JPH0869139A - Method and device for image forming - Google Patents

Abstract

PURPOSE: To obtain a higher quality image by simultaneously attaining optimization in each image signal for high image quality and suitability for an image forming device having various kinds of performance, even if a picture element density is made high and a picture element width is relatively made small with respect to the diameter of a laser beam spot. CONSTITUTION: An image is formed with the laser beam spot on the surface of a photoreceptor drum 100 by a laser beam scanner 110 and an electrostatic latent image is formed. After a well-known electrophotographic process, the image is recorded on a recording paper. At this time, an output signal which is expected in a prescribed notice picture element is expressed by the function of an input signal including adjacent picture elements and in the function, the output signal is equated with a reference signal as an output desired value, in each picture element, to obtain simultaneous equations. They are solved so as to make the difference between the reference signal and the output signal small in each of all the picture elements, on the input signal and an output image is formed with the input signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming method and apparatus, for example, an image forming method and apparatus using an electrophotographic process.

[0002]

2. Description of the Related Art Among image forming apparatuses, there is a laser beam printer that employs an electrophotographic method as a high-speed and low-noise printer. A typical recording method is a binary recording method in which an image such as a character or a figure is formed by applying or not applying a laser beam to a photoconductor. Generally, the binary recording method for characters and figures does not require halftones, and therefore the printer structure can be easily realized. However, there are printers that can express halftones even with the binary recording method. As such a printer, a printer that employs a dither method, a density pattern method, or the like is well known. However, as is well known, high resolution cannot be obtained with a printer that employs a dither method, a density pattern method, or the like.

Therefore, in recent years, a method has been proposed in which halftone pixels are formed in each pixel while obtaining high resolution without lowering the recording density. This method forms a halftone pixel by modulating (PWM) the pulse width of irradiating a laser beam with an image signal. According to this PWM method, an image with high resolution and high gradation can be formed. Especially, this method is indispensable for a color image forming apparatus which requires high resolution and high gradation. That is, according to this PWM method, the area gradation of dots formed by the beam spot for each pixel can be taken, and the halftone can be expressed at the same time without lowering the pixel density (recording density) to be recorded. can do.

[0004]

However, the above-mentioned P
Even in the WM system, when the pixel density is further increased, the pixel width becomes relatively small with respect to the laser spot diameter. Therefore, in a low-density pixel, the contrast potential of the dot latent image becomes small, so that development is performed. Becomes difficult,
On the contrary, in high-density pixels, due to the enlargement of the dot latent image,
The influence on the potential of the adjacent pixels increases, so that the contrast between the pixels cannot be sufficiently obtained, and the PW within the pixels is increased.
There is a problem that the gradation due to M modulation cannot be sufficiently obtained.

That is, if the writing pixel density of the conventional image forming apparatus is simply increased, the deterioration of the low density reproducibility and the increase of the noise due to the adjacent pixels cause the deterioration of the resolution. There is a need to.

[0006]

The present invention has been made for the purpose of solving the above-mentioned problems, and has the following constitution as one means for solving the above-mentioned problems. That is,
An input unit for inputting an image signal, a multi-valued unit for converting the image signal input by the input unit into a multi-valued unit, and an image forming unit for forming an output image multi-valued by the multi-valued unit. The multi-value quantization means has a reference signal determination means for determining a reference signal which is an ideal output value for an input signal for each pixel input by the input means, and an output signal expected in a predetermined target pixel. A first functionalization unit that expresses a function of the input signal including adjacent pixels, and the output signal is determined by the reference signal determination unit for each pixel in the function expressed by the first functionalization unit. And a calculation means for solving the simultaneous equations obtained by the second functionalization means with respect to the input signal. For each pixel, the input signal is solved in the direction in which the difference between the reference signal and the output signal is reduced, and the image forming means forms an output image by the input signal solved by the computing means. Characterize.

For example, the output signal includes signal deterioration factors such as a decrease in density reproducibility due to the specification of the photoconductor, the optical system, and the developing device and an increase in noise due to an adjacent pixel. The output signal expresses a function of the input signal by an influence amount of adjacent pixels and a reduction amount of low density reproducibility and a reduction amount of high density reproducibility, and the image forming unit forms an image by density gradation by an area modulation method. Forming is performed.

Further, the multi-value quantization means includes maximum density assumption means for assuming the maximum density within one pixel to be larger than the maximum density of the image area over the entire image area or the image area. It is characterized in that the density difference between the binarized density values or the multi-valued number is increased, and the multi-valued means multi-values the input signal density of the pixel by comparison with a threshold value, and occurs at that time. The feature is that the density error is distributed to peripheral pixels by an error diffusion method.
According to another configuration of the present invention, an input unit for inputting an image signal, a multi-valued unit for multi-valued the image signal input by the input unit by an error diffusion method, and the multi-valued unit. Image forming means for forming a multi-valued output image by means of said multi-valued means, and said multi-valued means assumes that the maximum density within one pixel is larger than the maximum density of the image area within the entire image or image area. The feature is to increase the density difference between the multivalued density values and the multivalued number as much as possible.

[0009]

With the above structure, even if the pixel density is increased to improve the image quality, the deterioration of the dot reproducibility in the low density pixel is reduced, and the dot latent image in the high density pixel is enlarged. It is possible to reduce the influence on the image signal of the adjacent pixel, optimize each image signal for high image quality, and optimize the image forming means having various performances at the same time. A high quality image can be obtained. Further, according to another configuration of the present invention, when the output image is multi-valued, the density difference between the densities can be enlarged to a stable size, and the multi-valued number can be sufficiently increased. Therefore, even in a high-resolution digital image, the gradation and the resolution can be stably compatible with each other, and a higher quality image can be obtained.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment according to the present invention will be described in detail below with reference to the drawings. <First Embodiment> A first embodiment according to the present invention will be described with reference to FIGS.
Will be described below. In this embodiment, a digital electrophotographic system is used as the image forming means.

FIG. 1 is a sectional view of a digital electrophotographic printer apparatus which is an embodiment of the image forming apparatus according to the present invention. In FIG. 1, the paper feeding unit 117 to the paper feeding roller 1
The recording paper is held on the outer circumference of the transfer drum 120 by 18. The photosensitive drum 100 is uniformly charged to a predetermined polarity by the charger 112, is output from the laser beam scanner 110, and is exposed by the laser beam light L via the reflection mirror 111, whereby a latent image for each color is formed on the photosensitive drum 100. It is formed. The latent image formed on the photosensitive drum 100 is visualized by the color developing devices Dy, Dm, Dc, and Dk, and transferred to the recording paper around the transfer drum 120 multiple times to form a color image.

After that, the recording paper is separated from the transfer drum 120 by the separation claw 114, the color image transferred by the fixing unit 115 is fixed, and the recording paper is discharged to the paper discharge tray 116. In addition, 113 is a cleaner, and the photosensitive drum 10
The toner of each color remaining on the surface of 0 is removed.

FIG. 2 shows a detailed structure of the laser beam scanner 110 shown in FIG. In FIG. 2, a laser driver 101 drives a semiconductor laser 102 according to a digital image signal input from an image information signal source (not shown), and outputs a laser beam L. The laser beam L scans the photosensitive drum 100 via the collimator 103, the polygon mirror 104, and the f-θ lens 105.

In this embodiment, as described above, a laser beam spot is formed on the surface of the photosensitive drum 100, an electrostatic latent image is formed, and a known electrophotographic process is performed to realize image recording on recording paper. It is a thing. Here, in order to properly explain the present embodiment, the symbols are defined as follows. As shown in FIG. 3, with respect to the pixel a, the vertical position is m, the horizontal position is n, and the pixel located in the m-th row and the n-th column is “a [m,
n] ”, where 1 ≦ m ≦ M and 1 ≦ n ≦ N.

Further, the image signal desired to be output to the apparatus of this embodiment is used as the reference signal "R", and the photoconductor indicated by the photoconductor drum 100 and the laser beam scanner 1 described above.
An image signal input to the latent image forming unit configured by the optical system 10 is defined as an input signal “X”. Further, an image signal output including a decrease in low density reproducibility due to the characteristics of the photoconductor, the optical system and the developing device and an increase in noise due to an adjacent pixel is referred to as an output signal "Y".

Similarly, with respect to the above-mentioned "R", "X", and "Y" signals, the expression of the position is expressed as "X [m, n]" for the input signal in the m-th row and the n-th column, and m-th row. The function f for the variable x in the nth column is expressed as "f [m, n] (x)". In addition, the exponentiation is represented by "^", and other symbols are the same as the conventions of the programming language for electronic computers. However, the product is represented by “·”.

Based on the above symbols, the operation of this embodiment will be described below with reference to FIGS. In the digital electrophotographic process of this embodiment, the signal X input to a certain target pixel a [m, n] shown in the center of FIG. 3 has a Gaussian distribution in the spot light quantity distribution by the laser beam.

Therefore, when the pixel density is high, that is, the pixel width is smaller than the laser spot diameter, the target pixel a [m,
n] adjacent pixel areas (for example, a [m-1, n], a [m + 1, n], etc.) increase in exposure amount, and the influence of the pixel of interest a [m, n] on adjacent pixels Grows larger. Further, due to the effect of an edge effect for sharpening the edge, the developing range increases around the exposed latent image depending on the developing method.

In this embodiment, the influence f2 of the exposure amount on the adjacent pixel with respect to the exposure amount x on the above-mentioned pixel of interest.
(x) and the like are approximately represented by the following equations, as shown in FIG. f2 (x) = 0: x ≦ β (1) f2 (x) = B · (x−β): β ≦ x (2) In the above formula (2), The value of the constant "B" can take different values depending on the adjacent positions that affect it.

Further, in the digital electrophotographic process of this embodiment, when the latent image on the surface of the photoconductor 100 is small and the potential difference is small, the change in the electric field is smaller at a position distant from the vicinity of the surface of the photoconductor 100. Therefore, there is a signal range in which development with toner is not performed. The reason for this is that the developing device D
There are characteristics such as y, Dm, Dc, and Dk, geometrical limits due to toner particle size, and limit of developability due to the ratio of induced charges generated by toner charges and latent image charges as signals.

Further, due to the upper limit of the potential attenuation amount due to the exposure and the rise of the surface potential of the photosensitive member due to the lamination of the charged toner, the toner amount developed on the photosensitive member 100 becomes constant from a certain exposure amount and the input signal increases. On the other hand, the density reproducibility is relatively lowered. In this embodiment, the developing toner amount f1 (x) with respect to the exposure amount x in the target pixel described above is as shown in FIG.
Approximately represented by the following equation.

F1 (x) = 0: x ≦ α1 (3) f1 (x) = A · (x−α1): α1 ≦ x ≦ α2 (4) f1 (x ) = A · (α2−α1): α2 ≦ x (5) In the above formulas (4) and (5), the constant “A” relates to the amount of developing toner determined by the device characteristics and the like. It is a constant.

By combining the above equations (1) to (5), the output signal Y can be expressed by the following equation using the input signal X. Y [m, n] = f1 (ΣΣf2 [im, jn] (X [i, j])) (6) (ΣΣ is m-1 ≦ i ≦ m + 1, n-1 ≦ j Addition for ≦ n + 1) where f2 [0,0] (X) ≡ X, and outside the adjacent image, that is, i ≦ m-1, m + 1 ≦ i, j ≦ n-1, n F for + 1 ≦ j
Let 2 ≡ 0. For each of the remaining f2 [im, jn], the values of B and β representing the influence amount may be different depending on the values of im and jn representing the adjacent positions. Note that here, pixels that influence the pixel a [m, n] are m-1 ≦ i ≦ m + 1, n-1 ≦ j ≦ n + 1.
However, the range is not limited to the present embodiment.

In the present embodiment, after expressing each variable, constant, and function as described above, the difference (Y−R) between the reference signal R and the output signal Y for each [m, n] pixel is expressed. ) Is adjusted to the minimum, X [m, n] is adjusted. In the present embodiment, for each [m, n], (M · N) nonlinear simultaneous equations shown below are solved. R [m, n] -Y [m, n] = 0 (7) The above (M · N) nonlinear simultaneous equations (7) are converted into X [m, n] by an appropriate numerical calculation method. ] Is sequentially calculated, and the (k + 1) th value X is calculated from the value X obtained by the kth sequential calculation. At this time, the number of times of sequential calculation is variable depending on the reference signal R [m, n] of each pixel [m, n], and the processing method in this embodiment can be dynamic.

In the above process, the following formula is defined for [m, n]. ε = (ΣΣ ((R [m, n] −Y [m, n]) ^ 2)) / (M · N) (8) (ΣΣ is 1 ≦ m ≦ M, 1 ≦ n ≦ Addition for N) [epsilon] obtained by the above equation (8) is compared with a predetermined value [epsilon] 0, and k is increased until [epsilon] ≤ [epsilon] 0.

As described above, in this embodiment, the signal input to the image output unit of the image forming apparatus is optimized so that the output image can be output as an image that is closest to the original image data depending on the performance of each image forming apparatus. It is possible to obtain high quality images. As a numerical calculation method for solving the above-mentioned nonlinear simultaneous equations (7),
For example, it is possible to use various well-known solution methods for solving the extreme problem of a multivariable function, such as the Newton-Raphson method and the successive approximation method.

Further, the value 0 of the functions f1 and f2 shown in the above equations (1) and (3) can be replaced with a minute value that does not cause a harmful error. Furthermore, in order to optimize the input signal X, the above nonlinear system (7) need not be solved with high accuracy. In the step of the sequential calculation, if the value of ε shown in Expression (8) is smaller than the value calculated sequentially in advance, the image quality is further improved. Therefore, when ε is increasing or the calculation amount is required to be reduced. In such a case, the calculation can be sequentially aborted at an appropriate number of times including zero.

Further, in order to reduce the oscillation of the calculated value of the input signal X, the calculated value change amount of the input signal X from the k-th to (k + 1) -th time has an appropriate value h such that 0 ≦ h ≦ 1. It is also possible to multiply by and calculate with gradual convergence. Therefore, in the image forming method according to the present embodiment, the input signal is dynamically changed depending on the property of the original image data, the influence amount to the adjacent pixel in the reproduction of the pixel dot of the given image forming apparatus, and the low density reproducibility decrease. X can be calculated and optimized.

A, B, α1, α used in this embodiment
For parameters such as 2 and β that depend on the image forming apparatus, effective values are obtained in advance by experiments for each image forming apparatus. As described above, according to this embodiment, the output signal Y of a certain pixel of interest is expressed by a function of the input signal X including the adjacent pixels, and the output signal Y is output for each pixel.
And the reference signal R are equal, the simultaneous equations obtained are solved for the input signal X, so that the difference between the reference signal R and the output signal Y for all pixels becomes as small as possible. The magnitude of the input signal X can be individually determined for each pixel.

That is, after considering the influence of the performance of various image output devices for each input of the image data, the increase of the developing amount and the decrease of the developing ability of the low density due to the influence of the adjacent pixels are taken into consideration for each pixel. By optimizing the input signal, there is a unique effect that the pixel density can be increased without lowering the resolution. Further, in the present embodiment, a specific numerical solution method, a specific convergence determination method, an influence amount of an increase in development amount due to the influence of an adjacent pixel with respect to a specific pixel, and an influence amount of a decrease in developing ability in a low density region are specified. I explained about the description by the variable of
Of course, it is also possible to use other numerical solution methods, other convergence determination methods, and similar expression methods of the above-mentioned respective influence quantities, such as using an appropriate polynomial.

In this embodiment, the input signal is optimized by including the parameters that depend on the performance of each image forming apparatus, and the number of times is variable depending on both the image data and the performance of the image forming apparatus. The point of performing the optimized signal processing calculation between pixels is that a normal filter or an error diffusion method (E
This is different from the density-preserving image forming method such as the D method). <Second Embodiment> The second embodiment according to the present invention will be described below.

In the above-described first embodiment, as a determination method for optimizing the input signal X, in the above equation (8), a predetermined value ε0 is compared, and ε ≦
The calculation was performed by increasing k until it reached ε0, but depending on the data of the original image and the performance of the image output device, ε
In some cases, a value of 0 cannot be treated as an optimal fixed value.

Therefore, in the second embodiment, the difference between the value ε in the k-th sequential calculation and the value ε in the (k + 1) -th sequential calculation in the sequential calculation of the numerical calculation method shown in the first embodiment. The calculation is performed until the absolute value of becomes smaller than a predetermined value ε1. Therefore, as described above, in the second embodiment, the value of ε shown in the equation (8) of the first embodiment is not determined due to the difference in the optimization limit for each data of the original image. In some cases,
It has the same effects as the first embodiment.

<Third Embodiment> The third embodiment according to the present invention will be described below. Since the device configuration of the third embodiment is the same as that of the first embodiment described above, the description of the device configuration will be omitted. In the third embodiment, an image forming method focusing on the multi-valued number of one pixel will be described in addition to the first embodiment described above.

In the multi-value density preservation image forming method such as the error diffusion method (ED method), by increasing the multi-value number of one pixel, the image deterioration caused by the image processing is reduced and the image quality becomes high. Therefore, formally, it is sufficient to increase the multi-valued number. However, in the electrophotographic process as in the third embodiment, the area value of the dots to be developed varies to some extent, so that the density difference ΔD of the multivalued density replacement in the output image is stably reproduced. Since there is a lower limit to the dot area change amount ΔA for
A lower limit also occurs in ΔD, and thus an upper limit occurs in the multi-valued number N.

Further, when the resolution is increased, the pixel area becomes smaller than the lower limit of ΔD determined by the lower limit of ΔA, so that the image density becomes analog, the γ value of the photosensitive member potential-density curve becomes large, and the image quality is improved. descend. In addition, the image is likely to be deteriorated due to changes in the environment. Due to the above factors, in order to stably reproduce the density difference ΔD between the density values, it is necessary to set ΔD to a relatively large value to determine the number of output gradations. N is not sufficiently taken, and the image deteriorates, such as mottled noise generated by image processing.

It is considered that the above problem is influenced by the fact that the output image density difference ΔD of one pixel in the digital electrophotographic process of the third embodiment has a lower limit on the size that can be stably reproduced. Therefore, in the third embodiment, in the electrophotographic process, the density difference ΔD of the output image is limited by the developing characteristics of the apparatus, the toner diameter and the laser spot diameter, and it is difficult to reduce ΔD. Further, the above problem is solved in consideration of the characteristic that the maximum density Dmax has a value sufficient for printing if the potential contrast of the photoconductor 100 is set sufficiently large.

That is, when performing the image processing as shown in the first embodiment, it is assumed that the maximum density that can be output is larger than the maximum density set as the hardware standard.
It is possible to stabilize the output density difference ΔD required for multi-value density conversion to a sufficiently large value and to secure a sufficient multi-value conversion number. In addition, the difference between the assumed maximum density generated at this time and the maximum density as a hardware standard is simultaneously error-diffused and removed together with a normal multi-valued density error generated between each pixel.

The details of the third embodiment will be described below with reference to FIGS. 6 to 8, Do is the output density, Di is the input density, Dmax is the maximum density value that is assumed to be actually output, and Domax is the third density value.
It is the maximum density value according to the hardware standard of the apparatus of the embodiment, and Dimax is the input maximum density with respect to Domax. Further, O (n) is each multi-value output density value when the error diffusion method is used, ΔD (n) is each density difference of each O (n) when multi-valued, and S (n) is Input density Di for each O (n)
Of each threshold.

6 to 8, FIGS. 6 and 7 show Dm.
FIG. 8 shows the case where ax is assumed to be equal to Domax, and FIG. 8 is the case where Dmax is assumed to be greater than Domax.
The value of the section from 0 to Dmax of the output signal Do is multi-valued by the multi-valued number N, and each multi-valued signal is made a multi-valued output density signal O (n). For O (n), n ranges from 0 to N-
It takes N values up to 1.

Here, in order to determine the output signal Do,
The threshold value S (n) for the input signal Di is changed from n = 1 to n =
It is provided for each n of N-1. Input signal Di is S (n)
And S (n + 1), the value of the output signal Do is O
Determined as (n). First, with reference to FIG. 6 and FIG. 7, let us consider multi-valued processing when Dmax and Domax are equal.

In FIG. 6, in order to obtain the density difference ΔD (n) in a sufficiently stable size, the multi-valued number N must be reduced (for example, N = 3 in FIG. 6), and the image processing is performed. Image deterioration occurs. In addition, in FIG.
, The density difference ΔD (n) becomes small, so that the density of the multi-value output density signal O (n) becomes unstable in the electrophotographic process as described above, and image deterioration also occurs.

Next, referring to FIG. 8, Dmax is set to Doma.
Consider the case where it is assumed to be larger than x. Figure 8
It is a figure which shows the system which determines the stable density difference (DELTA) D in 3rd Example. In FIG. 8, first, the maximum density value Dmax obtained by the potential contrast of the photoconductor is set to be larger than the maximum density value Domax of the hardware standard.

In the electrophotographic process apparatus, for example, when the standard maximum density Domax is set to 1.5 (reflection density), the maximum density value is output up to about 1.8 by appropriately setting the potential contrast Vcont. It is possible, and the maximum density value of the output can be increased by setting the device. In addition, the multi-valued number N in FIG.
Is determined as shown below. Do from 0 to Dmax
Up to the multi-value output density signal O for each n
Assuming that the density difference from (n) to O (n + 1) is ΔD (n + 1), n such that ΔD (n) for each n can be stably obtained
The maximum value of is determined as N.

ΔD (n) determined as described above is
Depending on the development characteristics of the device, the toner diameter, the laser spot diameter, the resolution, etc., there are differences depending on the device, but it is possible to output a digital density gradation chart and observe the dot image, or measure the density. , Can be specified. As described above, the multi-value output density O (n) determined by the method shown in FIG. 8 is used, and the image processing thereafter is performed by various known error diffusion methods including the first embodiment. Output. That is, the difference between the input density Di and the multi-valued output density O (n) for a certain pixel is distributed and added to Di of the peripheral pixel group, and the result is newly added to the input density D.
i and output density signal O of the next pixel in the same manner as above.
A method of determining (n) can be used.

The threshold value S used in the third embodiment is
(n), multi-valued number N, density difference ΔD (n), maximum density value Dmax obtained by the potential contrast Vcont of the photoconductor,
Regarding the parameters such as the standard output maximum density value Domax of the printer, the characteristics of the electrophotographic process, for example, the average density preservation method (MD method) and the normal ED with a fixed threshold value are used.
Depending on the type of error diffusion method such as the method, various values can be taken for the nature of the input image and environmental changes. Therefore, performing optimal control for the above parameters is also included in the third embodiment.

As described above, according to the third embodiment,
When the output image is multi-valued, the density difference between density values can be expanded to a stable size, and the number of multi-valued images can be increased sufficiently. It is possible to obtain both tonality and resolution in a stable manner and to obtain higher quality images. Although the third embodiment has been described with respect to the electrophotographic printer, the third embodiment is particularly useful for the LED printer. According to the third embodiment, since the difference ΔD between the density values of the multi-valued output density can be made large, in the LED printer, the image quality is deteriorated due to the density instability caused by the variation in the light amount of each element of the LED array head. Can be reduced, and a great effect can be obtained in improving the quality of the output image.

<Fourth Embodiment> In the above-described third embodiment, an example of image formation based on the relationship between the input density and the output density has been described, but the present invention is not limited to this example and is general. It includes the concept that it is regarded as the relationship between the input signal and the output signal, and therefore, the values of the electric signal, the light intensity luminance signal, the laser output, the photoconductor potential, and the like are used instead of the density, and substantially the same as those of the third embodiment. It is possible to present and realize an equivalent concept, and it is also possible to realize by combining the above values.

An example using the lookup table (LUT) shown in FIG. 9 will be described below as the fourth embodiment. In the fourth embodiment, first, by the LUT shown in FIG.
Convert the input density Di to a higher Di '. In the fourth embodiment, the maximum input density value Di'max after LUT conversion
Is determined to be equal to the actual maximum output density value Dmax shown in the above-described third embodiment.

Next, the threshold value of the input density is determined by the input density Di before the LUT conversion, and thereafter, the input density Di'after the LUT conversion is used as the input density, similarly to the third embodiment described above. Error diffusion processing is performed. As described above, also in the fourth embodiment, the same operational effect as in the third embodiment can be obtained. The third embodiment and the fourth embodiment are not limited to the electrophotographic process, but may be Dmax and Domax described above.
The present invention can also be applied to other image forming apparatuses such as a printer of a thermal transfer system and the like, which are compatible with each other.

<Fifth Embodiment> As a fifth embodiment of the present invention, a multiple development batch transfer electrophotographic system as shown in FIG. 10 will be described below. FIG. 10 is a diagram showing a schematic configuration of a multiple development batch transfer electrophotographic system. First, the photosensitive drum 100 is uniformly charged with a predetermined polarity by the charger 112. The laser beam output from the semiconductor laser 102 driven by the laser driver 101 scans the photosensitive drum 100 via the reflection mirror 111 and the like,
Write a latent image. Then, only the portion irradiated with the laser beam is visualized by the inversion phenomenon. This process is performed for each of the developing devices Dy, Dc, D for three colors of magenta, cyan, and yellow, or for four colors including black.
Repeatedly using m and Dk, the toner images are superimposed on the photosensitive drum 100 to form a color image.

Then, the above toner image is transferred to the transfer drum 10
Are collectively transferred onto a recording sheet by means of a pre-exposure lamp 5 to remove residual charges on the photosensitive drum 100. After that, the recording paper is separated from the transfer drum 10, and the fixing unit 11
The color image transferred in 5 is fixed, and the paper output tray 11
It is discharged to 6. A cleaner 113 removes each color toner remaining on the surface of the photosensitive drum 100.

In the multi-development batch transfer electrophotographic system as described above, the toner visualized on the photosensitive drum 100 at the time of laser exposure for the second and subsequent colors is used, as described in the first embodiment. The phenomenon such as an increase in the development amount due to the influence of adjacent pixels and a decrease in the development ability in the low density region occur. The above phenomenon can be expressed by the parameters α1, α2, β, A, B, etc. in the above-described first embodiment, and therefore the image formation similar to that in the first embodiment is also performed in the visualization of the toner of the second and subsequent colors. Can be optimized, that is, the fifth embodiment can be applied to all of the above-described first to fourth embodiments.

As described above, according to the fifth embodiment,
Even in the multi-development batch transfer electrophotographic system, the same effects as those of the third embodiment can be obtained. <Sixth Embodiment> The sixth embodiment of the present invention will be described below.
A multi-drum system as shown in FIG. 11 will be described.

FIG. 11 is a diagram showing a schematic structure of the multiple drum system. The apparatus of the sixth embodiment shown in FIG. 11 is provided with dedicated photosensitive drums 3Y (yellow), 3M (magenta), 3C (cyan), 3K (black) for each color, around which dedicated laser beam scanners are provided. 80Y,
80M, 80C, 80K, developing units 1Y, 1M, 1C, 1
K, transfer discharging devices 10Y, 10M, 10C, 10K, cleaning devices 12Y, 12M, 12C, 12K and the like are arranged.

The recording paper is conveyed through the paper feed guide 5a, the paper feed roller 6 and the paper feed guide 5b in this order, receives corona discharge from the attraction charger 81, and is reliably attracted to the conveyor belt 9a. After that, each photosensitive drum 3Y, 3M, 3C, 3K
The images formed on the transfer discharge devices 10Y, 10M, 10
The toner images are transferred to the recording paper by C and 10K while being synchronized with each other, and the conveying belt 9a is discharged by the discharging device 82. Then, the toner image is fixed on the recording paper by the fixing device 17, and a full-color image is obtained.

In the sixth embodiment, a plurality of laser beam scanners and photosensitive drums are arranged mainly for the purpose of high-speed output of a full-color image. In this case, each laser beam scanner 80Y, 80M, 80C, 80K is arranged.
Also, due to mechanical limitations of the photosensitive drums 3Y, 3M, 3C, 3K, etc., the stability of pixel dots becomes more important than that of the configuration described in the first embodiment.

Therefore, in the sixth embodiment, the above-described first to fourth embodiments can be applied to the image forming apparatus of the multi-drum type, and the pixel resolution and gradation can be improved with stable pixel reproduction. It becomes possible to measure. As described above, according to the sixth embodiment, also in the multi-drum type image forming apparatus, the same operational effect as that of the third embodiment can be obtained.

Although the digital copying machine has been mainly described in each of the above-described embodiments, the present invention is not limited to this. For example, an image recording apparatus using a similar electrophotographic process, such as an image recording apparatus, is used. It goes without saying that the present invention can be applied to a laser beam printer and the like. Furthermore,
The method of the present invention can be applied to a method using a laser beam other than the PWM method, and is also applied to optimization in accordance with the characteristics of another image forming apparatus such as an inkjet printer or a thermal transfer printer. It is also possible to do so.

In each of the above-described embodiments, the exposure and development steps in the electrophotographic process have been mainly described, but the image quality is improved in other processing steps such as transfer, separation, cleaning and fixing. Of course, a method of improving the image quality by combining with various methods is possible. Further, the optimization control in the present invention may be configured by software control in consideration of control flexibility and redundancy, or may be configured by hardware for high speed operation.

The features of image formation to which the present invention is applied will be additionally described. When an image signal (so-called solid image or solid black image) in which the image region maximum signal value is uniformly input to the entire image region or image region is used as the input image signal in the present invention, the output image signal is uniform. However, the image signal pattern may be generated due to error diffusion without being a constant value.

However, the above-mentioned image signal pattern has a high resolution and a high multivalue which can be applied in the present invention.
In terms of image quality, it hardly causes deterioration. Further, even when an image signal (so-called grayscale chart image or the like) in which an image area signal smaller than the image area maximum signal value is uniformly input is used as the input image signal, any of the pixels on the output image The output signal value of 1 may exceed the output signal value of any pixel of the maximum signal solid image, but similarly to the above, it does not cause deterioration of image quality.

The present invention may be applied to a system composed of a plurality of devices or an apparatus composed of a single device. Further, it goes without saying that the present invention can be applied to the case where it is achieved by supplying a program to a system or an apparatus.

[0064]

As described above, according to the present invention, even when the pixel density is increased and the pixel width is made relatively small with respect to the laser spot diameter in order to improve the image quality, the dots in the low density pixel are Reducing the deterioration of reproducibility, reducing the influence on the image signal of the adjacent pixel due to the enlargement of the dot latent image in the high density pixel, optimization for each image signal for high image quality, and various It is possible to simultaneously optimize each electrophotographic process of an image forming apparatus having high performance, and it is possible to obtain a higher quality image. or,
According to the present invention, when the output image is multi-valued, the density difference between the densities can be enlarged to a stable size, and the multi-valued number can be sufficiently increased. Even in images, stable gradation and resolution are both achieved,
A higher quality image can be obtained.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a detailed configuration of a laser beam scanner of this embodiment.

FIG. 3 is a diagram showing a target pixel and its adjacent pixels in the present embodiment.

FIG. 4 is a diagram showing a relationship between an exposure amount and an influence amount on an adjacent pixel in the present embodiment.

FIG. 5 is a diagram showing a relationship between an exposure amount and a toner development amount in this embodiment.

FIG. 6 is a diagram showing an example in which the multilevel halftoning number cannot be increased in the third example of the present invention.

FIG. 7 is a diagram showing an example in which a density difference cannot be increased in a third embodiment according to the present invention.

FIG. 8 is a diagram showing an example in which a maximum output density value is assumed to be high in a third embodiment according to the present invention.

FIG. 9 is a diagram showing an example of an LUT in a fourth example according to the present invention.

FIG. 10 is a diagram showing a schematic configuration of a multiple development batch transfer electrophotographic image forming apparatus according to a fifth embodiment of the present invention.

FIG. 11 is a diagram showing a schematic configuration of a multi-drum type image forming apparatus according to a fourth embodiment of the present invention.

[Explanation of symbols]

 100 Photosensitive Drum 101 Laser Driver 102 Semiconductor Laser 103 Collimator 104 Polygon Mirror 105 f-θ Lens 110 Laser Beam Scanner 111 Reflection Mirror 112 Charger 113 Cleaner 114 Separation Claw 115 Fixing Roller 116 Paper Ejection Section 117 Paper Feeding Section 118 Paper Feeding Roller 120 Transfer drum

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display location G03G 15/01 113 A H04N 1/40

Claims (18)

[Claims] 1. An input step of inputting an image signal, a multi-valued step of converting the image signal input by the input step into multi-valued data, and an output image multi-valued by the multi-valued output step are formed. An image forming step, and the multi-value quantization step includes a reference signal determination step of determining a reference signal that is an ideal output value for an input signal of each pixel input in the input step, and a prediction in a predetermined pixel of interest. A first functionalization step for expressing the output signal to be expressed by a function of the input signal including adjacent pixels, and the output signal for each pixel in the function expressed by the first functionalization step is the reference signal. A second functionalization step for obtaining a simultaneous equation that is equal to the reference signal determined by the determination step; and a calculation step for solving the simultaneous equation obtained by the second functionalization step for the input signal, In the calculation step, the input signal is solved in the direction in which the difference between the reference signal and the output signal becomes smaller for every pixel, and the image forming step forms an output image by the input signal solved in the calculation step. An image forming method comprising: 2. The output signal includes signal deterioration factors such as a decrease in density reproducibility due to the characteristics of the photoconductor, the optical system, and the developing device and an increase in noise due to adjacent pixels. The image forming method described. 3. The first functionalization step is to express the output signal as a function of the input signal by an influence amount of an adjacent pixel and a reduction amount of low density reproducibility and a reduction amount of high density reproducibility. The image forming method according to claim 2, which is characterized in that. 4. The image forming method according to claim 3, wherein in the image forming step, an image is formed by density gradation according to an area modulation method. 5. The multi-value quantization step includes a maximum density assumption step in which the maximum density in one pixel is assumed to be larger than the maximum density in the image area in the entire image or in the image area,
5. The image forming method according to claim 4, wherein the density difference between the multivalued density values is increased by the maximum density assuming step. 6. The multi-value quantization step is characterized in that the input signal density of a pixel is multi-valued by comparison with a threshold value and a density error generated at that time is distributed to neighboring pixels by an error diffusion method. Item 6. The image forming method according to Item 5. 7. The multi-value quantization step includes a maximum density assumption step of assuming that the maximum density within a pixel is larger than the maximum density within the image area in the entire image or in the image area,
The image forming method according to claim 4, wherein the multi-valued number is increased by the maximum density assuming step. 8. The multi-value quantization step is characterized in that the input signal density of a pixel is multi-valued by comparison with a threshold value and a density error generated at that time is distributed to neighboring pixels by an error diffusion method. Item 7. The image forming method according to Item 7. 9. An input unit for inputting an image signal, a multi-valued unit for converting the image signal input by the input unit into multiple values, and an output image multi-valued by the multi-valued unit. Image forming means, the multi-value quantization means determines a reference signal which is an ideal output value for an input signal for each pixel input by the input means, and a prediction signal at a predetermined pixel of interest. The output signal is expressed by a function of the input signal including adjacent pixels, and in the function expressed by the first functionalization means, the output signal is the reference signal for each pixel. A second functionalization means for obtaining a simultaneous equation as being equal to the reference signal determined by the determination means; and a computing means for solving the simultaneous equation obtained by the second functionalization means for the input signal, The arithmetic means solves the input signal in a direction in which the difference between the reference signal and the output signal decreases for every pixel, and the image forming means forms an output image by the input signal solved by the arithmetic means. An image forming apparatus comprising: 10. The output signal includes a signal deterioration factor such as a decrease in density reproducibility due to the characteristics of the photoconductor, the optical system and the developing device and an increase in noise due to an adjacent pixel. Image forming device. 11. The first functionalization means represents the output signal with respect to the input signal by an influence amount of an adjacent pixel, a reduction amount of low density reproducibility and a reduction amount of high density reproducibility. The image forming apparatus according to claim 10. 12. The image forming apparatus according to claim 11, wherein the image forming unit forms an image by density gradation according to an area modulation method. 13. The multi-value quantization means includes a maximum density assumption means for assuming the maximum density within one pixel to be larger than the maximum density of the image area in the entire image or in the image area, and the multi-valued multi-valued image is obtained by the maximum density assumption means. 13. The image forming apparatus according to claim 12, wherein the density difference between the individualized density values is increased. 14. The multi-value quantization means multi-values an input signal density of a pixel by comparing it with a threshold value and distributes a density error generated at that time to peripheral pixels by an error diffusion method. Item 13. The image forming apparatus according to item 13. 15. The multi-value quantization means includes maximum density assumption means for assuming the maximum density within a pixel within one pixel to be greater than the maximum density of the image area in the entire image area or image area, and the multi-valued image data is obtained by the maximum density assumption means. 13. The image forming apparatus according to claim 12, wherein the number of conversions is increased. 16. The multi-value quantization means multi-values an input signal density of a pixel by comparing it with a threshold value and distributes a density error generated at that time to peripheral pixels by an error diffusion method. Item 15. The image forming apparatus according to Item 15. 17. An input step of inputting an image signal, a multi-valued step of converting the image signal input by the input step into a multi-valued one by an error diffusion method, and an output multi-valued by the multi-valued step. An image forming step of forming an image, wherein the multi-valued step is multi-valued by assuming that the maximum density in one pixel is larger than the maximum density in the image area in the entire image or in the image area. An image forming method characterized by increasing a density difference between respective density values and a multi-valued number as much as possible. 18. Input means for inputting an image signal, multi-valued means for converting the image signal input by the input means into multi-valued data by an error diffusion method, and output multi-valued by the multi-valued data conversion means. An image forming unit for forming an image, wherein the multi-valued unit is multi-valued by assuming that the maximum density in one pixel is larger than the maximum density in the image region in the entire image or in the image region. An image forming apparatus, wherein a density difference between density values and a multi-valued number are increased as much as possible.