JP3598608B2 - Image output device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention is directed to a method of printing a color image processed, edited, and created by a personal computer or a workstation on a recording medium such as paper, using ink of a plurality of colors such as cyan, magenta, yellow, and black. ), Such as an ink jet printer.
[0002]
[Prior art]
Conventionally, in a color ink jet printer, a so-called print head (pixel printing means) for adhering a color material such as ink to a recording medium such as paper requires individual pixels in view of easiness of device manufacturing and stability of printing control. The tone reproduction capability for two gradations (that is, two types of whether or not to attach a color material) (hereinafter, referred to as a binary head) was mainly used.
[0003]
As described above, when an image is reproduced by a binary head having only two gradations for each pixel, when a color image having a rich gradation expression is input, the systematic dither method is used. And various kinds of binarization processing called an error diffusion method are performed, and a gray scale is reproduced using a pseudo gray scale expression.
[0004]
Since such a binarization process is intended to reproduce the gradation by the number of colors arranged in the image processing unit area, if the image processing unit area is increased, the gradation expression becomes smooth. Inevitably, the resolution is reduced, resulting in a coarse image. The only solution to this problem is to reduce the unit area of image processing and to reduce the size of each pixel of the color material. Also, reproducing various mixed colors by controlling whether or not to attach a color material means that the color material density is always constant, so the colors reproduced by the mixed colors are generally dull colors, The color reproduction ability is impaired.
[0005]
As a method of solving both of them simultaneously, a print head (hereinafter, referred to as a multi-value head) capable of changing the ejection amount of each ink (color material) to multiple gradations and providing multiple gradations for each pixel. There is something.
[0006]
This is because there is abundant gradation reproduction capability for one pixel, so that it is not necessary to reproduce gradation using an area larger than the pixel as in the tissue dither method, and a coarse image is not reproduced. . Further, performing tone reproduction within one pixel necessarily changes the amount of color material applied per pixel, so that so-called density gradation expression can be performed. Such a density gradation has an advantage that compared with a so-called area gradation used at the time of binarization, a mixed color by a color material becomes a relatively vivid color, and the reproducibility of the above-described color is improved.
[0007]
[Problems to be solved by the invention]
However, reproducing the multi-valued gray scale for one pixel in this manner is difficult with simple control such as whether or not to discharge a color material, as in the case of reproducing a binary gray scale. In other words, the control is performed in multiple stages, such as control of not discharging the color material, discharging slightly, discharging a little, discharging a lot, and so the control is very complicated and difficult. Furthermore, since the purpose of providing multi-value gradation to the print head is to reproduce good image quality, stable reproducibility of individual levels of multi-value gradation is also important, but in order to achieve this, However, the control and correction of the print head become more complicated. In other words, in order to achieve multi-valued gradation for one pixel, various sensors and complicated control devices are required, so that the print head device and control mechanism become very expensive. The problem that occurred.
[0008]
Further, the image data after binarization, since the information of one pixel one color per 1bi t, entire image data volume is relatively small in size. Therefore, when image data is transferred to a printer, the transfer time is shortened, and when the image data is stored in a storage unit such as a hard disk, a small storage capacity is required. However, as described above, when multi-value conversion is performed for one pixel, information per pixel per color of the image data increases, so that the transmission time of the image data becomes longer and the required storage capacity becomes larger. As a result, problems such as a decrease in the processing capacity of the printer and a rise in the price are caused.
[0009]
The present invention has been made in order to solve the above-described problems, and focuses on the point that the degree of influence on image quality varies depending on the color of a color material. It is an object of the present invention to provide an inexpensive image output device that can transmit data.
[0010]
[Means for Solving the Problems]
In order to achieve this object, the image output apparatus according to the first aspect of the present invention is an image output apparatus including a pixel printing unit that attaches a color material to each of a plurality of types of colors for each pixel of a recording medium. gradations per the pixel of the pixel printing means for at least one color material, which is constituted to be different from the number of gradations per the pixel of the pixel printing means for the other color materials.
[0011]
Further, the image output apparatus of the invention described in claim 2, in the image output apparatus of the invention described in claim 1, the number of gradations included in the pixel printing means for applying a magenta color material, the other the pixel printing means for any colorant of Kano color is to set as larger than the number of gradations included in.
[0012]
Further, the image output apparatus of the invention described in claim 3, in the image output apparatus of the invention described in claim 1, the number of gradations included in the pixel printing means for attaching the colorant of the yellow color, the other the pixel printing means for any of the color coloring materials are those set smaller than the number of gradations included in.
[0013]
According to a fourth aspect of the present invention, in the image output device according to the first aspect of the present invention, the order of attaching the plurality of types of color materials to a recording medium is as follows. , Is determined based on the number of gradations of each pixel printing unit.
[0014]
According to a fifth aspect of the present invention, in the image output device according to any one of the first to fourth aspects, the color materials are attached in the order of increasing the number of density gradations per pixel. is there.
[0015]
According to a sixth aspect of the present invention, in the image output device according to any one of the first to fifth aspects, the color having the smallest number of gradations is yellow.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0017]
First, the configuration of an inkjet printer 1 as an image output device will be described with reference to a functional block diagram shown in FIG. A CPU (central processing unit) 10 in the ink jet printer 1 includes a ROM 11 storing a control program, a RAM 12 storing various data, a buffer memory 16 for temporarily storing image data, and a print head 13. Are respectively connected to the drive control unit 14 via a bus.
[0018]
Image data stored in an external device 15 such as a personal computer is stored in a buffer memory 16 from the CPU 10 connected via an interface (not shown).
[0019]
The print head 13 is a pixel printing unit that can attach a color material (ink) of each color to the surface of the recording medium 20 for each pixel formed of a minute area. from the yellow head 13y for printing yellow ink as the magenta head 13m for printing magenta ink, a cyan head 13c for printing cyan ink, a black ink-jet head 13k for printing black color ink It is configured. As shown in FIG. 2, each print head is disposed so as to be displaced by a predetermined distance P in the sub-scanning direction (that is, the paper feed direction) of the recording medium 20 such as paper. They are arranged in order.
[0020]
Next, the operation of the printer 1 configured as described above will be described. The CPU 10 reads the image data stored in the external device 15, temporarily stores the image data in the buffer memory 16, and converts the image data into control signals for the respective inks of cyan, magenta, yellow, and black. The converted control signal is stored and stored in a predetermined area of the RAM 12. When the control signal for one main scan is accumulated, the CPU 10 reads the control signal of the RAM 12 and sends it to the print head 13. The print head 13 discharges ink of each color material onto the recording medium 20 based on the control signal. At this time, when the print head 13 scans in the main scanning direction (see FIG. 2), if each ink (color material) is simultaneously ejected to one area 31a of the image processing shown in FIG. When the liquid ink of another color is mixed with the ink that is not present, the reproduced color becomes turbid (degraded in sharpness). Therefore, in the above-described embodiment, the magenta head 13m, a black head 13k is located behind the subsequent distance P, a cyan head 13c is located behind the distance P, and a yellow head 13y is located at the rearmost end in the paper feed direction. In addition, the print heads 13y, 13c, 13k, and 13m corresponding to the respective colors have different arrangement positions by a predetermined amount P in the sub-scanning direction. Therefore, for example, the control signal of the black head 13k is the control signal of the magenta head 13m, it is necessary to shift by an amount ejection timing corresponding to 31a of FIG. That is, the storage area of the control signal to the black color that is built on top RAM12, it is necessary to increase only the storage capacity of which corresponds to the 31a portion to the storage area of the magenta color. Similarly, the storage area of the control signals of cyan, should only large amount corresponding to 31b portion than in the storage area of the control signal to the magenta color, further, a storage area for storing the control signals of yellow The (storage capacity) needs to be increased by an amount corresponding to the portion 31c in comparison with the storage area of the control signal for the magenta color . That is, the storage area for storing the control signal of the yellow color to be discharged last is set to be the largest.
[0021]
When explaining the operation characteristics of the print head 13 further head 13m and a black head 13k for magenta are those capable of performing both 3 or more steps of gradation reproduction in one pixel region (dot region), the In the embodiment, it is configured to be capable of 17-step gradation reproduction. Cyan head 13c is a one that can perform a slight tone reproduction in one pixel region (dot region), the in this embodiment are those capable of performing tone reproduction out of 5. Head 13y for yellow, multi-tone reproduction which does not perform in one pixel region (dot region), is to construct at those only whether two gradations discharging ink can not be reproduced.
[0022]
A method of performing tone reproduction by using heads for inks of each color having different characteristics will be described with reference to FIG. The input image data will be described as having 17 levels of image data, but it goes without saying that the present invention can be applied even if the number of gradations of the input image data is different.
[0023]
First, a description will be given gradation reproduction method in the yellow head 13y. Head 13y for yellow are the do eject ink in one pixel region (dot region), the discharge control of the second gradation is either not ejected as described above, tone reproduction of even 17 stages In order to achieve this, an area gradation method used in a dither method or the like is adopted. That is, a pixel area of 4 × 4 dots is assumed to be a unit area for gradation processing for gradation reproduction, and gradation reproduction is performed by the number of ink ejections in this area. As shown in the yellow column of FIG. 3, when the input gradation level is 1, the number of image points ejected in a unit area of gradation processing is set to 1, and when the input gradation level is 4, Is to set the number of image points to 4, and to dot dots at appropriately scattered positions, and sequentially increase the number of image points to eject ink as the input gradation level increases.
[0024]
Subsequently, when explaining a tone reproduction method using the cyan head 13c, the cyan head 13c may be carried out a tone reproduction out of 5 in one pixel region, as described above, the input image The ability to perform 17-step multi-tone reproduction of data is insufficient. Therefore, taking the idea of similarly area gradation and when the head 13y for yellow described above. However, since the cyan head 13c has multiple tone reproduction capacity for one pixel region, the gradation processing unit area requires a narrow pixel region 2 × 2 dots.
[0025]
For example, five gradation levels that can be reproduced by one pixel in the cyan head 13c, the ink ejection without the ink small amount ejection, ink in ejection amount, ink mass ejection, expressed over the entire surface discharge, cyan FIG 3 (Cyan In the column of (), for the sake of convenience, the display is made such that the tone reproduction level of the pixel can be identified by the dot diameter. In this case, when the input gradation level is 1, a dot of a small-diameter dot is arranged in one pixel region of the 2 × 2 dot gradation processing unit area, and no ink is discharged in the other three pixel regions. It is. When the input gradation level is 4, dots of medium diameter dots are arranged in two pixel regions in a 2 × 2 dot gradation processing unit area, and no ink is discharged in other pixel regions. Hereinafter, as shown in FIG. 3, as the input gradation level changes, the gradation reproduction capability of one pixel and the multi-gradation reproduction capability of the 2 × 2 dot area by area gradation are shared. Thus, 17-stage multi-tone reproduction of input image data can be achieved.
[0026]
Next, a description will be given tone reproduction method using the head 13m, and a black head 13k magenta. As head 13m, and a black head 13k for magenta was described above, in both one pixel region, because it has a 17-step tone reproduction capability of some of the ink discharge amount, the gray level of the input image data 1 It can be reproduced in one pixel region (gradation processing unit area).
[0027]
That is, it can be said that one pixel region corresponds to the unit area of gradation processing in this case. In this case, as shown in the magenta (Magenta) and black (Black) columns, as the input gradation level changes, the gradation level reproduced by each pixel changes. I do.
[0028]
For example, in FIG. 3, in order to make it easy to identify the change in the gradation level, the ratio of the area occupied by the ink dots to the individual pixel regions is displayed so as to change gradually.
[0029]
According to the image output device having such a configuration, the following effects can be obtained. When ejecting the ink dots using a multi-tone of the head in one pixel region, as head 13m and a black head 13k for the above-mentioned magenta, that even with a small gradation processing unit area to output a high-definition image Can be.
[0030]
However, as described in detail in the above problem, such a head is very expensive due to complicated control and manufacturing.
[0031]
On the other hand, human visual characteristics differ depending on colors and do not have the same effect. For example, magenta having an absorption characteristic near a wavelength of 550 nm (nanometer) of light showing a peak of human visual sensitivity (color vision) can easily identify the resolution and gradation reproducibility. Yellow, which has an absorption characteristic at a wavelength of about 450 nm, has low human visual sensitivity, so that it is very difficult to identify differences in resolution and gradation reproducibility.
[0032]
Therefore, a high-definition image was reproduced by using a head having multi-tone reproduction characteristics in one pixel area as a head for ejecting yellow ink ( color material) for which it is difficult to distinguish the difference in resolution and gradation reproducibility. Even so, humans cannot easily distinguish the difference, so that the need for expensive heads is low.
[0033]
On the other hand, if a head having multi-tone reproduction characteristics in one pixel region is used as a head for ejecting magenta or black ink , which can easily identify differences in resolution and gradation reproducibility, these heads are expensive. Even so, a high-definition (high-quality) color image that can withstand human viewing can be obtained.
[0034]
Therefore, if a configuration such as the present embodiment is used, a head capable of reproducing an expensive multi-gradation is adopted as a head that ejects magenta or black ink that has a large effect on image quality, and the image quality is reduced. Since a low-impact yellow can use an inexpensive head, there is an effect that both high image quality and low price can be achieved.
[0035]
Further, since the head for ejecting the above-described magenta or black ink performs 17-step gradation reproduction for one pixel, 5 bits of information are required to set the reproduction level of one pixel. Become. On the other hand, the head that discharges yellow ink is a so-called binary head, in which one pixel can be set with 1-bit information. The number of bits needed to set the point color is very small. In general, since color image data is formed from a huge number of image points, and the amount of data relating to color is also huge, the use of the above-described binary head can reduce the amount of data to be stored. This can be expected to have the effect of shortening the transfer time and contributing to the achievement of high-speed printing.
[0036]
Further, as shown in FIG. 2, among the print heads of each color, printing is performed from a print head having a large gradation level for one pixel, and a print head having a small gradation level is printed last. Thereby, the storage area for constructing in the RAM 12 can be reduced.
[0037]
That is, in one image processing, for the yellow having the smallest number of bits for expressing the gradation level per pixel, the image area in which the color data must be stored (31d in FIG. 2). Corresponding to the colors magenta and black which require a large number of bits to represent the gradation level per pixel (the areas 31a and 31b in FIG. 2). By storing (corresponding), the storage area required as a whole can be reduced.
[0038]
Furthermore, when trying to reproduce a multi-tone color image for one pixel, generally, the area of the ink adhering to the surface of the recording medium 20 and the thickness of the ink naturally change. That is, as shown in FIG. 4, as the gradation level increases from low to high, the area of the ink 33 adhering to the surface of the recording medium 20 (the ink adhesion area with respect to one pixel region) increases. In addition, the thickness H of the ink 33 adhering to the surface of the recording medium 20 increases, so that a so-called density gradation-like gradation change can be performed, and the color reproducibility is further improved. You can also expect a great effect.
[0039]
In the present embodiment, by changing the gradation processing unit area, the gradation reproduction numbers of the respective colors are set to be equal.However, it is not necessary to stick to this, and the gradation processing unit area is fixed for each color. There is no problem even if the characteristic is such that the tone reproduction number of each color is different.
[0040]
【The invention's effect】
As is apparent from the above description, the image output device according to the first aspect of the present invention includes a pixel printing unit that attaches a color material to each of a plurality of types of colors for each pixel of a recording medium. in, which tone number per the pixel of the pixel printing means for the at least one colorant, and configured to be different from the number of gradations per the pixel of the pixel printing means for other color materials It is.
[0041]
Therefore, the number of gradations possessed by the pixel printing means can be made different for each color material. Pixels having a high number of gradations are used for colors which are likely to affect the image quality. By using a small number of pixel printing units, high image quality can be obtained with a low-cost configuration. That is, according to the present invention, in consideration of the fact that the degree of influence on the image quality differs depending on the color material, an effect that an inexpensive image output device can be provided while maintaining the advantages of multi-valued gradation as much as possible. Play.
[0042]
The image output apparatus of the invention described in claim 2 is the image output apparatus of the invention described in claim 1, the number of gradations included in the pixel printing means for applying a magenta color material, the other in which was set to one larger than the number of gradations included in the pixel printing unit for the color material of Kano color. That is, with regard to the pixel printing means for attaching the magenta color material which easily affects the color perception of humans, by increasing the number of gradations as compared with the pixel printing means for the color materials of other colors , high precision is achieved. This makes it possible to easily reproduce a color image and to provide an inexpensive image output device while maintaining the advantages of multi-valued gradation as much as possible.
[0043]
Further, the image output apparatus of the invention described in claim 3 is the image output apparatus of the invention described in claim 1, the number of gradations included in the pixel printing means for attaching the colorant of the yellow color, the other The number of gradations of the color material of any color is set to be smaller than that of the pixel printing means.
[0044]
On the other hand, the yellow color hardly affects human color perception, and the image quality is hardly deteriorated even if the number of gradations possessed by the pixel printing means for the color material is reduced. A good image output device can be provided.
[0045]
An image output device according to a fourth aspect of the present invention is the image output device according to any one of the first to third aspects, wherein the color material for each of a plurality of colors is applied to the recording medium. The attachment order is determined based on the number of gradations of the pixel printing unit.
[0046]
Accordingly, by printing the colors that require a large storage capacity first, the storage capacity can be reduced, and the transmission speed of the image data including the color data can be increased. This is advantageous in that an output is possible and an inexpensive image output device can be provided.
[0047]
According to a fifth aspect of the present invention, in the image output device according to any one of the first to fourth aspects, the color materials are attached in the order of increasing the number of density gradations per pixel. is there. With such a configuration, it is possible to reduce a storage area to be constructed in the data storage unit (RAM) of the image output device. Further, as the gradation level increases from low to high, the area of the ink (color material) adhering to the surface of the recording medium (the area of ink adhering to one pixel region) increases, so that the so-called area gradation is obtained. The thickness of the (coloring material) adhering to the surface of the recording medium is also increased, so that it is possible to produce a so-called density gradation-like gradation change, and an effect such that the color reproducibility is further improved is expected. You can also.
[0048]
According to a sixth aspect of the present invention, in the image output device according to any one of the first to fifth aspects, the color having the smallest number of gradations is yellow. This is because the yellow color hardly affects human color perception, and the image quality does not easily deteriorate even if the number of gradations of the pixel material for the color material is reduced.
[Brief description of the drawings]
FIG. 1 is a functional block diagram of a printer according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating an ejection order for each color of ink on a recording medium.
FIG. 3 is a diagram illustrating an example of a multi-tone reproduction method for a head of each color material in the embodiment.
FIG. 4A is a diagram illustrating a printing state of area gradation ink, and FIG. 4B is a diagram illustrating a printing state of density gradation ink.
[Explanation of symbols]
1 Printer 10 CPU
13 print head 13y yellow head 13m magenta head 13c cyan head 13k black head 14 drive circuit 15 external device

Claims (6)

In an image output apparatus including a pixel printing unit that attaches a coloring material to each of a plurality of types of colors for each pixel of a recording medium,
Characterized in that the number of gradations per the pixel of the pixel printing means for the at least one colorant, which are configured differently from the gray scale per the pixel of the pixel printing means for other color materials Image output device. Number of gradations included in the pixel printing means for applying a magenta colorant, a request, wherein more than the number of gradations included in the pixel printing unit for the color material of the other one Kano color Item 2. The image output device according to Item 1. Number of gradations included in the pixel printing means for attaching the yellow colorant is claimed, characterized in that less than the number of gradations included in the pixel printing unit for any other color of the colorant Item 2. The image output device according to Item 1. 4. The method according to claim 1, wherein the order in which the plurality of types of color materials are attached to a recording medium is determined based on the number of gradations of each of the pixel printing units. An image output device according to any one of the above. The image output apparatus according to claim 1, wherein the order in which the color materials are adhered is an order in which the number of density gradations per pixel is large. 6. The image output device according to claim 1, wherein the color having the smallest number of gradations is yellow.

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