JPH01243782A - Gradation display method in picture output device - Google Patents

Abstract

PURPOSE:To execute stable gradation display by inverting and forming the colored fine picture element and non-colored fine picture element of a dot to have an area rate (1-A) when an area rate A, which is defined according to the rate of the colored fine picture element to all the fine picture elements, is A>0.5. CONSTITUTION:A picture processing part is formed by fine picture elements (S11-S66), in which one picture element forms a 6X6 matric and constituted so as to execute the gradation display. The analog output of a picture reading part 11 is A/D converted and stored in a line buffer 121 of the picture processing part as picture data B. These picture data B execute the display of 36 gradation and specifies dots (P0-P36). When the area rate A, which is defined according to the rate of the colored fine picture element to all the fine picture elements S11-S66 is A>0.5, the dots P0-P36 inverts and forms the colored fine picture elements and non-colored fine picture elements of the dots P17-P0 to have the area rate (1-A) by an inverting part 127. Thus, the number of the gradation, in which the width of an interval between the adjacent dots is one fine picture element part, can be decreased.

Description

Detailed Description of the Invention A0 Object of the Invention (1) Industrial Field of Application The present invention relates to a gradation display method in an image output device, and in particular, divides an image to be reproduced into pixels of minute area, and further divides the pixels. The present invention relates to a gradation display method in which the pixel is divided into micropixels having a microscopic area, and the gradation is displayed based on the ratio of colored micropixels forming a halftone dot within the pixel to the total micropixels.

(2) Conventional technology Conventionally, when creating an image with gradation in an image output device such as a printing press, printer, or digital copying machine,
A method of displaying gradations in a pseudo manner has been adopted.

In the pseudo gradation display method, the gradation is determined by dividing the image into minute unit pixels, and dividing the image into minute unit pixels (
For example, depending on the size of the area occupied by the dots or lines, the shading is displayed in a manner similar to continuous tone.

A method is often adopted in which regularly arranged large and small halftone dots are used as minute elements within the unit pixel.

A density pattern method (ie, area gradation method) is known as a method using the halftone dots. This density pattern method is applied to the display side (image output device side) corresponding to one pixel of the original image.
Divide one pixel into multiple micropixels, select a predetermined number of micropixels corresponding to the gradation of the pixel from among the micropixels, and color the selected micropixels in a predetermined color (for example, black). This is a method of displaying the In this method, a halftone dot is formed from a predetermined number of colored fine pixels corresponding to the gradation.

In the density pattern method, gradation display can be performed in stages corresponding to the number of fine pixels forming one pixel on the display side.

For example, as shown in FIG. 8, if the number of micropixels S forming one pixel is 4X4=16, and each micropixel S performs binary display, the total number of pixels S is (4X4). +1
It can be reproduced with =17 gradations. That is, when each micropixel S is all white, it is the OP1st tone, when only one of the 16 micropixels S is colored, it is the first gradation, and when only two of the 16 micropixels S are colored. The second gradation is when the color is colored.
. . . By setting the time when all 16 of the 16 fine pixels S are colored as the 16th gradation, the pixels can be displayed in a total of 17 gradations.

If the number of fine pixels forming one pixel is m in -a, then
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, depending on how the fine pixels to be colored are selected, the shape of the halftone dot differs even if the number of colored fine pixels is the same. The quality of the displayed image varies depending on the shape of the halftone dots.

Therefore, how to set the shape of halftone dots is an important issue, and various proposals have been made in the past. Currently, there are roughly two methods for setting the shape of halftone dots.

The first method is to use a font-type screen generator, in which the shape of the halftone dot formed by colored micropixels is set appropriately corresponding to each gradation level, and at each gradation level, the shape of the halftone dot is set appropriately. This is a method of coloring minute pixels so as to form halftone dots with a certain shape. In this first method, the halftone dot shape can be set independently for each gradation level, so that the optimal halftone dot shape can be generated.

However, since it requires memory to store the halftone dot shape corresponding to each gradation level, it is necessary to store data equal to the number of micropixels that form one pixel multiplied by the number of gradation levels. Memory capacity is required.

The second method is to use a dark value type screen generator, in which all of the plurality of micropixels forming one pixel are ranked in order of coloring, and at the first gradation level, the first priority micropixel is colored. At the second gradation level, the first and second order micropixels are colored, and at the final gradation level, all the micropixels from the first to the final order are colored.
This is the method. This second method can generate halftone dot patterns corresponding to all gradation levels by simply holding darkness value data corresponding to the number of micropixels forming one pixel. Although it has the advantage of requiring a small memory capacity, it has the problem that it is difficult to set the optimal halftone dot shape because it is not possible to set the halftone dot shape independently for each gradation level. Contains.

In either of the first and second methods, the shape of the halftone dots differs depending on which micropixel is colored in each gradation, resulting in a difference in the quality of the displayed image.

Therefore, various proposals have been made regarding which micropixel to be colored at each gradation among the micropixels constituting one pixel.

As for the conventional method of determining colored fine pixels, for example, "Image Processing Handbook" (edited by the Image Processing Handbook Editorial Committee, Shokodo Co., Ltd., published June 8, 1986, pp. 75-76) What is described is known.

It describes how to define colored fine pixels, such as the spiral shape shown in Figure 9-A, the Bayer shape shown in Figure 9-B, or the halftone shape shown in Figure 9-C. There is. In addition,
In this FIG. 9, one pixel is composed of a plurality of fine pixels S1 to
The subscripts 1 to 16 of each fine pixel St''''SI6 indicate the order in which the fine pixels are colored.

By the way, the size of the micropixels that make up the halftone dots is usually set close to the resolution limit of the image output device, so the number of colored micropixels that form the halftone dots may be one, or the number of colored micropixels that form the halftone dots may be one. If there is a small protrusion of one fine pixel in one cluster of colored fine pixels, it is not easy to reproduce accurately. Therefore, the Bayer (Bayer) shown in FIG.
er) shape or halftone dot shape shown in Figure 9-C, where a large number of minute colored micropixels are arranged separately, the problem is that the image reproducibility is unstable and the image quality is likely to deteriorate. There is. Such a difficulty is that when a halftone dot is formed from a cluster of colored fine pixels like the spiral shape shown in FIG. 9-A,
As the number of colored micropixels increases and the cluster of colored micropixels becomes larger, the problem is somewhat relaxed.

(S) Problem to be Solved by the Invention As described above, it is sometimes convenient to form halftone dots by clusters of colored micropixels, but the area ratio of colored micropixels forming halftone dots to all micropixels is 50. There is a problem in that image reproduction tends to become unstable at gradation levels where the halftone dots increase to nearly 50% and adjacent halftone dots begin to touch each other.

According to research conducted by the present applicants, if there is a gap of two micropixels between adjacent halftone dots, the independence of the halftone dots is maintained, and a relatively stable reproduced image can be obtained. However, when the width of the gap between halftone dots becomes one micropixel, the image reproducibility suddenly becomes unstable and the image quality deteriorates.

The present invention has been made in view of the above-mentioned circumstances, and includes a method for determining colored micropixels that form halftone dots (a method for selecting colored micropixels).
The objective is to generate a pattern of halftone dots that can accurately reproduce the gradation of each level.

B0 Structure 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 of minute area, and further divides the pixels into The halftone dots are divided into micropixels with a microscopic area, and the halftone dots are formed by the colored micropixels within the pixel, and the gradation is displayed according to the ratio of the colored micropixels to the total micropixels, and the halftone dots are always connected. In the gradation display method in an image output device, the halftone dot is formed from one cluster of micropixels, and the colored micropixels are determined corresponding to each gradation, wherein the halftone dot is determined by the ratio of the colored micropixels to the total micropixels. When the area ratio A defined by A > 0.5,
It is characterized by being formed by reversing the colored fine pixels and the uncolored fine pixels of the halftone dots having an area ratio of (1-A).

(2) Effect In the gradation display method in the image output device of the present invention having the above-described configuration, the halftone dot is formed when the area A defined by the ratio of colored micropixels to all micropixels is A>0.5. , are formed by reversing the colored fine pixels and non-colored fine pixels of the halftone dots with the area ratio (1-A).

Therefore, the shape of a halftone dot with an area ratio A > 0.5 is
The micropixels at the periphery of the pixel are colored, and the micropixels in a cluster of l at the center of the pixel become uncolored micropixels. Therefore, since adjacent halftone dots with A > 0.5 are connected to each other, the number of gradations in which the image reproducibility is unstable, that is, the width of the gap between adjacent halftone dots is one micropixel. It becomes possible to reduce the number of gradations.

(S) Embodiment An embodiment of a gradation display method in an image output device according to the present invention will be described below with reference to the drawings.

FIG. 2 is an overall explanatory diagram of a digital copying machine F to which the present invention is applied. The digital copying machine F is composed of a machine main body F and a cover F2 hingedly connected to the top surface of the machine main body F.

The machine main body F is provided with a platen (original table) 1 made of transparent glass on its upper surface. An exposure optical system 2 is disposed below the platen 1. This exposure optical system 2 includes a movable lamp unit 3
The lamp unit 3 is constructed by integrating a lamp 4 for illuminating the document and a first mirror 5. Further, the exposure optical system 2 includes a movable mirror unit 6 that moves at half the moving speed of the lamp unit 3. This moving mirror unit 6 is composed of a second mirror 7 and a third mirror 8. Further, the exposure optical system 2 includes a lens 9, a fourth mirror lO
etc. Then, when the lamp unit 3 moves in the front-back direction parallel to the original, and the movable mirror unit 6 moves by a distance of 1/2 at a speed of 1/2 of the moving speed of the lamp unit 3, the original Since the distance between the lens 9 and the lens 9 is kept constant, the reflected light from the original illuminated by the lamp 4 passes through the exposure optical system 2 and is converged on the image reading section 11. has been done. The image reading section 11 converts the amount of reflected light at each pixel of the document into an electrical signal. This electric signal is converted into density data and sent to the image processing unit 12.The image processing unit 12 converts the density data into an area ratio of halftone dots, and scans each scan so that it can be output as a rask image by a laser scanner 13, which will be described later. Convert as binary serial data for each line. An image is written on the photoreceptor 15 on the drum by turning on or off the laser beam 14 emitted from the laser scanner 13 in accordance with the serial data.

A charger 16 for charging, a developing unit 17, a charger for transfer 18, a cleaner unit 19, etc. are arranged around the photoreceptor 15 along the rotational direction of the photoreceptor 15. Further, the machine main body part F1 includes a transfer paper storage tray 20, and transfer paper in the transfer paper storage tray 20 is transferred to the photoreceptor 15 and the transfer charger 18.
A paper feeding mechanism 21 is disposed between the
A conveyance mechanism 22 is also provided that passes between the photoreceptor 15 and the transfer charger 18 and conveys the transfer-completed paper on which the transfer has been completed, peeling it off from the photoreceptor 15. Further, the machine main body F1 is provided with a fixing unit 23 for fixing the transfer-completed paper conveyed by the conveyance mechanism 22, and a paper discharge tray 24 for receiving and receiving the transfer-completed paper discharged from the fixing unit 23. has been done.

Next, a first embodiment in which the image processing section 12 is constituted by a font-type screen generator shown in FIG. 3 will be described in detail.

The image processing unit 12 has one pixel of 6 pixels as shown in FIG. 4-A.
Fine pixels S11 to S, 19 forming a ×6 matrix
1-A and 1-B, and is configured to perform gradation display as shown in Figures 1-A and 1-B. In addition, the first
The pixels in the figure are denoted by symbols Sll to S4. Although not described, a fine pixel Sll""'511 similar to the pixel in Fig. 4-A
It is formed from m.

FIG. 1 is a diagram showing the shape of halftone dots in this embodiment, and the shaded areas represent colored pixels. Then, the halftone dot P0 is the 0th
The gradation, the halftone dot P, is the shape of the first gradation, and the halftone dot P36 is the halftone dot shape of the 36th gradation.

In addition, Figure 4-B is a diagram showing the relationship between the values of X and Y addresses described later and the fine pixels specified by the values, and Figures 4-C and D are diagrams showing the relationship between , Y address value and image data B, which will be described later, specifying the halftone dots P0 to Pff&.
FIG.

However, in this embodiment, the halftone dot P0 shown in FIG.
Only the data of ~pH1 is stored in the font memory 123, which will be described later, and the data of the halftone dots P4~psb shown in FIG.
” is created by reversing it. Its configuration will be described later.

The image reading unit 11 is constituted by a sensor such as a CCD, and its analog output signal is converted from analog to digital and is sent as image data B to the image processing unit 1 shown in FIG.
The data is stored in the line buffer 121 of No. 2. This image data B displays 36 gradations, so r000000+~
rloo100", and the halftone dots P, ~psi are specified according to this value. The line buffer 121 is composed of a shift register, etc.
Image data B for 47 minutes is stored. Since the pixels are formed by a 6 x 6 matrix with fine pixels 311 to 36h as elements, the image data B indicating the gradation of each pixel is read out six times while outputting one line of pixels. Ru. The reading and writing of this line buffer 121 is controlled by a controller 122. Controller 1
22 is composed of a counter, etc., and the laser beam 14
(See Figure 2) is an X clock signal synchronized with the timing when each fine pixel is scanned, an X reset signal generated each time a laser beam scans each pixel, Y clock signal generated every time the pixel rotates,
It operates by a Y reset signal generated every time it rotates by 6 micropixels. Then, in accordance with these signals, the X and Y address signals each take on a value of "OOO" to "rlo1", and it is specified which fine pixel in the 6×6 matrix it is. The font memory 123 is composed of a storage element such as a ROM. The comparator 124 compares the image data B and the data R stored in the register 125, and outputs r19 when it is RIB. The register 125 stores the value "01001O" of the image data B that specifies the halftone dot pts when the area ratio A defined by the ratio of colored micropixels to all the micropixels is A-0,5. When the comparator 124 outputs ", 1", the calculation unit 12d outputs a value obtained by subtracting the value of the input image data B from the maximum value of the image data B, and otherwise outputs the value as is. . Then, when the font memory 123 is accessed using the X, Y address and image data B as addresses, the data read out by the inverting unit 127 is changed to "0" and "0" when the comparator 124 outputs "l". 1
” is inverted, otherwise it is output as is.

This output signal is input to the laser scanner 13, and the laser scanner 13 is configured to turn off the laser beam 14 when the input signal is "1" and 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-mentioned configuration is as follows.
This will be explained mainly with reference to FIGS. 1 and 4.

When the image data B is "rooooO", the fourth-C
As shown in the figure, a halftone dot P is identified.

All of the fine pixels forming this halftone dot P6 are "0".
The value of is memorized. Therefore, the output signal of the image output unit 12 is from the fine pixels S, ~S&& (see Figures 4-A and B).
is '0' while is scanned.

Therefore, all the fine pixels 311'''S && are laser beam 14
Therefore, the shape of the output halftone dot is the halftone dot P shown in FIG. 1-A.

Next, when image data B is "roooool", the fourth -
As shown in Figure C, a halftone dot P is identified.

Then, the fine pixel S lt −S forming this halftone dot P1
h, the values of the X and Y addresses ro10J, r.

"1" is stored only in the micropixel S, specified by "10", and "0" is stored in all other micropixels. Therefore, the output signal of the image output unit 12 is "1" only when the fine pixel S33 is scanned, and is "0" otherwise.
'', therefore, all the micropixels except the micropixel S0 are irradiated with the laser beam 14, so the shape of the output halftone dot becomes the halftone dot P shown in FIG. 1-A.

Then, in the same way, the value of image data B is "00001
0J, "0O0011", Old..., "010010J
In this case, the shape of the output halftone dot is P as shown in Figure 1-A.
z, P+... pH.

Next, image data B has a value “01001” indicating the 19th gradation.
When it reaches 1J, the output of the comparator 124 becomes r19, and the arithmetic unit 126 and the inversion unit 127 operate. Therefore, the value ro of image data B is stored in the font memory 123.
10011", the image data of the 36th gradation (1
00100) to 19th gradation image data (01001
1), that is, (100100)z
(010011)z=(010001)z is input as an address. That is, the signal input as an address to the font memory 123 is the same signal as the value ro10001 of the image data B of the 17th gradation. Therefore, the data of the 17th gradation is output from the font memory 123, and "0" and "1" of the data are output from the inverting unit 123.
Inverted by 7. Therefore, the output signal of the image output unit 12 has a value of ro1 of the image data B in FIG. 4-D.
0011'', that is, for halftone dot P19,
The shape of the output halftone dot is PI9 shown in FIG. 1-B.

Then, in the same way, the value of image data B is "010100".
J, "0IO101", ..., "100100
'', the shape of the output halftone dot is P2°+P21...Po shown in FIG. 1-B.

Therefore, by setting the data stored in the font memory 123 as shown in FIG. 4-C, 1-A corresponds to the value of image data B.

Halftone dots P0 to P36 shown in Figure B are output and displayed in 37 levels.

At this time, the data stored in the font memory 123 is such that the shape factor defined by the ratio of the area to the square of the perimeter of the halftone dot is the maximum for each colored fine pixel forming the halftone dot. Furthermore, when there are a plurality of halftone dot shapes with the maximum shape coefficient, colored micropixels are determined so that the radius of the circumscribed circle of the halftone dot is the smallest. Therefore, since the shape of the halftone dots is set to be square or something close to it, graininess is improved and texture is less likely to occur.

Further, if the halftone dot has a protruding portion formed by one colored fine pixel, the fine pixel forming the protruding portion is arranged in the process direction. Therefore,
Since the colored fine pixels forming the protruding portion are arranged in a direction that facilitates stable reproduction, image reproducibility is improved. Furthermore, when the area ratio A defined by the ratio of the colored fine pixels to the total pixels of the halftone dot is A > 0.5,
Since the colored fine pixels and non-colored fine pixels of the halftone dots having the area ratio (1-A) are formed by reversing them, the halftone dots PI9 to P36 can be formed from the data of the halftone dots P17 to P0, respectively.

Therefore, the font memory 123 stores halftone dots P0 to
All you need to do is memorize the pat and pH data.
The capacity of font memory, which requires a large capacity, can be roughly halved.

Next, a second embodiment in which the image processing section 12 is constituted by a threshold type screen generator shown in FIG. 6 will be described in detail.

This embodiment differs from the embodiment shown in FIG. 3 above in that a dark value table 123" and a comparator 1231 are provided in place of the font memory 123. It has a configuration similar to that of the first embodiment.

Therefore, detailed explanation that overlaps with the embodiment shown in FIG. 3 will be omitted.

The image processing unit 12 is configured such that one pixel is 6 as shown in FIG. 7-A.
Fine pixels 31 to S1.x6 forming a matrix. (However, there are 18 S19s per pixel.) and is configured to perform gradation display as shown in Figures 5-A and 5-B. Note that the pixels in FIG.
It is formed from fine pixels S to SI9 similar to the pixels in Figure A.

FIG. 5 is a diagram showing the shape of halftone dots in this embodiment, and the shaded areas represent colored pixels. Then, the halftone dot P is oth
PJ tone, halftone dot P1 is the first gradation, halftone dot P3
6 is the shape of the halftone dot of the 36th gradation.

Moreover, FIG. 7-B is a diagram showing the relationship between data A stored in the dark value table 123', which will be described later, and (direct X, Y) of the X, Y addresses.

As can be seen from FIG. 5, the data A stored in the darkness value table 123' is such that the halftone dot at each gradation is formed from one set of colored micropixels, and from one colored micropixel. In order to prevent more than two protrusions from being formed, one protrusion from three or more colored micropixels arranged in a row is further
The colored micropixels are arranged so as to be connected to the other colored micropixel in the center of the three or more colored micropixels lined up.

The dark value table 123' is composed of a storage element such as a ROM. The comparator 124 compares the image data B with the data R stored in the register 125, and outputs "1" when the data is RIB. The register 125 stores an area ratio A defined by the ratio of colored micropixels to all micropixels.
The value "010010J" of image data B that specifies the halftone dot pH+ when is A -0,5 is stored. Arithmetic unit 1
26, when the comparator 124 outputs "1",
That is, when image data B is a signal indicating the gradation of halftone dots P19 to psi, the maximum value of image data B is rlo0100.
Outputs the value obtained by subtracting the value of input image data B from
Otherwise, output as is.

Then, the comparator 123' compares the 36 fine pixels SI to S1 . (However, as mentioned above, there are 18 fine pixels Sll.)
The threshold value data A of the calculation unit 126 is compared with the output signal B′ of the calculation unit 126, and (dark value data A)>(output signal B′ of the calculation unit 126).
), outputs “1”. And this comparator 123
The output signal from the comparator 1
When 24 outputs "l", "0" and "1" are inverted, and otherwise they are output as is. This data is then input to the laser scanner 13 to modulate the laser beam.

Next, the operation of the embodiment of the present invention having the above-described configuration will be explained mainly with reference to FIGS. 5 and 7.

When the image data B is “rooooooo”, the seventh-B
As shown in the figure, all fine pixels 31~S1° (however, 31°
There are 18 9s. ), the darkness value data A is such that threshold data A>image data B. Therefore, the comparator 123
The output signal of 1 is "1" while all the fine pixels 5t-3+* (see Figure 7-A) are scanned. At this time, the output signal of the comparator 124 is 0, so it is inverted. Since the device 127 is not activated, all the micropixels S1 to S19 are irradiated with the laser beam 14, and the shape of the output halftone dot is as follows.
The halftone dot P shown in FIG. 5 is obtained.

Next, when the image data B is "roooool", the seventh-
As shown in figure B, the threshold data A, where the dark value data A>image data B, has the values ro 10J of the X and Y addresses,
It is stored in all the fine pixels 38 to S19 except the fine pixel SI specified by ro 10J. Therefore, the output signal of the comparator 123° is "0" only when the fine pixel S1 is scanned, and is "1" otherwise. Therefore, for all the fine pixels 5i-s+* except the fine pixel SI Since the laser beam 14 is irradiated, the shape of the output halftone dot is
This results in halftone dot P1 shown in the figure.

Then, in the same way, the value of image data B is "00001
0'', rooooll'', =, rQlooloJ, the shape of the output halftone dot is Pt, P shown in Figure 5-A.
x...P19.

Next, image data B has a value “01001” indicating the 19th gradation.
When it reaches 1J, the output of the comparator 124 becomes "1", and the arithmetic section 126 and the inverting section 127 operate. Therefore, the image data B indicating the 19th gradation is stored in the comparator 123''.
Instead of "value r010011", (100100),
-(010011)t=(010001)t is input as an address. That is, the signal inputted as an address to the comparator 123° is the same signal as the image data B value ro 10001 J of the 17th gradation.

Therefore, the halftone data outputted from the comparator 123'' is the same as the halftone data pH of the 17th gradation, and "o" and r19 of the data are inverted by the inverter 127. Therefore, the reproduced halftone dot PI9 is halftone dot PIT
The colored micropixel and the non-colored micropixel are inverted, resulting in p+q shown in FIG. 5-B.

Then, in the same way, the value of image data B is "010100".
J, "010101", ..., "100100
'', the shape of the output halftone dot is Pff111+P! shown in FIG. 5-B. ＋・・・・・・P3. becomes.

Therefore, by setting the data stored in the darkness value table 123' as shown in FIG.

Halftone dots P0 to P3k shown in Figure B are output and displayed in 37 levels.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the embodiments described above, and various design changes can be made without departing from the scope of the invention described in the claims. Is possible.

For example, in the embodiment, each pixel is formed by a 6 x 6 matrix with a screen angle of 0° and whose elements are micropixels,
Although the case of displaying 37 gradations has been shown, it is also possible to display other matrix sizes, other screen angles, and other numbers of gradations. In that case, a configuration with a bit number corresponding to those numbers may be used. Furthermore, increase the number of bits to 8
It is also possible to use general-purpose bits that are easily available for each configuration, and use the required number of lower or higher focus points. Furthermore, the fine pixels that form the pixels,
Instead of a square or rectangular matrix, other shapes are also possible.

In the above embodiment, the case of monochrome display was shown, but it is also possible to apply to each color of color display.Also, although the example used in digital copying machines was shown, it can also be applied to printers. It is. Furthermore, the present invention can be applied to other image output devices as long as they are capable of displaying gradations using halftone dots.

C9 Effects of the Invention According to the gradation display method in the image display device of the present invention described above, a halftone dot formed by one cluster of colored micropixels has an area ratio defined by the ratio of colored micropixels to all micropixels. When A > 0.5, the area ratio (1-A
) are formed by reversing the colored and non-colored fine pixels of the halftone dots. Therefore, since the halftone dots with A > 0.5 are connected to each other, the number of gradations in which the image reproducibility is unstable, that is, the width of the gap between adjacent halftone dots is one micropixel. It becomes possible to reduce the number of gradations.

Therefore, stable gradation display can be performed.

[Brief explanation of the drawing]

Figures 1-A and B are explanatory diagrams of halftone dot shapes in the first embodiment of the gradation display method according to the present invention, Figure 2 is an overall explanatory diagram of a digital copying machine to which the present invention is applied, and Figure 3 is its Figure 4-A is a diagram showing the configuration of the image processing unit, Figure 4-A is a diagram showing the arrangement of fine pixels forming a pixel, and Figure 4-B is a diagram showing the relationship between fine pixels specified by X and Y addresses and their values. The figure shown in Figure 4-C is x
, a fourth diagram showing the relationship between the Y address value, the image data value corresponding to the 0th to 18th gradation, and the output signal of the image processing unit, and also showing the data stored in the font memory.
Figure 5-D is a diagram showing the relationship between the values of X and Y addresses, image data corresponding to the 19th to 36th gradation, and the output signal of the image processing section, and Figures 5-A and B are gradation levels according to the present invention. An explanatory diagram of the halftone dot shape of the second embodiment of the display method, FIG. 6 is a diagram showing the configuration of the image processing section of the second embodiment, and FIG. 7-A is specified by the X and Y addresses and their values. A diagram showing the relationship with fine pixels,
FIG. 7-B is a diagram showing dark value data A of a fine pixel specified by the value of the x1Y address, and FIGS. 8-9-A to 9-C are diagrams for explaining a conventional example.

Claims (1)

[Claims] Divide an image into pixels with a minute area, further divide the pixels into fine pixels (S_1_1 to S_6_6) with a minute area,
The colored micropixels in the pixel form halftone dots (P_0 to P_3_6), and the gradation is displayed according to the ratio of the colored micropixels to all the micropixels, and the halftone dots (P_0 to P_3_6) are always connected. In the gradation display method in an image output device, the halftone dots (P_1_9 to P_3_6) are formed from one cluster of micropixels, and the colored micropixels are defined corresponding to each gradation, wherein the halftone dots (P_1_9 to P_3_6) Area ratio A defined by the ratio to all micropixels
When A > 0.5, the halftone dot (P_
A gradation display method characterized in that colored micropixels and non-colored micropixels (1_7 to P_0) are formed by reversing them.