JP3848017B2 - Image processing apparatus and image processing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image processing apparatus and an image processing method, and in particular, an image processing apparatus that expresses pseudo gradation when a multi-value image input by, for example, a scanner or a computer is repeatedly developed and output to a low gradation device. And an image processing method.
[0002]
[Prior art]
Conventionally, an error diffusion method and a dither method are known as pseudo gradation expression methods. Among these, in the error diffusion method, as shown in FIG. 10, a diffusion coefficient is assigned to several subsequent pixels with respect to the target pixel, and the quantization error generated in the target pixel is changed according to the diffusion coefficient. Sort to pixels. By this processing, the density value of the entire image is saved, and a favorable pseudo gradation expression is possible.
[0003]
In the dither method, as shown in FIG. 11, a dither matrix (in FIG. 11, the matrix size is 4 × 4) prepared in advance is prepared, and this matrix and the input multi-value image data are stored. A one-to-one pixel comparison with each pixel is performed. At this time, if the value of the input multivalued image data is larger than the threshold value, the pixel is turned on, and if the value is smaller, the binarized output is obtained. In this dither method, because of the artificial pattern generated by the regular arrangement of dots, there is a graininess in the pseudo-gradation image, and in general, the image quality tends to deteriorate compared to an image using the error diffusion method. is there.
[0004]
Now, considering a repeating pattern as seen on a pattern such as a tie or a handkerchief, as shown in FIG. 12, the basic pattern (FIG. 12 (a)) is simply horizontal. And a pattern repeatedly generated in the vertical direction (FIG. 12B) and a pattern repeated in the horizontal direction and the vertical direction while shifting the basic pattern by 1/2 (FIG. 12C). However, if the number of repetitions is large, it is inefficient to perform pseudo gradation processing on the entire repeated image. If this processing is performed by software, it is impractical from the viewpoint of processing speed.
[0005]
Further, if only the basic pattern is binarized and the binary data is simply repeated to form an image, noise that is easily noticeable at the boundary between the basic pattern and the basic pattern as shown in FIG. 13 (this is called boundary noise). Will occur. As this cause, the discontinuity of the binarization process in the boundary part can be considered.
[0006]
Therefore, in order to reduce the boundary noise, an outer frame addition method in which an outer frame is added to the basic pattern and the pattern is drawn as shown in FIG. 14 (a), or a basic as shown in FIG. 14 (b). A boundary smoothing method has been proposed in which smoothing processing is performed on the boundary of a pattern. In the outer frame addition method, the same multivalued image having a certain size is added so as to surround the basic pattern, and binarization processing is performed on the entire image to obtain binary data of the basic pattern. However, even if binary data obtained in this way is repeatedly formed, boundary noise still occurs due to the discontinuity of the boundary portion.
[0007]
Further, in order to reduce the boundary noise of the obtained binary data as in the boundary smoothing method, for example, an edge region such as a thin line may be applied to the boundary portion even if the boundary portion of the binary data is subjected to the smoothing process. In the case of an image including the image, there is a problem that the image at the boundary becomes unclear due to this processing.
[0008]
[Problems to be solved by the invention]
In view of this, Japanese Patent Laid-Open No. 10-233923 discloses a method of involving an error at an end portion of a basic image generated by an error diffusion method in data of an unprocessed area on the opposite side.
[0009]
However, if the binary basic image formed by this process is repeatedly recorded, the image quality at the boundary portion may be deteriorated due to the influence of the unique stripe pattern of the error diffusion method process.
[0010]
In addition, if the process involving the error is sequentially advanced in the vertical direction, the diffusion error occurring at the lower end of the basic image cannot be diffused to the upper end, so that the continuity of repetition in the vertical direction is lost.
[0011]
Therefore, in the above-mentioned publication, the auxiliary image of the lower part of the basic image is added to the upper part of the basic image in advance, the processing is performed, and when the processing is completed, the auxiliary image and the lower area data of the basic image are used, The binary data at the bottom end of the basic image is determined.
[0012]
Specifically, in the above-mentioned publication, when determining binarized data, only the average value of data around the pixel of interest or the average value of errors generated by binarization around the pixel of interest is used.
[0013]
In this case, since the value of the input multi-value data around the pixel of interest is not taken into account, there is a risk of image quality degradation.
[0014]
The present invention aims to solve the above-described problems of the prior art, reduces boundary noise associated with repetition of an image represented by pseudo-tones, and reverses the processing direction of the error diffusion method for each line, It is another object of the present invention to provide an image processing apparatus and an image processing method capable of obtaining high-quality repetitive images with suppressed generation of boundary noise.
[0015]
Further, the present invention performs processing by adding an auxiliary image of the lower part of the basic image in advance to the upper part of the basic image, and uses the auxiliary image and the data of the lower area of the basic image when the processing is completed. When the binary data at the bottom end of the pixel of interest is determined, a value obtained by adding the average value of the error due to the binarization around the pixel of interest to the input multivalued data of the pixel of interest is used. An object of the present invention is to provide an image processing apparatus and an image processing method capable of suppressing boundary noise generation and obtaining high-quality repetitive images.
[0016]
[Means for Solving the Problems]
In order to achieve the above-described object, the image processing apparatus of the present invention provides: In an image processing apparatus for converting a basic image expressed by multi-value data into a binary image expressing pseudo gradation, a combined image is formed by adjoining an auxiliary image consisting of a part of the basic image to the basic image Combining means, binarizing means for sequentially comparing the value of each pixel representing the combined image with a predetermined threshold value, and binarizing according to the comparison result, and an error caused by the binarization By applying an error diffusion matrix of a predetermined size and distributing to the peripheral pixels of the pixel of interest, among the errors distributed by the distributing means, errors that protrude outside the basic image are determined by the binarizing means. A capturing unit that captures a binarization process in an unprocessed area; an image data value of a first area that includes a line in contact with the basic image in the auxiliary image after the binarization process; and the first Corresponding to Correction means for comparing the image data values of the second area in the basic image and correcting the image data values of the first and second areas based on the comparison result, Means for calculating a difference value between an original multi-value data value in the peripheral pixel and a binary data value after the error is taken in by the capturing means in the peripheral pixel; and the difference value calculation A weighted average means for weighted averaging the difference values of the surrounding pixels obtained by the means, an adding means for adding the weighted average value by the weighted average means to the multi-value data of the target pixel, and the adding means Comparing the obtained weighted average value with a predetermined threshold value, and comprising correction value generation means for generating a correction value according to the comparison result It is characterized by that.
[0017]
Further, the image processing method of the present invention includes: In an image processing method for converting a basic image expressed by multi-value data into a binary image expressing a pseudo gradation, a combined image is formed by adjoining an auxiliary image consisting of a part of the basic image to the basic image A combining step, a value of each pixel representing the combined image is sequentially compared with a predetermined threshold value, and a binarization step of binarizing according to the comparison result, and an error caused by the binarization By applying an error diffusion matrix of a predetermined size and distributing to peripheral pixels of the pixel of interest, among errors distributed by the distributing step, errors that protrude outside the basic image are determined by the binarizing step. A capturing process for capturing the binarization process into an unprocessed area; an image data value of a first area including a line in contact with the basic image in the auxiliary image after the binarization process; and the first Corresponding to A correction step of comparing the image data values of the second area in the basic image and correcting the image data values of the first and second areas based on the comparison result, The step includes a difference value calculation step for obtaining a difference value between the original multi-value data value in the peripheral pixel and a binary data value after the capturing step in the peripheral pixel takes in an error, and the difference value calculation A weighted average step of weighted averaging the difference values of the surrounding pixels obtained in the step, an addition step of adding the weighted average value in the weighted average step to the multi-value data of the pixel of interest, and the addition step Comparing the obtained weighted average value with a predetermined threshold value, and a correction value generating step of generating a correction value according to the comparison result It is characterized by that.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[0021]
FIG. 1 is a block diagram showing a configuration of an image processing apparatus which is a representative embodiment of the present invention. As shown in FIG. 1, the image processing apparatus includes an image reading unit 109 that reads an image original 100, an image processing unit 104 that processes the read image, and a recording medium (paper) based on the image-processed data. , A board, a cloth, etc.), a printer unit 105 that prints an image, an image reading unit 109, an image processing unit 104, and a control unit 110 that controls the printer unit 105.
[0022]
The image reading unit 109 includes a lens 101, a CCD sensor 102, an analog signal processing unit 103, and the like. Based on the original image formed on the CCD sensor 102 via the lens 101, analog electrical signals of R (Red), G (Green), and B (Blue) are generated by the CCD sensor 102. Then, the electrical signal is input to the analog signal processing unit 103, where sample and hold, dark level correction, and the like are performed for each of the R, G, and B color components, and then analog / digital conversion (A / D conversion), and digital image data composed of RGB components is generated.
[0023]
The digitized full color signal is input to the image processing unit 104. In the image processing unit 104, necessary correction processing due to reading processing in the image reading unit 109 such as shading correction, color correction, and γ correction, preprocessing such as luminance density conversion processing, UCR processing, smoothing processing, edge enhancement, After processing and the like, density image data composed of YMCK components obtained as a result is output to the printer unit 105.
[0024]
The printer unit 105 is an ink jet printer that records an image on a recording medium by ejecting ink onto the recording medium using a recording head according to an ink jet system.
[0025]
FIG. 2 is an external perspective view showing the configuration of the printer unit 105.
[0026]
In FIG. 2, 1 is a recording medium such as recording paper, plastic sheet, or cloth, and 2-3 are conveying rollers that are arranged above and below the recording area of the recording paper 1 and convey the recording paper 1 in the direction of arrow A. 4 is a sheet feeding motor for driving the conveying rollers 2 to 3, 5 is a guide shaft which is located between the conveying rollers 2 and 3 and is provided in parallel with the rotation axis of the conveying rollers 2 to 3, and 6 is a guide shaft 5. A carriage that reciprocates along (B), 7 is a carriage motor that moves the carriage, and 8 is a belt that transmits the driving force of the carriage motor 7 to the carriage 6.
[0027]
The carriage 6 is mounted with recording heads 9A to 9D (hereinafter referred to as recording head 9 when these four recording heads are collectively referred to) that perform recording by discharging ink droplets according to an ink jet method. ing. The recording head 9 is for recording a color image and is arranged in the moving direction of the carriage 6 and is provided corresponding to each color ink of cyan (C), magenta (M), yellow (Y), and black (Bk), respectively. The recording head (K head) 9A, recording head (C head) 9B, recording head (M head) 9C, and recording head (Y head) 9D. A plurality of (for example, 64 or 128) ink discharge ports are provided on the front surface of each of the recording heads 9A to 9D, that is, the surface facing the recording surface of the recording paper 1 with a predetermined interval (for example, 0.8 mm). Are arranged in a vertical line in a direction intersecting the scanning direction of the carriage 6. The logic circuits of the recording heads 9A to 9D have the same configuration.
[0028]
An operation panel 64 attached to the exterior case (not shown) of the printer includes an alarm setting in addition to a key setting unit such as an online / offline switching key 60A, a line feed key 60B, a recording mode switching key 60C, and a reset key 60D. An LED lamp such as a warning lamp for the lamp 61A and the power lamp 61B and an LCD 65 for displaying various messages are provided.
[0029]
Reference numeral 80 denotes a platen, and 92 denotes an ink tank for storing ink for recording a desired image on the recording medium 1. The ink tank 92 includes four ink compartments 92A to 92D that store inks of four colors (cyan (C), magenta (M), yellow (Y), and black (Bk)) corresponding to the recording heads 9A to 9D. It is configured.
[0030]
A control unit including a CPU for controlling the printer and a ROM, a RAM, and the like attached to the CPU is connected to a host computer (hereinafter referred to as a host) 200, and command signals and data signals (recording information) sent from the host computer Based on the above, it is possible to execute printing by driving various motors or the like and applying a driving power source (heat power source) to the electrothermal transducers (heaters) included in the recording heads 9A to 9D and energizing them.
[0031]
FIG. 3 is a block diagram showing a schematic configuration of the control unit shown in FIG.
[0032]
The CPU 21 in the form of a microprocessor is connected to the host 200 via the interface 22 and to the image processing unit 104 and the image reading unit 109 via another interface 83. Then, a ROM 24 storing a control program, an EEPROM 23 storing an updatable control program, a processing program, various constant data, and the like, a command signal (command) or a recording signal received from the host 100 via the interface 22, or The RAM 25 that stores the density image data transferred from the image processing unit 104 via the interface 83 is accessed, and the recording operation is controlled based on the information stored in these memories.
[0033]
Further, the CPU 21 moves the carriage 6 by operating the carriage motor 7 via the output port 26 and the carriage motor control circuit 42, and moves the sheet feed motor 4 via the output port 26 and the sheet feed motor control circuit 44. By operating, a transport mechanism such as the transport rollers 2 to 3 is operated. Further, the CPU 21 can record a desired image on the recording medium 1 by driving the recording heads 9 </ b> A to 9 </ b> D via the head driving circuit 29 based on the recording information stored in the RAM 25.
[0034]
Further, from the power supply circuit 28, a logic driving voltage Vcc (for example, 5V) for operating the CPU 21 and the recording head control circuit 29, various motor driving voltages Vm (for example, 30V), and a heat voltage Vh for driving the recording head 9 are used. (For example, 25 V) and the backup voltage VDDH for protecting the recording head 9 are output. The heat voltage Vh is applied to the recording head 9, and the backup voltage VDDH is applied to the recording head control circuit 29 and the recording head 9, respectively.
[0035]
Furthermore, instructions input from the operation keys 60A to 60D are transmitted to the CPU 21 via the input port 32, and when an instruction from the CPU 21 is transmitted to the LED light emission control circuit 62 via the output port 36, the LEDs 61A and 61B are turned on. When the message is transmitted to the display control circuit 66, a message is displayed on the LCD 65.
[0036]
Further, a recording medium width detection sensor 81 is mounted on the carriage 6, and a signal for detecting the width of the recording medium width 1 is sent to the CPU 21 via the A / D conversion circuit 82.
[0037]
Next, the basic pattern “A” as shown in FIG. 12 is continuously printed in a horizontal direction and a vertical direction on a recording medium such as a woven fabric by using the image processing apparatus configured as described above. The image processing for this will be described.
[0038]
FIG. 4 is a diagram showing how the error diffusion method is applied when the basic pattern is repeatedly printed in the horizontal direction.
[0039]
Each pixel is binarized using a predetermined threshold in the right direction sequentially from the upper left end of the image, and further, for example, binarization processing is performed while performing error diffusion by applying an error matrix 700 as shown in FIG. , The range of application of the error matrix protrudes from the right end of the image.
[0040]
In this embodiment, for example, when the target pixel reaches the right end of the image and three pixels of the error matrix 700 protrude outside the image, binarization is not processed as indicated by 701 in FIG. Error diffusion is performed by incorporating the error that protrudes into the region (shaded area 701 in FIG. 4).
[0041]
That is, the protrusion error at the right end portion is taken into the left end portion here in order to guarantee horizontal continuity regarding the repetition of the basic pattern. In the example indicated by reference numeral 701 in FIG. 4, since the binarization process has already been completed for the line to which the target pixel belongs, the line below it takes in an error.
[0042]
Further, in this embodiment, as shown in FIG. 15, the processing direction by the error diffusion method is switched for each line.
[0043]
As a result, the generation of texture noise (stripe pattern) peculiar to the error diffusion method can be reduced. As a result, when the basic pattern is repeated, the boundary noise at the boundary portion can also be reduced.
[0044]
The diffusion error processing when the processing direction by the error diffusion method is switched in this way will be described with reference to FIG.
[0045]
(A) to (d) of FIG. 16 show processing performed in the present embodiment.
[0046]
FIG. 16A shows a process of diffusing an overflow error 801 generated at the right end into an unprocessed area at the left end when processing is performed from the left side to the right side.
[0047]
FIG. 16B shows a process of diffusing an overflow error 802 generated at the left end portion into an unprocessed area at the right end portion when processing from the right side to the left side.
[0048]
FIG. 16C shows a process of diffusing an overflow error 803 generated at the left end portion into the unprocessed area at the right end portion when processing is performed from the left side to the right side.
[0049]
FIG. 16D shows a process of diffusing an overflow error 804 generated at the right end to an unprocessed area at the left end when the process is performed from the right side to the left side.
[0050]
Note that the error diffusion coefficient can be changed in accordance with the processing direction, thereby further suppressing the occurrence of texture noise.
[0051]
Now, when such a series of processing is repeated up to the last line of the image, as shown at 702 in FIG. 4, an error protrudes at the lower end of the image. Ideally, it is desirable to capture this error in the upper left corner of the image, but the binarization process has already been completed for that portion, and the capture is impossible. Therefore, if the basic pattern is repeatedly recorded while performing the above-described capturing only with the processing as it is, the boundary noise in the vertical direction can be reduced as shown by reference numeral 703 in FIG. The noise remains.
[0052]
Therefore, in this embodiment, the following processing is executed in addition to the above-described capturing processing.
[0053]
FIG. 5 is a diagram showing how the error diffusion method is applied when a basic pattern is repeatedly printed in the vertical direction.
[0054]
First, an auxiliary pattern 801 having a certain size, which is a part of the basic pattern, is added to the upper part of the basic pattern 800. Then, binarization processing is performed on the entire combined pattern 802 to which the auxiliary image has been added by applying the error diffusion method including the error capturing processing described above. Then, after this processing is completed, “area 1”, which is the lowest line of the auxiliary pattern, is compared with “area 2”, which is the lowest line of the basic image.
[0055]
Since the auxiliary pattern 801 consists of a part of the basic pattern 800, these areas 1 and 2 originally represent the same position in the basic pattern 800. Therefore, if the binary data in both areas completely match, even if the basic pattern 800 is repeatedly recorded by applying only the error diffusion method including the error capturing process described above, the boundary noise However, in actuality, the data in the respective areas do not match completely as indicated by reference numeral 803 in FIG. This is because the dot value changes in the binarization process. Therefore, it is necessary to adjust these different dot arrangements so that they are visually good.
[0056]
Therefore, in this embodiment, the region 1 and the region 2 are compared, and when the binary data matches, the matched data is used as it is. However, for non-matching ones, the following processing is executed so as to consider the values of surrounding pixels, and it is determined to match either value.
[0057]
FIG. 6 is a diagram showing a configuration of an average value calculation filter used for the determination, and FIG. 7 is a flowchart showing a procedure of the comparison process.
[0058]
In FIG. 6, the pixel indicated by diagonal lines is the pixel of interest, and the values described in other pixels are weights for calculating the average value of the binarization error in the peripheral region where the binarization processing has been completed. It is a coefficient. Here, the position of the mismatched pixel is set as the position of the target pixel.
[0059]
In step S101, (input multi-valued data−binary data) of each peripheral pixel that has already been binarized is obtained.
[0060]
In step S102, the error data average value of the error data is calculated by multiplying the error data of each pixel obtained in step S101 by the coefficient shown in FIG. 6 and further obtaining the sum. The value 1/69 is multiplied by all the weighting factors.
[0061]
In step S103, the weighted average value of the error data calculated in step S102 is added to the input multi-value data of the target pixel.
[0062]
In step S104, the addition result in step S103 is compared with 128 which is a threshold value. If the addition result is 128 or more, the value of the target pixel is set to ON (“1”), whereas the addition result is less than 128. If so, the value of the target pixel is set to OFF (“0”).
[0063]
In this way, with respect to the area 1 and the area 2 shown in FIG. 5, only when the values of the corresponding pixels in the two areas do not match, the correction taking into account the average value of errors generated by the peripheral pixel binarization To do. Accordingly, horizontal boundary noise seen in 703 in FIG. 4 is reduced, image quality deterioration can be suppressed, the density of the input image can be guaranteed, and a binarized result faithful to the input data can be obtained. Can do.
[0064]
Finally, the series of image processing described above can be summarized as a flowchart shown in FIG.
[0065]
First, in step S10, a combined pattern 802 obtained by combining the auxiliary pattern and the basic pattern is input as shown in FIG. In step S20, multi-value data for one pixel is input. In step S25, a setting for converting the processing direction is performed. The first line is processed from left to right, and the second line is processed from right to left. That is, for each line, processing is performed by switching the right direction, the left direction, and the processing direction. In step S30, a predetermined threshold value and its input multi-value data are compared, and each image data of each line is binarized.
[0066]
In step S40, the error diffusion matrix 700 is applied to the error caused by the binarization, and the error is diffused into an unprocessed area according to the matrix.
[0067]
Next, in step S50, as shown in FIG. 4, it is checked whether or not the location where the error is diffused is outside the combined pattern image. Here, if there is no such “extrusion”, the process returns to step S20 to process the next pixel. On the other hand, if there is such a “protruding”, the process proceeds to step S60, and the error that protrudes is regarded as the end of the “protruding” after the next line that is an unprocessed area. Diffuses to the opposite end.
[0068]
Note that error diffusion by the process of step S60 is not executed when the binarization process proceeds and the location of error diffusion protrudes downward from the final line of the combined pattern.
[0069]
In step S70, it is checked whether or not the binarization processing in steps S10 to S60 has reached the final pixel of the final line. If it is determined that the processing of the final pixel is complete, the processing is not completed yet in step S80. If it is determined that there is, the process returns to step S20 to process the next pixel.
[0070]
In step S80, the process compares a pair of pixels with respect to the corresponding pixels in region 1 and region 2, as shown in FIG. In step S90, it is determined whether or not the values of the two corresponding pixels match as a result of the comparison. If they do not match, the process proceeds to step S100. This correction is not executed, and the process proceeds to step S110.
[0071]
In step S100, the same processing as described with reference to the flowchart of FIG. 7 is executed, and the value of the target pixel is corrected with reference to the values of the surrounding pixels. Thereafter, the process proceeds to step S110. In step S110, it is checked whether the comparison and correction processes for all corresponding pixels have been completed. Here, if it is determined that these processes have not been completed, the process returns to step S80, and the comparison for the next pair of pixels is executed.
[0072]
On the other hand, if it is determined that all the corresponding pixels have been processed, the process ends.
[0073]
As described above, even if the binarization process is not performed on the entire image recorded on the recording medium, the binarization process is performed only on the basic pattern of the repeated recording, and the pattern is repeated as many times as necessary. By repeating the recording, it is possible to obtain a good image quality without boundary noise as much as when the entire image is binarized.
[0074]
In addition, by setting the processing direction of the error diffusion method in the reverse direction for each line, it is possible to obtain a high-quality repetitive image in which the generation of boundary noise is almost completely suppressed.
[0075]
In addition, the auxiliary image of the lower part of the basic image is added to the upper part of the basic image in advance, and processing is performed.When the processing is completed, the auxiliary image and the data of the lower area of the basic image are used to When determining binary data, a value obtained by adding the average value of the error due to binarization around the pixel of interest to the input multivalue data of the pixel of interest is used, so the density of the input multivalue data is saved and boundary noise is generated In addition, it is possible to obtain repeated images with high image quality.
[0076]
In addition, for example, when a specific pattern is repeatedly printed by ejecting ink onto a recording medium such as a woven fabric, efficient image processing is performed, and a higher processing speed can be achieved. it can.
[0077]
The binarization process as described above can be executed by the image processing unit 104 using a logic circuit. However, considering the flexibility of the process, if the CPU 21 has high performance, the software can be used. It is also possible to execute using.
[0078]
In addition, the relative position between the target pixel and the diffusion coefficient, the specific positional relationship at the time of taking in the error, and the comparison processing method in this embodiment are merely examples, and it goes without saying that there are various variations. Furthermore, although this embodiment deals with binarization processing, the present invention can also be applied to, for example, a multi-value error diffusion method.
[0079]
Hereinafter, modified examples will be described.
[0080]
[Modification]
In the above-described embodiment, the case where the reference pattern is repeatedly recorded as shown in FIG. 12B has been described as an example. However, when the repeated recording as shown in FIG. 12C is performed, the basic patterns arranged in the horizontal direction are arranged. Since the pattern error is shifted by 1/2 of the size of the pattern in the vertical direction, if the cyclic error diffusion method is applied as it is as described above, the processing for reducing the boundary noise in the horizontal direction becomes complicated. The process as shown is executed.
[0081]
That is, the error capturing process is performed by changing the processing direction of the cyclic error diffusion method from the horizontal direction to the vertical direction.
[0082]
FIG. 9 is a diagram showing how the cyclic error diffusion method is applied in the vertical direction.
[0083]
In this case, an auxiliary pattern is added to the left side of the basic pattern in the vertical direction by a half of the size. Then, binarization of the basic pattern is executed by applying the error diffusion matrix in the vertical direction from the lower left end of the pattern of the composite image formed by the addition. When the processing reaches the upper end, the same processing is continued while taking the error protruding from the upper end into the lower end of the next row, and binarization processing is performed up to the final row of the combined pattern.
[0084]
The comparison process as described above is performed on the area 1 and the area 2 of the binary image formed in this way, and in a place where the values do not coincide with each other in the corresponding pixels in the two areas, as described above Correction is performed in consideration of the pixel value.
[0085]
As a result, similarly to the case where the basic pattern is simply repeatedly printed in the horizontal direction and the vertical direction, the boundary noise can be reduced by using the cyclic error diffusion method, and the deterioration of the image quality can be suppressed.
[0086]
In the above-described embodiment, particularly in the ink jet recording system, a means (for example, an electrothermal converter or a laser beam) that generates thermal energy as energy used for performing ink ejection is provided, and the thermal energy By using a system that causes a change in the state of the ink, it is possible to achieve higher recording density and higher definition.
[0087]
As its typical configuration and principle, for example, those performed using the basic principle disclosed in US Pat. Nos. 4,723,129 and 4,740,796 are preferable. This method can be applied to both the so-called on-demand type and continuous type. In particular, in the case of the on-demand type, it is arranged corresponding to the sheet or liquid path holding the liquid (ink). By applying at least one drive signal corresponding to the recording information and applying a rapid temperature rise exceeding the film boiling to the electrothermal transducer, the thermal energy is generated in the electrothermal transducer, and the recording head This is effective because film boiling occurs on the heat acting surface of the liquid, and as a result, bubbles in the liquid (ink) corresponding to the drive signal on a one-to-one basis can be formed. By the growth and contraction of the bubbles, liquid (ink) is ejected through the ejection opening to form at least one droplet. When the drive signal is pulse-shaped, the bubble growth and contraction is performed immediately and appropriately, and thus it is possible to achieve the discharge of liquid (ink) with particularly excellent responsiveness.
[0088]
As this pulse-shaped drive signal, those described in US Pat. Nos. 4,463,359 and 4,345,262 are suitable. Further excellent recording can be performed by employing the conditions described in US Pat. No. 4,313,124 of the invention relating to the temperature rise rate of the heat acting surface.
[0089]
As the configuration of the recording head, in addition to the combination configuration (straight liquid flow path or right-angle liquid flow path) of the discharge port, the liquid path, and the electrothermal transducer as disclosed in each of the above-mentioned specifications, the heat acting surface The configurations using US Pat. No. 4,558,383 and US Pat. No. 4,459,600, which disclose a configuration in which the first and second portions are arranged in the bent region, are also included in the present invention. In addition, Japanese Patent Application Laid-Open No. 59-123670, which discloses a configuration in which a common slot is used as a discharge portion of an electrothermal transducer, or an opening that absorbs a pressure wave of thermal energy is discharged to a plurality of electrothermal transducers. A configuration based on Japanese Patent Laid-Open No. 59-138461 disclosing a configuration corresponding to each part may be adopted.
[0090]
Furthermore, as a full-line type recording head having a length corresponding to the width of the maximum recording medium that can be recorded by the recording apparatus, the length is satisfied by a combination of a plurality of recording heads as disclosed in the above specification. Either a configuration or a configuration as a single recording head formed integrally may be used.
[0091]
In addition to the cartridge-type recording head in which the ink tank is integrally provided in the recording head itself described in the above embodiment, it can be electrically connected to the apparatus body by being attached to the apparatus body. A replaceable chip type recording head that can supply ink from the apparatus main body may be used.
[0092]
In addition, it is preferable to add recovery means for the recording head, preliminary means, etc. to the configuration of the recording apparatus described above, since the recording operation can be further stabilized. Specific examples thereof include a capping unit for the recording head, a cleaning unit, a pressure or suction unit, an electrothermal converter, a heating element different from this, or a preheating unit using a combination thereof. In addition, it is effective to provide a preliminary ejection mode for performing ejection different from recording in order to perform stable recording.
[0093]
Further, the recording mode of the recording apparatus is not limited to the recording mode of only the mainstream color such as black, but the recording head may be integrated or may be a combination of a plurality of colors. A device with at least one of the full colors can also be provided.
[0094]
In the embodiment described above, the description is made on the assumption that the ink is a liquid, but it may be an ink that is solidified at room temperature or lower, or an ink that is softened or liquefied at room temperature, Alternatively, in the ink jet system, the temperature of the ink itself is generally adjusted within a range of 30 ° C. or higher and 70 ° C. or lower to control the temperature so that the viscosity of the ink is within a stable discharge range. Any material may be used if it is liquid.
[0095]
In addition, in order to actively prevent the temperature rise by energy as a state energy from the ink solid state to the liquid state change, or to prevent ink evaporation, An ink that is solidified and liquefied by heating may be used. In any case, by applying heat energy according to the application of thermal energy according to the recording signal, the ink is liquefied and liquid ink is ejected, or when it reaches the recording medium, it already starts to solidify. The present invention can also be applied to the case of using ink having the property of being liquefied for the first time. In such a case, the ink is held as a liquid or solid in a porous sheet recess or through-hole as described in JP-A-54-56847 or JP-A-60-71260, It is good also as a form which opposes with respect to an electrothermal converter. In the present invention, the most effective one for each of the above-described inks is to execute the above-described film boiling method.
[0096]
In addition, as a form of the recording apparatus according to the present invention, a copying apparatus combined with a reader or the like as well as an image output terminal of an information processing device such as a computer or a separate apparatus, and a transmission / reception function are provided. It may take the form of a facsimile machine.
[0097]
The present invention can also be applied to a system constituted by a plurality of devices such as a host computer, an interface device, a reader, and a printer, and can be applied to a single device such as a copying machine and a facsimile machine.
[0098]
In addition, a storage medium in which a program code of software that realizes the functions of the above-described embodiments is supplied to a system or apparatus, and the computer (or CPU or MPU) of the system or apparatus stores the program code in the storage medium. It can also be applied to reading out and executing.
[0099]
In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiment, and the storage medium storing the program code constitutes the present invention.
[0100]
As a storage medium for supplying the program code, for example, a floppy disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a CD-R, a magnetic tape, a nonvolatile memory card, a ROM, or the like can be used.
[0101]
Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also an OS (operating system) or the like running on the computer based on the instruction of the program code. It goes without saying that a case where the function of the above-described embodiment is realized by performing part or all of the actual processing and the processing is included.
[0102]
Furthermore, after the program code read from the storage medium is written into a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, the program code is read based on the instruction of the program code. It goes without saying that the CPU or the like provided in the function expansion board or the function expansion unit performs part or all of the actual processing, and the functions of the above-described embodiments are realized by the processing.
[0103]
【The invention's effect】
As described above, according to the present invention, the binarization process is performed only on the basic pattern of the repeated recording without performing the binarization process on the image recorded on the entire recording medium, and the necessary number of times is obtained. By repeating this pattern recording only, it is possible to obtain a good image quality free from boundary noise as much as when the entire image is binarized.
[0104]
In addition, by setting the processing direction of the error diffusion method in the reverse direction for each line, it is possible to obtain a high-quality repetitive image in which the generation of boundary noise is almost completely suppressed.
[0105]
In addition, the auxiliary image of the lower part of the basic image is added to the upper part of the basic image in advance, and processing is performed.When the processing is completed, the auxiliary image and the data of the lower area of the basic image are used to When determining binary data, a value obtained by adding the average value of the error due to binarization around the pixel of interest to the input multivalue data of the pixel of interest is used, so the density of the input multivalue data is saved and boundary noise is generated In addition, it is possible to obtain repeated images with high image quality.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of an image processing apparatus according to a representative embodiment of the present invention.
2 is an external perspective view showing a configuration of a printer including a recording head that performs recording in accordance with an ink jet method corresponding to the printer shown in FIG. 1;
FIG. 3 is a block diagram showing a configuration of a control unit shown in FIG. 1;
FIG. 4 is a diagram showing a horizontal error capturing process to which a cyclic error diffusion method according to the embodiment is applied.
FIG. 5 is a diagram conceptually showing a comparison process in the vertical direction to which a cyclic error diffusion method according to the embodiment is applied.
FIG. 6 is a diagram illustrating an average value calculation filter used for the comparison process.
FIG. 7 is a flowchart showing comparison processing according to the embodiment;
FIG. 8 is a flowchart showing an overview of the entire binarization process according to the embodiment;
FIG. 9 is a diagram showing a state in which a cyclic error diffusion method according to a modification of the embodiment is applied.
FIG. 10 is a diagram illustrating a relationship between a target pixel and a diffusion coefficient in the error diffusion method.
FIG. 11 is a diagram illustrating binarization processing by a dither method.
FIG. 12 is a diagram illustrating a relationship between a basic image and a repeated image.
FIG. 13 is a diagram illustrating boundary noise due to repetition of binary data.
FIG. 14 is a diagram for explaining a conventional boundary noise reduction method;
FIG. 15 is a diagram for explaining a bidirectional error diffusion method;
FIG. 16 is a diagram showing a horizontal error capturing process when bidirectional error diffusion is performed;
[Explanation of symbols]
100 image original
101 lens
102 CCD sensor
103 Analog signal processor
104 Image processing unit
105 Printer section
109 Image reader
110 Control unit

Claims (2)

In an image processing apparatus for converting a basic image expressed by multi-value data into a binary image expressing pseudo gradation,
A combining unit that forms a combined image by adjoining the basic image to an auxiliary image that is a partial image of the basic image;
Binarization means for sequentially comparing the value of each pixel representing the combined image with a predetermined threshold value and binarizing according to the comparison result;
Distribution means for distributing an error generated by the binarization to a peripheral pixel of a target pixel by applying an error diffusion matrix of a predetermined size;
A fetching unit that fetches, out of the errors distributed by the distributing unit, an error that protrudes outside the basic image into an unprocessed area by the binarization processing by the binarizing unit;
After the binarization processing is completed, the image data value of the first area including the line in contact with the basic image in the auxiliary image, and the image of the second area in the basic image corresponding to the first area A correction means for comparing data values and correcting the image data values of the first and second regions based on the comparison results;
The correction means includes
Difference value calculation means for obtaining a difference value between the original multi-value data value in the surrounding pixels and the binary data value after the capturing means in the surrounding pixels has taken in an error;
A weighted average means for weighted average of the difference values of the surrounding pixels obtained by the difference value calculating means;
Adding means for adding the weighted average value by the weighted average means to the multi-value data of the target pixel;
An image processing apparatus comprising: a correction value generation unit that compares the weighted average value obtained by the addition unit with a predetermined threshold value and generates a correction value according to the comparison result. In an image processing method for converting a basic image expressed by multi-value data into a binary image expressing pseudo gradation,
A combining step of forming a combined image by adjoining the basic image with an auxiliary image consisting of a part of the basic image;
A binarization step of sequentially comparing the value of each pixel representing the combined image with a predetermined threshold value, and binarizing according to the comparison result;
A distribution step of distributing an error generated by the binarization to peripheral pixels of the target pixel by applying an error diffusion matrix of a predetermined size;
A process of taking in errors out of the basic image out of errors distributed by the distribution process into a region that is not processed by the binarization process by the binarization process;
After the binarization processing is completed, the image data value of the first area including the line in contact with the basic image in the auxiliary image, and the image of the second area in the basic image corresponding to the first area A correction step of comparing data values and correcting the image data values of the first and second regions based on the comparison results,
The correction step includes
A difference value calculation step for obtaining a difference value between an original multi-value data value in the peripheral pixels and a binary data value after the capturing step in the peripheral pixels takes in an error;
A weighted average step of performing a weighted average of the difference values of the surrounding pixels obtained in the difference value calculation step;
An addition step of adding the weighted average value in the weighted average step to the multi-value data of the target pixel;
An image processing method comprising: a correction value generation step of comparing the weighted average value obtained in the addition step with a predetermined threshold value and generating a correction value according to the comparison result.

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