JPH111006A - Recording apparatus and recording method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To record images having a density gradient with high quality, by generating recording data so that a direction in which a gradation changes from a high density to a low density is a record scan direction, selecting ink of a density according to a density value specified by the recording data, and recording images with the ink. SOLUTION: Ink density data are read out from a ROM, and an ink and an image data density value are made to correspond to each other (S10). A threshold value for switching an ink to be used is calculated (S20). Image data are input (S30). A multilevel error diffusion process is carried out in a record scan direction, and each pixel density value is converted into a multilevel value (S40). A change rate of density gradients of adjacent multivalued data is obtained (S50). Forward scan record image data and rearward scan record image data are formed (S60, S70), and an error diffusion process is executed (S80). Record multivalued data in a forward and a rearward scan directions are converted to ink discharge control data respectively and output to a recording head. Since the ink is switched to a smaller density, discontinuity of dot densities when the ink is switched becomes difficult to see.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printing apparatus and a printing method, and more particularly to a printing apparatus and a printing method for printing a gradation image by discharging ink droplets according to an ink jet system.

[0002]

2. Description of the Related Art With the spread of information processing devices such as copiers, word processors and computers, and communication devices, a recording head of an ink jet system is used as one of image forming (recording) devices of those devices. Those that perform digital image recording are rapidly spreading. Also,
With the increase in quality and color of visual information output from such information processing devices and communication devices, output of high-quality color images from images output from recording devices is also desired.

In such a printing apparatus, in order to print an image at a high resolution, generally, a plurality of printing elements are integrated and arranged, and a printing head (hereinafter, referred to as a printing head) in which a plurality of ink discharge ports and liquid paths are integrated at high density. , A multi-head). Further, for color image recording, for example, a head unit having a plurality of multi-heads corresponding to each ink of cyan (C), magenta (M), yellow (Y), and black (K) is used.

However, there is a certain limit to the high-density integration of ink discharge ports and liquid paths, and therefore, there is also a certain limit to the miniaturization of each pixel of a recorded image, and the dot size for forming each pixel is also limited. It has to be larger than a certain size. Therefore, especially in a low-density highlight portion of the recorded image, a granular feeling may appear in the image, and the quality of the image may be degraded.

On the other hand, instead of increasing the integration density of the ink discharge ports and liquid paths, ie, instead of reducing the size of one pixel, the dot size formed by the discharged ink droplets is reduced, In some cases, recording is performed using a so-called multi-drop method in which pixels are formed by a number of ink droplets corresponding to the recording density. In the multi-drop system, the diameter of the ink dots recorded on the recording paper can be made relatively small, so that it is possible to suppress the granularity in a low density portion such as a highlight portion.

However, even with the multi-drop method, in order to stably eject ink droplets having a small particle diameter, there is a certain limit to the miniaturization of the ink droplets, and thus there is also a limit to high image quality. is there. Also, in this method, the higher the density, the more the number of ink droplets ejected to one pixel increases, and the lower the recording speed. Therefore, if an attempt is made to obtain a high-quality image, there arises a problem that the recording speed is reduced.

As another method for improving the image quality without increasing the integration density of the ink discharge ports of the recording head, there is known a light and shade recording method using similar shades of ink having different ink densities. According to this method, a highlight portion or the like is recorded with low-density light ink to make the granularity of recording dots inconspicuous, and a high-density portion is recorded with dark ink to suppress a decrease in recording speed. be able to.

FIG. 8 is a diagram for explaining how three types of dark and light inks are used in accordance with the density level of an input image signal. Since these three types of inks are prepared for each color ink, when performing color recording using such inks, 12 recording heads are used for each ink. According to FIG. 8, three types of inks (light ink (dill.), Medium density ink (mid.), And dark ink (conc.)) Are provided according to the density level (0 to 255) of the input image signal. One of them is selected and recording is performed.

The input image data is subjected to a multi-value processing or a shading distribution, and then subjected to a binarization processing by a binarization circuit and transferred to twelve recording heads. Kinds of image signals K conc., K med., K dil
l, C conc., C med., C dill., M conc., M me
d., M dill., Y conc., Y med., Y dill. Here, K, M, C, and Y correspond to the colors of the ink, respectively, and the subscripts conc., Med., And dill. Correspond to the ink density.

In an image recorded using such an ink and a recording head, a highlight portion (low-density area) of the recorded image is recorded with light ink to reduce the granularity of dots, Are recorded with medium density ink or dark ink. As a result, while keeping the recording speed higher than the multi-drop method,
Image quality can be improved.

As the pseudo halftone processing method by the above-mentioned binarization processing, a dither method, an error diffusion method, an average density preservation method, and the like are known.

In the dither method, data of each pixel is binarized by a threshold value for each pixel determined by a dither matrix.

In the error diffusion method, for example, R. FLOYD
& L. STINBERG, "ANAADAPTIVE A
LGORITHM FOR SPETIAL GRAY
SCALE ", SID 75 DIGEST, PP36
As described in -37, the multi-valued image data of the target pixel is binarized (converted to the darkest level or the lightest level)
Then, the difference between the binarization level and the value of the multi-valued data before binarization is distributed and diffused to the vicinity of the pixel of interest and added.

In the mean density preservation method, for example, as described in Japanese Patent Application Laid-Open No. 2-210962, already binarized data in the vicinity of a pixel of interest or a pixel of interest is converted to black or white. A threshold value is obtained based on the value including the converted value, and the threshold value is used to binarize the pixel data of the target pixel.

Further, as a method of expressing multi-gradation using dark and light inks, not only one kind of ink but also two or more kinds of dark and light inks are recorded for one pixel so that one pixel can be used for ink. There is also a method of expressing more gradations than the number of types.

[0016]

However, the above conventional example has the following problems.

In a recording apparatus capable of reciprocal recording by a recording head, for example, when an image in which the density (gradation) continuously increases from the left end to the right end of the recording paper is drawn, it is necessary to correspond to this. When printing is performed while scanning the print head from left to right (forward direction), printing is performed by switching to a different type of ink at a location exceeding a predetermined density value. Dots become noticeable for the following reasons:

That is, if there is no ink ejection from the recording head for a while, the ink adhering to the ejection surface of the recording head and the ink at the ink ejection port dries, and the density of the ink in that portion increases. . When the ink is ejected in such a state, dots are formed with ink having a higher density than the density assumed in advance. Such dots appear as discontinuities in the density when recording an image that continuously changes from a low density to a high density as described above, and are easily noticeable.

For example, in a portion A where the used ink is switched as shown in FIG. 8, dots of medium density ink are formed among several dots formed of light ink. However, since the medium density ink is used here for the first time, a dot having a higher density than the ink density assumed in advance is formed. As a result, the density difference between the dot group formed by only the light ink and the dot group formed by the light ink and the medium-density ink becomes larger than necessary, which is easily noticeable. And this density difference appeared as a decrease in image quality.

This phenomenon generally occurs. However, due to the visual sensitivity of the human eye, particularly, an image (transmission image) covered with a thin veil or a light ink in a highlight portion is used. It is conspicuous in a transition region where the density changes to a slightly increased intermediate density.

The present invention has been made in view of the above conventional example, and has as its object to provide a recording apparatus and a recording method capable of recording an image having a density gradient (gradation change) with high quality.

[0022]

In order to achieve the above object, a recording apparatus according to the present invention has the following arrangement.

That is, the printing apparatus is capable of supplying inks of a plurality of densities and is capable of printing both in the forward scan and the backward scan of the reciprocating scan of the print head according to the ink jet system, and inputs multi-valued image data. Input means, analysis means for analyzing a gradation change of continuous pixels in the multi-valued image data input by the input means, and a direction in which the gradation changes from a high density to a low density according to the analysis result by the analysis means A data generating means for generating print data based on the multi-valued image data input by the input means so that the print data is in a print scanning direction by the print head; and a density represented by the print data generated by the data generating means. Print control means for controlling one of the plurality of ink densities to be printed in accordance with a value. A recording apparatus characterized.

Here, when the number of inks having a plurality of densities is "N", the data generating means converts the multi-level image data to "N +" according to the density value of the input multi-level image data.
The data is quantized to 1 "level data, and an error diffusion process is performed by an error diffusion method so that an error generated by the quantization is reflected on multi-value image data of another pixel.

The above-mentioned printing control means controls the printing head to print the same area of the printing medium by the forward scan and the backward scan, and when the generated print data is printed on the same area of the print medium, The print head is used for either forward scan or backward scan.

Further, the recording apparatus is provided with a number of recording heads equal to the number of inks of a plurality of densities, and the inks of the plurality of densities have different dye densities.

Further, the multi-valued image data may be monochrome image data or color image data. If the image data is color image data, the data may include cyan (C) component data and magenta (M) component data. , Yellow (Y) component data, and black (K) component data.

The recording head is a recording head that discharges ink by using thermal energy, and preferably includes a thermal energy converter for generating thermal energy to be applied to the ink.

According to another aspect of the present invention, there is provided a printing method for performing printing in both forward and backward scanning of reciprocating scanning of a printing head according to an ink jet method while supplying inks of a plurality of densities. An input step of inputting data, an analyzing step of analyzing a gradation change of continuous pixels in the input multi-valued image data, and a direction in which the gradation changes from a high density to a low density according to the analysis result in the analysis step. A data generating step of generating print data based on the input multi-valued image data so as to be in a print scanning direction by the print head; and, according to density values represented by the generated print data, And a recording control step of controlling to perform recording by selecting one of the recording methods.

According to the present invention, when printing is performed in both the forward scan and the backward scan of the reciprocating scan of the recording head according to the ink jet system while supplying inks of a plurality of densities, multi-valued image data is input. Analyzing the gradation change of continuous pixels in the input multi-valued image data, and according to the analysis result, the direction in which the gradation changes from a high density to a low density is the print scanning direction by the print head,
Print data is generated based on the input multi-valued image data, and control is performed so that one of a plurality of inks of a plurality of densities is selected and printed according to the density value represented by the generated print data.

[0031]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a perspective view showing a configuration of a recording apparatus using a recording head according to an ink jet system, which is a typical embodiment of the present invention.

According to the ink jet recording method used in this recording apparatus, recording is performed by discharging ink droplets from nozzles of a recording head using various driving principles. As a typical example of such a method, for example,
Japanese Patent No. 9936 discloses a recording method in which ink subjected to the action of thermal energy causes a sudden change in volume, and the ink is ejected from a nozzle by the action force due to this state change.

In FIG. 1, reference numeral 61 denotes a blade as a wiping member, one end of which is held by a blade holding member to become a fixed end, and serves as a cantilever. The blade 61 is disposed adjacent to the recording area of the recording head. In the case of the example shown in FIG. 1, the blade 61 is held so as to protrude into the moving path of the recording head. Reference numeral 62 denotes a cap, which is disposed at a home position adjacent to the blade 61 and moves in a direction perpendicular to the moving direction of the recording head,
The recording head is brought into contact with the ink ejection port surface, and the surface is capped.

Reference numeral 63 denotes an ink absorber provided adjacent to the blade 61. Like the blade 61, the ink absorber 63 is held so as to protrude into the movement path of the recording head. The blade 61, the cap 62, and the absorber 63 are included in the recovery section 64, and the blade 61 and the absorber 63 remove moisture, dust, and the like from the ink ejection port surface.

A recording head 65 is provided with a heater for heating the ink in the ink flow path, and performs recording by discharging ink onto a recording medium facing the ink discharge port surface.
5 is a carriage that carries a reciprocating movement with the carriage 5 mounted thereon. The carriage 66 is slidably engaged with the guide shaft 67, and a part of the carriage 66 is connected to a belt 69 driven by a carrier motor 68 (not shown). This allows the carriage 66 to move along the guide shaft 67,
The recording head 65 can reciprocate in a recording area and an adjacent area.

Reference numeral 51 denotes a paper feed unit for inserting a recording medium;
52 is a paper feed roller driven by a transport motor (not shown). Thus, the recording medium is moved to the recording head 6.
The sheet is fed to a position facing the ink ejection port surface of No. 5, and is discharged to a sheet discharge section provided with a sheet discharge roller 53 as the recording operation proceeds.

In the above configuration, when the recording head 65 returns to the home position at the end of recording or the like, the head recovery unit 64
Is retracted from the moving path of the recording head 65, while the blade 61 protrudes into the moving path.
As a result, the ink ejection port surface of the recording head 65 is wiped. When capping is performed by contacting the cap 62 with the protruding surface of the recording head 65, the cap 62 moves so as to protrude into the moving path of the recording head.

When the recording head 65 moves from the home position to the recording start position, the cap 62 and the blade 61 are at the same position as the position at the time of wiping described above.
As a result, even in this movement, the ink ejection port surface of the recording head 65 is wiped.

The movement of the recording head 65 to the home position is not only at the end of recording or at the time of ejection recovery, but also at a predetermined time interval adjacent to the recording area while the recording head moves through the recording area for recording. The wiping is performed in accordance with the movement.

The ink used for recording by the recording head 65 may be supplied from an ink tank integrated with the recording head 65, or may be supplied separately from or separate from the recording head. May be supplied.

When a plurality of types of inks having different densities are used as described in the conventional example, each ink is supplied to each of a plurality of recording heads from an ink tank containing each type of ink. In this case, the recording heads corresponding to the respective inks may be arranged on the carriage 66 along the carriage moving direction. Alternatively, the print head may be divided into predetermined nozzle groups, and different inks may be supplied to the respective nozzle groups.

When color printing is performed in the printing apparatus shown in FIG.
The recording heads integrated with the ink tanks containing cyan (C), magenta (M), and yellow (Y) inks are arranged on the carriage 66 along the carriage moving direction. Alternatively, color printing may be performed by dividing the nozzles of one printing head into four nozzles without arranging a plurality of printing heads. Further, the inks are not limited to four colors, but may be three colors of cyan, magenta, and yellow.

Next, a control configuration for executing the recording control of the above-described apparatus will be described.

FIG. 2 is a block diagram showing a configuration of a control circuit of the printing apparatus shown in FIG. In the figure showing a control circuit, 1700 is an interface for inputting a recording signal, 1
Reference numeral 701 denotes an MPU; 1702, a ROM for storing a control program executed by the MPU 1701; and 1703, a DRAM for storing various data (such as the print signal and print data supplied to the print head 65). Reference numeral 1704 denotes a gate array (GA) for controlling supply of print data to the print head 65, and an interface 170.
0, data transfer control between the MPU 1701 and the RAM 1703. Reference numeral 68 denotes a carrier motor for transporting the recording head 65, and reference numeral 1709 denotes a transport motor for transporting the recording paper. Reference numeral 1705 denotes a head driver for driving the recording head 65, and reference numerals 1706 and 1707 denote transport motors 17 respectively.
09, a motor driver for driving the carrier motor 68.

The operation of the above control configuration will be described. When a recording signal enters the interface 1700, the gate array 17
04 and the MPU 1701 converts the recording signal into recording data for printing. Then, the motor driver 17
06 and 1707 are driven, and the head driver 1
The recording head 65 is driven according to the recording data sent to 705, and recording is performed.

FIGS. 3 to 5 are views showing the structure of the recording head 65. FIG. FIG. 3 is an enlarged cross-sectional view showing one of the ink flow paths of the recording head 65, FIG. 4 is a cross-sectional view of the ink flow path taken along line AB shown in FIG. 3, and FIG. FIG. 3 is an external perspective view illustrating a state of an ink ejection surface in which a multi-head is formed by arranging a large number of the illustrated ink flow paths.

As shown in FIG. 3 to FIG.
Is a substrate 13 made of glass, ceramic or plastic plate having a groove 14 through which ink passes,
Substrate 2 with good heat dissipation, such as alumina, on which heating element 15 is formed
Obtained by bonding with 0. The heating element 15 is formed by stacking a protective film 16 made of silicon oxide or the like, aluminum electrodes 17-1 and 17-2, a heating resistor layer 18 made of nichrome or the like, and a heat storage layer 19 on a substrate 20. Is done.

Now, as shown in FIG. 3, the ink 21 reaches the orifice 22 and forms a meniscus 23 by the pressure P.

Here, when an electric signal is applied to the electrodes 17-1 and 17-2, the region indicated by n of the heating element 15 shown in FIG. 3 generates heat rapidly, and bubbles are generated in the ink 21 in contact therewith. Is generated, and the meniscus 23 protrudes by the pressure.
As a result, the ink 21 is ejected from the orifice 22 as an ink droplet 24 and flies toward the recording paper 25.

Next, in the recording apparatus having the above configuration, 4
An example will be described in which a black-and-white image of 256 gradations is printed using black inks of different densities. here,
It is assumed that the printing apparatus having the above configuration can perform printing in both the forward scan and the backward scan of the reciprocating movement of the print head, and printing of an area corresponding to the print width of the print head is completed by both the forward scan and the backward scan. Let it be.

Therefore, image data used for printing in an area corresponding to the print width of the print head requires image data for forward scan and image data for backward scan.

FIG. 6 is a flowchart showing image processing when a monochrome image is recorded.

First, in step S10, the ink density data is read from the ROM 1702, and the correspondence between the ink and the density value of the image data is made in accordance with the type of ink to be used. The ink density data stores data relating to the ink used. The following four types of inks are used in this embodiment, and are numbered k = 0, 1, 2, 3 in descending order of density. Further, for the convenience of image processing, the state without ink is set to k = 4. Table 1 is a table showing the pigment density and the transmission density of the ink corresponding to k = 0 to 4, respectively. The ink is composed of a pigment and a solvent, and the solvent contains various additives such as a surfactant and a humectant. These additives control the ejection characteristics from the recording head and the absorption characteristics on the recording paper.

[0055]

[Table 1]

[0056] In Table 1, the quantization level dl [k] = 0 corresponds to black, and dl [k] = 255 corresponds to white. In this case, the input image data has many pixels in which one pixel is represented by 8 bits. It is value data.

With reference to the values shown in Table 1, an appropriate quantization density level is selected depending on the type of ink used. The ink density and the density value of the image data are related by a relational expression usually called a Y characteristic curve.
The present invention is not particularly limited by this, and can be appropriately selected according to the image. Here, the association is made assuming that the ink density and the density value of the image data are in a proportional relationship (Y = 1).

When input image data is quantized on the assumption that four types of inks as shown in Table 1 are used, the image data f (x, y) of each pixel is converted into a quinary (“0”, “10”).
2 "," 172 "," 214 "," 255 ").

Next, in step S20, a threshold value for switching the used ink is calculated. In the example shown in Table 1, the threshold value dl [k] is set to the midpoint between the two quantization levels. However, the present invention is not particularly limited to this, and the two quantization levels dl [k] to be referred to. And d
It suffices if it is between 1 [k-1].

In step S30, image data f (x, y) are sequentially input so as to perform raster scan from image data corresponding to an image to be recorded on the upper left of the recording paper. A multi-level error diffusion process is executed according to the scanning direction. That is, starting from the upper left of the recording sheet, even-numbered (0, 2, 4,...) Scanning lines (forward scanning) of recording scanning by the recording head are performed from the left to the right using the above-described quantization levels. And error diffusion processing.
5, multi-level error diffusion processing is performed from the right side to the left side. As a result, the influence of the quantization error is evenly diffused on the left and right sides. Further, by this processing, the input image data f (x, y) becomes 5
It becomes the quantified data B (i, j).

FIG. 7 is a diagram for explaining the error diffusion processing.

FIG. 7A shows a part (4) of the input image data.
(Horizontal) × 3 (vertical) pixels), and each pixel is represented by 8 bits (0 to 255). In FIG. 7A, (i, j) indicates a target pixel to be multivalued, and data of a pixel above the broken line, that is, f (i−2, j−1) to
f (i, j-1) has already been multivalued, and
It shows a state where it is converted into (i-2, j-1) to B (i, j-1). That is, FIG. 7A shows the processing in the even-numbered scan lines. Therefore, after the multi-value processing of the image data f (i, j) of the target pixel, the multi-value processing sequentially moves to the pixels (i + 1, j), (i + 2, j).

Here, the multi-value processing is the error diffusion processing, and the density value of each pixel of the input image data is represented by dl [0], dl [1], dl [2], dl [3] shown in Table 1. , D
This is a process of converting the data into a quinary value in any one of l [4].

When the multi-value processing is shifted to the odd-numbered scanning line, the processing is performed, for example, on the target pixel (i,
j) to (i-1, j), (i-2, j)...

Next, in step S50, the obtained adjacent quinary data B (i, j) and B (i, j) are obtained.
-1) to compare the rate of change of the density (gradation) gradient B ′ (i,
j) is obtained. This calculation follows equation (1) if the pixel to be processed is on an even scan line, while
If the scan line is an odd-numbered scan line, Equation (2) is followed.

B ′ (i, j) = B (i, j) −B (i, j−1) (1) B ′ (i, j) = − ｛B (i, j) −B (i , J + 1) (2) Here, if B ′ (i, j) ≧ 0, the process proceeds to step S60, in which the quinary data B (i, j) is converted into image data for forward scan recording. (Fwd (i, j)) and B ′
If (i, j) <0, the process proceeds to step S70, and the quinary data B (i, j) is set as image data (rev (i, j)) for backward scan recording. In step S60, the image data fwd for forward scan recording is read.
(I, j) is prepared, and the image data rev (i, j) for the backward scan recording is represented by rev (i, j).
j) = 255 (ink ejection does not occur). Similarly, in step S70, image data r for backward scan recording
ev (i, j) is prepared, and the image data fwd (i, j) for forward scan recording is fwd (i, j).
(I, j) = 255 (no ink ejection occurs).

After executing step S60 or S70, the process proceeds to step S80, where an error diffusion process is performed.

FIG. 7B is a diagram showing an error diffusion matrix used for multi-value processing. With this matrix, an error generated as a result of the multi-value processing is diffused to other pixels. In FIG. 7B, “*” is a target pixel.

First, in the error diffusion processing, the target pixel (i,
The density value f (i, j) of j) is compared with the threshold value th [k], and the maximum value of “k” that satisfies the expression (3) (if not, k =
Select 0).

Th [k] ≦ f (i, j) (3) Next, as shown in Expression (4), the quantization level corresponding to k is set as a quinary-valued density value.

B (i, j) = dl [k] (4) In this way, the density value of the pixel of interest (i, j) after multilevel conversion is determined.

At this time, the quantization error (e) shown in equation (5)
rr) is diffused to each pixel according to equation (6) according to the value (distribution value) of the error diffusion matrix shown in FIG. Thereafter, the value f ′ (i, i,
Similarly, the multi-value processing is performed using j).

Err = f (i, j) −dl [k] (5) f ′ (x, y) = f (x, y) + err × M (xi, y−j) (6) It should be noted that the value of the error diffusion matrix is normalized and used in the calculation processing of Expression (6).

The multivalued data B (i, i) generated for recording in the forward scan direction and the backward scan direction in this manner.
j) is converted into each ink ejection control data, and is output to the recording head in conjunction with the scanning and paper feeding of the recording head,
As a result, the ink is ejected to form a gradation image.

Finally, in step S90, it is determined whether or not the processing for all the image data has been completed. If the processing has not been completed, the processing returns to step S30.
If completed, the process ends.

Therefore, according to the embodiment described above, printing in an area corresponding to the print width of the print head is performed by both the forward scan and the backward scan of the print head. Control is performed so that printing is performed by ejecting ink when the print head moves in the lowering direction. Therefore, even if the ink used for printing is switched from one type to another, the newly used ink has a higher density. Becomes pale ink.

As a result, discontinuity in the density of dots recorded at the time of ink switching becomes less noticeable, and a recorded image of good quality can be obtained.

For example, by applying the control described above,
Nozzles and the nozzle array density is 360 dpi
Using four corresponding print heads, a multi-level image of 256 gradations with a print resolution of 720 dpi in the main scanning direction (scanning direction of the print head) × 360 dpi in the sub-scanning direction (nozzle arrangement direction or recording paper transport direction) When recording was performed using the data, as a result, it was possible to obtain a good gradation image in which dark portions were not conspicuous.

Incidentally, to calculate the gradation change rate, as described above, a method of directly comparing the input image data with the adjacent pixel data on the left side is generally used, but the present invention is limited by this method. Not something. For example, when performing the error diffusion processing, the comparison may be performed using a value including the error, or after performing the multi-value processing, the resulting multi-valued data may be compared. Furthermore, since the change rate of the gradation of the image used here is sufficient with macroscopic information, the change rate may be obtained after performing the smoothing process.

[0080]

[Other Embodiments] In the above embodiment, recording of a black-and-white gradation image is taken as an example. However, here, recording of a color image having 256 gradations for each of the C, M, Y, and K color components is described. Will be described. In the following description, the configurations of the recording apparatus and the recording head are common to the above-described configurations, and description thereof will be omitted.

Table 2 shows the density and optical characteristics of the color ink used in this embodiment.

Here, dyes are used in the inks of the respective colors, and k represents the type of the ink. The smaller the value, the darker the ink, and the larger the value, the lighter the ink.

[0083]

[Table 2]

[0084] Also in this embodiment, the image processing as shown in FIG. 6 is performed on the image data of each color component. In particular, in the calculation process of the gradation change rate in step S50, the C component and the M
As using the data of three consecutive pixels for the component,
Equation (7) is applied.

B ′ (i, j) = f (i, j) − {f (i−3, j) + f (i−2, j) + f (i−1, j)} / 3 (7 Then, in step S50, based on the value obtained by the equation (7), when B ′ (i, j)> 0, B (i, j)
Is the print data in the forward scanning direction, and the change rate B ′ (i,
j) When <0, let B (i, j) be print data in the backward scanning direction. Further, when B ′ (i, j) = 0, 1
Data is distributed for each pixel in the forward scan direction and the backward scan direction.

The Y component data and the K component data are each subjected to ordinary binarization processing in step S40,
Instead of the processing in steps S50 to S70, the forward scan direction and the backward scan direction data are distributed every other pixel.

Therefore, according to the embodiment described above, with respect to the image data of the C component and the M component which are easily perceived by the human eye, the printing of the area corresponding to the print width of the print head is performed by the forward scan and the backward scan of the print head. When printing with both, the printing is performed by ejecting ink when the print head moves in a direction in which the gradation of successive pixels becomes lower, and
If there is no gradation change, control is performed so that printing is performed by ejecting ink every other pixel in the forward scan direction and the backward scan direction. Therefore, for example, the ink used for printing is changed from one type to another type. Even after the switching, the newly used ink becomes an ink having a low density.

The Y component image data, which is difficult for human eyes, is binarized and controlled so that ink is ejected every other pixel in the forward scan direction and the backward scan direction so that printing is performed.

By such control, discontinuity of the density of dots recorded at the time of ink switching becomes less noticeable, and a high quality color recorded image can be obtained.

For example, by applying the control described above,
In the main scanning direction (scanning direction of the recording head) 360 dpi × sub-scanning direction, using 12 recording heads having 64 nozzles corresponding to the inks shown in FIG. (Nozzle arrangement direction or recording paper transport direction) When printing is performed using multi-valued image data of 256 gradations of each color component at a recording resolution of 360 dpi, as a result, a good gradation color image in which a dark portion is inconspicuous is obtained. I got it.

In the above example of color image recording, only one type of black ink is used.
The component data can also be controlled so that the Y, M, and C inks are mixed to perform appropriate density expression.

The above-described embodiment is particularly provided with a means (for example, an electrothermal converter or a laser beam) for generating thermal energy as energy used for performing ink ejection even in an ink jet recording system. By using a method in which a change in the state of the ink is caused by energy, it is possible to achieve higher density and higher definition of recording.

The typical structure and principle are described in, for example, US Pat. Nos. 4,723,129 and 4,740.
It is preferable to use the basic principle disclosed in the specification of Japanese Patent No. 796. 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, liquid (ink)
By applying at least one drive signal corresponding to the recorded information and providing a rapid temperature rise exceeding the film boiling to the electrothermal transducer arranged corresponding to the sheet or the liquid path holding the Since thermal energy is generated in the electrothermal transducer and film boiling occurs on the heat-acting surface of the recording head, bubbles in the liquid (ink) corresponding to this drive signal on a one-to-one basis can be formed. It is valid. By discharging the liquid (ink) through the discharge opening by the growth and contraction of the bubble, at least one droplet is formed. When the drive signal is formed into a pulse shape, the growth and shrinkage of the bubble are performed immediately and appropriately, so that the ejection of the liquid (ink) having particularly excellent responsiveness can be achieved, which is more preferable.

As the pulse-shaped drive signal, those described in US Pat. Nos. 4,463,359 and 4,345,262 are suitable. Further, if the conditions described in US Pat. No. 4,313,124 relating to the temperature rise rate of the heat acting surface are adopted, more excellent recording can be performed.

The configuration of the recording head is not limited to the combination of a discharge port, a liquid path, and an electrothermal converter (a linear liquid flow path or a right-angled liquid flow path) as disclosed in the above-mentioned respective specifications. A configuration using U.S. Pat. No. 4,558,333 or U.S. Pat. No. 4,459,600, which discloses a configuration in which a heat acting surface is arranged in a bent region, is also included in the present invention. In addition, for multiple electrothermal transducers,
JP-A-59-123670 which discloses a configuration in which a common slot is used as a discharge part of an electrothermal transducer, and JP-A-59-123670 which discloses a configuration in which an opening for absorbing a pressure wave of thermal energy corresponds to a discharge part. A configuration based on 138461 may be adopted.

Further, 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 determined by combining a plurality of recording heads as disclosed in the above-mentioned specification. This may be either a configuration satisfying the above requirements or a configuration as a single recording head formed integrally.

In addition to the cartridge type recording head in which the ink tank is provided integrally with the recording head itself described in the above embodiment, the recording head is electrically connected to the apparatus main body by being mounted on the apparatus main body. A replaceable chip-type recording head, which enables a simple connection and supply of ink from the apparatus main body, may be used.

It is preferable to add recovery means for the print head, preliminary auxiliary means, and the like to the configuration of the printing apparatus described above, since the printing operation can be further stabilized. Specific examples thereof include capping means for the recording head, cleaning means, pressurizing or suction means, preheating means using an electrothermal transducer or another heating element or a combination thereof. It is also effective to provide a preliminary ejection mode for performing ejection that is different from printing, in order to perform stable printing.

Further, the recording mode of the recording apparatus is not limited to the recording mode of only the mainstream color such as black, and may be a single recording head or a combination of plural recording heads. Alternatively, the apparatus may be provided with at least one of full colors by color mixture.

In the embodiments described above, the description is made on the assumption that the ink is a liquid. However, even if the ink solidifies at room temperature or lower, it is possible to use an ink that softens or liquefies at room temperature. Or, in the ink jet method, generally, the temperature of the ink itself is controlled within a range of 30 ° C. or more and 70 ° C. or less to control the temperature so that the viscosity of the ink is in a stable ejection range.
It is sufficient that the ink is in a liquid state when the use recording signal is applied.

In addition, in order to positively prevent the temperature rise due to thermal energy as energy for changing the state of the ink from a solid state to a liquid state, the temperature is positively prevented.
Alternatively, in order to prevent evaporation of the ink, an ink which solidifies in a standing state and liquefies by heating may be used. In any case, the application of heat energy causes the ink to be liquefied by the application of the heat energy recording signal and the liquid ink to be ejected, or by the time the ink reaches the recording medium, the solidification of the ink already begun. The present invention is also applicable to a case where an ink having a property of liquefying for the first time is used. In such a case, as described in JP-A-54-56847 or JP-A-60-71260, the ink is held in a liquid state or a solid state in the concave portion or through hole of the porous sheet. It is good also as a form which opposes an electrothermal transducer. In the present invention, the most effective one for each of the above-mentioned inks is to execute the above-mentioned film boiling method.

In addition, as a form of the recording apparatus according to the present invention, in addition to those provided integrally or separately as an image output terminal of an information processing apparatus such as a computer, a copying apparatus combined with a reader and the like, It may take the form of a facsimile machine having functions.

The present invention can be applied to a system composed of a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.), and can be applied to a single device (for example, a copier, a facsimile). Device).

[0104]

As described above, according to the present invention, when printing is performed in both the forward scan and the backward scan of the reciprocating scan of the recording head according to the ink jet system while supplying inks of a plurality of densities, multi-value printing is performed. The image data is input, and the gradation change of continuous pixels in the input multi-valued image data is analyzed. According to the analysis result, the direction in which the gradation changes from a high density to a low density is a print scanning direction by the print head. As described above, print data is generated based on the input multi-valued image data, and control is performed such that one of a plurality of density inks is selected and printed according to the density value represented by the generated print data. In gradation image recording, even if the ink used for recording is switched from one type to another type, the newly used ink is a light ink with a low density, Discontinuity of the concentration of dots recorded at the time of switching becomes as difficult conspicuous, there is an effect that it is possible to record a high-quality image.

[0105]

[Brief description of the drawings]

FIG. 1 is a perspective view showing a configuration of a recording apparatus using a recording head according to an ink jet system, which is a typical embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a control circuit of the printing apparatus shown in FIG.

FIG. 3 is an enlarged cross-sectional view showing one of the ink flow paths of the recording head 65.

FIG. 4 is a cross-sectional view of the ink flow path taken along a line AB shown in FIG.

FIG. 5 is an external perspective view showing a state of an ink ejection surface where a multi-head is formed by arranging a large number of ink channels shown in FIG.

FIG. 6 is a flowchart illustrating image processing.

FIG. 7 is a diagram illustrating an error diffusion process.

FIG. 8 is a diagram illustrating how three types of light and dark inks are used in accordance with the density level of an input image signal.

[Explanation of symbols]

 13, 20 Substrate 14 Groove 15 Heating element 16 Protective film 17-1, 17-2 Aluminum electrode 18 Heating resistor layer 19 Heat storage layer 21 Ink 22 Orifice 23 Meniscus 24 Ink droplet 25 Recording paper 51 Paper feed section 52 Paper feed roller 53 Paper discharge roller 61 Blade 62 Cap 63 Ink absorber 64 Recovery unit 65 Recording head 66 Carriage 67 Guide shaft 68 Carrier motor 69 Belt 1700 Interface 1701 MPU 1702 ROM 1703 DRAM 1704 Gate array 1705 Head driver 1706, 1707 Motor driver 1709 Transport motor

Claims (10)

[Claims] 1. A printing apparatus capable of supplying inks of a plurality of densities and capable of printing both in a forward scan and a backward scan of a reciprocating scan of a print head in accordance with an ink jet system. Means, analysis means for analyzing a gradation change of continuous pixels in the multi-valued image data input by the input means, and a direction in which the gradation changes from a high density to a low density according to the analysis result by the analysis means. Data generating means for generating print data based on the multi-valued image data input by the input means so as to be in a print scanning direction by the print head; and a density value represented by the print data generated by the data generating means. According to one of the plurality of ink densities
A recording control means for controlling recording to be performed by selecting one of them. 2. When the number of inks of the plurality of densities is “N”, the data generating unit converts the multi-valued image data into “N” according to the density value of the multi-valued image data input by the input unit. A quantizing unit for quantizing the data into N + 1 ″ level data; and a process of performing an error diffusion process so that an error generated by the quantization by the quantizing unit is reflected on multi-value image data of another pixel by an error diffusion method. 2. The recording apparatus according to claim 1, further comprising means. 3. The printing apparatus according to claim 1, wherein the print control unit controls the print head to print the same area of the print medium by forward scan and backward scan. 4. A printing method according to claim 1, wherein the print data generated by said data generating means is used for either forward scan or backward scan of said print head in printing on the same area of said print medium. 4. The recording device according to 3. 5. The recording apparatus according to claim 1, further comprising a number of recording heads equal to the number of the plurality of density inks. 6. The recording apparatus according to claim 1, wherein the inks having different densities have different dye densities. 7. The recording apparatus according to claim 1, wherein the multi-valued image data is monochrome image data. 8. The multi-valued image data is color image data, and the color image data is cyan (C) component data, magenta (M) component data, yellow (Y) component data, and black (K) component data. 2. The recording apparatus according to claim 1, wherein the recording apparatus comprises: 9. The recording head according to claim 1, wherein the recording head ejects ink by using thermal energy, and includes a thermal energy generator for generating thermal energy to be applied to the ink. Item 2. The recording device according to Item 1. 10. A recording method for performing recording in both forward and backward scanning of reciprocating scanning of a recording head according to an ink jet system while supplying a plurality of density inks, wherein an input step of inputting multi-valued image data An analysis step of analyzing a gradation change of a continuous pixel in the input multi-valued image data; and a print scan by the print head in which a direction in which a gradation changes from a high density to a low density according to an analysis result in the analysis step. A data generating step of generating print data based on the input multi-valued image data so as to be in a direction; and selecting one of the plurality of density inks according to a density value represented by the generated print data. A recording control step of controlling the recording to be performed.