JPH04227370A - Image forming device - Google Patents

Abstract

PURPOSE:To realize a high definition picture and also to realize a stable high definition heat tone picture by solving problems in the pulse width modulation system and in the light intensity modulation so ad to employ a laser printer resulting from the combination of the laser scanning technology and the electrophotographic technology. CONSTITUTION:The image forming device is provided with a 1st means 11 setting a pulse width not causing 100% of the exposure time corresponding to a minimum picture element to be recorded and varying the exposed light quantity according to each inputted picture element information, a 2nd means 10 converting the inputted picture element information into picture element information of predetermined MXN sets of patterns based on the MXN sets of picture element information inputted as above, and a 3rd means (selection calculation means) selecting the 1st or 2nd means according to the picture information inputted as above.

Description

[Detailed description of the invention]

0001

TECHNICAL FIELD The present invention relates to an image forming apparatus, more specifically,
Regarding laser printers, the present invention is suitable for application to, for example, digital copying machines, digital color copying machines, and the like.

0002

[Prior Art] Laser printers, which combine electrophotographic technology and laser scanning technology, can use plain paper and produce high-quality images at high speed, so they have rapidly become popular as computer output devices or digital copying machines. I've been doing it. In order to obtain even higher quality images under these conditions,
An effective method is a recording method that achieves both resolution and gradation using a one-dot multi-value recording method.

Multilevel recording methods can be broadly divided into semiconductor laser light intensity modulation methods and pulse width modulation methods.The pulse width modulation method is close to binary recording and is relatively stable against external fluctuation factors. Can record. However, increasing laser scanning speed (increasing write pixel clock)
As a result, the time step for changing the pulse width becomes very short. For example, if the pixel clock is 20 MHz, if you try to express 256 tones with one dot, it will be approximately 0.
2ns. This requires time increments, which poses a serious problem from the viewpoint of accuracy and cost.

On the other hand, in the method of modulating the light intensity of a semiconductor laser, since the intermediate exposure area of the photoreceptor is used, exposure energy control precision is required, but this technique uses a high-speed optical/electrical negative feedback loop. This is achieved by forming. With this control technology, the pixel clock can easily reach 20M.
256 gradations can be achieved at Hz.

However, when an image is formed by an electrophotographic process using a method of changing the light intensity of a semiconductor laser, the following problems arise. 1. There are density fluctuations due to speed fluctuations of the photoreceptor. 2. There are density fluctuations due to the tilt of the polygon. 3. Since the photoreceptor surface potential does not have a steep distribution in low density areas, dot reproduction deteriorates. 4. Image smoothness in a uniform density area is improved when gradation is reproduced using a plurality of dots, but the resolution is lower than when gradation is expressed using one dot.

Conventionally, as a method of compensating for the above-mentioned drawback 4, in an image output device that performs matrix multi-gradation recording, the size of the matrix is reduced when the spatial frequency in the information of the original image is high, and when the spatial frequency is low. A method has been proposed to increase the size of the
No. 159173), a specific implementation method of detecting the spatial frequency and switching the matrix is not presented. In addition, in both pulse width modulation and light intensity modulation modulation methods, in the currently widely used dry electrophotographic process, due to reasons such as large toner particle size,
The drawback is that minute dots smaller than a dot cannot be faithfully reproduced, resulting in a noisy image.

[0007]

[Purpose] The present invention has been made in view of the above-mentioned circumstances, and in particular solves the problems in the above-mentioned pulse width modulation method and also solves the problems in light intensity modulation. Our goal is to provide an image forming device that provides high-quality images using a laser printer that combines technology and electrophotography technology, and furthermore, to realize an image forming device that provides stable, high-quality halftone images. It has been done.

[0008]

[Structure] In order to achieve the above objects, the present invention provides (1)
a first means for setting the exposure time corresponding to the minimum pixel to be recorded to a pulse width that is not 100% and then changing the exposure light amount according to each input pixel information; and M×N of the input pixel information. a second means for converting pixel information into predetermined M×N patterns of pixel information based on the input pixel information;
and a third means for selecting the second means; and (2) in (1) above,
The light output of the driven semiconductor laser is detected by a light receiving section, and the forward current of the semiconductor laser is adjusted so that a light reception signal proportional to the light output of the semiconductor laser obtained from the light receiving section is equal to a light emission level command signal. A photoelectric negative feedback loop to be controlled, an optical output/forward current characteristic of the semiconductor laser, and a coupling coefficient between the optical receiver and the optical output of the semiconductor laser so that the optical reception signal and the emission level command signal are equal to each other. , a conversion means for converting the light emission level command signal into a forward current of the semiconductor laser based on the optical input/light reception signal characteristics of the light receiving section, and a control current of the photoelectric negative feedback loop and the conversion means or (3) means for controlling the semiconductor laser by means of the sum or difference of the current generated by the a first means for selecting one pulse width for each pixel from among the pulse widths set as the pulse width and changing the exposure light amount according to the information of each pixel; and M×N of the input pixel information. a second means for converting pixel information into predetermined M×N patterns of pixel information, and a second means for selecting the first means and the second means according to the inputted pixel information. (4) In (3) above, the optical output of the driven semiconductor laser is detected by the light receiving section;
a photoelectric negative feedback loop that controls the forward current of the semiconductor laser so that a light reception signal proportional to the optical output of the semiconductor laser obtained from the light receiving section is equal to a light emission level command signal; Based on the optical output and forward current characteristics of the semiconductor laser, the coupling coefficient between the light receiving section and the optical output of the semiconductor laser, and the optical input and light receiving signal characteristics of the light receiving section so that the light emission level command signal is equal to the light emission level command signal. converting means for converting the light emission level command signal into a forward current of the semiconductor laser; (5) The exposure time corresponding to the minimum pixel to be recorded is 1.
a first means of setting a pulse width other than 00% and then changing the exposure light amount according to each input pixel information; a second means for converting into ×N patterns of pixel information; and a second means for selecting the first means and the second means according to the differential coefficient of the inputted K×L pixel information. (6) In (5) above, the optical output of the driven semiconductor laser is detected by the light receiving section, and the optical output of the semiconductor laser obtained from the light receiving section is proportional to the optical output of the semiconductor laser obtained from the light receiving section. a photoelectric negative feedback loop that controls the forward current of the semiconductor laser so that the light reception signal and the light emission level command signal become equal; and a photoelectric negative feedback loop that controls the forward current of the semiconductor laser so that the light reception signal and the light emission level command signal become equal; Converting the light emission level command signal into a forward current of the semiconductor laser based on the output/forward current characteristics, the coupling coefficient between the light receiving section and the optical output of the semiconductor laser, and the light input/light receiving signal characteristics of the light receiving section. and means for controlling the semiconductor laser using a current that is the sum or difference between the control current of the optical/electrical negative feedback loop and the current generated by the converting means, forming a semiconductor laser control section. or (7) a first means for setting the exposure time corresponding to the minimum pixel to be recorded to a pulse width that is not 100% and then changing the exposure light amount according to each input pixel information; In an image forming apparatus that forms a matrix consisting of pixels, and records a halftone image by changing the exposure amount according to image information in matrix units, the size M in the sub-scanning direction of the matrix is 2.
As described above, the matrix size N in the main scanning direction is 1 or more, and the second means sets the exposure pattern in the matrix so that the spatial frequency in the sub-scanning direction is the highest; and (8) in (7) above, the recording light source is a semiconductor laser. The light output of the driven semiconductor laser is detected by a light receiving section, and the order of the semiconductor lasers is adjusted so that a light reception signal proportional to the light output of the semiconductor laser obtained from the light receiving section is equal to a light emission level command signal. A photoelectric negative feedback loop that controls a directional current, and optical output/forward current characteristics of the semiconductor laser and optical outputs of the light receiving section and the semiconductor laser so that the light reception signal and the light emission level command signal are equal to each other. and a conversion means for converting the light emission level command signal into a forward current of the semiconductor laser based on the coupling coefficient of the light receiving section and the light input/light receiving signal characteristics of the light receiving section, and a control current of the light/electrical negative feedback loop. and means for controlling the semiconductor laser by the sum or difference of the current generated by the converting means, or (9) 100% based on input image information. a first means for selecting one pulse width for each pixel from among a plurality of pulse widths set to different pulse widths and changing the exposure light amount according to each pixel information; M×N predetermined by M×N pixel information
a second means for converting the pixel information into K×L patterns of pixel information, and a third means for selecting the first means and the second means according to the differential coefficient of the inputted K×L pixel information. (10) In (9) above, the light output of the driven semiconductor laser is detected by the light receiving section, and the light receiving section obtains a light receiving signal proportional to the light output of the semiconductor laser. an opto-electrical negative feedback loop that controls the forward current of the semiconductor laser so that the signal and the emission level command signal are equal;
conversion of the light emission level command signal into a forward current of the semiconductor laser based on forward current characteristics, a coupling coefficient between the light receiving section and the optical output of the semiconductor laser, and light input/light receiving signal characteristics of the light receiving section; and a means for controlling the semiconductor laser using a current that is the sum or difference between the control current of the optical/electrical negative feedback loop and the current generated by the conversion means. It is characterized by Hereinafter, the present invention will be explained based on examples.

FIG. 1 is a diagram for explaining the basic operation of the present invention. In the diagram, T is the pulse width for modulating the light intensity, and d
is a pixel pitch, M is a light intensity modulation section, and the present invention is constructed using an optical writing method in which the pulse width T is not the pixel pitch d, that is, the light intensity is modulated at a pulse width that is not 100%. be.

FIG. 2 shows a pulse width of 25% (curve A), 50%
% (Curve B), 75% (Curve C), 100% (Curve D)
This is a diagram showing an example of the relationship between the relative density of one dot pixel and the unsaturated density region depending on the intermediate exposure region of the photoreceptor when using power modulation and pulse width modulation (curve E). The smaller the density ratio, the steeper the potential well formed on the photoreceptor, and the better the dot reproducibility. That is, the effect is clearly visible when the pulse width is 100% or less.

FIG. 3 is a diagram showing density fluctuations caused by speed fluctuations of the photoreceptor or writing optical system (or fluctuations in laser scanning position), where curve A1 represents power modulation, curve A2 represents power modulation with a duty of 50%, and curve A2 represents power modulation with a duty of 50%. A3 has a duty of 25%
Curve B shows pulse width modulation, and this figure also clearly shows the effectiveness of performing light intensity modulation with the pulse width of 100% or less. Furthermore, 100%
Since only one pulse width is used among the different pulse widths, it can be realized with a very simple configuration without switching the pulse width. In the above explanation, only pulse widths of 25%, 50%, 75%, and 100% have been described, but the same effect can be obtained even if the pulse width is set to a different value.

The above is a matter regarding the first means of the present invention, but in dry electrophotography, the above method alone still lacks dot reproducibility. Areas where dot reproducibility is required are areas where image density changes are gradual (low spatial frequency), and in electrophotography, dot reproducibility is particularly poor in low density areas, so can express a smooth image by using a pseudo-halftone expression method using a dot-concentrated matrix.

FIG. 4 is a diagram for explaining an example of the case where the present invention is applied to dry electrophotography. In the figure, 10 is a matrix pattern generation section, and 11 is a pulse width (not 100%) and light intensity setting. In the figure, the part that performs selection calculations either performs pseudo halftone expression using a matrix based on the input image information, or selects a preset pulse width and then changes the optical output of the semiconductor laser. By modulating it, it is possible to select whether to perform a multi-level recording method that expresses gradation using one dot. An example of a dot pattern obtained in this manner is shown in FIG. In FIG. 5, the expression gradations differ within the same pattern because the optical output intensity of the semiconductor laser is changed. In addition, in Fig. 5, the set pulse width is 50%, and since adjacent dots are combined, the pulse width appears to be 100%, but this is the exposure corresponding to the minimum pixel to be recorded. The time is 50%. Above, the pulse width is 5
It is clear that the effects of the present invention can be obtained even if the amount is not 0%.

As described above, the present invention provides a laser printer that is less susceptible to changes in the speed of the photoreceptor or changes in the laser scanning position, has good dot reproducibility, and has good exposure energy control accuracy. Therefore, it is possible to provide an image forming apparatus that can obtain high-quality images.

FIG. 6 is a diagram for explaining the operating principle of another embodiment of the present invention. In the diagram, A1, A2, and A3 are pulse widths, and B1, B2, and B3 are light intensities at each pulse width. In the modulation depth range, the pulse width is expressed as a percentage of the pixel pitch, and in FIG. 6, A1 is 25%, A2 is 50%,
A3 shows the case of 75%. As shown in FIG. 6, this embodiment is constructed by combining an optical writing method that modulates the light intensity at each pulse width for a plurality of pulse widths according to input image data. .

In FIG. 2, as mentioned above, the pulse width is set to 25%.
(A), 50% (B), 75% (C), 100% (D)
This is a diagram showing an example of the relationship between the relative density of one dot pixel and the unsaturated density region depending on the intermediate exposure region of the photoreceptor when power modulation and pulse width modulation (E) are used. The smaller the ratio, the steeper the potential well formed on the photoreceptor, and the better the dot reproducibility. However, for example, in the case of 25% (curve A), the density does not increase even if the exposure energy is increased. So, for example, from 25% (curve A) pulse width to 50%
By switching to the pulse width of (curve B) at a relative density of 0.6, it is possible to set the unsaturated concentration region to a portion where the area is smaller than when pulse width modulation (curve E) is performed. Furthermore, 75
% (curve C) at a density of 0.8, and record with this pulse width until the maximum density, the part that depends on the intermediate exposure area of the photoreceptor remains small, and the pulse width can be set again. Since the number is small, it is easy to increase the accuracy of setting the pulse width. In other words, the pulse width is 10
Even if the pulse width is not set to 0%, the pulse width that can output the maximum density may be set as the maximum pulse width. Furthermore, the control speed of the optical/electrical negative feedback loop is set to 10 ns to control the semiconductor laser.
If this is achieved at a certain level, light control accuracy can be easily achieved even when the pixel clock is 20 MHz. Further, since the density can be detected based on the value of the image data, the pulse width may be selected according to the image data.

FIG. 3 is a diagram showing density fluctuations caused by speed fluctuations of the photoreceptor or writing optical system (or fluctuations in laser scanning position), as described above, where curve A1 is power modulation and curve A2 is power modulation. Curve A3 shows power modulation with a duty of 50%, curve B shows pulse width modulation, and the effectiveness of light intensity modulation in which the pulse width is changed depending on the image density is clearly understood from this figure. Ru. In the above explanation, the pulse width is 25%, 50%, and 75%.
, only explained the 100% case,
A similar effect can be obtained even if the pulse width is set to a different value.

The above is a matter concerning the first means of the present invention, but in dry electrophotography, the above method alone still lacks dot reproducibility. Areas where dot reproducibility is required are areas where image density changes are slow (spatial frequency is low), and in electrophotography, dot reproducibility is particularly poor in low density areas, so dot concentration is required for such image areas. A smooth image can be expressed by using a pseudo halftone expression method using a type matrix.

FIG. 7 is a diagram for explaining an example of the case where the present invention is applied to dry electrophotography. In the figure, 10 is a matrix pattern generation section, 12 is a pulse width and light intensity setting section, and , the part that performs the selection calculation performs pseudo halftone expression using a matrix based on the input image information, or selects a preset pulse width and modulates the optical output of the semiconductor laser to generate one dot. Select whether to use the multi-level recording method that expresses gradations. An example of a dot pattern obtained in this manner is shown in FIG. In Figure 8, (a) and (b) are examples when performing pseudo-intermediate expression, and (c) and (d) are examples when performing one-dot multilevel recording. This is because the optical output intensity of the semiconductor laser is changed. In FIG. 8, the inversion is performed depending on whether the matrix in the main scanning direction is even or odd. Also, the pulse width set in Fig. 8 is 4
However, it is clear that the effects of the present invention can be obtained even if the number is not 4. As mentioned above, according to the present invention, it is possible to construct a laser printer that is not easily affected by speed fluctuations of the photoconductor or fluctuations in the laser scanning position, has good dot reproducibility, and has high exposure energy control accuracy, resulting in high quality. An image forming apparatus capable of obtaining images can be provided.

FIG. 9 is a diagram for explaining the operating principle of another embodiment of the present invention. In the figure, A1, A2, A3, and A4 are pulse widths, and B1, B2, B3, and B4 are respective pulse widths. In the light intensity modulation degree range in width, the pulse width is shown in % with respect to pixel bits, and in FIG. 9, A1 is 25%, A
2 indicates 50%, A3 indicates 75%, and A4 indicates 100%. Therefore, the present invention uses an optical writing method that modulates the light intensity with a pulse width that is not 100%.

In FIG. 2, as mentioned above, the pulse width is set to 25%.
(Curve A), 50% (Curve B), 75% (Curve C), 1
00% (curve D) power modulation and pulse width modulation (curve E) is a diagram showing an example of the relationship between the relative density of one dot pixel and the unsaturated density region depending on the intermediate exposure region of the photoreceptor, In this figure, the smaller the unsaturated concentration ratio, the steeper the potential well formed on the photoreceptor, and the better the dot reproducibility. That is, if the pulse width is 10
The effect is clearly visible when the amount is 0% or less.

FIG. 3 is a diagram showing a graph of density fluctuations caused by speed fluctuations of the photoreceptor or writing optical system (or fluctuations in the laser scanning position), as described above.
1 shows power modulation, curve A2 shows power modulation with a duty of 50%, curve A3 shows power modulation with a duty of 25%, and curve B shows pulse width modulation. From this figure, it can also be seen that light intensity modulation is performed when the pulse width is 100% or less. The effectiveness of doing this is clearly demonstrated. Furthermore, since only one pulse width among pulse widths other than 100% is used, the pulse width can be realized with a very simple configuration without switching the pulse width. For above, the pulse width is 25%, 50%, 75%.
, 100%, the same effect can be obtained even if the pulse width is set to a different value.

The above is a matter regarding the first means of the present invention, but in dry electrophotography, dot reproducibility is still lacking even with the above method. The areas where dot reproducibility is required are areas where image density changes are gradual (low spatial frequency), and in electrophotography, dot reproducibility is particularly poor in low density areas, so such images For the area, a smooth image can be expressed by using a pseudo halftone expression method using a dot-concentrated matrix. This method is related to the second means of the present invention, and a high-quality image can be obtained by using the first means and this second means together. Here, the switching between the first means and the second means is
This is performed according to the differential coefficients of K×L pieces of input pixel information. An embodiment configured in this manner is shown in FIG.

FIG. 10 is a diagram for explaining an example of means for switching between the first means and the second means. In the figure, 10 is a matrix pattern generating section (M×N dot pattern); is the pulse width and emission intensity setting section (1 x 1)
, 13 is a differential coefficient calculation unit, and 14 is a digital comparator.The reason why the differential coefficient is used as a switching means is that the differential coefficient is the magnitude of the density change, so it is possible to constantly detect the image density change part. 1 in areas where the concentration changes greatly, that is, areas where the differential coefficient is large.
This is because dot multi-gradation expression is performed, and pseudo-halftone expression can be performed using a matrix in an area where the density does not change much, that is, an area where the differential coefficient is small.

A specific example of this differential coefficient calculation will be explained with reference to FIGS. 11 and 12. First, Figures 11(a) and (b)
Consider 2×2 or 3×3 image information as shown in FIG. Now, let the pixel of interest be (i, j) and the pixel density be Ai, j
, the differential coefficient is f(i,j). First, as an example of calculating a differential coefficient using 2×2 pixel information, the differential coefficient f (i, j) is calculated as the average root of the sum of squares of the differential coefficients in the i and j directions, that is, f (i, j) = [(Ai-1,j-Ai,j
)2+(Ai,j-Ai,j-1)2]1/2. In addition, as an example of calculating the differential coefficient in 3×3 pixel information as shown in FIG. 11(b), FIG.
Consider a second-order differential spatial filter as shown in a) and (b). The differential coefficient f(i, j) can be calculated by applying these filters to the pixel information in FIG. 11(b) and taking the sum. Here, it is not necessary that the size of the matrix for calculating the differential coefficient and the matrix for performing pseudo halftone expression be the same. Furthermore, in the above example, the region for detecting the differential coefficient is set as a 2×2 or 3×3 matrix, but any region may be set. There are many other means than those described above, and it goes without saying that the present invention is effective even if these methods are used.

Next, a specific example of switching between the first means and the second means described above will be explained. First, input the absolute value of the previously calculated value of f(i, j) into a digital comparator to determine whether the value of f(i, j) is larger or smaller than a certain reference value, and use that output to calculate the The first and second means
Switching of methods. Here, as an example of setting this reference value, the absolute value of the value of f (i, j) is 0 to 100.
Considering the case, the reference value is set to 50. and,
If the absolute value of f (i, j) is 0 to 50, pseudo halftone expression is performed using a matrix, and if the absolute value of f (i, j) is 51 to 100, multilevel expression is performed with one dot. Performs tonal expression. Here, the reference value was set to half the absolute value of the maximum value of the differential coefficient, but this setting also involves the method of calculating the differential coefficient and various other factors, so it may be set in any way depending on the situation. . Furthermore, when switching, a certain dot in the matrix that performs pseudo-halftone expression may have to perform multi-tone expression, but in this case, any one dot in the matrix If multi-gradation expression is required, switching may be performed by making all dots in this matrix into one-dot multi-gradation expression.

Examples of dot patterns obtained in this manner are shown in FIGS. 5 and 13. In this figure, the gradations are set so that 256 gradations can be expressed in both 1-dot multi-gradation expression (Figure 13) and pseudo-halftone expression using a matrix (Figure 5), but it is not limited to 256 gradations. You may also set a gradation like this. Furthermore, in the figure, the expression gradation differs within the same pattern because the optical output intensity of the semiconductor laser is changed. Furthermore, although the pulse width set in FIG. 5 is 4, it is clear that the effects of the present invention can be obtained even if the pulse width is not 4. As described above, the present invention is less susceptible to changes in the speed of the photoreceptor or changes in the laser scanning position, has good dot reproducibility, and furthermore,
Since it is possible to configure a laser printer with high exposure energy control accuracy, it is possible to provide a specific configuration of an image forming apparatus that can obtain high-quality images.

Next, an embodiment in which the pulse width is not 100% will be described. FIG. 14 is a diagram showing the relationship between the optical output waveform (a) diagram in the conventional technology (duty 100%) and the optical output waveform (b) diagram in the present invention (duty < 100%). It is a laser beam. Normally, the recording light pulse T0 is given by T0=d/v (where d: pixel pitch=1/recording density, V: recording light scanning speed), but in the present invention, the pulse width T<
This is characterized in that recording is performed as T0.

FIG. 15 is a diagram showing the relationship between exposure amount and image density in electrophotographic recording, in which I represents an unsaturated density region;
II is the saturated density region, and the image density is divided into the unsaturated density region I, where the density increases according to the exposure amount up to the exposure amount E0, and the saturated density region II, where the density is saturated above E0, as shown in the figure. have

FIG. 16 shows the relative density of one dot pixel when the pulse width is 100% (curve A) and when it is 50% (curve B) and the unsaturated density depending on the intermediate exposure area of the photoreceptor. This is a diagram showing the relationship with the area, and in this diagram,
It can be seen that the smaller the unsaturated concentration ratio, the steeper the potential well formed on the photoreceptor, and the better the dot reproducibility. Note that FIG. 17 is a diagram showing the potential well described above. When the curve (a) is 100% duty, the curve (b) is a diagram showing the potential well.
) shows the case of the present invention.

FIG. 18 shows density fluctuations caused by speed fluctuations of the photoreceptor or writing optical system (or fluctuations in laser scanning position), and curve A shows density fluctuations caused by power modulation (duty 10).
0%), curve B is power modulation (duty 50%),
This figure also shows that the modulation pulse duty is 50% (100%).
% or less) is clearly seen. Above,
Although only pulse widths of 50% and 100% have been described, similar effects can be obtained even if the pulse width is set to a different value of T0 or less (100% or less). However, in the currently widely used dry electrophotographic process using only the above-mentioned means, due to reasons such as the large toner particle size,
Microscopic dots smaller than a dot are not faithfully reproduced, resulting in a noisy image. In electrophotography, as a method to improve this, a pseudo halftone expression method using a matrix composed of a plurality of pixels is used.

FIGS. 19 and 20 are diagrams showing embodiments of the present invention, respectively, and FIG. 19 (a) is a matrix configuration diagram;
(b) The figure shows the optical output waveform when using pulse width modulation, (
c) The figure shows the light intensity in the case of light intensity modulation (power modulation).
, is an example of 8-level halftone output (4 types of pulse widths) in the sub-scanning direction of 2 (hereinafter referred to as 1×2). 2×4) is 1
This is an example of six-level halftone output (two types of pulse widths). In both examples in FIGS. 20(b) and 20(c), the halftone level is 8.
(i.e. low-density areas), adjacent pixels in the sub-scanning direction are not exposed, and the pattern is filled in the main-scanning direction (an exposure pattern in which the spatial frequency increases in the sub-scanning direction).
Therefore, the exposure energy distribution in the sub-scanning direction on the recording medium (photoreceptor) is as shown in FIG. In such a case, even if the exposure beam has a Gaussian distribution with a wide tail, there will be no overlap with adjacent pixels, and exposure unevenness will not occur even if there are fluctuations in the feeding speed of the recording medium. Therefore, density unevenness will not occur. It is possible to obtain high-quality images with almost no occurrences. Similarly, for FIGS. 19(b) and 19(c), the halftone level is 4.
It is possible to obtain high-quality images with almost no density unevenness.

FIG. 22 is a diagram showing density fluctuations caused by speed fluctuations of the photoreceptor or writing optical system (or fluctuations in laser scanning position), where curve A is 1×1 light intensity modulation, curve B is
indicates 1×1 pulse width modulation, and curve C indicates a 1×2 matrix. As an example of a matrix size of 2 or more in the sub-scanning direction, when the matrix size is 1×2 (curve C), It is clearly shown that concentration fluctuations are reduced.

FIG. 23 shows a conventional example (matrix size 1×
1, 16-value power modulation), but in this case, since there is overlap with adjacent beams between pixels, exposure unevenness △E occurs due to fluctuations in recording medium feed speed, etc., and density It becomes uneven. more than,
Although we have explained cases where the matrix size is 2 x 4 or 1 x 2, similar effects can be obtained by using exposure patterns such as those shown in Figs. 24 and 25 in cases where the matrix size is 2 x 2 or 1 x 4. , generally, the matrix size M in the sub-scanning direction
If is 2 or more, the effects of the present invention can be obtained. The present invention is also effective when pulse width modulation and optical intensity modulation are used in combination. The above is a matter regarding the second means of the invention, and although it is true that this method improves the smoothness of the image only in the low-density area or only in the high-density area, it also improves the smoothness of the image at the boundary between the low-density area and the high-density area. Because it is written in a matrix, the resolution at the boundary is reduced. Therefore, in areas where the density changes are small, pseudo-halftone expression using the matrix is used, and in areas where the density changes greatly, switching is made to use the multi-tone expression using only one dot, which is the first means of the present invention. For example, higher resolution and higher quality images can be obtained.

[0035] Here, switching between the first means and the second means is performed in accordance with the differential coefficient of the K×L pieces of input pixel information. The above-mentioned FIG. 10 is a diagram for explaining one embodiment configured in this manner, in which 10 is a matrix pattern generation section, 12 is a pulse width and emission intensity setting section, 13 is a differential coefficient calculation section, and 14 is a The reason why a digital comparator uses a differential coefficient as a switching means is that the differential coefficient is the magnitude of the density change, so it is possible to constantly detect areas where the image density changes. In areas where the coefficient is large, one-dot multi-gradation expression can be performed, and in areas where the density does not change much, that is, areas where the differential coefficient is small, pseudo-halftone expression can be performed using a matrix.

The aforementioned FIGS. 11 and 12 are diagrams for explaining a specific example of the above-mentioned differential coefficient calculation, and similarly to the above, FIG.
Consider 2×2 or 3×3 image information as shown in 1(a) and 1(b). Now, assume that the pixel of interest is (i, j), the pixel density is Ai, j, and the differential coefficient is f(i, j). First, as an example of calculating a differential coefficient using 2×2 pixel information, the differential coefficient f(i, j) is the average root of the sum of squares of the differential coefficients in the i and j directions, that is, f(i, j) = [(Ai-1,j-Ai,j)2+
There is a method of setting (Ai, j-Ai, j-1)2]1/2. In addition, 3 as shown in FIG. 11(b)
As an example of calculating a differential coefficient in ×3 pixel information, consider a spatial filter for quadratic differential as shown in FIGS. 12(a) and 12(b). The differential coefficient f(i, j) can be calculated by applying these filters to the pixel information in FIG. 11(b) and taking the sum. Here, it is not necessary that the size of the matrix for calculating the differential coefficient and the matrix for performing pseudo halftone expression be the same. Furthermore, in the above example, the region for detecting the differential coefficient is set as a 2×2 or 3×3 matrix, but any region may be set. There are many other means than those described above, and it goes without saying that the present invention is effective even if these methods are used.

Next, a specific example of switching between the first means and the second means mentioned above will be explained. First, input the absolute value of the previously calculated value of f(i, j) into a digital comparator to determine whether the value of f(i, j) is larger or smaller than a certain reference value, and use that output to calculate the The first and second means
Switching of methods. Here, as an example of setting this reference value, the absolute value of the value of f (i, j) is 0 to 100.
Considering the case, the reference value is set to 50. and,
If the absolute value of f (i, j) is 0 to 50, pseudo halftone expression is performed using a matrix, and if the absolute value of f (i, j) is 51 to 100, multilevel expression is performed with one dot. Performs tonal expression. Here, the reference value was set to half the absolute value of the maximum value of the differential coefficient, but this setting also involves the method of calculating the differential coefficient and various other factors, so it may be set in any way depending on the situation. . Furthermore, when switching, a certain dot in the matrix that performs pseudo-halftone expression may have to perform multi-tone expression, but in this case, any one dot in the matrix If multi-gradation expression is required, switching may be performed by making all dots in this matrix into one-dot multi-gradation expression.

[0038] Furthermore, the above-mentioned invention and the above-mentioned Japanese Unexamined Patent Publication No. 57-
When compared with the invention described in Publication No. 159173,
Although the above publication does not describe a specific implementation method for detecting the spatial frequency and switching the matrix,
This is specifically shown in the present invention. Further, in the above-mentioned publication, the size of the matrix is increased or decreased, but in the present invention, the size of the matrix is switched between 1 dot (1×1) and the matrix (M×N). Further, in the above-mentioned publication, the spatial frequency is detected, but in the present invention, the differential coefficient is calculated because it is only necessary to detect areas where the density of pixel information changes significantly. As described above, the present invention makes it possible to configure a laser printer that is less susceptible to changes in the speed of the photoreceptor or changes in the laser scanning position and has good dot reproducibility, making it possible to obtain high-quality images. A concrete configuration of a possible image forming apparatus can be provided.

FIG. 9 is a diagram for explaining the operating principle of another embodiment of the present invention. In the figure, A1, A2, A3, A
4 is the pulse width, B1, B2, B3, and B4 are the light intensity modulation ranges at each pulse width, and the pulse width is expressed as a percentage of the pixel bit. In FIG. 9, A1 is 25%.
, A2 shows the case of 50%, A3 shows the case of 75%, and A4 shows the case of 100%. As shown in FIG. 9, the present invention is constructed by combining an optical writing method that modulates the light intensity at each pulse width for a plurality of pulse widths in accordance with input image data.

In FIG. 2, as mentioned above, the pulse width is set to 25%.
(Curve A), 50% (Curve B), 75% (Curve C), 1
00% (curve D) power modulation and pulse width modulation (curve E) shows an example of the relationship between the relative density of one dot pixel and the unsaturated density region depending on the intermediate exposure region of the photoreceptor, In this figure, the smaller the unsaturated concentration ratio, the steeper the potential well formed on the photoreceptor, and the better the dot reproducibility. However, for example,
In the case of 25% (curve A), the density does not increase even if the exposure energy is increased. So, for example, 25% (curve A
) to a pulse width of 50% (curve B) at a relative concentration of 0.6, it is possible to set the unsaturated concentration region to a portion with fewer regions than when pulse width modulation (curve E) is performed. Furthermore, if you switch to a pulse width of 75% (curve C) at a density of 0.8 and record with this pulse width up to the maximum density, the part that depends on the intermediate exposure area of the photoreceptor remains small, and the pulse Since the number of width settings is small, it is easy to increase the accuracy of pulse width settings. That is, the maximum pulse width may be set to a pulse width that can output the maximum density without setting the pulse width to 100%. Furthermore, the control speed of the optical/electrical negative feedback loop is set to 10 ns to control the semiconductor laser. If this is achieved at a certain level, light control accuracy can be easily achieved even when the pixel clock is 20 MHz. Furthermore, since the density can be detected from the value of the image data, the pulse width may be selected according to the image data.

As described above, FIG. 3 is a diagram showing density fluctuations caused by speed fluctuations of the photoreceptor or writing optical system (or fluctuations in laser scanning position), where curve A1 is power modulation and curve A2 is duty 50. % power modulation, curve A3
curve B shows power modulation with a duty of 25%, and curve B shows pulse width modulation. From this figure as well, the effectiveness of light intensity modulation in which the pulse width is varied depending on the image density is clearly seen. Although only cases where the pulse width is 25%, 50%, 75%, and 100% have been described above, the same effect can be obtained even if the pulse width is set to a different value.

The above is a matter regarding the first means of the present invention, but in dry electrophotography, the above method alone still lacks dot reproducibility. The areas where dot reproducibility is required are areas where image density changes are gradual (low spatial frequency), and in electrophotography, dot reproducibility is particularly poor in low density areas, so such images For the area, a smooth image can be expressed by using a pseudo halftone expression method using a dot-concentrated matrix. This method is related to the second means of the present invention, and a high-quality image can be obtained by using the first means and this second means together.

[0043] Here, switching between the first means and the second means is performed according to the differential coefficient of the K×L input pixel information. An embodiment configured in this manner is shown in FIG. FIG. 10 is a diagram for explaining an example of means for switching between the first means and the second means, as described above.
In the figure, 10 is a matrix pattern generation section (M x N dot pattern), 12 is a pulse width and emission intensity setting section (1 x
1), 13 is a differential coefficient calculation unit, and 14 is a digital comparator.The reason why the differential coefficient is used as a means for switching is that, as mentioned above, the differential coefficient is the magnitude of the density change, so the image density change part This makes it possible to constantly detect areas where the density changes greatly, that is, areas where the differential coefficient is large, and performs one-dot multi-tone expression, and in areas where the density does not change much, that is, areas where the differential coefficient is small, pseudo-halftone expression is performed using a matrix. This is because it can be done.

This differential coefficient calculation is performed as shown in FIG. 11 and FIG.
This is the same as the explanation in 2. First, consider 2×2 or 3×3 image information as shown in FIGS. 11(a) and 11(b). Now, let the pixel of interest be (i, j), the pixel density be Ai, j,
Let the differential coefficient be f(i,j). First, as an example of calculating a differential coefficient using 2×2 pixel information, the differential coefficient f
(i, j) is the average root of the sum of squares of the differential coefficients in the i, j direction,
That is, f(i,j)=[(Ai-1,j-Ai,j)2+
There is a method of setting (Ai, j-Ai, j-1)2]1/2. In addition, 3 as shown in FIG. 11(b)
As an example of calculating the differential coefficient in ×3 pixel information,
Consider a second-order differential spatial filter as shown in FIGS. 12(a) and 12(b). The differential coefficient f(i, j
) can be calculated. Here, it is not necessary that the size of the matrix for calculating the differential coefficient and the matrix for performing pseudo halftone expression be the same. Furthermore, in the above example, the region for detecting the differential coefficient is set as a 2×2 or 3×3 matrix, but any region may be set. There are many other means than those described above, and it goes without saying that the present invention is effective even if these methods are used.

Next, a specific example of switching between the first means and the second means mentioned above will be explained. First, input the absolute value of the previously calculated value of f(i, j) into a digital comparator to determine whether the value of f(i, j) is larger or smaller than a certain reference value, and use that output to calculate the The first and second means
Switching of methods. Here, as an example of setting this reference value, the absolute value of the value of f (i, j) is 0 to 100.
Considering the case, the reference value is set to 50. and,
If the absolute value of f (i, j) is 0 to 50, pseudo halftone expression is performed using a matrix, and if the absolute value of f (i, j) is 51 to 100, multilevel expression is performed with one dot. Performs tonal expression. Here, the reference value was set to half the absolute value of the maximum value of the differential coefficient, but this setting also involves the method of calculating the differential coefficient and various other factors, so it may be set in any way depending on the situation. .

Furthermore, when switching, a certain dot in the matrix that performs pseudo-halftone expression may have to perform multi-tone expression; in this case, which one dot in the matrix However, if one-dot multi-gradation expression is required, switching can be done by making all the dots in this matrix one-dot multi-gradation expression. An example of a dot pattern obtained in this manner is shown in FIG. In FIG. 26, (a1), (a2
) are the respective embodiments that perform pseudo halftone expression, (b1), (
b2) shows each example in the case of 1-dot multi-level recording, but in this figure, 1-dot multi-level recording (b1, b2)
), but the matrix allows pseudo-halftone expression (a1, a2)
Although the gradations are set so that 256 gradations can be expressed, any gradation may be set, not limited to 256 gradations. Furthermore, in the figure, the expression gradation differs within the same pattern because the optical output intensity of the semiconductor laser is changed. Furthermore, although the pulse width set in FIG. 7 is 4, it is clear that the effects of the present invention can be obtained even if the pulse width is not 4. As described above, the present invention provides a laser printer that is less susceptible to fluctuations in the speed of the photoreceptor or fluctuations in the laser scanning position, has good dot reproducibility, and has good exposure energy control accuracy. Therefore, it is possible to provide a specific configuration of an image forming apparatus that can obtain high-quality images.

Next, the operation of the light guide laser control section will be explained with reference to FIG. However, the case where a plurality of types of pulse widths are provided has already been explained, so a description thereof will be omitted. FIG. 27 is a diagram showing the configuration of the semiconductor laser control section, and the operation of the semiconductor laser control section will be described below with reference to FIG. 27. In FIG. 27, 1 is a comparison amplifier, 2 is a current converter, 3 is a semiconductor laser, and 4 is a light receiving element. As shown in the figure, a light emission level command signal is input to the comparison amplifier 1 and current converter 2, A portion of the optical output of the driving semiconductor laser 3 is monitored by the light receiving element 4. The comparison amplifier 1, the semiconductor laser 3, and the photodetector 4 form an optical/electrical negative feedback loop, and the comparison amplifier 1 is proportional to the photovoltaic current (proportional to the optical output of the semiconductor laser 3) induced in the photodetector 4. The light reception signal and the light emission level command signal are compared, and based on the result, the forward current of the semiconductor laser 3 is controlled so that the light reception signal and the light emission level indication signal are equal. The current converter 2 also generates a current that is preset according to the light emission level command signal (the optical output and forward current characteristics of the semiconductor laser 3 and the light receiving element 4 and semiconductor Coupling coefficient with laser 3,
A preset current is output based on the light input and light reception signal characteristics of the light receiving element 4. The sum of the output current of the current converter 2 and the control current output from the comparator amplifier 1 becomes the forward current of the semiconductor laser 3.

Here, the cross frequency in the open loop of the optical/electrical negative feedback loop is set to f0, and the DC gain is 10000.
In this case, the step response characteristic of the optical output Pout of the semiconductor laser 3 can be approximated as follows. Pout=PL+(PS-PL)exp(-2πf0t
) (PL: optical output at t=∞ PS: light intensity set by current converter 2) Since the DC gain in the open loop of the optical/electrical negative feedback loop is 10000,
If the allowable range of setting error is 0.1% or less, PL
is considered to be equal to the set light amount.

Therefore, if the light amount PS set by the current converter 2 is equal to PL, the optical output of the semiconductor laser 3 instantly becomes equal to PL. Furthermore, even if the PS fluctuates by 5% due to disturbance etc., if f0=40MHz, it will change in 10ns. Afterwards, the optical output of the semiconductor laser 3 has an error of 0.4% or less with respect to the set value. By using the high-speed, high-precision, high-resolution semiconductor laser control circuit realized in this way, the amount of exposure light can be controlled with high accuracy even when the pulse width is shortened, so that speed fluctuations of the photoreceptor or
Since it is possible to configure a laser printer that is less susceptible to fluctuations in the laser scanning position, has good dot reproducibility, and has good exposure energy control accuracy, it is possible to provide an image forming apparatus that can obtain high-quality images. .

[0050]

[Effect] According to the image forming apparatus according to claim 1, 100
The first one performs light intensity modulation set to a pulse width that is not %.
This method switches between the above method and the pseudo-halftone expression method using a matrix based on the image information, so it is less susceptible to photoconductor speed fluctuations and laser scanning position fluctuations, and the exposure energy control accuracy is high, and the configuration is simple. Since it is possible to realize a laser printer that can obtain smooth images, it is possible to provide an image forming apparatus that can obtain high-quality images. According to the image forming apparatus according to the second aspect, since the semiconductor laser is controlled by the high-speed, high-precision, high-resolution semiconductor laser control circuit, the control precision of the exposure energy is high, and the pulse width is not set to 100%. Since the light intensity is modulated, fluctuations in the speed of the photoreceptor,
Since it is possible to realize a laser printer that is less susceptible to fluctuations in the laser scanning position and has good exposure energy control accuracy, it is possible to provide an image forming apparatus that can obtain high-quality images. According to the image forming apparatus according to claim 3, light intensity modulation is performed with a plurality of pulse widths set, and one pulse width is selected from the plurality of pulse widths based on image information, and then the exposure light amount is adjusted. Since the first means of changing and the pseudo-intermediate expression method using a matrix are switched based on the image information, it is less susceptible to the effects of photoreceptor speed fluctuations and laser scanning position fluctuations, and the exposure energy is controlled accurately and smoothly. Since it is possible to realize a laser printer that can obtain high-quality images, it is possible to provide an image forming apparatus that can obtain high-quality images. In the image forming apparatus according to claim 4, since the semiconductor laser is controlled by a high-speed, high-precision, high-resolution semiconductor laser control circuit, the exposure energy can be controlled with high accuracy, and the light intensity can be set to a plurality of pulse widths. Since modulation is performed, it is possible to realize a laser printer that is less susceptible to changes in the speed of the photoreceptor and laser scanning position, and can control exposure energy with good accuracy, thereby providing an image forming apparatus that can obtain high-quality images. . According to the image forming apparatus according to claim 5, the first means for performing light intensity modulation with a pulse width that is not 100%, and the one-dot multi-gradation expression method can be easily performed based on the differential coefficient of image information. Since it has a concrete means that can switch between the pseudo halftone expression method using a matrix, smooth and high resolution images can be obtained, and the effects of photoreceptor speed fluctuations and laser scanning position fluctuations can be obtained. A specific example of an image forming apparatus that can obtain high-quality images by realizing a laser printer that is not easily exposed to light, has good exposure energy control accuracy, and can be realized with a simple configuration and can obtain smooth images. can provide a specific structure. According to the image forming apparatus according to claim 6, since the semiconductor laser is controlled by the high-speed, high-precision, high-resolution semiconductor laser control circuit, the control accuracy of exposure energy is high, and 100%
Specific means for performing light intensity modulation with a pulse width set to a pulse width that is not equal to 1, and for easily switching between a 1-dot multi-gradation expression method and a pseudo-halftone expression method using a matrix based on the differential coefficient of image information. This makes it possible to obtain smooth, high-resolution images, making it less susceptible to fluctuations in the speed of the photoconductor and laser scanning position, and realizing a laser printer with good exposure energy control accuracy. Therefore, it is possible to provide a specific configuration of an image forming apparatus that can obtain high-quality images. According to the image forming apparatus according to the seventh aspect, since the light intensity modulation is performed with the pulse width set to a duty of 100% or less, the potential well formed on the photoreceptor becomes steeper and the reproducibility of dots is improved. In addition, since there is little overlap between adjacent beams (dots) in the sub-scanning direction in the low-density area, there is less deterioration in image quality due to density unevenness caused by fluctuations in the speed of the photoreceptor and fluctuations in the laser scanning position. Since we have a concrete means that can easily switch between the one-dot multi-gradation expression method and the pseudo-halftone expression method using a matrix based on image information, it is possible to produce smooth, high-resolution, high-quality images. A specific configuration of an image forming apparatus that can be obtained can be provided. According to the image forming apparatus according to claim 8, since the light intensity modulation is performed with the pulse width set to a duty of 100% or less, the potential well formed on the photoreceptor becomes steep, and the reproducibility of dots is improved. ,
Since the semiconductor laser is controlled by a high-speed, high-precision, high-resolution semiconductor laser control circuit, the exposure energy is controlled with high precision.In low-density areas, there is little overlap between adjacent beams (dots) in the sub-scanning direction. Deterioration of image quality due to density unevenness caused by body speed fluctuations and laser scanning position fluctuations is reduced, and based on image information, it is easy to use single-dot multi-gradation expression methods and matrix-based pseudo-halftone expression methods. Since the image forming apparatus has a specific means for switching the image forming apparatus, it is possible to provide a specific configuration of an image forming apparatus that can obtain a smooth, high-resolution, and high-quality image. According to the image forming apparatus according to claim 9, the light intensity modulation is performed with a plurality of pulse widths that are not 100%, and one pulse width is selected from the plurality of pulse widths based on the image information. The present invention has a first means for changing the amount of exposure light, and a specific means for easily switching between a one-dot multi-tone expression method and a pseudo-halftone expression method using a matrix based on a differential coefficient of image information. Because of this, it is possible to obtain smooth and high-resolution images, and it is less susceptible to fluctuations in the speed of the photoreceptor and laser scanning position.Also, the exposure energy can be controlled with good precision, making it possible to obtain smooth images. Since it is possible to realize a laser printer that can produce high-quality images, it is possible to provide a specific configuration of an image forming apparatus that can obtain high-quality images. According to the image forming apparatus according to claim 10, since the semiconductor laser is controlled by the high-speed, high-precision, high-resolution semiconductor laser control circuit, the exposure energy can be controlled with high precision, and the pulse width can be set to a plurality of pulse widths. Since it has a specific means for performing light intensity modulation and easily switching between a one-dot multi-gradation expression method and a pseudo-halftone expression method using a matrix based on the differential coefficient of image information, it is possible to perform light intensity modulation smoothly. It is possible to create a laser printer that can obtain high-resolution images, is less susceptible to photoreceptor speed fluctuations and laser scanning position fluctuations, and has good exposure energy control accuracy, making it possible to form images that provide high-quality images. We can provide the specific configuration of the device.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the operating principle of the present invention.

FIG. 2 is a diagram showing the relationship between relative concentration and unsaturated concentration ratio.

FIG. 3 is a diagram showing the relationship between image density and density unevenness.

FIG. 4 is a diagram for explaining an example of the case where the present invention is applied to dry electrophotography.

FIG. 5 is a diagram showing an example of a dot pattern in that case.

FIG. 6 is a diagram for explaining the operating principle of another embodiment of the present invention.

FIG. 7 is a diagram for explaining an example of the case where the present invention is applied to dry electrophotography.

FIG. 8 is a diagram showing an example of a dot pattern in that case.

FIG. 9 is a diagram for explaining the operating principle of another embodiment of the present invention.

FIG. 10 is a diagram for explaining an example of the case where the present invention is applied to dry electrophotography.

FIG. 11 is a diagram for explaining a specific example of calculating a differential coefficient.

FIG. 12 is a diagram for explaining a specific example of calculating a differential coefficient.

FIG. 13 is a diagram showing an example of performing one-dot multivalue recording.

FIG. 14 is a diagram showing an optical output waveform in the conventional technology (duty 100%) and an optical output waveform in the present invention (duty <100%).

FIG. 15 is a diagram showing the relationship between exposure amount and image density in electrophotographic recording.

[Figure 16] Relationship between the relative density of one dot pixel and the unsaturated density region depending on the intermediate exposure region of the photoreceptor when the pulse width is 100% (curve A) and 50% (curve B) FIG.

FIG. 17 is a diagram showing a potential well.

FIG. 18 is a diagram showing density fluctuations caused by speed fluctuations of the photoreceptor or writing optical system.

FIG. 19 is a diagram for explaining an embodiment of the present invention.

FIG. 20 is a diagram for explaining an embodiment of the present invention.

FIG. 21 is a diagram showing the exposure energy distribution in the sub-scanning direction on a recording medium according to the present invention.

FIG. 22 is a diagram showing the relationship between image density and density unevenness.

FIG. 23 is a diagram showing an exposure amount distribution at a halftone level in a conventional technique.

FIG. 24 is a diagram showing another example of a matrix configuration to which the present invention is applied.

FIG. 25 is a diagram showing another example of a matrix configuration to which the present invention is applied.

FIG. 26 is a diagram showing an example of a dot pattern, (a1
), (a2) when performing pseudo halftone expression, (b1),
(b2) is a diagram showing a case where one-dot multivalue recording is performed.

FIG. 27 is a diagram showing an example of a semiconductor laser control section.

[Explanation of symbols]

1... Comparison amplifier, 2... Current converter, 3... Semiconductor laser,
4... Light receiving element, 10... Matrix pattern generating section, 1
1, 12... Pulse width and light intensity setting section, 13... Differential coefficient calculation section, 14... Digital comparator.

Claims (10)

[Claims] 1. A first means for setting an exposure time corresponding to a minimum pixel to be recorded to a pulse width other than 100% and then changing an exposure light amount according to input pixel information; a second means for converting the M×N pixel information into pixel information of a predetermined M×N pattern; and the first means and the second means according to the inputted pixel information. and third means for selecting. 2. The light output of the driven semiconductor laser is detected by a light receiving section, and the semiconductor laser is controlled so that a light reception signal proportional to the light output of the semiconductor laser obtained from the light receiving section is equal to a light emission level command signal. and a photoelectric negative feedback loop that controls the forward current of the semiconductor laser and the optical output/forward current characteristics of the semiconductor laser and the light of the light receiving section and the semiconductor laser so that the light reception signal and the light emission level command signal are equal to each other. a conversion means for converting the light emission level command signal into a forward current of the semiconductor laser based on a coupling coefficient with an output and a light input/light reception signal characteristic of the light receiving section;
1. A semiconductor laser control unit is configured by means for controlling the semiconductor laser using a current that is the sum or difference between the control current of the photoelectric negative feedback loop and the current generated by the conversion means. The image forming apparatus described above. [Claim 3] Based on the input image information, 100
a first means for selecting one pulse width for each pixel from among the plurality of pulse widths set to a plurality of pulse widths other than %, and then changing the exposure light amount according to the information of each pixel;
a second means for converting the input pixel information into pixel information of a predetermined M×N pattern based on the M×N pixel information; and the first means according to the input pixel information. An image forming apparatus comprising: the second means; and a third means for selecting the second means. 4. The light output of the driven semiconductor laser is detected by a light receiving section, and the semiconductor laser is controlled so that a light reception signal proportional to the light output of the semiconductor laser obtained from the light receiving section is equal to a light emission level command signal. and a photoelectric negative feedback loop that controls the forward current of the semiconductor laser and the optical output/forward current characteristics of the semiconductor laser and the light of the light receiving section and the semiconductor laser so that the light reception signal and the light emission level command signal are equal to each other. a conversion means for converting the light emission level command signal into a forward current of the semiconductor laser based on a coupling coefficient with an output and a light input/light reception signal characteristic of the light receiving section;
3. A semiconductor laser control unit is configured by means for controlling the semiconductor laser using a current that is the sum or difference between the control current of the photoelectric negative feedback loop and the current generated by the conversion means. The image forming apparatus described above. 5. A first means for setting the exposure time corresponding to the minimum pixel to be recorded to a pulse width other than 100% and then changing the exposure light amount according to input pixel information; and a second means for converting the M×N pixel information into pixel information in a predetermined M×N pattern; An image forming apparatus comprising a first means and a third means for selecting the second means. 6. The light output of the driven semiconductor laser is detected by a light receiving section, and the semiconductor laser is controlled so that a light reception signal proportional to the light output of the semiconductor laser obtained from the light receiving section is equal to a light emission level command signal. and a photoelectric negative feedback loop that controls the forward current of the semiconductor laser and the optical output/forward current characteristics of the semiconductor laser and the light of the light receiving section and the semiconductor laser so that the light reception signal and the light emission level command signal are equal to each other. a conversion means for converting the light emission level command signal into a forward current of the semiconductor laser based on a coupling coefficient with an output and a light input/light reception signal characteristic of the light receiving section;
A semiconductor laser control unit is configured by means for controlling the semiconductor laser using a current that is the sum or difference between the control current of the optical/electrical negative feedback loop and the current generated by the conversion means. 5. The image forming apparatus according to 5. 7. A first step in which the exposure time corresponding to the minimum pixel to be recorded is set to a pulse width that is not 100%, and the amount of exposure light is varied according to input pixel information.
In an image forming apparatus that forms a matrix consisting of a plurality of pixels and records a halftone image by changing the exposure amount in each matrix according to image information, the size M of the matrix in the sub-scanning direction is 2 or more, and the main a matrix size N in the scanning direction is 1 or more, and a second means for setting the exposure pattern in the matrix so that the spatial frequency in the sub-scanning direction is the highest; and An image forming apparatus comprising: a third means for selecting the first means and the second means according to a differential coefficient. 8. The recording light source is a semiconductor laser, the light output of the driven semiconductor laser is detected by a light receiving section, and a light receiving signal proportional to the light output of the semiconductor laser and a light emission level command signal obtained from the light receiving section are generated. a photoelectric negative feedback loop that controls the forward current of the semiconductor laser so that the signals are equal to each other; a conversion means for converting the light emission level command signal into a forward current of the semiconductor laser based on a coupling coefficient between a light receiving section and the optical output of the semiconductor laser, and a light input/light receiving signal characteristic of the light receiving section; A semiconductor laser control unit is configured by means for controlling the semiconductor laser using a current that is the sum or difference between the control current of the optical/electrical negative feedback loop and the current generated by the conversion means. 7. The image forming apparatus according to 7. Claim 9: 100 based on input image information.
a first means for selecting one pulse width for each pixel from among a plurality of pulse widths set to a plurality of pulse widths other than %, and changing the exposure light amount according to each pixel information; and the input pixel information. a second means for converting the M×N pixel information into a predetermined M×N pattern of pixel information; 1. An image forming apparatus comprising the first means and a third means for selecting the second means. 10. The light output of the driven semiconductor laser is detected by a light receiving section, and the semiconductor laser is controlled so that a light reception signal proportional to the light output of the semiconductor laser obtained from the light receiving section is equal to a light emission level command signal. and a photoelectric negative feedback loop that controls the forward current of the semiconductor laser and the optical output/forward current characteristics of the semiconductor laser and the light of the light receiving section and the semiconductor laser so that the light reception signal and the light emission level command signal are equal to each other. The coupling coefficient with the output, the optical input of the light receiving section,
conversion means for converting the light emission level command signal into a forward current of the semiconductor laser based on the characteristics of the light reception signal, the control current of the optical/electrical negative feedback loop and the current generated by the conversion means; 10. The image forming apparatus according to claim 9, wherein a semiconductor laser control section includes means for controlling the semiconductor laser using a sum or a difference current.