JP3040236B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser printer and an LED.
The present invention relates to a printer, such as a printer, a liquid crystal printer, a thermal transfer printer, and an ink jet printer, that is, relates to a configuration of an image forming apparatus. The present invention relates to an image forming apparatus to be improved.

[0002]

2. Description of the Related Art At present, a printer of 300 dpi is mainly used as an image forming apparatus. Therefore, the signal output from the computer often corresponds to 300 dpi. However, a low-resolution printer such as 300 dpi has a disadvantage that the jaggies shown in FIG. 15 are noticeable. To eliminate this determination, the pixel density may be increased. However, if the pixel density is simply increased, in addition to the increase in the page buffer and the increase in the printer cost due to the higher precision of the engine, (1) the bitmap fonts for 300 dpi that are spread around the street Not available. (2) There is a drawback that 300 dpi input devices (scanners, etc.) that are widely distributed cannot be used. By the way, in a laser printer, the pixel density in the sub-scanning direction is increased. That is,
It is difficult to increase the pitch of paper feed / drum feed, and even if it can be done, it will be expensive. On the other hand, in order to increase the pixel density in the main scanning direction, it is only necessary to increase the frequency for modulating the laser beam, and this can be realized relatively easily and at low cost. Therefore, a method of improving the image quality by triple the positioning accuracy of the pixels in the main scanning direction and changing the pixel size to 12 levels has been proposed (USP).
4,847,641). In this method, pixels of an input image are cut out using a mask of a predetermined size, and RO
This is a method of comparing the pattern written in M and correcting the position and size of the corresponding pixel when the pattern matches the pattern.

FIG. 16 is an explanatory diagram of this correction method. In the figure, input data 1 is converted to sampling window 2
Then, the position and size of the corresponding pixel are changed when the data matches, as compared with the template 3 on the right.

Further, in order to reduce jaggies at an angle close to a horizontal straight line as shown in FIG. 15, an image to be originally represented by one recording dot is divided into two dots in the sub-scanning direction to obtain image quality. There are ways to make improvements. The size of each of the two recording dots to be replaced has been determined by actually recording characters and figures and performing tuning so that jaggies are not noticeable in cut and try.

[0005]

However, FIG.
In the method described in the above section, it is necessary to have many mask patterns, so that the speed is slow, the amount of memory for storing the mask pattern is large, and the pixel arrangement that completely matches the limited mask pattern is considered. There was a problem that only the correction was made.

In the case of using a method in which one recording dot is divided into two dots in the sub-scanning direction and recorded, enormous manual labor is required for tuning.
When the dot diameter of the printer for recording changes, the tuning operation is repeated again, and if the tuning is insufficient, there is a problem that the effect of improving the image quality is small.

Further, when one dot is divided into two dots in the sub-scanning direction as described above, two dots may be too close due to a change in the paper feed amount in the sub-scanning direction.
Alternatively, there is also a problem that the image quality is not improved as expected due to being too far away.

The present invention detects the angle of a horizontal straight line of a jaggy portion with respect to the main scanning direction, and divides one recording dot into two sub-scanning recording dots in accordance with the angle. The purpose of the present invention is to improve the image quality by determining the size of the divided recording dots, detecting the paper feed amount, and keeping the recording width of the two divided recording dots constant.

[0009]

FIG. 1 is a block diagram showing the principle of the present invention. FIG. 1 is a block diagram showing the principle of an image forming apparatus that records a high-quality straight line with less jaggies and improves the image quality of an input image while using a low-resolution recording method.

In FIG. 1, a tilt detecting means 6 detects a tilt of a straight line in a jagged portion in a main scanning direction from input image data in a bit map memory, for example. This inclination detection is performed, for example, by comparison with a template. The single dot diameter designating means 7 is, for example, a dot diameter register. The single dot diameter designating means 7 designates the size of a single recording dot in the input image data, for example, the diameter.
Is a dot interval register, for example, which specifies the interval between single recording dots when the paper feed amount does not change, that is, the dot pitch.

The divided recording dot shape determining means 9 is, for example, a look-up table, and the inclination of the straight line of the jaggy portion output from the inclination detecting means 6 with respect to the main scanning direction, and the single recording dot designated by the single dot diameter designating means 7 Of the recording width when two divided recording dots are arranged so that the center is on a straight line in the sub-scanning direction, using the diameter of the dot and the dot pitch designated by the standard dot interval designation means 8. The shape of the two divided recording dots is determined so that the interval becomes equal to the diameter of the single recording dot.

Further, the dot recording position determining means 10 is, for example, a look-up table, which detects the paper feed amount which is the actual dot interval in the sub-scanning direction, and uses the detection result and the output of the inclination detecting means 6. By changing the recording position of one of the two divided recording dots in the main scanning direction such that the distance between the envelopes of the two divided recording dots in the sub-scanning direction is equal to the diameter of the single recording dot, Determine the dot recording position.

[0013]

In the present invention, when a single recording dot is divided into two recording dots in the sub-scanning direction, the recording width is made equal to the diameter of the single recording dot so that the width of the recording dot is equal to the width of the straight line at every portion of the straight line. That is, the image quality is improved so that the intervals between the envelopes become equal.

In order to equalize the intervals between the envelopes, the diameter of a single recording dot and the recording in the sub-scanning direction of two recording dots divided and recorded in the case where the paper feed amount does not change. The radius of the two divided recording dots is determined so that the widths are equal. The recording dot divided into two is a part of the recording dots, and the other recording dots are not divided and are recorded as single recording dots.

The center of each of the recording dots divided into two must naturally be on the main scanning line. Therefore, the interval between the centers of the two recording dots divided in the sub-scanning direction is the dot pitch in the sub-scanning direction. Matches. For example, in order to reduce jaggies in the upper right straight line, a certain main scanning line and its one
The shape of the divided recording dots is determined so that the center of the two divided recording dots is located above the main scanning line on the book.

In FIG. 1, the divided recording dot shape determining means 9 uses the inclination of the straight line of the jaggy portion in the main scanning direction, the size of the single recording dot, and the interval between the single recording dots to form two recording dots. The shape is determined according to the equation for calculating the radius of. By providing a look-up table that stores the relationship between them, instead of actually performing the calculation, the shape of the two divided recording dots can be determined.

However, when the paper feed amount, that is, the actual dot interval in the sub-scanning direction fluctuates and deviates from the standard dot interval, the recording widths of the two recording dots determined as described above are, of course, independent. It is not equal to the diameter of the recording dot. Therefore, in the present invention, the actual dot interval in the sub-scanning direction, that is, the paper feed amount, is detected by the dot recording position determining means 10, and the recording width of the two divided recording dots, that is, the interval in the sub-scanning direction of the envelope is determined. The recording position of one of the two divided recording dots in the main scanning direction is changed so as to be equal to the diameter of the single recording dot. For example, when the paper feed amount is larger than the standard dot interval, the lower dot of the two divided dots is moved to the left, and when the paper feed amount is shorter than the reference interval, the lower dot is moved to the right. The recording dot position is determined so that the recording width of the dots, that is, the interval between the envelopes is constant.

As described above, according to the present invention, the straight line at the jaggy portion can be corrected to a straight line without jaggies having envelopes with equal intervals.

[0019]

FIG. 2 is an explanatory diagram (part 1) of a jaggy correction system according to the present invention. FIG. 7A shows an example of a straight upper right jaggy. FIG. 3B shows the result of jaggy correction when there is no change in the paper feed amount. By dividing a part of the single recording dot in FIG. Has been reduced. The division into the two recording dots is performed so that the interval between straight envelopes as a correction result is constant. The two divided recording dots are recorded so that the center is located on a certain main scanning line and the main scanning line one line above.

FIG. 2C is an explanatory diagram of a method for determining two divided recording dots. In the figure, the scale on the horizontal axis indicates the dot interval in the main scanning direction, and the unit interval corresponds to the dot pitch in the main scanning direction. The scale on the vertical axis indicates the sub-scanning dot interval, and the unit interval corresponds to the paper feed pitch in the sub-scanning direction. In this embodiment, these pitches are assumed to be equal.

In FIG. 2C, r _n and _m indicate the dot radius of the m-th recording dot in the sub-scanning direction (vertical direction) on the n-th line in the main scanning direction. Radius r ₀ of the recording dots at the origin, ₀ is the radius of a single recording dots which do not change under the corrected and uncorrected image. For example, radii r ₀ , ₂
And r _{1, 2} of the recording dots is obtained by dividing the uncorrected single recording dots to two, each of the center is in the main scanning line.

[0022] In FIG. 2 (c), the relationship between the radius r _{1, 2} and r _{0, 2} of radius r _{0, 0} and two divided recording dots alone recording dot is given by the following equation.

[0023]

(Equation 1)

Here, "pitch" is a paper feed pitch in the sub-scanning direction. In equation (1), by using the angle θ between the straight line having a jaggy and the main scanning direction, the radii r ₀ , ₂
And r ₁ , ₂ are given by the following equations.

[0025]

(Equation 2)

Here, "pitch" is the main scan as described above,
It is assumed to be the same in both sub-scanning directions. FIG. 3 is an explanatory diagram of determining the size of the recording dot to be divided.
This is to explain equation (3). In FIG.
= 2 pitch × tanθ holds,

[0027]

(Equation 3)

Equation (2) is derived from equation (2). Further, in FIG. 3B, CD = 2 pitch × tan θ holds.

[0029]

(Equation 4)

Equation (3) is derived from equation (3). Similarly, the radius of the divided recording dot is generally given by the following equation.

[0031]

(Equation 5)

Here, r is the radius of the single recording dot (=
r _{0, 0)} and is, for m is 4 or more (4) are performed in repetition calculation equation (5). FIG. 4 is an explanatory diagram (part 2) of the jaggy correction method according to the present invention. FIG. 7 is an explanatory diagram of a jaggy correction method when the paper feed amount deviates from the standard dot pitch. FIG. 7A shows a correction method when the paper feed amount does not change, which is the correction method described with reference to FIGS.

Generally, in a printer, the resolution in the main scanning direction is determined by an LED head and an optical scanning system and is stable. However, the paper feed pitch in the sub-scanning direction varies depending on the accuracy of paper feed and is not always stable. . When the pitch in the sub-scanning direction changes, the recording width of the two divided recording dots, that is, the width of the envelope changes, and the above-mentioned (1)
The formula will not hold. Fluctuations in the paper feed amount can be reduced by performing servo control, etc.However, a minimum time of several hundred ms is required from detection of the fluctuation to mechanical correction, and printers that perform high-speed printing require this. It is difficult to reduce.

FIG. 4B is an explanatory diagram of the jaggy correction method when the paper feed amount is longer than the standard dot interval (reference paper feed pitch). In the figure, of the divided recording dots (including undivided dots), the dots on the lower line are
It is shifted to the left of position (a). The amount of movement Δ
S is the main scan of the straight line to be recorded with the paper feed fluctuation amount Δ outside

[0035]

[Outside 1]

Is given by the following equation using the direction inclination θ.

[0037]

(Equation 6)

FIG. 4C is an explanatory diagram of a correction method when the paper feed amount is shorter than the reference paper feed pitch. In the figure, all the dots in the lower line are shifted to the right side as compared to FIG. The amount of movement is defined as a negative value of the paper feed fluctuation amount Δ outside in Eq. (6).

[0039]

[Outside 2]

As a result, the movement amount ΔS is also negative, that is, it indicates movement to the right. As described above, according to the present embodiment, the width of the envelope of the divided recording dots can be kept constant even if the actual dot interval in the sub-scanning direction changes due to a change in the paper feed amount.

FIG. 5 is a system configuration block diagram of a first embodiment of the image forming apparatus. In FIG. 1, an image forming apparatus includes a bitmap memory 21 for storing input bitmap image data, and line buffer memories 22 _{1 to} 22 as a group of registers for temporarily holding data read serially from the bitmap memory 21. _m , a register 23 for holding data cut out from these line buffer memories, an angle detector 24 for detecting the inclination of a straight line with jaggies from the bitmap image data cut out in the register 23, and holding a radius of a single recording dot. A dot diameter register 25, a dot coordinate register 26 for indicating a coordinate position determined from the cut-out image held in the register 23 and the image data in the bitmap memory 21, and a dot interval in the sub-scanning direction, that is, a standard paper feed amount. Dot interval register 27 that holds A line interval register 28 for holding the paper feed amount of recording paper; a difference unit 29 for calculating a difference between a standard dot interval output from the dot interval register 27 and an actual dot interval output from the line interval register 28; , Standard dot spacing,
From the dot coordinates and the inclination of the straight line, the radius of the two recording dots is set such that the recording width when the two divided recording dots are arranged in the sub-scanning direction is equal to the diameter of the single recording dot.
A dot shape calculation look-up table (LUT) 30 which tabulates the results calculated from the equations (4) and (5), the difference between the standard dot interval as the output of the differentiator 29 and the actual paper feed amount, and a straight line Dot recording position calculation LU that tabulates the result calculated from equation (6) using the inclination of
T31, a laser drive driver 32 for controlling actual dot recording using outputs of the two lookup tables 30, 31, an exposure optical system 33 for forming a latent image on an electrophotographic process, a drum 34, and a paper feed roller 35, an encoder 3 for detecting the rotation amount of the paper feed roller 35
6. A line interval calculator 37 for calculating the actual paper feed amount, that is, the line interval, from the output of the encoder 36.

[0042] In FIG. 5, the image data is transferred from the outside of the printer interface (not shown) in the bit map memory 21, the print command is output from the external interface, the bit map data pages top line buffer memory 22 ₁ through 22 _m Sent from. The line buffer memories 22 _{1 to} 22 _m are serial input registers. When bitmap data is taken into these registers (M pieces), N bitmap data are taken out from each serial input register in parallel, and N
The data of the image area of the bit map of the pixels of × M is stored in the register 23.

The bitmap image data of N × M pixels cut out in the register 23 is inputted to the angle detector 24, and the inclination of the straight line is detected. The detected angle is used for determining the dot shape by the dot shape calculation LUT 30 and for determining the dot recording position by the dot recording position calculation LUT 31.

When determining the actual dot shape, the dot shape calculation LU is calculated using the radius of the single recording dot, the standard dot interval, and the dot coordinates in addition to the detected angle of the straight line.
The dot diameter is determined by T30. The dot pitch in the sub-scanning direction, that is, the standard dot interval, is normally set in the dot diameter register 25 at the time of factory shipment.

In determining the dot recording position, that is, the dot movement amount, it is necessary to detect the paper feed amount in addition to the detection result by the angle detector 24 described above. The paper feed amount is measured using an encoder attached to the rotation shaft of a paper feed roller 35 that conveys the recording paper. The encoder 36 generates a pulse in accordance with the rotation of the roller 35. The pulse interval becomes longer when the rotation is slower, and the pulse interval is narrower when the rotation is faster. For example, the pulse interval is converted into a paper feed amount by the line interval calculator 37, and the result is stored in the line interval register 28. The stored result is compared with the standard dot interval held in the dot interval register 27 by the differentiator 29, and the difference result is input to the dot recording position calculation LUT 31, and the dot recording position, that is, the dot movement amount is changed by the laser drive. Driver 32
Given to. The laser drive driver 32 controls the laser light source of the exposure optical system 33 according to the size of the dot input from the dot shape calculation LUT 30 and the position of the dot input from the dot recording position calculation LUT 31.

The operation of the angle detector 24 and the laser driver 32 as the main components of the components shown in FIG. 5 will be described in further detail. FIG. 6 is a configuration block diagram of an embodiment of the angle detector. In the figure, a pattern comparison unit 40 stores N × M pixel data, that is, cut-out image data, and an angle detection read-only memory (ROM) 4.
1 is input, and these two inputs are compared for each dot. If all the dots match, a detection signal is output from the pattern comparison unit 40. The address of the angle detection ROM 41 is given from the output of the counter 42, and the output of the counter 42 is incremented according to the clock output from the clock control circuit 43. The count value output from the counter 42 is also output to an angle conversion LUT 44. When the pattern comparison unit 40 outputs a detection signal, the angle conversion LUT
An angle signal corresponding to the detection pattern output by the OM 41 is output.

FIG. 7 shows an example of the angle detection pattern stored in the angle detection ROM 41 of FIG. FIG. 9 shows an example of a detection pattern for image data of 9 pixels on each of 7 lines, that is, 9 × 7 pixels.

FIG. 8 is a time chart of an embodiment of the operation of the angle detector of FIG. In FIG. 6, the clock control circuit 4
3 starts the supply of the clock to the counter 42 in response to the input of the start signal, and at the same time, resets the count value of the counter. The counter 42 increments the count value each time the clock is input from the clock control circuit 43, and The value is output to the angle detection ROM 41. Pattern comparison unit 4
The 0 detection signal is also supplied to the clock control circuit 43, and when the angle is detected, the supply of the clock from the clock control circuit 43 to the counter 42 is stopped.

In FIG. 8, the output of the clock control circuit is supplied to the counter together with the input of the start signal, and the counter increments its count value one after another. During this time, the cut-out image pattern and the detection pattern are compared, and when a match is detected and the detection signal becomes “H”, the output of the clock control circuit is stopped and the operation of the counter is also stopped.

Next, the change in the dot diameter by the laser driver 32 will be described. FIG. 9 is an example of the relationship between the light emission time and the dot diameter. The figure plots the actual measurement results, and it can be seen that the dot diameter changes significantly when the light emission time is shorter than 0.6 μs.

FIG. 10 shows an example of the relationship between the change in light emission time, the amount of exposure, and the dot shape. In the figure, it can be seen that the exposure amount changes according to the light emission time, and the dot diameter determined by the exposure amount required for development changes.

FIG. 11 is a block diagram showing the configuration of an embodiment of the laser driving driver. In the figure, a laser drive driver stores a dot diameter data memory 47 for storing dot diameter data output in pixel units from the dot shape calculation LUT 30 in FIG. 5, and a dot for storing dot position data output from the dot recording position calculation LUT 31. Position data memory 4
6. a dot diameter data / emission data converter 48 for converting the dot diameter data into laser emission time data; a shift register group 49 for controlling the laser emission time by the output of the dot diameter data / emission data converter 48; Latch 5
0, print clock 5 for instructing dot print timing
1. Sub clock 52, laser 53, laser 5 for instructing the shift timing of the contents stored in shift register group 49
3 is configured by a driver 54 for driving the driving circuit 3.

In FIG. 11, the dot diameter data is level 0
To the level 7; the light emission time is “0” for the level 0; the light emission time for the level 1 is one clock of the subclock;
In this case, the length is 7 clocks of the subclock.
Therefore the number of shift registers among shift registers 49 ₁ to 49 ₇ light emission time depending stores '1' is 8 steps, when the size of the dots may not hit the dot and eight, including being formed Become.

FIG. 12 is a timing chart of an embodiment of the exposure control in the laser driver shown in FIG. In this figure, as shown in FIG. 2 (c), the dots whose diameters are changed in the main scanning direction such as radii r ₀ , ₁ , r ₀ , ₂ ,. The case of hitting will be described. In FIG. 11, the dot diameter data memory 47 stores dot diameter data for each pixel from the dot shape calculation LUT 30,
The dot position data memory 46 stores dot recording positions from the dot recording position calculation LUT 31.

In FIG. 12, in order to print dots of dot diameter data r ₀ , ₁ at print clock timing C ₁ , the dot diameter data is first stored in the dot diameter data memory 47, and the dot position data s ₀ , ₁ is stored in the dot position. The data is read from the position data memory 46 and converted into light emission data by the dot data / light emission data converter 48. If the dot diameter data r _{0, 1} and level 5, in order to move the recording position to the right, from the shift register 49 ₇ 4
9 Data to five shift register up to _three emission data so that "1" is output. The correspondence between the light emission data, the dot diameter data, and the dot position data can be arbitrarily converted by using the PROM or the ROM in the normal dot data / light emission data converter 48.

Data input to the shift registers 49 ₁ to 49 ₇ is performed in synchronization with the parallel load signal P ₁ , and after storing the data, the contents of each shift register are synchronized with the sub clock and the contents of the shift registers 49 ₇ to 49 ₁ , And the output of the shift register 49 ₁ is
Set to 0. By causing the laser 53 to emit light by the output of the latch 50, the exposure time of the laser can be controlled by an integral multiple of the subclock cycle.

At timing C ₂ of the print clock, a dot of radius r ₀ , ₂ is formed. The size of this dot is, for example, level 4, and seven shift registers 4
9 _1-49 as emission data to 49 _{4-49 7} 4 among ₇ '1' is output. The light emission of the laser 53 after the output of the light emission data is performed in the same manner as described above.

FIG. 13 is a system configuration block diagram of a second embodiment of the image forming apparatus. The first diagram shown in FIG.
The only difference is that the encoder 36 is mounted not on the roller 35 but on the rotating shaft of the drum 34 for forming an electrostatic latent image.

FIG. 14 is a system configuration block diagram of a third embodiment of the image forming apparatus. Comparing this figure with FIG. 5 showing the first embodiment, the only difference is that the interval alarm generator 55 is provided on the output side of the difference unit 29 which calculates the difference between the standard dot interval and the actual paper feed amount. Is different. The interval alarm generator 55 generates an alarm signal when the fluctuation of the paper feed amount deviates from the dot recording position correction range by the dot recording position calculation LUT 31.

In the above description, the dot size is changed by controlling the laser emission time. However, the same effect can be obtained by controlling the laser drive voltage or drive current while keeping the emission time constant. Of course.

[0061]

As described in detail above, according to the present invention, a jaggy-free straight line having an envelope having an equal interval in all parts can be drawn even in a low-resolution printer, and in the sub-scanning direction. Even if there is fluctuation due to jitter or the like, recording can be performed without affecting the interval between envelopes, and high-quality recorded images comparable to those drawn with a high-resolution printer on a straight line can be realized. It becomes possible.

[Brief description of the drawings]

FIG. 1 is a principle block diagram of the present invention.

FIG. 2 is a diagram (part 1) for explaining a jaggy correction method according to the present invention.

FIG. 3 is a diagram illustrating how to determine the size of a recording dot to be divided.

FIG. 4 is a diagram (part 2) for explaining a jaggy correction method according to the present invention.

FIG. 5 is a block diagram illustrating a system configuration of a first embodiment of the image forming apparatus.

FIG. 6 is a block diagram illustrating a configuration of an angle detector.

FIG. 7 is a diagram illustrating an example of an angle detection pattern.

FIG. 8 is a time chart of an operation example of the angle detector.

FIG. 9 is a diagram illustrating a change in dot diameter according to a light emission time.

FIG. 10 is a diagram showing changes in the exposure amount and the dot shape with a change in the light emission time.

FIG. 11 is a block diagram illustrating a configuration of a laser driving driver.

FIG. 12 is a time chart of the embodiment of the exposure control in FIG. 11;

FIG. 13 is a block diagram illustrating a system configuration of a second embodiment of the image forming apparatus.

FIG. 14 is a block diagram illustrating a system configuration of a third embodiment of the image forming apparatus.

FIG. 15 is a diagram illustrating an example of jaggies of an input image.

FIG. 16 is a diagram illustrating a conventional example of an image quality improving method.

[Explanation of symbols]

 6 Tilt detecting means 7 Single dot diameter specifying means 8 Standard dot interval specifying means 9 Divided recording dot shape determining means 10 Dot recording position determining means 24 Angle detector 25 Dot diameter register 26 Dot coordinate register 27 Dot interval register 28 Line interval register 29 Difference device 30 Dot shape calculation LUT 31 Dot recording position calculation LUT 32 Laser drive driver 36 Encoder

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Jun Juno 1015 Uedanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Prefecture Inside Fujitsu Co., Ltd. (56) References JP-A-5-91321 (JP, A) JP-A-5-48879 (JP, A) JP-A-5-8448 (JP, A) JP-A-4-3233054 (JP, A) JP-A-4-155385 (JP, A) JP-A-60-194531 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) B41J 2/485 G06T 5/30 G09G 5/28 610 H04N 1/387

Claims (4)

(57) [Claims] And 1. A tilt detection hand stage straight jaggy portion from the input image data to detect the inclination formed between the main scanning direction, and the single dot diameter specified means to specify the size of a single recording dot in the input image data , the sole and the standard dot interval specified means to specify a standard spacing of recording dots, identical to each center part of said single recording dot in the printing dots for jaggy reduction the sole recording dots
In cutting the two recording dots of the vertical at the main scanning position, using inclined-out detection hand stage, alone dot diameter specified hand stage, and the output of the standard dot interval specified hand stage, the two divided recording dots The shape of the two divided recording dots is set such that the interval in the sub-scanning direction of the envelope indicating the recording width when the centers are arranged on a straight line in the sub-scanning direction is equal to the diameter of the single recording dot. divided recording dot shape decision hand stage the decision to
When detects the paper feed amount in the sub-scanning direction, the detection result and the using the output of the tilt detection hand stage, the two divided recording dots in the sub-scanning direction interval the single recording dots of the envelope Dot recording position determining means for changing the recording position of one of the two divided recording dots in the main scanning direction so as to be equal to the diameter of the two divided recording dots.
A stage to record, yet less jagged high quality linear low resolution, the image forming apparatus and performing image quality improvement. Wherein said dot recording position determining hands stage, and wherein for the detection in the sub-scanning direction of the paper feed amount, using the output of an encoder attached to the rotation shaft of the roller for conveying the recording sheet The image forming apparatus according to claim 1. Wherein the dot recording position determining hands stage, in order to detect the sheet feeding amount of the sub-scanning direction, using the output of an encoder attached to the rotation shaft of the electrostatic latent image recording medium for image forming The image forming apparatus according to claim 1, wherein: Wherein said dot recording position determining hands stage, when the amount of change in said detected paper feed amount is not be corrected only by changing the recording position of one main scanning direction of the divided recording dots, alarm The image forming apparatus according to claim 1, further comprising an alarm generator that outputs a signal.