JP2009135885A - Image forming apparatus, image forming method, and print data generation program - Google Patents

Abstract

An image forming apparatus that performs a process for supplying a color material for each color, and that can perform a correction process for a so-called registration error caused by the process with higher quality. To do.
An image forming apparatus that uses a plurality of color materials for image formation and performs image formation based on bitmap data in which each pixel has a gradation value of each color of the color material. Of these, a correction unit that executes a correction process for correcting the gradation value for the bitmap data in a correction target region that is a single color region and is adjacent to a pixel of another color that does not include the single color Among the correction target areas, the correction process is not performed on a predetermined area adjacent to the white pixel.
[Selection] Figure 2

Description

  The present invention relates to an image forming apparatus that performs a process for supplying a color material for each color, and more particularly to an image forming apparatus that can perform a correction process for a so-called registration error caused by the process with high quality. .

  In an image forming apparatus such as a laser printer, the process of supplying each color material to a sheet, an intermediate medium or a photoconductor and attaching it is performed independently for each color. Accordingly, there may be a problem that the images of the respective colors to be formed are relatively displaced due to the mechanical accuracy of the apparatus. When such misregistration (also referred to as color misregistration) occurs, for example, a white part that does not originally exist at the boundary between the character and the background appears (white spots), which adversely affects the output quality. In order to prevent this, processing for correcting image data to be output has been performed in advance.

  Japanese Patent Application Laid-Open No. 2004-228667 proposes an apparatus that can effectively prevent so-called edge lightening and perform high-speed processing in the technical field.

Japanese Patent Application Laid-Open No. 2004-228561 discloses a device that performs a trapping process in which an object looks as large as an actual object even when a plate displacement occurs.
Japanese Patent No. 3852234 JP 2002-165104 A

  However, there is a case where an adverse effect is caused by performing a correction process for preventing a problem due to the registration error. For example, in the above correction processing, processing for adding a color that the region originally did not have to the correction target region is usually performed, but if the region is adjacent to a white part, Depending on the deviation, a color that does not exist originally appears around the white color, which is not preferable.

  In the said patent document, consideration is not made about this point.

  Accordingly, an object of the present invention is an image forming apparatus that performs a process for supplying a color material for each color, and an image that can perform a correction process for a so-called registration error caused by the process with higher quality. Forming apparatus, and the like.

  In order to achieve the above object, according to one aspect of the present invention, an image is formed based on bitmap data in which a plurality of color materials are used for image formation and each pixel has a gradation value of each color of the color material. The image forming apparatus that performs the correction for the bitmap data of the correction target area adjacent to a pixel that is a single color area of the image formation target and does not include the single color. A correction unit that executes a correction process for correcting a gradation value, and the correction process is not performed for a predetermined area adjacent to a white pixel in the correction target area;

  Furthermore, in the above invention, according to one aspect, the correction unit corrects the bitmap data for a predetermined area adjacent to the white pixel after executing the correction process for the correction target area. It returns to the state before a process, It is characterized by the above-mentioned.

  Furthermore, in the above invention, a preferable aspect is characterized in that the single color is black.

  Furthermore, in the above invention, a preferable aspect is characterized in that the correction processing is executed for a predetermined region on the pixel side made of another color not including the single color in the correction target region. .

  In order to achieve the above object, according to another aspect of the present invention, the image formation is performed based on bitmap data in which a plurality of color materials are used for image formation and each pixel has a gradation value of each color of the color material. In the image forming method in the image forming apparatus, the bitmap data in the correction target area adjacent to a pixel of another color that does not include the single color, of the image formation target, is a single color area. On the other hand, there is a correction process for executing a correction process for correcting the gradation value, and the correction process is not performed for a predetermined area adjacent to the white pixel in the correction target area. It is.

  In order to achieve the above object, according to still another aspect of the present invention, a plurality of color materials are used for image formation, and each image is based on bitmap data in which each pixel has a gradation value of each color of the color material. A print data generation program that causes the host device of the image forming apparatus to generate the bitmap data of the image forming apparatus that performs the formation is a single color area of the image forming target, and does not include the single color. A correction step of executing a correction process for correcting the gradation value for the bitmap data in the correction target area adjacent to the pixel of the color of The correction process is not performed for a predetermined area adjacent to a white pixel.

  Further objects and features of the present invention will become apparent from the embodiments of the invention described below.

  Embodiments of the present invention will be described below with reference to the drawings. However, such an embodiment does not limit the technical scope of the present invention. In the drawings, the same or similar elements are denoted by the same reference numerals or reference symbols.

  FIG. 1 is a configuration diagram according to an embodiment of a printer which is an image forming apparatus to which the present invention is applied. The printer 2 shown in FIG. 1 is a printer to which the present invention is applied. For a target region for correction processing for so-called registration misalignment, a portion adjacent to a white pixel is processed so as not to execute the correction processing. This is intended to prevent the harmful effects caused by the correction processing and to perform higher quality processing.

  A host computer 1 shown in FIG. 1 is a host device that makes a print request to the printer 2, and is composed of a personal computer or the like. The host computer 1 includes a printer driver 11. When a print request is made, the printer driver 11 generates print data including image data and a control command based on a user operation or the like and transmits the print data to the printer 2. Here, it is assumed that the data transmitted from the printer driver 11 to the printer 2 is described in PDL. The printer driver 11 can be configured by a program that executes the above-described processing, a control device (not shown) of the host computer 1 that executes processing according to the program, and the like. The program for the printer driver 11 can be installed in the host computer 1 by downloading from a predetermined site via a network such as the Internet or from a storage medium such as a CD.

  Next, as shown in FIG. 1, the printer 2 is a so-called laser printer including a controller 21, an engine 22, and the like.

  The controller 21 receives a print request from the host computer 1 and issues a print instruction to the engine 22. As shown in FIG. 1, the controller 21 includes an I / F 23, a CPU 24, a RAM 25, a ROM 26, and an engine I / F 27. Prepare.

  The I / F 23 is a part that receives the print data transmitted from the host computer 1.

  The CPU 24 is a part that controls various processes performed in the controller 21. When a print request is received from the host computer 1, the CPU 24 performs predetermined image processing on the image data included in the received print data and performs the engine 22. It controls processing for generating bitmap data (plane data for each color) to be output to the side, processing for instructing an appropriate print processing to the engine 22 by interpreting a control command included in the print data, and the like. Further, the CPU 24 executes a correction process as a measure against registration misregistration regarding the process of generating the bitmap data. The printer 2 is characterized by the correction process, and the specific contents thereof will be described later. . Note that the processing executed by the CPU 24 is mainly performed according to a program stored in the ROM 26.

  The RAM 25 is a memory that stores received print data, image data after each process, and the like. Bit map data (plane data) of each color described above, and type data (type plane) generated for the bit map data Is stored. Details of these bitmap data and type data will be described later.

  The ROM 26 is a memory that stores a program and the like of each process executed by the CPU 24.

  Next, when the engine 22 executes printing, the engine I / F 27 reads the image data (bitmap data after the correction process) stored in the RAM 25 described above at a predetermined timing and stores them in a predetermined manner. This is the part that controls the interface between the controller 21 and the engine 22 side, which is handed over to the engine 22 side after processing. Although not shown, the engine I / F 27 is provided with a memory for temporarily storing data, a decompression unit, a screen processing unit, and the like, and is compressed data with respect to image data read from the RAM 25. Decompression and screen processing to convert to dot data. Further, the engine I / F 27 is specifically composed of an ASIC.

  Next, the engine 22 includes a mechanical controller and a printing mechanism (not shown). The printing mechanism includes a photosensitive drum, a charging unit, an exposure unit, a developing device, a transfer unit, and the like (not shown). It is done. When printing is performed, the photosensitive drum is charged by the charging unit, and the charged photosensitive drum is irradiated with a beam from a light source such as a laser or an LED array built in the exposure unit to form a latent image by static electricity. Thereafter, the latent image is developed into an image by the developing material by a developing device including a toner cartridge that accommodates the developing material (toner), and the toner image developed by the transfer unit is transferred to a printing medium such as paper, and is fixed by the fixing unit. It is fixed and discharged out of the printer 2. In this printer 2, color materials of CMYK colors are used as developing materials. Among the supply of color materials to the photosensitive member, the supply of color materials to the intermediate transfer medium, and the supply of color materials onto the print medium, In at least one process, the color material is supplied independently for each color. Accordingly, in the printer 2 as well, there is a possibility that the image position on the print medium is shifted depending on the color.

  In the printer 2 having the configuration as described above, when a print request is received from the host computer 1, the print data is interpreted, and the gradation value of each color is obtained for each pixel from the image data in the PDL format. Bitmap data is generated. The bitmap data is composed of CMYK color plane data as color materials for one print medium, and is stored in the image buffer of the RAM 25. Thereafter, correction processing is performed on the bitmap as a measure against misregistration, bitmap data after the correction processing is read from the engine I / F 27, and after the processing described above, printing processing in the engine 22 is performed. Executed.

  As described above, the printer 2 has a feature in the correction process as a countermeasure for the registration error, and the specific contents of the process will be described below.

  FIG. 2 is a flowchart illustrating the overall procedure of the correction process performed by the CPU 24. As described above, when the generation of bitmap data is completed by the CPU 24 upon reception of a print request, the correction process is started, and first, a labeling process is performed (step S100). Specifically, based on the generated bitmap data, each pixel is classified into a predetermined group, and a label corresponding to the classified group is added to each pixel. More specifically, the above-described type data (type plane) is generated.

  FIG. 3 is a diagram illustrating bitmap data and type data. FIG. 3A illustrates the generated bitmap data, which is composed of a C plane, an M plane, a Y plane, and a K plane as described above. Each pixel (p in the figure) of each plane has a gradation value of each color. Here, each pixel is represented by 0 to 255, assuming that each color is expressed by 256 gradations of 0 to 255. It has either value.

  FIG. 3B illustrates the type plane generated from the bitmap data shown in FIG. 3A, and each pixel (p in the figure) has the label. In the printer 2, the predetermined group includes five types of “white”, “color”, “mixed color K”, “single color K light”, and “single color K dark”, and all values of CMYK of the bitmap data are included. Pixels with 0 are classified as “white”, and any of CMY of the bitmap data is a non-zero value and pixels with a K value of 0 are classified as “color”, and the CMY of the bitmap data A pixel having a non-zero value and a non-zero K value is classified as “mixed color K”, and all the CMY values of the bitmap data are 0 and the K value is a predetermined value a (for example, 4 ≦ a ≦ 255) is classified as “monochromatic K light”, and pixels having all the CMY values of the bitmap data of 0 and a K value equal to or greater than the predetermined value a are designated as “monochrome K darkness”. ".

  Therefore, the CPU 24 first classifies each pixel from the value of each plane of the bitmap data according to the above rule, and sets the label of the classified group as the value of the type plane. For example, for a pixel classified as “white”, the label is set to 0, for a pixel classified as “color”, the label is set to 1, and for a pixel classified as “mixed color K”, the label is set to 2. For a pixel classified as “monochromatic K light”, the label is set to 3, and for a pixel classified as “monochromatic K dark”, the label is set to a gradation value (a to 255) of K (plane).

  When the labeling process is completed in this way, the CPU 24 detects a correction target area of the target bitmap data using the type data (plane), and performs a process of appropriately correcting the area. (Step S200). The specific contents of such processing will be described later.

  Next, the CPU 24 executes adjustment processing based on the total amount of color material for the bitmap data after correction (step S400), and further changes processing for a portion in contact with the pixel classified as the group “white”. (Step S500) is executed. Since the adjustment process may cause a problem when the total amount of the color material attached to the print medium exceeds a predetermined value, the gradation value of each pixel after the correction is adjusted to be equal to or less than the predetermined value. In addition, the change process is to change the corrected bitmap data in order to remove the adverse effect caused by the correction for the registration error in the portion adjacent to the white area. The specific contents of these processes will be described later.

  The entire process as a countermeasure for registration misalignment is performed in such a procedure. Next, the process of step S200 described above, that is, the process of detecting and correcting the correction target area will be described in detail. FIG. 4 is a diagram illustrating bitmap data exemplified for explaining the processing. FIG. 5 is a flowchart illustrating the procedure of the processing.

  First, the CPU 24 selects one target pixel (step S210). Here, for example, the selection of pixels starts from the upper left pixel of the bitmap data, sequentially selects the right side of the row, moves to the lower row when the right end is reached, and sequentially selects from the left end to the right. This procedure is repeated. In the example shown in FIG. 4, each square indicated by p represents a pixel, and the pixels are selected in the order indicated by the arrow from the upper left.

  Next, it is checked whether or not the selected pixel of interest is “color” (step S220). That is, it is determined whether or not the pixel of interest is classified into the “color” group in the labeling process described above. Specifically, it is checked whether or not the pixel has a value of 1 with reference to the generated type plane. If the pixel does not have a value of 1, it is determined that the pixel is not “color” (No in step S220), the process relating to the pixel of interest is terminated, and the process is performed for all the pixels of the target bitmap data. If not completed (No in step S390), the next pixel of interest is selected in the above order (S210).

  In the example shown in FIG. 4, a pixel represented by white (C in the figure) is a white pixel classified into the group of “white”, and a pixel represented by gray (A in the figure) Dark gray or black pixels classified into the “monochrome K dark” group, and pixels (B in the figure) represented by dots or diagonal lines are pixels classified into the “color” group. . In this example, when the upper left pixel is the target pixel, the pixel is “white” and not “color”, so that the target pixel shifts to the pixel on the right. This process is repeated until the pixel indicated by X in the figure is selected as the target pixel.

  Returning to step S220, if it is determined that the type data of the target pixel is 1 and the pixel is “color” (Yes in step S220), one peripheral pixel of the target pixel is selected. (Step S230). FIG. 6 is a diagram for explaining peripheral pixels and detection directions. X shown in FIG. 6 represents the pixel of interest, and 8 pixels (1 to 8 in the drawing) adjacent to the pixel of interest are peripheral pixels. The numbers of the peripheral pixels illustrate the order of selection. Therefore, in this example, first, the pixel “1” is selected as the peripheral pixel. Further, the arrows shown for each peripheral pixel indicate the detection direction of the region to be corrected, which will be described below, which is performed with the peripheral pixel as a base point. Therefore, in the printer 2, it is determined whether or not correction is performed for the eight directions around the pixel, and correction processing is performed for the direction that needs correction.

  Next, it is determined whether or not the selected peripheral pixel is “monochromatic K dark” (step S240). Also in this process, if the type plane described above is referred to and the values of the peripheral pixels are a to 255, it is determined that the color is “monochromatic K dark”, and otherwise, it is not “monochromatic K dark”. to decide.

  As a result of the determination, if it is determined that the color is not “monochrome K dark” (No in step S240), the periphery ends the process, and the process for all the eight peripheral pixels for the target pixel ends. If not, that is, if the processing has not been completed for all eight directions (No in step S380), the next peripheral pixel is selected (S230). In the example shown in FIGS. 4 and 6, the peripheral pixels “2”, “4”, and “8” are not “monochromatic K dark”, and thus the processing is performed as described above. Will not be done.

  On the other hand, if it is determined that the peripheral pixel is “monochromatic K dark” (Yes in step S240), there is a K area having the same gradation value in the detection direction (main direction) of the peripheral pixel. Determine whether or not. Specifically, the type data is checked for a predetermined number b (for example, 5) pixels in the main direction and the left and right directions from the peripheral pixels, and the peripheral pixels and the gradation values are determined for these pixels. When different “single color K dark”, “single color K light”, or “mixed color K” is not included, the processing is sequentially advanced while shifting by one pixel in the main direction. If a “color” or “white” pixel appears in the main direction, it is determined that the area from the peripheral pixel to the pixel in the main direction is a K area having the same gradation value. Accordingly, it is determined that a K area having the same gradation value as that of the pixel of interest that is “color” is adjacent, and the K area in the main direction is set as a correction target. On the other hand, before the “color” or “white” pixel appears in the main direction in the process, the “monochromatic K dark”, “monochromatic K light”, or “mixed color K”, which has a gradation value different from that of the surrounding pixels. ”Appears, it is determined that there is no K area having the same gradation value in that direction, and the process is shifted to the next peripheral pixel (direction).

  More specifically, the correction target detection process for the selected peripheral pixels is realized by steps S250 to S360 in FIG. FIG. 7 is a diagram for explaining correction target detection processing when the main direction is upward.

  First, the selected peripheral pixel is set as a start pixel (step S250), and it is sequentially checked with the type data whether the gradation value of the next pixel is the same as that of the peripheral pixel in the main direction (steps S260, S270,. And S280 No). Then, if the b pixels have the same gradation value (Yes in step S280), the process shifts in either the left or right direction with respect to the main direction. Sequentially, it is checked from the type data whether the gradation value of the next pixel is the same as that of the surrounding pixels (No in steps S290, S300, and S310). Then, if b pixels have the same gradation value (Yes in step S310), the process proceeds in either the left or right direction in which the process remains (steps S320 and S330). Similarly, it is sequentially checked whether or not b pixels have the same gradation value. As a result, when the same gradation value is set for b pixels in the direction, the series of processes for the set start pixel is completed, and the next pixel is set as the start pixel in the main direction (step S350). The same processing is sequentially performed (to S260).

  In the example shown in FIG. 7, first, the peripheral pixel indicated by “0” is set as a start pixel, and the above check is performed on five pixels (pixel “1” in the drawing) in the upper direction, which is the main direction. . Next, the above check is sequentially performed for five pixels in the left direction (pixel “2” in the drawing) and five pixels in the right direction (pixel “3” in the drawing). Thereafter, the start pixel is set to a pixel (p1 in the figure) that is one pixel above the surrounding pixels, and the same processing is sequentially performed.

  In the same gradation check (S300) in the left-right direction, if the gradation is not the same (No in step S300), it is determined whether the pixel is “color” or “white”. Is checked (step S340), and if it is either “color” or “white” (Yes in step S340), the process in that direction is terminated and the process proceeds to S320. On the other hand, if it is not “color” or “white” (No in step S340), the processing of the surrounding pixels is terminated, and the process proceeds to S380.

  If a pixel that does not have the same gradation value appears in the processing in the main direction (No in step S270), it is checked in the type data whether the pixel is “color” or “white”. (Step S360). As a result, if it is not either “color” or “white” (No in step S360), the processing of the peripheral pixels is terminated, and the process proceeds to S380.

  On the other hand, if it is either “color” or “white” (Yes in step S360), as described above, the correction range for the peripheral pixel (main direction) is determined, and the process proceeds to step S370. .

  In the example shown in FIG. 4, for example, when the correction target range is detected in the upward direction of the target pixel X (solid arrow L1), the main direction described above in the direction of the arrow indicated by the dotted line in FIG. Processing in the left-right direction is performed, the processing ends at the upper “white” pixel, and the solid line arrow L1 portion is determined as the correction target range.

  In step S370, an actual correction process is performed on the bitmap data. Details of the processing will be described later.

  The processing for one peripheral pixel described above is executed for all the eight peripheral pixels described above. FIG. 8 is a diagram showing processing for the upper right peripheral pixel. In FIG. 8, similarly to FIG. 7, correction target detection processing in the main direction (upper right direction) is shown for the upper right peripheral pixel. Also in this direction, first, the main pixel and its left-right direction are checked using the peripheral pixel (0 in the figure) as the start pixel, and if necessary, the start pixel sequentially moves in the main direction to perform similar processing. Will be repeated.

  With respect to the target pixel X shown in FIG. 4 and FIG. 6, when the processing for all the peripheral pixels is performed, the solid arrows in FIG. 4 indicate five peripheral pixels (1, 3, 5, 6, and 7 in FIG. 6). Correction processing is performed until the “white” region is reached in the direction of.

  In this way, the process for one target pixel is completed (Yes in step S380), and similarly, when the process is completed for all pixels of the target bitmap data in the order described above (Yes in step S390), The correction target detection and correction processing (S200) ends.

  In the correction target detection and correction processing in the printer 2 described above, attention is paid to the “color” pixel, and the processing is performed on the dark black region of the same gradation adjacent to the pixel as the correction target. Further, as described above, the printer 2 checks the predetermined width in the left-right direction with respect to the main direction in the processing for the peripheral pixels, and “monochrome K dark”, “ If “single color K light” or “mixed color K” appears, correction processing is not performed for the main direction. This is because the “monochromatic K dark” pixels present in the main direction are determined not to be part of a dark black area of the same gradation but to a part of a photographic image or a black gradation area. Therefore, the printer 2 does not perform the correction process on the photographic image or the black gradation area.

  By performing such processing, the printer 2 can effectively correct white spots caused by misregistration that occur outside of black characters and figures having a color background, and can also produce photographic images and black. The original color is maintained in the gradation area, and the image quality is not deteriorated.

  In the example shown in FIG. 4, the above correction process is performed on the dark gray or black pixel area indicated by A.

  Next, the above-described correction process (S370) will be described in detail. FIG. 9 is a flowchart illustrating the procedure of the correction process for the detected correction location. As described above, when it is decided to perform the correction process on one peripheral pixel of a certain target pixel (Yes in S360), it is checked whether or not the K gradation value of the peripheral pixel is 255. (Step S371). That is, it is determined whether it is true black, which is the highest gradation of K, or dark gray, which is the predetermined value a or more. Specifically, the determination is made with reference to the type data of the surrounding pixels.

  As a result, if the K gradation value of the peripheral pixel is 255 (Yes in step S371), the gradation value of each color of the pixel of interest (“color”) is acquired from the bitmap data (step S372). .

  On the other hand, if the K gradation value of the peripheral pixel is not 255 (No in step S371), the composite K corresponding to the gradation value of the peripheral pixel is referred to by referring to a composite K correspondence table prepared in advance. The gradation value of each color is acquired (step S373). FIG. 10 is a diagram illustrating an example of the composite K correspondence table. Here, the composite K represents a single color K expressed by a mixed color of CMYK, and the gradation value of each color is determined by the printer model or the like for the single color K value. In the example shown in FIG. 10, for example, when the gradation value of a single color K is 203, the gradation values of each color of the composite K representing that color are 128 (C) and 114 (M), respectively. 96 (Y) and 139 (K). In the above process, such a table is referred to, and the gradation value of each corresponding color is acquired. The correspondence table is stored in the ROM 26 or the like.

  Next, when the above-described gradation value acquisition (S372 or S373) is performed, first, the peripheral pixel is selected (step S374), and the correction process using the acquired gradation value for the pixel is performed (step S375). ). That is, the bitmap data of the pixel is changed according to the acquired gradation value.

  When the gradation value of the target pixel is acquired in the acquisition process (S372), a process of adding the acquired gradation value to the bitmap data value at that time is performed. When the correction processing is performed for the pixel for the first time, the gradation value of each color of the bitmap data is (0, 0, 0, 255) in the order of CMYK, so the pixel of interest (“color”, K = 0) CMY value cmy is added and the bitmap data of the pixel is corrected to (c, m, y, 255). For example, if the gradation value of the target pixel is (100, 0, 0, 0), it is corrected to (100, 0, 0, 255). If the pixel has already been subjected to the correction process and CMY has a value other than 0, the average value of the value already added and the value added this time is corrected for each color. Value. For example, when correction processing is performed with the gradation value of the target pixel being (50, 0, 0, 0) in the state of (100, 0, 0, 255), it is referred to as (75, 0, 0, 255). It is corrected to the value.

  When the composite K gradation value is acquired in the acquisition process (S373), the bitmap data at that time is replaced with the acquired composite K gradation value. For example, in the case of (0, 0, 0, 203), the value is changed to (128, 114, 96, 139) shown in the table of FIG.

  When the correction for the pixel is completed in this way, the next pixel is selected in the main direction (step S376). If the pixel is not “white” or “color” (No in step S377), the process is performed. Returning to S375, the correction processing described above is performed for the selected pixel.

  This next pixel selection and correction process is repeated until reaching the “white” or “color” pixel. If the “white” or “color” pixel is reached (Yes in step S377), the correction process (S370) is performed. ) Ends. Whether the pixel is “white” or “color” is determined based on the type data described above.

  With the processing described above, processing is executed for one peripheral pixel (one direction of the target pixel). Specifically, it is a column of dark gray pixels having the same gradation value continuing from the “color” pixel as the target pixel in the direction of the peripheral pixel, and “white” or “color” on the opposite side of the target pixel. ”Is applied to the column in contact with the pixel“ ”, and the bitmap data has any one of CMY gradation values for the pixel in the column. In the example illustrated in FIG. 4, for example, with respect to the upward direction of the target pixel X, correction processing is performed on the pixels in the column indicated by the solid line arrow L1.

  As described above, even when the supply process of the K color material is shifted in the direction away from the target pixel due to the registration shift, the color of a color other than K is displayed in the region adjacent to the target pixel. Since the image data is supplied from the material, so-called white spots do not occur.

  Further, in the printer 2, the correction process differs depending on the K gradation value of the correction target region as described above, and the color of the pixel of interest is added if the maximum gradation value (255) is greater than or equal to a predetermined gradation value. If it is dark gray, it will be replaced with composite K. This is because if the color of the pixel of interest is added to a gray portion that is not true black, the color may visually change, leading to degradation of image quality. By using the composite K for such a portion, This harmful effect can be prevented.

  Next, the adjustment process (S400) based on the total amount of the color material described above will be described. When the processing up to the correction of the entire bitmap data as a target is completed by the above-described processing, the CPU 24 determines in advance for each pixel the total gradation value of each color of the bitmap data at that time. Check whether the total amount is exceeded. For the exceeding pixels, the bitmap data is corrected so that the total of the gradation values of each color is within the total amount. Specifically, each CMY tone value is a value obtained by proportionally distributing the remainder obtained by subtracting the K tone value from the total amount according to each CMY tone value at that time. For example, when the bitmap data at that time is (255, 0, 255, 255) and the total amount is 612 (240% with the maximum gradation value 255 as 100%), the value of the bitmap data Is corrected to (178, 0, 178, 255). By performing such total amount adjustment processing, it is possible to prevent the total amount of the color material to be adhered to the print medium from being too large and causing problems.

  Next, the specific processing content of the change processing (S500) for the portion in contact with the above-described “white” will be described. FIG. 11 is a flowchart illustrating the procedure of the change process.

  When the total amount adjustment process (S400) described above is completed, the CPU 24 detects an area adjacent to the “white” pixel and subjected to the above-described correction process (S370), and the detected area is bitmapped. Perform data change processing. Specifically, in the same manner as the detection of the correction location described with reference to FIG. 5, each pixel is sequentially selected as the target pixel, and in the case of the “white” target pixel, correction is performed in the surrounding eight directions. It is detected whether or not the direction is corrected, and a predetermined change process is executed for the corrected direction. More specifically, the process is executed as follows.

  First, each pixel of the bitmap data is selected as a pixel of interest in the same order as in the case of detecting a correction location (step S501). Whether or not the pixel is “white” is determined based on the type data (step S502). If it is not “white”, the next pixel is selected as the target pixel (No in S502, No in S510, and S501). .

  On the other hand, if it is “white” (Yes in step S502), one peripheral pixel is selected (step S503) as in the case of detecting the correction portion, and whether or not the pixel is “monochromatic K dark”. Is determined from the type data (step S504).

  If it is not “single color K dark” (No in step S504), it is determined that there is no correction portion in that direction, the process proceeds to the next direction, and the next peripheral pixel is selected (No in S509). S503).

  On the other hand, if it is “Monochrome K Dark” (Yes in Step S504), the next pixel is selected in the main direction (Step S505), and it is checked based on the type data whether the pixel is “Color”. (Step S506). If it is not “color” (No in step S506), it is checked whether or not the pixel is “monochromatic K dark” having the same gradation value as the surrounding pixels (step S507). If it is “monochrome K dark” with the same gradation value (Yes in step S507), the process returns to S505 to select the next pixel in the main direction.

  In this way, the process proceeds sequentially in the main direction until reaching a “color” pixel or a pixel that is not “monochromatic K dark” having the same gradation value as the peripheral pixel, and has the same gradation value as that of the peripheral pixel. When a pixel that is not “monochrome K dark” has been reached (No in step S507), it is determined that there is no corrected area in that direction, and the process proceeds to the next direction (No in S509, S503). .

  On the other hand, when the pixel reaches “color” (Yes in step S506), it is determined that there is an area corrected in the direction, and bitmap data change processing is performed (step S508). Specifically, the correction processing is performed on the pixel on the target pixel (“white”) side in the pixel row subjected to the correction processing between the pixel of interest (“white”) and the “color” pixel. Change back to the previous bitmap data state. That is, the gradation values of colors other than K are set to zero.

  More specifically, when the K gradation value of the corrected pixel is 255, the gradation value of the added target pixel (“color”) is erased and the corrected pixel is applied. If the gradation value of K is not 255, the composite K representation is returned to the original monochrome K representation. In addition, the range in which the change process is performed is a portion in which a predetermined number of pixels are excluded from the “color” pixel side in the pixel row subjected to the correction process. The predetermined number is a value of a maximum positional shift between colors that can occur due to a registration shift. That is, for example, when there is a possibility that the position of a maximum of 5 pixels may be shifted due to a registration error, the predetermined number is set to 5. When the number of pixels included in the pixel row is less than the predetermined number, the above change is applied to one pixel on the “white” side.

  FIG. 12 is a diagram for explaining the change process. FIG. 12A shows a case where correction is performed on a “monochromatic K dark” pixel column with K = 255, and then the above-described change processing is performed due to contact with a “white” pixel at the left end. Yes. In the figure, “100” indicates that 100% of the gradation value of the “color” pixel at the right end is added to the pixel below it. In this case, the predetermined number described above is 5, and therefore, the five pixels on the “color” pixel side are not changed, and the five pixels on the “white” pixel side are changed and changed to “100”. The addition has been erased.

  The example shown in FIG. 12B is a case where a pixel row of “monochromatic K dark” with K = 255 is sandwiched between “color” pixels on both sides, and is not in contact with “white” pixels. The processing is not performed, and the correction processing result (“100”) remains as it is.

  FIG. 12C shows a case where the above-described change processing is performed by correcting the “single color K dark” pixel row other than K = 255 and then contacting the “white” pixel at the left end. Show. As in the case of FIG. 12A, the five pixels on the right “color” pixel side remain in the composite K state by the correction process, and the five pixels on the “white” pixel side remain. The original single color K is obtained by the change process.

  The example shown in (d) of FIG. 12 is a case where a pixel row of “monochromatic K dark” other than K = 255 is sandwiched between “color” pixels on both sides, and is not in contact with “white” pixels. The processing is not performed, and the correction processing result (composite K) remains as it is.

  In the above description, the result of the correction process is left as it is for a predetermined number of pixels on the “color” pixel side, but the value of “color” added by the correction process goes to the “white” pixel side. You may make it reduce gradually. For example, the value can be decreased linearly so that the additional amount becomes 0 at the pixel next to a predetermined number of pixels. In the example shown in D of FIG. 4, 100% gradation value of the “color” pixel on the right side is added to the rightmost pixel of the correction target pixel row, and sequentially 80%, 60%, The added gradation values of 40% and 20% are reduced, and the sixth pixel is not corrected.

  Returning to FIG. 11, when the change process (S508) is performed as described above, the process for the direction (peripheral pixels) is completed.

  When the process as described above is completed for all eight directions (Yes in step S509), the process for the pixel of interest ends. Similarly, when the process is completed for all the pixels of the bitmap data (Yes in step S510), the change process (S500) is terminated.

  As described above, in this printer 2, correction processing as a measure against registration displacement is performed on a black or dark gray area adjacent to “color”, that is, any one of CMY colors is added, but the area is “white”. If it touches, the addition of the color on the “white” side is canceled. As a result, when the K color material is shifted in the direction away from the “white” due to the misregistration, it is possible to prevent a problem that the CMY color added by the correction process which is not necessary originally appears. At that time, since the necessary amount of the corrected area remains on the “color” side, there is no problem in the countermeasure against the misregistration on the “color” side.

  In the above description, after the correction process is performed on all the correction target areas of the image formation target, the change process of the portion in contact with the “white” is performed. However, the correction process and the above process are performed for each correction target area. The process may be performed according to another processing procedure such as a change process.

  In the present embodiment described above, the correction process (the process shown in FIG. 2) as a measure against registration error is the process of the CPU 24 according to the program. However, the correction process is executed by an ASIC process such as the engine I / F 27. May be. In the printing system that generates the bitmap data on the host computer 1 side, the correction process may be executed by the printer driver 11. In this case, the corrected data is transmitted to the printer 2 and the same printing is executed.

  As described above, in the printer 2 according to the present embodiment, correction processing as a measure against registration deviation is performed on a correction target region that is a single color region and is in contact with a pixel having a color other than the color. Then, a change process is performed on the portion of the correction target area that is in contact with the white pixel, and the original color is restored. Therefore, even in the correction target region, the correction process is not performed for a predetermined portion adjacent to the white pixel. Thereby, when the color material of the single color is shifted in the direction away from the white pixel due to misregistration, it is possible to prevent a problem that an unnecessary color added by the correction process appears. In the correction process, since a necessary amount of the corrected region remains on the side of the pixel having a color other than the single color, there is no hindrance to the measure against the registration error on the pixel side.

  In the printer 2, correction processing as a measure against registration misalignment is executed in units of pixels after the bitmap data is generated. First, labeling for identifying each pixel is executed, a correction target portion is detected using data for identifying each pixel obtained by the labeling, and correction is executed based on the detection result. Therefore, there is no omission of the correction target as in the object unit process, and a reliable process can be executed, and the process can be performed simply and at high speed by the labeling.

  The correction target is a “monochrome K dark” area of the same gradation adjacent to the “color” area, and colors other than K are added to the area. Therefore, even if the position of K shifts away from the “color” region due to misregistration, so-called white spots can be prevented. That is, it is possible to effectively prevent problems due to the register misalignment that occurs most frequently in business use.

  In addition, the above-described processing does not perform correction processing on a region such as a photographic image in which K and other colors are mixed or a region having a gradation of K, so that the image quality of the region is not deteriorated. .

  Further, in the correction target detection process described above, since it is checked whether or not correction is performed in all directions of the target pixel, it is possible to take a reliable countermeasure against misregistration without missing.

  In the above embodiment, the image forming apparatus to which the present invention is applied is a printer. However, the present invention can also be applied to a copying machine or the like.

  The protection scope of the present invention is not limited to the above-described embodiment, but covers the invention described in the claims and equivalents thereof.

1 is a configuration diagram according to an embodiment of a printer which is an image forming apparatus to which the present invention is applied. FIG. It is the flowchart which illustrated the whole procedure of the correction process which CPU24 performs. It is the figure which illustrated bitmap data and classification data. It is a figure which shows the bitmap data illustrated in order to demonstrate the detection of correction | amendment object, and the process of correction | amendment. 5 is a flowchart illustrating an example of correction target detection and correction processing. It is a figure for demonstrating a surrounding pixel and a detection direction. It is a figure for demonstrating the correction target detection process in case a main direction is up. It is the figure which showed the process about the upper right peripheral pixel. It is the flowchart which illustrated the procedure of the correction process with respect to the detected correction | amendment location. It is the figure which illustrated the correspondence table of composite K. It is the flowchart which illustrated the procedure of the change process of the part which touches white. It is a figure for demonstrating the change process of the part which touches white.

Explanation of symbols

  1 host computer, 2 printer, 11 printer driver, 21 controller (correction means), 22 engine, 23 I / F, 24 CPU, 25 RAM, 26 ROM, 27 engine I / F

Claims (6)

An image forming apparatus that uses a plurality of color materials for image formation and performs image formation based on bitmap data in which each pixel has a gradation value of each color of the color material,
Correction that corrects the gradation value for the bitmap data in a correction target area adjacent to a pixel of another color that does not include the single color in the image formation target. Having correction means for executing processing;
The image forming apparatus, wherein the correction process is not performed for a predetermined area adjacent to the white pixel in the correction target area. In claim 1,
The correction means returns the bitmap data to a state before the correction process for a predetermined area adjacent to the white pixel after executing the correction process for the correction target area. Forming equipment. In claim 1 or claim 2,
The image forming apparatus according to claim 1, wherein the single color is black. In any one of Claim 1 thru | or 3,
The image forming apparatus, wherein the correction processing is executed for a predetermined area on a pixel side including other colors not including the single color in the correction target area. An image forming method in an image forming apparatus that uses a plurality of color materials for image formation and performs image formation based on bitmap data in which each pixel has a gradation value of each color of the color material,
Correction that corrects the gradation value for the bitmap data in a correction target area that is adjacent to a pixel of another color that does not include the single color in the image formation target. A correction process for executing the process;
The image forming method, wherein the correction processing is not performed for a predetermined area adjacent to the white pixel in the correction target area. An image forming apparatus that uses a plurality of color materials for image formation and that performs image formation based on bitmap data in which each pixel has a gradation value of each color of the color material. A print data generation program to be generated by a host device,
Correction that corrects the gradation value for the bitmap data in a correction target area that is adjacent to a pixel of another color that does not include the single color in the image formation target. Causing the host device to execute a correction process for executing processing;
The print data generation program, wherein the correction processing is not performed for a predetermined area adjacent to the white pixel in the correction target area.