JP2007083605A - Image formation device and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image formation device and a method which are able to reduce the possibility of moire generation even if forming a color picture. <P>SOLUTION: A threshold value matrix wherein the number of lines included in the shortest period of a sub-scanning direction is 1/2 of the number of the surfaces of polygons is used. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus and method, and more particularly to an image forming apparatus and method that suppresses the generation of moire due to jitter and halftone dots.

  In an image forming apparatus such as a printer, a photosensitive member is scanned with a laser beam using a polygon (rotating polygon mirror) to record a latent image on a screen (halftone dot), and an image developed with toner is printed on a sheet. There is something to record.

  In this type of image forming apparatus, jitter may occur due to fluctuations in the scanning speed of the rotation period of the polygon due to a slight axis tilt of the motor that rotates the polygon, and the surface accuracy of the polygon. Due to the interference, moire (striped pattern) is generated in the image, and the image quality may be deteriorated.

  As a technique for preventing such deterioration in image quality, there is a technique for suppressing moire by setting the number of polygon faces to an integral multiple of the period in the sub-scanning direction of the threshold matrix of the screen (for example, Patent Document 1). reference).

  In addition to this, a technique for detecting deterioration of image quality by detecting the phase of a polygon or using polygons at intervals of n planes (see, for example, Patent Document 2), and a sub-scanning direction period of a threshold matrix. There is also a technique for preventing deterioration of image quality by making the number of polygon planes an integer multiple (see, for example, Patent Document 3).

By the way, when considering colorization of image forming apparatuses,
(1) Avoidance of moire due to jitter (2) Avoidance of moire due to color superposition (3) Avoidance of color change due to registration shift (4) It is necessary to satisfy all the conditions that the tone difference of each color is small.

In order to satisfy the condition of (1), that is, to avoid moire due to jitter,
(A) All screens are lined. (B) A method of using a threshold matrix as described in Patent Document 1 can be used.

  When the method (a) is adopted, it is necessary to sufficiently separate the angles of the four color screens in order to satisfy the condition (2). However, when the screen angle is more than 45 degrees (when the screen is tilted in the main scanning direction), there are a few areas where the screen becomes dot-shaped in the highlight area, and the condition (1) is satisfied. Have difficulty. Further, the graininess may be deteriorated.

  Further, although it is conceivable to arrange four color line screens between 45 degrees and 135 degrees, it is difficult to satisfy the condition (2) in this case.

  On the other hand, when the method (b) is adopted, a normal orthogonal screen has a small selection range of usable screens, and it is difficult to satisfy the condition (2). Further, if two or more same screens are stacked, the condition (3) cannot be satisfied.

  Therefore, it is conceivable to use an oblique screen in order to widen the selection range of the screen. In the orthogonal screen, the angle is uniquely determined with respect to the number of lines of the halftone dots (that is, the number of gradations). The condition (4) can be satisfied.

  However, even when the oblique screen is used and the condition (b) is satisfied, the moire caused by the interference between the jitter and the halftone dot does not occur in the single color. Although it is not visually recognized in a good region, a phenomenon in which moire due to color overlap is visually recognized in a region having poor jitter characteristics occurs.

  For example, when 6-sided polygons are used, it is assumed that an oblique screen with a minimum period of 2 lines in the sub-scanning direction as shown in FIG. 19 is used. FIG. 19A shows a screen used for the first color, and FIG. 19B shows a screen used for the second color. In addition, here, a screen for two colors will be described in order to simplify the description.

  In this case, the dot shape when the jitter characteristic is good is as shown in FIG. 20A for the first color and as shown in FIG. 20E for the second color. Further, when the first color has an influence as shown in FIG. 20C due to the jitter characteristic as shown in FIG. 20B, the dot shape becomes as shown in FIG. 20D. Similarly, when the second color is affected by the jitter characteristics as shown in FIG. 20 (f), the dot shape is as shown in FIG. 20 (h). .

  That is, when the jitter characteristic is deteriorated, the first color has three types A, B, and C shown in FIG. 21A, and the second color has D, E, and D shown in FIG. There are three types of F.

  As a result, in the region where the jitter characteristics are good, when the first color image shown in FIG. 22A and the second color image shown in FIG. Such an image is formed. In this case, the majority of the first color dots and the second color dots overlap, resulting in a secondary color dot having a slightly different shape and color. A + B in which the dots having the shapes indicated by A and B overlap. This dot appears in a cycle of 10 lines in the sub-scanning direction of the screen.

  On the other hand, in an area where the jitter characteristic is poor, when the first color image shown in FIG. 23A and the second color image shown in FIG. 23B are superimposed, as shown in FIG. An image is formed. In this case, most of the first color dots and the second color dots overlap to form a secondary color dot having a slightly different shape and color. A + D in which the dots having the shapes indicated by A and D overlap. Dots, C + F dots with overlapping dots in the shape of C and F, and B + E dots with overlapping dots in the shape of B and E, appearing with a period of 30 lines in the sub-scanning direction of the screen. To do. The A + D dots, C + F dots, and B + E dots appear to be visually different colors because the two original dot shapes of the two colors are different.

  As described above, in the combination of the two screens shown in FIG. 19, since the secondary color dots are arranged in a region having a poor jitter characteristic at a period three times that of the region having a good jitter characteristic, the result is visually recognized as a moire. It will be.

  Further, when eight polygons are used, it is assumed that an oblique screen having a minimum period of 2 lines in the sub-scanning direction as shown in FIG. 24 is used. FIG. 24A shows a screen used for the first color, and FIG. 24B shows a screen used for the second color. Here, similarly, a screen for two colors will be described.

  In this case, the dot shape when the jitter characteristic is good is as shown in FIG. 25A for the first color and as shown in FIG. 25E for the second color. Further, when the first color has an influence as shown in FIG. 25C due to the jitter characteristic as shown in FIG. 25B, the dot shape is as shown in FIG. 25D. Similarly, when the second color has an influence as shown in FIG. 25G due to the jitter characteristic as shown in FIG. 25F, the dot shape becomes as shown in FIG. 25H. .

  That is, when the jitter characteristic is deteriorated, the dot shape has four types of A, B, C, and D shown in FIG. 26A for the first color, and E and E shown in FIG. 26B for the second color. There are four types of F, G, and H.

  As a result, in the region where the jitter characteristics are good, when the first color image shown in FIG. 22A and the second color image shown in FIG. Such an image is formed. In this case, the majority of the first color dots and the second color dots overlap, resulting in a secondary color dot having a slightly different shape and color. A + B in which the dots having the shapes indicated by A and B overlap. This dot appears in a cycle of 10 lines in the sub-scanning direction of the screen.

  On the other hand, in an area where the jitter characteristic is bad, when the first color image shown in FIG. 27A and the second color image shown in FIG. 27B are superimposed, as shown in FIG. An image is formed. In this case, most of the dots of the first color and the dots of the second color overlap to form a secondary color dot having a slightly different shape and color. A + E in which the dots of the shapes indicated by A and E overlap. Dot, B + F dot with overlapping dots shown by B and F, C + G dot with overlapping dots with C and G, D + H dot with overlapping dots with D and H, The dots appear with a period of 40 lines in the sub-scanning direction of the screen.

In this way, in the region having poor jitter characteristics, the secondary color dots are arranged at a period four times that of the region having good jitter characteristics, and as a result, it is visually recognized as moire.
Japanese Patent Laid-Open No. 63-237022 Japanese Patent Laid-Open No. 4-40070 JP 61-114650 A

  As described above, when the color formation of the image forming apparatus is studied, the period in which the secondary color dots are arranged changes depending on the quality of the jitter characteristics, and as a result, moire may occur.

  Accordingly, an object of the present invention is to provide an image forming apparatus and method capable of reducing the possibility of moire even when a color image is formed.

  In order to achieve the above-described object, according to the first aspect of the present invention, laser light is modulated using a threshold value matrix of halftone dots that differ for each color, and the modulated laser light is scanned on a photosensitive member by a rotating polygon mirror. Thus, in the image forming apparatus for forming a latent image by halftone dots, a threshold matrix is provided in which the number of lines included in the shortest cycle in the sub-scanning direction is one half of the number of surfaces of the rotary polygon mirror. And

  Further, the invention of claim 2 modulates laser light using a threshold matrix of halftone dots that differ for each color, and scans the modulated laser light on the photosensitive member with a rotating polygon mirror, thereby making it possible to use halftone dots. An image forming apparatus for forming a latent image includes a rotary polygon mirror having a number of surfaces that is twice the number of lines included in the shortest cycle in the sub-scanning direction of the threshold value matrix.

  According to a third aspect of the present invention, a laser beam is modulated using a threshold matrix of halftone dots that differ for each color, and the modulated laser light is scanned on a photosensitive member by a rotating polygon mirror, thereby producing a halftone dot. In the image forming apparatus for forming a latent image, the ratio between the number of surfaces of the rotating polygon mirror and the number of lines included in the shortest period of the threshold matrix in the sub-scanning direction is set to 2: 1.

  According to a fourth aspect of the present invention, a laser beam is modulated using a threshold matrix of halftone dots that differ for each color, and the modulated laser beam is scanned on a photoconductor by a rotating polygon mirror, thereby producing a halftone dot. In the image forming apparatus for forming a latent image, the period of jitter generated based on the rotary polygon mirror is matched with the number of lines included in a plurality of periods in the sub-scanning direction of the threshold matrix.

  Further, the invention of claim 5 modulates laser light using a threshold matrix of halftone dots that differ for each color, and scans the modulated laser light on the photosensitive member with a rotating polygon mirror, thereby producing a halftone dot. In the image forming method for forming a latent image, the laser light is modulated with a threshold matrix in which the number of lines included in the shortest cycle in the sub-scanning direction is one half of the number of surfaces of the rotary polygon mirror. To do.

  According to a sixth aspect of the present invention, a laser beam is modulated using a threshold value matrix of halftone dots that differ for each color, and the modulated laser light is scanned on a photosensitive member by a rotating polygon mirror, thereby producing a halftone dot. In the image forming method for forming a latent image, the laser beam is scanned onto the photosensitive member by a rotating polygon mirror whose number of surfaces is twice the number of lines included in the shortest period of the threshold matrix in the sub-scanning direction. It is characterized by.

  The invention according to claim 7 modulates laser light by using a threshold matrix of halftone dots which differ for each color, and scans the modulated laser light on the photosensitive member with a rotating polygon mirror, thereby producing a halftone dot. In the image forming method for forming a latent image, the ratio between the number of surfaces of the rotary polygon mirror and the number of lines included in the shortest period of the threshold matrix in the sub-scanning direction is set to 2: 1.

  The invention of claim 8 modulates laser light using a threshold matrix of halftone dots that differ for each color, and scans the modulated laser light on the photosensitive member with a rotating polygon mirror, thereby producing a halftone dot. In the image forming apparatus for forming a latent image, the period of jitter generated based on the rotary polygon mirror is matched with the number of lines included in a plurality of periods in the sub-scanning direction of the threshold matrix.

  According to the present invention, it is possible to avoid moiré caused by interference between the jitter and the screen that occurs in an area having poor jitter characteristics.

  It is also possible to avoid moiré caused by overlapping of two color halftone dots in an area having poor jitter characteristics.

  Hereinafter, an embodiment of an image forming apparatus and method according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a diagram for explaining a schematic configuration of an image forming apparatus to which the present invention is applied. As shown in the figure, the image forming apparatus to which the present invention is applied reflects the laser beam irradiated by the laser 1 by the polygon 3 through the lens 2, and the reflected light irradiates the photoconductor 5 through the lens 4. Is done. At this time, since the polygon 3 rotates in the direction of the arrow A in the figure, the photosensitive member 5 is scanned, and this scanning is the main scanning. At the same time, since the photosensitive member 5 is also rotated in the direction of the arrow B in the figure, the laser light reflected by the polygon 3 is also scanned in a direction perpendicular to the main scanning direction. Become.

  Further, since the laser light emitted by the laser 1 is modulated in accordance with a signal for forming an image, a latent image is formed on the photoconductor 5.

  FIG. 2 is a block diagram showing a configuration for modulating the laser light emitted by the laser 1. As shown in the figure, the laser light emitted from the laser 1 is determined by the binarization circuit 11 comparing the input image signal with the threshold value matrix 12 to determine the modulation pattern of the laser light. The laser modulator 13 modulates the laser light emitted from the laser 1. The threshold matrix 12 is a matrix for applying a screen to an image signal, and is used to convert an image signal that represents a gradation by level into an image that represents a gradation by area.

  The configuration shown in FIGS. 1 and 2 is basically the same as the configuration of the conventional image forming apparatus, but the characteristics when the present invention is applied will be described in each embodiment.

  FIG. 3 is a diagram illustrating a screen used in the first embodiment. In the first embodiment, a screen for two colors will be described in order to simplify the description.

  The screen shown in FIG. 3 is an oblique screen in the case of using 6-sided polygons (corresponding to polygon 3 in FIG. 1), and the shortest cycle is 3 lines with half the number of polygonal faces. It is a screen. The screen shown in FIG. 3A is a screen used for the first color, and the screen shown in FIG. 3B is a screen used for the second color.

  When the screen shown in FIG. 3 is used, the dot shape when the jitter characteristic is good is as shown in FIG. 4A for the first color and as shown in FIG. 4E for the second color. . Further, when the first color has an influence as shown in FIG. 4C due to the sinusoidal jitter characteristic as shown in FIG. 4B, the dot shape is as shown in FIG. 4D. become. Similarly, when the second color has an influence as shown in FIG. 4G due to the sinusoidal jitter characteristic as shown in FIG. 4F, the dot shape is shown in FIG. 4H. It becomes like this.

  Accordingly, when the jitter characteristics are deteriorated, the dot shape has two types of A and B shown in FIG. 5A for the first color, and two types C and D shown in FIG. 5B for the second color. It becomes.

  As a result, in a region having good jitter characteristics, when the first color image shown in FIG. 6A and the second color image shown in FIG. Such an image is formed. In this case, most of the dots of the first color and the dots of the second color overlap to form secondary color dots having slightly different shapes and colors. It can be seen that overlapping dots are indicated by A + B, and the dots appear with a period of 6 lines in the sub-scanning direction of the screen.

  On the other hand, in the region where the jitter characteristic is bad, when the first color image shown in FIG. 7A and the second color image shown in FIG. 7B are superimposed, as shown in FIG. An image is formed. In this case, the majority of the first color dots and the second color dots overlap, resulting in secondary color dots that have slightly different shapes and colors. It can be seen that there are overlapping A + C dots, and these dots appear with a period of 6 lines in the sub-scanning direction of the screen.

  As is apparent from a comparison between the image shown in FIG. 6C and the image shown in FIG. 7C, when the screen shown in FIG. 3 is used, the jitter characteristic is good and the jitter characteristic is bad. In some cases, secondary color dots are arranged in the same cycle. Therefore, it is not visually recognized as moire.

  FIG. 8 is a diagram illustrating a screen used in the second embodiment. In the second embodiment, a screen for two colors will be described in order to simplify the description.

  The screen shown in FIG. 8 is an oblique screen in the case of using eight polygons (corresponding to the polygon 3 in FIG. 1), and the shortest cycle is four lines, which is half the number of polygon faces. It is a screen. The screen shown in FIG. 8A is a screen used for the first color, and the screen shown in FIG. 8B is a screen used for the second color.

  When the screen shown in FIG. 8 is used, the dot shape when the jitter characteristic is good is as shown in FIG. 9A for the first color and as shown in FIG. 9E for the second color. . Further, when the first color has an influence as shown in FIG. 9C due to the sinusoidal jitter characteristic as shown in FIG. 9B, the dot shape is as shown in FIG. 9D. become. Similarly, when the second color is affected by the sinusoidal jitter characteristic as shown in FIG. 9F, the dot shape is as shown in FIG. 9H. It becomes like this.

  Accordingly, when the jitter characteristic is deteriorated, the dot shape is two types of A and B shown in FIG. 10A, and the second color is two types of C and D shown in FIG. 10B. It becomes.

  As a result, in the region where the jitter characteristics are good, when the first color image shown in FIG. 11A and the second color image shown in FIG. Such an image is formed. In this case, most of the dots of the first color and the dots of the second color overlap to form secondary color dots having slightly different shapes and colors. It can be seen that overlapping dots are indicated by A + B, and the dots appear with a period of 8 lines in the sub-scanning direction of the screen.

  On the other hand, in the region where the jitter characteristic is bad, when the first color image shown in FIG. 12A and the second color image shown in FIG. 12B are superimposed, as shown in FIG. An image is formed. In this case, the majority of the first color dots and the second color dots overlap, resulting in secondary color dots that have slightly different shapes and colors. It can be seen that overlapping A + C dots appear, and the dots appear with a period of 8 lines in the sub-scanning direction of the screen.

  As is apparent from a comparison between the image shown in FIG. 11C and the image shown in FIG. 12C, when the screen shown in FIG. 8 is used, the jitter characteristic is good and the jitter characteristic is bad. In some cases, secondary color dots are arranged in the same cycle. Therefore, it is not visually recognized as moire.

  The third embodiment is an example in which the screen (see FIG. 3) described in the first embodiment is used. However, in the third embodiment, a surface having a polygon (corresponding to the polygon 3 in FIG. 1) is deformed. A case will be described in which sudden jitter occurs periodically due to reasons such as this. Here, it is assumed that sudden jitter appears at a period that coincides with the shortest period of the screen in the sub-scanning direction.

  When the screen shown in FIG. 3 is used, the dot shape when the jitter characteristic is good is such that the first color is as shown in FIG. 13A and the second color is as shown in FIG. These are the same as those shown in FIGS. 4 (a) and 4 (e), respectively). Further, when the first color has an influence as shown in FIG. 13C due to the jitter characteristic as shown in FIG. 13B, the dot shape becomes as shown in FIG. 13D. Similarly, when the second color is affected by the jitter characteristics as shown in FIG. 13 (f), the dot shape is as shown in FIG. 13 (h). .

  Accordingly, when the jitter characteristic is deteriorated, the first color is one type of A shown in FIG. 14A and the second color is one type of B shown in FIG. 14B.

  As a result, in the region where the jitter characteristics are poor, when the first color image shown in FIG. 15A and the second color image shown in FIG. Such an image is formed. In this case, most of the dots of the first color and the dots of the second color overlap to form secondary color dots having slightly different shapes and colors. It can be seen that there are overlapping A + B dots, and the dots appear with a period of 6 lines in the sub-scanning direction of the screen.

  As is apparent from a comparison between the image shown in FIG. 6C referred to in Example 1 and the image shown in FIG. 15C, the jitter characteristic is good when the screen shown in FIG. 3 is used. Secondary color dots are arranged in the same cycle depending on the case and the case where the jitter characteristic is poor. Therefore, it is not visually recognized as moire.

  The fourth embodiment is an example in which the screen (see FIG. 3) described in the first embodiment is used. However, as in the third embodiment, a surface having a polygon (corresponding to the polygon 3 in FIG. 1) is deformed. A case will be described in which sudden jitter occurs periodically due to reasons such as this. Here, it is assumed that sudden jitter appears at a period twice as short as the shortest period of the screen in the sub-scanning direction.

  When the screen shown in FIG. 3 is used, the dot shape when the jitter characteristic is good is such that the first color is as shown in FIG. 16A and the second color is as shown in FIG. These are the same as those shown in FIGS. 4 (a) and 4 (e), respectively). Further, when the first color has an influence as shown in FIG. 16C due to the jitter characteristic as shown in FIG. 16B, the dot shape becomes as shown in FIG. 16D. Similarly, when the second color is affected as shown in FIG. 16G due to the jitter characteristics as shown in FIG. 16F, the dot shape is as shown in FIG. 16H. .

  Accordingly, when the jitter characteristic is deteriorated, the first color has two types A and B shown in FIG. 17A, and the second color has two types C and D shown in FIG. 17B. It becomes.

  As a result, in an area where the jitter characteristic is poor, when the first color image shown in FIG. 18A and the second color image shown in FIG. Such an image is formed. In this case, the majority of the first color dots and the second color dots overlap, resulting in secondary color dots that have slightly different shapes and colors. It can be seen that there are overlapping A + C dots, and these dots appear with a period of 6 lines in the sub-scanning direction of the screen.

  As is apparent from a comparison between the image shown in FIG. 6C referred to in the first embodiment and the image shown in FIG. 18C, when the screen shown in FIG. 3 is used, jitter characteristics are good. Secondary color dots are arranged in the same cycle depending on the case and the case where the jitter characteristic is poor. Therefore, it is not visually recognized as moire.

1 is a diagram illustrating a schematic configuration of an image forming apparatus to which the present invention is applied. It is the block diagram which showed the structure for modulating the laser beam which the laser 1 irradiates. FIG. 3 is a diagram showing a screen used in Example 1. (Example 1) for demonstrating the deformation | transformation of the dot shape by jitter. FIG. 3 is a diagram showing a dot shape deformed by jitter (Example 1). (Example 1) which was the figure which showed the image formed when a jitter characteristic is good. (Example 1) which was the figure which showed the image formed when a jitter characteristic is bad. 6 is a diagram showing a screen used in Example 2. FIG. (Example 2) for demonstrating the deformation | transformation of the dot shape by jitter. (Example 2) which was the figure which showed the dot shape deform | transformed by the jitter. (Example 2) which was the figure which showed the image formed when a jitter characteristic is good. (Example 2) which was the figure which showed the image formed when a jitter characteristic is bad. (Example 3) for demonstrating the deformation | transformation of the dot shape by jitter. (Example 3) which was the figure which showed the dot shape deform | transformed by the jitter. (Example 3) which was the figure which showed the image formed when a jitter characteristic is bad. (Example 4) for demonstrating the deformation | transformation of the dot shape by jitter. (Example 4) which was the figure which showed the dot shape deform | transformed by the jitter. (Example 4) which was the figure which showed the image formed when a jitter characteristic is bad. It is the figure which showed the example of the screen used by the conventional structure. It is a figure for demonstrating the deformation | transformation of the dot shape by jitter. It is the figure which showed the dot shape deform | transformed by the jitter. It is the figure which showed the image formed when a jitter characteristic is good. It is the figure which showed the image formed when a jitter characteristic is bad. It is the figure which showed the example of the screen used by the conventional structure. It is a figure for demonstrating the deformation | transformation of the dot shape by jitter. It is the figure which showed the dot shape deform | transformed by the jitter. It is the figure which showed the image formed when a jitter characteristic is bad.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laser 2 Lens 3 Polygon 4 Lens 5 Photoconductor 11 Binary circuit 12 Threshold matrix 13 Laser modulator

Claims (8)

In an image forming apparatus that forms a latent image by halftone dots by modulating laser light using a threshold matrix of different halftone dots for each color and scanning the modulated laser light on a photoreceptor with a rotating polygon mirror ,
An image forming apparatus comprising: a threshold matrix in which the number of lines included in the shortest cycle in the sub-scanning direction is one half of the number of surfaces of the rotary polygon mirror. In an image forming apparatus that forms a latent image by halftone dots by modulating laser light using a threshold matrix of different halftone dots for each color and scanning the modulated laser light on a photoreceptor with a rotating polygon mirror ,
An image forming apparatus comprising a rotary polygon mirror having a number of surfaces that is twice the number of lines included in the shortest cycle in the sub-scanning direction of the threshold matrix. In an image forming apparatus that forms a latent image by halftone dots by modulating laser light using a threshold matrix of different halftone dots for each color and scanning the modulated laser light on a photoreceptor with a rotating polygon mirror ,
2. An image forming apparatus according to claim 1, wherein a ratio between the number of surfaces of the rotary polygon mirror and the number of lines included in the shortest cycle in the sub-scanning direction of the threshold matrix is set to 2: 1. In an image forming apparatus that forms a latent image by halftone dots by modulating laser light using a threshold matrix of different halftone dots for each color and scanning the modulated laser light on a photoreceptor with a rotating polygon mirror ,
An image forming apparatus, wherein a period of jitter generated based on the rotary polygon mirror is matched with a number of lines included in a plurality of periods in the sub-scanning direction of the threshold matrix. In an image forming method for forming a latent image by halftone dots by modulating laser light using a threshold matrix of different halftone dots for each color and scanning the modulated laser light on a photoreceptor with a rotating polygon mirror ,
An image forming method characterized in that the laser beam is modulated with a threshold matrix in which the number of lines included in the shortest cycle in the sub-scanning direction is one half of the number of surfaces of the rotary polygon mirror. In an image forming method for forming a latent image by halftone dots by modulating laser light using a threshold matrix of different halftone dots for each color and scanning the modulated laser light on a photoreceptor with a rotating polygon mirror ,
An image forming method, wherein the laser beam is scanned onto the photosensitive member by a rotating polygon mirror having a number of surfaces which is twice the number of lines included in the shortest cycle in the sub-scanning direction of the threshold matrix. In an image forming method for forming a latent image by halftone dots by modulating laser light using a threshold matrix of different halftone dots for each color and scanning the modulated laser light on a photoreceptor with a rotating polygon mirror ,
2. An image forming method according to claim 1, wherein a ratio between the number of surfaces of the rotary polygon mirror and the number of lines included in the shortest cycle in the sub-scanning direction of the threshold matrix is set to 2: 1. In an image forming apparatus that forms a latent image by halftone dots by modulating laser light using a threshold matrix of different halftone dots for each color and scanning the modulated laser light on a photoreceptor with a rotating polygon mirror ,
An image forming method, wherein a cycle of jitter generated based on the rotary polygon mirror is matched with a number of lines included in a plurality of cycles in the sub-scanning direction of the threshold matrix.

Images