JP2623639B2 - Gradation display method in image output device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Object of the Invention (1) Field of the Invention The present invention relates to a gradation display method in an image output device,
In particular, an image to be reproduced is divided into small-area pixels, the pixels are further divided into small-area fine pixels, and the gradation is determined by the ratio of colored beautiful pixels that form halftone dots to all the fine pixels in the pixel. The present invention relates to a gradation display method for displaying.

(2) Conventional technology Conventionally, in an image output device such as a printing machine, a printer, or a digital copying machine, a method of pseudo-displaying a gradation when an image having the gradation is created has been adopted.

In the pseudo gradation display method, the gradation is obtained by dividing an image into minute unit pixels and determining the size of the area occupied by minute elements (for example, points or lines) in the unit pixels.
The shade is displayed in a manner similar to continuous tone.

And, a method of using regularly arranged large and small halftone dots as minute elements in the unit pixel has been adopted.

As a method using the halftone dot, a density pattern method (that is, an area gradation method) is known. According to this density pattern method, one pixel on the display side (image output device side) corresponding to one pixel of an original image is divided into a plurality of fine pixels, and a predetermined number of fine pixels corresponding to the gradation of the pixel are selected from the fine pixels. In this method, a pixel is selected, and the selected fine pixel is colored and displayed in a predetermined color (for example, black). In this method, halftone dots are formed from a predetermined number of colored fine pixels corresponding to the gradation.

According to the density pattern method, it is possible to perform gradation display at a stage corresponding to the number of fine pixels forming one pixel on the display side.

For example, as shown in FIG. 10, if the number of the fine pixels S forming the one pixel is 4 × 4 = 16, and each fine pixel S performs a binary display, the total number of the one pixel is ( 4 × 4) +1
= 17 tones. That is, the 0th gradation is when all the white pixels S are all white, the 1st gradation when only one of the 16 subpixels S is colored, and 2 pixels among the 16 subpixels S. .., The 16th gradation when all 16 of the 16 fine pixels S are colored,
By doing so, the pixels can be displayed with a total of 17 gradations.

In general, if the number of fine pixels forming one pixel is m, the number of gradations that can be expressed is m + 1.

As described above, halftone dots are formed from colored micropixels among a plurality of micropixels forming one pixel, and the gradation is determined by the number of colored micropixels forming the halftone dot. Further, the shape of the halftone dot differs depending on the selection method of the minute pixel to be colored, even if the number of the colored pixels is the same. Then, the quality of the displayed image varies depending on the shape of the halftone dot.

Therefore, how to set the shape of the halftone dot is an important problem, and various proposals have been made. At present, there are roughly two methods of setting the shape of a halftone dot.

The first method is a method using a font type screen generator, in which the shape of a halftone dot formed by colored fine pixels is appropriately set corresponding to each gradation level, and the setting is performed at each gradation level. This is a method of coloring the fine pixels so as to form a halftone dot of a given shape. In the first method, since the halftone dot shape can be set independently for each gradation level, it is easy to generate an optimum halftone dot shape. However, since a memory for storing a halftone dot shape corresponding to each gradation level is required, data of a number obtained by multiplying the number of fine pixels forming one pixel by the number of gradations must be held. Requires memory capacity.

The second method is to use a threshold-type screen generator, in which all of a plurality of micropixels forming one pixel are colored, and the first gradation micropixel is assigned to the first gradation level. In this method, the first and second order fine pixels are colored in the second gradation level, and all the fine pixels from the first to last order are colored in the final gradation level. . According to the second method, a halftone dot pattern corresponding to all gradation levels can be generated only by holding threshold data of a number corresponding to the number of fine pixels forming one pixel. Although it has the advantage of being able to use a small memory capacity, it is difficult to set the optimum dot shape because the dot shape cannot be set independently for each gradation level. Contains.

In any of the first and second methods, since the halftone dot shape is different depending on which fine pixel is colored in each gradation, the quality of the displayed image is different.

Therefore, various proposals have been conventionally made as to which of the fine pixels constituting the one pixel is to be colored in each gradation.

For example, as a method of determining the colored fine pixels belonging to the second method, "Image processing handbook" (edited by Image Processing Handbook Editing Committee, Shokodo Co., Ltd., Showa
Published on June 8, 1987, pp. 75-76). There is a spiral shape shown in Fig. 11-A,
It describes how to determine colored micropixels such as the Bayer type shown in FIG. B or the halftone type shown in FIG. 11-C.
In FIG. 11, one pixel is composed of a plurality of fine pixels.
S _{1 to} S ₁₆ , and each sub-pixel S _{1 to} S _{16 has} a suffix 1
Reference numerals 16 indicate the order in which the fine pixels are colored.

By the way, usually, the size of the fine pixels forming the halftone dot is set close to the resolution limit of the image output device, so that the number of the colored fine pixels forming the halftone dot is one or the halftone dot is not formed. If there is a small protruding portion corresponding to one fine pixel in one group of colored fine pixels, it is not easy to reproduce accurately. Therefore, the Bayer shown in FIG.
r) When a large number of minute colored fine pixels are arranged separately as in the shape or the halftone dot shape shown in FIG. 11-C, the reproducibility of the image is unstable and the image quality is easily deteriorated. There is. This difficulty is caused by the fact that when halftone dots are formed from a group of colored micropixels as in the spiral shape shown in FIG. 11-A, the number of colored micropixels increases and the mass of the colored micropixels increases. Somewhat relaxed.

(3) Problems to be Solved by the Invention However, when the _fifth , _seventh , _tenth , and thirteenth gradations are displayed in the spiral shape shown in FIG. 11-A, the fine pixels S ₅ , S ₇ , S ₁₀
And small protruding portion of the area in a halftone dot is formed by S _13. In addition, the protruding portion for one fine pixel also has a problem that the reproducibility of the image is unstable and the image quality is easily deteriorated.

It is considered that such a problem arises for the following reasons. That is, high resolution is required to reproduce minute colored micropixels and minute projections from a group of colored micropixels as an image, and such portions cannot be reproduced by a normal image output device. Stable and
It is difficult to reproduce the image while keeping the colored area at a predetermined value. Therefore, accurate gradation reproduction becomes difficult.

However, in the pseudo gradation display method in the image output device, in order to display all gradation levels, a protruding portion formed from one fine pixel colored somewhere in the gradation level occurs. It is unavoidable.

By the way, one projecting from three or more colored micropixels
When a halftone dot projecting portion is formed by the colored micropixels, it is better to project from the colored micropixel arranged in the center of the three or more colored micropixels arranged at the end. It has been experimentally confirmed that an image can be reproduced more stably than when it is projected from colored micropixels.

The present invention has been made in view of the above circumstances, and in the case of a grayscale level where a protruding portion formed from one colored fine pixel, that is, a protruding portion that is difficult to reproduce stably, exists. By devising the arrangement of the colored micropixels, that is, by devising the method of selecting (selecting) the colored micropixels that form the halftone dots, it is possible to reproduce each gradation level as stably as possible and improve the image quality. Make it an issue.

B. Configuration of the Invention (1) Means for Solving the Problems In order to solve the above problems, a gradation display method in an image output device of the present invention divides an image into pixels having a small area, and further divides the pixels into pixels. The pixel is divided into fine pixels having a small area, a halftone dot is formed by the colored fine pixels in the pixel, and a gray scale is displayed by a ratio of the colored fine pixels to all the fine pixels, and the halftone dots are always connected. In a gradation display method in an image output device formed from a set of fine pixels and the colored fine pixels are determined corresponding to each gradation, a halftone dot formed from the one set of colored fine pixels is 1
The colored micropixels are formed so as not to have two or more protruding portions formed from the colored micropixels, and one colored micropixel protruding from the three or more colored micropixels is arranged in the three or more colored micropixels. It is characterized in that it protrudes from the colored micro pixel arranged in the center of the micro pixel.

(2) Operation In the gradation display method of the image output device of the present invention having the above-described configuration, the number of protruding portions that are difficult to accurately reproduce in the fine pixels forming the halftone dots is determined by Are limited to one or less. For this reason, since the halftone dots have few portions where reproducibility is unstable, the reproduction of an image is more stable. Further, one colored micropixel projecting from the three or more colored micropixels is projected from the colored micropixel arranged at the center of the three or more colored micropixels. Image reproduction is stable.

(3) Embodiment Hereinafter, a first embodiment of a gradation display method in an image output device according to the present invention will be described with reference to the drawings.

FIG. 2 is an overall explanatory diagram of a monochrome digital copying machine F to which the present invention is applied. Digital copier F is composed of the hinged cover F ₂ Metropolitan a machine body portion F ₁ to the upper surface of the machine body portion F _1.

The machine body portion F ₁ is provided with a platen (document holder) 1 and the transparent glass on its upper surface. An exposure optical system 2 is provided below the platen 1. The exposure optical system 2 has a movable lamp unit 3, and the lamp unit 3 is configured by integrating a document illumination lamp 4 and a first mirror 5. Further, the exposure optical system 2 has a movable mirror unit 6 that moves at half the speed of the lamp unit 3. The movable mirror unit 6 includes a second mirror 7 and a third mirror 8. The exposure optical system 2 also has a lens 9, a fourth mirror 10, and the like. When the lamp unit 3 moves in the front-rear direction parallel to the document and the movable mirror unit 6 moves at a speed half the moving speed of the lamp unit 3 and at a distance of 1/2, Since the distance from the lens 9 is kept constant, the reflected light of the document illuminated by the lamp 4 is converged on the image reading unit 11 through the exposure optical system 2 during that time. Have been. The image reading unit 11 converts the amount of reflected light at each pixel of the document into an electric signal. This electric signal is transmitted to the image processing unit 12 as density data. In the image processing unit 12,
The density data is converted into an area ratio of halftone dots, and is converted as binary serial data for each scanning line so that a laser scanner 13 described below can output a raster image. By turning on or off the laser beam 14 emitted from the laser scanner 13 in accordance with the serial data, an image is written on the photoconductor 15 on the drum.

Around the photoconductor 15, a charging charger 16, a developing unit 17, a transfer charger 18, a cleaner unit 19, and the like are arranged along the rotation direction of the photoconductor 15. Further, the machine body portion F ₁ is transfer paper storage tray
20 and a paper feed mechanism 21 for supplying the transfer paper in the transfer paper storage tray 20 between the photoconductor 15 and the transfer charger 18 are provided. A transfer mechanism 22 is also provided for transferring the transfer-completed paper, which has passed through the space between the sheet and the transfer-completed sheet, from the photoreceptor 15 to be transferred. Further, the machine body portion F _1, the transfer mechanism 22
Unit that fixes the transfer end paper conveyed by
23, and a paper discharge tray 24 for receiving the transfer completed paper discharged from the fixing unit 23 are provided.

Next, the configuration of the image processing unit 12 in the first embodiment of the present invention will be described in detail.

The image processing unit 12 determines that one pixel is a 4 pixel as shown in FIG.
It is formed from micropixels S _{1 to} S ₁₆ forming a × 4 matrix and is configured to display gradations P _{0 to} P ₁₆ as shown in FIG. The pixel in FIG.
Although not denoted by reference numerals S _{1 to} S _16, they are formed from fine pixels S _{1 to} S ₁₆ similar to the pixels in FIG. 4-A. And
A fine pixel fine pixel S ₁ is being colored with the lowest threshold, a fine pixel fine pixels S ₁₆ is colored with the highest threshold.

FIG. 1 is a diagram showing the shape of a halftone dot of the present embodiment, in which hatched portions represent colored fine pixels. Then, dot P ₀ is 0th gradation, dot P ₁ is the first gradation, ..., dot P ₁₆ is in the form of a dot of the 16 gradation.

Then, the first 4-A diagram is a fine pixel S ₁ to S _16, a diagram illustrating X, Y address values X, the relationship between Y that identify those of each micro pixel.

FIG. 4-B is a diagram showing a relationship between threshold data A stored in a threshold table 123 to be described later and values X and Y of X and Y addresses. As shown in FIG. 1, the data A stored in the threshold value table 123 is such that halftone dots in each gradation are formed from a group of colored fine pixels and one colored fine pixel Is defined so as not to generate two or more protrusions. In addition, as shown by halftone dots P ₇ , P ₁₀ , and P ₁₂ in FIG. 1, one colored fine pixel projecting from three or more colored fine pixels arranged is the colored fine pixel arranged three or more. It is determined so as to protrude from the colored micro pixel arranged in the center of the pixel.

The image processing section 12 shown in FIG. 3 is constituted by a so-called threshold matrix type screen generator. Image data B is input to the image processing unit 12 from the image reading unit 11. The image data B is a signal obtained by performing an analog-to-digital conversion on an analog output signal obtained by a sensor such as a CCD in the image reading unit 11, and is stored in the line buffer 121 of the image processing unit 12. .
Since this image data B is displayed at 17 gradations, "0000"
It is 5-bit data of "0" to "10000". The line buffer 121 is composed of a shift register and the like.
The image data B for the line is stored. Then, since the pixels are formed in a 4 × 4 matrix having the fine pixels S _{1 to} S ₁₆ as elements, the image data of each pixel is read four times while outputting one line of pixels. Reading and writing of the line buffer 121 are controlled by the controller 122. The controller 122 comprises a counter or the like, an X clock signal synchronized with the timing at which the laser beam 14 (see FIG. 2) scans each fine pixel, and an X reset generated each time the laser beam scans each pixel. A signal, a Y clock signal generated each time the drum-shaped photoreceptor 15 (see FIG. 2) rotates by one fine pixel, and a Y reset signal generated every time the photosensitive member 15 rotates by a fine pixel. Then, the X and Y address signals take on the values of “00” to “11” in accordance with those signals, and it is specified which fine pixel of the 4 × 4 matrix. Threshold table 123
It is constituted by a storage device such as ROM, wherein X, X threshold data A (first 4-B see figure) fine pixels S ₁ to S ₁₆ to color the fine pixel specified by the Y address signal, The comparator 124 stored corresponding to the Y address compares the threshold data A read from the threshold table 123 with the image data B read from the line buffer 121, and determines that the image data B is equal to or larger than the threshold. (Ie, when A ≦ B), output “1”,
When A> B, "0" is output. The output signal of the comparator 124 is input to the laser scanner 13. The laser scanner 13 is configured to turn off the laser beam 14 when the input signal is "1" and to turn on the laser beam 14 when the input signal is "0". .

Next, the operation of the first embodiment of the present invention having the above-described configuration will be described mainly with reference to FIGS.

When the image data B is “00000”, as shown in FIG. 4-B, the threshold data A satisfying (threshold data A) ≦ (image data B) is not stored, and all the fine pixels S ₁ to S ₁₆
Is (threshold data A)> (image data B). Therefore, the output signal of the comparator 124 is
While all fine pixel S ₁₅ to S ₈ (see section 4-A view) is scanned,
It is "0". Therefore, since the laser beam 14 is applied to all the fine pixels S _{1 to} S ₁₆ , the shape of the output halftone dot is the first.
The dot P ₀ shown in FIG.

Next, when the image data B is “00001”, as shown in FIG. 4-B, the threshold data A satisfying the threshold data A ≦ the image data B is determined by the X and Y address values “10” and “01”. is stored only in the fine pixel S ₁ to be identified, other threshold data a stored in all fine pixel S ₂ to S ₁₆ of a a> B. Therefore, the output signal of the comparator 124 is a "1" only when the fine pixel S ₁ is being scanned, the others are "0". Therefore, the laser beam 14 in all fine pixel S ₂ to S ₁₆ except fine pixel S ₁ is being irradiated, the shape of the halftone dots to be output,
The halftone dots P ₁ shown in Figure 1.

Next, when the image data B is “00010”, as shown in FIG. 4-B, the threshold data A that satisfies the threshold data A ≦ the image data B has the X and Y address values “10” and “01”. , And the threshold data A stored in only the fine pixels S ₁ and S ₂ specified by “10” and “10”, and the threshold data A stored in all the other fine pixels S _{3 to} S ₁₆ is A> B. It is. Therefore, the comparator
The output signal of 124 is "1" only when the fine pixels S ₁ and S ₂ are scanned, the others are "0". Therefore,
The laser light 14 in all fine pixel S ₃ to S ₁₆ except fine pixel S _1, S ₂ is irradiated, the shape of the halftone dots are output halftone dots shown in Figure 1
The P _2.

Then, similarly, the image data B is “00011”, “0”
0100 ", ..., when the 10000", the shape of the halftone dots to be output halftone shown in FIG. 1 P _3, P _4, ... the P _16.

Therefore, by storing the data A shown in 4-B view of the threshold table 123, dot P ₀ to P ₁₆ shown in FIG. 1 corresponds to the value of the image data B is output, 17 tone Is displayed.

Next, a second embodiment of the present invention will be described. The configuration of the second embodiment is the same as that of the first embodiment except that the storage contents of the threshold table of the image processing unit 12 of the first embodiment are different.

Therefore, the second embodiment has the same configuration as that shown in FIGS. 2 and 3 in the first embodiment, and the second embodiment will be described below with reference to FIGS. 2, 3, 5, and 6. explain. A detailed description overlapping with the first embodiment will be omitted.

The image processing unit 12 outputs one pixel as shown in FIG. 6-A.
It is composed of fine pixels S _{1 to} S ₁₆ forming a × 4 matrix, and is configured to perform a gradation display as shown in FIG. The pixel of FIG. 5, the letter S ₁ designates
To S ₁₆ is not described, but is formed from the 6-A view of the pixel and the same fine pixels S ₁ to S _16. And the fine pixel S
₁ is a fine pixel colored at the lowest threshold, and the fine pixel S ₁₆
Are micropixels colored with the highest threshold.

FIG. 5 is a diagram showing the shape of a halftone dot of the second embodiment,
The shaded portions represent colored micropixels. Then, dot P ₀ is 0th gradation, dot P ₁ is the first gradation, ..., dot P ₁₆ is in the form of a dot of the 16 gradation.

Then, the first 6-A diagram is a fine pixel S ₁ to S _16, a diagram illustrating X, Y address values X, the relationship between Y that identify those of each micro pixel.

FIG. 6B is a diagram showing the relationship between the threshold data A stored in the threshold table 123 of FIG. 3 and the values X and Y of the X and Y addresses.

The data A stored in the threshold table 123 is
It is set to satisfy the following conditions.

(A) At a predetermined gradation (ninth gradation) level, of the fine pixels arranged in a matrix, all of the fine pixels arranged along one of the upper and lower edges and the one of the left and right edges. All nine fine pixels that are not colored and form the remaining squares are colored.

(B) At each gradation level until the predetermined gradation level is reached, and at each gradation level after the predetermined gradation level is exceeded, the colored fine pixels forming the halftone dot are stably reproduced in the image. It is formed in preference to the process direction.

(C) three or more side by side colored one coloring fine pixels projecting from fine pixels (see the fifth dot of Figure P _7, P ₁₀₎ is arranged in the center portion of the colored fine pixels arranged the three or more And connected to the colored micropixel.

Next, the operation of the second embodiment of the present invention having the above-described configuration will be described mainly with reference to FIGS.

When the image data B is “00000”, as shown in FIG. 6-B, the threshold data A satisfying (threshold data A) ≦ (image data B) is not stored, and all the fine pixels S ₁ to S ₁₆
Is (threshold data A)> (image data B). Therefore, the output signal of the comparator 124 is
While all the fine pixels S _{16 to} S ₈ (see FIG. 6-A) are scanned,
It is "0". Therefore, the laser light 14 in all fine pixel S ₁ to S ₁₆ is illuminated, the shape of the halftone dots to be output is a dot P ₀ shown in FIG. 5.

Next, when the image data B is “00001”, as shown in FIG. 6-B, the threshold data A satisfying (threshold data A) ≦ (image data B) has the X and Y address values “10”. , "01"
Threshold data A stored in the micro pixel S ₁ is stored only, all other micro-pixels S ₂ to S ₁₆ identified by
Is A> B. Therefore, the output signal of the comparator 124 is
"1" only when the fine pixel S ₁ is being scanned, the others are "0". Therefore, all the fine pixels S ₂ except the fine pixel S ₁
The laser beam 14 on to S ₁₆ is irradiated, the shape of the halftone dots to be output is a halftone dot P ₁ shown in FIG. 5.

Next, when the image data B is “00010”, as shown in FIG. 6-B, the threshold data A satisfying (threshold data A) ≦ (image data B) has the X and Y address values “10”. , "0
1 ", and micropixel S specified by" 10 "," 10 "
₁ and S ₂ only, and all other fine pixels S _{3 to} S ₁₆
Are threshold data A> B. Therefore, the output signal of the comparator 124 is “1” only when the micropixels S ₁ and S ₂ are scanned, and is “0” otherwise. Therefore, the laser beam 14 in all fine pixel S ₃ to S ₁₆ except fine pixel S _1, S ₂ is irradiated, the shape of the halftone dots to be output is dot P ₂ shown in FIG. 5.

Then, similarly, the image data B is “00011”, “0”
0100 ", ..., when" 10000 ", the shape of the halftone dots to be output halftone shown in FIG. 5 P _3, P _4, ... the P _16.

Therefore, by setting the data A stored in the threshold table 123 as shown in FIG. 6-B, the halftone dots P _{0 to} P ₁₆ shown in FIG. Then, a display of 17 gradations is performed.

According to the second embodiment described above, a halftone dot having a protruding portion that is difficult to reproduce accurately due to a high spatial frequency somewhere in each gradation level, that is, coloring that protrudes in a direction in which image reproducibility is unstable. fine pixel (e.g., the fourth fine pixel S ₄ of the gradation of halftone P _4, fine pixels S ₁₃ of the seventh micro pixel S ₇ of dot P ₇ of gradation, and the 13 gradation of the dot P ₁₃ ) Is formed,
At the next gradation level, a halftone dot having colored micropixels adjacent to the protruding colored micropixel and located in a direction that is easy to stably reproduce is formed. Therefore, among the halftone dots corresponding to each gradation level, the number of halftone dots having unstable reproducibility is reduced, so that the image quality is improved.

Next, a third embodiment of the present invention will be described. The configuration of the third embodiment is the same as that of the first embodiment except that the configuration of the image processing unit 12 of the first embodiment is different from that of the first embodiment.

Therefore, the third embodiment has the same configuration as that shown in FIG. 2 in the first embodiment.
Hereinafter, the third embodiment will be described with reference to FIGS. 2, 7, 8 and 9-A, 9-B.

The image processing section 12 is constituted by a so-called font type screen generator. Then, the fine pixel one pixel to form a 4 × 4 matrix as shown in 9-A view S ₁₁ to S
₄₄ and a dot P ₀ as shown in FIG.
PP ₁₆ to display a total of 17 gradations from the 0 th gradation to the 16 th gradation. The pixel of FIG. 7 is the code S ₁₁ to S ₄₄ is not described, is formed from a 9-A view of the pixel and the same fine pixels S ₁₁ to S _44, the hatched portions colored fine Represents a pixel. 9-A,
A fine pixel S ₁₁ ~S _44, X specifying each micro pixel S ₁₁ to S ₄₄ thereof, Y address values X, is a diagram showing the relationship between Y.

FIG. 9-B shows the relationship between the halftone data P stored in the font memory 125 described later and the X, Y address values X, Y. Halftone data P stored in the font memory 125, the 0th gradation to be able to view the dot P ₀ to P ₁₆ of the total 17 gradations up to the 16 gray levels, each halftone dot P
₀ Each correspondingly colored fine pixels to P ₁₆ "1", the non-colored pixels are data stored to "0". And
Dot P ₀ to P _16, which is formed by a colored fine pixels, as shown in the Figure 7, halftone dots in gradations and one as being formed from the colored fine pixels of one mass It is determined that two or more protruding portions formed from the colored micropixels are not generated. Further, as shown by the halftone dots P ₅ , P ₇ , and P ₁₁ in FIG. ₇ , one colored fine pixel projecting from a cluster of four or more colored fine pixels is located in the sub-scanning direction, that is, the process direction. (In FIG. 7, the Y direction, that is, the direction in which the drum-shaped photoconductor 15 shown in FIG. 2 rotates when forming a latent image) One protruding colored pixel (dots P ₇ , P _{11 in} FIG. ₇₎
Is connected to the colored micropixel arranged at the center of the three or more colored micropixels.

Image data B is input from the image reading unit 11 to the image processing unit 12 shown in FIG. This image data B
Is a signal obtained by performing an analog-to-digital conversion on an analog output signal obtained by a sensor such as a CCD in the image reading unit 11, and is stored in the line buffer 121 of the image processing unit 12. The image data B is a 5-bit data of "00000" to "10000" because 17-gradation display is performed.

The line buffer 121 is constituted by a shift register or the like, and stores image data B for one line.
Then, since the pixels are formed in a 4 × 4 matrix having the fine pixels S _{11 to} S ₄₄ as elements, each pixel is read four times while outputting one line of pixels. Reading and writing of the line buffer 121 are controlled by the controller 122. The controller 122 comprises a counter or the like, an X clock signal synchronized with the timing at which the laser beam 14 (see FIG. 2) scans each fine pixel, and an X reset generated each time the laser beam scans each pixel. A signal, a Y clock signal generated each time the drum-shaped photoreceptor 15 (see FIG. 2) rotates by one fine pixel, and a Y reset signal generated every time the photosensitive member 15 rotates by a fine pixel. Then, the X and Y address signals take on the values of “00” to “11” in accordance with those signals, and it is specified which fine pixel of the 4 × 4 matrix.

The font memory 125 is configured by a storage element such as a ROM, and stores the dot data P corresponding to each gradation level. Then, the image data B signal dot P ₀ is stored in the font memory 125 by to P ₁₆ specifying the gradation level (see 9-B view) are identified. That is, the image data B input to the font memory 125
Is “00000” representing the 0th gradation, data for displaying the 0th gradation halftone dot P ₀ stored in the font memory 125 is selected, and “00001” representing the 1st gradation is selected. if a ", data for displaying the dot P ₁ of the first gray level stored in the font memory 125 is selected, ... if it is the" 10000 "representing the 16th gradation, font memory data for displaying a dot P ₁₆ of the 16 gradation stored in 125 is selected.

Data of the dot P ₀ to P _16, which is stored corresponding to the gradation is specified by the image data B representing the gradation, fine pixel S ₁₁ to S ₄₄ for forming the halftone dots the X, Y Specified by the address signal.

Therefore, when the image data B and the X and Y address signals are inputted as addresses, the font memory 125 stores the data of the fine pixels S _{11 to} S ₄₄ forming the halftone dots P _{0 to} P ₁₆ defined by the image data B. (Data in which “1” is stored in the colored fine pixel and “0” is stored in the non-colored fine pixel shown in FIG. 7-B), and the fine pixels S _{11 to} S ₄₄ specified by the X and Y addresses are read out. Output data "1" or "0".

The output signal of the font memory 125 is input to the laser scanner 13 (see FIG. 2). The laser scanner 13 turns off the laser beam 14 when the input signal is "1".
It is configured to turn on when it is “0”.

Next, the operation of the third embodiment of the present invention having the above-described configuration will be described mainly with reference to FIGS. 7 and 9.

When the image data B is "00000" indicating the 0th gradation, but dot P ₀ which displays the 0th gradation is specified, the 9-
As shown in Figure B, all fine pixel data of the halftone dot P ₀ is S ₁₁ to S ₄₄
0 for Therefore, the output signal of the font memory 125 remains “0” while all the fine pixels S _{11 to} S ₄₄ are scanned. Therefore, the laser beam to all fine pixel S ₁₁ to S ₄₄
Since 14 is irradiated, the shape of the halftone dots to be output is a dot P ₀ no colored fine pixels shown in Figure 7.

Then, when the image data B is "00001", halftone dots P ₁ to display the first gray level is specified. At this time, as shown in 9-B Figure, "1" is stored in the data of the halftone P ₁
X, the value of the Y address is (10,01), X, when the value of the Y address other is the data of the dot P ₁ is stored is "0". Further, the X, Y address "10", fine pixel corresponding to "01", as shown in 9-A view is a fine pixel S _23. Therefore, the font memory 125 outputs "1" when the fine pixels S ₂₃ is scanned, otherwise outputs "0". Therefore, the laser beam 14 is irradiated to the entire fine pixels except fine pixel S _23, the shape of the halftone dots to be output is dot P ₁ shown in FIG. 5.

When the image data B is "00010", halftone dots P ₂ for displaying the second gradation is specified. At this time, as shown in FIG. 9-B, the values of the X and Y addresses where "1" is stored in the dot data P are (10, 01) and (10, 10), respectively. , Y address is “0” when it has any other value. The fine pixel corresponding to the X and Y addresses is the ninth pixel.
As shown in A view is a fine pixel S ₂₃ and S _33. Therefore, the font memory 125 outputs "1" when the fine pixels S ₂₃ and S ₃₃ are scanned, otherwise outputs "0". Therefore, the laser beam 14 is irradiated to the entire fine pixels except fine pixels S ₂₃ and S _33, the shape of the halftone dots to be output is dot P ₂ shown in Figure 7.

Then, similarly, the image data B is “00011”, “0”
0100 ", ..., when" 10000 ", the shape of the halftone dots to be output halftone shown in FIG. 7 P _3, P _4, ... the P _16.

Therefore, by storing the dot data P shown in 9-B view of the font memory 125, dot P ₀ to P ₁₆ shown in FIG. 7 corresponds to the value of the image data B is output, 17 A gradation display is performed.

At this time, as is apparent from FIG. 7, at the ninth gradation, the fine pixels S
₁₁ to S _44, the upper and lower one edge and the left and right of one of the fine pixels disposed along the edge _{S 11, S 12, S 13} , S 14, S 21, S 31, S
₄₁ are all uncolored and the remaining micropixels are all colored, and the micropixels S arranged along the upper and lower edges and the left and right edges until the ninth gradation is exceeded. ₁₁ ,
S ₁₂ , S ₁₃ , S ₁₄ , S ₂₁ , S ₃₁ , and S ₄₁ are not colored. When such gradation display is performed, the number of gradations at which adjacent halftone dots contact each other is reduced, so that the granularity of the reproduced image is improved. Similarly, as is apparent from FIG.
In the gradation, the fine pixels S ₁₁ , S ₁₄ , S ₄₁ , which are arranged in the four corners of the fine pixels arranged in a matrix.
Is S ₄₄ are in a state in which the remaining fine pixel is colored all in all uncolored. Such gradation display improves the granularity of the reproduced image.

According to the above-described third embodiment, among the fine pixels forming the halftone dot, the protruding portion having a high spatial frequency and difficult to reproduce accurately is arranged in a direction that is stable and easy to reproduce. It is possible to reproduce a stable gradation.

As described above, the embodiment of the gradation display method in the image output device according to the present invention has been described in detail. However, the present invention is not limited to the above-described embodiment, and may deviate from the present invention described in the claims. It is possible to make various design changes without performing.

For example, when displaying the 17 types of dot P ₀ to P ₁₆ shown in FIG. 1, instead of using a threshold matrix screen generator shown in the FIG. 3, the font type screen generator shown in FIG. 8 It can be used. In this case, the image processing unit 12 replaces the threshold value table 123 and the comparator 124 shown in FIG.
The font memory 125 shown in the figure is used. Then, this font memory 125, allowed to store 17 different halftone dot P ₀ to P ₁₆ corresponding to the respective gradations shown in the first FIG. At this time, “1” is stored in association with the colored fine pixel, and “0” is stored in association with the non-colored fine pixel. For example, in the 0th gradation, “0” is stored in all the fine pixels S _{0 to} S ₁₆ , and in the first gradation, the fine pixel S ₁
In the second gradation, “1” is stored in the other fine pixels S _{1 to} S _2, and “1” is stored in the other fine pixels S _{2 to} S _{16. 3} to S ₁₆ is stored to "0", ..., the 16th gradation all fine pixel S ₁ to S ₁₆
Is stored in the memory. Output from the controller 122 to the font memory 125 storing such data
When the X and Y addresses and the image data B output from the line buffer 121 are input as addresses, the gradations P _{0 to} P ₁₆ are designated by the image data B, and the fine pixels S _{1 to} S ₁₆ are designated by the X and Y address signals. _{Since 16} is designated, it is possible to output the halftone dots shown in FIG. 1 of the gradation corresponding to the image data B.

Further, in the embodiment, the pixel is 4 × 4 having fine pixels as elements.
Although a case where the display is formed by a matrix having a screen angle of 0 ° and 17 gradations are displayed, display of another matrix size, another screen angle, and another number of gradations can be performed. In that case, a configuration of the number of bits corresponding to those numbers may be used. Further, the number of bits is set to 8 bits, and a general-purpose one that can easily obtain each configuration is used.
It is also possible to use the required number of lower or upper bits. Furthermore, instead of a square matrix, the fine pixels forming the pixel can be a rectangular matrix or another shape.

In the above-described embodiment, the case of monochrome display has been described, but it is also possible to apply to each color of color display,
Also, an example in which the present invention is applied to a digital copying machine has been described, but the present invention is also applicable to a laser printer. Further, the present invention can be applied to other image output devices as long as the image output device is capable of gradation display by halftone dots and has different reproducibility depending on directions.

C. Effects of the Invention According to the above-described gradation display method in the image output device of the present invention, the number of protruding portions that are difficult to accurately reproduce in the fine pixels forming the halftone dots indicates each gradation. The number of halftone dots is limited to one or less. For this reason, since the halftone dots have few portions where reproducibility is unstable, the reproduction of an image is more stable. Further, one colored micropixel projecting from the three or more colored micropixels is projected from the colored micropixel arranged at the center of the three or more colored micropixels. Image reproduction is stable. Therefore, since the portion where the reproducibility is unstable in the halftone dots is reduced, the image quality can be improved.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a halftone dot shape of a first embodiment of a gradation display method according to the present invention, FIG. 2 is an overall explanatory diagram of a digital copying machine to which the present invention is applied, and FIG. FIG. 4-A is a diagram showing a configuration, FIG. 4-A is a diagram showing an arrangement relationship between X and Y addresses and fine pixels, and a diagram is a diagram showing a relationship between threshold data stored in a threshold table of FIG. 4-B and X and Y addresses. FIG. 5 is an explanatory diagram of a halftone dot shape of a second embodiment of the gradation display method according to the present invention, and FIG. 6-A is a diagram showing an arrangement relationship between X and Y addresses and fine pixels.
FIG. 6B shows threshold data stored in the threshold table and X,
FIG. 7 is a diagram showing a relationship with a Y address, FIG. 7 is an explanatory diagram of a halftone dot shape of a third embodiment of a gradation display method according to the present invention, and FIG. 8 shows a configuration of an image processing unit of the third embodiment. FIG. 9-A is a diagram showing an arrangement relationship between X and Y addresses and fine pixels, and FIG.
FIGS. 10 and 11 show the relationship between the halftone data stored in the font memory of the third embodiment and the X and Y addresses. FIGS.
FIGS. 7A to 7C are explanatory diagrams of the related art. _{S 1 ~S 16, S 11 ~S} 44 ...... fine pixel, P ₀ ~P ₁₆ ...... halftone

Claims (3)

(57) [Claims] An image is divided into pixels having a very small area, the pixels are further divided into fine pixels having a small area, and a halftone dot is formed by the fine pixels which are colored in the pixel. The gray scale is displayed by the ratio to all the fine pixels, and the halftone dot is always formed from a group of connected fine pixels, and the gray scale in the pixel output device in which the colored fine pixels are determined corresponding to each gray scale. In the display method, the halftone dots formed from the one group of colored micropixels are formed so that two or more protruding portions formed from one colored micropixel are not generated, and three or more colored dots are arranged. A gradation display method characterized in that one colored fine pixel projecting from a fine pixel is projected from a beautiful colored pixel arranged at the center of the three or more colored fine pixels arranged in a row. 2. The method according to claim 1, wherein the pixel is formed of a plurality of fine pixels arranged in a matrix, and at a predetermined gradation level, one of the upper and lower edges and the left and right edges of the fine pixels arranged in the matrix. All of the fine pixels arranged along one edge are erased and all the remaining fine pixels are colored, and one of the upper and lower edges and one of the right and left until the predetermined gradation level is exceeded. 2. A gradation display method in an image output device according to claim 1, wherein the fine pixels arranged along the edge of the image output device are not colored. 3. The pixel is formed of a plurality of fine pixels arranged in a matrix. At a predetermined gradation level, a predetermined one of four corners of the fine pixels arranged in the matrix is provided. 3. The floor in the image output device according to claim 1, wherein all the fine pixels arranged in the three corners are uncolored and all the remaining fine pixels are colored. Key display method.