JP2674048B2 - 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 the colored fine pixels forming 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 gray scale display method, the gray scale is determined by dividing an image into minute unit pixels and determining the size of an area occupied by minute elements (for example, colored portions such as dots or lines) in the unit pixels. A shade similar to the key is displayed.

And, as a minute element in the unit pixel, a method of using large and small halftone dots arranged in a regulated manner is often 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 of a number corresponding to the number of fine pixels forming one pixel on the display side.

For example, the number of the fine pixels forming the one pixel is
As shown in FIG. 5, assuming that 4 × 4 = 16 and binary display is performed in each fine pixel S, the total of one pixel is (4 × 4) +
It can be reproduced with 1 = 17 tones. That is, when all of the fine pixels S are uncolored, the gray scale is 0. When only one of the 16 fine pixels S is colored, the first gray scale. When only the individual is colored, the second gradation, ...,
By setting the time when all 16 of the 16 fine pixels S are colored as the 16th gradation, the pixel 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.

Then, depending on which micro pixel is colored in each gradation,
Since the dot shapes are different, a difference occurs in the quality of the displayed image.

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, how to determine colored micropixels is described in "Image Processing Handbook" (edited by the Editing Committee for Image Processing Handbook, Shokodo Co., Ltd., published on June 8, 1987, pp. 75-76). There, the spiral shape shown in FIG. 6-A, the 6-
A method for defining colored fine pixels such as a Bayer shape shown in FIG. B or a halftone dot shape shown in FIG. 6-C is described.
In addition, in FIG. 6, one pixel is a plurality of fine pixels.
It is composed of S _i (i = 1, 2, ..., 16), and the subscript of each fine pixel indicates the order in which the fine pixels are colored.

By the way, it has been proposed to increase the number of gradations while making the number of fine pixels in one pixel the same by performing multi-value display with each fine pixel forming the pixel.

Next, one example of the gradation display method by such multi-value display will be described with reference to FIG.

FIG. 7 (A) shows a pixel formed of 16 fine pixels S _{11 to} S ₄₄ , and a density pattern in which each fine pixel shown in FIG. 6-A is colored spirally. Law and multi-valued display apply.

Therefore, the fine pixels S _{11 to} S ₄₄ of FIG. 7A are the same as the fine pixels S _{1 to} S ₁₆ described with reference to FIG. 6, and 16 fine pixels S _{11 to} S ₄₄ are arranged in a spiral order. in colored, the coloring order is indicated by the numeral in the upper left corner of each micro pixel S ₁₁ to S _44. Then, the colored area of each micro-pixel S ₁₁ to S ₄₄ is set to three levels (e.g., level L _0, L _5, and L _10). The level L ₀ display is a non-colored display.
L ₅ is a display in which 50% of the area of fine pixels is colored, and the display of level L ₁₀ is a display in which the entire area of fine pixels is colored.

The fine pixels S _{11 to} S ₄₄ shown in FIG.
In the gradation, all the fine pixels S _{11 to} S ₄₄ are uncolored, 50% of the area of the fine pixel S ₂₂ is colored in the first gradation, and the entire area of the fine pixel S ₂₂ is colored in the second gradation. , ..., Fine pixel S in the fifth gradation
The total area of ₂₂ and S ₃₂ and 50% of the area of fine pixel S ₃₃ are colored,
..., in the first 32 tones all fine pixel S ₁₁ to S ₄₄ is adapted to be colored.

The shaded portion in FIG. 7 (A) shows the shape of the halftone dot when displaying the fifth gradation, and in this fifth gradation, the fine pixels S _{11 to} S ₄₄ forming the halftone dot are shown. Among them, the first and second fine pixels S ₂₂ and S ₃₂ are colored and displayed at the level L ₁₀ , and the third fine pixel S ₃₃ is colored and displayed at the level L _5.
It is colored and displayed.

In this way, the display of each fine pixel S _ij (i, j = 1,2,3,4) is multi-valued so that the number of gradations that can be expressed is the same while the number of fine pixels in one pixel is the same. Can be increased.

The method of multi-valued display of each fine pixel as described above differs depending on the type of image output device. For example, in a laser printer, a method of setting the power of laser light to several stages or a method of A method of setting the irradiation time at several stages is employed.

Even if the laser light is multi-valued by power modulation, it is difficult to faithfully reproduce an image corresponding to the multi-valued image on the electrophotographic apparatus side. It is thought to be due to the following reasons.

FIG. 7 (B) shows that one pixel is formed on a photoconductor that forms an electrostatic latent image when the display shown in FIG. 7 (A) is performed.
The power of the laser light irradiated to the 16 fine pixels S _{11 to} S ₄₄ is shown. As can be seen from FIG. 7 (B), the fine pixels (uncolored fine pixels) displayed at the level L ₀ are irradiated with the laser light having the power level R ₁₀ , and the fine pixels displayed at the level L ₅ have power. Laser light of level R ₅ is emitted,
The fine pixels displayed at level L ₁₀ are not irradiated with laser light.

Also, FIG. 7C shows fine pixels when displaying the fifth gradation.
The relationship between S _{11 to} S ₄₄ and the potential of the electrostatic latent image on the photoconductor 15 is shown.

The fifth when displaying gradation, fine pixel S ₂₃ around the fine pixels S ₃₃ to be displayed in multi-value that is uncolored displayed, S _34, S
_{There are 43} and fine pixels S ₃₂ that are colored. Then, the laser beam of the fine pixels S _23, S _34, large power levels R ₁₀ is the intensity S ₄₃ is uncolored display is illuminated, the laser light is not irradiated to the fine pixel S ₃₂ which is the color display . Therefore, the fine pixel S _33, the non-colored displayed are fine pixel S _23, S _34, S ₄₃ and of the boundary fine pixel S _23, S _34, S
The outer peripheral portion of the laser beam with the power level R _{10 that} is emitted to ₄₃ is emitted. Therefore, the boundary between the fine pixel S ₃₃ and the fine pixels S ₂₃ , S ₃₄ , and S ₄₃ is closer to the fine pixel S _32.
A large amount of laser light is irradiated as compared with the boundary portion between and. Then, since the charges on the photoconductor disappear according to the integrated value of the irradiated laser light amount, in the case of multi-value display by power modulation, as can be seen from FIG.
₃₃ , the potential of the electrostatic latent image at the boundary with the non-colored fine pixels S ₂₃ , S ₃₄ , S ₄₃ becomes smaller than the potential at the boundary with the colored fine pixel S ₃₂ .

Therefore, each fine pixel S ₁₁ when displaying the fifth gradation
Potential of the electrostatic latent image to S _44, when displayed in each line,
It can be represented in FIG. 7 (C).

If reproducing an image by developing the electrostatic latent image caused by the irradiation of the laser beam, and transfers the toner developed on the part of the developing threshold level TH ₀ or more of the potential of the electrostatic latent image. Therefore, by appropriately setting the development threshold level TH ₀ , the fine pixel S ₃₃ becomes
50% of the area is blackened and displayed in multiple values.

In the following description, since the above-described levels L ₀ and L ₁₀ are the same as in the case where multi-value display is not performed,
Unless otherwise specified, level L ₅ is displayed in multi-valued display.

(3) Problems to be Solved by the Invention In FIG. 7, as described above, since the toner adheres to the photoconductor portion having the potential of the development threshold level TH ₀ or more and is developed, the fine pixels S ₂₂ , S ₃₂ is a colored fine pixel, and the fine pixel S ₃₃ is multi-valued displayed at level L ₅ .

However, the development threshold level TH ₀ fluctuates, and the development threshold level TH ₁ (Fig. 7 (C)).
Reference), the fine pixel S ₃₃ to be colored and displayed at level L ₅
Becomes a non-colored fine pixel close to the level L ₀ , and becomes a colored fine pixel close to the level L ₁₀ at the development threshold level TH ₂ .

As described above, the fine pixels for multi-value display are easily affected by the fluctuation of the development threshold level TH ₀ ,
There is a problem that it is difficult to perform stable gradation display.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to reduce the influence of power modulation on multilevel display even if the development threshold level TH ₀ changes.

B. Structure of the Invention (1) Means for Solving the Problems In order to achieve the above object, a gradation display method in an image output device of the present invention is to develop an electrostatic latent image formed by irradiation of laser light. By reproducing the image, the image is divided into pixels having a minute area, the pixel is further divided into minute pixels having a minute area, and all minute pixels of colored minute pixels forming halftone dots in the pixel. In the gradation display method in the image output device, the gradation is displayed by a ratio to the above, and the number of gradations that can be displayed is increased by displaying multivalued colored fine pixels by changing the power level of the laser light. When displaying a multi-valued fine pixel in contact with a fine pixel, the power level of the laser beam for irradiating the uncolored fine pixel in contact with the multi-valued fine pixel is irradiated to the other uncolored fine pixel. Leh It characterized by being stronger than the power level of light.

(2) Operation In the gradation display method in the image output device of the present invention described above, when the fine pixel for multi-value display is the fine pixel in contact with the colored fine pixel, the fine pixel for multi-value display is provided. The power level (that is, the intensity) of the laser light for the uncolored fine pixels in contact with the surroundings of is made stronger than the power level for the other uncolored fine pixels. Therefore, the fine pixels for performing multi-valued display on the photoconductor are irradiated with the peripheral portion of the laser light having high intensity that is applied to the surrounding uncolored fine pixels.
Therefore, the potential of the fine pixel for multi-value display on the photoconductor is
It decreases from the portion of the fine pixel that performs multi-value display that is in contact with the colored fine pixel to the portion that is in contact with the surrounding uncolored fine pixel. At that time, the potential on the photoconductor corresponding to the fine pixel for multi-value display does not become the conventional stepwise curve shown in FIG. 7-C, but from the portion in contact with the colored fine pixel to its surroundings. As it goes to the part in contact with the non-colored fine pixels, it gradually and smoothly decreases.

(3) Embodiment Hereinafter, an 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 view of a 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 in the image reading unit 11 through the exposure optical system 2 during that time. ing. 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 as density data to the image processing unit 12 described later in detail. The image processing unit 12 converts the density data into an area ratio of halftone dots, and also converts the data into binary data for each scanning line so that a laser scanner 13 described later can output the raster image. An image is written on the photosensitive member 15 on the drum by modulating the laser beam 14 emitted from the laser scanner 13 according to this data.

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 that receives the transfer-finished paper discharged from the fixing unit 23.

FIG. 3 is a block diagram showing an example of a specific configuration of the image processing unit 12 described above.

The image reading unit 11 (see FIG. 2) is composed of a sensor such as a CCD, and its analog gradation signal is input to the analog-digital converter 121 (see FIG. 3) of the image processing unit 12. It The analog-to-digital converter 121 converts the analog gradation signal into, for example, an 8-bit digital gradation signal. The line buffer 122 has a capacity capable of storing the digital gradation signal for one line. The controller 123 outputs a timing signal and the like for operating the image reading unit 11, the analog-to-digital converter 121, and the line buffer 122.

The digital gradation signal stored in the line buffer 122 is such that the fine pixels forming the image are 4 × 4 as in this embodiment.
Is read out four times while outputting pixels of one line. Then, the read signal is converted by the look-up table 124 from the 8-bit digital gradation signal into a 6-bit digital gradation signal "000000" to "100000" sufficient for displaying the gradation number 33. To be done. The look-up table 124 is configured by a storage element such as a ROM and a RAM, and uses an input signal as an address and data stored at the address as an output signal. Therefore, by storing data in consideration of non-linearity during reproduction of a signal read from a document, for example, non-linearity between a blackened area ratio and a density of a pixel, the non-linearity is stored. Tone reproduction corrector (To
ne Reproduction Corrector). The output signal of the look-up table 124 is “000000” when displaying the 0th gradation, “000001” when displaying the 1st gradation, ... When displaying, it is "100000".

The controller 123 generates a timing signal in a cycle in which the laser beam 14 scans one fine pixel, and the ring counter 125 counts the timing signal of the controller 123, and the count value is "00" to "." 11 '' is repeatedly counted, and the output signal is the fine pixels S _{11 to} S _44.
Specify the X address of. Also, ring counter 126
Is for counting the timing signal generated from the controller 123 every time the photoconductor 15 (see FIG. 2) rotates by one fine pixel, and repeatedly counting the count value between "00" and "11". And the output signal is Y of the fine pixels S _{11 to} S ₄₄ .
Specify the address.

The output signals of the look-up table 124 and the ring counters 125 and 126 are input as address designation signals of the font memory 127. The font memory 127 is composed of a storage element such as a ROM, and the data of the font memory 127 is the power level of the laser light 14 (that is, as shown in FIGS. 4-B and C).
2-bit data "0" to specify 4 levels
It is from 0 ”to“ 11 ”. In the data of the font memory 127 shown in FIGS. 4-B and C, halftone dots P _{0 to} P ₃₂ are specified by the output signal of the look-up table 124, and X and Y addresses are specified by the ring counters 125 and 126. . Then, the 2-bit output signal of the font memory 127 is converted into an analog signal by the digital-analog converter 128, and the laser modulator of the laser scanner 13 is controlled by this analog signal.

The laser scanner 13 turns off the laser light 14 when the input signal from the font memory 125 is “11” (non-irradiation),
It is configured to turn on (irradiate) at power level R ₅ when “10”, turn on at power level R ₁₀ when “01”, and turn on at power level R ₁₁ when “00”.

FIG. 1 (A) shows fine pixels S ₂₂ , S colored at level L _10.
An example in which the fifth gradation is displayed by ₃₂ and the fine pixels S ₃₃ colored at the level L ₅ is shown, and the shaded portion shows the colored portion. Halftone dots P _i (i = 0, 1, ..., 32) for displaying the fifth gradation and other gradations are determined by the data (see FIGS. 4-B and C) stored in the font memory 127. Has been.

FIG. 1B shows each fine pixel when displaying the fifth gradation.
The power level of the laser light 14 applied to S _{11 to} S ₄₄ is shown, the power level R ₀ is (R ₀ = 0), and the intensity of the laser light is 0, that is, the laser light is off. . Therefore, the fine pixels S ₂₂ , S ₃₂ on the photoconductor 15 irradiated with the laser light of the power level R ₀ are not irradiated with the laser light, and the charging potential does not decrease, so that the fine pixels S ₂₂ and S ₃₂ are colored at the level L _10. It will be.

The power level R ₅ is a laser light intensity for displaying fine pixels at a level L ₅ , and is a laser light intensity for removing approximately half of the charge amount on the photoconductor 15.

The power level R ₁₀ is the laser light intensity for displaying the fine pixels at the level L ₀ (non-colored display), and is the laser light intensity for eliminating all the charge amount on the photoconductor 15.

Power level R ₁₁ is a laser beam intensity stronger than the power level R _10, the laser beam 1 of the power level R ₁₁
As will be described later in detail, 4 is a non-colored fine pixel (fifth gray scale) that is in contact with the fine pixel displayed at level L ₅ (S _{33 in} the fifth gradation).
The tone are irradiated only to _{S 23, S 34, S 43} ).

Note that FIG. 1C shows charging of the electrostatic latent image on the photoconductor 15 when the fine pixels S _{11 to} S ₄₄ are irradiated with the laser light 14 having the power level as shown in FIG. 1B. is a diagram showing the relationship between the electric range and threshold level TH _0.

Next, the operation of the embodiment of the gradation display method in the image output apparatus according to the present invention described above will be described mainly with reference to FIGS.

For example, when displaying the fifth gradation shown in FIG. 1 (A), the output signal of the look-up table 124 is
The signal "000101" for instructing the fifth gradation is obtained. At this time,
Among the halftone dots P _{0 to} P ₃₂ stored in the font memory 127, the halftone dot P ₅ is specified. As can be seen from FIG. 4-A, the ring counter 125 (see FIG. 3) designating the X address has a count value of “00” and the ring counter 126 designating the Y address has a count value of “00”. At this time, the fine pixel S ₁₁ is specified. The data of the fine pixel S ₁₁ (that is, the data stored in the font memory 127 whose address is the value of these output signals of the look-up table 124 and the ring counters 125 and 126) is "01" as shown in FIG. 4-B. "
It is. Therefore, the fine pixels S ₁₁ on the photoconductor 15 are irradiated with the laser light 14 having the power level R ₁₀ , and the potential thereof becomes 0 (threshold level TH ₀ or less) as shown in FIG. Displayed at level L ₀ (no color display). Similarly, fine pixels S ₁₂ , S ₁₃ , S ₁₄ , S ₂₁ , S ₂₄ , S ₃₁ ,
S ₄₁ , S ₄₂ , and S ₄₄ are displayed without coloring.

The ring counter 125 for designating the X address in the count of "01", when the ring counter 126 to specify the Y addresses of the count value of "01", micro pixel S ₂₂ is identified. The data of this fine pixel S ₂₂ becomes “11” as shown in FIG. 4-B. At this time, the fine pixel S ₂₂ on the photoconductor 15 is not irradiated with the laser beam 14, and the potential thereof is shown in FIG.
As shown in, the threshold level TH ₀ or higher is maintained, so that the level L ₁₀ is displayed (colored display). Similarly, the fine pixel S ₃₂ is colored and displayed at the level L ₁₀ .

The ring counter 125 for designating the X address in the count of "10", when the ring counter 126 to specify the Y addresses of the count value of "01", micro pixel S ₂₃ is identified. The data of fine pixels S ₂₃ is "00" as shown in 4-B view. At this time, the fine pixels S ₂₃ on the photoconductor 15 are irradiated with the laser light 14 having the power level R ₁₁ , and the potential thereof becomes 0 (threshold level TH ₀ or less), so that the display is performed at the level L ₀ (colorless display). ) Will be done. Similarly, the fine pixels S ₂₄ and S ₄₃ are displayed without coloring.

In the fifth gradation, the uncolored fine pixels S ₂₃ , S ₃₄ , S
The outer peripheral portion of the laser beam 14 having the power level R ₁₁ irradiated on ₄₃ is the same as the non-colored fine pixels S ₂₃ , S ₃₄ , and S ₄₃ of the outer peripheral portion of the fine pixel S _{33 that} performs multi-value display on the photoconductor 15. The area near the boundary is also irradiated. For this reason, in the outer peripheral portion of the fine pixel S ₃₃ for multi-value display, the portion near the boundary with the uncolored fine pixels S ₂₃ , S ₃₄ , S ₄₃ has a significantly reduced amount of charge.

Then, when the ring counter 125 designating the X address has a count value of "10" and the ring counter 126 designating the Y address has a count value of "10", the fine pixel _S33 is specified. The data of the fine pixel S ₃₃ becomes "10" as shown in FIG. 4-B. At this time, the fine pixels S ₃₃ on the photoconductor 15 are irradiated with the laser light 14 having the power level R ₅ and the photoconductor 15
The potential of the electrostatic latent image above is as shown in FIG.
Then, the potential of the fine pixel S ₃₃ becomes equal to or higher than the threshold level TH ₀ only in the half of the area thereof, so that the level L ₅
Is displayed in multi-value.

In FIG. 1 (C), the charging potential of the fine pixel S ₃₃ displayed at the level L ₅ is from the colored fine pixel S ₃₂ side to the uncolored fine pixel.
The inclination to the S ₃₄ side and the decrease is due to the outer peripheral portion of the laser light 14 of high power level R _{11 with which} the uncolored fine pixels S ₃₄ are irradiated, and the fine pixels S ₃₃ displayed at the level L ₅ This is because the portion close to the uncolored fine pixel S ₃₄ is irradiated and the charge is removed.

The configuration and operation of the embodiment of the present invention has been described above mainly regarding the case of displaying the fifth gradation, but other gradations are also displayed in the same manner.

 Next, effects specific to the above-described embodiment will be described.

According to the above-described embodiment, the non-linearity can be corrected by the look-up table 124. Further, when the look-up table 124 is constituted by a RAM, various image processing such as negative / positive inversion and emphasis of a specific gradation can be easily performed by changing the stored data.

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 deviates from the present invention described in the claims. Various design changes can be made without the need.

For example, although the example applied to a digital copying machine is shown, it can also be applied to a laser printer. Further, any image output device can be applied as long as it can perform gradation display by halftone dots, such as a thermal printer or an ink jet printer. In that case, the irradiation time of the laser light may correspond to the energizing time of the thermal head, the ejection time of the ink mist, and the like, and the power of the laser light may correspond to the current value of the thermal head, the amount of the ink mist, and the like. .

In the embodiment, the fine pixels forming the pixels are displayed in a matrix of 4 × 4, the screen angle is set to 0 °, and the fine pixels are displayed in a multi-valued display of four stages, and a total of 32 gradations are displayed.
Other matrix sizes, other screen angles, and other levels of multi-level display may be used. In that case, a configuration of the number of bits corresponding to those numbers may be used. further,
Of course, it is also possible to use a general-purpose one whose number of bits is 8 bits and each configuration is easily available, and use only the lower bits or the upper bits. Still further, instead of using a square or rectangular matrix, the fine pixels forming the pixel can have another shape.

Further, in the embodiment, the case of the monochrome display is described, but the present invention can be applied to each color of the color display.

C. Effect of the Invention According to the gradation display method in the image processing apparatus of the present invention described above, the potential on the photoconductor corresponding to the fine pixel for multi-value display is colored from the portion in contact with the colored fine pixel. It gradually decreases as it goes to the part in contact with the fine pixels. Therefore, even if the development threshold level changes, the fine pixels for multi-value display do not change to colored fine pixels or uncolored fine pixels, and the multi-value display level only slightly changes. Therefore, it is possible to perform highly stable gradation display that is not easily affected by the fluctuation of the development threshold level.

[Brief description of the drawings]

FIGS. 1 (A), (B) and (C) are explanatory views of multi-value display according to the embodiment of the present invention, FIG. 2 is a view showing a digital copying machine to which the embodiment is applied, and FIG. FIG. 4A is a diagram showing a configuration example of an image processing unit of the embodiment, FIG. 4-A is a diagram showing an arrangement relationship of X, Y addresses and fine pixels of the embodiment, and FIGS. 4-B, C are of the embodiment. The figure which shows the relationship between the halftone dot data which is stored in the font memory and the X and Y address, Figure 5-7 is the explanation drawing of former example,
FIG. 5 is an explanatory diagram of fine pixels constituting pixels, 6-A, B, C
FIG. 7 is a diagram for explaining a conventional halftone dot shape, and FIG. 7 is a diagram for explaining a conventional technique of multivalue display. P ₀ ~ P ₄₈ ...... Halftone dots, R ₁₀ , R ₁₁ ...... Power level, S ₁ ~ S ₁₆
...... Fine pixels, 14 ...... Laser light

Claims (1)

(57) [Claims] 1. An image is reproduced by developing an electrostatic latent image formed by irradiation with a laser beam (14), and
The image is divided into pixels having a minute area, and the pixel is further divided into minute pixels (S _{11 to} S ₄₄ ) having a smaller area, and a halftone dot (P _{0 to} P ₃₂ ) is formed in the pixel. An image output device that displays gradation by the ratio of the pixels to all the fine pixels, and multivalue-displays the colored fine pixels by changing the power level of the laser light (14) to increase the number of gradations that can be displayed. in the gradation display method in, colored fine pixel fine pixels that are in contact with (S ₃₂₎ a (S ₃₃₎ in case of multi-value display, uncolored in contact with fine pixel to multilevel display (S ₃₃₎ The power level (R ₁₁ ) of the laser beam (14) for irradiating the fine pixels (S ₂₃ , S ₃₄ , S ₄₃ ) is set to the other non-colored fine pixels (S
₁₁ , S ₁₂ , S ₁₃ , S ₁₄ , S ₂₁ , S ₂₄ , S ₃₁ , S ₄₁ , S ₄₂ , S ₄₄ ) is higher than the power level (R ₁₀ ) of the laser beam (14). A gradation display method in a characteristic image output device.