JP3459693B2 - Image recording method and apparatus - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording method and a recording apparatus for recording an image by a dot matrix method, and more particularly to an image recording method and an image recording apparatus capable of performing an emphasized recording of an image by recording an emphasis dot.

[0002]

2. Description of the Related Art With the spread of copiers, word processors, information processing equipment such as computers, and further communication equipment, there is an image forming (recording) equipment for these equipments which performs digital image recording by a dot matrix system. It is rapidly becoming popular.

In the digital recording method, since it is impossible to perform analog adjustment on a dot-by-dot basis, a pseudo halftone is represented by the area covered by a plurality of dots on the paper surface. But,
In recent years, in order to realize higher image quality, there is an increasing demand for image quality closer to analog recording such as silver halide photography.

One of the improvements to the high gradation required for a digital image is to increase the density of the high duty portion. Usually, the size of one dot is set to a predetermined value in advance so that an appropriate density can be obtained in all gradations. However, if the dots are filled in all the pixels, the density may be insufficient in the high duty portion. In such a case, an emphasis printing method is applied in which more dots are simply overlapped and recorded at the same place. In this emphasizing method, since dots are overlapped at the same place, it is possible to increase the density as a whole without threatening the area gradation on the low duty side so much. Especially in ink jet recording devices, the density that can be expressed by the same recording method often differs depending on the medium, so there are some that emphasize all colors of the color ink for each recording mode, or only a specific color (for example, black) depending on the application. May be emphasized. This method can increase the density with a relatively simple structure, and can be easily incorporated into a printer for personal use.

However, another problem of digital recording is the granularity of dots on the low duty side, and the problem of granularity is exacerbated when the above-described emphasized printing is performed. I was sick. In digital recording, only dots of a predetermined size can be recorded, so on the low duty side where the recorded dots are scattered at a distance, each dot visually increases the graininess and stands out. It ends up. Therefore, especially in a natural image that requires smoothness, it cannot be said that the emphasizing method in which dots are simply overlapped and recorded at the same location does not necessarily realize high image quality.

Further, such an emphasizing method sacrifices a reliable increase in density for each gradation required for superior gradation. In particular, if the ink drop added during emphasis expands the original dot diameter, as in the inkjet method, dots will cover the paper surface with a lower duty than when not emphasized, increasing the gradation. Area with a small number of steps for substantial density increase,
That is, the region where the gradient of increasing the density becomes gentle spreads toward the lower duty side.

Even for a digital image having the above problems, the recording apparatus receives multi-valued data and records in advance by a plurality of types of multi-dots, so that analog recording can be performed on both the low duty side and the high duty side. It is possible to record a close image. However, handling multi-valued data in the main body of the recording device requires data transfer, RAM capacity,
The hardware configuration required for data development, and the processing time and cost required for it all become large and complicated, which is not so realistic for personal use in recent years.

In such a situation, considering a proper method of emphasizing a digital image again, it suffices if the emphasizing can be selectively performed only on a specific duty such as a solid portion. That is, it suffices if it is possible to create a state in which the original density is fixed on the low duty side while expanding the area (100% duty side) including special objects such as characters and ruled lines to a higher density. .

The following proposals have been made as a method for selectively emphasizing a certain part of an image.

Japanese Unexamined Patent Publication (JP-A-62-50977)
No.), the edge part and the non-edge part of the image are identified by the image signal that has passed through the band pass filter, the wide-area enhanced image signal is binarized at the edge part, and smoothed at the non-edge part. It discloses that a character image or a halftone image is faithfully reproduced by binarizing the image signal.

Further, Japanese Patent Laid-Open Publication No. Sho 63-28885.
No. 66) discloses that an edge portion and a non-edge portion of an image are identified by using an average value in a specific block of a Laplacian filter output, and the matrix size of the error diffusion method used for each binarization is made different. ing. In this case, a small matrix is used in the area determined to be the edge portion, and a large matrix is used in the area determined to be the non-edge portion, so that both image qualities are compatible.

In addition, although it is not the emphasizing process, in Japanese Patent Laid-Open Publication No. Sho 54-78222, the time when the recording position is recorded in order to improve the end point (oblique line) of the contour extending laterally with respect to the recording direction. Is delayed with respect to the clock used for recording so that the last recording position is shifted in the direction of the contour for recording.

[0013]

However, it is possible to distinguish between an edge portion of a character or the like and a non-edge portion of a halftone pattern or the like shown in the above publication to add emphasis and smoothing smoothing to a character or a thin line. Alternatively, the purpose was to reduce image deterioration that occurs when a halftone image is processed into a digital signal. The above-mentioned emphasis for expanding the density area of the entire image, reliable increase of density for each gradation required for better gradation, and reduction of graininess peculiar to digital images remain unsupported. there were. Therefore, when the dots are simply recorded in an overlapping manner in order to increase the image density, the above-mentioned disadvantage that the granularity of dots is increased in the low-duty area, and further, the reliability of each gradation required for gradation is ensured. The current situation is that none of the drawbacks, such as the sacrifice of increased density, are addressed.

Further, when dots are simply overlaid and simply recorded, there is a drawback that the ink bleeds more than necessary into an adjacent white portion in the contour portion of the image, and the image is crushed in the high-definition portion. It was

The present invention has been made in view of the above-mentioned problems, and by adding an emphasis dot to a high duty portion of an image, it is possible to surely increase the density in the high duty portion and to increase the density for each gradation. reliable concentrations up, with reduced graininess in the low-duty unit, and the bleeding of the ink in the edge portion can be prevented, secondary color
By adding a specific ink color to the
It is an object of the present invention to provide an image recording method and an image recording apparatus capable of correcting the tint of a secondary color .

[0016]

According to the present invention, in an image recording method for recording an image by a dot matrix method according to a digital input image signal, adjacent recording to be recorded at a pixel position adjacent to a target recording pixel to be recorded. There is a pixel
To case, the intermediate of the adjacent recording pixels and the target recording pixel
It records the dots for image enhancement on the position of the
The target recording pixel and the adjacent recording pixel both have specific two colors.
If the secondary color is composed by mixing, the above noted record
The secondary color is formed at an intermediate position between the pixel and the adjacent recording pixel.
It is characterized in that an emphasis dot of one of two specific colors to be formed is recorded. Further, according to the present invention, the print scan (main scan) of the print head in which the print elements are arranged at the pitch equal to the resolution of the print pixel and the paper feed of a predetermined amount (sub scan).
In the ink jet recording apparatus that forms an image with a dot matrix configuration according to a digital input image signal, a pixel adjacent to a target recording pixel to be recorded
If adjacent recording pixels to be recorded in position exists, and records a dot for image enhancement in an intermediate position of the adjacent recording pixels and the Note <br/> th recording pixel, the target recording pixel before
Both adjacent recording pixels are made up of a mixture of two specific colors.
When the secondary color is a secondary color,
Two specific colors forming the secondary color in the middle position of the recorded pixels
It is characterized by recording an emphasis dot of one of the colors .

[0017]

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A recording method of an ink jet recording apparatus for selectively emphasizing black ink only when forming a color graphic image on plain paper will be described below.

FIG. 7 shows the construction of the printing section of the ink jet recording apparatus used in the present invention. In this figure, reference numeral 701 is an ink cartridge. Here, 4
Ink tanks filled with color color inks (for example, black, cyan, magenta, and yellow) respectively, and 702 multi-heads (for example, 128 nozzles per nozzle)
One color head, one composed of four heads, or one in which four heads are integrated).

A paper feed roller 703 rotates in the direction of the arrow in the figure while holding the print paper 707 together with the auxiliary roller of 704 and feeds the print paper 707 at any time in the y direction. Further, reference numeral 705 denotes a paper feed roller which feeds the printing paper and also plays a role of suppressing the printing paper 707 similarly to 703 and 704. Reference numeral 706 is a carriage that supports four ink cartridges and moves them with printing. This is to stand by at the home position (h) at the position shown by the dotted line in the figure when not printing or when performing multihead recovery work.

Prior to the start of printing, the carriage (706) at the position (home position) shown in the figure moves in the x direction when the print start command arrives, and then the multi-head (702).
Printing is performed on the paper surface by the above n multi-nozzles. When the printing of the data is completed up to the end of the paper, the carriage returns to the original home position and printing is performed again in the x direction.
Alternatively, in the case of reciprocal printing, the next printing is also performed at the stage of moving in the -x direction. After the first printing is completed and before the second printing is started, the paper feed roller (7
03) rotates in the direction of the arrow to feed the paper in the y direction by a predetermined width. In this way, by repeating the carriage scan and the paper feed, the data printing on one paper surface is completed.

Although not shown, in the recording apparatus of the present embodiment, a controller for controlling recording and image processing of the recording apparatus, a control unit including a ROM and a RAM, and an external host computer are provided. To exchange data with
An interface for connecting to an external host computer, a motor for driving a carriage, a motor for driving a paper feed motor, a motor driver for driving a motor for driving a paper conveyance roller, and a recording head for driving a recording head. A driver for driving is provided.

In the present embodiment, a method of recording an original image of four colors (binary image data sent from an external host computer) in the forward scan and recording black-only emphasized dots in the backward scan will be described. To do. First, in the first print scan,
All color original images are recorded by forward scanning. The paper feed scan is not performed after the first print scan, and the second print scan uses only the black head to print the emphasized dots in the backward scan. After that, the paper is fed by the width of the print head, and the original image in the image area following the print area is printed again in the forward scan similarly to the first print scan in the third print scan. Thereafter, the original image, the emphasized dot recording scan, and the paper feed scan are sequentially repeated to complete the image.

FIG. 1 shows the positions where the highlighted dots are to be recorded in the backward scan. On the left side of the figure, the arrangement state of the original image,
The position of the emphasis dot to be recorded is shown on the right side. Figure 1
In Nos. A and b, since there are no adjacent pixels in the head recording direction, no emphasis dot is recorded between these pixels. On the other hand, in FIG. 1C, since the adjacent pixels exist without spacing the pixels, the emphasis dot is recorded at the intermediate position between them.

That is, when the interval of one pixel or more is open, no emphasis dot is recorded. In other words, if the dots are smaller than the maximum diameter of the dots and the dots are adjacent to each other, the highlighted dots are recorded.

FIG. 2 shows a state of recording in a wider range according to this rule, in comparison with the conventional example. FIG. 2B shows a recorded image emphasized by the conventional simple double hitting. Emphasis dots are printed on all recorded pixels including the boundary area,
The bleeding of dots in the boundary area may disturb the shape of the original recorded image, and the smoothness of the contour may be lost. On the other hand, FIG. 2 in which emphasizing dots are added between the dots of this embodiment
In the case of a, the shape can be kept relatively smooth. Since it corresponds to c of FIG. 1 inside the recording area,
Except for the boundary portion, the emphasis dots are efficiently recorded at positions shifted by half a pixel in the entire recording area, and the density can be surely increased. On the other hand, since the outline portion does not correspond to c of FIG. 1, the emphasis dots are recorded. Therefore, the outline of the object is not smeared with excessive dots, and the recording area itself is not widened to the left or right. Therefore, the contrast of the character or the like can be increased without losing the smoothness and fineness of the contour.

In order to explain the most important effect of the present invention, each printing duty and the recording state of the emphasis dot in the dither method (Bayer type) in which uniformity is emphasized are compared with the conventional emphasis method as shown in FIG. Shown in. 3A to 3D show the recording method of this embodiment, and FIGS. 3E to 3F show the conventional recording method. In the conventional 2-dot emphasized printing shown in the right column of the figure, the same number of emphasized dots as the recorded dots of the original image are always added at any duty.

On the other hand, no emphasis dots are recorded in the 25% and 50% areas of this embodiment. This is because at the duty at this stage, the dots are arranged only in a state where they are not adjacent to each other, and there is no portion that satisfies the condition of c in FIG. In this way, in the binarization method that emphasizes uniformity such as dither processing, the image duty is 5
The highlight dots are recorded only when 0% is exceeded. However, as can be seen by comparing c and g at the 75% stage, emphasis dots are not added to all recording pixels at this stage as in the conventional example in this embodiment. That is, the number and density of the emphasis dots also gradually increase with the duty. And finally 100% of Figure 3
As seen from the duty, the same number of emphasis dots as the recording original image are recorded in almost the entire area. That is, a high density can be obtained in the high duty portion. In this case also, since the emphasis dot is not added at the edge portion, the image quality deterioration due to the ink bleeding at the edge portion does not occur.

FIG. 4 shows the relationship between the print duty and the image density in a case where emphasis printing is not performed, a case where emphasis printing is performed by the conventional method, and a case where emphasis printing is performed by the method of this embodiment.

As described above, since the size of one dot diameter is often designed to be larger than the area of the recording pixels, the dots recorded on the paper surface reach a certain or more or less duty. Sometimes, it covers the entire surface of the paper. In this embodiment, it is assumed that the area has reached approximately 50%. Therefore, the image density is surely increased according to the number of recorded dots (that is, the covered area) up to the duty of 0 to 50% where the dots do not overlap each other in the curve a. However, in the area of 50% or more where the dots are overlapped with each other, the density increase rate (slope) is gradually decreased (capped). The ideal gradation is that the actually measured density is surely increased according to the input signal (horizontal axis of the graph) designating the image duty. In the case of using the Bayer type dither method (binarization method) shown here, since importance is attached to the uniformity, such a new problem that deteriorates the gradation is caused. To solve this, at each recording duty (especially on the high duty side)
By replacing the input signal with a lower signal value, the density can be suppressed to a value lower than usual, and the relationship between the signal value and the image density can be reset linearly (print γ correction). However, in this method, it is also a fact that the resolution of the density with respect to the input signal value (particularly in the low duty portion) is deteriorated.

The curve b is simply the number of dots of the curve a of 2
This is the simplest image enhancement method than ever before. This curve has a higher overall density than curve a, and the same input signal area (0-100%)
We have succeeded in expanding the expressible density range in (Duty). However, while the high-density portion, which has been a problem with the curve a, reaches a wider range more and more, the slope up to 50% is almost twice as large as that of the curve A, so that the gap of the measured density with respect to the input signal becomes severe. In particular, on the low duty side, the dots are emphasized to have a density twice as high as usual and scattered, so that the graininess is conspicuous in the image and the smoothness is lost.

The curve c is obtained by using the density emphasizing method according to the embodiment of the present invention. As described above, in the present embodiment, the emphasis dot cannot be added up to the 50% duty. Therefore, the same curve as the curve a is followed up to the 50% duty. Emphasis dots are gradually added from the area exceeding 50%, and in the final 100% duty, emphasis dots almost equal to the curve b are added, and the density is also coincident with this. However, the emphasized dots are gradually increased after the point where the duty of 50% has passed, so that the state does not fall into a capped state like the curve b, and a relatively linear and smooth density curve can be obtained. If such a curve of print duty and density is obtained in advance, it is not necessary to perform unreasonable signal value conversion even when γ correction is added.

Thus, by using the emphasizing method of this embodiment,
It is possible to obtain a smooth and wide range of gradation in a recorded image by the dither method that emphasizes uniformity like the Bayer type. As another binarization method that emphasizes uniformity, there is a method in which a recording dot is determined by a calculation process like the error diffusion method. In this case, although not completely equivalent, it can be considered that the results similar to those of FIGS. 3 and 4 can be obtained almost in the same manner as the Bayer type in that recording is performed while dots are uniformly dispersed.

The recording state of the present embodiment for the binarization method that emphasizes uniformity has been described above. However, some of the binarization methods differ from this in that new dots are added adjacent to the already recorded dots. FIG. 5 shows a state in which the highlight recording of this embodiment is performed as an example.

In such a dither method, the cluster of recorded dot groups gradually increases as the gradation increases. Therefore, as the gradation increases, the ink coating area on the paper surface increases linearly with the print duty. As a result, the relationship between the print duty and the measured density is also as shown in FIG. 6 (a in FIG. 6).

Further, as shown in FIG. 5, the number of highlight dots is
Almost the same as the dots of the original image, it increases according to the gradation. Therefore, a curve that is smooth with respect to the print duty is formed as shown in FIG. 6 while maintaining a slope that is higher than that of the density curve when no emphasis is performed, almost constant (b in FIG. 6).

In this way, applying this embodiment to emphasize printing not only widens the range of expression of gradation, but also obtains a curve of a smooth slope with respect to gradation in any dither method. It is possible to provide an image having more excellent gradation.

The configuration for realizing the present embodiment can be realized with a very simple configuration because it only compares two consecutive dots in the raster direction in which the image data is arranged. For example, a method of sequentially comparing a fixed mask and data as shown in c of FIG. 1 may be used. In this case, it can be realized with a simple 1 × 2 mask configuration. Further, the present invention can be easily realized with a simple hardware configuration without using a mask.

Further, in the present embodiment, the method of comparing only two pixels in the raster direction is adopted as the simplest example, but actually, the pixels are adjacent to each other in the direction different from the traveling direction of the recording head (arrangement direction of recording elements of the multi-head). 2 pixels is enough (Fig. 8
A), 4 pixels of 2 pixels in each of the vertical and horizontal directions may be detected, and an emphasis dot may be added to the center when printing is performed as shown in FIG. 8B. In the former case, a paper feed scan with a 1/2 pixel pitch is required for the emphasis dot recording. In the latter case, the range of adjacent pixels for recording the emphasized dots is widened, so that the position where the emphasized dots are added is further inclined to the high duty side. Therefore, it is possible to further suppress the bleeding at the boundary and the thickening of the thin line. Since the present invention is not intended to accurately extract the contour portion, the effects already described can be sufficiently obtained only by detecting the adjacent pixels in the area of 2 pixel width.

Further, in the present embodiment, it has been described that the printing of the highlighted dots is performed by another scanning, but this is not limited. In the present embodiment or when the highlighted dots are printed by shifting only in the main scanning direction as shown in FIG. 8B, the recording frequency of the recording head is increased or the scanning speed of the recording head is decreased. It is also possible to print with the same printing scan as the original image.

FIG. 15 is a block diagram showing each stage of the image processing performed in this embodiment. In FIG. 15, the process from the logarithmic conversion process 10 to the binarization process 50 is executed by an external host, and the printer 60 inputs the binarized data by the host. Red (R), Green (G), Blue (B)
The 8-bit data is converted into cyan (C), magenta (M), and yellow (Y) by the logarithmic conversion unit 10. The black generation unit 20 generates black data (K) to be recorded by the black ink from the C, M and Y data. After that, the masking process (30) and the printer gamma process (40) are performed to convert the output signal into an output signal optimized for the recording apparatus, and then the binarization unit 50 performs 2 for each color by the dither method or the error diffusion method.
The value-converted signal is input to the recording device main body 60.
The binarized data is rasterized in the output buffer 602 for each color, but the black signal is simultaneously transmitted to the emphasis dot generation circuit 601 and the emphasis dot signal (K ′) is transmitted based on the conditions shown in FIG. To generate. And
The image is rasterized in the buffer 602 at a timing different from that of the original image, and is recorded by a different recording scan.

FIG. 16 is a flowchart showing a data processing method in the highlighted dot generating circuit. This control is executed by the emphasized dot generation circuit 601. Here, the original image Bk (Last, rasterized as black data is
(row) is detected in the raster direction, the enhancement dot Bk ′ (Last, r
ow) is generated. The emphasized dot Bk '(Last, row) generated here is sent to the black head recording buffer while being shifted in timing from the original image dot Bk (Last, row), and is recorded by independent scanning.

When the flowchart starts, Last =
The initial settings are 1, row = 1 and left = 0.

Next, in step S1, Last =
It is determined whether the pixel of 1, row = 1 is a black pixel, that is, 1 or not.

If it is 1, the process proceeds to step S2, and it is determined whether or not the adjacent left pixel is black. If it is black, the process proceeds to step S5, and Bk ′ (L
Write 1 at the position (ast, row). This allows
When the black dots are adjacent to each other, the emphasis dot Bk 'can be printed.

Incidentally, Bk '(Las shown in FIG. 16b)
printing based on the data stored in (t, row) and FIG.
The printing based on the data stored in Bk '(Last, row) shown in c is shifted by half a pixel, which enables the printing of the emphasized dot at the intermediate position between the dots shown in FIG. 2a. Becomes In step S5, left = 1 is set for the next process. In step S7, row is incremented, and in step S8, row is incremented.
S1 to S7 are repeated until becomes MAX. In step S9, Last is incremented by setting row = 1. When row = 1, left is the same as in the initial state.
Set to = 0. In S10, it is determined whether or not Last or MAX is exceeded, and S1 to S9 are repeated until MAX is exceeded.

Further, Bk (Last, row) = 1 in S1
If not, left = in S3 for processing the next pixel.
0, and Bk ′ (Last, row) = 0 is set in S6.

If left = 0 in S2, it is determined that two black pixels are not consecutive, left = 0 in S4, and Bk '(Last, row) = 0 in S6.

(Other Embodiments) The second embodiment will be described below. Although the first embodiment has described the simplest method of emphasizing only black, the second embodiment will explain a method of emphasizing all four colors of black, cyan, magenta, and yellow. However, in this embodiment, a different emphasis method is used for each color,
It also aims to adjust the color balance of the entire image.

In this embodiment, division printing of four divisions is performed. Here, a brief description will be added to the divided printing method. Unlike a monochrome printer that prints only characters, various elements such as color development, gradation, and uniformity are required to print an image. Especially for inkjet printers,
A slight variation in the nozzle unit that occurs due to the difference in the multi-head manufacturing process affects the ink ejection amount of each nozzle and the direction of the ejection direction when printing, and ultimately the image quality is uneven as density unevenness of the printed image. It causes deterioration.

A specific example will be described with reference to FIGS. In FIG. 9a, reference numeral 91 is a multi-head, and here, for simplicity, it is assumed that it is composed of eight multi-nozzles (92). Reference numeral 93 is an ink droplet ejected from the multi-nozzle 92. Normally, it is ideal that ink is ejected in a uniform direction with a uniform ejection amount as shown in this figure. If such recording is performed, dots of uniform size are landed on the paper surface as shown in FIG. 9b, and a uniform image without density unevenness is obtained as a whole (FIG. 9c). . However, in reality, each nozzle has a variation, and if printing is performed as it is in the same manner as described above, the size of the ink drop ejected from each nozzle as shown in FIG. Variations occur in the direction, and the paper is landed on the paper surface as shown by 10b. According to this figure, there is a white paper portion that cannot periodically satisfy the area factor 100% with respect to the main scanning direction of the head, and conversely dots are overlapped more than necessary, or as seen in the center of this figure. There are some white streaks. The collection of dots landed in such a state has the density distribution shown in FIG. 10C in the nozzle arrangement direction, and as a result, these phenomena are perceived as density unevenness as seen by human eyes. It

Therefore, the following method is generally taken as a measure against this density unevenness. This will be described with reference to FIGS. 11 and 12. According to this method, the multi-head 91 is scanned three times to complete the print area shown in FIGS. 9 and 10, but half the area in units of 4 pixels is 2.
It is completed with a pass. In this case, the 8 nozzles of the multi-head are divided into a group of 4 upper nozzles and 4 lower nozzles,
The dots printed by one nozzle in one scan are defined image data thinned to about half according to a predetermined image data array. Then, at the time of the second scan, dots are embedded in the remaining half of the image data to complete the printing of the 4-pixel unit area. The recording method as described above is called a divided recording method. If such a divided recording method is used, even if the same recording head as that used in FIG. 10 is used, the effect on the printed image peculiar to each nozzle is halved, so the printed image is as shown in FIG. 11b. The black streak and the white streak as shown in FIG. 10b become less noticeable. Therefore, the uneven density is also shown in FIG.
As shown in FIG. 10, it is considerably relaxed as compared with the case of FIG. 10c.

When such divided recording is performed, the image data is divided in the first and second scans so as to fill each other according to a certain arrangement, but here, for simplicity, the arrangement state (thinning pattern) is shown. As shown in FIG. 12, a pixel that exactly forms a houndstooth check is used for each vertical and horizontal pixel. Therefore, in the unit printing area (here, in units of 4 pixels), the printing is completed by the first scan for printing the zigzag lattice and the second scan for printing the inverse zigzag lattice. FIGS. 12a, 12b, 12c, 12c, 12c and 12c show how recording of a certain area is completed when using the zigzag and inverse zigzag patterns, respectively, as in FIGS.
This is explained using a multi-head having 8 nozzles. First, in the first scan, the staggered pattern is recorded using the lower 4 nozzles (FIG. 12a). Next, in the second scan, the paper is fed by 4 pixels (1/2 of the head length) to record an inverted zigzag pattern (FIG. 12b). Further, in the third scan, the paper is fed again by 4 pixels (1/2 of the head length), and the staggered pattern is recorded again (FIG. 12c).
In this way, the paper feeding in units of 4 pixels and the recording of the staggered pattern and the reverse zigzag pattern are alternately performed in this manner to complete the recording region in units of 4 pixels for each scan. As described above, by completing printing with two different types of nozzles in the same area, it is possible to obtain a high-quality image without density unevenness.

As described above, the same area is divided into 2 areas as the divided recording method.
The configuration has been described in which an image is completed by one recording scan. Such a two-division division recording system is often used when it is desired to record a color image quickly without having a low absorption capacity like plain paper. However, the effect of the divided recording method on the image quality becomes more pronounced as the number of divisions is increased, and even when plain paper is desired to obtain high image quality, or when the recording medium itself such as coated paper or glossy paper is used. Is expensive, halves the number of pixels recorded in one scan,
The width of the paper feed scan may be set to 2 pixels (1/4 of the head length). In this case, since the image is completed by four kinds of nozzles in the same scanning direction, it is possible to obtain a smoother and better image although the printing speed is inferior. In addition, by printing the same area multiple times in this way, it is possible to complete the image while reliably fixing a small amount of ink on an OHP film or the like having low ink absorbency, and therefore, it is possible to blur the boundary between different colors. Of course,
It is also possible to prevent a beading phenomenon in which ink droplets that have not been completely absorbed are fixed as large lumps of ink droplets that can be visually recognized on the medium surface due to the surface tension.

FIG. 13 shows the printing state of this embodiment. In this embodiment, a multi-head having 64 nozzles for each color is used,
Performs division printing. The original image is divided and printed in four divisions, and all the image areas are completed by four forward scan scans (original image print) and one backward scan scan (emphasized image print). According to this figure, paper feed with a width of 16 nozzles and back scan of the carriage are performed during each of the recording scans 1 to 4.
After the end of the fourth print scan, the print head prints all the emphasized dots at one time in the backward scan without performing the paper feed scan. After the fifth print scan, a paper feed scan with a width of 16 nozzles is performed, and the same print scan is sequentially repeated again from the first print scan.

FIG. 14 shows the highlighted dot recording conditions of this embodiment.
And the recording position is shown for each color. In this embodiment, one of the purposes is to achieve color balance of each color relatively easily, in addition to the enhancement of a single color, which was the main purpose in the first embodiment. At present, it is impossible to completely satisfy the ideal color space with the practically used ink. In this case, not only single-color shifts of cyan, magenta, and yellow but also larger shifts occur in the mixed colors of red, green, and blue.

In the present embodiment, in order to bring these mixed color portions closer to the ideal tint as much as possible, one of the single color inks is added to the portion made of the two color inks to emphasize the color tone. It is intended to form a transparent image.

In FIG. 14, black is subjected to monochromatic enhancement similar to that of the first embodiment. For cyan, one dot is added to the middle part of two pixels only when two blue pixels formed of cyan and magenta are continuously recorded. This is based on the assumption that the blue formed by the ink used in this embodiment is inclined toward the magenta side as compared with the ideal blue. Magenta is added for red color correction. Again, it is assumed that red in the ink used in this embodiment is recognized as being inclined toward the yellow side. In this case, magenta dots for tint correction are added to the positions in these figures to emphasize only when the two adjacent vertical and horizontal dots are all red as shown in the figure. Compared to the case of correcting blue to cyan, emphasis dots are added on the higher duty side. Yellow ink is used for correcting green. Also in this case, as in the case where magenta is emphasized with red, yellow dots for color correction are added only when the adjacent two dots in the vertical and horizontal directions are all green.

Normally, in color space correction, multivalued data processing is often performed by a printer driver or the like before binary data is input to the printer. In this case, it is possible to form an ideal color space with all gradations, but on the other hand, it requires a great deal of processing time for conversion and may cause a decrease in recording speed. . On the other hand, in the present embodiment, regardless of the multi-valued data of each color, similar to the first embodiment, the configuration is simple and there is no special time cost.
The tint correction can be realized. According to the present embodiment, the correction dots (emphasized dots) are not recorded on the dither image up to the vicinity of the 50% duty. However, since the correction dots gradually increase at 50% or more,
With uniform gradation, the tint does not suddenly switch to the ink side of the highlighted dot. Actually, the color space deviation is regarded as the most problematic at 100% duty, and in the present embodiment, the ideal tint gradually approaches from around 50%.

Further, in the present embodiment, the original image is divided and printed four times, whereas the emphasizing dots complete the entire printing by one printing scan. This is because it is certain that dots of the same color will always be printed on at least both sides at the position where the highlighted dots are printed, so there is no need to worry about blurring in the image boundary or uneven density, and the printing speed should be reduced as much as possible. This is to complete the image without it. However, in the present embodiment, this is not a limitation, and even with the emphasizing dots, the division recording of four divisions may be performed similarly to the original image. For example, it is effective to prevent the beading by separately recording the emphasized dots on a recording medium such as OHP paper which absorbs ink slowly. Therefore, even if the recording division number of the emphasized dots is changed for each recording medium. This embodiment is effective.

Further, although the emphasizing method as shown in FIG. 14 is shown in this embodiment, it is needless to say that the emphasizing method is not limited to this.
All colors may be emphasized in a single color as in the first embodiment,
Some ink colors may not be emphasized. Further, even if the same ink is used, the density and color space obtained by each recording medium are different, so it is also possible to set a printing mode in which these emphasis methods are changed for each recording medium.

Next, as a third embodiment, in the case where a multi-valued image is formed by using inks of the same color but having high density (hereinafter referred to as dark ink) and inks having low density (hereinafter referred to as light ink). The density enhancement method will be described. FIG. 20 shows conversion output signal values of dark ink and light ink for 8-bit input signals. The dotted line shows the output value of light ink, and the solid line shows the output value of dark ink. When the input signal is between 0 and 128, only light ink is converted
When it reaches 8, the output signal value becomes 255. At this time, the image is 100% printed with only the light ink. The dark ink output signal is generated from the area where the input signal exceeds 255, and at the same time, the light ink output is decreased. When the input signal finally reaches 255, the dark ink output value is 2
55, the output value of the light ink becomes 0. Such signal value conversion makes it possible to obtain an image closer to analog compared to the simple binary image described so far. Since only the light ink is used where the input signal value is low, the graininess peculiar to the digital image is reduced compared to the simple binary image, and in the high density portion, the area is filled with high density ink. Sufficient concentration can be obtained. After the input multi-valued data is distributed to the dark ink output signal and the light ink output signal as described above, the multi-valued signal is binarized for each ink.

In FIG. 19, the above-described process is a binarization process for distributing light and shade, and each of the emphasized dots (K) from the generated dark ink signal (Kk) and light ink signal (Ku) of black.
FIG. 6 is a block diagram of the present embodiment for generating k ′, Ku ′). In this embodiment, only the black ink is emphasized as in the first embodiment, but emphasis dots are generated for both the dark ink black ink and the light ink black ink.

FIG. 17 shows the relationship between the input signal and the output density of the image binarized by the Bayer type dither pattern after the gradation is distributed. Curve a in this figure
Indicates a case where normal printing is performed with dark and light ink without emphasis.
When two types of ink are selectively used according to the input signal as in the present embodiment, as shown in the figure, two types of dark ink and light ink are used.
Although the number of times of capped state occurs a little, as a whole, a more reliable increase in density is obtained for the input signal than in the case of a simple binary image. However, when the simple emphasis is performed in this state, the density curve becomes the curve b and the expressible density range is widened, but the inconspicuous capped state is emphasized rather. Further, the granularity of the light ink dots near the duty of 0% and the dark ink dots near the duty of 50% is also emphasized.

The curve c represents the concentration curve of this embodiment. In the present embodiment as well, as in the first embodiment, the emphasis dots of the dark ink and the light ink are recorded only in the portions that satisfy the conditions shown in FIG. Therefore, since the emphasized dot of the light ink is not added in the portion where the print duty is close to 0 and the dark ink is emphasized in the area exceeding 50% for a while, the increase is gentle like the curve b. Then, when the print duty is around 50% and 100%, the curve b is gently approached again. Therefore, while the range of the expression density is surely expanded from the curve a, the state of the peak is small, and the density can be surely increased at any printing duty.
Further, the graininess around 0% and 50% emphasized by the curve b can be returned to the same level as the curve a.

As described above, according to the present embodiment, even in the emphasized printing in which the multivalued representation is made by using the black dark ink and the light ink, the use of the present invention does not require the complicated processing with the multivalued data. It is possible to perform emphasis printing without deteriorating the image by simple signal processing after binarization.

As the fourth embodiment, 300% emphasis printing will be described below. In the present embodiment, the density enhancement degree of the first embodiment is set higher, and the position for printing the enhancement dot is the same as that in the first embodiment shown in FIG. 2 dots at a time. In the ink jet recording apparatus, recording on various media has been realized in recent years, but in this case, an appropriate ink ejection amount is different for each recording medium. Normally, 100% is applied to plain paper or coated paper for exclusive use of ink jet, and even if 200% is applied during emphasizing, sufficient density is obtained, but in a medium such as cloth, which is 200% even in normal recording, When emphasizing, a concentration of 300% may be required. This embodiment is a recording mode assuming such a situation. When four color inks of black, cyan, magenta and yellow are used, only black is emphasized by 300% and other colors are emphasized by 200%. Shall be performed. The emphasizing dots in this embodiment are also determined under the same conditions as in the first or second embodiment. For cyan, magenta, and yellow, the 200% emphasizing method shown in the first embodiment is applied, and As a result, the highlighted dots are recorded at the position shown in FIG.

FIG. 18 shows the relationship between the input signal and the output density of the image binarized by the Bayer type dither pattern in this embodiment. However, here, for comparison with the curve used in FIG. 4 of the first embodiment, it is shown as a result of recording on a recording medium similar to that of the first embodiment. Therefore, the output density when emphasized is higher than when actually printed on a recording medium such as cloth. In this case, the reference curve a is the same as the curve a of FIG. 4 described in the first embodiment. Figure 1 shows the density curve for black.
It becomes like c of 8. Here, b in FIG. 4 shows a case where the emphasizing method of recording 3 dots at a time is applied to a normal original image, and the capped area is further increased as compared with the case of emphasizing with 2 dots shown in b of FIG. It's gone. In contrast,
The curve c finally coincides with the curve b which is the target density while obtaining a reliable density increase.

In the first to fourth embodiments, the example in which the highlight dots are generated on the recording device side based on the data sent from the host has been described, but the present invention generates the highlight dots on the host side. The same can be used when performing the processing for. The structure in this case is shown in FIG. 10
The processes up to 70 are executed on the host side.

As described above, according to the present embodiment, in the image enhancing method of the recording apparatus for forming an image with a dot matrix configuration while scanning the recording head on the recording medium, among the binarized original images, By detecting a recording pixel group adjacent to an area within two pixels in the recording head scanning direction and the sub-scanning direction and recording an emphasis dot at an intermediate position between the adjacent recording pixel groups, emphasis dots are formed only in the contour portion. In addition, emphasis dots can be added in the high-duty area where high density is required without adding emphasis dots in the low-duty area that emphasizes uniformity, and it is possible to realize a wide gradation range in a linear state. became.

Further, by adding a specific ink color to the secondary color as an emphasis dot, it is possible to correct the tint of the secondary color at the same time as the above effect.

The present embodiment results in recording at a pitch twice the normal resolution in the head scanning direction (or sub-scanning direction). However, since the object of the present invention is density enhancement, an image of a predetermined resolution or higher is obtained. The method of recording is different.

Further, a specific area such as 1 × 2 or 2 × 2 is detected, and the emphasis dot to be recorded therein is determined according to the content thereof. It does not represent the multi-valued expression in 1 above, but simply adds the emphasized dots depending on the dot arrangement state of the binary image.

[0074]

As described above, according to the present invention, by adding the emphasizing dots to the high duty portion of the image, it is possible to surely increase the density in the high duty portion and to emphasize between the dots. since configurations for printing dots reliable concentrations up for each gradation, reduced graininess in the low-duty portion, and bleeding can be prevented in the ink in the outline portion, further specific Lee secondary color
The secondary color of the secondary color
The tint can be corrected.

[Brief description of drawings]

FIG. 1 is a diagram showing an emphasis dot according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating an example of image formation according to the first embodiment of the present invention.

FIG. 3 is a diagram corresponding to one example of dithering according to the first embodiment of the present invention.

FIG. 4 is a diagram showing gradation characteristics obtained by the first embodiment of the present invention corresponding to one example of dither.

FIG. 5 is a diagram corresponding to another example of the dither according to the first embodiment of the present invention.

FIG. 6 is a diagram showing gradation characteristics obtained by the first embodiment of the present invention corresponding to another example of dither.

FIG. 7 is a diagram showing an inkjet recording apparatus used in the present invention.

FIG. 8 is a diagram showing another example of the first embodiment of the present invention.

FIG. 9 is an explanatory diagram of divided printing.

FIG. 10 is an explanatory diagram of divided printing.

FIG. 11 is an explanatory diagram of divided printing.

FIG. 12 is an explanatory diagram of divided printing.

FIG. 13 is a diagram showing a recording state of the second embodiment of the present invention.

FIG. 14 is a diagram showing an emphasis dot according to a second embodiment of the present invention.

FIG. 15 is an image processing block diagram of the first embodiment of the present invention.

FIG. 16 is a flowchart for generating highlighted dots according to the first embodiment of the present invention.

FIG. 17 is a diagram showing gradation characteristics obtained by the third embodiment of the present invention corresponding to one example of dither.

FIG. 18 is a diagram showing a gradation property obtained by the fourth embodiment of the present invention corresponding to one example of dither.

FIG. 19 is an image processing block diagram of a third embodiment of the present invention.

FIG. 20 is a diagram showing dark ink and light ink signal output with respect to an input signal according to the third embodiment of the present invention.

FIG. 21 is a block diagram according to another embodiment.

[Explanation of symbols]

10 Logarithmic converter 20 black generator 30 Masking part 40 Printer gamma correction unit 50 Binarization unit 60 recording device 601 Emphasis dot generation circuit 602 output buffer

Continuation of front page (51) Int.Cl. ⁷ Identification code FI H04N 1/46 H04N 1/46 Z (72) Inventor Hiromitsu Hirabayashi 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) References JP-A 5-124219 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B41J 2/205 B41J 2/01 B41J 2/51 B41J 2/52 H04N 1/409 H04N 1/46

Claims (2)

(57) [Claims] 1. An image recording method for recording an image in a dot matrix method according to a digital input image signal, wherein recording is performed at a pixel position adjacent to a target recording pixel to be recorded.
If it comes adjacent recording pixel exists, the target recording pixel before
Serial records the dots for image enhancement in an intermediate position of the adjacent recording pixels, the target recording pixel and the adjacent recording pixels are both specific 2
If the secondary color is a mixture of colors,
The secondary color is provided at an intermediate position between the recording pixel and the adjacent recording pixel.
The image recording method is characterized by recording an emphasis dot of one of the two specific colors forming the image. 2. A dot-matrix configuration according to a digital input image signal by repeating a print scan (main scan) and a predetermined amount of paper feed (sub scan) of a print head in which print elements are arranged at a pitch equal to the resolution of print pixels. In an inkjet type recording apparatus for forming an image, an adjacent recording pixel to be recorded is located at a pixel position adjacent to a target recording pixel to be recorded.
When present, the target recording pixel and the adjacent recording pixels
An image enhancement dot is recorded at an intermediate position, and the target recording pixel and the adjacent recording pixel both have a specific value 2.
If the secondary color is a mixture of colors,
The secondary color is provided at an intermediate position between the recording pixel and the adjacent recording pixel.
The image recording apparatus is characterized by recording an emphasis dot of one of the two specific colors forming the image.