JP2004114301A - Image recording apparatus and image recording method - Google Patents

Abstract

Provided is an image recording apparatus capable of obtaining a high-density character image output without complicating the apparatus.
An image recording apparatus includes an image data input unit, an image processing unit, an image forming unit having a plurality of recording heads, and a central processing unit for controlling each unit. The central processing unit 10 has a function of selecting and outputting a dot size of the recording head 30 to be output according to an input image signal.
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image recording apparatus and an image recording method for increasing a character density by changing a dot size formed on a recording medium.
[0002]
[Prior art]
2. Description of the Related Art An image recording apparatus having functions such as a printer, a copying machine, and a facsimile is configured to record an image (character, picture, or the like) on a recording material such as paper based on image information. In recent years, in particular, an image recording apparatus of an ink jet type, which is excellent in miniaturization, silent operation, and high image quality of the apparatus, has attracted attention. The ink jet recording apparatus can discharge ink from a recording unit (hereinafter, a recording head) and perform recording on a recording material in a non-contact manner. By using a recording head that uses multicolor inks, it is easy to colorize, and with the establishment of technology for ejecting minute droplets of ink, higher-speed, higher-quality images can be obtained. I have.
The possibility of forming fine droplets has made it possible to obtain high-quality output with little graininess for (halftone) images such as photographs, The problem that the density is insufficient due to the small size of the dots has arisen.
Therefore, as disclosed in Japanese Patent Application Laid-Open No. 6-191040, there has been proposed a method of recording with a small dot density and a large dot diameter at the time of character recording, and a method of performing plural times of recording at the time of character recording.
Japanese Patent Application Laid-Open No. 11-208029, "Printing Apparatus, Printing Method, and Recording Medium", describes an overprinting method for eliminating dot position deviation during reciprocal printing. Further, there is a description that inks having different densities are properly used depending on the gradation to be expressed.
[Patent Document 1] JP-A-6-191040 [Patent Document 2] JP-A-11-202029 [0003]
[Problems to be solved by the invention]
However, in the related art, there is a problem that a recording head must be separately provided in order to perform recording with a large dot diameter, which leads to an increase in cost. In addition, it is difficult to print small dots at the same position even in multiple recordings, and it is inevitable that some misalignment may occur. If misalignment occurs, the dot shape may be disturbed, leading to deterioration of image quality. Remains.
Accordingly, an object of the present invention is to provide an image recording apparatus and an image recording method capable of obtaining a high-density character image output without complicating the apparatus in order to solve the above-described problems.
[0004]
[Means for Solving the Problems]
In order to achieve the above object, an invention according to claim 1 is an image recording apparatus comprising an image data input unit, an image processing unit, an image forming unit having a plurality of recording heads, and a central processing unit for controlling each unit. The recording head forms a plurality of dots of different sizes, and the central processing unit is the most important image recording apparatus having the function of selecting and outputting the dot size of the recording head to be output according to the input image signal. Features.
According to a second aspect of the present invention, in the first aspect, when the input image signal is a character signal, the image recording apparatus performs overprinting a plurality of times using dots of different sizes.
According to a third aspect of the present invention, there is provided an image recording apparatus according to the second aspect, wherein, when printing is performed a plurality of times, after printing a dot having a relatively small size, a dot having a relatively large size is overlapped and printed. Characteristics.
According to a fourth aspect of the present invention, in the first aspect, the image processing means has an area determining function of determining an area of a character image portion and a halftone image portion of a document image, and determines an area from an input image signal. The main feature of the present invention is an image recording apparatus that selects and outputs a dot size.
According to a fifth aspect of the present invention, there is provided an image recording apparatus according to the fourth aspect, wherein when the area is determined to be a character image portion by the area determining function of the image processing means, overlapping printing is performed a plurality of times using dots of different sizes. And
According to a sixth aspect of the present invention, there is provided an image recording apparatus according to the fifth aspect, wherein when printing is performed a plurality of times, after printing a dot having a relatively small size, a dot having a relatively large size is overlapped and printed. Characteristics.
According to a seventh aspect of the present invention, in the first aspect, the recording head is mainly characterized by an image recording apparatus of an ink jet system.
An eighth aspect of the present invention is characterized in that, in the fourth and seventh aspects, an image recording apparatus which controls an output dot size selected in accordance with an area determination result by an ink ejection amount.
According to a ninth aspect of the present invention, there is provided an image recording method comprising: an image reading step of reading a document image by a digital signal; and an image forming step of forming an image by a plurality of recording heads. The most main feature is an image recording method of forming dots of the above type and selecting and outputting a dot size to be output according to an input image signal.
[0005]
A tenth aspect of the present invention is characterized in that, in the ninth aspect, when the input image signal is a character signal, an image recording method of performing a plurality of overprints by using dots of different sizes.
According to an eleventh aspect of the present invention, there is provided an image recording method according to the tenth aspect, wherein when performing printing a plurality of times, after printing a dot having a relatively small size, a dot having a relatively large size is superimposed and printed. Characteristics.
According to a twelfth aspect of the present invention, in the ninth aspect, after the image reading step, there is provided an area determining step of determining an area of a character image portion and a halftone image portion of the original image. The main feature is an image recording method for selecting and outputting a dot size to be output according to (1).
According to a thirteenth aspect of the present invention, in the twelfth aspect, an image recording method is characterized in that when an area is determined to be a character image portion in the area determining step, overlapping printing is performed a plurality of times using dots of different sizes.
According to a fourteenth aspect of the present invention, there is provided an image recording method according to the thirteenth aspect, wherein when printing is performed a plurality of times, after printing a dot having a relatively small size, a dot having a relatively large size is overlapped and printed. Characteristics.
[0006]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram of an image recording apparatus according to an embodiment of the present invention. The image recording apparatus includes a central processing unit (CPU) 10 for performing overall control, an image data input unit 11 for inputting image data from an external photographing device or the like, and γ correction of input image data and processing such as area determination. The image processing unit 12 includes a ROM 13 storing various programs, a RAM 14 serving as a work field, and an image forming unit 15 for forming an image based on a processing result of the image processing unit 12.
The image data input unit 11 inputs RGB data obtained by converting analog data read by the CCD into a digital value of 8 bits per pixel to the image processing unit 12. An example of digital image processing performed by the image processing unit 12 in response to the input data will be described.
FIG. 2 is a block diagram illustrating a configuration example of the image processing unit. Here, after the scanner γ correction is performed on the input data by the scanner γ correction unit 20, filter processing such as smoothing and edge enhancement is performed by the filter processing unit 21. A process is performed to remove the background of the document while maintaining the reproducibility of the low density portion of the picture.
The data from which the background is removed is converted from RGB data into CMYK data in the color correction processing unit 23, and the UCR / UCA processing unit 24 performs UCR / UCA processing. After the printer γ correction is performed on this data by the printer γ correction unit 25, the number of output bits (about 1 to 2 bits) of the printer is calculated by a halftone processing unit 26 by a halftone processing method such as dither processing or error diffusion processing. ) And send it out. The configuration of the image processing unit 12 has various forms other than the configuration shown in FIG. 2, and is not limited to the configuration shown in FIG. 2.
[0007]
Next, determination of an area of a document image will be described. The area determination is performed by using the density characteristics of the image data after the scanner γ correction of the input data. For example, a means for determining a halftone image such as a photograph utilizes the fact that a photographic image generally has a wide range of intermediate density areas and an image other than a photograph (a character image or a halftone image) has a small area of intermediate density. Then, it is determined whether or not it is a photograph area.
Specifically, a predetermined area (for example, a 5 × 5 pixel area centered on a pixel of interest as shown in FIG. 3) is referred to, and when all the pixels in the area have an intermediate density, the pixel is referred to as a photographic area. Is determined, and in other cases, the area is determined to be a region other than the photograph. When determining a character image, the continuity of black pixels (high density) or white pixels (low density) can be used to determine the character image using pattern matching. As described above, the image can be determined based on the density histogram of the character image portion detection result and the halftone image portion detection result.
The image forming unit 15 forms an image in response to the processing result of the image processing unit 12. Hereinafter, in the embodiment of the present invention, description will be given of a case where recording is performed on the image forming unit 15 using an inkjet head. However, for example, an image forming unit using electrophotography can output a different dot diameter. If it is a means, the effect of the present invention can be obtained similarly.
A so-called ink jet head that discharges ink onto a recording material to perform recording, has a very low level of noise during recording, is capable of high-speed printing, and can use inexpensive plain paper with a high degree of freedom of usable ink. It has many advantages and is used as many output machines. Among them, the so-called ink-on-demand method, which discharges ink droplets only when recording is necessary, is currently the mainstream because it does not require collection of ink droplets unnecessary for recording. The ink-on-demand method includes a method using a piezoelectric element, a method using a heating element, and a method using an electrostatic force as means for generating ejection energy (pressure).
[0008]
FIG. 4 is an external view of the inkjet recording head unit. As shown in FIG. 4, the recording head 30 is mounted on a carriage 31 movable in the main scanning direction together with a replaceable ink cartridge 32 that supplies ink to the recording head 30. The ink cartridge 32 is filled with inks of four colors of yellow (Y), magenta (M), cyan (C) and black (BK), respectively. Sometimes ink is used. At the time of recording, the recording head 30 is driven in accordance with an image signal while moving the carriage 32, thereby discharging ink from nozzles and causing ink to adhere to a recording material to perform recording (not shown).
A recovery device for recovering ink ejection failure from the recording head 30 is disposed at a position outside the recording area on one of the left and right ends in the carriage movement direction. FIG. 5 is an external view of a recovery device for recovering ink ejection failure in the print head.
The recovery device has capping means by a cap 33, suction means by a suction pump 34, and cleaning means by a wiper blade 35. The carriage 32 is moved to the recovery device side during printing standby, the recording head 30 is capped by the capping means, and the ejection port is kept in a wet state, thereby preventing ejection failure due to ink drying. In addition, by discharging ink that is not related to printing during printing or the like, the ink viscosity of all the discharge ports is kept constant, and stable discharge performance is maintained.
When a discharge failure occurs, the discharge port of the recording head 30 is sealed with a capping unit, bubbles are sucked out of the discharge port with the ink by a suction unit through a tube, and ink and dust adhered to the discharge port surface are cleaned. The ejection failure is recovered by the means. The sucked ink is discharged to a waste ink reservoir (not shown) provided at a lower portion of the main body, and is absorbed and held by an ink absorber inside the waste ink reservoir.
Important characteristics when ejecting ink and forming an image are the ejection amount (Mj) of the ejected ink droplet and the flying speed (Vj) of the ink droplet. In particular, since the ejection amount (Mj) is the first factor that determines the dot size when the ink adheres to the recording material, it has a deep relationship with the resolution and image quality of the image. On the other hand, the flying speed (Vj) is the value of the dot adhering to the recording material in the case where ink is continuously ejected to form a line drawing, or in the case where an image is formed by ejecting ink from a plurality of nozzles. In order to prevent the displacement, it is important that the flying speed is always stable.
[0009]
Here, means and a method for outputting different dots in the ink jet recording head will be described. FIG. 6 is a block diagram of the recording head drive control unit according to the present invention in the image forming unit. The central processing unit 10 supplies data for generating drive waveforms (p1 to p3) to the waveform generation circuit 40, and supplies a print signal, a shift clock, a latch signal, and the like to the driver IC 41.
The waveform generating circuit 40 generates and outputs drive waveforms p1 to p3 having the same or different pulse widths in time series by performing D / A conversion of voltage data supplied from the central processing unit 10 using a D / A converter. I am trying to do it. As shown in FIG. 7A, the drive waveform Pv is generated in a time series by repeating the pulse drive waveforms p1 to p3 used for ink ejection in one drive cycle of the recording head 30.
The driver IC 41 selects a pulse (hereinafter, referred to as an ejection pulse) to be used for ink ejection in accordance with a print signal from Pv input in a time series, and performs control to supply the pulse to the individual electrode 42 of the recording head 30. The driver IC 41 includes a shift register 43 for inputting a clock and a print signal from the central processing unit 10, a latch circuit 44 for latching a register value of the shift register 43 with a latch signal from the central processing unit 10, and an output value of the latch circuit 44. , And an analog switch array 46 whose on / off is controlled by the level conversion circuit 45. The analog switch array 46 includes analog switches AS1 to Asm connected to m individual electrodes 41 of the recording head 30 (the number of nozzles capable of ejecting ink is m).
Then, a print signal corresponding to the clock is fetched into the shift register 43, and the latch circuit 44 latches the print signal fetched into the shift register 43 by the latch signal, and inputs the latched print signal to the level conversion circuit 45. The level conversion circuit 45 turns on / off the analog switch Asm (m = 1 to m) connected to each individual electrode 42 according to the data content.
Since the drive waveform Pv is given to the analog switch Asm (m = 1 to m) from the waveform generation circuit 40 via the amplifier 47, the drive waveform (m = 1 to m) is turned on when the analog switch Asm (m = 1 to m) is turned on. p1 to p3) are selectively applied to the individual electrodes 42. 48 is a common electrode.
[0010]
The operation of the recording head drive control unit configured as described above will be described with reference to FIGS. As shown in (1) of FIG. 7, three driving waveforms from the first driving waveform p1 to the third driving waveform p3 are generated and output in time series within one driving waveform, and this is the analog switch AS1 of the driver IC 41. ~ Asm. Then, by giving a print signal from the central processing unit 10, the analog switch Asn (any one of n = 1 to m) of the driver IC 41 is turned on or off, and Asn is turned on, for example, as shown in (2) of FIG. During this operation, the ejection pulse inputted during the operation is selected and applied to the individual electrodes 42 of the recording head 30 as shown in FIG.
FIG. 7C shows a pulse applied to an individual electrode corresponding to one nozzle, and this nozzle performs ink ejection at p1 to p3 in the first driving cycle shown in FIG. In the next driving cycle, the ejection is performed only by p1 (b), and in the next driving cycle, the ejection is performed by p1 and p2 (c). In addition, it shows that the ejection is not performed in the final driving cycle shown in FIG.
Also, the dots formed by ink ejected according to (a), (b), and (c) in FIG. 7C are (a ′), (b ′), and (c ′) in FIG. ), The size of the dot can be relatively changed. Here, in order to select an ejection pulse within one driving cycle, the print signal given from the central processing unit 10 is configured to rewrite data (DATA) four times within one driving cycle as shown in FIG. I have.
Next, a first embodiment of the present invention based on the above embodiment will be described with reference to FIG. When the digital signal of the document image read by the image data input unit 11 is determined to be a character image portion by the area determination unit of the image processing unit 12, a drive waveform used for ejection is selected according to FIGS. . In this case, in the present embodiment, a case is described in which the repetitive movement of the carriage 31 movable in the main scanning direction is used to perform the overprinting. When it is determined that the image is a character image, first, the dot (b ′) of FIG. 7 (4) is printed by the waveform of FIG. According to the waveform of (a) (or (c)), printing was performed by superimposing dots of (a ') (or (c')) at the same position as in the forward movement.
[0011]
FIG. 9 is a diagram showing a state of dots when overprinting is performed. By first printing small dots and then printing large dots, it is possible to prevent bleeding when dots printed earlier on the paper are dried or penetrated to some extent, and then printed over and over. it can. Furthermore, by overprinting dots of different sizes, a certain degree of deviation of the printing position can be absorbed, image deterioration can be prevented, and a character image with high density can be obtained.
Next, a second embodiment will be described with reference to FIG. FIG. 10 is a diagram showing the nozzle arrangement of the recording head as viewed from the ejection side. Each recording head 30 mounted on the movable carriage 31 has a plurality of nozzles (ink discharge ports), and can be arranged in a plurality of rows as shown in FIG. In this embodiment, four rows are arranged in a staggered arrangement, and positions a to f in the nozzle arrangement direction are the same in the first row, the third row, the second row, and the fourth row. In the second embodiment, a character image with high density could be obtained by utilizing large and small dots by utilizing this inter-row pitch, even if the printing is not reciprocating.
Specifically, when the carriage 31 scans in the right direction in the drawing, the waveform in FIG. 5D is changed from the first column −a (hereinafter referred to as 1−a) by the waveform in FIG. (B ') Dots are printed, and then (a') (or (c ')) dots are printed from 3-a to (a) (or (c)) waveforms in FIG. 7 (3). At this time, the dots printed on the paper are dried or permeated to some extent by controlling the dots to overlap at the same position on the paper by converting between the nozzle rows a and c and the carriage movement speed. Can be prevented from being bleeding when printing is performed over the image, and the effect of the present invention can be obtained as in the first embodiment.
[0012]
【The invention's effect】
As described above, according to the image recording apparatus of the first aspect, the dot size to be output can be selected according to the input image signal, so that the dots suitable for the image type such as characters and halftones can be selected. Output results can be obtained in size, and image quality can be improved.
According to the image recording apparatus of the second aspect, when the input image signal is a character signal, by performing overprinting with dots of different sizes, a character image with a high density can be obtained and the character image quality is improved. Can be done.
According to the image recording apparatus of the third aspect, by recording relatively large dots after recording relatively small dots, large dots are recorded after drying or fixing of small dots that easily penetrate. Therefore, it is possible to prevent bleeding due to overprinting and improve image quality.
According to the image recording apparatus of the fourth aspect, the dot size to be output can be selected based on the area discrimination result of the original image, so that the output result can be output in a dot size suitable for an image type such as characters and halftones. And image quality can be improved.
According to the image recording apparatus of the fifth aspect, when the input image signal is a character signal, by performing overprinting with dots of different sizes, a character image with high density can be obtained and the character image quality is improved. Can be done.
According to the image recording apparatus of the present invention, by printing a relatively large dot after printing a relatively small dot, a large dot is printed after fixing a small dot that is easy to dry or permeate. Therefore, it is possible to prevent bleeding due to overprinting and improve image quality.
According to the image recording apparatus of the seventh aspect, by adopting the ink jet system for the recording head, it is possible to easily achieve the miniaturization and colorization of the apparatus.
According to the image recording apparatus of the eighth aspect, by controlling the dot size based on the amount of ink discharged, dot modulation can be performed without increasing the size of the apparatus.
According to the image recording method of the ninth aspect, since the dot size to be output can be selected according to the input image signal, an output result is obtained with a dot size suitable for an image type such as a character or a halftone. Image quality can be improved.
[0013]
According to the image recording method of the present invention, when the input image signal is a character signal, a method of performing overprinting with dots of different sizes is used, so that a character image with a high density can be obtained. Quality can be improved.
According to the image recording method of the present invention, by printing a relatively small dot and then printing a relatively large dot in a superimposed manner, a large dot is dried or fixed after a small dot is easily fixed. Can be recorded, and bleeding due to overprinting can be prevented, and image quality can be improved.
According to the image recording method of the twelfth aspect, the dot size to be output can be selected based on the area discrimination result of the original image, so that the output result can be output in a dot size suitable for an image type such as characters and halftones. And image quality can be improved.
According to the image recording method of the present invention, when the input image signal is a character signal, a method of performing overprinting with dots of different sizes is used, so that a character image with a high density can be obtained. Quality can be improved.
According to the image recording method of the present invention, by printing a relatively large dot after recording a relatively small dot, a large dot can be formed after drying or fixing of a small dot which easily penetrates. Can be recorded, so that bleeding due to overprinting can be prevented and the image quality can be improved.
[Brief description of the drawings]
FIG. 1 is a block diagram of an image recording apparatus according to an embodiment of the present invention.
FIG. 2 is a block diagram of an image processing unit.
FIG. 3 is a diagram showing a 5 × 5 pixel area centered on a pixel of interest.
FIG. 4 is an external view of an inkjet recording head unit.
FIG. 5 is an external view of a recovery device for recovering ink ejection failure in a print head.
FIG. 6 is a block diagram of a recording head drive control unit according to the present invention in the image forming unit.
FIG. 7 is a diagram illustrating an operation of a recording head drive control unit.
FIG. 8 is a diagram illustrating the operation of a printhead drive control unit.
FIG. 9 is a diagram illustrating the appearance of dots when overprinting is performed.
FIG. 10 is a diagram illustrating a nozzle arrangement of a recording head as viewed from an ejection side.
[Explanation of symbols]
Reference Signs List 10 central processing unit (central processing unit), 11 image data input unit (image data input unit), 12 image processing unit (image processing unit), 15 image forming unit (image forming unit), 30 recording head

Claims (14)

Image data input means, image processing means, image forming means having a plurality of recording heads, in an image recording apparatus equipped with a central processing means for controlling each of the means, the recording head forms a plurality of dots of different sizes, An image recording apparatus, characterized in that the central processing means has a function of selecting and outputting a dot size of a recording head to be output according to an input image signal. 2. The image recording apparatus according to claim 1, wherein, when the input image signal is a character signal, overlapping printing is performed a plurality of times using dots of different sizes. 3. The image recording apparatus according to claim 2, wherein when performing the overprinting a plurality of times, a relatively small dot is printed, and then a relatively large dot is overprinted. 2. The image processing device according to claim 1, wherein the image processing unit has an area determining function of determining an area of a character image portion and an area of a halftone image portion of the original image, and determines an area from an input image signal to select a dot size. An image recording apparatus characterized by outputting. 5. The image recording apparatus according to claim 4, wherein when the area is determined to be a character image portion by the area determining function of the image processing means, the overlapping recording is performed a plurality of times using dots of different sizes. 6. The image recording apparatus according to claim 5, wherein when performing the overprinting a plurality of times, a relatively small dot is printed, and then a relatively large dot is printed. 2. The image recording apparatus according to claim 1, wherein the recording head is of an ink jet type. 8. The image recording apparatus according to claim 4, wherein an output dot size selected according to the area determination result is controlled by an ink ejection amount. In an image recording method including an image reading step of reading a document image by a digital signal and an image forming step of forming an image with a plurality of recording heads, in the image forming step, a plurality of dots having different sizes are formed and input. An image recording method for selecting and outputting a dot size to be output in accordance with the output image signal. 10. The image recording method according to claim 9, wherein when the input image signal is a character signal, the recording is performed a plurality of times by using dots of different sizes. 11. The image recording method according to claim 10, wherein, when performing the overprinting a plurality of times, a relatively small dot is printed, and then a relatively large dot is overprinted. 10. The image forming method according to claim 9, further comprising, after the image reading step, an area discriminating step of discriminating an area of a character image portion and a halftone image portion of the document image. An image recording method characterized by outputting. 13. The image recording method according to claim 12, wherein when the image is determined to be a character image portion in the area determination step, the printing is performed a plurality of times using dots of different sizes. 14. The image recording method according to claim 13, wherein when performing the multiple-time recording, a relatively small-sized dot is recorded, and then a relatively large-sized dot is superimposed and recorded.

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