JP2002361930A - Imaging apparatus and imaging method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging apparatus in which a pulse width corresponding to a code being generated from a pattern detecting circuit can be set such that an image output comprising a set of dot patterns has the same density even if a code being generated from the pattern detecting circuit is different due to positional relation of an image pattern and a pattern detection matrix. SOLUTION: A plurality of test patterns having the same on pixel density and a different relative position to a pattern detection matrix are outputted and a pulse width corresponding to a code is set such that their densities are equalized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an image output apparatus comprising the same set of halftone dot patterns having the same density even when codes generated by a pattern detection processing circuit differ depending on the positional relationship between an image pattern and a pattern detection matrix. The present invention relates to an image forming apparatus and an image forming method capable of setting a pulse width corresponding to a code generated by a pattern detection processing circuit such that

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus of an electrophotographic system using a so-called negative / positive process system, in which an image portion on a photoreceptor is irradiated with a laser beam and toner is adhered to the irradiated portion to form an image. As a method for doubling the pixel density in the sub-scanning direction, a method called an overlap scanning method is known. In this method, the recording medium is scanned with a light beam having a beam diameter larger than the sub-scanning pitch, and an image is formed at a position where a plurality of beams overlap.

For example, a binary image data input of 1200 dpi is converted to a multi-valued PWM of a write cycle of 600 dpi.
It has the function of converting to output, and does not make any optical or mechanical changes to the 600 dpi print engine.
There is also known a product capable of printing output equivalent to 0 dpi.

The operation of the write signal processing section of the image forming apparatus using the overlapping scanning method will be described with reference to FIG. Note that here, 600d in both the main and sub-scanning directions.
using an image forming apparatus having a recording density of pi.
A case in which an image having a recording density of 1200 dpi is formed in both the sub-scanning direction will be described.

In FIG. 16, a write signal processing section of an image forming apparatus according to a conventional example includes a line memory 1, a pattern detection processing circuit 2, an LUT (look-up table) circuit 3, a PWM (pulse width modulation) circuit 4, and an LD ( Laser diode) driver 5 and LD (laser diode) 6
It is composed of The line memory 1 holds 1200 dpi image data for three lines, and sends image data corresponding to the position in the main scanning direction to be recorded to the pattern detection processing unit 2. The pattern detection processing circuit 2 includes 1200
The on / off information of two consecutive dots in the main scanning direction to be recorded, four dots above and below the dots, and a total of six dots in the image data of dpi (hereinafter referred to as main 2 × sub 3 The matrix corresponding to the pattern is sent to the LUT circuit 3. The LUT circuit 3 sends a preset pulse width and pulse position signal to the PWM circuit 4 corresponding to the code sent from the pattern detection processing circuit 2. The PWM circuit 4 sends a PWM signal to the LD driver 5 based on the received pulse width and pulse position signal. The PWM signal is
It is output in synchronization with the video clock signal (600 dpi frequency). The LD driver 5 supplies a drive current to the LD 6 when receiving the “ON” signal and an offset current when receiving the “OFF” signal.

FIG. 17 shows an example of a detection matrix of image data and a pattern. "X0", "x1" in FIG.
Indicates a scanning position at 600 dpi in the main scanning direction. "Y0", "y1",... Indicate the scanning positions at 600 dpi in the sub-scanning direction. In this example, P
The WM circuit 4 outputs a PWM signal having a set pulse width at the same position in the main scanning direction over two lines. At this time, an image is formed in a region where the light beam irradiation regions overlap. Thus, using an image forming apparatus having a recording density of 600 dpi, it is possible to form an image of 1200 dpi without changing the video clock frequency or the feed speed in the sub-scanning direction.

As described above, it is necessary to set a pulse width and a pulse position corresponding to the code sent from the pattern detection processing circuit 2 in the LUT circuit 3. When the pulse width is set, the maximum pulse width is set so that the black solid portion will have an appropriate density when the following black solid image is output. When a plurality of one-dot-width horizontal lines whose positions in the sub-scanning direction are shifted by 1200 dpi are output, a horizontal line formed at the scanning position of the light beam and a horizontal line formed between the two scanning positions are output. , The pulse width for the corresponding code is set such that the respective densities are the same. The pulse width corresponding to each code is set so that the gray scale density change is continuous when a gray scale consisting of a halftone dot pattern in which the ON pixel density continuously changes is output. It is necessary to execute the following three points.

[0008]

However, according to the above-mentioned prior art, an LUT set in consideration of the above points is set.
When an image is output using, a problem may occur. For example, when an image composed of a set of dot patterns shown in FIG. 18 is output, the output images may have different densities even though the density of the ON pixels is the same in both patterns. This is shown in FIG. 18A and FIG.
This is because, in the two patterns, the positions of the halftone dots in the main scanning direction are shifted by one dot of 1200 dpi, so that the codes generated by the pattern detection processing circuit are different.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and a first object of the present invention is to provide the same technique even when codes generated by a pattern detection processing circuit differ depending on the positional relationship between an image pattern and a pattern detection matrix. An object of the present invention is to provide an image forming apparatus and an image forming method capable of setting a pulse width corresponding to a code generated by a pattern detection processing circuit so that the density of an image output composed of a set of halftone patterns becomes the same.

Further, when the pulse widths corresponding to the codes of all classes are set so that the above-mentioned densities become the same, the pulse widths of all the codes generated by the pattern detection processing circuit are compared by the density comparison. Setting is not efficient.

Therefore, a second object of the present invention is to determine the positional relationship between an image pattern and a pattern detection matrix.
Even if the codes generated by the pattern detection processing circuit are different, it is efficient to set the pulse width corresponding to the code generated by the pattern detection processing circuit so that the density of the image output consisting of the same set of halftone patterns is the same. An object of the present invention is to provide an image forming apparatus and an image forming method that can be performed well.

[0012]

To achieve the above object, according to an aspect of the first means, light with respect to the light intensity of the beam center, the beam diameter whose light intensity is defined by the value becomes 1 / e ² In an image forming apparatus for forming an image on a recording medium by scanning a beam on a recording medium at a sub-scanning pitch smaller than the beam diameter, a means for generating a code from a detection matrix from image data to be formed, By scanning the recording medium with a light beam having a pulse width set in accordance with this code, when forming an image on the recording medium at a pitch smaller than the mechanical sub-scanning pitch, Means for creating a pulse width of the light beam to be output from an image pattern having the same on-pixel density, and outputting a plurality of test patterns having different relative positions with respect to the detection matrix, Means for setting the formed test patterns having the same on-pixel density to have the same density.

The second means records a light beam having a beam diameter defined by a value such that the light intensity is 1 / e ² with respect to the light intensity at the beam center at a sub-scanning pitch smaller than the beam diameter. In an image forming apparatus for forming an image on a recording medium by scanning on a medium, a means for generating a plurality of classes of codes by a detection matrix from image data to be formed, and corresponding to the plurality of classes of codes. By scanning the recording medium with a light beam having a pulse width that has been set as described above, when forming an image on the recording medium at a pitch smaller than the mechanical sub-scanning pitch, the plurality of classes of codes The pulse width of the corresponding output light beam is
For at least three of the classes to be set, means for creating from an image pattern having the same on-pixel density, and outputting a plurality of test patterns having different relative positions with respect to the detection matrix, forming the same on-pixel density Set so that the density of the test pattern is the same,
The pulse widths corresponding to the remaining classes are provided with means for interpolating from the pulse width values for the predetermined classes.

A third means is the second means, wherein the means for interpolating and determining sets the pulse width determined by the interpolation as a temporary value, and uses the temporary value as an initial value, and A plurality of image patterns having different densities relative to the detection matrix are output, and the test patterns formed with the same on-pixel density are set to have the same density.

A fourth means according to the first to third means, wherein a plurality of density detectors for measuring the light reflectance of the recording medium surface are provided, and a plurality of test patterns having different relative positions with respect to the detection matrix are provided on the recording medium surface. It is characterized by further comprising means for measuring the density of the plurality of test patterns formed thereon and by the density detection unit.

A fifth means is the first to third means, further comprising means for setting a pulse width corresponding to the code when the power of the image forming apparatus is turned on from off. It is characterized by the following.

The sixth means records a light beam having a beam diameter defined by a value such that the light intensity is 1 / e ² with respect to the light intensity at the beam center at a sub-scanning pitch smaller than the beam diameter. In an image forming method for forming an image on a recording medium by scanning on a medium, a step of generating a code by a detection matrix from image data to be formed, and a step of generating a pulse width corresponding to the code. When an image is formed on a recording medium at a pitch smaller than the mechanical sub-scanning pitch by scanning the recording medium with a light beam, the pulse width of the light beam output corresponding to the code is set to the same ON pixel. A step of generating a plurality of test patterns having different positions relative to the detection matrix, and a step of outputting a plurality of test patterns having different relative positions with respect to the detection matrix. Setting the concentration of the turns to be the same.

The seventh means records a light beam having a beam diameter defined by a value such that the light intensity is 1 / e ² with respect to the light intensity at the beam center at a sub-scanning pitch smaller than the beam diameter. In an image forming method of forming an image on a recording medium by scanning on a medium, a step of generating a plurality of classes of codes by a detection matrix from image data to be formed, and corresponding to the plurality of classes of codes. By scanning the recording medium with a light beam having a pulse width that has been set as described above, when forming an image on the recording medium at a pitch smaller than the mechanical sub-scanning pitch, the plurality of classes of codes The pulse width of the corresponding output light beam is
For at least three classes among the number of classes to be set, a step of creating from an image pattern having the same on-pixel density, a step of outputting a plurality of test patterns having different positions relative to the detection matrix, A step of setting the density of the test pattern of the density to be the same, and a step of interpolating and determining a pulse width corresponding to the remaining classes from the value of the pulse width for the already determined class. I do.

An eighth means according to the sixth or seventh means, wherein a plurality of density detectors for measuring the light reflectance of the recording medium surface are provided, and a plurality of test patterns having different relative positions with respect to the detection matrix are provided on the recording medium surface. The method further includes the step of measuring the density of the plurality of test patterns formed on the test pattern with a density detection unit.

The ninth means in the sixth or seventh means further comprises the step of setting the pulse width corresponding to the code when the power supply of the image forming apparatus is turned on from off. It is characterized by the following.

[0021]

Embodiments of the present invention will be described below in detail with reference to the drawings.

<First Embodiment> FIG. 1 shows a first embodiment of the present invention.
FIG. 2 is a block diagram illustrating a configuration of an image forming apparatus according to an exemplary embodiment.

The image forming apparatus according to the first embodiment differs from the conventional write signal processing section shown in FIG. 16 in that a polygon mirror 7, a lens 8, a photosensitive drum 9, and a synchronous The image forming apparatus is further provided with a detector 10 and a memory control circuit 11. In addition, a line memory 1, a pattern detection processing circuit 2, an LUT (lookup table) circuit 3, a PWM
(Pulse width modulation) circuit 4, LD (laser diode) driver 5, and LD (laser diode) 6 related to the writing process are configured in the same manner as in the above-described conventional example, and thus redundant description is omitted.

In the image forming apparatus according to the first embodiment configured as described above, the beam emitted from the LD 6 is scanned in the main scanning direction by the polygon mirror 7 rotating at a constant speed, and is passed through the lens 8 to the photosensitive drum. Images are formed on nine surfaces. Thereafter, the image is output to a transfer material on which the image has been transferred through a known image forming process.

The synchronization detector 10 has a photoelectric conversion element and a signal waveform shaping circuit, detects a beam, and sends a detection signal to the memory control circuit 11 as a synchronization detection signal. The memory control circuit 11 controls the line memory 1 based on the synchronization detection signal.
Output the image data to the pattern detection processing circuit 2. The pattern detection processing circuit 2 includes two consecutive image data of 1200 dpi in the main scanning direction to be recorded.
The on / off information of the dots, the four dots above and below them, and a total of six dots is referred to. The main 2 × sub 3 matrix to be referred to is the above-described pattern detection matrix. Then, a code corresponding to this pattern is sent to the LUT circuit 3. The LUT circuit 3 sends a preset pulse width and pulse position signal to the PWM circuit 4 corresponding to the code sent from the pattern detection processing circuit 2.

The PWM circuit 4 sends a PWM signal to the LD driver 5 based on the received pulse width and pulse position signal. The PWM signal is a video clock signal (600 dp
(frequency of i). Here, P
As a WM circuit 4, within a write cycle of 600 dpi,
Set the pulse width and pulse start position to 書 き 込 み of the write cycle
Description will be made using a device capable of outputting a pulse signal set at 56 resolution. The LD driver 5 supplies a drive current to the LD 6 when receiving the “ON” signal and an offset current when receiving the “OFF” signal. The LD 6 is turned on by the drive current, emits a laser in synchronization with the rotation of the polygon mirror 7, and the laser beam reflected by the polygon mirror 7 and scanned at a constant angular velocity is converted by the lens 8 into a constant-speed deflection. Scan on the drum 9.

FIG. 2 shows codes generated by the pattern detection processing circuit 2 in accordance with the on / off information of the image data.
In the figure, the width code c is obtained from the detection results for each of the three dots in the left and right columns of the pattern detection matrix, by the following equations 1 to 3.
Determined by 4.

[0028]

(Equation 1) In Equations 2 and 3, li and ri represent on / off information of image data corresponding to the left and right columns of the pattern detection matrix, respectively (1 for on, 0 for off). The subscript i indicates the position in the vertical direction in the matrix (0, 1, 2 from the top). The pulse width W corresponding to the width code c is set in the LUT.

The pulse start position S in the write cycle is
It is determined by the following equation (5).

[0030]

(Equation 2) Here, P is the maximum class value (1) of the resolution in the writing cycle.
255) in the case of / 256 resolution. K is determined by the following equation (6).

[0031]

(Equation 3) When the pulse width W for the width code c is set as shown in FIG. 3, the pulse start position S is as shown in FIG.

FIGS. 5 to 10 show examples of test patterns output for setting the pulse width W corresponding to the width code c. FIG. 5 shows a 2-dot vertical line, FIG. 6 shows a 1-dot horizontal line, FIG. 7 shows a 3-dot horizontal line, and FIG.
9 shows an example of a horizontal 2-dot halftone, FIG. 9 shows an example of a 3-dot L-type halftone, and FIG. 10 shows an example of a 5-dot L-type halftone. The test patterns shown here have the same on-pixel density but have different width codes generated by the pattern detection processing circuit because they have different relative positions with respect to the pattern detection matrix. The patterns shown in FIGS. 5 to 10 are a part of the test pattern, and the size of the actually output pattern is 20 mm × 20 mm.

The procedure for setting the pulse width W is shown in the flowchart of FIG. W [0] to W [8] in the drawing represent W corresponding to the width codes c = 0 to 8. In the flowchart shown in FIG. 11, the processing from step S1 to step S25 is executed.

Step S1: The pulse width W corresponding to the width code c = 0 to 8 is set. This pulse width W [0] to W
[8] is a default value. Step S2: Output a solid black pattern. Step S3: Check whether the density of the solid black portion is appropriate. In this check, the image output on the transfer material is visually evaluated. Note that the following concentration check step employs the same evaluation method. If it is determined in this evaluation that it is not appropriate, the process proceeds to step S4, and if it is determined that it is appropriate, the process proceeds to step S5.

Step S4: The setting of the pulse width W [8] is changed, and the process returns to step S2 to execute the subsequent processes. Step S5: Output the 2-dot-width vertical line shown in FIG. Step S6: It is checked whether or not the output densities of the two-dot-width vertical lines (A) and (B) in FIG. 5 are the same.
If it is determined in this check that they are not the same, the process proceeds to step S7, and if it is determined that they are the same, the process proceeds to step S8. Step S7: The setting of the pulse width W [4] is changed, and the process returns to step S5 to execute the subsequent processes. Step S8: The one-dot-width horizontal line shown in FIG. 6 is output. Step S9: It is checked whether or not the output horizontal lines (A) and (B) each having one dot width in FIG. 6 have the same density.
If it is determined in this check that they are not the same, the process proceeds to step S10, and if it is determined that they are the same, the process proceeds to step S1.
Proceed to 1.

Step S10: The setting of the pulse width W [2] is changed, and the process returns to step S8 to execute the subsequent processes. Step S11: Output a 3-dot-width horizontal line shown in FIG. Step S12: It is checked whether or not the density of the output horizontal lines (A) and (B) having a width of three dots in FIG. 7 is the same. If it is determined in this check that they are not the same, the process proceeds to step S13, and if it is determined that they are the same, the process proceeds to step S14. Step S13: The setting of the pulse width W [6] is changed, and the process returns to step S11 to execute the subsequent processes. Step S14: Output the horizontal 2-dot halftone dot of FIG. Step S15: It is checked whether or not the outputted two-dot halftone dots (A) and (B) in FIG. 8 have the same density. If it is determined in this check that they are not the same, step S
If it is determined that they are the same, step S17
Proceed to.

Step S16: The setting of the pulse width W [1] is changed, and the process returns to step S14 to execute the subsequent processes. Step S17: Output the 3-dot L-shaped halftone dot of FIG. Step S18: It is checked whether or not the output three-dot L-shaped halftone dots (A) and (B) in FIG. 9 have the same density. If it is determined in this check that they are not the same, step S
If it is determined that they are the same, step S20
Proceed to. Step S19: The setting of the pulse width W [5] is changed, and the process returns to step S17 to execute the subsequent processes. Step S20: Output the 3-dot L-shaped halftone dot of FIG. Step S21: It is checked whether or not the densities of the outputted 3-dot L-shaped halftone dots (A) and (C) in FIG. 9 are the same. If it is determined in this check that they are not the same, step S
If it is determined that they are the same, the process proceeds to step S23.
Proceed to.

Step S22: The setting of the pulse width W [3] is changed, and the process returns to step S20 to execute the subsequent processes. Step S23: Output the 5-dot L-shaped halftone dot of FIG. Step S24: It is checked whether or not the densities of the outputted 5-dot L-shaped halftone dots (A) and (B) in FIG. 10 are the same. If it is determined in this check that they are not the same, step S
If the same, the process ends. Step S25: Change the setting of the pulse width W [7], return to the processing of step S20, and execute the subsequent processing. When the density becomes the same in step S24, the processing ends.

As described above, using the LUT in which the pulse width corresponding to the width code c is set according to this procedure,
An image including all of the test patterns of FIGS. 5 to 10 and a gray scale composed of a halftone dot pattern in which the ON pixel density continuously changes was output to a transfer material, and evaluated visually. As a result, the following results were obtained.

The density of the solid black portion is appropriate. The density of the 1-dot horizontal lines (A) and (B) is the same.・ Grayscale density changes are continuous. -The density of the 2-dot vertical lines (A) and (B) is the same. -The density of the 3-dot width horizontal lines (A) and (B) is the same. -The density of horizontal 2-dot halftone dots (A) and (B) is the same. -The density of 3dot L type halftone dots (A), (B) and (C) is the same. -The density of 5 dot L type halftone dots (A) and (B) are the same. Note that this result is obtained by repeating the process of changing the pulse width and comparing the densities again when the densities are different, by repeating the LU.
Since T is created, it is a matter of course that other conditions do not change, and a stable output result can be obtained.

<Second Embodiment> FIG. 12 shows the configuration of an image forming apparatus according to a second embodiment. This embodiment is different from the first embodiment shown in FIG. 4 in that first and second density detectors 12 for measuring the light reflectance of the surface of the photosensitive drum 9 are provided.
13 and a comparator 14 for comparing the outputs from the density detectors 11 and 13. The other components are configured in the same manner as in the first embodiment described above, and thus redundant description will be omitted.

In the second embodiment thus constructed, a pair of test latent images having the same density should be formed in the measurement areas of the density detectors 12 and 13 so that toner is adhered. Then, the light reflectance of the toner-attached portion is measured by the density detectors 12 and 13, the measurement results are sequentially compared by the comparator 14, and the comparison result is sent to the controller of the image forming apparatus main body. With this configuration, the density comparison determination portion in the flowchart of FIG. 11 in the first embodiment can be implemented by hardware. FIG.
The LUT setting procedure according to the flowchart of 1 can be automated by control software of the image forming apparatus main body.

Other parts not specifically described are the same as those of the first embodiment.
And functions similarly.

<Third Embodiment> FIG. 13 is a flowchart showing the procedure for setting the pulse width W of the image forming apparatus according to the third embodiment. In addition, this 3rd embodiment is:
Only the procedure shown in the flowchart of FIG. 13 differs from that of the first embodiment described above.
Since the test patterns shown in FIG. 10 are the same as those in FIG.

In FIG. 13, W [0] to W [8]
Represents W corresponding to the width code c = 0 to 8.
W [0] corresponds to a case where all the image data in the matrix is off. However, if an optical pulse is output at this time, an unnecessary image may be drawn on a white background of the image, that is, a so-called background stain may occur. , W [0] = 0.

In the flowchart shown in FIG. 13, the processing from step S31 to step S41 is executed.

Step S31: The pulse width W corresponding to the width code c = 0 to 8 is set. This pulse width W [0]-
W [8] becomes the fault value. Step S32: Output a solid black pattern. Step S33: Check whether the density of the solid black portion is appropriate. If it is determined in this check that it is not appropriate, the process proceeds to step S34, and if it is determined that it is appropriate, step S35 is performed.
To each step.

Step S34: The setting of the pulse width W [8] is changed, and the process returns to step S32 to execute the subsequent processes. Step S35: Output the 2-dot-width vertical line in FIG. Step S36: It is checked whether or not the output densities of the two-dot-width vertical lines (A) and (B) in FIG. 5 are the same. If it is determined in this check that they are not the same, the process proceeds to step S37, and if it is determined that they are the same, the process proceeds to step S38. Step S37: The setting of the pulse width W [4] is changed, and the process returns to step S35 to execute the subsequent processes. Step S38: The one-dot-width horizontal line of FIG. 6 is output. Step S39: It is checked whether or not the output horizontal lines (A) and (B) of one dot width in FIG. 6 have the same density. If it is determined in this check that they are not the same, the process proceeds to step S40, and if it is determined that they are the same, the process proceeds to step S41.

Step S40: The setting of the pulse width W [2] is changed, and the process returns to step S38 to execute the subsequent processes. Step S41: Set pulse width W [8], W
From [4], W [0], W [7], W
[6], W [5], W [3], W [1] are determined.

Using the LUT in which the pulse width corresponding to the width code c is set in accordance with this procedure, all the test patterns shown in FIG. 5 and the gray scale made up of the halftone dot pattern in which the ON pixel density changes continuously. The image containing the image was output to a transfer material and visually evaluated. The density of the solid black area was appropriate. -The density of the 1 dot width horizontal lines (A) and (B) is the same. -Gray scale density changes are continuous. -The density of the 2-dot width vertical lines (A) and (B) is the same. -The density of the 3-dot width horizontal lines (A) and (B) is the same. -The density of horizontal 2 dot halftone dots (A) and (B) is the same. 3dot L-shaped halftone dots (A), (B) and (C) have the same density. -The density of 5dot L-shaped halftone dots (A) and (B) is the same. Met.

The same setting of the pulse width W as in the first embodiment is performed according to the procedure shown in the flowchart of FIG. 11, and the LU in which the pulse width corresponding to the width code c is set is set.
Using T, an image including all of the test patterns in FIG. 5 and a gray scale composed of a halftone dot pattern in which the ON pixel density continuously changes is output to the transfer material, and the result of the visual evaluation is as follows. 3 was equivalent to the third embodiment.

When the procedure shown in the flowchart of FIG. 13 is implemented by hardware, the procedure is the same as that of the second embodiment. The LUT setting procedure according to the flowchart can be automated by control software of the image forming apparatus main body.

<Fourth Embodiment> The processing procedure according to this embodiment is shown in the flowchart of FIG. In this embodiment, once determined LUT (pulse width corresponding to code)
In the case where is continuously used, the image formed at the sub-scanning position and the image formed at the intermediate position between the two sub-scannings are different from each other due to the temporal change in the characteristics of the photosensitive drum and the decrease in the light amount due to the temporal deterioration of the LD. For example, the density differs depending on the image density, but the LUT is set every time the power of the image forming apparatus is turned on, so that the density does not differ.

That is, in this processing, when the power is turned on (step S51), a process for image formation is set (step S52), and then an LUT is set (step S53). Then, the standby state is established in this state (step S54). Thus, the LUT is set each time the power of the image forming apparatus is turned on, so that there is no difference in density.

Other parts which are not particularly described are the same as those described in the first embodiment.
And it is comprised equivalently to 3rd Embodiment and functions similarly.

<Fifth Embodiment> In the third embodiment, at least three of the classes to be set have the same on-pixel density and different positions relative to the pattern detection matrix. By outputting the test patterns, setting the pulse width corresponding to the code so that their densities are the same, and for the remaining classes, using the already determined class values, determine them by interpolation. The pulse width setting procedure has been simplified.

However, if the LUT is set by simplifying the pulse width setting procedure in such a procedure, a problem may occur in the output image. For example, in an image forming apparatus using a photoconductor having a certain exposure amount-output image density characteristic, an LUT is set by the method of the third embodiment,
When a test pattern image is output, an image using a photoreceptor with the same on-pixel density and the same density of a test pattern with a different position relative to the pattern detection matrix, but with different exposure-to-output image density characteristics In the forming apparatus, a phenomenon in which the density differs between test patterns having the same on-pixel density and having a different relative position with respect to the pattern detection matrix has occurred. It is considered that the value of the pulse width determined by interpolation using the previously determined class value was not appropriate.

Therefore, in the fifth embodiment, even if the code generated by the pattern detection processing circuit differs depending on the positional relationship between the image pattern and the pattern detection matrix, an image output consisting of the same set of halftone patterns is obtained. The pulse width corresponding to the code generated by the pattern detection processing circuit can be set efficiently so that the densities are the same.

The procedure for setting the pulse width W according to the fifth embodiment is shown in the flowchart of FIG. W in the figure
[0] to W [8] are W corresponding to width codes c = 0 to 8
Is represented. W [0] corresponds to a case where all the image data in the matrix is off. However, if an optical pulse is output at this time, an unnecessary image may be drawn on a white background of the image, that is, a so-called background stain may occur. , W [0] = 0.

This embodiment is a step subsequent to step S9 of the third embodiment shown in FIG.
Step S26 has been inserted in the previous stage of FIG. In step S26, if the densities of the one-dot-width horizontal lines (A) and (B) are the same in step S26: step S9, W
The initial values of the pulse widths used for the density comparison of [1], W [3], W [5], W [6], W [7] are set to W [2], W [4], W Determined by interpolation from [8]. In step S11, a three-dot-width horizontal line is output based on the initial value of the pulse width determined in this process. In addition, steps S1 and S2
The processing of No. 5 is the same as that of the first embodiment.

Using an LUT in which a pulse width corresponding to the width code c is set in accordance with this procedure, all the test patterns shown in FIGS. 5 to 10 and a gray pattern consisting of a halftone dot pattern in which the ON pixel density changes continuously. The image including the scale was output to the transfer material and visually evaluated.-The density of the solid black portion was appropriate. -The density of the 1 dot width horizontal lines (A) and (B) is the same. -Gray scale density changes are continuous. -The density of the 2-dot width vertical lines (A) and (B) is the same. -The density of the 3-dot width horizontal lines (A) and (B) is the same. -The density of horizontal 2 dot halftone dots (A) and (B) is the same. 3dot L-shaped halftone dots (A), (B) and (C) have the same density. -The density of 5dot L-shaped halftone dots (A) and (B) is the same. Met.

The method according to the present embodiment employs W [1], W [1]
[3], the initial value of the pulse width used when comparing the density of W [5], W [6], and W [7] is set to W [2],
Since the values are determined by interpolation from W [4] and W [8], W [1], W [1] and W [8] are different from those in the method of the first embodiment.
The number of repetitions of the density comparison work for determining the pulse widths of [3], W [5], W [6], and W [7] is small and efficient.

On the other hand, the setting of the pulse width W similar to that of the fifth embodiment was performed according to the procedure shown in the flowchart of FIG. 13 according to the third embodiment, and the pulse width corresponding to the width code c was set. Using the LUT, an image containing all of the test patterns of FIGS. 5 to 10 and a gray scale composed of a halftone dot pattern in which the ON pixel density continuously changes was output to a transfer material, and the result of visual evaluation・ The density of solid black area is appropriate. -The density of the 1 dot width horizontal lines (A) and (B) is the same. -Gray scale density changes are continuous. -The density of the 2-dot width vertical lines (A) and (B) is the same. The density of the 3-dot width horizontal lines (A) and (B) is (A)
> (B). -The density of horizontal 2 dot halftone dots (A) and (B) is (A)>
(B). -The density of 3dot L-shaped halftone dots (A), (B) and (C) is (A)> (B) = (C). -The density of 5dot L-shaped halftone dots (A) and (B) is the same. Met.

As in the image forming apparatus according to the second embodiment shown in FIG. 12, the density detector for measuring the light reflectance of the surface of the photosensitive drum 9 is composed of the first and second density detectors. Two density detectors 12 and 13 are provided.
Forming an electrostatic latent image of a pair of test patterns having the same density in the measurement area, applying toner, and measuring the light reflectance of the toner-attached portion by the density detectors 12 and 13;
It is also possible to sequentially compare the measurement results and send the comparison results to the image forming apparatus main body control unit. With this configuration, the density comparison determination portion in the flowchart of FIG. 15 can be implemented by hardware, and the LUT setting procedure according to the flowchart can be automated by the control software of the image forming apparatus main body.

As shown in the flow chart of FIG. 14, when the LUT (pulse width corresponding to the code) once determined is continuously used, the image formed at the sub-scanning position and the two sub-scanning The image formed at the intermediate position differs in density due to a change in the characteristics of the photosensitive drum with time and a decrease in the amount of light due to the aging of the LD, but the LUT is reset each time the image forming apparatus is turned on. By setting, there is no difference in density.

The other parts which are not particularly described are constituted in the same manner as in the above-described first, second and third embodiments, so that duplicate explanations will be omitted.

[0067]

As is apparent from the above description, according to the first and fifth aspects of the present invention, a plurality of test patterns having the same on-pixel density and having different relative positions with respect to the pattern detection matrix are output. Since the pulse widths corresponding to the codes are set so that their densities are the same, even if an image is output with the same halftone pattern but a different position relative to the pattern detection matrix, the pattern detection processing circuit There is no difference in density due to the difference in the code generated by.

According to the second and sixth aspects of the present invention, at least three of the classes to be set have the same on-pixel density and a plurality of tests having different relative positions with respect to the pattern detection matrix. The patterns were output, the pulse widths corresponding to the codes were set so that their densities would be the same, and the remaining classes were determined by interpolation using the previously determined class values. Even when an image having a point pattern and a relative position different from the pattern detection matrix is output, a difference in density due to a difference in a code generated by the pattern detection processing circuit does not occur.

According to the third aspect of the present invention, since the density comparison is performed by using the already determined class value and the value determined by interpolation as the initial value, the number of times of the density comparison work is reduced and the efficiency is reduced. An output result with a stable density can be obtained.

According to the fourth aspect of the present invention, a test pattern having the same density is formed at a plurality of positions, and the density of the test pattern is measured and compared. It can be implemented in hardware.

According to the seventh aspect of the present invention, the pulse width of the light beam output corresponding to the codes of a plurality of classes is set to the same on-pixel for at least three of the classes to be set. Created from density image patterns,
A plurality of test patterns having different relative positions with respect to the detection matrix are output, and the density of the formed test pattern having the same on-pixel density is set so as to be the same. Since the corresponding pulse width is interpolated and determined, even if an image with the same dot pattern and a different relative position to the pattern detection matrix is output, a difference in density occurs due to a difference in the code generated by the pattern detection processing circuit. There is no.

According to the present invention, the density of the test pattern is measured by the density detector as the amount of decrease in the reflectivity of the photoreceptor surface due to the toner attached to the photoreceptor drum surface. Procedures can be automated.

Further, according to the ninth aspect of the present invention, L
Since the UT setting is performed every time the power supply of the image forming apparatus is turned on, an image formed at the sub-scanning position due to a change in the characteristics of the photosensitive drum with time or a decrease in the amount of light due to the deterioration of the LD with time is used. There is no density difference from the image formed at the middle position of the scanning.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an example of a pattern detection processing circuit generation code used in the embodiment of the present invention.

FIG. 3 is a diagram showing a setting example of an LUT used in the embodiment of the present invention.

FIG. 4 shows a pulse start position S used in the embodiment of the present invention.
It is a figure showing the example of setting of.

FIG. 5 is a diagram showing an example of an image pattern and a width code of a 2-dot width vertical line used in the embodiment of the present invention.

FIG. 6 is a diagram showing an example of an image pattern and a width code of a 1-dot width horizontal line used in the embodiment of the present invention.

FIG. 7 is a diagram illustrating an example of an image pattern and a width code of a 3-dot width horizontal line used in the embodiment of the present invention.

FIG. 8 is a diagram illustrating an example of an image pattern and a width code of a horizontal 2 dot halftone dot used in the embodiment of the present invention.

FIG. 9 is a diagram showing an example of an image pattern and a width code of a 3-dot L-shaped halftone dot used in the embodiment of the present invention.

FIG. 10 shows a 5-dot L used in an embodiment of the present invention.
It is a figure which shows the example of the image pattern of a halftone dot, and a width code.

FIG. 11 is a flowchart illustrating a processing procedure of the image forming apparatus according to the first embodiment of the present invention.

FIG. 12 is a block diagram illustrating a configuration of an image forming apparatus according to a second embodiment of the present invention.

FIG. 13 is a flowchart illustrating a processing procedure of the image forming apparatus according to the third embodiment of the present invention.

FIG. 14 is a flowchart illustrating a processing procedure of an image forming apparatus according to a fourth embodiment of the present invention.

FIG. 15 is a flowchart illustrating a processing procedure of an image forming apparatus according to a fifth embodiment of the present invention.

FIG. 16 is a block diagram illustrating a configuration of a write signal processing unit of an image forming apparatus that has been conventionally implemented.

FIG. 17 is a diagram showing an example of conventionally used image data and a pattern detection matrix.

FIG. 18 is a diagram illustrating an example of a conventionally used halftone dot pattern image.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Line memory 2 Pattern detection circuit 3 LUT circuit 4 PWM circuit 5 LD driver 6 LD 7 Polygon mirror 8 Lens 9 Photoconductor drum 10 Synchronization detector 11 Memory control circuit 12, 13 Density detector 14 Comparator

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) H04N 1/405 H04N 1/40 B 5C077 F term (Reference) 2C362 CA04 CA09 CA13 2H027 DA10 DB01 DE02 EA02 EB01 EC03 EC07 EC11 ED04 EF01 5B057 AA11 CA02 CA08 CA12 CA16 CB02 CB08 CB12 CB16 CC01 CE13 CH07 CH08 5C072 AA03 BA15 HA02 HA13 UA17 XA05 5C074 AA05 BB03 BB26 CC22 DD05 DD07 EE11 FF05 5C077 LL04 MM27 NN17 PQ12 P023

Claims (9)

[Claims] 1. A light beam having a beam diameter defined by a value such that the light intensity is 1 / e ² with respect to the light intensity at the beam center is scanned on a recording medium at a sub-scanning pitch smaller than the beam diameter. In the image forming apparatus for forming an image on a recording medium, means for generating a code from the image data to be formed by a detection matrix, and recording with a light beam having a pulse width set corresponding to the code When an image is formed on a recording medium at a pitch smaller than the mechanical sub-scanning pitch by scanning the medium, the pulse width of the light beam output corresponding to the code is changed to an image pattern having the same on-pixel density. A plurality of test patterns having different relative positions with respect to the detection matrix, and the density of the formed test pattern having the same on-pixel density is An image forming apparatus characterized by comprising means for setting to Flip become, the. 2. A light beam having a beam diameter defined by a value such that the light intensity is 1 / e ² with respect to the light intensity at the beam center is scanned on the recording medium at a sub-scanning pitch smaller than the beam diameter. In the image forming apparatus for forming an image on a recording medium, means for generating a plurality of classes of codes from the image data to be formed by a detection matrix, and setting each of the plurality of classes corresponding to the plurality of classes of codes. By scanning the recording medium with a light beam having a pulse width that has been set, when an image is formed on the recording medium at a pitch smaller than the mechanical sub-scanning pitch, output corresponding to the plurality of classes of codes is performed. Means for generating a pulse width of a light beam to be formed from image patterns having the same on-pixel density for at least three of the classes to be set; A plurality of test patterns having different relative positions are output, and the formed test patterns having the same on-pixel density are set so that the densities thereof are the same. The pulse widths corresponding to the remaining classes are pulse widths corresponding to the predetermined classes. Means for interpolating and determining from the value of the width. 3. The image pattern having the same on-pixel density, wherein the interpolating and determining means determines the pulse width determined by the interpolation as a temporary value, and sets the temporary value as an initial value. 3. The image forming apparatus according to claim 2, wherein a plurality of test patterns having different relative positions with respect to are output and the densities of the formed test patterns having the same on-pixel density are set to be the same. 4. A plurality of density detectors for measuring the light reflectance of the recording medium surface, a plurality of test patterns having different positions relative to the detection matrix are formed on the recording medium surface, and the plurality of test patterns formed are formed. The image forming apparatus according to claim 1, further comprising a unit configured to measure a density by a density detection unit. 5. The image processing apparatus according to claim 1, further comprising a unit configured to set a pulse width corresponding to the code when the power of the image forming apparatus is turned on from off.
The image forming apparatus according to any one of claims 1 to 3. 6. A light beam having a beam diameter defined by a value such that the light intensity is 1 / e ² with respect to the light intensity at the beam center is scanned on the recording medium at a sub-scanning pitch smaller than the beam diameter. In the image forming method for forming an image on a recording medium, a code is generated from image data to be formed by a detection matrix, and recording is performed with a light beam having a pulse width set corresponding to the code. When an image is formed on a recording medium at a pitch smaller than the mechanical sub-scanning pitch by scanning the medium, the pulse width of the light beam output corresponding to the code is changed to an image pattern having the same on-pixel density. And outputting a plurality of test patterns having different relative positions with respect to the detection matrix. There the image forming method characterized in that it and a step of setting to be the same. 7. A recording medium is scanned with a light beam having a beam diameter defined by a value such that the light intensity is 1 / e ² with respect to the light intensity at the center of the beam at a sub-scanning pitch smaller than the beam diameter. In the image forming method for forming an image on a recording medium, a plurality of classes of codes are generated from image data to be formed by a detection matrix, and each of the plurality of classes of codes is set in accordance with the plurality of classes of codes. By scanning the recording medium with a light beam having a pulse width that has been set, when an image is formed on the recording medium at a pitch smaller than the mechanical sub-scanning pitch, output corresponding to the plurality of classes of codes is performed. Generating a pulse width of a light beam to be formed from image patterns having the same on-pixel density for at least three of the classes to be set; A step of outputting a plurality of test patterns having different pairs of positions, a step of setting the formed test patterns having the same on-pixel density so that the densities thereof are the same, and a step of outputting the remaining classes from the pulse width value for the predetermined class. A step of interpolating and determining a pulse width corresponding to the image forming method. 8. A plurality of density detectors for measuring light reflectance of a recording medium surface, a plurality of test patterns having different relative positions with respect to a detection matrix are formed on the recording medium surface, and the plurality of test patterns formed are formed. The image forming method according to claim 6, further comprising a step of measuring the density by a density detection unit. 9. The method according to claim 6, further comprising the step of setting a pulse width corresponding to the code when the power of the image forming apparatus is turned on from off.
Or the image forming method according to 7.