JPH07254984A - Image processing method - Google Patents

Abstract

PURPOSE:To provide a high-quality image by correcting a gradation for which the relation between the gradation of a recording pattern defining a prescribed area as one picture element and optical density is discontinuously changed. CONSTITUTION:Concerning a digital ink jet recorder, since a dot contour is made digital in the case of dedicated paper, the discontinuity of gradations is clearly actualized. Therefore, when the pattern of respective dots is regularly repeated at a certain density gradation in the case of executing digital recording while using a simple density pattern, the number of dots in the pattern of the gradation is not changed but dot positions are irregularly arranged and corrected. Otherwise, the pattern provided with the almost middle number of dots as many as the number of dots in the pattern of a gradation lower than this gradation value just for one gradation is replaced with the non-corrected gradation value and corrected. Thus, the image of the gradation provided with linear optical density can be provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is capable of reproducing binary data from ordinary multi-valued data (analog gradation data) with good reproducibility in a binary recording device such as an ink jet or electrophotographic recording device. The present invention relates to a pseudo halftone processing method for obtaining a recorded image and the like.

[0002]

2. Description of the Related Art Pseudo halftone processing methods used to obtain binarized data with good reproducibility from conventional multivalued data include, for example, 1) density pattern method, 2) systematic dither method, and 3) ) The error diffusion method is used.

In the method 1), one pixel is expressed as a binary gradation by area modulation of recording dots such as M × N (M and N are natural numbers of 1 or more). In an apparatus or the like, the area of the ink droplets is modulated by keeping the diameter of the ink droplets constant and varying the number of ink particles to be recorded per unit area.

That is, in this method, dots are turned on and off for each pixel (dots are recorded or not recorded).
Is recorded as a binary combination corresponding to, and a pseudo halftone is expressed by this combination.

The above method 2) is a typical dither method, typically Bayer's systematic dither method.

This method is a method of obtaining halftone by performing threshold processing on pixels and dots in a one-to-one correspondence.

The method 3) corresponds to the dither method which is a conditional decision method. This method is a method of determining a halftone in consideration of the influence of the surroundings and the conversion result.

In any case, in the above pseudo halftone processing method, it is possible to artificially approximate the actual density by utilizing the difference in the area occupied by the dots and the difference in the arrangement of the dots in a predetermined area. It is what

Basically, what has been further improved or combined with the above method has been actually used in the past, and a pseudo-halftone was expressed to obtain a temporary effect.

Conventionally, as an apparatus combined with the above method, an ink jet recording apparatus or a thermal transfer recording apparatus in which the contours of recording dots are not so clear, or, in the case of electrophotography, an analog copying machine And LBP (laser beam printer).

[0011]

However, in recent years, the performance of the recording apparatus itself has been remarkably improved, and in response to this, the actual user side also makes the dots finer, improves the dot contour, and The demand for colorization and multi-gradation is gradually increasing.

However, since the conventional image processing method is almost limited to the above-mentioned methods, a high-quality image sufficiently satisfying the user's sophistication is required despite the high performance of the recording apparatus. The problem that has not been obtained has arisen.

In particular, when a digital recording apparatus is used, the quality is often unfavorable if the conventional pseudo halftone processing is used.

For example, specifically, the gradation of halftone becomes discontinuous, resulting in a so-called dirty image.

[0015]

In order to solve the above-mentioned problems, the present invention uses a plurality of gradation recording patterns that realize the arrangement of recording dots corresponding to gradations, and digitally images an image for each predetermined area. An image processing method of an image recording method for recording, wherein at least one of the plurality of gradation recording patterns is recorded so that the relationship between the plurality of gradations and the optical density exhibits substantially linearity. This is an image processing method in which a pattern is changed and used as a new recording pattern.

More specifically, the gradation is changed by changing the gradation recording pattern in which the arrangement of the recording dots is regular to a recording pattern having the arrangement of the recording dots that is less regular than the recording pattern. And the optical density are compensated for linearity.

For example, in a recording pattern having an arrangement of recording dots which does not have regularity, the number of recording dots which realizes a gradation from a gradation in which the arrangement of recording dots exhibits regularity to a predetermined gradation and the arrangement of the recording dots. Is newly determined so as to have a dot number between the number of recorded dots and the number of recorded dots at which the gradation showing regularity is realized.

Alternatively, the recording pattern having the arrangement of the recording dots having no regularity is a recording pattern having a predetermined gradation from a gradation recording pattern in which the arrangement of the recording dots exhibits substantially regularity, and the predetermined pattern is used. The gradation-graded recording pattern is newly determined so as to have a number of dots between the number of dots in the recording pattern and the number of dots in the recording pattern that is lower than the gradation by a predetermined degree.

Digital recording is performed by a combination of special paper and an ink jet recording device or by an organic photoconductor in which an organic charge generating material is dispersed.

[0020]

With the above construction, in digital recording, the gradation and the optical density of the recording pattern have a substantially linear relationship.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Prior to a specific embodiment, when a digital recording apparatus is used and conventional pseudo halftone processing is used,
The cause of the discontinuous halftone gradation and unfavorable image quality will be described in detail below.

According to the study by the inventor of the present application, the discontinuity of gradation is caused by the area ratio occupied by dots and the optical density (OD value).
Dependence on the relative relationship with and, if the relationship deviates from the linearity, the discontinuity of the gradation becomes conspicuous, and the closer to the linearity, the more the halftone tends to become continuous.

Actually, the area occupied by dots and the optical density (O
When the dots are made square, the relationship between them is not a straight line but shows a monotonous continuous increase, as shown in FIG.

In this case, 8 × 8 as shown in FIG.
A recording dot pattern composed of dots was used.

This recorded dot pattern is used as a representative of those used when the pseudo intermediate processing method described in the conventional example is carried out. The dots are sequentially arranged according to a certain rule to increase the density. In the process of increasing the density, at least one place has a characteristic that regularity such as symmetry appears in the dot arrangement pattern, as will be described later.

As described above, in the conventional pseudo intermediate processing method, the relationship between the area ratio of the dots originally contained and the optical density does not show an ideal linear relationship. Is considered to be the main cause of discontinuity.

Therefore, it can be seen that by making the linearity, which cannot be obtained by the conventional processing technique, as close to the ideal as possible, a substantially continuous gradation can be obtained.

In order to realize this linearity, the area ratio and the optical density may be directly used, but instead, attention is paid to the relationship between the gradation and the optical density, and as shown in FIG. If a new gradation pattern that can be realized is newly provided, the gradation of the intermediate gradation can be made continuous.

Here, the gradation 0 value indicates a white solid value, which indicates the reflection density of only the recording paper, and the gradation 9 value indicates a black solid value (entire black).

The reason why the discontinuity in gradation becomes more conspicuous as a result of deviation from linearity in the relationship between the area ratio of dots and optical density or the relationship between gradation and optical density is as follows. It is conceivable that the contour state of the has become clearer.

That is, in the conventional analog recording apparatus, the outline of dots is not clear, and is in a so-called blurred state, and it is clear that a clear outline of dots can be seen like a printed matter such as gravure. Is different.

As described above, since the dot contour is not clear, even when the conventional pseudo halftone processing method is used, the non-linearity inherent in them is canceled out, and a proper continuous halftone is obtained. It is thought that it was done.

Due to the recent technological advances, it has become possible for an ink jet recording apparatus, an electrophotographic apparatus, or the like to perform digital recording as long as the dot reproducibility with a clear contour is good.

Therefore, it is considered that the deviation of the linearity between the dot area ratio and the optical density and the gradation and the optical density in the conventional processing method becomes apparent, and the discontinuity of the halftone becomes conspicuous.

In the following specific examples, the present invention will be described in more detail by taking an ink jet recording apparatus which is a digital recording apparatus and an electrophotographic apparatus as an example.

(Embodiment 1) Hereinafter, a first embodiment of the present invention will be described in detail with reference to the drawings.

In this embodiment, an ink jet recording apparatus having a variable ink ejection amount was used.

The ink ejected from the head of this ink jet device flies in the recording paper direction as a substantially circular ink droplet in a cross section perpendicular to the ejection direction, and reaches the recording paper surface to form a substantially circular ink dot. .

In the case of an ink jet recording apparatus, the shape of dots on the recording paper greatly depends on the characteristics of the recording paper.

For example, in the case of plain paper (sheet), the adhered ink spreads in the lateral direction of the paper surface, and the dot shape is almost circular as a whole, but more microscopically in the direction along the paper fiber. Spread out.

Therefore, the average density from the dot center changes while gradually decreasing, which is shown in FIG.
It is schematically shown in (a).

On the other hand, in the case of special paper (coated paper), since the surface of the paper is coated with a uniform ink absorbing layer, when ink drops adhere to this surface, it is quickly and isotropically absorbed (adsorbed). To be done.

As a result, as shown in FIG. 1B, the density change at the dot boundary is large, and as a result, a dot having a clear contour is formed.

A recording device capable of forming dots with a clear contour is called a digital (binary) recording device.

Further, in this embodiment, the Macbeth densitometer (RD919) was used as an evaluation measuring method of the density gradation, but as the evaluation method of the gradation, there is no dot in the specified area. The state (hereinafter referred to as white solid) and the state where all dots are occupied (hereinafter referred to as black solid) are set as 0 and 1, respectively.

More specifically, the black solid state is, more specifically, a state in which the entire range is occupied by dots at a prescribed interval and the minimum dot diameter and the number of dots are such that no white portion remains. Say.

The actual gradation pattern divided into a predetermined number so that the optical density, that is, the OD value, is compensated for the linearity will be described in more detail below.

(Embodiment 1-1) In this embodiment, an ink jet recording apparatus having a dot density of 300 DPI is used by using a simple density pattern of 16 gradations with 8 × 8 dots as one pixel shown in FIG. Dots were formed on plain paper.

Then, the gradation was sequentially changed from the white solid value with the OD value of 0.1 to the black solid value with the OD value of 1.05, and the result of examining the relationship between the gradation and the OD value was obtained. Is shown in FIG.

As is known from FIG. 5, when the simple density pattern as shown in FIG. 3 is used, the dots are overlapped with each other in the high density area, so that the inclination is not constant, but from low density to high density. The density change is steadily increasing and continuous, and therefore, the discontinuity of gradation is unnoticeable, resulting in practically unacceptable results.

(Embodiment 1-2) Next, similarly, using a simple density pattern as shown in FIG. 3, the dot density is 300D.
Dots were formed on a special paper by an inkjet recording device which is PI.

Then, the gradation was sequentially changed from the white solid value with the OD value of 0.1 or less to the black solid value with the OD value of 1.34, and the relationship between the gradation and the OD value was investigated. The results are shown in Figure 6.

Since the special paper has good ink absorbency, under the same discharge condition as the plain paper, a white portion remains between the dots, so that the ink discharge amount is temporarily increased to completely It has a solid black color and has an OD value of 1.34.
It has become.

From FIG. 6, in 16 gradations, the density of 8 gradations (area ratio 50%) is extremely higher than that of 7 gradations, and
It can be seen that the value is close to the density of the gradation.

The discontinuity between gradations is a cause of an image that appears discontinuous in pseudo gradation recording using a digital recording device.

That is, when the plain paper is used, the dot contour is not clear because it is diffused as shown in FIG. 1A, but in the case of the special paper, the dot contour is shown in FIG. 1B. As shown in Fig. 6, since it is clear and digital, the discontinuity of the gradation is clearer before and after the 8 gradations in the part (in the case of 8 × 8) where the ratio of continuous dots increases rapidly. It is something that has become apparent in.

Regarding the digital recording shown in the present embodiment, there is a deviation from linearity (monotonic increase) especially at the eighth gradation which is a regular repeating pattern, and therefore, there are two types of recording as follows. Corrected.

The specific patterns for 7 gradations and 8 gradations used in this embodiment are the patterns shown in FIG. (1) Correction by changing dot arrangement This correction is a correction for changing the regularity from a regular dot arrangement to an irregular direction without changing the number of dots (area ratio). Specifically, FIG. In this correction, the left pattern before the correction of a) is changed to the right pattern. (2) Correction for moving the dots so that the gradation becomes the intermediate gradation In this correction, the pattern of the eighth gradation actually used is 50%.
Since the area ratio is 8 and the dots are arranged regularly, as shown in FIG.
The gradation pattern is corrected to an intermediate gradation pattern of the seventh gradation.

That is, the pattern was corrected in a state where a total of two dots were put in the blank portion of the dot of the pattern of the 7th gradation (shown by the circle mark of the 8 gradation pattern after correction in FIG. 7).

The results of processing using the pattern of the eighth gradation after the corrections of (1) and (2) are shown in FIG. 8, and (I) in the figure is the correction of (1). In this case, (II) corresponds to the result when the correction of (2) is performed, and it can be seen that the linearity of the optical density is actually compensated.

From the above, when digital recording is performed using a simple density pattern, at a certain density gradation,
When the pattern of each dot repeats regularly, as a correction processing method, the number of dots of this gradation pattern is not changed, and the dot positions are irregularly arranged.
Alternatively, a linear optical density can be obtained by correcting a pattern having a dot number close to the middle of the dot number of a pattern having a gradation lower than this gradation value by the gradation value before correction. It can be seen that it is possible to obtain an image with good gradation having

The method described above is not limited to ink jet printing, but can be applied to digital printing such as electrophotography, and even if the dot shape is not circular, clear printing of the dot contour is possible. It goes without saying that the same effect as in the present embodiment can be obtained if it is performed.

Further, in the present embodiment, since the area having the area ratio of 50% corresponds to the eighth gradation, the eight gradations are corrected, but it is not exactly 50% when the number of dots is different.

For example, in the case of 5 × 5 dots, the gradation area ratio close to 50% is 52%, but the dot arrangement is regular and the area ratio is substantially 50%. By correcting the gradation that is as in this embodiment, the continuity can be compensated.

(Second Embodiment) A second embodiment of the present invention will be described in detail below with reference to the drawings.

As described above, the recording device for forming recording dots on the recording paper for digital recording is not limited to the case of the ink jet recording device using the special paper.
A thermal transfer recording device having other digital characteristics, an electrophotographic device, or the like can be considered.

In this embodiment, as a recording device having another digital recording characteristic, a single-layer organic photoconductor (OPC),
Specifically, using a laser printer that forms an electrostatic latent image using a single-layer organic photoreceptor of a dispersion system in which an organic compound having a charge generation function and a charge transport function is dispersed in a binder, The actual gradation pattern in which the optical density, that is, the OD value, is divided in a predetermined manner so as to compensate the linearity will be described in more detail.

The substance having the charge generating function and the charge transporting function in this case may be a single compound or a plurality of compounds.

Further, not only a single layer but also a laminated type organic photoconductor may be used as long as the contour formation of dots by the electrostatic latent image is clear.

First, a 240 DPI laser beam printer was used as a recording device, and a single-layer OPC having the above digital characteristics was used as a photoconductor.

As the gradation, the simple density pattern (8 × 8 dots) used in Example 1 was used.

Then, the gradation is sequentially changed from a white solid value having an OD value of about 0.1 to a black solid value having an OD value of about 1.4, and the relationship between the gradation and the OD value is investigated. The results are shown in FIG.

As can be seen from the dotted curve in FIG.
Before the correction, there is a discontinuity point particularly at the eighth gradation, and to a lesser extent, discontinuity is also found at the fourth gradation and the twelfth gradation.

That is, in this case, the area ratio of dots is 25, not only in the eighth gradation where the area ratio of dots is 50%.
% Even at the 4th gradation and 75% at the 12th gradation
There is a non-linear relationship between the value and the gradation.

Examining the reason for this, as will be understood with reference to FIG. 3, in the 4th and 12th gradations, although the degree is lower than in the 8th gradation,
The arrangement of dots has regularity, and the outline of dots that are electrostatic latent images is clearer in the present embodiment than in the digital recording device in the first embodiment. Alternatively, it is considered that the characteristics of the 12th gradation pattern have actually become apparent.

Regarding the correction, the method of the first embodiment is effective, but in this embodiment, the following other method is considered. (1) Correction by deletion of target gradation 1 Referring to FIG. 10 schematically showing this correction method,
explain.

Actually, the area ratio is 25, 50, 75.
% Discontinuity exists in 3 areas, but typically 1
The points are shown and the correction method is shown.

Specifically, the gradation of D in the drawing is deleted, and the pattern C one gradation below that is moved to the D gradation to be the c gradation, and the gradation is made continuous.

Further, in order to make it more continuous, the gradation of C is also deleted if necessary, and the intermediate pattern BC of the gradations of B and C, which is one gradation below, is set as bc gradation and changed to gradation C. Moved to avoid discontinuity. (2) Correction by deletion of target gradation 2 This correction method is also the same in principle, but shows a method of application particularly when a large gradation is taken.

In the case of (1) above, since the gradation is rough,
Although only D is substantially the gradation that causes discontinuity, when the gradation is increased, as shown in FIG. 11, it is substantially 3 in A, B, and C in the figure. Since these gradations are the cause of discontinuity in gradation, these 3 gradations are deleted and corrected in the same manner as in the above example (1).

The processing result by the above correction is schematically shown as a solid curve in FIG. 10, and the linearity of the optical density and the gradation is sufficiently compensated.

In this embodiment, the dot regularity is
The pattern appears in the area ratio of 25, 50, and 75%, but the number of dots, the array, and the like are changed to, for example, 5 × 5, 6 × 7.
When using a pattern such as, the regularity of dots is not always seen at these area ratios, and the regularity is seen at an area ratio of 52%, which is slightly deviated, but it becomes a regular dot arrangement, In addition, if the gradation having the area ratio of substantially 25, 50, and 75% is corrected as in this embodiment, the continuity can be compensated.

[0083]

According to the present invention, with the above configuration, when recording is performed using a binary recording device having digital characteristics, when the predetermined area is set to one pixel, the number and arrangement of dots in this pixel are set. By correcting the gradation in which the relationship between the gradation and the optical density changes discontinuously so that the pattern, that is, the recording pattern does not have regularity, a high-quality image with good reproducibility of the original image can be obtained. it can.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a dot shape depending on a recording paper used in an inkjet recording apparatus.

FIG. 2 is a diagram showing the relationship between dot area ratio and optical density.

FIG. 3 is a diagram showing a simple density pattern of 8 × 8 dots.

FIG. 4 is a diagram showing an ideal linear relationship between gradation and optical density.

FIG. 5 is a diagram showing a relationship between recording gradation and optical density of an inkjet recording apparatus using plain paper.

FIG. 6 is a diagram showing the relationship between the recording gradation and the optical density of an inkjet recording apparatus using special paper.

FIG. 7 is a diagram showing a correction method according to the first embodiment of the present invention.

FIG. 8 is a diagram showing a result of correction by the correction method according to the first embodiment of the present invention.

FIG. 9 is a diagram showing the relationship between the gradation before correction and the optical density of Example 2 of the present invention, and the result of correction by the correction method.

FIG. 10 is a diagram showing a correction method according to the second embodiment of the present invention.

FIG. 11 is a diagram showing a correction method according to the second embodiment of the present invention.

Front page continuation (72) Inventor Koji Taniguchi, 3-10-1, Higashisanda, Tama-ku, Kawasaki, Kanagawa Matsushita Giken Co., Ltd. (72) Takahiro Asano 3--10-1, Higashisanda, Tama-ku, Kawasaki, Kanagawa No. Matsushita Giken Co., Ltd.

Claims (6)

[Claims] 1. An image processing method of an image recording method for digitally recording an image for each predetermined area by using a plurality of gradation recording patterns for realizing the arrangement of recording dots corresponding to gradations. The image processing method in which at least one recording pattern among the plurality of gradation recording patterns is changed and used as a new recording pattern so that the relationship between the gradation and the optical density is substantially linear. 2. The image processing method according to claim 1, wherein the gradation recording pattern in which the arrangement of recording dots exhibits regularity is changed to a recording pattern having an arrangement of recording dots having less regularity than the recording pattern. . 3. A recording pattern having an arrangement of recording dots that does not have regularity, wherein the number of recording dots that realizes a gradation from a gradation in which the arrangement of recording dots exhibits regularity to a gradation below a predetermined gradation, and the arrangement of the recording dots. 3. The image processing method according to claim 2, wherein is newly determined so as to have a number of dots between the number of recorded dots and the number of recorded dots at which the gradation showing regularity is realized. 4. The recording pattern having an arrangement of recording dots having no regularity is a recording pattern having a predetermined gradation from a gradation recording pattern in which the arrangement of recording dots exhibits substantially regularity. The recording pattern under gradation is
3. The image processing method according to claim 2, wherein the image number is newly determined so as to have a number of dots between the number of dots of the recording pattern and the number of dots of the recording pattern under the predetermined gradation than the gradation. 5. The image processing method according to claim 1, wherein the digital recording is performed by a combination of special paper and an inkjet recording device. 6. The digital recording is performed by an organic photoconductor in which an organic charge generating material is dispersed.
The image processing method according to any one of 1.