JPS62184855A - Image recorder - Google Patents

Abstract

PURPOSE:To obtain favorable gradation properties and accurate color reproduction properties both at the time of monochroic recording and at the time of mixed color recording, by providing a means for discriminating the presence or absence of an input image density signal for a hue for the first printing, and a gradation-correcting means for an image density signal for a hue for subsequent printing. CONSTITUTION:When sequentially ejecting at least two inks of different hues onto a recording paper with a time gap to print a color image, the presence or absence of the ink in which printing is to be performed first is discriminated. Both in the case of monochroic printing and in the case of mixed color printing, when the ink for the first printing is absent, an image density signal 5A for the first printing is subjected to gamma correction so that the gamma characteristic of monochrome will be linear. When the ink for the first printing is present, image density signals 5B for the second and later printings are subjected to gamma correction so that the gamma characteristic of each color component in a mixed color on the paper will be linear. Accordingly, gradation properties with favorable linearity and accurate color reproduction properties can be constantly maintained, both in the case of monochroic printing and in the case of mixed color printing.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention forms a color image on recording paper by ejecting ink of a plurality of colors, each of which has a different hue, onto recording paper separately for each color. The present invention relates to an image recording device.

[Prior Art] Conventionally, inkjet recording devices are known that form images on recording paper by ejecting ink from nozzles with minute diameters.

This type of inkjet recording device is widely used as a color image recording device because it can easily obtain color images on recording paper by overlapping printing (superimposed printing) with multiple colors of ink of different hues. ing.

FIG. 3 shows the main structure of an ink ejecting section of an inkjet recording apparatus that records a color image by overlapping three colors of ink having different hues. Multi-nozzle head IA that ejects yellow Y color ink, multi-nozzle head IB that ejects magenta M color ink, and cyan C.
Multi-nozzle heads IC that eject ink are arranged at a distance @D from each other, and each nozzle head IA, IB.

The IC moves (scans) at a speed V in the direction of an arrow 4 on the opposing recording paper 3 while discharging ink of three colors, each having a different hue, from an orifice 2 provided in the IC. In this way, the ink droplets are ejected and attached to the recording paper 3 in the order of yellow, Y1, magenta, M1, and cyan.
A multicolor image is formed thereon by subtractive color mixing of three colors: yellow Y, magenta M, and cyan C.

FIG. 4 shows an example of an image signal processing circuit of the conventional inkjet recording apparatus as described above.

an image density signal 5A indicating the image density of the hue of yellow Y;
an image density signal 5B indicating the image density of magenta M hue;
and an image density signal 5 indicating the image density of the hue of cyan C.
C is input to the color processing section 6, respectively. After the image density signals 5A, 5B, and 5C are subjected to color processing such as masking processing in the color processing section 6, they are sent to the γ correction circuit (gradation correction circuit) 7), where they are processed by γ-Yamamasa. be exposed.

Among the three color image density signals subjected to γ (gamma) correction in the γ correction circuit 7, only the yellow Y image density signal 5A is
It is sent as is to the recording head IA.

However, the magenta M image density signal 5B and the cyan C image density signal are each stored in the buffer 8A.

After being stored once in 8B, the recording head IA.

For the time corresponding to the interval in the scanning direction of IB and IC, that is, for the yellow signal 5A, the magenta signal 5B is D/
V, cyan signal 5C is delayed by 2 D/V and sent to head IB and IC. As a result, each color ink of yellow Y, magenta M, and cyan C is printed at the same location on the recording paper 3, and a multicolor image is reproduced by subtractive color mixing.

The γ correction in the γ correction circuit 7 described above is performed so that the relationship between the density of the printed image and the amplitude level of the input image density signals 5A, 5B, and 5C is linear for each color of yellow, Y1, magenta, M, and cyan C. The relationship between the level of the input image density signal and the output image density was as shown in FIG.

However, the relationship shown in Figure 5 is that yellow Y, magenta M
, γ when each color of cyan C is printed as a single color
It shows the characteristics, and the situation is different when printing as a mixture of two or three colors. That is, when a plurality of colors are mixed, the γ characteristics of each color component differ depending on the order in which the inks are stacked.

FIG. 6 shows how, in the case of a mixture of a plurality of colors, the γ characteristics of an image of each color actually differ depending on the order in which the inks are stacked. That is, the levels of the image density signals corresponding to each color of Y, M, and C are made the same, and the ink of yellow Y, magenta M, and cyan C is printed on the same location on the recording paper 3 in the order of layers. The curve 10A of the gamma characteristics of the yellow Y ink color component printed first remains linear, whereas the gamma characteristic curve 10B of the magenta M ink color component printed next to yellow Y is relatively linear. high level (
Curve 10C of the gamma characteristic of the cyan C ink component printed third becomes nonlinear and saturates in the high density part, which is even lower than the above-mentioned curve 10B. .

This non-linear phenomenon associated with overlapping printing does not matter what color ink is used for printing, but no matter what color ink is used, as long as the order of printing is the second or later. , a nonlinear γ such as IOB or IOC shown in FIG.
Show characteristics. When printing multiple colors of ink sequentially, the phenomenon in which the γ characteristics change nonlinearly from the second onward is thought to be due to the nonlinear mechanism when the ink is absorbed by the paper. The following problems occur regarding color reproducibility.

For example, if the signal levels of the input image density signals of three colors (yellow, Y, magenta, M, cyan, C) are made the same and are printed so that they increase simultaneously at the same rate, each hue is the same, and the image It is necessary to reproduce an output image in which only the density changes. However, when the output image is actually reproduced, as the level of the input image density signal increases due to the above-mentioned phenomenon shown in FIG. As the color components printed at the beginning are gradually emphasized, the resulting color image is accompanied by a change in hue. As a result, the hue changes depending on the image density, resulting in the inconvenience that the color that should originally be reproduced cannot be sufficiently reproduced.

As a measure to eliminate such a drawback, it is conceivable to make the γ correction curve different for each image density signal of each hue depending on the order in which the color heads corresponding to each hue are arranged. For example, if the heads are arranged in the order of yellow, Y1, magenta, M1, and cyan C as shown in Figure 3, the gamma characteristics of each single color are shown in (A), (B), and (C) in Figure 7, respectively. If the curves are made as shown in FIG. ,? Naomu r
Do it.

In FIG. 8, 11A is the γ characteristic of the yellow component in which ink is ejected first when mixing three colors, IIB,
IIC indicates the γ characteristics of the second and subsequent magenta components and cyan components, respectively. In this way, by setting the γ characteristics for each single color as shown in FIGS. 7(B) and (C) for the image density signal of the magenta component and the image density signal of the cyan component, each color component at the time of color mixing is As a result, the inconvenience that the hue changes depending on the density level when printed on the recording paper 3 is eliminated even though the ratio of the input image density signal of each color component is constant.

[Problems to be Solved by the Invention] However, as described above, the conventional method of performing γ correction on image signals of the second and subsequent color components, which is different from that on the first image signal, It is effective when mixing three colors in the order of , cyan C, when mixing two colors in the order of yellow Y and magenta M, and when mixing two colors in the order of yellow Y and cyan C. However, when mixing two colors, magenta M and cyan C, magenta M is printed first and cyan C is printed second, so the γ characteristic of the magenta component is as shown in the curve in Figure 9. 12A
The γ characteristic of the 1-cyan component becomes as shown by curve 12B in FIG. 9, which is disadvantageous in that the hue changes depending on the density of the image.

In addition, in the conventional method described above, when magenta M or cyan C to be printed from the second onwards is printed in a single color, the seventh
There is also a drawback that the γ characteristic as shown in Figures (B) or (C) occurs, and the gradation becomes unnatural.

An object of the present invention is to eliminate the above-mentioned drawbacks, to always obtain linear γ characteristics both during monochrome recording and mixed color recording, and to maintain good gradation and accurate color reproducibility. An object of the present invention is to provide an image recording device.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides an image recording apparatus that forms a color image by ejecting ink of a plurality of hues from different recording heads according to an input image density signal. A determining means for determining the presence or absence of an input image density signal of a hue to be printed first, and a gradation correction value for the input image density signal of a hue to be printed later depending on the determination result of the determining means. The present invention is characterized by comprising a gradation correction means.

[Function] In the present invention, when color images corresponding to image density signals of a plurality of hues are sequentially printed via the recording head with time differences, the signals to be printed from the second onward on the same printing location are When printing in a superimposed manner, it is determined whether there is a signal to be printed first, and if it is determined that the signal to be printed first exists, the first signal is A different gamma correction than that for the first signal is performed to prevent deterioration in color reproducibility when mixing colors.

[Embodiment 1] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an example of the basic configuration of an embodiment of the present invention.

101 is an input terminal for manually inputting an image density signal A of a first hue among image density signals of a plurality of colors; and 102 is an input terminal for manually inputting an image density signal B of a second hue among image density signals of a plurality of colors. This is an input terminal.

200 is a determination circuit that determines the presence or absence of the first signal.

301 is a γ correction that performs linear γ correction on the first signal A.
A correction circuit 302 changes the γ correction coefficient for the second signal B according to the output of the discrimination circuit 200 to calculate γ.
This is a γ correction circuit that performs correction.

400 is a delay circuit (buffer) that provides a predetermined time difference to the output of the γ correction circuit 302.

501 is a print head that prints an image according to the output of the γ correction circuit 301, and 502 is a print head that prints an image according to the output of the buffer 40G.

The γ correction circuit 302 can perform different γ corrections on the second signal B depending on whether the first signal A is present or not.

FIG. 2 shows a main part configuration of an image signal processing section of an image recording apparatus according to an embodiment of the present invention. The inkjet heads IA, IB, and IC are arranged to print yellow Y, magenta M, and cyan C in the order shown in FIG.
Assume that the recording paper 3 is scanned in the same manner as in FIG.

In FIG. 2, 7A is a γ correction circuit that performs γ correction on the yellow Y input image density signal 5A, and performs γ correction so that the output image density becomes linear with respect to the input image density signal. 7B is a γ correction circuit that performs γ correction on the input image density signal 5B of magenta M, and when the output of the discrimination circuit 9A described later is “O”, that is, there is no input image density signal 5A of yellow Y. , when the magenta M color ink is ejected first, the linear γ characteristic is corrected, and when the output of the discrimination circuit 9A is °゛1'', that is, after the yellow Y ink is ejected. When magenta M color ink is to be ejected, the nonlinear γ characteristic is corrected as shown in FIG. 7(B).

Further, 7C is a γ correction circuit that performs γ correction on the cyan C input image density signal 5C, and a discrimination circuit 9A described later.
When both outputs of 5A and 9B are "O", that is, yellow Y and magenta M input image density signals 5A and 5B.
If there is no color ink and cyan C color ink is ejected first, the linear γ characteristic is corrected and the discrimination circuit 9A or 9B
When either output is "1", that is, when cyan C ink is ejected second or third after at least either yellow Y or magenta M ink has been ejected. is the nonlinear γ as shown in Figure 7(C).
Correct the characteristics.

Each of the above-mentioned γ correction circuits 7A, 7B, and 7C is composed of, for example, a ROM (read-only memory), and a value obtained by multiplying the address value by a γ coefficient is stored in each address of the ROM in advance, and the value of the input image density signal is Input the level as address data and read out the γ-corrected signal from the output side.

9A and 9B are discrimination circuits, respectively. The former discrimination circuit 9A discriminates the presence or absence of the yellow Y image density signal 5A, and the latter discrimination circuit 9B discriminates the presence or absence of the magenta M image density signal 15B. Discern.

If the input image density signals 5A, 5B, and 5C are, for example, 8-bit digital signals, the discrimination circuits 9A and 9B are constituted by multi-input OR (logical sum) circuits as shown in FIG. 1θ. In this OR circuit, an 8-bit image density signal 15A (or 15B), which has been subjected to masking processing etc. in the color processing section 6, is manually inputted in parallel to the manual density signal 5A (or 5B), and the human input density signal 15A (or 15B) is ) when all bits are 0'', the output is °0'' and 1
When the bit is also "1", an image density signal exists, so "1" is output.

The output of the discrimination circuit 9A is supplied to the γ correction circuit 7B as a γ coefficient selection signal 17A. The γ correction circuit 7B manually inputs the input γ coefficient selection signal 17A as an upper address, and when this signal 17A is 0°, it means that the yellow Y image density signal 15A does not exist, so the γ correction coefficient is outputs a γ correction output having a linear characteristic, and when the γ coefficient selection signal 17A is II II II, it means that the yellow Y image density signal 15A is present, so the γ correction coefficient has a nonlinear (curve) characteristic. A γ-corrected output with .

Further, 10 is an output signal 17A of the discrimination circuits 9A and 9B.
It is an OR circuit that takes the logical sum of and 17B, and the output signal 1
When either one of 7A and 17B is at °°1°, a Bi output signal 17C is output. The output signal 17C of this OR circuit 10 is supplied to the γ correction circuit 7C.

When the output signal 17c of the OR circuit 10 is 0'', neither the yellow Y image density signal 15A nor the magenta M image density signal 15B exists, that is, the discrimination circuit output 1
Since both 7A and 17B are llo''°, the γ correction circuit 7C outputs a γ correction whose γ correction coefficient has linear characteristics.

When the output signal 17C of the OR circuit 10 is 1°, this means that either or both of the yellow Y image density signal 15A and the magenta M image density signal 15B are present, so the γ correction circuit 7C performs a γ correction output in which the γ correction coefficient curve has a non-linear characteristic.

Next, the operation of the embodiment of the present invention with the above configuration will be explained.

First, the image density signal 5A of the yellow Y component is subjected to masking processing in the color processing circuit 6, and then input as a signal 15A to the γ correction circuit 7A, where linear γ correction is performed, and the γ
The corrected output signal 20A is immediately supplied to the recording head IA.

The head IA discharges yellow Y ink onto the recording paper 3 according to the gradation level (amplitude level) of the image density signal 2OA of the yellow Y component supplied from the γ correction circuit 7A.
As a result, an image of yellow and Y components is first printed on the recording paper 3.

The output signal 15A of the color processing circuit 6 described above is simultaneously supplied to the discrimination circuit 9A to discriminate the presence or absence of the signal, and the discrimination result is supplied as the output signal 17A to the γ correction circuit 7B.

On the other hand, the image density signal 5B of the magenta M component is subjected to masking processing in the color processing circuit 6, and is then processed as a signal 15B by γ.
The signal is supplied to the correction circuit 7B.

When the output signal 17A of the discrimination circuit 9A is 0'', the γ correction circuit 7B performs linear γ correction processing on the No. 6 15B.
1”, the signal 15B is output in the γ correction circuit 7B.
A non-linear γ correction process is performed on the

That is, when the image density signal 5A for ejecting ink first does not exist, the image density signal 5B for magenta M is as follows.
Since this signal itself becomes the signal for ejecting ink first, it is corrected using the linear γ characteristic. When there is an image density signal 5A that causes ink to be ejected first, the magenta M image density signal becomes a signal that causes ink to be ejected second. Nonlinear γ characteristic correction for compensating for saturation of the image density curve is performed on the magenta M component image density signal 15B.

The image density signal 20B of the magenta M component output from the γ correction circuit 7B is delayed by the buffer 8A by the scanning time (corresponding to the head interval) during which the magenta head IB moves to the printed area of the yellow head IA by the D/V. and supplied to the head IB.

The head IB ejects magenta M ink onto the recording paper 3 according to the density level of the magenta M component image density signal 20B supplied from the buffer 8A. At this time, if a yellow Y component signal exists first, then the head I
In B, magenta M ink is printed in an overlapping manner at the same location as the one ejected by the head IA to form a color image.

Further, the image density signal 15B of the magenta M component is supplied to the determination circuit 9B, and the presence or absence of the signal is determined. on the other hand,
The image density signal 5C of the cyan C component is subjected to masking processing in the color processing circuit 6 and then supplied to the γ correction circuit 7C as an output signal 15C. When the output signal 17C of the OR circuit 10 that performs the OR operation of the signals 17A and 17B is "0", the γ correction circuit 7C performs linear γ correction processing on the signal 15C, and the output signal of the OR circuit 10 17C
When is °°1°, the signal 1 is output in the γ correction circuit 7C.
Nonlinear γ correction processing is performed on 5C.

That is, when the first yellow signal 5A and the second magenta signal 5B are not present, the cyan C image density signal itself becomes the image density signal for ejecting ink first, so the linear γ characteristic is Given.

When at least one of the image density signals 5A and 5B is present, the output signals 17A and 17A of the discrimination circuits 9A and 9B are
Since at least one of 17B is "1°",
The output 17C of the OR circuit 10 becomes °11", and the cyan C
Since the image density signal is the second or third signal to be printed, nonlinear γ correction is applied to compensate for the saturation of the input signal amplitude level vs. output image density curve in the high density area. This is performed for the image density signal 15C of the C component.

The image density signal 20C of the cyan C component outputted from the γ correction circuit 7C is delayed by the buffer 8B by the scanning time (equivalent to the head interval) 2D/V during which the cyan head IC moves to the printed area of the yellow head IA. and supplied to the head IC.

The head 1c discharges cyan C ink onto the recording paper 3 in accordance with the amplitude level (gradation level) of the cyan C component image density signal 20C supplied from the buffer 8B. At this time, if at least either the yellow Y component or the magenta M component existed first, the head IC prints cyan C ink overlappingly on the same location as that ejected by heads IA and IB, and prints a color image. form.

As mentioned above, when using a single color (printing) or mixed colors (printing)
Even when the corresponding color is printed for the first time, γ correction is performed so that the γ characteristic at the time of monochrome becomes linear, and the corresponding color is printed for the second time.
When printing after the th, γ correction is performed so that the γ characteristics of the color component when mixing colors are linear, so it is possible to always maintain linear gradation and accurate color reproducibility. becomes.

Next, other embodiments of the present invention will be described.

In the previous embodiment, when detecting the presence of an image density signal, the presence of the image density signal was divided into cases where all the constituent bits were 0'' and cases where the other bits were not. Even if there is, if the value is relatively small, the influence of the previously printed ink is small, and it may be desirable to perform linear γ correction for the second and subsequent printings.

Figure 11 shows an example of a discrimination circuit in such a case, where a certain threshold is determined and input values below the threshold are
The input terminal of the OR circuit is configured to be limited to a certain number of bits in order to output the input value as "0" and output the input value equal to or higher than the threshold value as "1".For example, the discriminator circuits 9A and 9B are Increase the number of bits of input signals 15A and 15B to 8
, ag, al, a2 in order from the least significant bit.
・・・・・・・・・・・・・・・ When it is set as al, the remaining upper signal a4 after removing the lower 4 bits a□, ・・・・・・・・・・・・ a3 ．．・・・・・・・・・・・・
...Al is input and the logical sum is calculated.

In this case, the levels 0 to 15 of the gradation levels 0 to 255 (signal amplitude levels) are determined by the discrimination circuits 9A and 9B.
In this case, linear γ correction is performed in the γ correction circuit, and nonlinear γ correction for color mixing is performed at levels 16 or higher.This makes it possible to obtain a more natural image. can.

Note that the discrimination circuits 9A and 9B are not constituted by OR circuits as shown in FIGS. 10 and 11, but input the output level of the input image density signal to the ROM as address data.
Of course, the discrimination output "1" or "0" may be extracted from the ROM.

In this way, even when a ROM is used, all input signals below a predetermined threshold are output as 0 and all input signals above the predetermined threshold are output as 1.

Discrimination circuits 9A and 9B using an OR circuit as shown in FIG.
For example, in the case of 8-bit manual power, the threshold values that can be set are the human power level of 0.2°4, 8.18.64, and 12.
However, when a ROM is used, there is an advantage that the threshold value can be freely set between input levels 0 to 255.

Furthermore, in the above embodiment, the γ correction circuit 7A.

7B and 7C, the density level of the input image density signal is multiplied by a predetermined γ coefficient to obtain the γ correction output, but in a recording apparatus that forms the gradation of the output signal by the dither method, A similar effect can be achieved by manipulating the threshold of the dither matrix according to the density level of the input image density signal without changing the γ coefficient.

For example, if the water-like γ characteristic in Figure 7 (A) is obtained when the dither thresholds are equally spaced, then by making the dither thresholds wider in the low-density parts of the image and narrower in the high-density parts of the image, , γ characteristics as shown in FIG. 7(B) or (C) can be obtained. Therefore, two types of dither matrices are prepared for the image density signals of magenta M and cyan C, and the dither matrix is changed depending on the selection signals 17A and 17C when the first dither matrix is selected and when it is the first dither matrix. The present invention can also be carried out by selectively switching between the two.

In addition, in this embodiment described above, the type of ink for each hue is
It was explained as three colors: yellow, magenta, and cyan,
The present invention can be carried out in the same manner as described above even if four colors of ink are used, including black.

Furthermore, although this embodiment has been explained by printing ink in the order of yellow, maze, ivy, and cyan, the present invention is not limited to this printing order of ink, and the present invention can be carried out in any other printing order. Of course.

[Effects of the Invention] As explained above, according to the present invention, ink of two or more plural hues is sequentially ejected onto a recording paper at a time difference to print a color image. It determines the presence or absence of ink to be printed, and determines whether it is a single color or a mixed color print.If there is no ink to be printed first, the monochrome γ Gamma correction is performed so that the characteristics are linear, and if there is ink that is printed first, the C color component when mixed colors on the recording paper is calculated for the image density signal that is printed after the second one. Since the γ correction is performed to compensate for the γ characteristics so that the γ characteristics are linear, it is possible to always maintain good linear gradation and accurate color reproducibility, whether in monochrome or mixed colors. Effects can be obtained.

Further, according to the present invention, when determining the output level of the input image density signal, a predetermined threshold value is provided, and only when the signal of the previously printed color exceeds this threshold value, the signal of the previously printed color is determined. By performing nonlinear gradation correction of γ characteristics on other signals following the signal, more natural gradation and color reproducibility can be realized.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the basic configuration of an embodiment of the present invention. FIG. 2 is a block diagram showing the circuit configuration of one embodiment of the present invention. FIG. 3 is a block diagram showing the circuit configuration of an embodiment of the present invention. FIG. 4 is a block diagram showing the circuit configuration of a conventional image recording apparatus; FIG. 5 is a γ characteristic diagram showing the input image density signal level versus output image density characteristic in the case of monochrome printing; Fig. 6 is a γ characteristic diagram showing the actual input image density signal level versus output image density characteristic in the case of conventional mixed color printing. Fig. 7 (A), (B), and (tl:) are the printing order. Figure 8 is a characteristic diagram showing the γ characteristics of the image density signal of each hue when three colors are mixed under the conditions of Figure 7. , FIG. 9 is a characteristic diagram showing the γ characteristic when two colors are mixed, and FIGS. 10 and 11 are block diagrams each showing a configuration example of a discrimination circuit in an embodiment of the present invention. IA, IB, IC...multi-nozzle head for recording, 5
A, 5B, 5C... Image signal, 6... Color processing section, 7.7A, 7B, 7C... γ correction circuit, 8A, 8B.
... Buffer, 9A, 9B... Discrimination circuit, 10... OR circuit. ＼３＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼＼ﾆ; Figure 6 Zeta 2 The Bank 0 Figure 7's 3rd floor! , The characteristics of the hook in the case where the grass is yellow, the characteristics of the whistle in Figure 8, Figure Z, and the color of the cow ζ 2 in Figure Z. Pro showing circuit configuration 1,
Whistle 10 Figure 11
figure

Claims (2)

[Claims] (1) In an image recording device that forms a color image by ejecting ink of multiple hues from different recording heads according to an input image density signal, it is determined whether there is an input image density signal of the hue to be printed first. What is claimed is: 1. An image recording apparatus comprising: a determining means for determining the color of the image; and a gradation correcting means for varying a gradation correction value for an input image density signal of a hue to be printed later, depending on the determination result of the determining means. (2) The image recording apparatus according to claim 1, wherein the determining means determines the presence or absence of the input image density signal based on a predetermined threshold value.