JPH03289869A - Gradation display device - Google Patents

Abstract

PURPOSE:To reduce dispersion in a difference of colored areas between adjacent gradation orders in a displayed picture by dividing a picture element into minute picture elements more in gradation number than that to be displayed and setting a difference from colored minute picture element number in adjacent gradation orders between a prescribed gradation order and other gradation order. CONSTITUTION:One picture element consists of 5X5=25 minute picture elements, all minute picture elements are not colored at dots P0 of 0-th gradation and two minute picture elements are colored at dots P1 of 1st gradation. Then a difference between colored minute picture elements of adjacent gradation order at low density gradation order from 0th gradation dots P0 to 5th order dots P5 is set to two. Then a difference from colored minute picture elements between adjacent gradation orders at an intermediate gradation order from 5th gradation dots P5 to 12th gradation dots P12 is set to 1, and a difference from colored minute picture elements between adjacent gradation orders at a high gradation order from 12th gradation dots P12 to 16th gradation dots P16 is set to 2.

Description

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

2) Conventional technology Conventionally, when displaying 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 gradation display method similar to IIi, one image is divided into minute unit pixels, and the gradation is expressed as a continuous tone depending on the size of the area occupied by minute elements (for example, dots or lines) within each unit pixel. displayed similar to.

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, in FIG. 11, the number of micropixels S forming one pixel is 4X4=16, and each micropixel 5i (i-1 to 16
) for binary display, the halftone dot Pi(i
= (1 to 16), the above 1 pixel is (4X
4) Can be displayed with +1=17 gradations. That is, the 0th gradation is when all of the micropixels 81 to S16 are white (see halftone dot PO), and the 1st gradation is when only one micropixel S1 among the 16 micropixels Si is colored. tone (see halftone dot P1), when only two of the 16 micropixels St are colored, the second gradation..., 14 of the 16 micropixels Si
The 14th gradation is when a single pixel is colored, the 15th gradation is when 15 of the 16 micropixels Si are colored, and the 15th gradation is when all 16 of the 16 micropixels Si are colored. No. 16 # (
(see halftone dot P16), the pixels can be displayed with a total of 17 gradations.

Generally, if the number of micropixels forming one pixel is m,
The number of gradations that can be expressed is m+l.

As mentioned above, halftone dots Pi (i=0 to 16) are formed from colored micropixels among the plurality of micropixels Si forming one pixel, and the grade is determined by the number of colored micropixels forming halftone dot Pi. The key is determined.

3) Problems to be Solved by the Invention When exposing to a light beam to form an electrostatic latent image on the surface of a photoreceptor and developing it to display the halftone dots Pi, the background exposure is not colored. Fine pixels are exposed, and in image exposure, colored fine pixels are exposed. For example, when attempting to display the halftone dot P1 in FIG. 11 using background exposure, the light beam is irradiated to the uncolored fine pixels S2 to S16, and the light beam is not irradiated to the colored fine pixel S1. An input density signal Cin for gradation display for driving the exposure device is input to the exposure device. If the spot diameter of the light beam on the photoreceptor surface at this time is large,
Non-colored fine pixels S2. are arranged adjacent to the colored fine pixels St. S4. S6. When irradiating a light beam to S8 etc.,
The outer edge portion of the light beam is also irradiated to the outer edge portion of the colored fine pixel S1, and the outer edge portion of the colored fine pixel S1 is exposed. Therefore, the halftone dot P1 of the first gradation
When displaying , the entire area of the colored fine pixel S1 is not colored, but its outer edge portion is not colored. That is, the input density signal Cin input to the exposure device colors only one of the 16 fine pixels S1 to SI6 (that is, colors an area of 1/16 of one pixel), and colors the first floor. Even if it is a signal that displays the key, the actual displayed fil! II (
Output density) (out becomes thinner than that. The relationship between C4n and Cout in this case is shown by Ll in FIG. 13.

Also, in the background exposure, the halftone dot P15 in FIG.
When attempting to display, the input density signal Cin for #adjustment display is used to drive the exposure device so that the uncolored fine pixel S16 is irradiated with a light beam and the colored fine pixels 81 to S15 are not irradiated with the light beam. is input to the exposure device. In this case, the light beam is irradiated only to the non-colored fine pixel S16, but
If the spot diameter of the light beam on the surface of the photoreceptor at this time is small, the amount of exposure at the peripheral edge of the non-colored fine pixel S16 is insufficient, and the peripheral area where the amount of exposure is insufficient is colored.
That is, the input density signal Ci input to the exposure apparatus
Even if n is a signal that displays the 15th gradation by coloring only 15 of the 16 fine pixels 81 to S16 (that is, by coloring an area of 15/16 of one pixel), it is actually The displayed gradation (output density) Cout is darker than that.

The relationship between C1n and Cout in this case is shown by L3 in FIG.

Generally, when the number of colored fine pixels is small like the halftone dots PI and P2, or when the halftone dot P15. When the number of uncolored fine pixels is small like PI3, it is not easy to accurately reproduce halftone dots. In other words, fine colored parts and uncolored parts require high resolution to reproduce as an image. The reproduction of such parts is unstable in ordinary image output devices, and it is difficult to reproduce such parts while keeping the colored area of the image at a predetermined value.

Generally, when performing gradation display using halftone dots, an input density signal Cin input to an exposure device for gradation display is used.
The relationship between Cout and the output density Cout is not like LO in Figs. 12 and 13, but Ll in Fig. 12 or L in Fig. 13.
Ll in FIG. 12, which is often like L3.
When displaying a certain gradation by setting the spot diameter of the light beam on the photoreceptor surface to an appropriate value, even if you try to color the micropixels to form halftone dots corresponding to that gradation. At low density levels, where the density of micropixels that should be colored is small, those micropixels are not stably colored and are displayed as uncolored, and at high density levels, where the density of micropixels that should be colored is small. On the density side, this indicates that even the smallest pixels are often displayed in a colored manner.

As mentioned above, in conventional gradation display devices using halftone dots, even if the spot diameter of the light beam on the photoreceptor surface is set to an appropriate value, it is difficult to display low-density gradations. In some cases, a lower gradation than the desired gradation is likely to be displayed, and
When attempting to display high-density gradations, a gradation higher than the desired gradation is likely to be displayed, making it impossible to stably reproduce low-density gradation and high-density RIv4 images.
There was a problem in that the quality of the reproduced image deteriorated. Also,
When the spot diameter of the light beam on the photoreceptor surface is large, the area of colored micropixels on the low density side tends to decrease during background exposure, and the area of colored micropixels on the high density side increases during image exposure. It becomes difficult. In addition, when the spot diameter of the light beam on the photoreceptor surface is small, the area of uncolored micropixels on the high density side tends to decrease in background exposure, and the area of colored micropixels on the low density side tends to decrease in image exposure. tends to decrease.

As can be seen from FIG. 12, C1n-Cout
In the part where the slope of the curve L1 is gentle, the jump between adjacent gradations is small, but in the part where the slope is steep, the jump between adjacent lv tones becomes large, and there is a problem that smooth gradation cannot be expressed. Ta.

The present invention has been made in view of the above-mentioned circumstances, and improves image quality by reducing the variation in the jump between adjacent gradations in a gradation display device using halftone dots, allowing smooth gradation expression. The challenge is to improve.

B9 Structure of the Invention ■) Means for Solving the Problems In order to solve the above problems, the gradation display device of the present invention includes:
When displaying an image by developing an electrostatic latent image formed by irradiation with a light beam, the image is divided into pixels with a minute area, and the pixels are further divided into fine pixels with a minute area, and then displayed. Micropixels set according to the gradation are irradiated with the light beam to obtain colored micropixels, and the gradation is displayed based on the ratio of the colored micropixels forming halftone dots to the total micropixels within the pixel. In the gradation display device, the pixel is divided into a number of micro-pixels greater than the number of gradations to be displayed, and between a predetermined gradation area and other gradation areas, colored micro-pixels between adjacent gradations are divided. It is characterized by setting the difference in numbers to different values.

2) Effect The gradation display device of the present invention having the above-described configuration divides the pixel into a number of fine pixels that is greater than the number of gradations to be displayed;
Since the difference in the number of colored fine pixels between adjacent gradations is set to a value between a predetermined gradation area to be displayed and other gradation areas, the coloring between adjacent gradations in the displayed image is Variations in area differences can be reduced.

In addition, in gradation areas where the colored or uncolored area is small and gradation reproduction is unstable, by increasing the number of micropixels between adjacent gradations, clusters of colored or uncolored micropixels can be prevented. Therefore, the gradation reproducibility of the image is stabilized.

3) Examples Examples of the gradation display device of the present invention will be described below with reference to the drawings.

First, a first embodiment of the present invention will be described with reference to FIGS. 1 to 5.

FIG. 1 is an explanatory diagram of a reproduced image of the first embodiment, and one pixel is composed of 5×5=25 fine pixels. Pi (i = O to 16) in FIG. 1 indicates a halftone dot of the first gradation. At the halftone dot PO of the 0111th tone, all the micropixels are uncolored, and at the halftone dot P1 of the first gradation, two micropixels are colored.

In the low-density gradation area from halftone dot PO of the 0th gradation to halftone dot P5 of the 5th gradation, the difference in the number of colored fine pixels between adjacent gradations is set to two. And the fifth
In the intermediate gradation area from the halftone dot P5 of the gradation to the halftone dot P12 of the 12Nth tone, the difference in the number of colored fine pixels between adjacent gradations is set to 1, and the 12111th! In the high-density gradation area from the lit halftone dot P12 to the 16th gradation halftone dot P16, the difference in the number of colored fine pixels between adjacent gradations is set to two. In this way, in this embodiment, one pixel is divided into 5×5=25 micropixels, and these 25 micropixels are selectively colored.
-16th gradation, a total of 17 gradations are displayed.

Next, the configuration of a gradation display device that performs the display shown in FIG. 1 mentioned above will be explained.

The second section is an overall explanatory diagram of a digital copying machine F to which the present invention is applied. The digital copying machine F is comprised of a machine body part F1 and a cover F2 hingedly connected to the upper surface of the machine body part F1.

The machine main body part F1 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 10
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. The image reading section 11 converts the amount of reflected light at each pixel of the document into an electrical signal. This electrical signal is sent to the image processing section 12 as image data (density data).

The image processing unit 12 converts the density data into an area ratio of halftone dots, and also converts the density data into binary serial data for each scanning line so that it can be output as a rask image by a laser scanner 13, which will be described later. An image is written on a photoreceptor 15 on a drum by turning on or off a laser beam (that is, a light beam) 14 emitted from a laser scanner 13 according to the serial data.

A charging charger 16, a developing unit 17, a transfer charger 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, the configuration of the front J self-image processing section 12 in the first embodiment of the present invention will be described in detail.

The image processing section 12 shown in FIG. 3A is composed of a threshold type halftone dot generator, and receives image data (density data) B from the il image reading section 11. This image data B is generated by digitally converting an analog output signal obtained by a sensor such as a CCD in the image reading section 11.
This is the value obtained by analog conversion, and is rooooooo
o” (=0) to rllllllll” (=255
) is 8-bit digital data. This image data B is read out by the controller 121 of the image processing section 12 and stored in a line buffer 122 whose writing is controlled. The line buffer 122 is a shift register,
It is composed of a memory, etc., and has a capacity to store one line of image data B. The controller 1
21 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 micropixel is scanned, an X reset signal generated every time the laser beam 14 scans each pixel (5 micropixels), A Y clock signal generated every time one line is scanned on the top, a Y reset signal generated every time a line (that is, a line containing five micropixels (one pixel worth of micropixels) lined up in the sub-scanning direction) is scanned, 1 It operates using a page clear signal generated at the beginning of printing a page and a line clear signal generated at the beginning of each line scan.

The timing of generation of each of these signals is shown in Figures 3B and 3C. Then, in response to these signals, the X ring counter 123 outputs a 3-bit X address signal rX2
I XOJ (see Figure 3B) is output, and Y
3-bit Y address signal r from ring counter 124
Y2 YI YOJ (see Figure 3C) is output. As shown in FIGS. 3B and 3C, the X address rX2XI

Figures 4A, 4B, and 4C show the X and Y address signals roo
A threshold table 125 (to which OJ~rloOJ is input)
FIG. 3 is an explanatory diagram of 3A. FIG. 4A shows fine pixels S arranged in a 5×5 matrix forming one pixel.
ll~S55 and the above X.

7 is a diagram showing the relationship with Y address signals roooJ to rlooj. FIG. As can be seen from FIG. 4A, one of the fine pixels Sll to S55 is specified by the X and Y address signals. FIG. 4B shows each fine pixel Sll.
This is a diagram showing the threshold data set in ~S55 in decimal code, and this threshold data is actually shown in Figure 4C as A(
The data is stored in binary code as shown in (threshold value data).

The threshold data A stored in the threshold table 125 is the X output from the X, Y ring counters 123 and 124,
It is read out according to the Y address signal and output to the comparator 126.

The threshold data A and the image data B from the line buffer 122 are input to the comparator 126,
Outputs "1" when A2B, "0" when A<B
is configured to output.

In this embodiment, the laser scanner 13 is "1".
It operates to emit laser light when "0" is input, and not to emit laser light when "0" is input.

Next, the operation of the first embodiment of the present invention having the above-described configuration will be explained mainly with reference to FIGS. 3A to 5.

When scanning the first pixel row (5 rows of fine pixels),
The page clear signal shown in Figure 3C causes the Y address to be "0".
00'' (scanning of the first row of fine pixels, that is, scanning of the first row in the sub-scanning direction) is started. Then, scanning in the main scanning direction is started by a line clear signal shown in FIG. 3B.

Now, for example, image data B is rooololooJ
(-20) (a pixel consisting of 25 fine pixels) is scanned. The comparator 126 has B=roo.

10100+=(20) is input.

And the X and Y addresses are (rooo", r.

00''), the threshold data A read from the threshold table 125 and input to the comparator 126 is rllllloo as shown in FIGS. 4B and 4C.
oo"(=240>. In this case, since A>B, "1" is output from the comparator 126. Therefore, the fine pixel Sll is irradiated with the laser light. Similarly, the fine pixel Sll is irradiated with the laser beam. When scanning 812 to S15 as well, since A>B, the fine pixels S12 to S15 are irradiated with laser light.

In this way, when the scanning of the fine pixels Sll to S15 is completed, the fine pixels of other pixels lined up next to each other in the main scanning direction are scanned by the X reset signal shown in FIG. 3B. When scanning for one line of all micropixels lined up in the direction is completed, the Y address signal rY2YIYO, becomes rooIJ by the Y clock signal in FIG. 2nd row scanning) is started. Then, scanning in the main scanning direction is started by a line clear signal shown in FIG. 3B.

Then, the image data B=rooololoo again
J = (20) is input to comparator 126.

Fine pixel S with XY address ('0OOJ, '0OIJ)
21, the threshold data A read from the threshold table 125 and input to the comparator 126 is the 4th B,
As shown in Figure 4C, “11100000J (=22
4). In this case, since A>B, the comparator 12
6 outputs "1". Therefore, the fine pixel Sl
1 is irradiated with a laser beam. Similarly, when scanning the fine pixel S21, since A>B, the fine pixel S21. S2
2 is irradiated with laser light. However, the fine pixel S23
When scanning , the threshold data A read from the threshold table 125 and input to the comparator 126 is "roooloooo" (=16) as shown in FIG. 4B40. In this case, since A<B, From the comparator 126, “
0" is output. Therefore, the fine pixel S23 is not irradiated with laser light.

Similar scanning is performed for the other micropixels 324 to S55, and the laser light is not irradiated to the micropixel S33, but
Other fine pixels are irradiated with laser light.

That is, in the pixel B = rooololoo'' = (20), the fine pixels 523333 that constitute that pixel
is not irradiated with laser light, but other micropixels are irradiated with laser light. Therefore, by performing background exposure with laser light, an input density signal Cin that displays halftone dot P1 in FIG. 1 is input to the laser scanner 13. In this embodiment, as shown in FIG. 1, at B=16 to 31, the input density signal Cin that displays halftone dot P1 is input to the laser scanner 13.

As shown in Fig. 1, when B=0 to 15, the halftone dot PO
An input density signal Cin that displays halftone dot P2 is input to the laser scanner 13, and at B=32 to 47, an input density signal Cjn that displays halftone dot P2 is input to the laser scanner 13, and...
When B=240 to 254, the input density signal Gin that displays halftone dot P15 is input to the laser scanner 13, and B=25.
At step 5, an input density signal Cin indicating halftone dot P16 is input to laser scanner 13.

As mentioned above, in the low density gradation area displayed by halftone dots PO to P5 and the high density gradation area displayed by halftone dots P12 to P16, the difference in the number of colored fine pixels between adjacent gradations is 2. In the intermediate gradation area displayed by halftone dots P5 to P12, the difference in the number of colored fine pixels between adjacent gradations is 1.

FIG. 5 is an explanatory diagram of the operation of this embodiment. As mentioned above, the relationship between the input concentration signal Cin and the output concentration Cout is generally not LO, but is often Ll.

When the C4n-Cout characteristic is shown by Ll in Fig. 5,
When a signal that displays the halftone dots PO to P16 is input to the laser scanner 13 as the input density signal Cin, the displayed output densities Cout become PO' to P16'. That is, the input density signal Cin for displaying each of the 0th to 16th gradations has a difference in the number of colored fine pixels between adjacent gradations, but The difference in colored area between each gradation has less variation. Therefore, the difference in colored area between the displayed gradations is made uniform, so that smooth gradation display is achieved.

Next, a second embodiment of the image processing section 12 will be described with reference to FIG. 6 and FIGS. 7A, 7B, and 7C.

The second embodiment is based on the first embodiment shown in the block diagram of FIG. 3A.
Although it has the same configuration as the embodiment, the threshold value data of the threshold value table 125 in FIG. 3A is the same as the first one shown in FIGS. 4A and 4B.
This is different from the example. The threshold data of this second embodiment is shown in FIGS. 7B and 7C. When the threshold data as shown in FIGS. 7A and 7B is stored, the 0th to 16111tm are determined by the halftone dots PO to P16 shown in FIG.
is displayed. The halftone dot PO of the second embodiment shown in FIG.
~P16 is the halftone dot PO of the first embodiment shown in FIG. 1~
This is the same as P16, but the values of image data B corresponding to each halftone dot are different. That is, as can be seen from FIG. 6, in this second embodiment, halftone dot PO is displayed when image data B is 0 to 7, and halftone dot P1 is displayed when image data B is 8 to 23. 1. Image data B is 232-247
When , halftone dot P15 is displayed, and image data B is 248~
255, halftone dot P16 is displayed.

Even if the threshold data is different from that of the first embodiment as in the second embodiment, the same gradation can be displayed with the same halftone dots as in the first embodiment. Therefore, by appropriately setting the threshold data in the threshold table 125, it is possible to adjust the relationship between the density of the original image and the density of the reproduced display image.

Next, a third embodiment of the image processing section 12 will be described.

The image processing section 12 in FIG. 8 is composed of a font type halftone dot generator. In the description of this third embodiment,
Components similar to those in the first embodiment are designated by the same reference numerals and redundant detailed explanations will be omitted.

The image processing section 12 shown in FIG. 8 is configured to display halftone dots PO to P16 shown in FIG. 1, as in the first embodiment. However, in the first embodiment, the display was performed by back-ground exposure, but in the third embodiment, the display was performed by image exposure.

Further, the timing charts of each actuation signal (page clear signal, X reset signal, etc.) are the same as those shown in FIGS. 3B and 3C.

J, the image processing section 12 has a lookup table 12.
7, and this lookup table 127 is
As shown in FIG. 9, the value of image data B is '0OO
OOOOOJ~rooo.

1111'' (-〇~15) is input, outputs ``rooooO'' (-〇) as image data B', and outputs '0OO100OOJ~r0001 as the value of image data B'.
1111'' (-16 to 31) is input, rooool as image data B'.

Output (-1), ..., r as the value of image data B
l 1110000J~rllllllllo” (=24
0 to 254) is input, r as image data B'
ollllJ (=15) is output, and when "11111111" (-255) is input as the value of image data B, rlooooJ (-1
6).

FIG. 10A is a diagram showing the relationship between the fine pixels Sll to S55 and the X, Y address signals "000" to rlooj, and FIG. 10B is a diagram showing the relationship between the fine pixels Sll to S55 and the image data B in which each of the fine pixels SLl to S55 is colored. It shows the value.

That is, in FIG. 10B, the X, Y address ('00
The fine pixel Sll specified by 0j, '0OOJ) is B≧2
40, X, Y address (roolJ, '0O
The fine pixel S12 specified by OJ) is colored when B≧112.

FIG. 10C shows the image data B' output from the lookup table 127 and the X, Y ring counter 123.
, 124 font rom 1 where the X, Y addresses are input.
The font data stored in 28 is shown. This font rom 128 is based on the lookup table 127
The value of image data B' input from '0OOOOJ~r
loo.

Depending on OJ (=O~16), the halftone dot P in Fig. 10C
Tables 0 to P16 are selected. And each halftone dot P
Each fine pixel S11 to S3 is shown in the table O to P16, respectively.
55 data "0" or "1" are stored. For example, if the output signal of the lookup table 127 is "0"
0000'' (-0), the table of halftone dots PO of the font rom 128 is selected. In this case, as can be seen from Fig. 10C, all the fine pixels SLl to S55 are set to
is memorized. Therefore, when the halftone dot PO is selected, the input density signal Cin input from the font rom 128 to the laser scanner 13 becomes "0" while scanning all the fine pixels Sll to S55. The output signal of table 127 is “00001J (
=1), the table of halftone dot P1 of font rom 128 is selected. In this case, as can be seen from FIG. 10C, "1" is stored in the fine pixel 323 S33,
r□ is stored in all other fine pixels. Therefore, when halftone dot P1 is selected, fine pixel 323. S3
3, the input density signal Cin input from the font rom 128 to the laser scanner 13 becomes "1"; however, when scanning other fine pixels, the input density signal Cin input from the font rom 128 to the laser scanner 13 The signal Cin is
It becomes "0".

In this embodiment, the laser scanner 13 is "1".
It operates to emit laser light when "0" is input, and not to emit laser light when "0" is input. As described above, since image exposure is used in this embodiment, only the minute pixels irradiated with the laser beam are colored.

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

The image data B is, for example, rooololooJ (
= 20), as can be seen from FIG.
J (=1) is output to the font rom 128. In the font rom 128, the value rooo of the image data B' is
A table of halftone dots PI corresponding to oIJ (=1) is selected. As can be seen from FIG. 10C, the fine pixel S23. When S33 is scanned, font rom 1
The input density signal Cin input from 28 to the laser scanner 13 is [1], but while other IR pixels are being scanned, the input density signal Cin input from the font rom 128 to the laser scanner 13 is "0". Then, the micropixels whose input density signal input to the laser scanner 13 is "1" are irradiated with laser light, and the micropixels whose input density signal is "0" are not irradiated with laser light.

That is, in the pixel B-roololoooJ- (20), the laser light is irradiated to the micropixel 523S33 that constitutes that pixel, but the laser light is not irradiated to the other micropixels. If exposure is performed, the same halftone dot P1 as in the first embodiment shown in FIG.
The input concentration signal C4n that displays
3 will be input. Note that in this third embodiment as well, as in the first embodiment, as shown in FIG.
31, the input density signal Cin that displays the halftone dot P1
will be input to the laser scanner 13.

Similarly to the first embodiment, in this third embodiment, as shown in FIG. 32 to 47, the input density signal C4n displaying the halftone dot P2 is input to the laser scanner 13, . . . , B=
At B=254, an input density signal Cin that displays halftone dot P15 is input to the laser scanner 13, and at B=255, an input density signal Cin that displays halftone dot P16 is input to laser scanner 13.

As mentioned above, in the low density gradation area displayed by halftone dots PO to P5 and the high density gradation area displayed by halftone dots P12 to P16, the difference in the number of colored fine pixels between adjacent gradations is 2. In the intermediate gradation area displayed by halftone dots P5 to P12, the difference in the number of colored fine pixels between adjacent gradations is 1.

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 composed of 5 x 5 = 25 micropixels arranged in a matrix, and is arranged at a screen angle of 0° to display 16 gradations, but other matrix sizes , other screen angles, and other Wl scales can also be displayed. Further, the fine pixels constituting the pixels may have other shapes instead of a square or rectangular matrix. moreover,
In the above embodiment, the case of monochrome display was shown, but it is also possible to apply to each color of color display, and although the case of application to a digital copying machine was shown, it is also possible to apply to a printer. . Furthermore, L in FIG.
The present invention can also be applied to a gradation display device having a C1n-Cout characteristic as shown in 2 or L3. In that case, the difference in the number of colored micropixels between adjacent gradations is set to multiple values in low-density gradation areas below a predetermined density or high-density gradation areas above a predetermined density, and in other gradation areas. is the adjacent NrII! It is possible to set the difference in the number of fine pixels between them to a small number, for example, one.

C9 Effects of the Invention According to the N-level display device of the present invention having the above-described configuration, the pixel is divided into a number of fine pixels greater than the number of gradations to be displayed, and a predetermined gradation area and other gradation areas are divided. Since the difference in the number of colored micropixels between adjacent gradations was set to different values for the regions, the adjacent gradations r! in the displayed image were set to different values. It becomes possible to reduce the variation in the difference in colored area between A. Therefore, smooth gradation can be expressed, and image quality can be improved.

In addition, in gradation areas where the colored or uncolored area is small and gradation reproduction is unstable, by increasing the number of micropixels between adjacent gradations, clusters of colored or uncolored micropixels can be prevented. Therefore, the gradation reproducibility of the image can be stabilized.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the display image of the 1st third embodiment, Fig. 2 is an overall explanatory diagram of the first embodiment (an embodiment applied to a digital copying machine), and Fig. 3A is an explanatory diagram of the first embodiment of the same. 3B and 3C are timing charts of each actuation signal shown in FIG. 3A, and FIG. 4A is a timing chart of each actuation signal shown in FIG.
FIG. 4B is a diagram showing the relationship between the micropixels constituting the pixels of the embodiment and the X, Y addresses of the micropixels, and FIG. 4B shows the relationship between the threshold data stored in the threshold table of the first embodiment and the FIG. 4C is a diagram showing the actual value (binary code) of the threshold data stored in the threshold table, FIG. 5 is an explanatory diagram of the operation of the first embodiment, and FIG. 6 is a diagram showing the relationship. FIG. 7A is an explanatory diagram of a display image according to the second embodiment of the present invention, and FIG.
FIG. 7B is a diagram showing the relationship between the threshold data stored in the threshold table of the second embodiment and X, Y addresses, and FIG. 7C is a diagram showing the relationship between the threshold data and the X and Y addresses stored in the threshold table of the second embodiment. A diagram showing the actual value (binary code) of threshold data, FIG. 8 is an explanatory diagram of the configuration of the image processing section of the third embodiment of the present invention, and FIG. 9 is a lookup table used in the third embodiment. FIG. 10A is a diagram showing the relationship between the micropixels constituting the pixels of the third embodiment and the X and Y addresses of the micropixels, and FIG. 10B is the address of the micropixels in the third embodiment. 10C is a diagram showing the actual value (binary code) of the font data stored in the font ROM of the third embodiment, and FIG. Explanatory diagram of a conventional gradation display device, 1st
2 and 13 show the input density signal C1 of the gradation display device.
FIG. 3 is an explanatory diagram of n-output density Cout characteristics.

Claims (3)

[Claims] (1) When displaying an image by developing an electrostatic latent image formed by irradiation with a light beam, the image is divided into pixels with a minute area, and those pixels are further divided into fine pixels with a minute area. , Obtain colored micropixels by irradiating micropixels set according to the gradation to be displayed with the light beam, and display the gradation based on the ratio of the colored micropixels forming halftone dots to the total micropixels in the pixel. In the gradation display device, the pixel is divided into a number of micropixels greater than the number of gradations to be displayed, and between a predetermined gradation area and other gradation areas, the difference between adjacent gradation levels is A gradation display device characterized in that the difference in the number of colored fine pixels is set to different values. (2) In the low-density gradation area and the high-density gradation area to be displayed, the difference in the number of colored fine pixels between adjacent gradations is set to a plurality of values, and the difference between the low-density gradation area and the high-density gradation area 2. The difference in the number of micropixels between adjacent gradations is set to be smaller than that in the low density gradation area and the high density gradation area in the intermediate gradation area between the two. The gradation display device described. (3) The gradation display device according to claim 2, wherein the small number is one.