JP6531484B2 - Device for discharging liquid, method for processing image data, program - Google Patents

Description

  The present invention relates to an apparatus for ejecting liquid, a method for processing image data, and a program.

  In an apparatus for discharging a liquid, when discharge failure occurs due to clogging of a nozzle or the like, the image quality is degraded.

  Therefore, conventionally, when converting multi-value data of an input image into an n-value dot pattern by multi-value error diffusion processing corresponding to n values (n ≧ 2 integers), a nozzle having an ejection failure (this is ), While quantizing error due to multi-level error diffusion processing is developed as it is to surrounding pixels, and drops required for solid printing in the development destination pixel It is known to compensate for image deterioration due to a defective discharge nozzle by performing processing of thinning the droplet or changing the droplet size to a smaller size when it is necessary to form a droplet larger than the size. (Patent Document 1).

JP, 2010-17918, A

  However, in the configuration disclosed in Patent Document 1, for example, when applied to an apparatus for scanning a head, quantization errors can only be developed in pixels downstream of the defective discharge nozzle in the scanning direction, so compensation for image quality deterioration is There is a problem that it is not enough.

  The present invention has been made in view of the above problems, and has as its object to reduce image deterioration due to a defective discharge nozzle.

To solve the above problems, apparatus for discharging liquid according to the present onset Ming,
An apparatus comprising a liquid discharge head having a plurality of nozzles for discharging a liquid, comprising:
When converting multi-value data of an input image into an n-value dot pattern by multi-value error diffusion processing corresponding to n values (n 整数 2 integer),
When the pixel value corresponding to the defective discharge nozzle is less than a predetermined first threshold value, the quantization error in the multi-level error diffusion processing is expanded to the peripheral pixels of the pixel corresponding to the defective discharge nozzle. ,
When the pixel value corresponding to the defective discharge nozzle is equal to or more than the first threshold and less than a second predetermined threshold larger than the first threshold, quantization error in the multi-level error diffusion process is Performing a process of developing by multiplying the peripheral pixels of the pixel corresponding to the defective discharge nozzle by a predetermined coefficient;
When the pixel value corresponding to the defective ejection nozzle is not less than the second threshold value, after conversion to a dot pattern of n value by the multi-level error diffusion process, using a predetermined mask pattern, before Symbol defective ejection nozzle Among the dots in the vicinity of the dot, small dots are replaced with large dots.

  According to the present invention, image deterioration due to a defective discharge nozzle can be reduced.

It is plane explanatory drawing of the mechanism part of an example of the apparatus which discharges the liquid which concerns on this invention. It is an explanatory view which serves to explain a head of the same device. It is block explanatory drawing of the outline | summary of the control part of the apparatus. It is block explanatory drawing of an example of the host side. FIG. 6 is a flowchart for describing compensation processing in the first embodiment of the present invention. It is the same flow chart. FIG. 6 is an explanatory view for explaining an example of the relationship between the droplet amount, the dot diameter, and the medium type. It is explanatory drawing of an example of the mask pattern of the 1st example of a mask pattern process (dot replacement process by a mask pattern). It is explanatory drawing of an example of the dot substitution which used the same mask pattern. It is explanatory drawing of an example of the mask pattern of the 2nd example of a mask pattern process (dot replacement process by a mask pattern). It is explanatory drawing of an example of the dot substitution using the mask pattern of FIG.8 and FIG.10.

  Hereinafter, embodiments of the present invention will be described with reference to the attached drawings. First, an example of a device for discharging a liquid according to the present invention will be described with reference to FIG. FIG. 1 is a plan view of the mechanical part of the same device.

  This device is a serial type device, and a carriage 3 is movably held by a guide member 1 or the like which is bridged between left and right side plates and the like. Then, the main scanning motor 5 reciprocates the carriage 3 in the main scanning direction (carriage movement direction) via the timing belt 8 bridged between the driving pulley 6 and the driven pulley 7.

  On the carriage 3, liquid discharge heads 4a and 4b (referred to as "head 4" when not distinguished) are mounted. The head 4 ejects, for example, ink droplets of each color of yellow (Y), cyan (C), magenta (M), and black (K). Further, the head 4 has a nozzle row 4n composed of a plurality of nozzles arranged in the sub-scanning direction orthogonal to the main scanning direction, and is mounted with the droplet discharge direction directed downward.

  As shown in FIG. 2, the head 4 has two nozzle rows Na and Nb in which a plurality of nozzles 4 n are arranged. One nozzle row Na of the head 4a discharges a droplet of black (K), and the other nozzle row Nb discharges a droplet of cyan (C). One nozzle row Na of the head 4b discharges droplets of magenta (M), and the other nozzle row Nb discharges droplets of yellow (Y).

  On the other hand, a transport belt 51 as transport means is provided as a transport mechanism 51 for transporting the sheet 10 as a medium opposite to the head 4. The conveyance belt 12 is an endless belt and is stretched between the conveyance roller 13 and the tension roller 14.

  The conveyance belt 12 is rotationally moved in the sub-scanning direction by the conveyance roller 13 being rotationally driven by the sub-scanning motor 16 via the timing belt 17 and the timing pulley 18.

  Further, a maintenance and recovery mechanism 20 for maintaining and recovering the head 4 is disposed on one side of the carriage 3 in the main scanning direction and the other side of the carriage 4 is empty from the head 4 on the other side. Unused discharge receptacles 21 for discharging are respectively arranged.

  The maintenance and recovery mechanism 20 includes, for example, a cap member 20a for capping the nozzle surface (surface on which the nozzle is formed) of the head 4 and a wiper member 20b for wiping the nozzle surface.

  Further, outside the recording area between the transport mechanism 51 and the maintenance and recovery mechanism 20, in the area that can face the head 4, the ejection detection unit 100 that constitutes ejection detection means for detecting the presence or absence of droplet ejection is disposed. It is done. On the other hand, the carriage 3 is provided with a wiping unit 200 that cleans the electrode 101 of the discharge detection unit 100.

  Further, an encoder scale 23 formed of a transmission type photosensor for reading the pattern of the encoder scale 23 is attached to the carriage 3 along the main scanning direction of the carriage 3 and between the side plates. Is provided. The encoder scale 23 and the encoder sensor 24 constitute a linear encoder (main scanning encoder) for detecting the movement of the carriage 3.

  In addition, a code wheel 25 is attached to the shaft of the conveyance roller 13, and an encoder sensor 26 formed of a transmission type photo sensor for detecting a pattern formed on the code wheel 25 is provided. The code wheel 25 and the encoder sensor 26 constitute a rotary encoder (sub scanning encoder) for detecting the movement amount and movement position of the conveyance belt 12.

  In the apparatus configured as described above, the sheet 10 is fed from the sheet feed tray onto the transport belt 12 and attracted, and the circumferential movement of the transport belt 12 transports the sheet 10 in the sub-scanning direction.

  Therefore, by moving the carriage 3 in the main scanning direction and driving the head 4 according to the image signal, ink droplets are discharged onto the stopped paper 10 to record one line. Then, after transporting the sheet 10 by a predetermined amount, the next line is recorded.

  The recording operation is ended by receiving the recording end signal or a signal that the rear end of the sheet 10 has reached the recording area, and the sheet 10 is discharged.

  Next, an outline of a control unit of this apparatus will be described with reference to FIG. This figure is a block diagram of the control unit.

  The control unit 500 includes a CPU 501 for controlling the entire apparatus, a ROM 502 for storing fixed data and programs including a program according to the present invention executed by the CPU 501, and a RAM 503 for temporarily storing image data and the like. A main control unit 500A is provided.

  The control unit 500 also includes a host I / F 506 that controls data transfer with a host (information processing apparatus) 600 such as a PC, an image output control unit 511 that controls driving of the head 4, and an encoder analysis unit 512. Have. The encoder analysis unit 512 receives and analyzes detection signals from the main scanning encoder sensor 24 and the sub scanning encoder sensor 26.

The control unit 500 further includes a main scan motor drive unit 513 for driving the main scan motor 5, a sub scan motor drive unit 514 for driving the sub scan motor 16, a temperature sensor 518, various sensors and actuators 517. It also has an I / O 516.
Is equipped.

  The control unit 500 also includes a discharge detection unit 531 that measures (detects) an electrical change when a droplet lands on the electrode 101 of the discharge detection unit 100 and determines discharge / non-discharge. The control unit 500 also includes a wiping unit drive unit 532 that drives the drive motor 203 of the wiping unit 200 that wipes the electrodes 101 of the ejection detection unit 100.

  The image output control unit 511 includes a data generation unit that generates print data, a drive waveform generation unit that generates a drive waveform for driving and controlling the head 4, a head control signal for selecting a required drive signal from the drive waveform, It includes data transfer means for transferring print data.

  Then, the image output control unit 511 outputs a drive waveform, a head control signal, print data, and the like to the head driver 510 which is a head drive circuit for driving the head 4 mounted on the carriage 3 side. Droplets are ejected from the nozzles of No. 4 according to the print data.

  The encoder analysis unit 512 also includes a direction detection unit 520 that detects the movement direction from the detection signal, and a counter unit 521 that detects the movement amount.

  The control unit 500 controls the movement of the carriage 3 by driving and controlling the main scanning motor 5 via the main scanning motor driving unit 513 based on the analysis result from the encoder analysis unit 512. Further, by controlling the driving of the sub scanning motor 16 via the sub scanning motor driving unit 514, the sheet 10 is controlled to be fed.

  The main control unit 500A of the control unit 500 moves the head 4 to a position facing the discharge detection unit 100 when the discharge detection of the head 4 is performed. Then, the main control unit 500A causes droplet discharge from a required nozzle of the head 4 via the image output control unit 511, and determines the droplet discharge state (discharge / non-discharge) by the detection signal from the discharge detection unit 531. Take control.

  When the apparatus for ejecting liquid performs processing to reduce image quality deterioration due to a defective ejection nozzle (referred to as “compensation processing”) on data of an input image, main control is performed by a program stored in the ROM 502. The compensation process is performed by the unit 500A.

  Next, an example of the host 600 will be described with reference to the block diagram of FIG.

  The host 600 is an information processing apparatus, and a CPU 611 and various ROMs 612 and RAMs 613 as memory means are connected by a bus line. In this bus line, a storage device 616 using a magnetic storage device such as a hard disk, an input device 614 such as a mouse or a keyboard, a monitor 615 such as an LCD or CRT, and an external I / I via a predetermined interface. F 617 is connected.

  The storage unit 616 stores an image processing program including a program according to the present invention. The image processing program is installed in the storage device 616 by reading from the storage medium by the storage medium reading device or downloading from a network such as the Internet. The image processing program may operate on a predetermined OS. Moreover, it may be a part of specific application software.

  The host 600 processes a print command from application software or the like with the printer driver 601 to generate multi-valued dot pattern data that can be output by a device that discharges liquid, and transfers the data to the device that discharges liquid.

  Examples of image processing performed on the host 600 side include color management processing (CMM) for color adjustment, gamma correction processing, halftone processing such as dither method and error diffusion method, background removal processing, total amount restriction processing, etc. There is. Then, the image-processed data is developed into raster data and transferred to a device that discharges liquid.

  When performing the compensation process on the host 600 side, the compensation process is performed by receiving the data of the detection result of the defective discharge nozzle from the apparatus side that discharges the liquid.

  Next, the compensation process in the first embodiment of the present invention will be described with reference to the flowcharts of FIGS. 5 and 6.

  When the moving direction of the carriage (head) in the serial type device is the main scanning direction and the direction for transporting the medium is the sub scanning direction, the image data is "main scanning direction" in the horizontal direction and "sub scanning in the vertical direction. "Direction".

  Before starting this process, confirmation (discharge detection) of the presence or absence of a defective discharge nozzle is performed. Although detection of a defective discharge nozzle is performed using the above-described discharge detection unit 100, a test pattern can be discharged onto a medium and visually confirmed, and the confirmation result can be input to the apparatus or host 600. .

  Here, the timing of the ejection detection may be either after the image data is input or before the image data is input.

  By performing the ejection detection after the print image data is input, it is possible to detect a defective ejection nozzle immediately before printing, and it is possible to reliably perform compensation when there is a defective ejection nozzle. However, since it is necessary to perform the determination process after the input of the print image data, the waiting time from the print start instruction to the actual start of printing becomes long.

  On the other hand, by performing the ejection detection before the image data is input, the waiting time from the print start instruction to the actual start of printing does not increase. However, when the time from the discharge detection to the start of printing becomes long, the detection result may fluctuate.

  Then, when a defective discharge nozzle is detected as a result of the discharge detection, information on the nozzle position of the defective nozzle (position information indicating which nozzle is located with respect to the reference nozzle) is acquired. By combining the position information of the defective discharge nozzle and the print quality (resolution) when printing the image data, it is possible to determine the pixel position on the print image formed by the defective discharge nozzle.

  Therefore, referring to FIG. 5, the image data of the input image for one scan is input, and the target pixel is moved.

  Then, it is determined whether the target pixel is a pixel to be recorded by the defective discharge nozzle.

  At this time, if the target pixel is not a pixel to be recorded by a defective discharge nozzle, multi-level error diffusion processing is performed.

  On the other hand, if the target pixel is a pixel to be recorded by the defective discharge nozzle, it is determined whether the gradation value (pixel value) of the target pixel is equal to or greater than a predetermined first threshold.

  At this time, if the gradation value of the target pixel to be recorded by the defective discharge nozzle is not equal to or greater than the first threshold, that is, less than the first threshold, multi-level error diffusion processing is performed. Then, the quantization error in the multi-level error diffusion process is developed to the peripheral pixels of the pixel corresponding to the defective discharge nozzle. Here, as processing for expanding to peripheral pixels, processing for distributing to pixels on the downstream side in the main scanning direction and sub scanning direction is performed.

  On the other hand, if the gradation value of the target pixel for which the target pixel is to be recorded by the defective ejection nozzle is equal to or greater than the first threshold, the gradation value of the target pixel for which the target pixel is to be recorded by the defective ejection nozzle is It is determined whether or not it is equal to or greater than a predetermined second threshold larger than a threshold of 1 (second threshold> first threshold).

  At this time, if the gradation value of the target pixel recorded in the defective discharge nozzle is not equal to or more than the second threshold, that is, if the number is equal to or more than the first threshold and less than the second threshold Perform diffusion processing. Then, the quantization error in the multi-level error diffusion processing is developed by multiplying the peripheral pixels of the pixel corresponding to the defective discharge nozzle by a predetermined coefficient. Here, as processing for multiplying peripheral pixels by a predetermined coefficient for expansion, processing for multiplying pixels in the main scanning direction and sub-scanning direction on the downstream side by multiplying the predetermined coefficient is performed.

  On the other hand, if the gradation value of the target pixel for which the target pixel is recorded by the defective discharge nozzle is equal to or greater than the second threshold, the coordinates of the target pixel are stored. Then, multi-level error diffusion processing is performed.

  After that, the entire quantization error is updated.

  Then, it is determined whether the n-value conversion process has been completed for all the pixels.

  At this time, if the n-value conversion process has not been completed for all the pixels, the above process is repeated while moving the target pixel.

  Then, when the n-value conversion process for all the pixels is completed, the process shifts to the process shown in FIG.

  Referring to FIG. 6, first, it is determined whether there are coordinates of a stored pixel, that is, whether there is a pixel whose coordinates are stored.

  At this time, if there is a pixel whose coordinate is stored, pattern matching processing is performed around the pixel of the stored coordinate to replace a small dot with a large dot (dot substitution).

  That is, when the pixel value corresponding to the defective discharge nozzle is equal to or greater than the second threshold, the defective discharge nozzle is formed by pattern matching using a predetermined mask pattern according to the size and arrangement of dots around the defective discharge nozzle. Perform processing to replace small dots of the dots in the periphery with large dots.

  Thereafter, it is determined whether the pattern matching process for all the pixels is completed.

  Then, when the pattern matching process for all the pixels is finished, this process is finished.

  As described above, in the present embodiment, for the pixels recorded by the defective discharge nozzle, when performing the quantization process, only dots having a small level at which dots are not generated or image quality is not affected are generated. After carrying out the process of discharging, the quantization error is expanded to the pixels recorded by the surrounding normal discharge nozzles, and the arrangement and the size of the droplets from the normal discharge nozzle are changed, thereby the pixels by the defective discharge nozzle The degradation of the image quality is reduced (compensated) by keeping the density in the vicinity of. Here, the quantization process converts the pixel value (tone value: multi-value data) of the input image into an n-value dot pattern by multi-value error diffusion processing corresponding to n-value (n 整数 2 integer) It is a process.

  As described above, when developing a thin color with a low dot density by expanding the quantization error to the peripheral pixels of the pixel recorded by the ejection failure nozzle, the improvement effect by changing one dot is large. Therefore, the deterioration of the image quality can be reduced only by the compensation process of changing the arrangement and the size of the droplet downstream of the pixel recorded by the defective discharge nozzle.

  However, when the dot density is high and the image is close to an image in which the medium is filled with droplets, when performing compensation processing to change the arrangement and size of droplets of peripheral pixels downstream of the pixels recorded by the defective ejection nozzle, The larger the pixel value of the input image, the larger the quantization error developed around it. Therefore, if the quantization error expanded to the periphery becomes too large, in the pixel in which the quantization error is expanded, as a result of performing the multi-level error diffusion processing, there is a high possibility that the dot of the maximum size continues to be generated. As a result, when the dots of the maximum size are continuous, the compensation effect for the defective discharge nozzle can be obtained, but the dots in the compensation portion are noticeable and the image quality is degraded.

  Furthermore, when the density of the input image is high, it is difficult to obtain a sufficient improvement in the image quality unless compensation processing upstream of the pixels recorded by the defective discharge nozzle is also performed simultaneously.

  Therefore, as described above, when the pixel value of the pixel determined to be recorded by the defective discharge nozzle is less than the first threshold, the arrangement or size of the droplet downstream of the pixel recorded by the defective discharge nozzle As a compensation process for changing V.sub.x, a process of expanding a quantization error in a multi-level error diffusion process to surrounding pixels is performed. Even with such processing, the improvement effect (deterioration reduction effect) of the image quality can be obtained.

  In addition, when the pixel value of the pixel recorded by the non-ejection nozzle is equal to or more than the first threshold and less than the second threshold larger than the first threshold, the size on the downstream side of the pixel recorded by the defective ejection nozzle In order to prevent the generation of large dots, the quantization error in the multi-level error diffusion process develops a value multiplied by a constant coefficient to surrounding pixels. This prevents the generation of large dots downstream in size.

  Further, when the pixel value recorded by the non-ejection nozzle is equal to or more than the second threshold value, only the compensation processing by the development of the quantization error to the downstream side by multi-level error diffusion processing of the pixel recorded by the defective ejection nozzle Is not enough. Therefore, pattern matching is performed by comparing the shape and arrangement of dots around the defective discharge nozzle with the mask pattern, and small dots are compensated for both upstream and downstream of the pixels recorded by the defective discharge nozzle. Perform processing to replace large dots.

  Therefore, as described in the above embodiment, when the pixel value is equal to or larger than the second threshold, the coordinates of the pixel are stored, and the pattern matching process is performed after the multi-level error diffusion process is completed.

  As described above, in the method of processing image data in the above embodiment, when converting multi-value data of the input image into n-value dot patterns by multi-value error diffusion processing corresponding to n values (n 整数 2 integer) When the pixel value corresponding to the defective discharge nozzle is less than a predetermined first threshold value, the quantization error in the multi-level error diffusion processing is processed to expand the peripheral pixels of the pixel corresponding to the defective discharge nozzle. When the pixel value corresponding to the defective discharge nozzle is equal to or greater than the first threshold and equal to or smaller than a second predetermined threshold greater than the first threshold, the quantization error in the multi-level error diffusion process is The peripheral pixels of the pixel corresponding to the pixel are expanded by multiplying them by a predetermined coefficient, and when the pixel value corresponding to the defective discharge nozzle is equal to or greater than the second threshold, the dot around the defective discharge nozzle is Using size and a predetermined mask pattern corresponding to the arrangement performs a process to replace the small dots to large dots among the dots around the defective ejection nozzle by pattern matching.

  Next, the first threshold and the second threshold used to determine the pixel value will be described with reference to FIG. FIG. 7 is an explanatory view for explaining an example of the relationship between the drop amount, the dot diameter, and the medium type.

  The first threshold and the second threshold can be set for each type of medium to be used, for example, for each sheet type.

  For example, in a medium in which liquid easily spreads, for example, so-called plain paper, the image is improved (image quality that occurs in the defective discharge nozzle even if image compensation on the upstream side of pixels recorded by the defective discharge nozzle is not performed. The threshold value can be set high because the effect of reducing the deterioration of

  On the other hand, in the case of coated paper whose surface is coated, the liquid is tightened to a small dot diameter due to the effect of the coating on the surface. Therefore, if the image compensation is not performed on the upstream side of the pixels recorded by the defective discharge nozzle, the image quality improvement effect is low, and the threshold value needs to be set low.

  FIG. 7 shows the difference in dot diameter according to the type of medium on the paper.

  In addition to the above, the first threshold and the second threshold used to determine the pixel value are dots after performing multi-level error diffusion processing corresponding to n values (n ≧ 2) (after execution) The arrangement may be determined in advance, and in the multi-level error diffusion processing, a gradation which is a dot arrangement at which the improvement effect of the image quality is weakened may be set as a threshold.

  For example, as multi-level error diffusion processing, an example will be described in which the 256 gradations of the input are converted into three values (no drop, small drop, large drop). When the dot arrangement is designed in advance so that the large droplet has a 100% dot arrangement via the small droplet 100%, the first threshold is a gradation in which the dots are scattered sparsely. Since the effect is high, it is set to the gradation value expressed by 80% of the droplets, and the second threshold is expressed by 50% of the large droplets and 50% of the droplets as the limit that the dot can compensate only downstream. Can be set up to

  Further, the first threshold and the second threshold used to determine the pixel value can be set in accordance with the concentration of the liquid used in the printing apparatus.

  For example, yellow and the like have high brightness and low visibility, and therefore are difficult to see even if they are defective discharge nozzles. Therefore, the yellow threshold can be set as a large gradation. On the other hand, since black has high visibility, the threshold is set smaller than yellow.

  Further, the first threshold and the second threshold used for the determination of the pixel value are set in accordance with the image density when the normal ejection is performed.

  Next, a first example of mask pattern processing (dot replacement processing using a mask pattern) will be described with reference to FIGS. 8 and 9. FIG. FIG. 8 is an explanatory view of an example of a mask pattern, and FIG. 9 is an explanatory view of an example of dot replacement using the same mask pattern.

  Here, n for n-value (nn2) conversion is taken as an example where a total of four values of three kinds of dot diameter dots (large dot, medium dot, small dot) and no drop are used. .

  The dot replacement by the mask pattern is determined based on the presence or absence of the coordinates stored as the target pixel, as described in the above-described compensation process (FIG. 5). Here, if there is no saved (stored) coordinate, pattern matching is not performed. However, in this case, since the compensation process of the defective discharge nozzle by multi-level error diffusion is performed, it is possible to obtain the printing result with the improved image quality.

  On the other hand, when there are stored coordinates, dot replacement is performed by pattern matching.

  In this first example, dot replacement is performed by pattern matching with the mask pattern M1 for dot replacement shown in FIG. The mask pattern M1 for dot replacement has a 4 × 3 matrix, and replaces medium dots with large dots for the pixels Db located upstream and downstream with respect to the pixels Da recorded by the defective discharge nozzle It is a pattern.

  For example, when pattern matching is performed on image data that has become n values after multilevel error diffusion and the mask pattern M1 as shown in FIG. 9A, replacement dots and image data of the mask pattern M1 are displayed in pixels D1 to D4. Match Accordingly, as shown in FIG. 9B, the dots of the pixels D1 to D4 are replaced with medium dots to large dots.

  As described above, by replacing dots on both the upstream side and the downstream side of the pixel recorded by the defective discharge nozzle, it is possible to convert the pattern having a compensation effect, rather than replacing the dots only on the downstream side.

  In addition, since the mask pattern described above is applied to the dot arrangement after performing the multi-level error diffusion processing corresponding to n value (n22) conversion, the individual individual dot size after the n value You can also set the mask pattern of.

  Next, a second example of the mask pattern process (dot replacement process by the mask pattern) will be described with reference to FIGS. 10 and 11. FIG. FIG. 10 is an explanatory view of an example of a mask pattern, and FIG. 11 is an explanatory view of an example of dot replacement using the mask patterns of FIG. 8 and FIG.

  Since this second example is applied to the dot arrangement after performing multi-level error diffusion processing corresponding to n-value (n) 2) conversion, an individual mask matched to each dot size after n-value It is an example which sets a pattern.

  Therefore, the mask pattern M2 for dot replacement shown in FIG. 10 is used together with the mask pattern M1 of the first example described above. This mask pattern M2 is a pattern having a 4 × 3 matrix and replacing small dots with medium dots for the pixels Dc located upstream and downstream with respect to the pixels Da recorded by the defective discharge nozzle. .

  Then, for example, when pattern matching is performed on the n-valued image data after multi-level error diffusion as shown in FIG. 11A and the mask pattern M1 described in the first example, the pixels D1 to D4 are masked. The replacement dot of the pattern M1 matches the image data. Further, when pattern matching between the image data and the mask pattern M2 is performed, the replacement dots of the mask pattern M2 and the image data coincide with each other in the pixels D5 to D11. Therefore, as shown in FIG. 11B, the dots of the pixels D1 to D4 are replaced with medium dots to large dots, and the dots of the pixels D5 to D11 are replaced with small dots to medium dots.

  As described above, by using the mask patterns M1 and M2, that is, by replacing dots using mask patterns individually set for each size of dots around a defective discharge nozzle, for example, only the mask pattern M1 can be obtained. The influence of the defective discharge nozzle can be mitigated compared to the case of using.

  The compensation process described above can be performed either on the apparatus side that discharges the liquid or on the host side. In this case, the program can be executed by storing the program according to the present invention for causing the computer to perform the above-described compensation processing in the ROM 502 or the ROM 612.

  In the present application, the “device for discharging a liquid” is a device including a liquid discharge head or a liquid discharge unit, and driving the liquid discharge head to discharge the liquid. The device for discharging the liquid includes a device capable of discharging the liquid to one to which the liquid can adhere.

  This "device for discharging liquid" can also include means related to feeding, transporting, and discharging of those to which the liquid can be attached, as well as a pre-processing device, a post-processing device, and the like.

  For example, as a “device for discharging liquid”, there is an image forming apparatus which is a device for discharging a liquid to form an image on a sheet.

  Further, the “device for discharging liquid” is not limited to a device in which a significant image such as characters and figures is visualized by the discharged liquid. For example, the one which forms the pattern etc. which does not have meaning itself is included.

  The above-mentioned "the liquid can be attached" means that the liquid can be attached even temporarily. The material of “the liquid to which the liquid adheres” may be any material that can temporarily adhere to the liquid such as paper, yarn, fiber, fabric, leather, metal, plastic, glass, wood, ceramics and the like.

  The "liquid" also includes an ink, a treatment liquid, a DNA sample, a resist, a pattern material, a binder, a modeling liquid, and the like.

  Further, the “device for discharging the liquid” includes both a serial type device for moving the liquid discharge head and a line type device for not moving the liquid discharge head unless particularly limited.

  Moreover, the "liquid discharge head" is not limited to the pressure generating means used. For example, in addition to the piezoelectric actuator (which may use a laminated piezoelectric element) as described in the above embodiment, the thermal actuator using an electrothermal transducer such as a heating resistor, a diaphragm and a counter electrode An electrostatic actuator or the like may be used.

  In the present application, image formation, recording, printing, printing, printing, and the like are all synonymous with each other.

Reference Signs List 3 carriage 4, 4a, 4b liquid discharge head 100 discharge detection unit 500 control unit

Claims (8)

An apparatus comprising a liquid discharge head having a plurality of nozzles for discharging a liquid, comprising:
When converting multi-value data of an input image into an n-value dot pattern by multi-value error diffusion processing corresponding to n values (n 整数 2 integer),
When the pixel value corresponding to the defective discharge nozzle is less than a predetermined first threshold value, the quantization error in the multi-level error diffusion processing is expanded to the peripheral pixels of the pixel corresponding to the defective discharge nozzle. ,
When the pixel value corresponding to the defective discharge nozzle is equal to or more than the first threshold and less than a second predetermined threshold larger than the first threshold, quantization error in the multi-level error diffusion process is Performing a process of developing by multiplying the peripheral pixels of the pixel corresponding to the defective discharge nozzle by a predetermined coefficient;
When the pixel value corresponding to the defective ejection nozzle is not less than the second threshold value, after conversion to a dot pattern of n value by the multi-level error diffusion process, using a predetermined mask pattern, before Symbol defective ejection nozzle An apparatus for discharging liquid characterized in that processing of replacing small dots of the dots in the vicinity of the dots with large dots is performed. When the pixel value corresponding to the defective discharge nozzle is equal to or greater than the second threshold, the coordinates of the pixel corresponding to the defective discharge nozzle are stored, and the small dots are converted into large dots based on the stored coordinates of the pixels. The apparatus for discharging a liquid according to claim 1, wherein the replacement process is performed. In the processing of replacing small dots with large dots, the n-values after converting multi-value data of the input image into n-value dot patterns by multi-value error diffusion processing corresponding to n values (an integer of n 整数 2) The apparatus for discharging a liquid according to claim 1, wherein the replacement of dots is performed using a mask pattern individually set for each size of dots in the vicinity of the defective discharge nozzle, corresponding to the above. When the pixel value corresponding to the defective discharge nozzle is equal to or more than the second threshold, the shape and arrangement of dots around the defective discharge nozzle after the multi-level error diffusion processing is compared with the predetermined mask pattern The apparatus according to any one of claims 1 to 3 , wherein pattern matching is performed to replace small dots of the dots around the defective discharge nozzle with large dots . The apparatus according to any one of claims 1 to 3, wherein the first threshold and the second threshold are set according to the type of medium. The apparatus according to any one of claims 1 to 3, wherein the first threshold and the second threshold are set in accordance with the color of the liquid. A method of processing image data for an apparatus comprising a liquid ejection head having a plurality of nozzles for ejecting liquid, comprising:
When converting multi-value data of an input image into an n-value dot pattern by multi-value error diffusion processing corresponding to n values (n 整数 2 integer),
When the pixel value corresponding to the defective discharge nozzle is less than a predetermined first threshold value, the quantization error in the multi-level error diffusion processing is expanded to the peripheral pixels of the pixel corresponding to the defective discharge nozzle. ,
When the pixel value corresponding to the defective ejection nozzle is equal to or more than the first threshold and equal to or less than a second predetermined threshold larger than the first threshold, quantization error in the multi-level error diffusion process is Performing a process of developing by multiplying the peripheral pixels of the pixel corresponding to the defective discharge nozzle by a predetermined coefficient;
When the pixel value corresponding to the defective ejection nozzle is not less than the second threshold value, after conversion to a dot pattern of n value by the multi-level error diffusion process, using a predetermined mask pattern, before Symbol defective ejection nozzle A method of processing image data comprising performing processing of replacing small dots of the dots in the periphery of the image with large dots. A program for causing a computer to process image data in an apparatus provided with a liquid discharge head having a plurality of nozzles for discharging a liquid.
When converting multi-value data of an input image into an n-value dot pattern by multi-value error diffusion processing corresponding to n values (n 整数 2 integer),
When the pixel value corresponding to the defective discharge nozzle is less than a predetermined first threshold value, the quantization error in the multi-level error diffusion process is developed to the peripheral pixels of the pixel corresponding to the defective discharge nozzle,
When the pixel value corresponding to the defective ejection nozzle is equal to or more than the first threshold and equal to or less than a second predetermined threshold larger than the first threshold, quantization error in the multi-level error diffusion process is Developing the peripheral pixels of the pixel corresponding to the defective discharge nozzle by multiplying the peripheral pixels by a predetermined coefficient;
When the pixel value corresponding to the defective ejection nozzle is not less than the second threshold value, after conversion to a dot pattern of n value by the multi-level error diffusion process, using a predetermined mask pattern, before Symbol defective ejection nozzle A program to make a computer process to replace small dots of the dots around with large dots.

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