with natural touch.  
     [0113] Second Embodiment:  
     [0114] The processing section shown in FIG. 3 and exemplified in the first embodiment may be replaced with a processing section configured as shown in FIG. 5. This case is explained below as a second embodiment. In FIG. 5, the same parts as those in FIG. 3 are denoted with the same reference numerals. The latch circuitries D 04  to D 44 , D 40  to D 43  and the 1-line buffer Lo shown in FIG. 3 are omitted from the configuration in FIG. 5. The configuration of FIG. 5 is such that the output data from the 1-line buffers L 3  to L 1  and image data D are latched in the latch circuitries D 00  to D 30  of FIG. 5. In addition, the output data of the target dot latch circuitry x is fed to both the determination section  200  and the adder  400 .  
     [0115] Operation of the second embodiment is explained next. The multilevel dither-processed 4-bit image data D shown in FIG. 5 is sequentially latched line by line in the latch circuitry D 30  and is also sequentially held in the 1-line buffer L 1  in synchronization with the synchronizing signal. At the next synchronized timing, the output data of the 1-line buffer L 1  is latched in the latch circuitry D 20  and also converted from 4 bits into 1 bit at the 4-bit/1-bit converter  100 , and then the converted image data is held in the 1-line buffer L 2  as 1-bit data.  
     [0116] At the next synchronized timing, the output data from the 1-line buffer L 2  is latched in the latch circuitry D 10  and is also held in the 1-line buffer L 3 . If the dot corresponding to the output data from the 1-line buffer L 1  is a space dot, the data from the 4-bit/1-bit converter  100  is “0” like in the first embodiment. In contrast, if the dot corresponding to the output data from the 1-line buffer L 1  is not a space dot, the data from the 4-bit/1-bit converter  100  is “1”.  
     [0117] At the next synchronized timing, the output data from the 1-line buffer L 3  is latched in the latch circuitry D 00 . Thereafter, like in the first embodiment, in synchronization with the synchronizing signal, the pieces of data respectively latched in the latch circuitries D 00  to D 30  are sequentially shifted from the latch circuitries D 01 , D 11 , the target dot latch circuitry x and the latch circuitry D 31 , through the latch circuitries D 02  to D 32 , to the latch circuitries D 03  to D 33 , respectively.  
     [0118] In the series of shift operations, the output data from the latch circuitries D 00  to D 30  and the latch circuitries D 01 , D 11 , D 31 , D 02  to D 32 , and D 03  to D 33  are fed to the determination section  200 , respectively. The output data from the target dot latch circuitry x is fed to the determination section  200  and the adder  400 .  
     [0119] The determination section  200  outputs the additional-on/off signal b of “1” if the output data from the target dot latch circuitry x is “0” and also satisfies the following &lt;Condition 3&gt; or &lt;Condition 4&gt;.  
     [0120] &lt;Condition 3&gt; 
     [0121] The output data from the latch circuitry D 22  is not “0”.  
     [0122] All pieces of the output data from the latch circuitries D 10  to D 13 , D 30  to D 33 , D 20 , and D 23  surrounding around the target dot latch circuitry x are “0”.  
     [0123] &lt;Condition 4&gt; 
     [0124] &lt;Condition 3&gt; is not satisfied.  
     [0125] The latch circuitry D 11  is not “0”.  
     [0126] All pieces of the output data from the latch circuitries D 00  to D 02 , D 10 , D 12 , D 20 , D 22 , and D 30  to  32  surrounding around the target dot latch circuitry x are “0”.  
     [0127] The &lt;Condition 3&gt; and &lt;Condition 4&gt; can be satisfied if the target dot is a dot solely present at least in the main scanning direction and the subscanning direction and if a dot located at the minimal distance from the target dot is space. If the &lt;Condition 3&gt; or &lt;Condition 4&gt; is satisfied, the determination section  200  outputs the additional-on/off signal b of “1” to the adder  400 .  
     [0128] The determination section  200  also outputs the phase signal S 2  of “0” to the writing section (not shown). Thus, the adder  400  adds the additional value m (“32” in this case) stored in the storage  300  to the target dot image data d latched in the target dot latch circuitry x. As a result, the density of the target dot image data d is corrected by the additional value m (=“32”). The density-corrected target dot is written into a recording medium.  
     [0129] If the phase signal S 2  is “0”, as shown in FIG. 6( a ) (Mode “0”, Right mode), the dot width of the target dot grows from the center to the left, and two dots are linked with each other at the center. Therefore, the target dot is dot-emphasized with natural touch.  
     [0130] If the &lt;Condition 3&gt; and &lt;Condition 4&gt; are not satisfied, the additional-on/off signal b is determined “0” and the phase signal S 2  is determined “1” so that the density correction with the additional value m is not executed. In this case, the determination section  200  outputs the target dot image data d from the target dot latch circuitry x to the writing section (not shown) as 8-bit write data S 1  without correcting the density of the target dot image data d. Thus, the density-uncorrected target dot is written into a recording medium.  
     [0131] If the phase signal S 2  is “1”, as shown in FIG. 6( b ) (Mode “1”, Left mode), the dot width of the target dot grows from the center to the right, and two dots are linked with each other at the center. Therefore, the target dot is dot-emphasized with natural touch. If the &lt;Condition 3&gt; is satisfied, a dot is formed as shown in FIG. 6( c ). In this formation, the additional value m is added to the target dot image data d corresponding to a single dot (target dot).  
     [0132] According to the first and second embodiments as explained above, based on the surrounding situation around the target dot, the target dot image data d corresponding to the target dot is increased. Therefore, it is possible to achieve optimal dot reproduction based on the surrounding situation around the target dot and improve reproducibility of a highlight.  
     [0133] Third Embodiment:  
     [0134] The processing section shown in FIG. 3 and exemplified in the first embodiment may be replaced with a processing section configured as shown in FIG. 7. This case is explained below as a third embodiment. In FIG. 7, image data DA has a weight of two bits and is dither-processed. A 1-line buffer Lo is a buffer that temporarily holds image data DA for one line. A 1-line buffer L 1  is a buffer that temporarily holds the image data DA delayed by one line from the 1-line buffer L 0 .  
     [0135] A 2-bit/1-bit converter  500  is interposed between the 1-line buffer L 1  and a 1-line buffer L 2  to convert the 2-bit weighed image data DA held in the 1-line buffer L 1  into data with a weight of one bit. Specifically, if all bits in the 2-bit weighed image data DA are “0”, the 2-bit/1-bit converter  500  converts the image data DA into 1-bit data of “0”. If any one of bits in the image data DA is “1”, it converts the image data DA into 1-bit data of “1”. In other words, the data from the 2-bit/1-bit converter  500  is data that indicates the presence or absence of written image data.  
     [0136] The 1-line buffer L 2  is a buffer that temporarily holds the 1-bit weighed image data converted by the 2-bit/1-bit converter  500 . A 1-line buffer L 3  is a buffer that temporarily holds the image data held in the 1-line buffer L 2 . Latch circuitries D 00 , D 03 , D 30 , D 32 , and D 34  are arranged corresponding to the 1-line buffers L 3  to L 0  and the input line to latch the output data from the 1-line buffers L 3  to L 0  and the image data DA on the input line in synchronization with a synchronizing signal.  
     [0137] The latch circuitries D 01 , D 04 , D 31 , D 33 , and D 35  are arranged corresponding to the latch circuitries D 00 , D 03 , D 30 , D 32 , and D 34  to latch the output data from the latch circuitries D 00 , D 03 , D 30 , D 32 , and D 34  in synchronization with the synchronizing signal, respectively. Latch circuitries D 02 , D 05 , a target dot latch circuitry x, and latch circuitries D 20  and D 23  are arranged corresponding to the latch circuitries D 00 , D 03 , D 30 , D 32 , and D 34  to latch the output data from the latch circuitries D 01 , D 04 , D 31 , D 33 , and D 35  in synchronization with the synchronizing signal, respectively.  
     [0138] The target dot latch circuitry x holds target dot image data DX 1  associated with a target dot. Latch circuitries D 10 , D 12 , D 14 , D 21 , and D 24  are arranged corresponding to the latch circuitries D 02 , D 05 , the target dot latch circuitry x, and the latch circuitries D 20  and D 23  to latch the output data from the latch circuitries D 02 , D 05 , the target dot latch circuitry x, and the latch circuitries D 20  and D 23  in synchronization with the synchronizing signal, respectively. Latch circuitries D 11 , D 13 , D 15 , D 22 , and D 25  are arranged corresponding to the latch circuitries D 10 , D 12 , D 14 , D 21 , and D 24  to latch the respective output data from the latch circuitries D 10 , D 12 , D 14 , D 21 , and D 24 .  
     [0139] Four areas in total referred to as multi-dot areas AR 0  to AR 3  are defined around the target dot corresponding to the target dot latch circuitry x. That is, there are 24 dots around the target dot, and the 24 dots are assigned to the four areas by six dots as a group. Specifically, six dots corresponding to the latch circuitries D 00  to D 05  are assigned to the multi-dot area AR 0 . Each of the multi-dot areas AR 0  to AR 3  is an area spread in the main and subscanning directions.  
     [0140] Six dots corresponding to the latch circuitries D 10  to D 15  are assigned to the multi-dot area AR 1 . Six dots corresponding to the latch circuitries D 20 ,to D 25  are assigned to the multi-dot area AR 2 . Finally, six dots corresponding to the latch circuitries D 30  to D 35  are assigned to the multi-dot area AR 3 .  
     [0141] A determination section  600  determines the surrounding situation around the target dot (such as the presence or absence of a dot) on an area-basis of the multi-dot area AR 0  to AR 3  by referring to the image data in each of the latch circuitries. The determination section  600  outputs the determined result as a conversion table code CD 1  (see FIG. 8( a )). Specifically, the determination section  600  determines if there is at least one image data of “1” (the presence of a dot) within six pieces of image data latched in the latch circuitries D 00  to D 05  within the multi-dot area AR 0 . Similarly, the determination section  600  determines if there is at least one image data of “1” (the presence of a dot) within six pieces of image data held in each of the multi-dot areas AR 1  to AR 3 , respectively.  
     [0142] The determination section  600  receives the determined results on the multi-dot areas AR 0  to AR 3  and determines the conversion table code CD 1  as shown in FIG. 8( a ). Specifically, if the number of multi-dot areas (the number of areas) each of which has at least one piece of image data of “1” (the presence of a dot) is “zero” among the multi-dot areas AR 0  to AR 3 , that is, there is no dot present in the surrounding of the target dot, the determination section  600  sets the conversion table code CD 1  to 0.  
     [0143] If the number of multi-dot areas (the number of areas) each of which has at least one piece of image data of “1” (the presence of a dot) is “one” among the multi-dot areas AR 1  to AR 3 , the determination section  600  sets the conversion table code CD 1  to 1. If the number of multi-dot areas (the number of areas) each of which has at least one piece of image data of “1” (the presence of a dot) is “two” among the multi-dot areas AR 0  to AR 3 , the determination section  600  sets the conversion table code CD 1  to 2.  
     [0144] If the number of multi-dot areas (the number of areas) each of which has at least one piece of image data of “1” (the presence of a dot) is “three” among the multi-dot areas AR 0  to AR 3 , the determination section  600  sets the conversion table code CD 1  to 3. Finally, if the number of multi-dot areas (the number of areas) each of which has at least one piece of image data of “1” (the presence of a dot) is “four” among the multi-dot areas AR 0  to AR 3 , that is, there are dots in the surrounding (the multi-dot areas AR 0  to AR 3 ) around the target dot, the determination section  600  sets the conversion table code CD 1  to 4. The determination section  600  also outputs a phase signal PH 1  later explained.  
     [0145] A storage  700  stores a conversion table T 1  shown in FIG. 8( a ). The conversion table T 1  is used to convert a level of the target dot image data DX 1  latched in the target dot latch circuitry x by a magnification corresponding to the conversion table code CD 1 . FIG. 8( b ) shows a graph G 1  obtained by graphing the conversion table T 1 . Referring back to FIG. 7, a converter  800  converts a level of the target dot image data DX 1  (2 bits) into target dot image data DX 1 ′ (3 bits) by referring to the conversion table code CD 1  and the conversion table T 1 .  
     [0146] Operation of the third embodiment is explained next. The dither-processed 2-bit image data DA shown in FIG. 7 is sequentially latched line by line in the latch circuitry D 34  and also sequentially held in the 1-line buffer L 0  in synchronization with the synchronizing signal. At the next synchronized timing, the output data from the 1-line buffer L 0  is latched in the latch circuitry D 32  and is also held in the 1-line buffer L 1 .  
     [0147] At the next synchronized timing, the output data from the 1-line buffer L 1  is latched in the latch circuitry D 30 , and is converted from 2 bits into 1 bit in the 2-bit/1-bit converter  500 , and then the converted data is held in the 1-line buffer L 2  as 1-bit data. At the next synchronized timing, the output data from the 1-line buffer L 2  is latched in the latch circuitry D 03  and is also held in the 1-line buffer L 3 . If the dot corresponding to the output data from the 1-line buffer L 1  is a space dot, the data from the 2-bit/1-bit converter  500  is “0”. In contrast, if the dot corresponding to the output data from the 1-line buffer L 1  is not a space dot, the data from the 2-bit/1-bit converter  500  is “1”.  
     [0148] At the next synchronized timing, the output data from the 1-line buffer L 3  is latched in the latch circuitry D 00 . Thereafter, in synchronization with the synchronizing signal, the each data latched in the latch circuitries D 00 , D 03 , D 30 , D 32 , and D 34  are sequentially shifted from the latch circuitries D 01 , D 04 , D 31 , D 33 , and D 35 , through the latch circuitries D 02 , D 05 , the target dot latch circuitry x, and the latch circuitries D 20  and D 23 , and through the latch circuitries D 10 , D 12 , D 14 , D 21 , and D 24 , to the latch circuitries D 11 , D 13 , D 15 , D 22 , and D 25 , respectively.  
     [0149] In the series of shift operations, the output data from the latch circuitries D 00 , D 03 , D 30 , D 32 , and D 34 , the latch circuitries D 01 , D 04 , D 31 , D 33 , and D 35 , the latch circuitries D 02  and D 05 , the latch circuitries D 20  and D 23 , the latch circuitries D 10 , D 12 , D 14 , D 21 , and D 24 , and the latch circuitries D 11 , D 13 , D 15 , D 22 , and D 25  are fed to the determination section  600 , respectively. The output data from the target dot latch circuitry x is fed to the converter  800 .  
     [0150] The determination section  600  determines the surrounding situation around the target dot (such as the presence or absence of a dot) on an area-basis of the multi-dot area AR 0  to AR 3  by referring to the image data in each of the latch circuitries other than the target dot latch circuitry x. The determination section  600  receives the determined results on the multi-dot areas AR 0  to AR 3  and determines the conversion table code CD 1  as shown in FIG. 8( a ). If the number of multi-dot areas (the number of areas) each of which has at least one piece of image data of “1” (the presence of a dot) is “zero” among the multi-dot areas AR 0  to AR 3 , that is, there is no dot in the surrounding around the target dot, the determination section  600  sets the conversion table code CD 1  to 0.  
     [0151] If the number of multi-dot areas (the number of areas) each of which has at least one piece of image data of “1” (the presence of a dot) is “one” among the multi-dot areas AR 0  to AR 3 , the determination section  600  sets the conversion table code CD 1  to 1. Similarly, if the number of multi-dot areas (the number of areas) each of which has at least one piece of image data of “1” (the presence of a dot) is “four” among the multi-dot areas AR 0  to AR 3 , the determination section  600  sets the conversion table code CD 1  to 4. In this case, it is assumed that the conversion table code CD 1  is set to 0.  
     [0152] When the converter  800  receives the conversion table code CD 1  (=0), the converter  800  reads out the conversion table T 1  shown in FIG. 8( a ) from the storage  700  to identify a part corresponding to the conversion table code CD 1 =0. In this case, the target dot image data DX 1  (2 bits) is level-converted (density-corrected) into the target dot image data DX 1 ′ (3 bits) as follows: 
     Target dot image data DX 1 =0→Target dot image data DX 1 ′=0 
     Target dot image data DX 1 =1→Target dot image data DX 1 ′=4 
     Target dot image data DX 1 =2→Target dot image data DX 1 ′=6 
     Target dot image data DX 1 =3→Target dot image data DX 1 ′=7 
     [0153] The density-corrected target dot image data DX 1 ′ is written into a recording medium. If the image data latched in the latch circuitry D 14  shown in FIG. 7 is “0”, the determination section  600  outputs a phase signal PH 1  of “0”. If the phase signal PH 1  is “0”, as shown in FIG. 9( a ) (Mode “0”, Right mode), the dot width of the target dot grows from the center to the left. if the phase signal PH 1  is “1”, as shown in FIGS.  9 ( a ),  10 ( a ) and  10 ( b ) (Mode “1”, Left mode), two dots are linked with each other at the center. Therefore, the target dot is formed with natural touch.  
     [0154] As shown in FIGS.  8 ( a ) and  8 ( b ), if the conversion table code CD 1 =0 in the third embodiment, there is no dot around the target dot. Therefore, the level of the target dot image data DX 1  is converted to a level slightly higher than a level that is supposed to be. If the conversion table code CD 1 =1, 2, or 3, the target dot image data DX 1  is level-converted linearly.  
     [0155] If the conversion table code CD 1 =4, there definitely exist dots around the target dot. Therefore, the level of the target dot image data DX 1  is converted to a level slightly lower than a level that is supposed to be. The conversion table code CD 1 =0 to 3 is referred to in a centralized dither processing. The conversion table code CD 1 =4 is referred to in a distributed dither processing. Therefore, in the third embodiment, it is possible to perform level conversion for writing to a recording medium optimally based on a dither type.  
     [0156] According to the third embodiment as explained above, based on the determined result by the determination section  600 , the converter  800  level-converts the target dot. Therefore, it is possible to achieve optimal dot reproduction even for a high-resolution dot based on the surrounding situation around the target dot.  
     [0157] Fourth Embodiment:  
     [0158] The processing section shown in FIG. 3 and exemplified in the first embodiment may be replaced with a processing section configured as shown in FIG. 11. This case is explained below as a fourth embodiment. In FIG. 11, image data DA has a weight of two bits and is dither-processed. The image data DA has resolutions of, for example, 1200 dpi in the main scanning direction and 600 dpi in the subscanning direction.  
     [0159] A serial/parallel converter  900  subjects the 2-bit image data DA to serial-parallel conversion to obtain 2-dot image data DA′. The image data DA′ is associated with a set of 2 dots. The serial/parallel converter  900  converts the image data DA with 1200 dpi in the main scanning direction and 600 dpi in the subscanning direction into the image data DA′ with 600 dpi in the main scanning direction and 600 dpi in the subscanning direction. A 1-line buffer L 0  is a buffer that temporarily holds image data DA′ for one line. A 1-line buffer L 1  is a buffer that temporarily holds the image data DA′ delayed by one line from the 1-line buffer L 0 .  
     [0160] Latch circuitries D 00  to D 02  are arranged corresponding to the serial/parallel converter  900  and to the 1-line buffers L 0  and L 1  to latch the output data from the serial/parallel converter  900  and the 1-line buffers L 0  and L 1  in synchronization with the synchronizing signal, respectively. A latch circuitry D 10 , a target dot latch circuitry x, and a latch circuitry D 12  are arranged corresponding to the latch circuitries D 00  to D 02  to latch the output data from the latch circuitries D 00  to D 02  in synchronization with the synchronizing signal, respectively. The target dot latch circuitry x holds target dot image data DX 2  associated with a target dot.  
     [0161] There are 8 sets of dots in total, each set consisting of 2 dots, around the target dot corresponding to the target dot latch circuitry x. The serial/parallel converter  900  allows these dots and the target dot to have the same resolution in the main and subscanning directions. Latch circuitries D 20 , D 21 , and D 22  are arranged corresponding to the latch circuitry D 10 , the target dot latch circuitry x, and the latch circuitry D 12  to latch the output data from the latch circuitry D 10 , the target dot latch circuitry x, and the latch circuitry D 12 .  
     [0162] A determination section  1000  determines the surrounding situation around the target dot (such as the presence or absence of a dot) by referring to the image data in each of the latch circuitries, and outputs the determined result as a conversion table code CD 2  (see FIG. 12( a )). Specifically, the determination section  1000  determines the number of image data of “1” (the presence of a dot) (the number of “1” data) among six pieces of image data latched in the latch circuitries D 00  to D 02 , D 10 , D 12 , and D 20  to D 22 . The determination section  1000  then outputs the conversion table code CD 2  corresponding to the number of “1” data.  
     [0163] A storage  1100  stores a conversion table T 2  shown in FIG. 12( a ). The conversion table T 2  is used to convert a level of the target dot image data DX 2  latched in the target dot latch circuitry x by a magnification corresponding to the conversion table code CD 2 . FIG. 12( b ) shows a graph G 2  obtained by graphing the conversion table T 2 . Referring back to FIG. 11, a converter  1200  converts a level of the target dot image data DX 2  (2 bits) into target dot image data DX 2  (3 bits) by referring to the conversion table code CD 2  and the conversion table T 2 .  
     [0164] Operation of the fourth embodiment is explained next. The dither-processed 2-bit image data DA shown in FIG. 11 is converted into the image data DA′ in the serial/parallel converter  900 . Thus, dots corresponding to the image data DA′ have the same resolution (600 dpi) in the main and subscanning directions. The image data DA′ is sequentially latched line by line in the latch circuitry D 00  and is also sequentially held in the 1-line buffer L 0  in synchronization with the synchronizing signal. At the next synchronized timing, the output data from the 1-line buffer L 0  is latched in the latch circuitry D 01  and is also held in the 1-line buffer L 1 .  
     [0165] At the next synchronized timing, the output data from the 1-line buffer L 1  is latched in the latch circuitry D 02 . Thereafter, in synchronization with the synchronizing signal, the data latched in the latch circuitries D 00  to D 02  are sequentially shifted, through the latch circuitry D 10 , the target dot latch circuitry x, and the latch circuitry D 12 , to the latch circuitries D 20  to D 22 , respectively.  
     [0166] In the series of shift operations, the output data from the latch circuitries D 00  to D 02 , the latch circuitry D 10 , the latch circuitry D 12  and the latch circuitries D 20  to D 22  are fed to the determination section  1000 , respectively. The output data from the target dot latch circuitry x is fed to the converter  1200 .  
     [0167] The determination section  1000  determines the surrounding situation around the target dot (such as the presence or absence of a dot) by referring to the image data in each of the latch circuitries other than the target dot latch circuitry x. The determination section  1000  receives the determined results and determines the conversion table code CD 2  as shown in FIG. 12( a ). If the number of latch circuitries holding image data of “1” (the presence of a dot) is zero among the latch circuitries D 00  to D 02 , the latch circuitry D 10 , the latch circuitry D 12 , and the latch circuitries D 20  to D 22 , that is, there is no dot in the surrounding around the target dot, the determination section  1000  sets the conversion table code CD 2  to 0.  
     [0168] If the number of latch circuitries holding image data of “1” (the presence of a dot) is one among the latch circuitries D 00  to D 02 , the latch circuitry D 10 , the latch circuitry D 12 , and the latch circuitries D 20  to D 22 , the determination section  1000  sets the conversion table code CD 2  to 1. If the number of latch circuitries holding image data of “1” (the presence of a dot) is two among the latch circuitries D 00  to D 02 , the latch circuitry D 10 , the latch circuitry D 12 , and the latch circuitries D 20  to D 22 , the determination section  1000  sets the conversion table code CD 2  to 2.  
     [0169] Similarly, if the number of latch circuitries holding image data of “1” (the presence of a dot) is eight among the latch circuitries D 00  to D 02 , the latch circuitry D 10 , the latch circuitry D 12 , and the latch circuitries D 20  to D 22 , the determination section  1000  sets the conversion table code CD 2  to 8. In this case, the conversion table code CD 2  is set to 0.  
     [0170] When the converter  1200  receives the conversion table code CD 2  (=0), the converter  1200  reads out the conversion table T 2  shown in FIG. 12( a ) from the storage  1100  to identify the part corresponding to the conversion table code CD 2 =0. In this case, the target dot image data DX 2  (2 bits) is level-converted (density-corrected) into target dot image data DX 2 ′ (3 bits) as follows: 
     Target dot image data DX 2 =0→Target dot image data DX 2 ′=0 
     Target dot image data DX 2 =1→Target dot image data DX 2 ′=4 
     Target dot image data DX 2 =2→Target dot image data DX 2 ′=5 
     Target dot image data DX 2 =3→Target dot image data DX 2 ′=7 
     [0171] The density-corrected target dot image data DX 2 ′ is written into a recording medium. In the fourth embodiment, as shown in FIGS.  12 ( a ) and  12 ( b ), the case of the conversion table code CD 2 =0 indicates that there is no dot around the target dot. Therefore, the level of the target dot image data DX 2  is converted to a level slightly higher than a level that is supposed to be. If the conversion table code CD 2 =1 to 7, the target dot image data DX 2  is level-converted linearly.  
     [0172] The case of the conversion table code CD 2 =8 indicates that there definitely exist dots around the target dot. Therefore, the level of the target dot image data DX 2  is converted to a level slightly lower than a level that is supposed to be. The conversion table code CD 2 =1 to 7 is referred to in a centralized dither processing. The conversion table code CD 2 =8 is referred to in a distributed dither processing. Therefore, in the fourth embodiment, it is possible to perform level conversion for writing to a recording medium optimally based on a dither type.  
     [0173] According to the fourth embodiment as explained above, based on the determined result from the determination section  1000 , the target dot is level-converted. Therefore, it is possible to achieve optimal dot reproduction even for a high-resolution dot based on the surrounding situation around the target dot.  
     [0174] Fifth Embodiment:  
     [0175] The processing section shown in FIG. 3 and exemplified in the first embodiment may be replaced with a processing section configured as shown in FIG. 14. This case is explained below as a fifth embodiment.  
     [0176]FIG. 13 is a block diagram that shows a configuration of a printer controller  1010  applied to a color image formation device according to the fifth embodiment of the present invention. The printer controller  1010  is interposed between a personal computer  1000   a  and a printer engine  1020 , and has a function of receiving a command and image data for printing from the personal computer  1000   a  and outputting later-explained dither-processed image data to the printer engine  1020  based on the command.  
     [0177] The command includes a line command for subjecting thin-line image data to dither processing for thin lines, and an image command for subjecting pictorial image data to dither processing for images.  
     [0178] The printer controller  1010  comprises a personal computer interface  1011  that is an interface for receiving the command and image data from the personal computer  1000   a . A CPU (Central Processing Unit)  1012  executes controls for processing in the sections such as a control for dither processing. A printer engine interface  1013  is an interface for feeding dither-processed image data to the printer engine  1020 .  
     [0179] A ROM  1014  stores a first thin-line dither threshold matrix  1300 , a second thin-line dither threshold matrix  1310 , and a third thin-line dither threshold matrix  1320  shown in FIG. 21. The ROM  1014  also stores a first image dither threshold matrix  1400 , a second image dither threshold matrix  1410 , and a third image dither threshold matrix  1420  shown in FIG. 22.  
     [0180] The first thin-line dither threshold matrix  1300 , the second thin-line dither threshold matrix  1310 , and the third thin-line dither threshold matrix  1320  are used for dither processing of the thin-line image data when the line command is input.  
     [0181] The first image dither threshold matrix  1400 , the second image dither threshold matrix  1   410 , and the third image dither threshold matrix  1420  are used for dither processing of the pictorial image data when the image command is input. Referring back to FIG. 13, a frame RAM  1015  stores bitmap data obtained by converting the image data sent from the personal computer  1000   a  to bitmap format. A bus  1016  connects the sections with each other in the printer controller  1010 .  
     [0182]FIG. 14 is a block diagram that shows a configuration of the processing section applied to the color image formation device according to the fifth embodiment of the present invention, in which the printer controller  1010  and the printer engine  1020  of FIG. 13 are shown as a functional block diagram. In FIG. 14, serial image data DS is 2-bit weighed and dither-processed. The image data DS has resolutions of, for example, 1200 dpi in the main scanning direction and 600 dpi in the subscanning direction.  
     [0183] A serial/parallel converter  1030  subjects 2-bit image data DS to serial-parallel conversion to obtain parallel image data DP for 2 lines. Specifically, as shown in FIGS.  15 ( a ) to  15 ( c ), the serial/parallel converter  1030  converts 2-line image data DS into parallel image data DP in a 1-line period T c  of a synchronizing signal CLK.  
     [0184] For example, image data DS 1  (the first line) and image data DS 2  (the second line) are converted into parallel image data DP 1  (the first line) and image data DP 2  (the second line). In the next 1-line period T c , image data DS 3  (the third line) and image data DS 4  (the fourth line) are converted into parallel image data DP 3  (the third line) and image data DP 4  (the fourth line).  
     [0185] The image data DP is data associated with a set of 2 dots. The serial/parallel converter  1030  converts the image data DS with 1200 dpi in the main scanning direction and 600 dpi in the subscanning direction into the image data DP with 600 dpi in the main scanning direction and 600 dpi in the subscanning direction. Referring back to FIG. 14, a 1-line buffer  1040  is a buffer that temporarily holds image data DP for one line. A 1-line buffer  1050  is also a buffer that temporarily holds image data DP for one line. A 1-line buffer  1060  is a buffer that temporarily holds the image data DP delayed by one line from the 1-line buffer  1050 .  
     [0186] The image data DP from the serial/parallel converter  1030  is output to an EVEN processing section  1070  and an ODD processing section  1080  as the image data DP for five lines (two lines from the serial/parallel converter  1030 , one line from the 1-line buffer  1040 , 1 line from the 1-line buffer  1050 , and one line from the 1-line buffer  1060 ) from the 1-line buffer  1040 , the 1-line buffer  1050 , and the 1-line buffer  1060 . The image data DP fed to the ODD processing section  1080  is delayed by one line relative to that fed to the EVEN processing section  1070 .  
     [0187] The EVEN processing section  1070  comprises a dummy latch circuitry EDM 0 , a latch circuitry ED 0 , a latch circuitry ED 1 , and a latch circuitry ED 2  that are arranged corresponding to the 1-line buffer  1050 , the 1-line buffer  1040 , and the serial/parallel converter  1030  to latch the image data DP in synchronization with the synchronizing signal, respectively.  
     [0188] A latch circuitry EA 0 , a latch circuitry EA 3 , a latch circuitry EA 5 , and a latch circuitry EC 0  are arranged corresponding to the dummy latch circuitry EDM 0 , the latch circuitry ED 0 , the latch circuitry ED 1 , and the latch circuitry ED 2  to latch the output data from the dummy latch circuitry EDM 0 , the latch circuitry ED 0 , the latch circuitry ED 1 , and the latch circuitry ED 2  in synchronization with the synchronizing signal, respectively.  
     [0189] A latch circuitry EA 1 , a target dot latch circuitry E x , a latch circuitry EA 6 , and a latch circuitry EC 1  are arranged corresponding to the latch circuitry EA 0 , the latch circuitry EA 3 , the latch circuitry EA 5 , and the latch circuitry EC 0  to latch the output data from the latch circuitry EA 0 , the latch circuitry EA 3 , the latch circuitry EA 5 , and the latch circuitry EC 0  in synchronization with the synchronizing signal, respectively.  
     [0190] A latch circuitry EA 2 , a latch circuitry EA 4 , a latch circuitry EA 7 , and a latch circuitry EC 2  are arranged corresponding to the latch circuitry EA 1 , the target dot latch circuitry E x , the latch circuitry EA 6 , and the latch circuitry EC 1  to latch the output data from the latch circuitry EA 1 , the target dot latch circuitry E x , the latch circuitry EA 6 , and the latch circuitry EC 1  in synchronization with the synchronizing signal, respectively. The target dot latch circuitry E x  holds target dot image data DX E  associated with a target dot. A latch circuitry EB 0 , a latch circuitry EB 1 , a latch circuitry EB 2 , and a dummy latch circuitry EDM 1  are arranged corresponding to the latch circuitry EA 2 , the latch circuitry EA 4 , the latch circuitry EA 7 , and the latch circuitry EC 2  to latch the output data.from the latch circuitry EA 2 , the latch circuitry EA 4 , the latch circuitry EA 7 , and the latch circuitry EC 2 , respectively.  
     [0191] Four areas in total including an area  1071 A, an area  1071 B, an area  1071 C, and an area  1071 D are defined around the target dot corresponding to the target dot latch circuitry E x . That is, the area  1071 A contains the latch circuitries EA 0  to EA 7 . The area  1071 B contains the latch circuitries EB 0  to EB 2 . The area  1071 C contains the latch circuitries EC 0  to EC 2 . The area  1071 D contains the latch circuitries ED 0  to ED 2 .  
     [0192] A converter  1072  identifies the surrounding situation around the target dot by referring to the image data in each of the latch circuitries. The converter  1072  selects one of conversion tables TT 1  to TT 3  (see FIGS.  17 ( a ),  18 ( a ) and  19 ( a )) stored in a storage  1090  under the later-described condition to level-convert the target dot image data DX E  and outputs it as target dot image data DX E ′.  
     [0193] The conversion table TT 1  shown in FIG. 17( a ) is used to convert a level of the target dot image data DX E  latched in the target dot latch circuitry E x  by a magnification corresponding to the conversion table code TC. FIG. 17( b ) shows a graph GG 1  obtained by graphing the conversion table TT 1 .  
     [0194] The conversion table TT 2  shown in FIG. 18( a ) is used to convert a level of the target dot image data DX E  latched in the target dot latch circuitry E x  by a magnification corresponding to the conversion table code TC. FIG. 18( b ) shows a graph GG 2  obtained by graphing the conversion table TT 2 .  
     [0195] The conversion table TT 3  shown in FIG. 19( a ) is used to convert a level of the target dot image data DX E  latched in the target dot latch circuitry E x  by a magnification corresponding to the conversion table code TC. FIG. 19( b ) shows a graph GG 3  obtained by graphing the conversion table TT 3 .  
     [0196] The ODD processing section  1080  comprises a dummy latch circuitry ODM 0 , a latch circuitry OD 0 , a latch circuitry OD 1 , and a latch circuitry OD 2  that are arranged corresponding to the 1-line buffer  1050 , the 1-line buffer  1040 , and the serial/parallel converter  1030  to latch the image data DP in synchronization with the synchronizing signal, respectively.  
     [0197] A latch circuitry OA 0 , a latch circuitry OA 3 , a latch circuitry OA 5 , and a latch circuitry OC 0  are arranged corresponding to the dummy latch circuitry ODM 0 , the latch circuitry OD 0 , the latch circuitry OD 1 , and the latch circuitry OD 2  to latch the output data from the dummy latch circuitry ODM 0 , the latch circuitry OD 0 , the latch circuitry OD 1 , and the latch circuitry OD 2  in synchronization with the synchronizing signal, respectively.  
     [0198] A latch circuitry OA 1 , a target dot latch circuitry O x , a latch circuitry OA 6 , and a latch circuitry OC 1  are arranged corresponding to the latch circuitry OA 0 , the latch circuitry OA 3 , the latch circuitry OA 5 , and the latch circuitry OC 0  to latch the output data from the latch circuitry OA 0 , the latch circuitry OA 3 , the latch circuitry OA 5 , and the latch circuitry OC 0  in synchronization with the synchronizing signal, respectively.  
     [0199] A latch circuitry OA 2 , a latch circuitry OA 4 , a latch circuitry OA 7 , and a latch circuitry OC 2  are arranged corresponding to the latch circuitry OA 1 , the target dot latch circuitry O x , the latch circuitry OA 6 , and the latch circuitry OC 1  to latch the output data from the latch circuitry OA 1 , the target dot latch circuitry O x , the latch circuitry OA 6 , and the latch circuitry OC 1  in synchronization with the synchronizing signal, respectively. The target dot latch circuitry O x  holds target dot image data DX O  associated with a target dot. A latch circuitry OB 0 , a latch circuitry OB 1 , a latch circuitry OB 2 , and a dummy latch circuitry ODM 1  are arranged corresponding to the latch circuitry OA 2 , the latch circuitry OA 4 , the latch circuitry OA 7 , and the latch circuitry OC 2  to latch the output data from the latch circuitry OA 2 , the latch circuitry OA 4 , the latch circuitry OA 7 , and the latch circuitry OC 2 , respectively.  
     [0200] Four areas in total including an area  1081 A, an area  1081 B, an area  1081 C, and an area  1081 D are defined around the target dot corresponding to the target dot latch circuitry O x . The area  1081 A contains the latch circuitries OA 0  to OA 7 . The area  1081 B contains the latch circuitries OB 0  to OB 2 . The area  1081 C contains the latch circuitries OC 0  to OC 2 . The area  1081 D contains the latch circuitries OD 0  to OD 2 .  
     [0201] A converter  1072  identifies the surrounding situation around the target dot by referring to the image data in each of the latch circuitries, and selects one of the conversion tables TT 1  to TT 3  stored in the storage  1090  (see FIGS.  17 ( a ),  18 ( a ), and  19 ( a )) under the later-described condition to level-convert the target dot image data DX O  and outputs it as target dot image data DX O ′.  
     [0202] A LD (laser diode) modulator  1200   a  modulates a writing laser beam, in response to the target dot image data DX E ′ and the target dot image data DX O ′, with respect to the optical writing time period, optical power time period, and optical power in combination.  
     [0203]FIG. 16 is a schematic diagram that shows a positional relation between the EVEN processing section  1070  and the ODD processing section  1080  in the subscanning direction. In this figure, an EVEN dot reference area  1210  corresponds to the EVEN processing section  1070 , and an ODD dot reference area  1220  corresponds to the ODD processing section  1080 .  
     [0204] A target dot  1210   x  corresponds to the target dot latch circuitry E x  in the EVEN processing section  1070 . A target dot  1220   x  corresponds to the target dot latch circuitry O x  in the ODD processing section  1080 . In an actual case, the EVEN dot reference area  1210  and the ODD dot reference area  1220  overlap each other in the subscanning direction. However, the ODD dot reference area  1220  is depicted as shifted in the main scanning direction from the EVEN dot reference area  1210  for easy understanding.  
     [0205] The writing laser beam in FIG. 16 is designed to have the number of beams=2. In the EVEN dot reference area  1210 , the number of lines following the target dot  1210   x  (the third line L 3  and the fourth line L 4  in the figure) is determined equal to the number of beams=2 (or an integral multiple of 2). Similarly, also in the ODD dot reference area  1220 , the number of lines following the target dot  1220   x  (the second line L 2  and the third line L 3  in the figure) is determined equal to the number of beams=2 (or an integral multiple of 2).  
     [0206] In combination of the EVEN dot reference area  1210  and the ODD dot reference area  1220 , a pair of target dots can be converted every two lines in the subscanning direction. For example, a pair includes the target dot  1220   x  on the first line L 1  and the target dot  1210   x  on the second line L 2 , and a pair includes the target dot  1220   x  on the third line L 3  and the target dot  1210   x  on the fourth line L 4 . Therefore, it is possible to minimize the use of the 1-line buffers.  
     [0207] Operation of the fifth embodiment is explained next. At step SA 1  shown in FIG. 20, the CPU  1012  (see FIG. 13) determines if any command is input from the personal computer  1000   a . If the determined result indicates “No”, the same determination is repeated. If a command is input, the CPU  1012  sets the determined result at step SA 1  to “Yes”.  
     [0208] At step SA 2 , the CPU  1012  analyzes the command. At step SA 3 , the CPU  1012  rasterizes image data from the personal computer  1000   a  to create bitmap data, and the bitmap data is then stored in the frame RAM  1015 . At step SA 4 , the CPU  1012  determines if the command is a line command.  
     [0209] If the command is a line command, the CPU  1012  sets the determined result at step SA 4  to “Yes”. At step SA 5 , the CPU  1012  executes the dither processing to the bitmap data using the first thin-line dither threshold matrix  1300 , the second thin-line dither threshold matrix  1310 , and the third thin-line dither threshold matrix  1320  shown in FIG. 21.  
     [0210] If the command is an image command on the other hand, the CPU  1012  sets the determined result at step SA 4  to “No”. At step SA 7 , the CPU  1012  executes the dither processing to the bitmap data using the first image dither threshold matrix  1400 , the second image dither threshold matrix  1410 , and the third image dither threshold matrix  1420  shown in FIG. 22.  
     [0211] In the dither processing, the original image of the bitmap data has 49 halftones. Multivalue bitmap data is expressed with 2 bits, and includes a first level through a third level. For the halftone 0, all dots are set to 0. In the thin-line dither processing, for the halftones 1 and 2, all dots are set to the first level. For the halftones 3 to 25, the corresponding dots are set to the second level. For the halftones 26 to 48, the corresponding dots are set to the third level.  
     [0212] In the image dither processing on the other hand, a dot located at (2, 2) from the upper left is set to the first level for the halftone  1 , the second level for the halftone 2, and the third level for the halftone 3. Similarly, a dot located at (4, 4) from the upper left is set to the first level for the halftone 4, the second level for the halftone 5, and the third level for the halftones 6 to 48.  
     [0213] At step SA 6 , the dither-processed 2-bit image data DS is transferred to the printer engine  1020 . Thus, the 2-line image data DS shown in FIG. 14 is converted into the parallel image data DP at the serial/parallel converter  1030  in synchronization with the synchronizing signal. The image data DP is stored in the 1-line buffer  1040 , the 1-line buffer  1050 , and the 1-line buffer  1060  in synchronization with the synchronizing signal. The image data DP is then latched as 5-line data in a latch circuitry on each first stage in the EVEN processing section  1070  and the ODD processing section  1080 .  
     [0214] In the EVEN processing section  1070 , the. image data DP on the first line is latched at the latch circuitry ED 1 . The image data DP on the second line is latched at the latch circuitry ED 2 . The image data DP on the third line (the output data from the 1-line buffer  1040 ) is latched at the latch circuitry ED 0 . The image data DP on the fourth line (the output data from the 1-line buffer  1050 ) is latched at the dummy latch circuitry EDM 0 .  
     [0215] On the other hand, in the ODD processing section  1080 , the image data DP on the first line is latched at the latch circuitry OD 2 . The image data DP on the third line (the output data from the 1-line buffer  1040 ) is latched at the latch circuitry OD 1 . The image data DP on the fourth line (the output data from the 1-line buffer  1050 ) is latched at the latch circuitry OD 0 . The image data DP on the fifth line (the output data from the 1-line buffer  1060 ) is latched at the dummy latch circuitry ODM 0 .  
     [0216] In the EVEN processing section  1070 , respective pieces of the data latched in the latch circuitry ED 1 , the latch circuitry ED 2 , the latch circuitry ED 0 , and the dummy latch circuitry EDM 0  are shifted in turn to the right in FIG. 14 in synchronization with the synchronizing signal. That is, the pieces of data are shifted from the latch circuitry EA 5 , the latch circuitry EC 0 , the latch circuitry EA 3 , and the latch circuitry EA 0 , through the latch circuitry EA 6 , the latch circuitry EC 1 , the target dot latch circuitry E x , and the latch circuitry EA 1 , and also through the latch circuitry EA 7 , the latch circuitry EC 2 , the latch circuitry EA 4 , and the latch circuitry EA 2 , to the latch circuitry EB 2 , the dummy latch circuitry EDM 1 , the latch circuitry EB 1 , and the latch circuitry EB 0 , respectively.  
     [0217] In the ODD processing section  1080 , on the other hand, respective pieces of the data delayed by one line from the EVEN processing section  1070  are shifted in turn to the right in FIG. 14 in synchronization with the synchronizing signal. That is, the pieces of the data latched in the latch circuitry OD 1 , the latch circuitry OD 2 , the latch circuitry OD 0 , and the dummy latch circuitry ODM 0  are shifted from the latch circuitry OA 5 , the latch circuitry OC 0 , the latch circuitry OA 3 , and the latch circuitry OA 0 , through the latch circuitry OA 6 , the latch circuitry OC 1 , the target dot latch circuitry O x , and the latch circuitry OA 1 , and also through the latch circuitry OA 7 , the latch circuitry OC 2 , the latch circuitry OA 4 , and the latch circuitry OA 2 , to the latch circuitry OB 2 , the dummy latch circuitry ODM 1 , the latch circuitry OB 1 , and the latch circuitry OB 0 , respectively.  
     [0218] In the series of shift operations in the EVEN processing section  1070 , the output data from the latch circuitries present in the areas  1071 A,  1071 B,  1071 C, and  1071 D are fed into the converter  1072 . The converter  1072  determines the surrounding situation around the target dot (such as the presence or absence of a dot) on an area-basis of an area  1071 A to  1071 D by referring to the image data in each of the latch circuitries other than the target dot latch circuitry E x  based on the following &lt;Condition A&gt; or &lt;Condition B&gt;.  
     [0219] &lt;Condition A&gt; If the target dot image data DX E  from the target dot latch circuitry E x  is 0:  
     [0220] Use the areas  1071 A to  1071 D.  
     [0221] Determine the following state (1) or state (2) that indicates if a dot (except for the target dot) is present in the area  1071 A.  
     [0222] (1) Output data=0 (space)  
     [0223] (2) Output data=1 to 3 (the presence of a dot)  
     [0224] Determine the following &lt;Case 1&gt; and &lt;Case 2&gt; 
     [0225] &lt;Case 1&gt; Output data from the latch circuitry EA 4  is not 0, output data from latch circuitries other than the latch circuitry EA 4  in the area  1071 A is 0, and all output data in the area  1071 B is 0 (space).  
     [0226] &lt;Case 2&gt; Output data from the latch circuitry EA 6  is not 0, output data from latch circuitries other than the latch circuitry EA 6  in the area  1071 A is 0, all output data in the area  1071 C is 0 (space), and all output data in the area  1071 D is 0 (space).  
     [0227] &lt;Condition B&gt; If the target dot image data DX E  from the target dot latch circuitry E x is not 0:  
     [0228] Use the area  1071 A.  
     [0229] Determine the following state (1), state (2), or state (3) that indicates if a dot (except for the target dot) is absent (output data=0: SPACE), present (output data=1 or 2: HALF), or present (output data=3: FULL) in the area  1071 A.  
     [0230] (1) Output data=0 (SPACE)  
     [0231] (2) Output data=1 or 2 (the presence of a half dot: HALF)  
     [0232] (3) Output data=3 (the presence of a full dot: FULL)  
     [0233] Determine the following &lt;Case 1&gt; through &lt;Case 3&gt; 
     [0234] &lt;Case 1&gt; All output data (except for the target dot) in the area  1071 A is 0 (space).  
     [0235] &lt;Case 2&gt; Output data in the area  1071 A is not all 0 and contains a half dot corresponding to the output data=1 or 2.  
     [0236] &lt;Case 3&gt; Output data in the area  1071 A is not all 0 and contain a full dot corresponding to the output data=3.  
     [0237] The converter  1072  selects a table for use in level conversion of the target dot image data DX E  in &lt;Case 1&gt;, &lt;Case 2&gt;, and &lt;Case 3&gt; under &lt;Condition A&gt; and &lt;Condition B&gt;. Specifically, in &lt;Case 1&gt;, based on the conversion table TT 1  shown in FIG. 17( a ), the converter  1072  level-converts (density-corrects) the target dot image data DX E  into the target dot image data DX E ′ and outputs the data to the LD modulator  1200   a.    
     [0238] In &lt;Case 2&gt;, based on the conversion table TT 2  shown in FIG. 18( a ), the converter  1072  level-converts (density-corrects) the target dot image data DX E  into the target dot image data DX E ′ and outputs the data to the LD modulator  1200   a . In &lt;Case 3&gt;, based on the conversion table TT 3  shown in FIG. 19( a ), the converter  1072  level-converts (density-corrects) the target dot image data DX E  into the target dot image data DX E ′ and outputs the data to the LD modulator  1200   a.    
     [0239] On the other hand, the converter  1082  of the ODD processing section  1080  also operates like the converter  1072 . That is, the converter  1082  determines the surrounding situation around the target dot (such as the presence or absence of a dot) on an area-basis of the areas  1081 A to  1081 D by referring to the image data in each of the latch circuitries other than the target dot latch circuitry O x  based on the following &lt;Condition A&gt; or &lt;Condition B&gt;.  
     [0240] &lt;Condition A&gt; If the target dot image data DX O  from the target dot latch circuitry O x  is 0:  
     [0241] Use the areas  1081 A to  1081 D.  
     [0242] Determine the following state (1) or state (2) that indicates if a dot (except for the target dot) is present in the area  1081 A.  
     [0243] (1) Output data=0 (space)  
     [0244] (2) Output data=1 to 3 (the presence of a dot)  
     [0245] Determine the following &lt;Case 1&gt; and &lt;Case 2&gt; 
     [0246] &lt;Case 1&gt; Output data from the latch circuitry OA 4  is not 0, output data from latch circuitries other than the latch circuitry OA 4  in the area  1081 A is 0, and all output data in the area  1081 B is 0 (space).  
     [0247] &lt;Case 2&gt; Output data from the latch circuitry OA 6  is not 0, output data from latch circuitries other than the latch circuitry OA 6  in the area  1081 A is 0, all output data in the area  1081 C is 0 (space), and all output data in the area  1081 D is 0 (space).  
     [0248] &lt;Condition B&gt; If the target dot image data DX O  from the target dot latch circuitry O x  is not 0:  
     [0249] Use the area  1081 A.  
     [0250] Determine the following state (1), state (2), or state (3) that indicates if a dot (except for the target dot) is absent (output data=0: SPACE), present (output data=1 or 2: HALF), or present (output data=3: FULL) in the area  1081 A.  
     [0251] (1) Output data=0 (SPACE)  
     [0252] (2) Output data=1 or 2 (the presence of a half dot: HALF)  
     [0253] (3) Output data=3 (the presence of a full dot: FULL)  
     [0254] Determine the following &lt;Case 1&gt; through &lt;Case 3&gt; 
     [0255] &lt;Case 1&gt; All output data (except for the target dot) in the area  1081 A is 0 (space).  
     [0256] &lt;Case 2&gt; Output data in the area  1081 A is not all 0 and contains a half dot corresponding to the output data=1 or 2.  
     [0257] &lt;Case 3&gt; Output data in the area  1081 A is not all 0 and contains a full dot corresponding to the output data=3.  
     [0258] It is explained in &lt;Condition A&gt; and &lt;Condition B&gt; that the output data is expressed with 2 bits while it may be expressed with 1 bit as well as 4 bits.  
     [0259] The converter  1082  selects a table for use in level conversion of the target dot image data DX O  according to any of &lt;Case 1&gt; to &lt;Case 3&gt; under &lt;Condition A&gt; and &lt;Condition B&gt;. Specifically, in &lt;Case 1&gt;, based on the conversion table TT 1  shown in FIG. 17( a ), the converter  1082  level-converts (density-corrects) the target dot image data DX o  into the target dot image data DX o ′ and outputs the data to the LD modulator  1200   a.    
     [0260] In &lt;Case 2&gt;, based on the conversion table TT 2  shown in FIG. 18( a ), the converter  1082  level-converts (density-corrects) the target dot image data DX o  into the target dot image data DX o ′ and outputs the data to the LD modulator  1200   a . In &lt;Case 3&gt;, based on the conversion table TT 3  shown in FIG. 19( a ), the converter  1082  level-converts (density-corrects) the target dot image data DX o  into the target dot image data DX o ′ and outputs the data to the LD modulator  1200   a.    
     [0261] The LD modulator  1200   a  modulates a writing laser beam, in response to the target dot image data DX E ′ and the target dot image data DX O ′, with respect to the optical writing time period, optical power time period, and optical power in combination. Thus, the density-corrected target dot image data DX E ′ and target dot image data DX O ′ are written into a recording medium.  
     [0262] According to the fifth embodiment as explained above, the target dot is subjected to level conversion based on the state of the peripheral dots in the adjacent area (the area  1071 A and the like) and plural areas (the areas  1071 B,  1071 C and the like) with respect to the target dot. Therefore, it is possible to achieve optimal dot reproduction even for a high-resolution dot based on the surrounding situation.  
     [0263] According to the fifth embodiment, any of the conversion tables (conversion tables TT 1 , TT 2 , TT 3 ) is selected based on the level state of the peripheral dot in the adjacent area (the area  1071 A and the like). Therefore, it is possible to achieve optimal dot reproduction corresponding to the halftone processing.  
     [0264] According to the fifth embodiment, the level conversion required for the case where the number of peripheral dots that are present is zero, is executed separately from the level conversion required for the case where the number is any other than zero. Therefore, it is possible to reduce a memory area required for management as compared to that for integrally managing both cases.  
     [0265] Sixth Embodiment:  
     [0266] A sixth embodiment is explained next. In FIG. 1, the photoreceptor  1  as the image carrier is composed of a flexible endless belt-like photoreceptor, is suspended around the rotating rollers  2  and  3  and conveyed clockwise in the figure. Those arranged around the photoreceptor  1  along the rotational direction thereof include the erasing lamp  21 , the charger  4 , the laser writing unit  5 , the developing devices  6  to  9  of C, M, Y and K, the intermediate transfer belt  10 , and the cleaning unit  15 . The laser writing unit  5  is housed in a support cabinet having a slit-like aperture for exposure formed on the upper surface of the support cabinet to be incorporated in the device body. A laser optical system  5  may also include, other than the laser writing unit  5 , an optical system integrally formed with a light emission section and a convergent optical transmission medium. The charger  4 , the laser writing unit  5 , and the cleaning unit  15  are arranged opposing one roller  2  of plural rollers that suspend the photoreceptor  1  around the rollers.  
     [0267] The developing devices  6  to  9  contain developers of, for example, yellow (Y), magenta (M), cyan (C), and black (BK), respectively. The developing devices  6  to  9  include development sleeves that are close to or in contact with the belt-like photoreceptor  1  at a certain position, and develop a latent image on the photoreceptor belt  1  by non-contact or contact development. The intermediate transfer belt  10  functions as a transferred image carrier. The intermediate transfer belt  10  is suspended around the rotating rollers  11  and  12 , and is driven by the rotating rollers  11  and  12  so as to be conveyed counterclockwise.  
     [0268] The photoreceptor  1  and the intermediate transfer belt  10  contact with each other at the rotating roller  3 . Thus, a first developed image on the photoreceptor  1  is transferred onto the intermediate transfer belt  10  via the bias roller  13  located inside the intermediate transfer belt  10 . When similar processes are repeated, second though fourth developed images are superimposed on one another on the intermediate transfer belt  10  so that the images are transferred without any positional deviation. The transfer roller  14  is disposed so as to be in contact with and separate from the intermediate transfer belt  10 . The cleaning unit  15  cleans the photoreceptor  1 , and another cleaning unit  16  cleans the intermediate transfer belt  10 . The cleaning unit  16  for the intermediate transfer belt  10  has a blade  16 A kept at a position separated from the surface of the intermediate transfer belt  10  during image formation. The blade  16 A is press-contacted with the surface of the intermediate transfer belt  10  as shown in FIG. 2 only during cleaning after the image formation to clean the intermediate transfer belt  10 . The reference numeral  16 B denotes a base of the blade  16 A attached pivotably about a pivot.  
     [0269] The laser writing unit  5  comprises a not-shown laser diode (LD) unit, a polygon motor  5 A, the polygon mirror  5 B, the fθ lens  5 C, and the reflective mirror  5 D to emit a laser beam for forming a dot-like latent image on the photoreceptor  1 . The laser writing unit  5  expresses a density gradation by a dot density or dot size with plural dots and 8 bits, and a dot phase (a right or left writing location).  
     [0270] A process of color image formation in the image formation device thus configured briefly is performed as follows.  
     [0271] In multi-color image formation, an image data processor operationally processes data obtained in a color image data input section in which an image pickup device scans an original draft, and once stores the data in an image memory. The image data stored in the image memory is then read out for recording and fed to the color image formation device (printer) as a recorder.  
     [0272] That is, a color image signal output from an image reader that is discretely disposed from the color image formation device is input to the laser writing unit  5 . In the laser writing unit  5 , the laser beam emitted from a semiconductor laser  5 E is scanned by the polygon mirror  5 B that is rotationally driven by the drive motor  5 A. After passing through the fθ lens  5 C, the optical path of the laser beam is bent at the mirror, and the laser beam is then exposed to the circumference of the photoreceptor  1  that is previously erased by the erasing lamp  21  and is charged uniformly by the charger  4 , and an electrostatic latent image is formed on the photoreceptor  1 . The image pattern to be exposed is one of monochromatic image patterns when a desired full-color image is decomposed into colors of Y, M, C and BK.  
     [0273] Electrostatic latent images formed for each color are developed by the developing devices of Y, M, C, and BK respectively of the rotary developing unit to be visualized. Monochromatic images visualized with different colors are formed in this case. The monochromatic images formed on the photoreceptor  1  are transferred onto the intermediate transfer belt  10  that rotates counterclockwise while coming into contact with the belt-like photoreceptor  1 . The color images of Y, M, C, and BK are sequentially superimposed on one another on the intermediate transfer belt  10 . The superimposed images of Y, M, C, and BK on the intermediate transfer belt  10  are transferred by the transfer roller  14  onto a transfer paper conveyed from the paper feed tray  17  by the paper feed roller  18  to the transfer portion by adjusting timing at the regist rollers  19 . After completion of the transfer, the transfer paper is subjected to fixing at the fixing device  20  to form a full-color image on the transfer paper.  
     [0274] As shown in FIG. 2, the intermediate transfer belt  10  has the six marks  41 A to  41 F on the edge thereof. When the mark detecting sensor  40  senses an arbitrary mark, for example, the mark  41 A, a color writing is started, and when it senses the mark  41 A again after one rotation, a second color writing is started. At this point in time, the number of the marks is managed so as to prevent the marks  41 B to  41 F from being used as write timings by masking the corresponding signals. At a location slightly upstream from the contact portion of the photoreceptor belt  1  with the intermediate transfer belt  10 , a toner density detecting sensor  22  is disposed so as to detect an amount of toner on the photoreceptor belt  1 .  
     [0275]FIG. 23 is a block diagram that shows a configuration of the image processor in the image formation device according to the sixth embodiment. In the figure, the image processor includes four 1-line buffers L 1 , L 2 , L 3 , and L 4 , 25 latches H 0  to H 15 , N 0  to N 3 , S 0  to S 3 , and X, two arithmetic sections A ( 2301 ) and B ( 2302 ), a bit conversion table (memory)  2303  for converting 4-bit data from each latch into 8-bit data, a correction table (memory)  2304  for density correction, a presence/absence determination section  2305  that determines the presence or absence of predetermined data in the data from the latch, and a latch  2306  for holding the determined result from the presence/absence determination section  2305 .  
     [0276] According to the configuration in FIG. 23, for example, dither-processed 4-bit image data is latched in the latch H 11  and is also applied to the 1-line buffer L 2  through the 1-line buffer L 1 . The output from the 1-line buffer L 2  is supplied to the latch H 2  and is also applied to the 1-line buffer L 3  on the upper line. The output from the 1-line buffer L 3  is supplied to the latch H 0  and is also applied to the 1-line buffer L 4  on the upper line. The output from the 1-line buffer L 4  is supplied to the latch H 6 .  
     [0277] Respective pieces of image data latched in the latches H 0 , H 2 , H 4  are shifted in synchronization with a synchronizing signal and latched at the latches S 0 , N 3 , S 3 , respectively. Similarly, respective pieces of the latched image data are shifted in synchronization with the synchronizing signal and latched at the latches (N 0 , x, N 2 ), (S 1 , N 1 , S 2 ), (H 3 , H 5 ), respectively. The data in the latches S 0 , S 1 , S 2 , S 3 , N 0 , N 1 , N 2 , and N 3  adjacent to a target pixel x are fed to the arithmetic section A ( 2301 ), and the latched data of the target pixel x is fed to the arithmetic section B ( 2302 ). The arithmetic section B ( 2302 ) supplies a constant value to an address section in the correction table  2304  only when a latch signal output from the latch  2306  is “0”, and also outputs a phase signal of mode “0”. A correction coefficient processed at the arithmetic section A ( 2301 ) is fed by an 8-bit width to the address section in the correction table  2304  and is converted into 8-bit data in the correction table  2304  to be output. The LD unit performs laser beam writing based on the 8-bit data.  
     [0278] Thus, 4-bit image data, corresponding to the following 5 dots in the main scanning direction×5 dots in the subscanning direction, can be latched in the 5×5 latches. The reference numeral for a latch is also used to denote a position and density of the corresponding dot in the following explanation.  
     [0279] H 6 , H 7 , H 8 , H 9 , H 10   
     [0280] H 0 , S 0 , N 0 , S 1 , H 1   
     [0281] H 2 , N 3 , x, N 1 , H 3   
     [0282] H 4 , S 3 , N 2 , S 2 , H 5   
     [0283] H 11 , H 12 , H 13 , H 14 , H 15   
     [0284] Among the 5×5 dots, 16 dots H 0  to H 15  are located on the line where the central dot x exists and on the upper and lower lines thereof, and spaced each 2 dots back and forth from the central dot x. Four dots S 0  to S 3  are located at the upper left, upper right, lower left, and lower right positions diagonally spaced from the central dot x, respectively. Four dots N 0  to N 3  are located at the upper, right, lower, and left positions of the central dot x, respectively.  
     [0285] The bit conversion table  2303  for converting 4-bit data input from each of the latches into 8-bit data is connected to the arithmetic section A ( 2301 ). Before operation of the arithmetic section A ( 2301 ), the bit conversion table  2304  converts 4-bit data into 8-bit data. The latched data in the latches H 0  to H 5 , S 0  to S 3 , N 1 , and N 3  are supplied to the presence/absence determination section  2305 , and the determined results are latched in the latch  2306  on the next stage. The presence/absence determination section  2305  outputs “0” when all data in H 0  to H 5 , S 0  to S 3 , N 1 , and N 3  are “0”, and outputs “1” in other cases.  
     [0286]FIG. 24 shows the contents written in the bit conversion table  2303  shown in FIG. 23. As for the contents in the bit conversion table  2303 , an 8-bit writing level is selected so that a solid patch density of 4-bit input data has a linear characteristic as shown in FIG. 26. Specifically, the contents of the table have relations as shown in FIG. 25.  
     [0287] When the latch data is input, the arithmetic section A ( 2301 ) operates as follows.  
     [0288] That is, based on 8-bit data s 0 , s 1 , s 2 , s 3 , n 0 , n 1 , n 2 , and n 3  converted at the image memory corresponding to the 4-bit reference data, S 0 , S 1 , S 2 , S 3 , N 0 , N 1 , N 2 , and N 3 ; a gain Gs, n 0 , n 1 , n 2 , n 3  corresponding to s 0 , s 1 , s 2 , s 3 ; and a gain Gn corresponding to  
     [0289] s 0 , n 0 , s 1   
     [0290] n 3 , x, n 1   
     [0291] s 3 , n 2 , s 2 ,  
     [0292] an output G as the correction coefficient is computed from: 
       G=GnΣ ( nt−x )+ GsΣ ( st−x )  (1) 
     [0293] where n, t=0, 1, 2, 3, and is output to the correction table memory  2304 .  
     [0294] Further, if H 6  to H 15  are all “0”, a correction amount Gt is added to the correction coefficient G of the equation (1). Thus, the equation (1) yields: 
       G=Gt{GnΣ ( nt−x )+ GsΣ ( st×x )}  (2) 
     [0295] In order to smoothen the gradation in accordance with the correction coefficient G as shown in FIG. 27, 256 operated results (conversion tables) for converting 4-bit data of the central dot x into 8-bit data are previously stored in the correction table  2304 . Among these, one conversion table is selected based on the correction coefficient G from the arithmetic section A. The 4-bit data of the central dot x is converted into 8-bit data using the conversion table.  
     [0296] Write phases of a printer are explained next with reference to FIG. 9. Normally, a dot is written in a phase of Mode “1” (Left mode). In this case, the dot width grows from the center to the right. On. the other hand, in a phase of Mode “0” (Right mode), the dot width grows from the center to the left. Therefore, the left and right dots are linked with each other, and thus the dot can be emphasized with natural touch.  
     [0297] According to the sixth embodiment as explained above, the function of detecting a dot density or dot size of the dot adjacent to the target dot and the function of detecting a dot density or dot size of a dot spaced at least one dot from the target dot are provided. A write level of the target dot is corrected based on the dot density or dot size of the dot spaced at least one dot. Therefore, it is possible to form an optimal dot. based on the surrounding situation around the target dot and improve reproducibility of a highlight.  
     [0298] In addition, the control unit that shifts a writing position of the target dot to the left or right based on the surrounding situation around the target dot is provided so as to smoothen the density gradation associated with the dot density or dot size. Therefore, it is possible to form an optimal dot based on the surrounding situation around the target dot and improve reproducibility of a highlight.  
     [0299] Seventh Embodiment:  
     [0300] A seventh embodiment is explained next. In FIG. 1, the photoreceptor  1  as an image carrier is composed of a flexible endless belt-like photoreceptor, and is suspended around the rotating rollers  2  and  3  to be conveyed clockwise in the figure. Those arranged around the photoreceptor  1  along the rotational direction thereof include the erasing lamp  21 , the charger  4 , the laser writing unit  5 , the developing devices  6  to  9  of C, M, Y and K, the intermediate transfer belt  10 , and the cleaning unit  15 .  
     [0301] The laser writing unit  5  is housed in a support cabinet having a slit-like aperture for exposure formed on the upper surface of the support cabinet to be incorporated in the device body. As the laser optical system  5 , an optical system integrally formed with a light emission section and a convergent optical transmission medium may be used other than the laser optical system  5 . The charger  4 , the laser writing unit  5 , and the cleaning unit  15  are arranged opposing one roller  2  of the plural rollers that suspend the photoreceptor  1  around the rollers.  
     [0302] The developing devices  6  to  9  contain developers of, for example, yellow (Y), magenta (M), cyan (C), and black (BK), respectively. The developing devices  6  to  9  include development sleeves that are close to or in contact with the belt-like photoreceptor  1  at a predetermined position, and develop a latent image on the photoreceptor belt  1  by non-contact or contact development. The intermediate transfer belt  10  functions as a transferred image carrier. The intermediate transfer belt  10  is suspended around the rotating rollers  11  and  12  and is conveyed counterclockwise when the rotating rollers  11 ,  12  are driven.  
     [0303] The photoreceptor  1  and the intermediate transfer belt  10  come into contact with each other at the rotating roller  3 . Thus, a first developed image on the photoreceptor  1  is transferred onto the intermediate transfer belt  10  by the bias roller  13  disposed inside the intermediate transfer belt  10 .  
     [0304] By repeating similar processes, second though fourth developed images are superimposed on one another on the intermediate transfer belt  10  so that the images are transferred without any positional deviation. The transfer roller  14  is located so as to come into contact with and separate from the intermediate transfer belt  10 . The cleaning unit  15  cleans the photoreceptor  1 , and another cleaning unit  16  (FIG. 2) cleans the intermediate transfer belt  10 . The cleaning unit  16  for the intermediate transfer belt  10  has the blade  16 A that is kept at a position separated from the surface of the intermediate transfer belt  10  during image formation and is kept at a position press-contacted with the surface of the intermediate transfer belt  10  as shown in FIG. 2 only during cleaning after the image formation to clean the intermediate transfer belt  10 . The reference numeral  16 B denotes the base of the blade  16 A that is disposed pivotably about the pivot.  
     [0305] The laser writing unit  5  comprises the not-shown laser diode (LD) unit, the polygon motor  5 A, the polygon mirror  5 B, the fθ lens  5 C, and the reflective mirror  5 D to emit a laser beam for forming a dot-like latent image on the photoreceptor  1 . The laser writing unit  5  expresses a density gradation by a dot density or dot size with plural dots and 8 bits, and a dot phase (a right or left writing location).  
     [0306] The process of color image formation in the image formation device thus configured briefly is performed as follows.  
     [0307] In multi-color image formation, the color image data input section can obtain data when the image pickup device scans an original draft. The data is operationally processed in the image data processor to create image data to be stored once in an image memory. The image data stored in the image memory is then read out for recording and fed to the color image formation device (printer) as a recorder.  
     [0308] A color image signal is output from the image reader discretely disposed from the color image formation device. When the color image signal is input to the laser writing unit  5 , the laser beam emitted from the not-shown semiconductor laser in the laser writing unit  5  is scanned by the polygon mirror  5 B rotationally driven by the drive motor  5 A. After passing through the fθ lens  5 C, the optical path of the scanned laser beam is bent at the reflective mirror  5 D, and then exposed to the circumference of the photoreceptor  1  that is erased by the erasing lamp  21  and is charged uniformly by the charger  4  in advance to form an electrostatic latent image thereon. The image pattern to be exposed is one of monochromatic image patterns when a desired full-color image is decomposed into colors of Y, M, C and BK.  
     [0309] Electrostatic latent images formed for different colors are developed at the developing devices of Y, M, C and BK of the rotary developing unit. Monochromatic images developed with different colors are formed in this case. The monochromatic images formed on the photoreceptor  1  are transferred onto the intermediate transfer belt  10  that rotates counterclockwise while coming into contact with the belt-like photoreceptor  1 . The color images of Y, M, C and BK are sequentially superimposed on one another on the intermediate transfer belt  10 . The color images of Y, M, C and BK superimposed on the intermediate transfer belt  10  are transferred, by the transfer roller  14 , to a transfer paper conveyed from the paper feed tray  17  to the transfer portion by the paper feed roller  18  and adjusted for timing at the regist rollers  19 . After completion of the transfer, the transfer paper is subjected to fixing at the fixing device  20  to form a full-color image on the transfer paper.  
     [0310] As shown in FIG. 2, the intermediate transfer belt  10  has the six marks  41 A to  41 F on the edge thereof. When the mark detecting sensor  40  senses an arbitrary mark, for example, the mark  41 A, a writing is started, and when it senses the mark  41 A again after one rotation, a second color writing is started. In this case, the signals corresponding to the marks  41 B to  41 F are masked by managing the number of marks so as to prevent these marks from being used as write timings. At a location slightly upstream from the contact portion of the photoreceptor belt  1  with the intermediate transfer belt  10 , the toner density detecting sensor  22  is disposed for detecting an amount of toner on the photoreceptor belt  1 .  
     [0311] In FIG. 28, for example, dither-processed 4-bit image data is latched by the latch H 4  and is also applied to the 1-line buffer L 2  through the 1-line buffer L 1 . At this point in time, the image data for the upper line of the latch H 2  is latched in the latch H 2  through the 1-line buffer L 1 . The image data for the upper line of the latch H 0  is latched in the latch H 0  through the 1-line buffer L 2 . Respective pieces of the image data latched in the latches H 0 , H 2 , H 4  are shifted in synchronization with a synchronizing signal and are latched in the latches S 0 , N 3 , H 4 , respectively. Similarly, they are shifted in synchronization with the synchronizing signal and latched in the latches (N 0 , x, N 2 ), (S 1 , N 1 , S 2 ), (H 1 , H 3 , H 5 ), respectively.  
     [0312] Thus, 4-bit image data corresponding to the following 5 dots in the main scanning direction×3 dots in the subscanning direction, can be latched in the 5×3 latches.  
     [0313] The reference numeral for a latch is also used to denote a position and density of the corresponding dot in the following explanation.  
     [0314] H 0 , S 0 , N 0 , S 1 , H 1   
     [0315] H 2 , N 3 , x, N 1 , H 3   
     [0316] H 4 , S 3 , N 2 , S 2 , H 5   
     [0317] Among the 5×3 dots, 6 dots H 0  to H 5  are spaced each 2 dots back and forth from the central dot x on the line where the central dot x exists and on the upper and lower lines thereof. Four dots S 0  to S 3  are located at the upper left, upper right, lower left and lower right positions diagonally spaced from the central dot x, respectively. Four dots N 0  to N 3  are located at the upper, right, lower and left positions of the central dot x, respectively.  
     [0318] Data on the following dot positions are applied to a dot situation determination section  3101 . It is noted that data on a dot position marked with xx indicates that the data is not supplied.  
     [0319] H 0 , S 0 , xx, S 1 , H 1   
     [0320] H 2 , N 3 , xx, N 1 , H 3   
     [0321] H 4 , S 3 , xx, S 2 , H 5   
     [0322] The dot situation determination section  3101  applies determined data=0 to the arithmetic section B through a latch  3102  if all of 4-bit data (=0 to 15) of the 12 dots H 0  to H 5 , S 0  to S 3 , N 1 , and N 3  is “0”, and applies the determined data=1 thereto in other cases,. Data on the following dot positions is fed to the arithmetic section A.  
     [0323] xx, S 0 , N 0 , S 1 , xx  
     [0324] xx, N 3 , x, N 1 , xx  
     [0325] xx, S 3 , N 2 , S 2 , xx  
     [0326] The arithmetic section A converts 4-bit data (=0 to 15) of the dots S 0  to S 3 , N 0  to N 3 , x into 8-bit data (=0 to 255) based on a bit conversion table  3103  like that as shown in FIG. 4 and FIG. 5. This conversion characteristic is just an example and is previously set so that linear output with respect to input is obtained based on the printer characteristic as shown in FIG. 26.  
     [0327] The 8-bit data is represented by s 0  to s 3 , n 0  to n 3 , and x. Then, using the 8-bit data s 0  to s 3 , n 0  to n 3 , and x, a gain Gs for 8-bit data s 0  to s 3 , and a gain Gn for 8-bit data n 0  to n 3 , an 8-bit correction coefficient G is computed and output to a correction table  3104 : 
       G=Gn Σ( nt−x )+ Gs Σ( st−x ) 
     [0328] where n, t=0 1, 2, 3.  
     [0329] The 4-bit data of the central dot x and the determined data from the dot situation determination section  3101  are fed to the arithmetic section B. The arithmetic section B outputs 4-bit data having a constant value to the correction table  3104  if the determined data=0, that is, all of 4-bit data (=0 to 15) of 12 dots H 0  to H 5 , S 0  to S 3 , N 1 , and N 3  is “0”. In addition, the arithmetic section B outputs a phase signal of Mode “0” (Right mode) to the laser writing unit  5  shown in FIG. 1. On the other hand, if the determined data=1, the arithmetic section B outputs 4-bit data of the central dot x directly to the correction table  3104  and outputs a phase signal of Mode “1” (Left mode) to the laser writing unit  5 .  
     [0330] The correction table  3104  previously stores 256 operated results (conversion tables) for converting 4-bit data of the central dot x into 8-bit data in order to smoothen the gradation in accordance with the correction coefficient G as shown in FIG. 27. One of the conversion tables is selected based on the correction coefficient G from the arithmetic section A. The 4-bit data of the central dot x is converted into 8-bit data using the conversion table. The correction table  3104  also stores a conversion table that has a characteristic for smoothening a density gradation by plural dots and a dot density or dot size if all the 4-bit data (=0 to 15) of dots H 0  to H 5 , S 0  to S 3 , N 1 , and N 3  is “0”.  
     [0331] Write phases for the printer are explained next with reference to FIG. 9. Normally, a dot is written in a phase of Mode “1” (Left mode). In this case, the dot width grows from the center to the right. On the other hand, in a phase of Mode “0” (Right mode), the dot width grows from the center to the left. Therefore, the left and right dots are linked with each other, and thus the dot can be emphasized with natural touch.  
     [0332] Eight Embodiment:  
     [0333]FIG. 29 is a block diagram that shows a system configuration of an image formation device according to an eighth embodiment. In the figure, image information in a command format such as line command or text command is sent from an external device such as a personal computer (PC)  3301  to a printer controller  3302  for the image formation device as a printer. When receiving the command, the printer controller  3302  converts the image information into a bit map format based on the command and sends image data on a line basis to a printer engine  3303 . The printer engine  3303  blinks or modulates the laser diode (LD) based on the sent image data to form an actual image.  
     [0334]FIG. 30 is a block diagram that shows a brief configuration of the printer controller  3302  shown in FIG. 29. The printer controller  3302  in this embodiment comprises a PC I/F section  3401  that receives an image command sent from the personal computer  3301  to the printer controller  3302 , a frame RAM  3402  for storing image data expanded from the command to bitmap data, a ROM  3403  for storing dither thresholds and so forth, a CPU  3404  that controls each section of the printer including the entire data processing, and an engine I/F  3405  for transferring finally processed data to the printer engine  3303 .  
     [0335] The printer controller  3302  thus configured analyzes the image command sent from the personal computer  3301  to the printer controller  3302  as shown in the flowchart of FIG. 31 (step  501 ). Then, the printer controller  3302  rasterizes the image data based on the input command (step  502 ). If the input command is a line command, the printer controller  3302  executes line dither processing (steps  503 ,  504 ) and transfers the data to the printer engine  3303  (step  506 ). To the contrary, if the input command is not a line command, it executes image dither processing (step  505 ), and transfers the data to the printer engine  3303  (step  506 ).  
     [0336]FIG. 32 shows dither thresholds, in which FIG. 32( a ) shows dither thresholds for thin lines and FIG. 32( b ) shows dither thresholds for images. Therefore, this embodiment uses the dither thresholds of FIG. 32( a ) at step  504  and the dither thresholds of FIG. 32( b ) at step  505 .  
     [0337] In the eighth embodiment, the original image has 49 halftones. One dot has a multilevel of 2 bits. Therefore, threshold levels of the halftone are set to be first level through third levels. For the halftone 0, all dots are “0”. In the thin-line dither processing, for the halftones “1” and “2”, all dots have the first level. For the halftones “3” through “25”, only the corresponding dots have the second level. For the halftones “26” through “48”, only the corresponding dots have the third level.  
     [0338] In the image dither processing, as shown in FIG. 32( b ), a dot located at a position spaced 2 to the left and 2 to the lower from the upper left has the first level for the halftone “1”. It has the second level for the halftone “2” and the third level for the halftone “3”. Similarly, a dot located at a position spaced 4 to the left and 4 to the lower from the upper left has the first level for the halftone “4”. It has the second level for the halftone “5” and the third level for the halftone “6”. Similarly, all other dots have the third level for the halftones up to “48”.  
     [0339]FIG. 33 is a block diagram that shows a brief configuration of the major part of the printer engine  3303 . The printer engine  3303  includes first and second 1-line buffers L 1  and L 2 , 8 latches H 0  to H 7 , a latch x corresponding to a target pixel, a counter  3701  that receives the output data of the latches H 0  to H 7 ; a latch x for storing the data of the target pixel, and a correction table  3702  that receives the output data from the counter  3701  to correct the data of the target pixel from the latch x and outputs it as an LD write signal.  
     [0340] The 2-bit data from the printer controller  3302  is fed to the latch H 5  and the first 1-line buffer L 1  in synchronization with a synchronizing signal, not shown. In synchronization with the next synchronizing signal, the data of the latch H 5  is fed to the latch H 6 , and the data of the first 1-line buffer L 1  is fed to the latch H 3  and the second 1-line buffer L 2 . Similarly, the data of H 0 , H 3 , H 5  are fed to H 1 , x, H 6 , and the data of H 1 , x, H 6  are fed to H 2 , H 4 , and H 7 , respectively. The values in the pixels H 0  to H 7  other than the target pixel x are supplied to the counter  3701  that counts the number of values close to “0” or the number of dots when the dots are present. The number of counts at the counter  3701  and the data of the target pixel x are input to the correction table  3702 . The correction table  3702  converts the data of the target pixel x based on a previously stored table, for example, as shown in FIG. 34, in accordance with the output from the counter  3701 , to output write data to LD.  
     [0341] As shown in FIG. 34, for writing to the LD, the data is modulated in 255 levels. In the table, if the counter data of the counter  3701  associated with 8 pixels adjacent to the target pixel x is “0” through “7”, that is, a space pixel is present in the surrounding of the target pixel, the input data for the target pixel is converted into “85” in the first level, “170” in the second level, and “255” in the third level, respectively. To the contrary, if the counter data of the counter  3701  associated with the 8 pixels is 8, that is, there are pixels all around the target pixel, the data is converted into “30” in the first level, “80” in the second level, and “255” in the third level, respectively.  
     [0342] According to the seventh and eighth embodiments as explained above, if the target dot is a single dot at least in the main scanning direction and spaces of two dots are present back and forth in the main scanning direction, the writing level of the target dot is controlled to smoothen the density gradation by plural dots and a dot density or dot size. Therefore, it is possible to form an optimal dot based on the surrounding situation around the dot to improve reproducibility of a highlight.  
     [0343] In addition, if the target dot is a single dot at least in the main scanning direction and spaces of two dots are present back and forth in the main scanning direction, the writing position of the target dot is shifted to the right or left to smoothen the density gradation by plural dots. Therefore, it is possible to form an optimal dot based on the surrounding situation around the dot to improve reproducibility of a highlight.  
     [0344] If a command from an external device is related to line formation, the unit that carries out pseudo halftone processing is switched to processing of improving line reproducibility. Therefore, it is possible to achieve optimal line reproduction.  
     [0345] The unit that carries out pseudo halftone processing performs conversion with the level “1” that is at least the lowest level in multivalue levels unless the data is “0”. Therefore, it is possible to achieve optimal line reproduction.  
     [0346] Peripheral data around the target dot is detected, and a writing value in multivalue levels is switched based on the detected data. Therefore, it is possible to form an optimal dot based on the surrounding situation around the dot to achieve optimal line reproduction.  
     [0347] The unit that carries out pseudo halftone processing switches between a distributed pseudo halftone processing for pseudo halftone processing for lines and a centralized pseudo halftone processing for those other than the line pseudo halftone processing. Therefore, it is possible to achieve optimal reproduction on line.  
     [0348] As explained above, according to the image formation device of the present invention, the data corresponding to the target dot is increased based on the result of detection by the peripheral dot detecting unit and the result of detection by the space dot detecting unit. Therefore, it is advantageously possible to achieve optimal dot reproduction based on the surrounding situation around the target dot and improve reproducibility of a highlight.  
     [0349] According to the image formation device of the invention, an arbitrary amount of additional data is added to the data corresponding to the target dot. Therefore, it is advantageously possible to achieve further optimal dot reproduction because the additional data can be varied.  
     [0350] According to the image formation device of the invention, the presence or absence of a peripheral dot located at a minimal distance from the target dot is detected and the data corresponding to the target dot is increased based on the detected result. Therefore, it is advantageously possible to achieve optimal dot reproduction based on the surrounding situation around the target dot and improve reproducibility of a highlight.  
     [0351] According to the image formation device of the invention, the phase of the target dot is shifted based on empty states of the peripheral dots in the main and subscanning directions. Therefore, it is advantageously possible to achieve optimal dot reproduction in consideration of the empty states of the peripheral dots.  
     [0352] According to the image formation device of the invention, the phase of the target dot is shifted to the opposite side to the space dot. Therefore, it is advantageously possible to achieve further optimal dot reproduction because the target dot can be emphasized while remaining the space dot.  
     [0353] According to the image formation device of the invention, the target dot is subjected to level conversion based on the result of detection by the number-of-areas detecting unit. Therefore, it is advantageously possible to achieve optimal dot reproduction even for a high-resolution dot based on the surrounding situation around the target dot.  
     [0354] According to the image formation device of the invention, a detection area is spread in the main and subscanning directions. Therefore, it is advantageously possible to allow influence of the surrounding (wide range) over the target dot to be reflected to the data conversion of the target dot.  
     [0355] According to the image formation device of the invention, plural detection areas are distributed among areas each spreading in the main and subscanning directions. Therefore, it is advantageously possible to allow a degree of the influence of the peripheral dot over the target dot to be reflected to the data conversion of the target dot.  
     [0356] According to the image formation device of the invention, the conversion table is applied to switch the degree of the level conversion based on the detected result. Therefore, it is advantageously possible to perform optimal data conversion automatically.  
     [0357] According to the image formation device of the invention, the target dot is subjected to level conversion based on the result of detection by the detecting unit. Therefore, it is advantageously possible to achieve optimal dot reproduction even for a high-resolution dot based on the surrounding situation around the target dot.  
     [0358] According to the image formation device of the invention, the set of peripheral dots is designed to have the same resolution in the main and subscanning directions. Therefore, it is advantageously possible to achieve optimal dot reproduction in the main and subscanning directions based on the surrounding situation around the target dot.  
     [0359] According to the image formation device of the invention, the target dot is designed to have the same resolution in the main and subscanning directions. Therefore, it is advantageously possible to achieve optimal dot reproduction in the main and subscanning directions based on the surrounding situation around the target dot.  
     [0360] According to the image formation device of the invention, the target dot is subjected to level conversion based on the state of the peripheral dots in the adjacent area to the target dot and plural areas. Therefore, it is advantageously possible to achieve optimal dot reproduction even for a high-resolution dot based on the surrounding situation.  
     [0361] According to the image formation device of the invention, one of the level conversion tables is selected based on the level state of the peripheral dot in the adjacent area. Therefore, it is advantageously possible to achieve optimal dot reproduction corresponding to a halftone processing.  
     [0362] According to the image formation device of the invention, the level conversion when the number of the peripheral dots that are present is zero is executed separately from the level conversion for the number other than zero. Therefore, it is advantageously possible to reduce a memory area required for management as compared to that for integrally managing both cases.  
     [0363] According to the image formation device of the invention, an arbitrary dot is generated based on the result of detection by the detecting unit even if the target dot has a level of zero. Therefore, it is advantageously possible to improve dropout of a single dot and failure of reproducibility.  
     [0364] According to the image formation device of the invention, when the dot image is written into the medium with multiple beams, respective positions of the target dot in the subscanning direction corresponding to the beams are laid out on positions corresponding to an integral multiple of the number of the beams. Therefore, it is advantageously possible to minimize the use of line buffers because the target dot can be converted per plural lines.  
     Industrial Applicability  
     [0365] As explained above, the image formation device according to the present invention is suitable for an image formation system applicable to a copier, a printer, a facsimile, and the like, that modulates light or ion flow based on image data to be applied to a recording medium to form a dot image on the recording medium based on an electrophotographic method.